GPL - real techie question about ramp angles and clutches

Warning: this posting contains a pretty technical question and some ugly ASCII art. And it's pretty long, too. I know this question has been talked about a lot, but I haven't yet seen an answer that allows me to understand what those beast are and how they work. And adjusting them without knowing how they work leads to nothing and is driving me nuts. So: what the heck are those clutches, where are they installed, and what do they do? Likewise for the ramp angles. Let me tell you how a standard differential gear looks like, and you tell me where the clutches and ramp angles come into play. Deal? [I don't have a proper dictionary for automotive terminology, and I know the names of most parts only in German, so I have to paraphrase a bit at times. Bear with me. Info about the proper English terminology is appreciated.] In the diff box, there is a huge gear that is driven by a smaller gear on the end of the driveshaft. In the center of the huge gear, there is a casing that contains four small conical gears. Two of those gears are connected to the two axleshafts. The other two gears sit on a separate pinion shaft. The whole thing looks (roughly :) like this: [Switch to Courier of another fixed pitch font, or it will look even less comprehensible...] |\ ||XXXXX|XXXXXX || | X || \\zz|zz// X || 0 | 0 X =================||==0 | 0==X=============== || 0 | 0 X || //zz|zz\\ X || | X ||XXXXX|XXXXXX |/ The bigger part on the left side is the big gear I wrote about. The things made of "=" signs are the axleshafts. The part made of "X"s is the casing. "\zz|zz/" is one of the conical gears with a part of its pinion shaft. "\ 0 0 0 /" is one of the gears at the end of the axleshafts. Now, where do the clutches come in? And to what do the ramp angles refer? Thanks for any insights! -- Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.

<snip the cool ascii art n stuff> I'm not sure of the physical layout of a 60's era differential, but I understand how it works. Ramp Angles... the two numbers for ramp angles, 85/30, correspond to power/coast values for when the diff locks up. Higher values on the power side means quicker lockup when you apply throttle, lower values on the power side means lazier lockup when you apply throttle. On the coast side, lower values means that when you lift off the throttle, the diff is slow to lockup, higher values means the diff locks at the slightest hint of throttle lift. (I find this undesireable) example...15/85 values would mean you pretty much gotta floor the gas to get the car to move, yet as soon as you begin to lift off the gas the diff would begin to lockup and try to slow the car. Clutches... this sets how tightly the diff locks up between the rear tires. More clutches means that the rear tires are allowed less ability to spin at different rates (like when turning a corner). Less clutches allows for a little more play between the tires. If you find that it's too hard to control a powerslide or trailbraking, try less clutches. Hope that helps

I didn't understand it too until now. Thanks Doc! Andre On Sat, 31 Jul 1999 07:03:12 -0700, "5th Doctor"

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>> Warning: this posting contains a pretty technical question and some >> ugly ASCII art. And it's pretty long, too. >> I know this question has been talked about a lot, but I haven't yet >> seen an answer that allows me to understand what those beast are and >> how they work. And adjusting them without knowing how they work leads >> to nothing and is driving me nuts. So: what the heck are those >> clutches, where are they installed, and what do they do? Likewise for >> the ramp angles. ><snip the cool ascii art n stuff> >I'm not sure of the physical layout of a 60's era differential, but I >understand how it works. >Ramp Angles... >the two numbers for ramp angles, 85/30, correspond to power/coast values for >when the diff locks up. Higher values on the power side means quicker >lockup when you apply throttle, lower values on the power side means lazier >lockup when you apply throttle. >On the coast side, lower values means that when you lift off the throttle, >the diff is slow to lockup, higher values means the diff locks at the >slightest hint of throttle lift. (I find this undesireable) >example...15/85 values would mean you pretty much gotta floor the gas to get >the car to move, yet as soon as you begin to lift off the gas the diff would >begin to lockup and try to slow the car. >Clutches... >this sets how tightly the diff locks up between the rear tires. More >clutches means that the rear tires are allowed less ability to spin at >different rates (like when turning a corner). Less clutches allows for a >little more play between the tires. If you find that it's too hard to >control a powerslide or trailbraking, try less clutches. >Hope that helps

