No real life experince here but what springs to mind:

From a CoG point of view, lowering the rear ride height will reduce weight transfer, slightly increasing the coefficient of friction of the rubber thanks to tyre load sensitivity. A minor change but could be noticable.

Thinking aero, both front and rear angles will be affected equally. I would have thought it unlikely that they are set to the same angle, so the aero balance will change. If your problem is only at high speeds then it does (potentially) point to an aero issue. Don't know how it would effect the undertray but lower rear is less downforce overall. If you need twice the rear angle of the front (for example) for a stable aero balance, e.g. 14 and 7 degrees, if you alter the pitch 2 degrees squat (a lot but just an example) then you have 12 and 5, this is now over double at the rear which should add understeer. Of course aero isn't linear but for small changes it should be near enough to get an idea.

Regarding static camber, you're not running rear camber, but what about front? I'm certainly no tyre expert but with castor and inclination adding camber to the front wheels, assuming camber gain from suspension geometry is equal (a big assumption too), then surely the rears are going to be lacking grip compared to the front (again, assuming you're not getting too much dynamic camber at the front).

Quote from Bob Smith :

From a CoG point of view, lowering the rear ride height will reduce weight transfer, slightly increasing the coefficient of friction of the rubber thanks to tyre load sensitivity. A minor change but could be noticable.

Sounds good.

Quote :

Thinking aero, both front and rear angles will be affected equally. I would have thought it unlikely that they are set to the same angle, so the aero balance will change. If your problem is only at high speeds then it does (potentially) point to an aero issue. Don't know how it would effect the undertray but lower rear is less downforce overall. If you need twice the rear angle of the front (for example) for a stable aero balance, e.g. 14 and 7 degrees, if you alter the pitch 2 degrees squat (a lot but just an example) then you have 12 and 5, this is now over double at the rear which should add understeer. Of course aero isn't linear but for small changes it should be near enough to get an idea.

I refuse to quote wing angles, because they don't make sense in real life. It's a curved wing at the front, of varying chord, so the 'angle' will change depending on where you measure along the wing. At the rear there are two planes, and again the angle isn't simple, as one plane is fixed, the other adjustable, with a slot inbetween. I try and tune the wings to make the balance, but I don't want to reduce wing angle at the other end to make the rear work. Seems counterproductive. Hence suspension playing.

Quote :

Regarding static camber, you're not running rear camber, but what about front? I'm certainly no tyre expert but with castor and inclination adding camber to the front wheels, assuming camber gain from suspension geometry is equal (a big assumption too), then surely the rears are going to be lacking grip compared to the front (again, assuming you're not getting too much dynamic camber at the front).

At the front we run about 0.25° negative camber. With steering axis inclination and castor there is obviously more when steering. But you can't run much camber with crossplies else you melt the inside edges - bad and expensive. It's one of the limitations of these tyres, and a big reason why we're changing to radials for next season.

I think lowering the rear could do a great deal because you not only change the max. (static) weight distribution but you also change your
cross-weight percentage wich will have a much greater effect.
But then , I really don't know IF setting cross-weight on a F3 car makes a great deal because they're pretty nicely balanced anyway opposed to the cars I use to work on.

Do you have the symptoms/problems in *every* corner or is it only in left- or righthanders ?

Cross weight percentage will remain the same. We set the cross-weight (corner weights) before each race to ensure there is equal load on both front tyres (for stability under braking). It's widely considered acceptable to leave the rears however they are to make the fronts equal.

Cross-weights on a formula car are vastly more important than a closed wheel car. You can tell if they are out easily.

Direction of corner doesn't make much difference really, although it's hard to tell because there are no tracks with identical corners but in different directions, so whilst into Paddock I'm doing something like 90mph over a crest to the right, in Surtees I'm doing 110 relatively little gradient to the left. There are almost too many variables to say it's better or worse in some corners than others, but it tends to manifest itself at the high speed corners. It's not really a problem in slow corners where it's natural understeer takes over (all F3 cars understeer in slow corners).

Do I take it that nobody disagress with the statement that lowering the rear will reduce oversteer in general terms (all other things being equal, and all within limits)?

