Vehicle Ride Height and Rake Questions

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Vehicle Ride Height and Rake Questions

Postby Loren » Tue Aug 08, 2017 7:54 pm

Rpwolf wrote:in my situation I'm limited to FAST stock rules so I can only adjust a single sway bar, so I have to make due with what I got.
SCCA only allows you to change one swaybar. FAST doesn't care what you do with swaybars. Or bushings. Or control arms. Or lots of things... just don't mess with the ride height or spring rates.
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Vehicle Ride Height and Rake Questions

Postby Rpwolf » Tue Aug 08, 2017 8:42 pm

Loren wrote:
Rpwolf wrote:in my situation I'm limited to FAST stock rules so I can only adjust a single sway bar, so I have to make due with what I got.
SCCA only allows you to change one swaybar. FAST doesn't care what you do with swaybars. Or bushings. Or control arms. Or lots of things... just don't mess with the ride height or spring rates.
oops, that's what I ment. thanks for the correction.
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Vehicle Ride Height and Rake Questions

Postby Rpwolf » Wed Aug 09, 2017 8:17 pm

forgot to mention. lowering your car may cause the roll centers to be out of wack but you'll gain more negative camber if the car is lower, and you'll counter the additional body roll with stiffer springs and increased damping.
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Vehicle Ride Height and Rake Questions

Postby SallyFinney » Thu Aug 10, 2017 4:40 am

""
jmdoc66 wrote:Don't forget about your tires. Have you done any testing to find the correct psi?
The advantage of having an adjustable suspension is you find and use the optimum PSI for the tires and leave them there.
Then use the adjustable suspension to change the characteristics of the car to changing conditions of different surfaces.

Maybe we can talk FAST into doing another skid pad at one of the future events in Brooksville. Lets say in October...since I'll be getting new tires about then, so people can find the magic PSI to get the most out of their tires.
""


I think a skid pad would be fantastic!! I had mechanical problems at the last one so only did one lap. I will have a dedicated autox car by then and would love to have a focused opportunity to get it right and have some veterans give me feedback.
Helmet hair dont care. Because Autocross!
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Vehicle Ride Height and Rake Questions

Postby CaptainSquirts » Thu Aug 10, 2017 10:16 am

Rpwolf wrote:
Wed Aug 09, 2017 8:17 pm
forgot to mention. lowering your car may cause the roll centers to be out of wack but you'll gain more negative camber if the car is lower, and you'll counter the additional body roll with stiffer springs and increased damping.
Kinda overwhelming on all the different kind of things and how they affect each other :read: . I think the best bet for me is to figure out a good ride height, keep it there so I don't have to mess with the toe/camber for a little bit. Gets kinda boring adjusting those after making a small change.

I'm assuming less body roll would mean less tire roll over?
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Vehicle Ride Height and Rake Questions

Postby Loren » Thu Aug 10, 2017 10:26 am

There's a reason they call suspension tuning a "black art". Sure, it's all science and engineering... but, the magic is in finding all of the right compromises to make the car work the way you want it to in the environment(s) that you use it while maintaining a level of comfort that is acceptable to you.

As for body roll... sort of depends on what you have for suspension. If you have a proper suspension that GAINS negative camber as it compresses, then if you have LESS body roll, you have LESS camber gain. There's always going to be a sweet spot in there where you're getting enough CONTROLLED body roll for the suspension to work and give you that camber gain to keep the contact patch flat in a turn.

And then there's the McPherson Strut. Which typically (always?) has a backwards camber curve. As it compresses, your camber goes more POSITIVE, or at least doesn't gain any negative. If your camber goes the wrong way on compression, you can sometimes benefit from almost completely locking down the suspension so that it doesn't get any WORSE. This is why certain front wheel drive car will benefit from a stiffer front sway bar... even though conventional logic says they'd want a stiffer rear bar.

