Front/Rear ride height differences

[KSaiyu]

Hi,

I've always assumed in GT that if you increased the one end's ride height more than the other, then that end of the car will have more weight transfer = less grip. When I started reading about roll centres, I was 99% sure I was right (since you were in essence raising that end's roll centre, which has a similar effect to increasing the roll stiffness of that end).

However, something I read in the Richard Burn's Rally manual (the ULTIMATE realistic car physics sim on any console) that made me think:

Strut platorm height: This adjusts the car's ride height in relationship to the ground. In addition, by adjusting the front in relation to the rear will alter the weight distribution and rake of the car. Raising the rear of the car moves the centre of gravity forward.

Since the CG has been moved forward, wouldn't this make the car understeer more - directly the opposite of what I described in the top paragraph? It is even stated in the GT3 manual:

Change the front/rear ride height balance to make fine adjustments to the car's front/rear weight distribution.

Also on the topic of ride height, do you think this is the measurement of the stroke length of the springs? I ask this because I noticed that the stock ride height in an RUF in GT4 was to have the rear about 10mm higher than the front. Using http://www.granturismobynumbers.com/ubb/Forum31/HTML/000572.html I came to the conclusion that this is because the weight is mostly at the rear, so the suspension will need more travel to accomodate for this - hence the increase in ride height.

 

[sukerkin]

Here's a quote I snipped from a r/c car site on the subject of ride height:

"HIGHER RIDE HEIGHT. The only time you would want to increase the ride height is when you run the car on low-traction surfaces. The higher CG of an increased ride height causes the car to roll more from side to side. This transfers more weight to the wheels on that side of the car, and additional weight on a tire equals more traction.

BEST BET. To change the handling, some racers adjust the ride height so that it’s different in the front and rear. By raising the front of the car, more weight will be transferred to the rear of the car when it’s under acceleration. This additional forward traction causes the car to steer less when it exits turns. Running the front ride height lower than the rear will have the opposite effect: more on-power steering when the car exits the turns. This is simply the effect of weight being transferred from the front to the rear instead of from side to side."

The stroke length question is a tricky one - I keep changing my mind . It would make sense if the Ride Height was the Stroke Length but who says the game designers have to make sense .

As to the RUF in GT4 ride height differential ... I'd be surprised if the only reason the rear ride height is greater is for stroke length. I would've thought that you'd solve that problem with stiffer rear springs. I can't say for sure of course but I'd guess it was to try and redistribute the weight a bit more evenly.

 

[KSaiyu]

I can't say for sure of course but I'd guess it was to try and redistribute the weight a bit more evenly.

See that's why I'm confused - changing ride height redistributes the weight (the higher the difference, the more the weight is moved in the lower ends direction), yet this conflicts the fact that it changes the amount of weight transfer difference front to rear. That R/C article seems to only address how having the weight shifted more to the rear by running a higher front will make the rear tyres grip better = understeer, and vice versa.

So confusing

 

[sukerkin]

Imagine the centre of gravity as the fulcrum for a lever.

If you move the CoG towards one end by altering the ride height then you are effectively changing the fulcrum position for the lever. The simple laws of reversed mechanical advantage then come into play (is that mechanical disadvantage then )?.

 

[KSaiyu]

I see, but I still don't get which "force" is the stronger. I'll take a FWD car as an example - the weight's mostly at the front (lets say 60/40), this will create a naturally understeering car since the CG is located nearer the front. Now if I took it to the extreme and raised the front and lowered the rear all the way, the CG would be moved back. Originally, I would thought that this would result in more weight transfer across the front end, but looking at the fact that the CG is moved towards the back, wouldn't this being doing the exact OPPOSITE.

There is my problem, there's two different explanations and I can't understand which affects the car more!!

 

[sukerkin]

Another little snippet, this time from the A1 Perfromance website:

"FWD cars suffer from 2 inherent problems, namely understeer and wheelspin under hard acceleration. This can be compensated to a large degree by having stiffer rear springs and a slightly lower ride height at the front. (NB. Understeer is a condition where the car tries to carry on forward after turning the steering wheel, whereas oversteer occurs when the back of the car breaks away and tries to overtake the front). To minimise rear end bump steer, anti-roll bars are a positive solution."

 

[KSaiyu]

Ahhh, so it definetly does clear up that it is how I thought - the lower end's ride height means better grip for that end, although I still can't find an explanation on the effects of redistributing the weight because of it.

 

[RedWolfRacer]

I usually do not adjust ride height on my cars as far as CoG adjustments. What I do with my road cars is lower it all the way for the sake of better aerodynamics. Then I adjust the spring rate and usually soften to further drop the car. But what I do is leave a tighter spring rate on the rear and a softer rate on the front. This lets the front tires transfer more weight in turns, especially in turns that require a lot of braking. I'll usually watch my replays and see on even cars like the 787B or the Toyota GTone that the body is shifting forward and the car's tires are doing almost exactly what I want, which is align perfectly with the ground with a zero camber angle to the tarmac. If you do this, I'd recommend experimenting with your camber angles.

 

[Der Alta]

Ahh... However, in GT3 they cannot adjust camber angles.

RWR, stop for a moment and realize what forum you're posting in, please.

You've demonstrated a good knowledge of why you adjust the suspension, so I'm asking that you please apply it to the correct forum.

Thanks,

AO

 

[RedWolfRacer]

Actually, yes you can adjust camber angle in GT3. You have to have racing suspension, though. Sports and stock suspension usually do not allow for camber adjustments. And of course it depends on the car.

I mean absolutely no offense, but I KNOW I am right. I played GT3 yesterday and played with camber on my RX-7 LM race car. Unless I got a screwy version of the game....

 

[Der Alta]

Yep, you're right. Serves me for not thinking it through.

For some reason I had Toe angle stuck in my head as being the only adjustment.

Thanks for catching that.

AO

 

[RedWolfRacer]

whew. Good. lol Didn't want to get in an argument with an admin my first week in. Heh heh.