Well, I'm not setup guru or technical man, I'm still learning but as far as I know, if you're talking about the rear of the car, softening rear suspension should really help. I remember testing that in a few sims(incl. LFS) and they all gave the same effect, lots more traction. If you're talking about medium to high speed corners, I think the roll bar comes into play big time so maybe softening the rear roll bar?

About the ride height bit, like Dan, all I can think of why the ride height would make a difference would be because of weight transfer. Have to say tho Tristan, you can't really think in the way that you don't want to change the settings at the front of the car because the front and the rear are equally important when it comes to car setup. The word balance is really spot on because its all about the front cooperating with the rear and vice versa.

Just reduce the front win... oh you don't want that.
Then increase rear wing ang... maxxed out already? Darn.
Ok, increase rear camb... no, doesn't work either.
Maybe soften rear rollba... what, for finetuning only? Ok.
Then raise... or lower... the rear and see what's better. You want a definite answer which is better? Ok, then not

Maybe you just need to redesign the rear wing to make it more efficient. This guy seems to know what he does, maybe you should copy his design

if i caught your drift the front is currently noticeably lower than the rear ? might be that you shift the point of attack for the undertray forces forwars that way inducing oversteer at speed
but tbh im more or less talking out of my arse here

Quote from Leprekaun :

Well, I'm not setup guru or technical man, I'm still learning but as far as I know, if you're talking about the rear of the car, softening rear suspension should really help. I remember testing that in a few sims(incl. LFS) and they all gave the same effect, lots more traction. If you're talking about medium to high speed corners, I think the roll bar comes into play big time so maybe softening the rear roll bar?

Although we recently increased the spring rates, that was because they were too soft, and the car was bottoming a bit too much. We've gone up by just 25lbs/in on the springs, and carefully made sure the wheel frequences also correlate. I don't think it's springs, and softer isn't an option. I am tempted to try slightly stiffer front though.

Quote :

About the ride height bit, like Dan, all I can think of why the ride height would make a difference would be because of weight transfer. Have to say tho Tristan, you can't really think in the way that you don't want to change the settings at the front of the car because the front and the rear are equally important when it comes to car setup. The word balance is really spot on because its all about the front cooperating with the rear and vice versa.

I don't want to change some settings at the front. I don't want to reduce front grip to balance the lack of grip at the rear if I can just increase the grip at the rear. Correcting aero problems at the rear with front wing is a sim attitude, and not safe or sensible in real life.

Quote from AndroidXP :

Just reduce the front win... oh you don't want that.
Then increase rear wing ang... maxxed out already? Darn.
Ok, increase rear camb... no, doesn't work either.
Maybe soften rear rollba... what, for finetuning only? Ok.
Then raise... or lower... the rear and see what's better. You want a definite answer which is better? Ok, then not

Maybe you just need to redesign the rear wing to make it more efficient. This guy seems to know what he does, maybe you should copy his design

Well, this topic was meant to be about ride heights, not wings, roll bars etc. They have all been considered before I made this thread. I am willing to admit that there isn't 'one magic cure', but the point of this thread was to see if reducing rear ride height might be a step in the right direction. Maybe I was hoping for more technical reasoning, with diagrams and equations, I don't know. But don't blame me for not being able to use more camber or knowing that the rear ARB is only a fine tuning tool. I don't have unlimted adjustment like in LFS. Do not confuse sims with reality - I am the first to admit how close LFS is to reality, but the setups are a joke, and have nothing to do with setting up a real car. Same in nK, same in GTR, same in rFactor. Real life isn't like that.

Quote from Shotglass :

if i caught your drift the front is currently noticeably lower than the rear ? might be that you shift the point of attack for the undertray forces forwars that way inducing oversteer at speed
but tbh im more or less talking out of my arse here

When used at the designed ride height, all formula cars have higher rear ride heights than front - underbody effects, combined with roll centre axis inclination. Various 'rules of thumb' apply, which I don't tend to trust. As we have to run at 40mm minimum, we kept the suggested 20mm of rake that the original setup data (seriously lacking) suggested. As the car is now quite quick (for it's age and tyres, and my experience) we having to improve elements on the car as well as allowing me to learn to drive. What might have been a stable car 3 races ago is less so now because I'm learning to exploit it more, highlight weaknesses in the driver/car combination - in this case oversteer).