Everything effects everything else, and you have to wrap your head around your particular suspension design and as many of those relationships as possible. I think your notion of "setting and forgetting" certain things like ride height is a good one. At our level, you're not chasing "perfection", you're chasing "good enough". (having driven your car... I'd say you're getting pretty close to that already)
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Vehicle Ride Height and Rake Questions

Postby CaptainSquirts » Thu Aug 10, 2017 10:53 am

Loren wrote:having driven your car... I'd say you're getting pretty close to that already
Yea I'm definitely happy on how the car handles. Totally different machine now compared to how it was when I first came out. Thing is, the strut is 11 years old and who knows when it'll go. I got a very great deal on coilovers which I'm sending to the company to rebuilt(rebuilding just for ease of mind). Nobody makes struts for the Evo except Bilstein which is costly not including good springs. So I think coils were the way to go now. Anywho, since the coilovers has ways to adjust the ride height and not just a fixed position like oem struts, I have to figure out where to set them at.. So I'm just trying to figure out a good setting to have them at and hopefully it be good enough to just leave it there.
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Vehicle Ride Height and Rake Questions

Postby Rpwolf » Thu Aug 10, 2017 8:27 pm

is your rebound and compression independently adjusted? I would assume it is, if it's not I wouldnt worry too much about the shock settings.

curious what your alignment specs are....

like Loren said, I would keep it simple. tires, maybe a sway bar, and a good alignment. rake and ride height is probably 5% of the car. I forgot that the evo's have McPherson strut suspension, you won't have a significant advantage by lowering it to gain camber like double wishbone designs. you gotta eye ball your tire and see if the front needs more camber or not (or get fancy and measure the Temps of the inside, middle, and outside of the tires after a hot lap)
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Vehicle Ride Height and Rake Questions

Postby twistedwankel » Thu Aug 10, 2017 11:32 pm

Some day Randy will buy some tires? Alignment to follow? Success remains a mystery!!
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Vehicle Ride Height and Rake Questions

Postby CaptainSquirts » Fri Aug 11, 2017 10:41 am

Rpwolf wrote: is your rebound and compression independently adjusted?
They're Simultaneous Rebound and Compression Adjustable Dampers. They can be converted to be rebound/compression independently for some $$$ but I def don't need that yet. Maybeeeee if I get good enough in the future and understand the whole setup more I would be interested in turning them 2 way.
Rpwolf wrote:curious what your alignment specs are....
They're -3 front, -1.5 rear and a stupid small amount of toe out in the front, like .20mm each side. Rears are 0 toe.
Rpwolf wrote:you gotta eye ball your tire and see if the front needs more camber or not (or get fancy and measure the Temps of the inside, middle, and outside of the tires after a hot lap)
Some type of temperature gauge sounds like a good idea. Would you normally want the inner, mid and outer be the same temp?
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Vehicle Ride Height and Rake Questions

Postby Rpwolf » Fri Aug 11, 2017 8:46 pm

twistedwankel wrote:
Thu Aug 10, 2017 11:32 pm
Some day Randy will buy some tires? Alignment to follow? Success remains a mystery!!
tires in the garage, wheels getting the hub bores cut, maybe painted? stay tuned!
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Vehicle Ride Height and Rake Questions

Postby Rpwolf » Fri Aug 11, 2017 8:55 pm

CaptainSquirts wrote:
Rpwolf wrote: is your rebound and compression independently adjusted?
They're Simultaneous Rebound and Compression Adjustable Dampers. They can be converted to be rebound/compression independently for some $$$ but I def don't need that yet. Maybeeeee if I get good enough in the future and understand the whole setup more I would be interested in turning them 2 way.
Rpwolf wrote:curious what your alignment specs are....
They're -3 front, -1.5 rear and a stupid small amount of toe out in the front, like .20mm each side. Rears are 0 toe.
Rpwolf wrote:you gotta eye ball your tire and see if the front needs more camber or not (or get fancy and measure the Temps of the inside, middle, and outside of the tires after a hot lap)
Some type of temperature gauge sounds like a good idea. Would you normally want the inner, mid and outer be the same temp?
yes, it shows you're making the most of your tire in the given situation.
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Vehicle Ride Height and Rake Questions