>I'm not sure of the physical layout of a 60's era differential, but I >understand how it works. <snip> >Higher values on the power side means quicker >lockup when you apply throttle, lower values on the power side means lazier >lockup when you apply throttle. Hmmmm. You might want to rethink that. :-) See quote at bottom from: http://simracing.com/alison/gpl/ferrari.htm Where Alison Hine and Dave Kaemmer are discussing GPL diff. settings. Give the article a peek if you haven't; it's food for thought, even if your car's not red. Cheers, Steve B. "Note that in a Salisbury-type differential such as those used by GPL's cars, a higher ramp angle (e.g. 85 degrees) gives less locking, while a lower ramp angle (e.g. 30 degrees) gives more locking. On the other hand, higher preload - more clutches - gives more locking." remove "edy" from address for email

>I'm not sure of the physical layout of a 60's era differential, but I >understand how it works. >Ramp Angles... >the two numbers for ramp angles, 85/30, correspond to power/coast values for >when the diff locks up. Higher values on the power side means quicker I hate to be an ahole, but this stuff was covered in the manual I got with the game :-) -- Header address intentionally scrambled to ward off the spamming hordes. cisko [AT] ix [DOT] netcom [DOT] com

See Carroll Smith's book, "Drive to Win" for a complete explanation with pictures. Much other useful stuff. bob

oh, but your so good at it Greg

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> >I'm not sure of the physical layout of a 60's era differential, but I > >understand how it works. > >Ramp Angles... > >the two numbers for ramp angles, 85/30, correspond to power/coast values > for > >when the diff locks up. Higher values on the power side means quicker > I hate to be an ahole, but this stuff was covered in the manual I > got with the game :-) > -- > Header address intentionally scrambled to ward off the spamming hordes. > cisko [AT] ix [DOT] netcom [DOT] com

I have messed with these settings alot, and, at least on my machine, the lower the number on the power side, the more I gotta mash the gas to accelerate. what gives? > >I'm not sure of the physical layout of a 60's era differential, but I > >understand how it works. > <snip> > >Higher values on the power side means quicker > >lockup when you apply throttle, lower values on the power side means lazier

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> >lockup when you apply throttle. > Hmmmm. You might want to rethink that. :-) > See quote at bottom from: > http://simracing.com/alison/gpl/ferrari.htm > Where Alison Hine and Dave Kaemmer are discussing GPL diff. settings.

Give the > article a peek if you haven't; it's food for thought, even if your car's not

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> red. > Cheers, > Steve B. > "Note that in a Salisbury-type differential such as those used by GPL's

cars, a > higher ramp angle (e.g. 85 degrees) gives less locking, while a lower ramp > angle (e.g. 30 degrees) gives more locking. On the other hand, higher preload - > more clutches - gives more locking." > remove "edy" from address for email

>Ramp Angles... >the two numbers for ramp angles, 85/30, correspond to power/coast values for

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>when the diff locks up. Higher values on the power side means quicker >lockup when you apply throttle, lower values on the power side means lazier >lockup when you apply throttle. >On the coast side, lower values means that when you lift off the throttle, >the diff is slow to lockup, higher values means the diff locks at the >slightest hint of throttle lift. (I find this undesireable) >example...15/85 values would mean you pretty much gotta floor the gas to

get >the car to move, yet as soon as you begin to lift off the gas the diff would

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>begin to lockup and try to slow the car. >Clutches... >this sets how tightly the diff locks up between the rear tires. More >clutches means that the rear tires are allowed less ability to spin at >different rates (like when turning a corner). Less clutches allows for a >little more play between the tires. If you find that it's too hard to >control a powerslide or trailbraking, try less clutches. >Hope that helps

Excellent explanation on what's going on with ramp angles and clutches. But I still have a few questions. For starters,I drive a Lotus,(and a Ferrari when I just can't seem to get the lotus to handle at all). 1- Almost every setup I've ever seen uses a ramp angle of 85/30. From your explanation,I take this to mean that the rear locks up slower when applying gas as well as locking up slowly when getting off the gas and on the brakes. Or would one be better off using a lower power number? 2- The more clutches the tighter the rear. Yet most of the latest setups have gone to 4 clutches rather than 2 for the Lotus and Ferrari. From your explanation,I would think that 2 would be a better choice. At the start of the race when I apply the gas (no matter how easy),the car pulls ***ly to the left. I always get left behind. Once I'm going,the steering is as it should be. This problem was never this bad until I installed the patch and started using a MSFF wheel rather than my T2. Slow corners that require 1st or 2nd gear usually wind up with *** oversteer when I apply the power. Joel Willstein

