Confused about weight vs spring rate

[chuyler1]

As a test, I took my '86 MR2 and added 96kg to the front. The MR2 has a 45/55 weight distribution so this essentially made it 50/50. I fitted it with even spring rates, dampers, and rollbars for front and rear. Spent some time tuning and came up with the following...

Height: -2 / -2
Spring: 6 / 6
Comp: 3 / 3
Ext: 3 / 3
Roll: 2 / 2
Camber: 0.5 / 0.5
Toe: 0.05 / 0.20

The car drives beautifully. Under WOT it will understeer before oversteering. Under braking it tracks straight but add slight trail braking and you can get the nose to rotate enough to help with turn-in. The suspension maintains composure over rough curbs and the tires maintain contact over rough roads like Trial Mountain.

However the additional weight drops the car to 446pp and there are no other mods to add. Racing last night I realized I am sacrificing straight-line speed by driving around with a 210lb corpse in my front boot.

So I started removing the weight without making any other changes. It began to oversteer very aggressively mid corner. The car would basically turn itself at high speeds...turn itself into the inside guard rail that is. The front end felt loose.

My first inclination was to reduce the front spring rate since there was less weight. I tried running 5 up front but that didn't really help. I also tried lowering the front damper settings and increasing the front rollbar and still that didn't help. I'm not sure if I'm heading in the right direction since anything I do tends to make the oversteer worse.

Then I consulted the GT4 tuning guide which says to run stiffer springs up front (increase understeer) or softer springs in the rear (decrease oversteer). Should I really be running stiffer springs on the end of the car that is lighter?

What other things should I try to clean up the front of this car? Can I assume that the rear settings across the board should be kept the same since they worked great prior to removing the weight in the front?

 

[charliec]

Stiffer suspension allows easier rotation, so softening the rear (or stiffening the front so the rear is softer in comparison) should help. Also you can try lowering the rear, maybe keep the front at -2 and drop the rear to -4 or -5?

 

[Rotary Junkie]

Then I consulted the GT4 tuning guide which says to run stiffer springs up front (increase understeer) or softer springs in the rear (decrease oversteer). Should I really be running stiffer springs on the end of the car that is lighter?

No.


Personally, I'd try stiffening the front anti-roll bar and the rear springs, as well as possibly using a bit more rear camber.

Although, just as a quick "phone tune" I'll throw some numbers at you that I believe should sort the car out.

Height: -2 / -2
Spring: 7.2/12.5
Comp: 8 / 8
Ext: 5 / 5
Roll: 3 / 2
Camber: 1.5 / 2.5
Toe: 0.05 / -0.05

If it still has excessive oversteer, lower the front to -5mm and then go down in 5mm increments. Some may think that the slight rear toe-out is a terrible idea on an oversteery car but I've found that it greatly depends on the car. Rear toe-in does indeed stabilize the car but only to a point; it will actually break away sooner with toe-in than neutral toe or a slight toe-out.

 

[charliec]

No.


Personally, I'd try stiffening the front anti-roll bar and the rear springs, as well as possibly using a bit more rear camber.

Although, just as a quick "phone tune" I'll throw some numbers at you that I believe should sort the car out.

Height: -2 / -2
Spring: 7.2/12.5
Comp: 8 / 8
Ext: 5 / 5
Roll: 3 / 2
Camber: 1.5 / 2.5
Toe: 0.05 / -0.05

If it still has excessive oversteer, lower the front to -5mm and then go down in 5mm increments. Some may think that the slight rear toe-out is a terrible idea on an oversteery car but I've found that it greatly depends on the car. Rear toe-in does indeed stabilize the car but only to a point; it will actually break away sooner with toe-in than neutral toe or a slight toe-out.

I always thought that having a stiffer, higher rear suspension would encourage more oversteer?

 

[chuyler1]

I'll try that setup but I think it will be too stiff for Trial Mountain. When I was running 50/50 I tried has high as 9.0/9.0 and without any downforce the car skipped over bumps. I kept lowering it until I got to 6.0/6.0.

 

[renagade]

I always thought that having a stiffer, higher rear suspension would encourage more oversteer?

you are totaly right ...

 

[Rotary Junkie]

I always thought that having a stiffer, higher rear suspension would encourage more oversteer?

you are totaly right ...

Not always. If the rear is too soft for the load being placed on it by cornering you'll have the outside rear tire get overstressed and as a result get oversteer. Also, too soft on the rear will contribute to off-throttle and braking oversteer (softer springs = more travel and more stored energy = more forward weight transfer under braking = oversteer unless it's extreme to the point of overloading the front tires).

If the above was true, the Yellowbird would be completely solved by max/min ride height and max/min springs... It's obviously not the case.

I'll try that setup but I think it will be too stiff for Trial Mountain. When I was running 50/50 I tried has high as 9.0/9.0 and without any downforce the car skipped over bumps. I kept lowering it until I got to 6.0/6.0.

Dampers were your problem there, not the springs. I've run as high as 19-20 kg/mm (albeit on race cars) at Trial without any skip or hop. Also of note is that high sway bars will make individual tires try to skip over pavement irregularities more than less anti-roll and more spring.

