Suspension Height

[NISMOPower]

Here is the situation...Posting here because of perspective...

I finally got some Cattman coilovers, upgrading from sprint/agx. All I care about handling no matter what it takes. I know there has been some discussion about control arm modifications and other things with being too low. Currently I have about 1 Finger Gap (Shown here) What is the optimum ride height for handling. I will be tracking this car and pretty much need a point of view to start before making minor adjustments. Also another thing is why at that suspension?

I'm thinking later I may get them revalved and get more race spec springs....

Chris

[d00df00d]

You want no more than a 1.5" drop.

[irish44j]

you want to make sure the LCAs are not pointing "upward," basically. Keep them slightly below level.

[jac121479]

Originally Posted by irish44j

you want to make sure the LCAs are not pointing "upward," basically. Keep them slightly below level.

if your gonna be hittin the track, a proper alignment (not Pep Boys) and corner balancing your ride would be helpful.

[NISMOPower]

What is done in corner balancing and as far as height as long as the control arm is pointing downwards toward the wheel if not level, am I correct on that?

Chris

[DrKlop]

IMO 1.8" - 2.0" drop will actually resut in better lap times than 1.5.

The car will indeed handle (not grip) better at 1.5" however, lower center of gravity (which allows the weight to be distributed more evenly) IMO is just as important, and sometimes (when stiff coilover springs significantly reduce body motion) it pays to sacrifice ideal suspension geometry for lower center of gravity.

[NISMOPower]

Well I finally got a corner balanced and alignment today. Ended up having my wheel gap 1.25" wheel gap...

[d00df00d]

Originally Posted by DrKlop

IMO is just as important, and sometimes (when stiff coilover springs significantly reduce body motion) it pays to sacrifice ideal suspension geometry for lower center of gravity.

Many experts disagree with you.

First, lowering your car to lower your center of gravity also lowers your roll center, which increases the amount of body roll for a given amount of load transfer.

Second, if you lower your car past the point at which your control arms make a 90 degree angle with your strut, suspension compression will give positive camber gain. Why that's bad shouldn't require much explanation...

[gdmaxse]

Originally Posted by d00df00d

Many experts disagree with you.

First, a lower center of gravity increases the amount of body roll for a given amount of load transfer.

Second, if you lower your car past the point at which your control arms make a 90 degree angle with your strut, suspension compression will give positive camber gain. That doesn't take much explanation.

I think you mean lower roll center, but you are both correct. The only problem with running super stiff springs is they lose traction over bumps which most roads and racetracks have. So for a dual purpose street/track car IMO it is better to go with a little less drop and softer springs and keep the geometry closer to ideal.

[jac121479]

Originally Posted by gdmaxse

I think you mean lower roll center, but you are both correct. The only problem with running super stiff springs is they lose traction over bumps which most roads and racetracks have. So for a dual purpose street/track car IMO it is better to go with a little less drop and softer springs and keep the geometry closer to ideal.

agreed!!!

[d00df00d]

Originally Posted by gdmaxse

I think you mean lower roll center, but you are both correct. The only problem with running super stiff springs is they lose traction over bumps which most roads and racetracks have. So for a dual purpose street/track car IMO it is better to go with a little less drop and softer springs and keep the geometry closer to ideal.

Ack, you're right. Thanks... Post duly edited.

[DrKlop]

Originally Posted by d00df00d

Many experts disagree with you.

First, lowering your car to lower your center of gravity also lowers your roll center, which increases the amount of body roll for a given amount of load transfer.

Second, if you lower your car past the point at which your control arms make a 90 degree angle with your strut, suspension compression will give positive camber gain. Why that's bad shouldn't require much explanation...

I don't think you understand what I'm trying to say.

Let's suppose your suspension goes out of it's best working range if you drop the car lower than 1.5" (a common belief, might be true, might be false) and you start experiencing positive camber gains and bump steer. The lower you go past that point the more noticeable it gets.

Than the change in performance (lap time,) only due to the change in control arm position, will be similar to the way it is shown on graph #2; and the change in performance only due to the lowered center of gravity will be similar to the way it looks on graph #1.

