A Blue Lude

I'll preface this by saying - I'm absolutely aware that there are no hard and fast answers to this and that's fine, I've searched around enough to know that. Ballpark suggestions, rules of thumb or any thoughts of any kind are appreciated

In another thread solo-x posted a form for helping the forum noob get blood out of the RR-AX stone, and I have filled it in below with slight modifications (since I'm looking for suspension travel, not spring rates)

My 2001 Prelude is used for untimed lapping and for this summer, a little bit of Solosprint in the Ontario region on Hoosier Koni Challenge tires. It has TBD amount of suspension travel, weighs ~2950 lbs. with 63/37 (magazine figure) weight distribution. The cg height is no idea and the shocks are OTS Koni Yellow and the front spring rate is 450lb/in.

Given that, any suggestions for the amount of suspension travel (before contacting the modded stock bumpstop) I should shoot for? Or is the answer going to be "a whole heck of a lot" given the fairly low spring rates I have (it's a street car).


Thes question was raised in my mind by the new tire I'm trying to run this year.

I've recently rejigged the amount of bumpstop (jounce bumper, woohoo) I'm running, since the previous setup allowed my newly acquired used 24.5" (allegedly) diameter tires to kiss the inner fenders quite a bit. (stock is 24.07) I now have bumpstops that are stock with the bottom (of 3) bulge cut off, which I hope will afford me adequate tire/fender clearance....

The setup as it stands has meant raising the car by about as much bumpstop as I added in, in an attempt to keep some pre-bumpstop suspension travel, which has ended up with the car fairly high. The highly technical measure of ride height would be an honest 3 finger gap F&R with 24" tires.

I understand that low is good in the centre of gravity sense, but I am curious as to how much suspension travel I should try to keep before the shock contacts the bumpstop. Lap times are not super critical, but having the car drive "well" would be nice. The tradeoff between ride height and suspension travel seems pretty tight in the Prelude...
I suspect running the "right" sized tire would help as well (since I would need smaller bumpstops), but these tires were inexpensive and I honestly didn't want to spend a bundle on my first set of dedicated track tires.

descartesfool

You need to know motion ratios, spring rates, track, corner weights, unsprung weights, c.g. height, g's you are cornering at. Car sits at some static height, so you need that as well, since any perch height adjustments affect where the damper piston is. Then as you corner or brake at a certain g force, one end/side goes up a given amount and the other end/side goes down a give amount. You add or subtract that from the static position and that gives you your maximum travel. The if you have bumps, you need more travel. Hard to give a quick answer without a lot of info.

beanbag

Oh oh! And don't forget roll center, ARB rates, and roll couple.

I note with a heavy dose of cynicism that much as in the diagnosis of computer problems, the mention of all these factors is more to get you to go away, rather than to have somebody take the numbers you came up with and hand you an answer. It's not like somebody went and wrote a suspension calculator that turns all these numbers into something useful. Ahem.

http://www.iwsti.com/forums/gd-suspe...ator-more.html

Next I note with a heavy dose of pedagoguery that the mention of all these factors are to help you realize that it's kind of a complicated problem and that these are the kinds of things you need to think about and understand to answer your question.

Finally, I note with a heavy dose of intellectual laziness (or pragmatism if you will) that yes, there are some basic rules of thumb that you can use to figure this out. These rules include:

Using the top hat "extendedness" as a variable, set the compression travel such that the bump stop hits first, and will get squished hard before any mechanical parts smack into each other, such as tire or uca hitting fender, or coil bind. If you have a bumpstop at all, it will be really hard to have the shock bottom out. Any more compression travel is wasted.

Measure your static spring compression (how much the spring is compressed when the weight of the car is on it.) Now take this number and double it (or 1.x it). Do you still have enough suspension travel? If not, you should raise your ride height or increase your spring rate.

Don't worry too much about droop travel. If there is a problem with springs coming lose, get helper springs or extend the top hats some more.