 

[charliec]

Not always. If the rear is too soft for the load being placed on it by cornering you'll have the outside rear tire get overstressed and as a result get oversteer.

But wouldn't raising the center of gravity (in relation to the front) mean it's overstressed more quickly? Stiffening the springs will decrease lateral weight transfer somewhat, but it seems like this would be offset by having a higher center of gravity, which would cause more body roll (relative to the front suspension).

Also, too soft on the rear will contribute to off-throttle and braking oversteer (softer springs = more travel and more stored energy = more forward weight transfer under braking = oversteer unless it's extreme to the point of overloading the front tires).

Wouldn't stiffening the front springs decrease weight transfer under braking? I didn't think stiffening the rear would prevent the front from compressing, which is what is transferring weight.

 

[Poppins]

Id just tighten the rear a bit if I were you. Also increase the ARB both front and rear, if you have them different it tends to roll alot more at the front or rear of the car which ****s up weight transfer.


Id go with something like 7/8 for spring rates, and 5/6 for ext/comp, 4 for ARB

 

[Rotary Junkie]

But wouldn't raising the center of gravity (in relation to the front) mean it's overstressed more quickly? Stiffening the springs will decrease lateral weight transfer somewhat, but it seems like this would be offset by having a higher center of gravity, which would cause more body roll (relative to the front suspension).

You'd think that but it seems to shift the CoG up and somewhat forward, and as a result you get more stress on the nose. Welcome to the wonderful world of Gran Turismo tuning.

Wouldn't stiffening the front springs decrease weight transfer under braking? I didn't think stiffening the rear would prevent the front from compressing, which is what is transferring weight.

Yes it would. But so does stiffening the rear for the exact same reason.

If we had no suspension, weight transfer would always be the same under the same braking force... Allowing one end to compress more increases weight transfer to that end by letting the center of gravity shift towards said end... The opposite applies to allowing one end to expand more. Softer springs will expand further when an accelerative force is applied in the opposite direction.

 

[Poppins]

Its an MR2 anyways man, its tiny. Its going to want to spin especially being MR.

 

[Rotary Junkie]

Its an MR2 anyways man, its tiny. Its going to want to spin especially being MR.

I don't see your point. Yes, it's a very short wheelbase MR car, a great recipe for twitchy behavior, but that doesn't mean it can't be tamed without sacrificing outright speed (and, in fact, it likely needs to be).

 

[veyron1001]

Well you just ruined the car. The idea is to have 50/50 weight under braking. You just basically turned the car into a 60/40 or worse FR car.

 

[Poppins]

You shouldnt be able to tame it running as hard as you can on S3 tires. Not all the way anyways.

Tightening the front will lead to a tighter and more responsive suspension and steering in general, but also can cause less weight transfer to the front which leads to understeer.

But since most of the weight is on the back end of that car you need the rear to be harder so it is technically the same as the front.

Taming it will make it no fun though

 

[Rotary Junkie]

Well you just ruined the car. The idea is to have 50/50 weight under braking. You just basically turned the car into a 60/40 or worse FR car.

No.

You shouldnt be able to tame it running as hard as you can on S3 tires. Not all the way anyways.

Tightening the front will lead to a tighter and more responsive suspension and steering in general, but also can cause less weight transfer to the front which leads to understeer.

But since most of the weight is on the back end of that car you need the rear to be harder so it is technically the same as the front.

Taming it will make it no fun though

You should damn well be able to tame it on S3s. I don't mean make it completely mindless to drive, I mean make it driveable. There's no point trying to drive a car that wants to make you dead every time you turn the wheel. Slight oversteer on entry, neutral through the center, slight push on exit = fun car that is actually fast.

Oversteer at any time extreme enough to require countersteer is slowwwwwwwwww. And we don't want slow.

 

[charliec]

You'd think that but it seems to shift the CoG up and somewhat forward, and as a result you get more stress on the nose. Welcome to the wonderful world of Gran Turismo tuning.

I'm guess I'm just thinking of the Ruf CTR; it's difficult to drive because of the rear weight bias. If you were to raise the rear (or just lower the front), it would just amplify that handling characteristic because the higher CoG would have more of a leveraging effect on the rear than the front, meaning more transferred load in the rear than in the front.

Yes it would. But so does stiffening the rear for the exact same reason.

If we had no suspension, weight transfer would always be the same under the same braking force... Allowing one end to compress more increases weight transfer to that end by letting the center of gravity shift towards said end... The opposite applies to allowing one end to expand more. Softer springs will expand further when an accelerative force is applied in the opposite direction.

Well, I guess using this idea, let's say you had a solid rear suspension (no travel, just steel beams instead of springs) and stock front springs, are you saying the front wouldn't compress at all because the rear couldn't travel/expand?

 

[Rotary Junkie]

You shouldnt be able to tame it running as hard as you can on S3 tires. Not all the way anyways.

Tightening the front will lead to a tighter and more responsive suspension and steering in general, but also can cause less weight transfer to the front which leads to understeer.