>"Note that in a Salisbury-type differential such as those used by GPL's cars, a >higher ramp angle (e.g. 85 degrees) gives less locking, while a lower ramp >angle (e.g. 30 degrees) gives more locking. On the other hand, higher preload - >more clutches - gives more locking." I think I got it - with the help of two pages from Carroll Smith's "Drive to Win", which someone kindly e-mailed me. Maybe some people are interested in the technical principles - if not, press the "skip message" button NOW. :) Everybody else, enjoy as much as possible. And those of you who really know about this stuff, please don't hesitate to correct me whenever I get something wrong. A usual "open" diff, which we have in our normal road cars, distributes the power to the wheels in such a way that - when going through a curve - the inner wheel can rotate less frequently than the outer wheel, which has to cover a greater distance. This is a Good Thing, but it has a downside to it: as soon as one of the wheels loses grip (f.i. the inner wheel in a curve), all the power goes to this wheel. In an extreme case, we have one wheel spinning madly, while the car stands still. Using NO diff is not an option on road courses, since the car wouldn't want to turn at all with such a setup. This leads to a lot of tire wear and a very ugly behavior in tight turns. Yet, the car would accelerate very nicely in a straight line. Champ Cars on large ovals do without a diff and use "stagger" (rear wheels of different sizes, a larger one on the outside) to facilitate turning. What we want is a diff that allows us to accelerate out of turns without having the inner wheel spinning, yet does not make the car understeer madly in turns. This is where a "limited slip" diff comes into play. In an open diff, the axle shafts can turn (more or less) independently from the diff housing. This goes so far that, when the car is jacked up, you can turn one wheel clockwise, and the other wheel will turn counter-clockwise. The diff housing will not move at all during this operation. The infamous clutches will prevent this from happening. They connect the axle shafts to the diff housing, but allow some slip. The more clutches you pack in there, the less slip they will allow. The static "clutch preload" does not depend on the torque of accelerating / braking. Therefore, if you put too little preload in there, you still will have wheel spin. If you dial in too much preload, OTOH, you get basically a completely locked diff, which is even less desirable. Fortunately, some folks (Smith mentions Mike Endean and Hewland) developed the concept of "ramps". It is difficult to describe how those ramps actually look, but they work like this: imagine a wedge that is located between the axle gears and the diff housing. When you apply power, the wedge will be pressed into the gap and make the two parts turn simultaneously - with a certain amount of slip. The force with which the wedge, or ramp, links the two parts depends on the torque applied (the more torque, the greater the force, the less slip allowed) and on the angle of the ramp - the ramp angle. A 30 angle will transmit the greatest force and give the least slip. (even sharper wegdes would supposedly give even higher pressure and locking power, but are not used, apparently.) A 90 angle is not really a wedge or ramp anymore, but a stop, and will not exert any pressure. The real nice aspect of this design is that you can use two different wedges, one for accelerating, and one for engine braking. When accelerating, the engine gives torque to the axles and the wheels, and the power, or drive side ramp comes into effect. When engine braking, the wheels are giving torque to the engine, and the coast side ramp starts working. Therefore, you could use a setup like 30/90 (30 power side ramp angle / 90 coast side ramp angle) to get very little diff slip while accelerating, and a completely open diff while coasting. I assume that the transition between "almost fully locked" and "open" (and vice versa) would be rather harsh, though, and might unsettle the car in mid-corner when you step on the throttle again. The clutches are used to give a certain amount of lock all the time and smoothen the transition between coast and power phase. Excuse me now, I have some testing to do at Monza. :) -- Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.

> >Ramp Angles... > >the two numbers for ramp angles, 85/30, correspond to power/coast values > for > >when the diff locks up. Higher values on the power side means quicker > >lockup when you apply throttle, lower values on the power side means lazier > >lockup when you apply throttle. > >On the coast side, lower values means that when you lift off the throttle,

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> >the diff is slow to lockup, higher values means the diff locks at the > >slightest hint of throttle lift. (I find this undesireable) > >example...15/85 values would mean you pretty much gotta floor the gas to > get > >the car to move, yet as soon as you begin to lift off the gas the diff > would > >begin to lockup and try to slow the car. > >Clutches... > >this sets how tightly the diff locks up between the rear tires. More > >clutches means that the rear tires are allowed less ability to spin at > >different rates (like when turning a corner). Less clutches allows for a > >little more play between the tires. If you find that it's too hard to > >control a powerslide or trailbraking, try less clutches. > >Hope that helps > Excellent explanation on what's going on with ramp angles and

