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Ride Height and Performance, lets discuss.

27K views 98 replies 45 participants last post by  02RSXN2ZAZT 
#1 ·
Alright,
so I want to start a discussion about how ride height and suspension geometry affect one another. I've been told anything below 1.5" (some say even an inch) is compensating looks for handling. Why is this? Optimal roll center? Superior range of action? Bump Steer? I believe the key argument is Roll Center ... but I'm uncertain... do we want non-rolling weight transfer effects? Wouldn't this be optimal when the arms are almost parallel? If you take a look at the Spoon and BC DC5's, they are low... custom fabrication involved?

I love discussing/understanding suspension geometry, so let the input flow. :thumbsup:

-Caleb
 
#2 · (Edited)
Two things off the top of my head.


1. Suspension travel... the Stock suspension only has about 3" of bump travel, lower it more then an inch or so and you've severely cut in to the cars bump travel.

2. Camber gain. Contrary to popular belief, strut type suspensions do gain camber when they compress. problem is, unlike wishbone types of suspensions, a strut will only gain camber so long as the angle between the lower control arm and the strut is less then 90 Deg. Once the suspension compresses to the point where that angle is greater then 90 Deg then that suspension will start to lose the camber that its gained up to that point. So, when you lower the car, you reduce the potential amount of camber gain you can have as well as start closer to that camber gain/Camber loss threshold, which can force you to run a stiffer suspension then you other wise would need to run... obviously increasing the cars suspension frequency, which reduces the potential mechanical grip of the car.
 
#4 ·
Its said sometimes that a slightly higher ride with stiffer sways will give you maximum grip, contrary to having the car to low with stiff sways which will result in more of a potential slide scenario / or having the car to low with stock sways which is too unbalanced. What to you think?
 
#8 · (Edited)
Anti-roll bars, in doing their jobs, actually increase the amount of weight the out side tire carries during a turn and decrease the amount of weight the inside carries... meaning, they actually decrease the maximum potential traction the car can make.

That being said Anti-roll bars are a great way to reduce camber loss when running soft springs, but only as a trade off when the amount of traction lost by stiffening the anti-roll bar is less then the amount of traction you'd lose by letting the chassis roll too much. This is most common on street cars where you find cars with relatively soft springs and Negligible amounts of static negative camber. Other wise you are doing more harm then good.

they are also very useful in tweaking the cars oversteer/understeer balance thanks to them reducing the amount of traction at the end of the car they are mounted to. so if you have a heavily understeering car, reducing the traction at the rear of the car by stiffening the rear anti-roll bar will greatly alleviate the problem. But then so would softening the front bar.
 
#9 ·
um ok...you can't compare time lost from wind resistance vs. camber loss. Wind resistance has such a negligable effect except for straight line acceleration. If you can lessen wind resistance while minimizing camber loss during a turn, then you would have a car that has control arms that are close to the ground (such as F1 and touring cars). The reason those cars are lower is because the chassis is laid out to have parallel control arms or slightly obtuse control arms while at rest.

Ever see a corvett or bimmer's rear control arms? They are 90 degrees for a reason. When you lower our cars, they get acute and affect camber during turns, especially up front.

Zzyzx knows more than I do, I am just talking right now because I need to procrastinate...
 
#10 · (Edited)
If...if...if you could lower the car without losing any suspension travel, or altering the suspension geometry, or exceeding an optimum spring rate, it would be a good thing. You'd have a lower center of gravity, less roll, and less wind resistance and you'd have a purpose built race car. But...but...but we're talking about lowering an RSX, and as ZZyzx said you lose a lot of suspension travel...not good, and you alter the suspension geometry detrimentally... not good. The optimum spring rate according to Carroll Smith in "Tune to Win" is the that rate which keeps the car off the ground and the bump stops, the rest is best dealt with using anti-roll bar and dampening, so if you have too stiff springs just to keep the car off the bump stops with the much reduced suspension travel you haven't gained anything. If you do all your racing on a perfectly smooth track, maybe you're OK, but I run on a rough track (Sebring) and the roads in Tampa/St. Pete are full of holes, so I'm sticking with the OEM ride height.
 
#11 ·
Camber relation makes perfect sense. I notice that at even with an inch or so drop, my front arms are much closer to the 90 degree mark. And since I'm not running a front sway, its a good thing I'm at this height.
 
#12 ·
there is a reason why you dont see an ITR DC5 or anything on our cars lowered more than an inch. It doesnt pay to be slammed.
 
#16 ·
The RSX does not perform well when lowered without significant geometry correction. Road & Track SPEED magazine tested an RSX that was lowered excessively, and it did very poorly in the slalom. The owner raised the ride height significantly and came back for a retest. The car went much, much faster.

My own experience with the car has yielded similar results. With the car quite low, it felt responsive right on center, but the front end washed out, steering feel and communication went away, and grip was poor. With the ride height closer to stock, the car performed very well.