Postby twistedwankel » Fri Aug 11, 2017 10:26 pm

Rpwolf wrote:
twistedwankel wrote:
Thu Aug 10, 2017 11:32 pm
Some day Randy will buy some tires? Alignment to follow? Success remains a mystery!!
tires in the garage, wheels getting the hub bores cut, maybe painted? stay tuned!
Success remains a mystery!! Bored wheels? Me too.
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Vehicle Ride Height and Rake Questions

Postby CaptainSquirts » Wed Sep 20, 2017 2:07 pm

I noticed a few of you talked about a person named Terry Glazer that did some work on the Evo. I'm having a rough time trying to find a decent ride height to have the car initially set at and would love to talk to someone that has a good idea about theEvo suspension setup. Getting some coilovers in today and I'm trying to find a good initial ride height. By any chance anyone have a way to contact him and ask if I would be able to contact him or he contact me?
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Postby CaptainSquirts » Fri Sep 22, 2017 7:50 am

Disregard above post, found the information I was looking for. Looks like I'll try 25.5" in the front and a slight bit higher in the rear to get a slight lower rake to give it that little little bit of oversteer(i hope it's just a little). All this is new to me so who knows what the hell will happen.
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Vehicle Ride Height and Rake Questions

Postby Loren » Fri Sep 22, 2017 1:03 pm

25.5"... seems like probably ground-to-fender lip measurement. Be aware that is a TIRE HEIGHT dependent measurement. If you want a more accurate measurement of what the suspension is doing from one setup to another independent of tire diameter, you want the center-of-hub to fender lip measurement.

Probably won't make more than a 1/2" difference one way or another, but it can be relevant.
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Suck Less - Drive something resembling a proper racing line.
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Vehicle Ride Height and Rake Questions

Postby CaptainSquirts » Fri Sep 22, 2017 2:45 pm

That's true. After more research seems like the area to measure from is the sill lip- the double sheet metal lip below rocker panels which should measure up around 7ish inches in the front and probably just do positive 1/2" in the rear. Or I can do the center of hub measurement, whichever I find easier at the time. Just sucks I don't have a good level at my residence when measuring stuff.
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Postby Loren » Fri Sep 22, 2017 3:00 pm

Nope. Sill height is still tire height dependent. Put a 1/2" taller tire on the car, you change that height (as well as the ground-to-fender height)

If you're looking for ground clearance or CG height, then those numbers are good. If you're looking for suspension height/travel info, you want to measure from the center of the hub to something on the body. That removes the tire size from the equation.

Think in extremes. You've lowered the car too much. You have 1/2" of suspension travel left. And you put baller 22" wheels on the car... it now sits an inch taller because of that. The numbers you are looking at will NOT identify that problem.

Measure hub-to-fender. Compare stock suspension to what you have. Now you have some useful information. The suspension was at this height, now it's at this height. I've reduced my SUSPENSION TRAVEL by this much. (but, I've increased my spring rates by this much to compensate for it, so I'm okay)

Based on how much you've changed your spring rates from stock, and knowing the stock suspension height, you should be able to calculate the "appropriate" suspension height for your spring rates.

(of course, then you throw in different swaybar rates and different bump stops and different shock valving, and everything gets all muddy again)
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Vehicle Ride Height and Rake Questions

Postby CaptainSquirts » Fri Sep 22, 2017 8:06 pm

Jesus they should just put suspension related things in big bright colored text just lIke children's books. Might make it easier to understand easier :read: . I tried measuring from my hub to fender and it's kinda hard to do since the center of the hub dips in kinda deep. I can see why people tend to (even thought it might not be the best method) measure from ground to fender since it's so much easier to do.
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Vehicle Ride Height and Rake Questions

Postby Loren » Fri Sep 22, 2017 8:52 pm

Yeah. I usually take a "close enough" approach to suspension. Everything changes as soon as you get in the car. As soon as you hit a bump. As soon as you turn the steering wheel a little... or a lot.

There's a lot of valid science to it, don't get me wrong. But, there's also a lot of magic. "Close enough" will usually get you there.
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