clutches. > But I still have a few questions. For starters,I drive a Lotus,(and a > Ferrari when I just can't seem to get the lotus to handle at all). > 1- Almost every setup I've ever seen uses a ramp angle of 85/30. From your > explanation,I take this to mean that the rear locks up slower when applying > gas as well as locking up slowly when getting off the gas and on the brakes. > Or would one be better off using a lower power number? Not exactly. With a power side value of 85 (the highest available) the diff will begin to lockup sooner as you apply throttle. The higher the value, the sooner the lockup. I find that with 2 clutches in the Lotus, with my setup, the car wants to push too much when I'm trying to power out of a turn. The rear tires don't want to break loose as easily. With 4 clutches in my setup, the rear wants to break loose very easily, and I may spin it under power,or worse ,have to lift exiting a turn to gather it up. I use 3 clutches in my setup. I use basically the same setup for every road course, and a different setup for ovals. Maybe your setup?? I dunno. I don't use a FF wheel. My suspension is symetrical, I don't use the clutch for starts, and I can usually launch the car straight. > Joel Willstein

Excellent info Wolfgang. I have to get that book. Here's my take on this (I hope I'm close to being on the right track, so to speak - comments please!): 1. More/faster locking of the differential results in more/faster oversteer response. 2. Decrease the power side ramp angles to quicken the locking and thus increase turn exit oversteer. Increase the power side ramp angle to slow the locking and thus decrease turn exit oversteer. 3. Decrease the coast side ramp angles to quicken the locking and thus increase turn entry oversteer. Increase the coast side ramp angle to slow the locking and thus decrease turn entry oversteer. (I change an 85/30 setting to an 85/45 setting when I'm into strong oversteer on turn entry). 4. Add clutches to increase mid corner oversteer. Remove clutches to decrease mid corner oversteer. 5. Do all the above before adjusting anything else (??) I'm not quite sure of the mid-corner contribution of the ramps as your note indicates that they change both the force (locking?) and the slip (speed of locking?).

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> <snip snip> > The force with which the wedge, or ramp, links the two parts depends > on the torque applied (the more torque, the greater the force, the > less slip allowed) and on the angle of the ramp - the ramp angle. A > 30 angle will transmit the greatest force and give the least slip. > (even sharper wegdes would supposedly give even higher pressure and > locking power, but are not used, apparently.) A 90 angle is not > really a wedge or ramp anymore, but a stop, and will not exert any > pressure. > <snip snip> > Therefore, you could use a setup like 30/90 (30 power side ramp angle > / 90 coast side ramp angle) to get very little diff slip while > accelerating, and a completely open diff while coasting. I assume that > the transition between "almost fully locked" and "open" (and vice > versa) would be rather harsh, though, and might unsettle the car in > mid-corner when you step on the throttle again. The clutches are used > to give a certain amount of lock all the time and smoothen the > transition between coast and power phase.

>Excuse me now, I have some testing to do at Monza. :) I know it's lame to follow-up one's own messages, but I did the testing and wanted to share the results. So I went to Monza and took a close look at my current ride, a Ferrari with a modified Alison Hine setup (modified means I changed the gearing and adjusted the roll bars and braking bias according to my personal needs, but left the rest unchanged. This setup used to be "Ali Silverstone neutral", not the Monza setup which has still too much understeer for my liking.) I was surprised to find the setting for the ramp angles set to 85/30. This should mean "little lock under power / lots of lock while coasting" according to what I've learned from C. Smith's book. More or less the opposite of what I expected to be a good setting... Since many people claim that the numbers in GPL actually mean the opposite to what Smith says in his book, I did a little skidpad testing. I reduced the number of clutches to the minimum (in order not to dilute the results regarding the ramp angles) and tested four different extreme configurations. [As an aside: each ramp can have 30, 45, 60, or 85 of angle. It's 85 instead of 90 since the 90 angle parts tended to chip, according to Smith. I find the pulldown menu in GPL somewhat confusing for a beginner: since all combinations are allowed, *two* pulldown lists of four items each would have been handier than one with 16 options.] I started doing donuts on the front stretch at Monza and found the following: 85/30 - only inside wheel leaves skidmarks 85/85 - again, skid marks only by the inside wheel 30/85 - both wheels leave marks 30/30 - both wheels leave skid marks This conclusively proves two things: 1. The first number refers to the power side, the second to the coasting side. Just as one would expect in reality - but this is software, so I thought it deserved a special mention. :) 2. A higher number means less lock-up of the diff, a lower number more lock-up. Sorry, 5thDoc, but you have to re-evaluate your info. Smith is right. Well, now I took the car with a 30/85 diff for a spin - literally. While braking for Parabolica on the outlap, the rear of the car overtook me. And no, this usually doesn't happen to me ( not anymore, not all the time, at least.) At first, I was - unpleasantly - surprised. But it really isn't that surprising when you think about it: a locked diff means the car is going in a straight line - which is what you want when braking for Parabolica! An open diff, OTOH, makes turning easier. But I don't want to turn when braking at full speed. (If you've seen today's German GP, you know what good a spinning car at 300 km/h is... ;) But the change made it much easier to induce throttle oversteer in mid-corner. A bit *too* easy, to be frank, but a step in the right direction. I drove a bit with a 45/60 ratio and will explore some other ratios as well. Suffice it to say that this setting has quite some effect on the car's handling. Try playing with it! -- Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.