Since, the change in C.G. and the change in control arm position affect performance at the same time, we have to add both of these graphs together to see the overall change in performance, which should look similar to the curve on graph # 3. (Which shows that the car performs best when it's dropped by a little more than 1.5")



Also, I can't find any specific proof right now, but as far as I remember Matt, BEJEY and BlackbirdVQ keep their cars lower then 1.5 inches. (Hopefully one of you guys will chime in )

edit: graph number 2 will look slightly different to the left of 1.5 inch line. I forgot to take into account the increase in body roll.

[d00df00d]

I fully understand what you're trying to say (I believed it myself for a while). I'm just presenting a counterpoint. I know for a fact that I have heard flat out, from people at LEAST as autocross crazy as the people you named, that "if you have to choose between CG and suspension geometry, choose suspension geometry".

Plus, Matt93SE has been very vocal about not exceeding a moderate drop; BEJAY1 has experimented all over the place and done some secret things to his car so there's no telling what he's actually doing nowadays; and BlackbirdVQ is obviously not aiming at perfect handling at all costs.

Plus plus, you can't use graphs drawn in MS Paint to prove anything.

[gdmaxse]

ok ok so:

Ideal Geometry= GOOD
Low=GOOD

Compromise: Lower with springs till the control arms are almost horizontal. Then use shorter TIRES to lower the car even more to get more grip.
Some good tire sizes are 225/50/15, 225/45/16, 225/40/17

[d00df00d]

Good call.

[michaelnyden]

suspension geometry always wins...cause in the end, if you can't get a lot of contact patch/rubber to ground as would be the case with gaining positive camber (dynamic camber), it doesn't matter how low your CG is, you will have no grip. The only way to effectively make use of running extremely low and not suffer the consequences of gaining positive camber is to resist gaining it as much as possible such as getting relocateable LCA's/links to do so or run extremely high spring rates such as what bejay is doing, essentially resisting compression which is the situation upon which the LCA moves and gains the positive camber and bump steer in the first place.

As for bumpier tracks and autoX environments, really high spring rates actually make traction worse (obviously), so in that case, softer is actually better (but the real goal is proper wheel rates and damping to control those spring rates) which can effectively mean the difference between being able to run those high spring rates on the slightly bumpy track vs. cheaper dampers and mismatched damping rates that will not allow you to get away with the high spring rates which is largely why when you drive an elise with sachs or moton CO's, they can get away with 12Kg or more and it feels just as smooth on a bumpy track as another car or even an elise with cheaper dampers at 8Kg...

and no, some good tire choices for our heavy cars start at 235 width and up if you really want to even think about being competitive. 225's and under are generally reserved for national champion miata's and the like lol...2500lbs or less

I definitely believe that urethane bushings help a great deal with less deflection and maintains suspension geometry a good deal better.

[Norm Peterson]

Originally Posted by michaelnyden

I definitely believe that urethane bushings help a great deal with less deflection and maintains suspension geometry a good deal better.

That's highly location-specific, at least if all you do is run the bushings straight from the box to the arm/link/bar/what-have-you.

I'll give you that bushings that lie along a single axis can be swapped to poly or Delrin without introducing what's commonly termed 'bind' (or induced wheel rate). That said, up front with most FWD cars with their rear steer setup, you will end up with slightly more compliance toe steer. In the understeer direction. Probably not much more, but it's there.

Bushing locations that permit multiaxis motion via bushing compliance will develop resistance to roll (and sometimes even pure bump/rebound) due to their greater rigidity. Simple cases can be tuned around with slightly softer springs and/or sta-bar at the end in question. In more involved situations, such as rear strut suspensions featuring twin lateral links plus a trailing arm, it is possible that things like toe gain will be affected (due to differences between the various stiffnesses of the lateral link bushings vs the trailing arm bushings).

Those geometric effects are generally too small to notice in anything that passes for sane driving while in traffic, but will make a difference at autocross or other forms of timed lapping.


