Vehicle Ride Height and Rake Questions

[CaptainSquirts]

Ok, I have a couple questions about vehicle ride height and the rake of the vehicle. Been researching this stuff all over the internet recently trying to understand it and the effects it has on the vehicle. Kinda confusing trying to understand them and how they affect each other. First, ride height....

Lets say you're going from a stock suspension system to something more complex(due to being able to make adjustments), like a coilover. With that, you being able to adjust the ride heights. What would be a good indication on where the set the ride height. Reading many different things I'm seeing stuff about ride height affecting roll center. Having ride height set too low will cause the roll center to go underground(for my vehicle people measure the roll center by the control arms. If the control arms are almost parallel, then roll center will basically make body roll worse. So preferred control arm angle is to be at a somewhat very small angle like / \(not that drastic of an angle) instead of _ _ ( almost parallel). So when adjusting ride height, would it be best to lower it to the point before control arms becoming almost parallel? I know every car is different and each probably require there own fine tuning and adjustments. Is there usually a universal rule of thumb about ride height and what a good height they should be set at?

Then from ride height there becomes rake. My car usually comes with the rear lowered 20mm compared to the front. So the rake would be negative causing the car be at a slight angle from front being higher and back being lower. I'm assuming whatever your ride height is setup for the front and back will affect the rake? So you would just need to measure the front and rear and just verify the rear is a little lower than the front?

Lastly, dialing in rebound/compression. Obviously having them set at the softest setting would be pretty street friendly compared to having it set to the hardest setting. Now for the performance part. How do you find that sweet spot when adjusting them for OPTIMAL PERFORMANCE .

If whatever I'm spewing out is incorrect, let me know. This crap is confusing and I'm trying to make sense of it.

[jbrannon7]

Ok, I have a couple questions about vehicle ride height and the rake of the vehicle. Been researching this stuff all over the internet recently trying to understand it and the effects it has on the vehicle. Kinda confusing trying to understand them and how they affect each other. First, ride height....

Lets say you're going from a stock suspension system to something more complex(due to being able to make adjustments), like a coilover. With that, you being able to adjust the ride heights. What would be a good indication on where the set the ride height. Reading many different things I'm seeing stuff about ride height affecting roll center. Having ride height set too low will cause the roll center to go underground(for my vehicle people measure the roll center by the control arms. If the control arms are almost parallel, then roll center will basically make body roll worse. So preferred control arm angle is to be at a somewhat very small angle like / \(not that drastic of an angle) instead of _ _ ( almost parallel). So when adjusting ride height, would it be best to lower it to the point before control arms becoming almost parallel? I know every car is different and each probably require there own fine tuning and adjustments. Is there usually a universal rule of thumb about ride height and what a good height they should be set at?

Then from ride height there becomes rake. My car usually comes with the rear lowered 20mm compared to the front. So the rake would be negative causing the car be at a slight angle from front being higher and back being lower. I'm assuming whatever your ride height is setup for the front and back will affect the rake? So you would just need to measure the front and rear and just verify the rear is a little lower than the front?

Lastly, dialing in rebound/compression. Obviously having them set at the softest setting would be pretty street friendly compared to having it set to the hardest setting. Now for the performance part. How do you find that sweet spot when adjusting them for OPTIMAL PERFORMANCE .

If whatever I'm spewing out is incorrect, let me know. This crap is confusing and I'm trying to make sense of it.

Took me a couple years to figure ALL that out on my car, most of the internet stuff was wrong, good luck. The easy route is to look thru the SCCA Solo results for people that run your car, do well, and ask them specific questions.

[CaptainSquirts]

The easy route is to look thru the SCCA Solo results for people that run your car, do well, and ask them specific questions.

Any National Championship drivers that drives an Evo on this forum?

[twistedwankel]

http://farnorthracing.com/autocross_secrets5.html

This might help. Dennis put a lot of time and effort into this website. Covers many aspects of racing.

I agree with Joe. Six people helped me save time and money on my last setup!! Never be in a hurry. Up until last year The Martin Club in Tavares/Orlando had a ton of Evo drivers in STU. I haven't been back since.

[jbrannon7]

The easy route is to look thru the SCCA Solo results for people that run your car, do well, and ask them specific questions.

Any National Championship drivers that drives an Evo on this forum?