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>Excellent info Wolfgang. I have to get that book. >Here's my take on this (I hope I'm close to being on the right track, so to speak - >comments please!): >1. More/faster locking of the differential results in more/faster oversteer >response.

It depends, I'd say. Let's assume a RWD car with a locked diff: if you are coasting slowly, the unwillingness of the rear axle to turn will induce understeer. If you are on the throttle, however, both rear wheels will eventually spin under power and you will have oversteer. With an open diff, the inside wheel will spin whereas the outside wheel will stay in its track and provide lateral force, so there is no oversteer. And no acceleration worth speaking of. ;) Under power, yes. This depends entirely on how you approach the corner. The lower the coast side ramp angle is, the more stable the car will be while (engine) braking in a straight line. And the less willing will it be to turn. If you are trail braking into the turn, a lower angle will mean more understeer. I agree with the first part of your statements - it's the part after the "thus" that I'm not sure about. This is under dispute among the authorities. Dave Kaemmer agrees with you, Alison Hine disagrees. I have no opinion yet (and am no authority either.) :) compare http://simracing.com/alison/gpl/ferrari.htm After fiddling with the ramp angles this afternoon, I tend to agree. They are pretty influential. I will try to make my terminology industry-standard compliant in the future. :) It seems I have to resort to a crude ASCII rendering again... This is my impression of the diagram on page 7-28 in Smith's book: _______ | |d | ||| \ ||| _\ b ||| /a\\ |||_______e______ \_// ||| / c ||| / ||| | ||| |_______| The huge lump in the middle is the side gear ring, aka ramp body. (a) - the planet bevel gear, which is supposed to be round. :) (b) - the coast side ramp. (c) - the power side ramp. (Both ramps have the same angle in this example. Too bad ther aren't "/" signs with different angles. :) (d) - the clutch packs. (e) - the axle. Now, when the car accelerates, the bevel gear is pressed against the power side ramp, which in turn is pressed to the right against the clutches. This maximizes the lock of the diff: _______ | |d | ----> ||| \ ||| \ b ||| _ \ |||_______e______ /a\/ ||| \_/ c ||| / ||| | ----> ||| |_______| When the car is coasting, the same happens on the other side: _______ | |d | ----> ||| \ ||| /a\ b ||| \_/\ |||_______e______ / ||| / c ||| / ||| | ----> ||| |_______| Now, what I wanted to say is simply that, when there are little or no clutches, the transition between coasting and accelerating in mid corner might be a bit harsh. In the worst case, it could go from "full lock" to "no lock" (when the bevel gear is in the middle) to "full lock" again within fractions of a second. I just feel this could be problematical.

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>> <snip snip> >> The force with which the wedge, or ramp, links the two parts depends >> on the torque applied (the more torque, the greater the force, the >> less slip allowed) and on the angle of the ramp - the ramp angle. A >> 30 angle will transmit the greatest force and give the least slip. >> (even sharper wegdes would supposedly give even higher pressure and >> locking power, but are not used, apparently.) A 90 angle is not >> really a wedge or ramp anymore, but a stop, and will not exert any >> pressure. >> <snip snip> >> Therefore, you could use a setup like 30/90 (30 power side ramp angle >> / 90 coast side ramp angle) to get very little diff slip while >> accelerating, and a completely open diff while coasting. I assume that >> the transition between "almost fully locked" and "open" (and vice >> versa) would be rather harsh, though, and might unsettle the car in >> mid-corner when you step on the throttle again. The clutches are used >> to give a certain amount of lock all the time and smoothen the >> transition between coast and power phase.

-- Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.

>I have messed with these settings alot, and, at least on my machine, the >lower the number on the power side, the more I gotta mash the gas to >accelerate. what gives? I've seen the same initial acceleration lag when testing low angles on the power side. My guess is that with more lockup(lower #'s), the peaky power curves make initial wheelspin a bit tougher to induce. When it comes, though, you've got a problem, since both rear wheels have checked out, grip-wise. Instant panoramic view. Nosir, I don't like it. In fact, I've yet to find a use for less than an 85 ramp angle on the power side. I know it doesn't ring quite true to life, but the car's a beast with low power side angles, and my basic setup philosophy is to just keep twisting all the knobs until the Lotus stops trying to kill me, then break them off. Cheers, Steve B. remove "edy" from address for email

Ok. Now I'm kinda confused. If I set my diff at 30/30, I pretty much have to floor the gas to get the car to move off pit lane, whereas with diff settings of 85/30 I can ease into the gas and the car starts to roll easily. Help me Obi Wan, your my only hope :)

I am humbled by your skills. Please, may I know the title of the book by Smith, and maybe the ISBN (sp?) number, so I may get my ignorant hands on a copy? Kenny L. the 5th Doctor size 3 hat, size 13 shoe

>I know it's lame to follow-up one's own messages, but I did the >testing and wanted to share the results. Don't apologize; it's called follow-up, and it's appreciated! Gee, that NEVER happens. :-) But with an 85 coast-side angle, it's probably almost impossible to avoid there.(unless you start braking in Ascari) That pretty much mirrors what I've settled on; for really heavy straightline braking, go to low coast angles and more clutches. Yep. I've found that using 45 or 60 on the coast side (instead of 30) makes it easier to adjust my line with slight changes in throttle position. But that. Indeed! My current interest is clutches. I'm convinced that less is more, and only tracks with very heavy braking zones need more than two, at least for the Lotus. I only use one at Brands and Monaco, and wish I could get by with it at more tracks. But getting the car hauled down from speed with one clutch is......interesting. The journey continues. Cheers, Steve B. remove "edy" from address for email

> At the start of the race when I apply the gas (no matter how easy),the > car pulls ***ly to the left. I always get left behind. Once I'm > going,the steering is as it should be. This problem was never this bad until > I installed the patch and started using a MSFF wheel rather than my T2. Slow > corners that require 1st or 2nd gear usually wind up with *** oversteer > when I apply the power. I wonder if this is due to the slow-speed variable steering ratio that Papy put in to allow easier negotiation of slow-speed turns? Apparently, at speeds below 60mph, the steering ratio is set somewhere between 7:1 and the ratio you specified in the setup (proportionate to speed), so when you start off the steering will be very twitchy indeed (ie. at 7:1). This can be turned off in 1.1 using disable_steer_ratio (or something like that) in the core.ini, so it may be worth trying this. I think it's explained on the vroc site under Alison Hine's pages somewhere.

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>> 2. A higher number means less lock-up of the diff, a lower number more >> lock-up. Sorry, 5thDoc, but you have to re-evaluate your info. Smith >> is right. >Ok. Now I'm kinda confused. If I set my diff at 30/30, I pretty much have >to floor the gas to get the car to move off pit lane, whereas with diff >settings of 85/30 I can ease into the gas and the car starts to roll easily. >Help me Obi Wan, your my only hope :)

I tried to duplicate this behavior, but my findings are inconclusive. It seemed indeed as if the car needed a tiny bit more throttle to start rolling with 30/30. But without telemetry data, the difference is too subtle for me to be sure. I have no idea what could cause this behavior. What conclusions do you draw from your observation? -- Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.

>I am humbled by your skills. No skills involved. :) I really did not have the faintest clue about all this when I started the thread. When I had read the pages from the book and the (conflicting) info in RAS, I just applied the ole scientific method to figure out how this was modelled in GPL. It seems *again* as if GPL accurately simulates the behavior of the real thing. This sim never fails to impress me. :) AUTHOR: Carroll Smith (note the spelling: two 'r's, two 'l's) TITLE: Drive to Win ISBN: 0965160009 Amazon has it in stock. I don't want to appear ungrateful, but I wasn't overly impressed by the two-page excerpt that I read. First of all, the text did not manage to convey the info to me on first reading. And not on second or third reading either. This is pretty technical stuff, so it's probably not Smith's fault, but I can imagine a more accessible way of explaining a limited slip diff to amateurs like me. Secondly, the two pages contain some typos ("toque" instead of "torque", "Powr" instead of "Power" - although this might be intentional in a proper name ("Hewland Powr Flow".) Yet, when there is one obvious typo, how can one be sure that this isn't one either?) I'm usually pretty tolerant of typos, but in a book, they are more often than not a sign of sloppy production Smith's strong point seems to be his experience in racing. If you're looking for "How do I use this?" info, you've come to the right place. If your approach is more in the vein of "How does this work?", there might be better books. What made me understand the principle wasn't Smith's text but a small diagram on one of the pages. But then again, I only read two pages, so I might not be doing him justice. -- Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.