John Grudinski at HyTech Exhaust told me this is because the roll centers get all screwed up at low ride height. When the car rolls, the roll center actually migrates way outside the track of the car, so the weight transfer is all screwed up. I haven't done an analysis, but it fits with what I went through with two different brands of coilovers and setup on my car.

The RSX geometry is problematic enough that RealTime Racing homolagated a new suspension component as late as the end of 2006 - they're still working to "get it right" at the ride heights they run. It is my belief that lowering an RSX to "race like" heights without a massive investment in geometry revisions will only lead to problems.

My basic formula for handling: Keep it fairly close to stock height, about 1/2 to 3/4 inch lowering. Stiff springs, with good dampers that will control the springs properly. Good anti-roll bars. I like the Comptech rear bar at full stiff, but it is kinda spendy. Add a little negative camber in the front. 1/32 to 1/16" total toe-in in the back, zero toe in the front. Works well for me.

I'd like to try spherical bearings on the inboard part of the front lower control arms to help control the front wheels. When you launch an RSX hard, the front wheels flop all over the place. Never got that far on my car, though.
 
#17 ·
I couldn't have said it better. Too bad most people don't understand that. It's kind of hard to understand, actually. Most people think that coilovers make a car handle like a dream. Another big misconception is that a "stiff" steering constitutes good handling. Wrong. It's all about the feedback. Here's a quick analogy. On a stock Type S, bump up the tire pressures to 40 Front, Rear 35. Compare that to 30 Front, 30 rear. The first set-up will result in a "looser" feeling. The latter setting will make the steering feel much more stiff. So is it better to run it at that setting? Autocrossers would nearly always use settings closer to the first example. It's better for the sidewalls. That's just an example, but a stiffer steering doesn't always result is better handling.
 
#19 · (Edited)
Zzyzx may have a comment of his own, but perhaps what he said is only partially true. An anti-roll bar works by compressing the spring on the uncompressed side (inboard) during roll. If we take an extreme example, an anti-roll bar that directly connected the other side without any twist (ie an infinitely stiff bar), it would double the spring rate during roll. If both front and rear anti-roll bars are equal in stiffness and the front and rear spring rates are equal I don't think that doubling the stiffness of the anti-roll bars will transfer any more weight to the outside and remove any from the inside. The car isn't putting any less pressure on the inside wheels it is just rolling less and one might argue that in the above scenario, since there is less roll, there is a more even distribution inside and outside.

HOWEVER, this is not the case is most cars and specifically not the case for the RSX. Since most of the weight is up front and we are trying to selectively improve the front grip there is a large negative bias in the front to rear roll reistance (more in the rear) due to stiffer rear anti-roll bars and stiffer rear springs. In this scenario there is substantially less pressure put on the inside rear (and as a result more on the outside rear) to the point that my inside wheel is not touching the ground on hard corners. With less roll stiffness up front the front inside wheel has more pressure on the pavement relative to the inside rear and this helps the car get more grip in the front.

An analogy is a go kart verus a tricycle. A go kart has infinite and equal stiffness at the front and rear so in a hard turn the front and rear inside wheels have essentially equal pressure (when coasting through a turn) and the front and rear outside wheels have essentially the same pressure albeit more than the inside. On a smooth surface I'm not convinced that there is less pressure on the inside than there would be with a suspension. On the tricyle the front has zero roll resistance and the rear has infinite roll resistance so in a hard turn the inside rear comes off the ground and all of the rear pressure is transferred to the outside. It is the bias towards one end that allows more pressure at one end and less at the other.

 
#20 ·
If you really want to understand all this, go get any of the good books out there on suspension and handling. It's not rocket science, you can understand it with pictures and hand waving. Spend the 15-20 dollars on learning from someone who's demonstrated their grasp of it, rather than just reading stuff on the internet. How many gallons of gas is that where you live?
 
#22 ·
justjim you are on the right track, And its important to note that I said "increase the amount of weight the out side tire carries during a turn and decrease the amount of weight the inside carries", rather then say that anti-roll bars increase weight transfer.

Surprisingly enough there is a very big difference. And here it is.

Imagine a suspension with a pair of springs both rated at 100LB/inch. For clarification that means when 100LB's is applied to one of them it will compress 1"

Take this suspension and put a static weight of 400 LBS on it evenly between the two springs, so that both are holding 100 LBS.

Now take this setup through a turn that transferes 100 LBS accross the chassis. So now the inside tire is holding 300 LBS and the out side tire is holding 500 LBS.
Simple.

Now Lets add an anti-roll bar, say one thats strong enough to transfer 25% of the force inputed. At this point with a 100LB imput force 25 LBS is going to be able to be transfered to the other spring. So now the inside tire will be holding 275 LBS and the outside tire will be holding 525, But the outside spiring will only be holding 475, where as the inside spring will be holding 325....

Meaning the outside spring is holding less weight Thus it compresses less, reducing body roll..... BUT the weight actually making it to the tires contact patch has increased, Thus Less available traction.