Stinkycheezmonky

Big words are not allowed here, you pedantic ***

Edit: Whoa, looked up that word, and pedantic is a synonym. Creepy!

descartesfool

Nice little spreadsheet, but without all the data...

Test: How many people know the sway bar rates for bars they have installed in lbs/in deflection at the ends of the roll bars based on actual clamping locations to body (they bend at those points) and the sway bar motion ratios in order to calculate wheel rate from sway bars front and rear?

You can just put a tie wrap on your damper shaft and get a rough idea of compression motion when cornering or braking at max g's or hitting a curb on track.

Then again you can just take the springs out and set the car at static ride height you are running and run the suspension through its range of motion and see what you get in terms of damper shaft motion.

Or let a competent damper company tell you what works.

A Blue Lude

That was the objective of putting in more bumpstop, and I hope I put in enough. It's a bit of guesswork but I'll find out this weekend at Mosport GP. The tires are stupidly wide so to what extent I can fully get away from some inside scrubbing I'm not sure...but I don't really want them to be touching under straight line braking at a minimum, I think (which they were previously with perilously little bumpstop installed).

I'll take a stab at measuring the amount the spring compresses and see what I get. Thanks for the advice!


edit: And I my suspicion is that if I did do the zip tie trick and did a few laps I would find it pegged on the bottom of the bumpstop - I have street car spring rates on my street car and I would be very surprised if they were enough for all circumstances all the time...but maybe it's something worth trying out. I'll probably try mount my GoPro to the side of the car to see if that will tell my what my wheels are doing.

solo-x

You're wasting your time trying not to get your suspension to NOT contact the bump stop. Modern car manufacturers design the suspension and spring rates so that the bump stops are an integral part of the suspension equation.

Our pedantic *** is trying to over complicate the question a bit though. All those numbers aren't really needed until you really crank up your game.

A 2900lb car (was that with or without the driver?) with roughly a .7 motion ratio needs a boatload more front spring then 450lbs. At anything much lower then a half inch below stock ride height and you'll effectively have run out of useable suspension travel. I like to start out with a spring that is roughly 50% of that corners static weight. In your case, that's roughly a 900lb main spring, for a wheel rate of ~450lbs/in. You might need to look into a revalved damper to do this, however I run 700lb front springs on 2000lb EF's with OTS Koni's and they ride damn nice. The rears are another story, especially if you want to run a rear biased spring rate on the street. Thank god you don't actually have to do that. Use that same 50% of static corner weight to get your rear spring rate. That works out to roughly a 500lb rear spring for a ~250lb/in wheel rate.

Gah!!!!! That setup will understeer like a dump truck! No, it won't. At least not if you put a proper alignment on the thing. Shoot for ~3 degrees of negative camber front, and start out with 1-1.5 degrees negative rear camber. Zero toe all around and see how you like it. For ride height, set it as low as you can get away with without rubbing too much or causing the handling to go to hell. Don't hesitate to play with bump rubbers (they aren't evil, just misunderstood). I can't really give you a set rule for how much bump travel you should have as it is car and course specific. My DSP car has about 1.5" of clear bump travel before engaging the bumpstop (measured at the wheel. that's a bit less then 1" of travel measured at the shock). A very short distance later, the control arm will contact the chassis.

Going back to the dampers, don't buy springs for the dampers, buy dampers for the springs. If you're worried about effectively doubling your spring rates, go halfway and see if you like the change. Springs are relatively cheap. If the car keeps getting better as you go stiffer, but the shocks seem to suck, get better shocks and keep going up on spring rates.

ps. I ran 900lb front springs on my 2100lb EG on street tires. My DSP ITR is stiffer still. However, there are new concerns once you go past 50% of static corner weight for your wheel rate so I do not recommend it unless absolutely necessary.

pps. Do NOT remove your front swaybar. In fact, get a bigger one. If you don't have a large rear bar yet, you need one of those too.

solo-x

Forgot to mention, if the car is tight with that alignment, reduce rear camber by a quarter degree at a time (moving towards zero camber). Finding out the car turns in really great and is effin loose at the same time on a road course isn't exactly fun.