The chapter in the book is some 15 pages long. Judging by your comments about the typos, I presume that the extract you read was from some way into the chapter and therefore didn't include the section on "basics". If so, that may explain the difficulty you had. I'm usually quite sensitive to typos, but having read the book several times I must admit that I missed both of those until I just searched for them <g>. On that basis there might be plenty more but I certainly didn't get the overall impression that the production is sloppy. Maybe I was just too engrossed with the content to bother about the typos though <g> That's a fair judgement IMO. Cheers, Richard

I THOUGHT I knew about this stuff. I re-read the pages in the stock GPL setup guide, and I found my thinking was ass-backwards. I am glad I first responded with incorrect info, then someone replied with correct info, got me thinking, then spent a day playing with diff settings. I ended up with 30/30 and one clutch for my lotus, and it's much easier to drive especially in the high speed turns. Not allot of work to get 1:29's at monza, but the car sure is different. More practice. Thanks everyone.

> >> 2. A higher number means less lock-up of the diff, a lower number more > >> lock-up. Sorry, 5thDoc, but you have to re-evaluate your info. Smith > >> is right. > >Ok. Now I'm kinda confused. If I set my diff at 30/30, I pretty much have > >to floor the gas to get the car to move off pit lane, whereas with diff > >settings of 85/30 I can ease into the gas and the car starts to roll easily.

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> >Help me Obi Wan, your my only hope :) > I tried to duplicate this behavior, but my findings are inconclusive. > It seemed indeed as if the car needed a tiny bit more throttle to > start rolling with 30/30. But without telemetry data, the difference > is too subtle for me to be sure. > I have no idea what could cause this behavior. What conclusions do you > draw from your observation?

That I'm probably brain dead. Seems before the 1.1 patch, it was allot worse. I figure, getting the car rolling is not a big factor. The benefits <sp?> of a 30/30 diff far outweigh the drawbacks. I've settled on a 30/30 one clutch. Thanks > -- > Wolfgang Preiss \ E-mail copies of replies to this posting are welcome. cancellation warned.

> > 1- Almost every setup I've ever seen uses a ramp angle of 85/30. From your > > explanation,I take this to mean that the rear locks up slower when > applying > > gas as well as locking up slowly when getting off the gas and on the > brakes. > > Or would one be better off using a lower power number? > Not exactly. With a power side value of 85 (the highest available) the diff > will begin to lockup sooner as you apply throttle. The higher the value, > the sooner the lockup. The lower the number the sooner the lockup occurs I use a MSFF wheel and can make straight starts nearly all the time even with assymetrical suspension. Try altering the linearity slider and/or steering ratio, it makes quite a difference. BTW mine is nearly totally linear about 1/8 th from left and I use the highest steering ratio I can get away with at each track. ie 14-1 at Monaco 18-1 at Spa and 16-1 at Monza and I still use the standard steering ratio adjust. -- Ian Parker UKGPL League [link lost in import]

> > At the start of the race when I apply the gas (no matter how easy),the > > car pulls ***ly to the left. I always get left behind. Once I'm > > going,the steering is as it should be. This problem was never this bad until > > I installed the patch and started using a MSFF wheel rather than my T2. Slow > > corners that require 1st or 2nd gear usually wind up with *** oversteer

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> > when I apply the power. > I wonder if this is due to the slow-speed variable steering ratio that > Papy put in to allow easier negotiation of slow-speed turns? > Apparently, at speeds below 60mph, the steering ratio is set somewhere > between 7:1 and the ratio you specified in the setup (proportionate to > speed), so when you start off the steering will be very twitchy indeed > (ie. at 7:1). > This can be turned off in 1.1 using disable_steer_ratio (or something > like that) in the core.ini, so it may be worth trying this. > I think it's explained on the vroc site under Alison Hine's pages > somewhere.