Sounds counter intuitive, but to understand why you have to look at the way anti-roll bars are doing their jobs. Remember Anti-roll bars are basically U shaped bars, so both ends move in the same direction. So in our instance above, as the outside suspension compressed, that anti-roll bar started to push UP on the inside spring. So Although the amount of weight over the inside suspension hasn't changed, the amount of that weight making it to the inside tires contact patch has been reduced. In this case a 25 LB upward thrust = 25LBS less making it to the ground. This 25LBS has to be supported some where, and it is... by the outside tire, not the outside spring...

See the difference?
 
#23 ·
Apologies for sort of hyjacking this thread but hey I may learn something. Zzyx I've always looked at your hypothetical example a bit differently, although I suspect you and I may end up tuning a car pretty much the same way and are in general agreement on the end result.

My thought is that, given your example, in a turn the outside spring compresses so that the outside tire feels 500 lbs and the inside spring extends and the inside tire feels 300 lbs. If you add the anti-roll bar in your example, the outside spring wants to compress as before but is inhibited from the same compression as before by the connection to the inside spring effectively increasing the outside spring rate by 25 lbs and thus generating less body roll in the turn. If there is no front to rear bias in spring rate or roll resistance there would actually be a net decrease in the former 100 lb lateral transfer of weight, due to less roll in the turn, so there would be a reduction in force on the outside wheel (something less than 500 lbs). This of course would not be the case when front to rear spring/bar bias is introduced.
 
#24 · (Edited)
Remember, Body roll is an effect of weight transfer, not a cause of it.

For clarification, once the car is in the turn the amount of weight pushing down on the suspension doesn't change, theres still 500 LBS pushing down on the outside suspension and 300 lbs pushing down on the inside suspension.

what does change with the addition of an anti-roll bar is which tire is holding that weight.

From the example above, with a 25LB thrust upward on the inside wheel (which translates to a 25 LB thrust down on the outside wheel, remember for every action there is an equal and opposite reaction). With this 25 LB upward thrust, that means that 25lbs of the weight pushing down on the inside suspension is now being transfered through the anti-roll bar to push down on the outside wheel. So, there will be 25 less pounds reaching the contact patch of the inside tire and 25 more pounds reaching the contact patch of the outside tire.


So with out an anti-roll bar you have

500 LBS pushing down on the outside suspension
300 LBS pushing down on the inside suspension
which yealds
500 LBS applied to the contact patch of outside tire
300 LBS applied to the contact patch of the inside tire
And,
the spring on the outside will be under 500LBS of force
the spring on the inside will be under 300LBS of force
and the suspension compresses 1" on the outside

where as if you add in an anti-roll bar that transferes 25LBS...

You still have
500 LBS pushing down on the outside suspension
300 LBS pushing down on the inside suspension
But now you have
525 LBS applied to the contact patch of outside tire
and 275 applied to the contact patch of inside tire
And
The spring on the outside will be under 475LB of force
and the spring on the inside will be under 325 LBS of force.
Thus, the suspension compresses only 3/4", thanks to the inside spring absorbing 25LB of the input force.
 
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#25 ·
Great Thread that should be stickied. Many of the reasons cited here are why I choose the A Spec Suspension, it just seriously makes no sense for anyone on the street to ride slammed, unless your suspension is fully tuned, which we all know its not. I love the way my car handles and wouldnt trade the height or performance for anything else.

The warranty coverage is a nice bonus too.
 
#28 · (Edited)
I had to think on this...big thoughts that hurt my head...and I in my infinite wisdom and in consultation with Carroll Smith and others have decided that Zzyzx is indeed correct:bow:

Although my car's suspension is perfect, I must now modify both my go kart and my tricycle.
 
#30 ·
i'm gonna raise it about 3/4" all around. I'm at 1 finger rear 2 fingers front right now. I just got new tie rod ends so i figure i'll install those while i do it and get it all done at once
 
#31 ·
wow i love this thread

do u guys have any idea wat is ideal ride height for BCN+?

right now i have 1 finger gap in front, and half finger gap in rear, and i believe it's way too low. I wanna raise it up to make it perform at its optimal

someone help me here
 
#34 ·
Depending on your spring rates, you want your angles to be obtuse (greater than 90 degrees), so that during compression, you don't lose that much camber and toe. If you have really stiff springs, then slightly obtuse, but near 90 degrees should be fine.

the ideal settings for any set up will vary by driver, temperature, tire composition and size, and a brazillion other factors. The only way to test all this out is seat time or on a skid pad. Since many of us don't have much access to either, just play with it, set it how you like it, and go from there. If you want to squeeze that last bit it out then try different settings during seat time.
 
#35 ·
1.4" will get you quite close to the 90 degree mark. I'm around 1.3-1.4" up front with -2.0 degrees of camber. I want to raise the front .4-.5" but I'll see how it goes this weekend and tune from there.
 
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