I'm going to go ahead with the ride height change, and I'll let you know how it goes. Next race (and last of the year) isn't until October 13th and 14th at Snetterton, so I'll let you know then.

Heh, I'm just kidding

It was a mere jab at the situation which seemed like "I have problem X and want to solve it with solution-that-might-work-or-not Z, but I don't know exactly how, and by the way I don't want to <lists top 5 most obvious solutions to problem>".
I'm not really suggesting that you're a fool* who neglects the easy way, and you have pointed out several reasons for why you have/want to resort to the ride height anyway. I agree, using LFS is probably the worst way to find out what to do, seeing that it's very likely an aero issue which is horribly modelled right now. Same goes for the setup options which are as far away from what is possible in reality as they could be, if you're not a multi-million £ racing team that is. I just found the overall situation kinda weird/funny.

Regarding the ride height, seems like the general opinion is that it could work either way. I fear you won't be able to avoid testing both and seeing which is better. Well, there's a chance that the first try already fixes the problem. Or neither. You have the choice to trust the theory or what the old boys say, but in my opinion simple methodical trial and error gives the best knowledge/results in the long run. The bad thing is it takes time to do all these adjustments and testing. If it was just as easy as in LFS...

*yes, I am

Quote from tristancliffe :

Although we recently increased the spring rates, that was because they were too soft, and the car was bottoming a bit too much. We've gone up by just 25lbs/in on the springs, and carefully made sure the wheel frequences also correlate. I don't think it's springs, and softer isn't an option. I am tempted to try slightly stiffer front though.

Well, that could work, yeah so stiffening front springs could help out but if you don't want to go near the front of the car for setup, I think you should lower the rear according to the front. If lets say, you have 50mm set for the front, maybe make the rear 40-45mm to give more stability at the back? but I guess that won't work if the track is too bumpy. Its a real toughie Tristan and considering your vast knowledge on car mechanics and you having a problem, must be a real pain in the ass problem. Well, thats the only thing I can think of if you want to change rear ride height (make the rear lower than the front to produce more downforce at the back), otherwise, you're just gonna have to make some human setup in your driving style to suit the car

Lep, please read my post (again) and think about why having a lower rear than front is a VERY VERY bad idea... Or do I have to show you LeMans-cars doing somersaults?

You may talking about LfS, please remember aero is far from finished in LfS...

The front is currently at 40mm. The rear is currently at 60mm. I'm suggesting a 5mm drop at the rear - so it will still be higher than the front

Quote from tristancliffe :

The front is currently at 40mm. The rear is currently at 60mm. I'm suggesting a 5mm drop at the rear - so it will still be higher than the front

Quote from bbman :

Lep[rekaun], [...]

okay... don't get that bb .

Cool . Well, please please please, let me know if it fixes it or not. I'm still learning car setup so I'm interested to see if my theory is correct

High nose not only would take away much of the efficiency of the wings, you'd also drive a big wedge of air under the car, which - given a high enough speed - would eventually flip the car. If you remember the spectacular vids of the merc and iirc the porsche at LeMans, that was just a short moment where the car went over a bump, but it caught enough air under the car to literally send it flying... Now you're suggesting that Tristan drives a car that is deliberately set up to do that?

Well, I'm not planning on getting into an argument about this but only Mercedes and Porsche really know why the car did that. True, it could've been the reason to why the cars did that but all true racing enthusiasts or racing drivers know that sometimes, you have to take risks. Its up to Tristan if he wants to go ahead with it or not.

No offence to Tristan, but i really doubt Tristan's on the ragged edge so much he's willing to flip his pride and joy over and potentially get decapited for a potential 0.05 second gain if (and i say if) he rides the car RIGHT on the limit

The CLR flip, technical, but written with very understandable language:
http://www.mulsannescorner.com/techarticle1.htm

A lot to do with the tear-drop body shape, which creates aerodynamic lift.