I think you could be right on this, i've been experimenting with my core.ini settings for my wheel (MSFF), and have currently turned of the steering ratio hack and I'm sure it feels easier to control at lower speeds, I was always spinning coming out of the hairpin at spa for instance, but now its a lot easier, on the other hand now i cant get round a lot of the bends at Monaco, just not enough steering lock. Mark London UK

Not sure where to break into this thread. I have been experimenting the last few weeks with ramp angles and clutches as well. I first started with the coast-side in hopes of getting better speed through some of the long sweeping corners. It can help, and when combined with other settings it can help alot. However, I have found that in order to balance out the car with a ramp angle of 85/45 or 85/60, I usually have to soften the rear (either spring rate or ARB). When testing with the power side, I couldn't find much use for it at most tracks. It is extremely difficult to apply power and keep the car straight (however, this can be compensated by adding more clutches). Since most tracks were I am concerned with apply alot of power it is on the straights (or while straightening the car coming out of a turn), I did't find much advantage to lowering the power side ramp angle. So far the one track where I have found it can be used is Monaco, where most of the straights aren't straight at all. I have been successful at using a 60/60 setting at Monaco (however only after considerable tests with different spring rates and ARB than normally used). The key is not just changing the ramp angles and expecting to find favorable results. This setting drastically alters the way the car handles and must be matched with a different philosophy with spring rate, ARB and camber settings along with clutches and sometimes even tire pressure (what did I leave out?). -- **************************** Michael E. Carver ************************* Upside out, or inside down...False alarm the only game in town. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=<[ /./. [- < ]>=-=-=-=-=-=-=-=-=-=-=-=-=-=

>The key is not just changing the ramp angles and expecting to find >favorable results. This setting drastically alters the way the car >handles and must be matched with a different philosophy with spring >rate, ARB and camber settings along with clutches and sometimes even >tire pressure (what did I leave out?). And I use to think that ICR2 was hard to setup a car in. Joel Willstien

Bump and rebound dampers. :) Anything you change in your setup influences everything else. Trying to figure this out often induces pain between my ears. But it's fun if you get it working. :) I experimented a bit with the ramp settings in Monza (still the only track I'm consistent enough on to properly evaluate setup changes) and found that 60/30 works better for me on that track than the previous default of 85/30. Especially in Curva Grande it is easier to keep the car away from the armco. In Ascari, the 85 power ramp angle allows some wheelspin of the inside wheel with my setups. The 60 angle cures this. OTOH, I need the 30 coast side angle to keep the car straight when braking for Parabolica. 60 also works, but the car becomes more nervous - too nervous for longer races. My main problem with setups is not to create one that's good to drive. It is to create one that's good to drive *and* fast. I tend to build cars that are nice but slow... -- Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.

After much clicking and laps, I went from 85/30 & 4 clutches to 30/30 & 2 clutches, also took 5# out of rear springs, 2/2 on the rear shocks, 18 psi in the rear tires. My Lotus now is much easier to steer with the throttle, I may "hang it out" with confidence. Very sensitive to throttle input changes (glad I have a PDPI) but with a little practice I found that it behaves predictably. It's a beast with cold tires, though. But, after a couple of laps, I can do 1:29's at Monza all day. I'm very happy we all had this discussion. Thanks to all who joined in.

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> >The key is not just changing the ramp angles and expecting to find > >favorable results. This setting drastically alters the way the car > >handles and must be matched with a different philosophy with spring > >rate, ARB and camber settings along with clutches and sometimes even > >tire pressure (what did I leave out?). > Bump and rebound dampers. :) Anything you change in your setup > influences everything else. Trying to figure this out often induces > pain between my ears. But it's fun if you get it working. :) > I experimented a bit with the ramp settings in Monza (still the only > track I'm consistent enough on to properly evaluate setup changes) and > found that 60/30 works better for me on that track than the previous > default of 85/30. Especially in Curva Grande it is easier to keep the > car away from the armco. In Ascari, the 85 power ramp angle allows > some wheelspin of the inside wheel with my setups. The 60 angle cures > this. > OTOH, I need the 30 coast side angle to keep the car straight when > braking for Parabolica. 60 also works, but the car becomes more > nervous - too nervous for longer races. > My main problem with setups is not to create one that's good to drive. > It is to create one that's good to drive *and* fast. I tend to build > cars that are nice but slow... > -- > Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.

cancellation warned.