solo-x

Oh yeah, final post in this thread for tonight. My car rubs the **** out of the tires. I run the car as low as I can to the point where occasionally the tires will contact the body if I hit a bump with it loaded up in a corner or whatever. My fender liners are 80% gone, and there are bare metal spots in the fender well where the tire has rubbed off the undercoating and paint. The point is rubbing isn't really a terrible thing, but you have to be careful you don't put unnecessary heat and wear into the tires due to the rubbing. Like bottoming out, it can happen, but it shouldn't happen all the time or excessively.

beanbag

Stinkycheezmonky

LOL!

Still, thanks as always for the plethora of information everyone We're all happy and lucky to have such knowledgeable and helpful folks asyou guys.

A Blue Lude

Yeah, I understand that - to some extent I wondered why I even bothered cutting the bottom of the front bumpstops off in the first place since they're at least initially much softer than my front springs, using the super scientific "squeeze with hands" testing method. Heck, I could put full stops back in the rear fairly easily that would probably help boost my low rear wheel rate.

With the car on front jack stands, and jacking a front UCA with the car only supported by the bumpstop the car was just coming off that side's jackstand with no tire clearance issues...although I didn't push it any further.

And my game is definitely not cranked up. This weekend will have the first timed event for the Prelude, and it's not something I imagine seriously being competitive in, if for no other reason than classing, and there are reasons beyond that (first full weekend running Rs, hopefully, first time at that race track, etc).

Something that drives reasonably nice is all I can ask for...even managing that out of a 3000lb FWD brick is impressive, I think.

Just to run through my setup (just for kicks),

Since the car doesn't drive empty, we should probably add 170lbs to the 2950 weight - that's just the curb weight by the way, but I haven't taken much off the car...and added Legend brakes, LSD trans, etc.

Beyond that
450lb front springs
325lb rear springs
stock front bar
ST rear bar (25mm?)
Stock camber curve

Probably dropped less than an inch currently.

As you hinted at, my concern about more spring (presumably not expensive from Ground Control, or Eibach direct, however it works) would be needing more shock - I was under the impression that you didn't want to run OTS Yellows much past what I have on the front.

Oh, and then there is something silly about "ride quality", ell oh ell :p

More camber would be next on the list, but I'm not sure if there is anything very good for 5g Preludes...the adjustable upper BJs get bashed on a lot.

I should probably learn how to do my own alignments so I can play around with the ride height more. Pretty easy to adjust.


This was the opinion of my mechanic as well, who runs a lot of crazy stuff on his 4th gen.

He was also yelling at me for putting in more bumpstop, saying that it will tend towards giving one an infinite springrate (makes sense) and be bad for the shocks (less sure about that).

I will say I think it was rubbing excessively before, and I might take out a bit more bumpstop if I never rub this weekend (is Mosport GP supposed to be bumpy?..it can't be as bad as the DDT)...but I'm running a 9.6" section width tire on a Honda with no (front) fender mods and a stock camber curve...if I don't get some sort of noise I'll be blown away.


Anyway, the advice is much appreciated, thanks

A Blue Lude

Only tape measure precise, but the right front spring compresses about 2 inches from free. Amazingly enough that seems be in the ballpark of what I would expect with (2950 * 0.63) * 0.50.

It's hard to measure but I have an inch and a little bit before the bumpstop with the car at its current ride height.

alterdcreations

for some strange reason i think you would do better with stiffer springs.
other than that i am learning in this thread

A Blue Lude

Well I don't have much to add except that

a) The Hoosiers were kept off the inner fenders by the additional amounts bumpstop,
b) The car as set up now is not loose at all, and
c) Mosport Big Track is tons of fun, and there is no way on earth I could put enough spring on the car to keep it from hitting some sort of bump limiter on that thing. But who cares.


oh, and electrical gremlins which knock the car out of the second half of the weekend suck, a lot.

beanbag

Given your constraints, sounds like you did the right thing, then.