But since most of the weight is on the back end of that car you need the rear to be harder so it is technically the same as the front.

Taming it will make it no fun though

I'm guess I'm just thinking of the Ruf CTR; it's difficult to drive because of the rear weight bias. If you were to raise the rear (or just lower the front), it would just amplify that handling characteristic because the higher CoG would have more of a leveraging effect on the rear than the front, meaning more transferred load in the rear than in the front.

Not so much... The CoG will be very slightly higher but also further forward, as I already stated. Try it, the CTR is actually likely to be a perfect example.

Well, I guess using this idea, let's say you had a solid rear suspension (no travel, just steel beams instead of springs) and stock front springs, are you saying the front wouldn't compress at all because the rear couldn't travel/expand?

Nope. Compression has ABSOLUTELY NOTHING to do with weight transfer beyond migration of the center of gravity (as an end compresses, CoG shifts down and towards said end, up and away for expansion).

What I am saying, however, is that your above example would transfer less weight forward than having extremely stiff rear springs, which would transfer less forward than extremely soft rear springs as the CoG doesn't migrate as far forward. Well, unless there's enough braking force to lift the rear tires off the ground... In which case it rather obviously doesn't matter as weight transfer is 100% at that point.

 

[Poppins]

No.



You should damn well be able to tame it on S3s. I don't mean make it completely mindless to drive, I mean make it driveable. There's no point trying to drive a car that wants to make you dead every time you turn the wheel. Slight oversteer on entry, neutral through the center, slight push on exit = fun car that is actually fast.

Oversteer at any time extreme enough to require countersteer is slowwwwwwwwww. And we don't want slow.

Ah yes I agree with that. That is basically how all of my cars are set and I really dont understand how he is getting "that much" oversteer out of the MR2 because I have the supercharged version fully tuned to over 300 hp. And it flies.

 

[charliec]

Not so much... The CoG will be very slightly higher but also further forward, as I already stated. Try it, the CTR is actually likely to be a perfect example.

I'll try it with the CTR. I've tried raising the rear in other cars though just playing around and experienced increased oversteer/rolling.

Nope. Compression has ABSOLUTELY NOTHING to do with weight transfer beyond migration of the center of gravity (as an end compresses, CoG shifts down and towards said end, up and away for expansion).

What I am saying, however, is that your above example would transfer less weight forward than having extremely stiff rear springs, which would transfer less forward than extremely soft rear springs as the CoG doesn't migrate as far forward. Well, unless there's enough braking force to lift the rear tires off the ground... In which case it rather obviously doesn't matter as weight transfer is 100% at that point.

I know, I was just responding to "allowing one end to compress more increases weight transfer...The opposite applies to allowing one end to expand more".

My whole point was that you could have a very stiff (even solid) rear suspension with little benefit to elimating off-throttle/braking oversteer because you'll still have a load transfer onto the front tires (unloading the rear). The reduced load transfer to the front tires from a stiffer rear may not outweigh the (potentially negative) effects of stiffening the rear suspension.

I'll try your recommendation on raising/stiffening the rear on the CTR and see how it feels 👍

 

[charliec]

OP, maybe try this just out of curiosity: http://www.club4ag.com/faq_and_tech_pages/aw11_mr2_tuning_guide.htm

Real life suspension tuning recommendations from a TRD test driver for the car. Just curious to see if their applicable in the game...

 

[chuyler1]

Although, just as a quick "phone tune" I'll throw some numbers at you that I believe should sort the car out.

Height: -2 / -2
Spring: 7.2/12.5
Comp: 8 / 8
Ext: 5 / 5
Roll: 3 / 2
Camber: 1.5 / 2.5
Toe: 0.05 / -0.05

These settings are actually quite good. No oversteer/understeer. However the springs are too tight for Trial Mountain. It skips and hops over the front stretch making hot laps inconsistent.

I dropped your spring rates down to 6.8/12.0 and it behaved a little better over the bumps but there was a little more play in the suspension and I lost cornering grip. Not sure how to make it softer without introducing slop.

Back to your original setup I did some runs on Cape Ring Periphery. I was able to shave a few 10ths off my time but more notably I could run faster speeds through the loop. I was seeing 115-116 instead of 110-112.

Well you just ruined the car. The idea is to have 50/50 weight under braking. You just basically turned the car into a 60/40 or worse FR car.

If braking were the issue with this car I'd tend to agree...but at this power level keeping momentum is most important so the car needs a neutral feel under acceleration and coasting more so than the few times you have to brake on most courses. Putting the weight up front will allow it to transfer to the rear when the car accelerates. ...but anyway, a lighter car is really the goal and that was why I started this thread. To find a tune that would be equal to the additional weight.

 

[charliec]

These settings are actually quite good. No oversteer/understeer. However the springs are too tight for Trial Mountain. It skips and hops over the front stretch making hot laps inconsistent.

I dropped your spring rates down to 6.8/12.0 and it behaved a little better over the bumps but there was a little more play in the suspension and I lost cornering grip. Not sure how to make it softer without introducing slop.

Try softening the compression.