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Slow in Fast out
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Discussion Starter #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
 

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Late Apexer
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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.
 

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F1 Crew #3
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in for response, I have theories but I dont know enough to know whats right or wrong
 

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<3 Bridget Regan
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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?
 

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i got killer fish
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what about wind resistance, i would assume the closer you are to the ground the less you would encounter
 

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Late Apexer
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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?


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.
 

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what about wind resistance, i would assume the closer you are to the ground the less you would encounter
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...
 

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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.
 

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Slow in Fast out
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Discussion Starter #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.
 

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Canon Crew
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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.
 

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<3 Bridget Regan
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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.
mugen ss FTW:thumbsup:

I remember a thread saying that the owner of Spoon said that they quit producing their suspension kit for the DC5R because they got better lap times on the stock DC5R suspension and that it was the optimal setup for the car.
 

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Canon Crew
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Kensai Racing team...

not slammed.

 

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The "slammed" track oriented DC5's that you do see have more then just coilovers. The whole suspension is carefully revised. If you were to take a glance underneath one of the wheel wells, it may not even resemble a stock DC5.
 

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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.
 

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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.
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.
 

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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.
Once again, Zzyzx providing counter-intuitive, or at least counter-to-what-I-have-been-led-to-believe information.

Could you expound on that? Maybe it's just the Hobgoblin I've been drinking, but I don't understand how that occurs.

Seems as if the outside tire carries the most weight during a turn, and an anti-roll bar causes the inside to carry more of the weight than it would without an anti-roll bar......thereby reducing the weight the outside tire carries...... :dontknow:
 

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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.

 

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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?
 
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