Norm

[gdmaxse]

Originally Posted by michaelnyden

and no, some good tire choices for our heavy cars start at 235 width and up if you really want to even think about being competitive. 225's and under are generally reserved for national champion miata's and the like lol...2500lbs or less

Well my 225/50/15 v710s have worked out great for me:
the lower gearing is perfect for autocrosses around here, i usually stay between 3-6k rpm in second
the smaller size keeps weight and inertia down,
i have more than enough traction coming out of corners,
also most r-comps are oversize for their size designation, the 710s in 225/50 have a 9.2" tread and 9.6" overall width on 8" wheels

i dont know if i would be able to get enough heat in the backs with a larger tire size, they are a little skittish when cold

the other thing is, most of the common mods for maximas put you in STS for autocross which has the tire size limited to 225 anyway

but, to contradict all that, i would love to try the new 275/35/15 hoosier A6 tires if i had the money

[michaelnyden]

gdmax, I was not specifically taking into account the colder weather out by you, I was purely speaking from california standards, where the tarmac's are around 120 on a sunny autox day, and you have to use tire sprayers after every run so the extra width is more usuable. Also, you don't want the rears to grip really hard/heat up anyway...gotta have more oversteer...keep in mind the V710's are largely a very soft compound requiring a lower effective operating range than the average r compound out there.

and norm, I was speaking purely about the levels of suspension travel introduced only at situations of autox or road racing level. But you are dead on about the difference in response and toe gain you would get considering each respective situation--single axis and multiaxis motion bushing dependance. Asking any suspension guru, will agree that the weakest link--stock rubber bushings have dramatically more bend and deflection than delrin or poly, commonly distorting suspension geometry at the limit depending on where you have the bushings of course--looking at race cars which typically have full metal bushings/eyeball bearing setups, reasoning to justify such is so they know what when they put dial in a desired amount of toe or camber/caster, it will for the most part stay that way under travel. Things do indeed get more complicated when you start looking at suspension geometries such as sophisticated multilink setups found on newer cars such as 350z's which the extra angled link serves to sedate any toe altering effects on an ordinary double wishbone suspension under large suspension travels or other scenarios which pull the suspension/wheel in multiple axis at once. On that suspension type, however, changing one bushing at a time (provided they had them available) would allow you to undeniably see the difference a more rigid bushing would create along only that one axis...as opposed to simply putting it in the lower or upper links/a-arms only--would serve as an interesting experiment.

[gdmaxse]

good point, i will probably have that same problem in the summer here. i see a tire sprayer in my near future. it would be nice to have a set of 275s for the summer and 225s for the colder events. oh well, ill keep dreaming...

[michaelnyden]

yeah but with 275's, even a 40 series profile is really high, we would have rubbing issues and the need for spacers and such would come into play if not rolling our fenders in the front, in the rear there is a lot of space and could fit 275's...

[gdmaxse]

yeah, the 275/35/15 Hoosier A6 is 22.8" tall and about 11.25" wide, it will stick out about 2" outside the fender but won't hit because the tire is so short.

[michaelnyden]

good point, but I was thinking on my 17's...lol...they definitely won't fit in the front without rolled fenders and some good spacers...I have 245/45/17 V710's and they already rub on the CO spring collar slightly due to my -2.3 degress of camber, all I need is the smallest 3mm spacers and they fit again though...the sidewalls on the 245's are effectively 110.25mm or about 4.41in height combined with the 9.8in width...things get pretty cramped (however, in the rear, they fit with room to spare)! I just wish they made 245/40 or 255/40 size...but of course that is with running a good deal of tire pressure...in the high 30's to maybe even 40, which is also in part why the rub slightly..but on hoosiers site, I see they make a 245/40/17 which is promising in the A6 and R6 series.

[jac121479]

Mike, do you have camber plates or bolts? i'm running the 245/45-17's (street tires) with -2 degrees of camber via camber plates and i'm not even close to rubbing. whats you wheel offset?

[michaelnyden]

they are on a set of enkei rpf1's...+35 offset I believe...8.5 width IIRC...what brand are those 245's jack..? you also have to keep that in mind as width's and even section sizes are entirely different from one tire manufacturer to another...as if the tire width is different so will the section height being as how it's a aspect ratio/percentage of the width.

case and point, a kumho v710 245/45/17 runs 9.6" on a 8" rim according to kumho's site...but with my street tires on my 18's, 235/40/18 toyo t1r, not even close to rubbing at all, they are listed on toyo's site as 9.5" width but when you put v710's which tend to run wide (and the t1r's clearly have much more than .1" between the CO spring collar/perch) but the sidewall's being only 40% of 235mm is a lot lower profile, leaving a lot more room since they are inclined towards the CO with the negative camber, add this along with about 40psi and up of pressure on the autocross course, things tend to get really close with the V710's, however, with my other road race tire, 255/40/17 toyo ra-1, a good deal more clearance than the V710's...

I have camber bolts.