In that LeMans they had 3 flips happen with Mercedes CLRs, one in qualifying, one in warmup and one in the race IIRC. So I suppose it's safe to presume it was a design flaw. The Porsche flip was in a different race I think. However, extra style-points and a higher difficulty rating together with an artistic expression of quite some finesse put Mercedes on the top of the flipping game.

Quote from Leprekaun :

Well, I'm not planning on getting into an argument about this but only Mercedes and Porsche really know why the car did that. True, it could've been the reason to why the cars did that but all true racing enthusiasts or racing drivers know that sometimes, you have to take risks. Its up to Tristan if he wants to go ahead with it or not.

You think a club racer should test risky setups because some forum wannabe reckons it might be a good idea?

Tristan: those ride heights are indeed quite high so I guess that the influence on underfloor aero won't be that big. What you are still doing with rake though is changing the AoA of the whole car body which itself acts like a wing.

I'd say give it a try. Although personally I would probably start with the front wing settings. You may lose a bit of overall grip but don't forget that you are also losing drag and maybe improving the lift/drag ratio.

Why would you use rollbars as finetuning only? I'd say a 5mm drop of the rear is probably more fine tuning than a rollbar adjustment..

While I agree that lowering the rear might help a bit, I doubt it will really solve the issue. Plus a downside of lowering, depending on how much the suspension generally moves, you may hit the bumpstops more often? I'd probably prefer a slightly softer higher car.

What about tires, and temperatures.. Perhaps the fronts get too warm or the rears stay too cold?

I'm really only talking out of my sim experienced arse, I have little practical knowledge of these type of cars..

Because the blade type adjusters don't really change the roll rate all that much. The difference between fully hard and fully soft isn't all that much in real terms. If I use full soft rear and full hard front, the car still has this excessive oversteer.

Lowering the rear should, in my opinion, lower the rear CoG and roll centre, increase the diffuser efficiency, and give a slight reduction in upper body aero.

The car is lowered on the rear pushrods, so bump and droop travel and wheel rates won't be changed by this change.

Tyre temps are pretty even, and well within limits according to Avon. Pressures end up at 20psi front and rear, which is what the tyres are meant to reach.

I might be speaking out of my arse, which is why I opened it to debate here. Some good points have been raised, but the overriding opinion seems to be that it's worth a try and might work, depending on how much rear wing/upper body aero is reduced.

Raise the rear

I didn't think it was right either, but today at the track we raised the rear ride height to counter oversteer.(Jim Russell@Infineon, race mechanic program)

It seems to me the effect of ride height can be opposite depending upon the rest of the car. In this case, from what I understand, the higher hear raises the CoG in the rear and transfers more force to the outside rear tire. It also slows down the movement and makes it more smooth in weight transfer.
-The cars are similar to Formula Russell cars
-Like you said, lower the rear if its an aero balance problem

Sometimes this works and sometimes that I think you need to figure out where in the corner and what kind of corner you are having issues in first, then solve.

You might find these images useful mate:

These photos come from Allan Staniforth's Race and Rally Car Source Book. A fantastic read and a must for any self respecting petrol head.

DSCN0480.JPG

DSCN0481.JPG

DSCN0482.JPG

DSCN0483.JPG

I read once that the lower roll centre should be at the lighter end of the vehicle.

At the end of the day there are lots of ways of achieving a particular handling balance and in my view there are no simple rules and no subsititute for hours and hours of on-track testing. Still it's all good fun you lucky bugger

Yup, got that book - is very good. Incidentally, I know the person who currently owns the Gould Terripin, and he [the current owner] briefly raced it a few years ago in the series I currently race in.

I think the lighter end will still have the lower roll center (although I can't confirm this until I get round to drawing the suspension accurately). But I've heard that greater rear:front ratio (i.e. a more steeply inclined line between front and rear roll centers) will encourage more understeer. On that basis lowering the rear with respect to the front might encourage more oversteer (but perhaps not in the same situations).

It's very difficult to be sure without a) drawing it b) implicitly understanding the causes and effects of geometry differences in all situations and c) testing.