As I recall, Terry Glazer was deep into Evo development a few years ago.

[twistedwankel]

As I recall, Terry Glazer was deep into Evo development a few years ago.

Don't think he watches any forums? You are right he and his son raced trailered matching Evo's STU for years up until recently. He certainly would know all about setting one up!! Lately he's been racing a Toyota 86 I think it is? I only see him at SCCA events.

[CaptainSquirts]

http://farnorthracing.com/autocross_secrets5.html

So much information, great stuff

[Solar]

As I recall, Terry Glazer was deep into Evo development a few years ago.

Yes he was, and pretty good with it too.

[twistedwankel]

Terry used to own a MisterBitchy (name of my 2 cars) Dealership. Don't piss him off. Otherwise a great guy.

[Rpwolf]

What would be a good indication on where the set the ride height. Reading many different things I'm seeing stuff about ride height affecting roll center. Having ride height set too low will cause the roll center to go underground(for my vehicle people measure the roll center by the control arms. If the control arms are almost parallel, then roll center will basically make body roll worse....I know every car is different and each probably require there own fine tuning and adjustments. Is there usually a universal rule of thumb about ride height and what a good height they should be set at?

Then from ride height there becomes rake. My car usually comes with the rear lowered 20mm compared to the front. So the rake would be negative causing the car be at a slight angle from front being higher and back being lower. I'm assuming whatever your ride height is setup for the front and back will affect the rake? So you would just need to measure the front and rear and just verify the rear is a little lower than the front?

Lastly, dialing in rebound/compression. Obviously having them set at the softest setting would be pretty street friendly compared to having it set to the hardest setting. Now for the performance part. How do you find that sweet spot when adjusting them for OPTIMAL PERFORMANCE .

all suspension tuning is about compromises: stiffer isnt always better, eventually there are negative returns
ie: in my car, stiffening the front sway bar makes it understeer more around town but is more controlled through a fast slalom.
when you think of tuning, think of tuning: the entry, middle, and the exit of the turn.

you could probably lower the car just enough (1-1.5"?) to lower the center of gravity without insulting roll centers.
you can get different suspension arms or maybe aftermarket ball joints to correct roll centers.
depending on your coilovers, lowering the car could also reduce shock travel....

rake is the comparison between front and rear ride height
does it need to be raked? that depends on the car and your driving style.
when you think of rake, think of it as "adding weight" to that end of the car.
lower front means more oversteer at the cost of stability

compression is stiff vs soft
rebound (extension) is slow vs fast
a shock works by managing the amount of fluid going from one side of the valving to another
increasing rebound= increasing shock extension RESISTANCE= slower rebound

rebound damping controls how fast the tire returns to the ground and compression controls how fast weight goes onto a tire.
here is a poorly adjusted vs well adjusted shock
https://www.gtplanet.net/forum/proxy.ph ... 7d02703c81

Here is a simple guide to explain the basics of shock tuning (when they say bump it means compression)
http://www.s2000.org/articles/suspension/

about roll centers (cause reading is fun)
http://thecartech.com/subjects/auto_eng ... Center.htm

the shocks used in this link are likely different but you might be able to use some of the info
https://robrobinette.com/S2000KWV3Tuning.htm

This should keep you busy lol
have fun!

[CaptainSquirts]

A lot of great information there Randy! I have a lot of reading to do now, exactly what I was looking for. Just one thing I noticed that might be wrong though. For the Rake part you talked about you said "think of it as "adding weight" to that end of the car." You didn't really state it is adding weight, but said just think of it doing that. A couple of places I've read, it only changes the balance by altering the roll axis line between the front and back roll center. So the weight doesn't actually change(ok it does but very very very very minimally).

Here's a good read I copied from an evo forum https://www.evolutionm.net/forums/evo-t ... -rake.html I'll just paste post #4 below from a person that uses math and what not so he can't be wrong right?





(Pasted text)
If you run the numbers, changing the rake of the car has effectively zero effect on weight distribution. I was trying to point this out in the other thread that links to here. Here's how the math works:

The Evo IX has a wheelbase of 103.3 inches. Using this, and assuming 1" of rake (i.e. 1" lower at the front suspension than at the rear) we can calculate how much it rotates the car forward:

arctan (1/103.3) = 0.554 degrees

Now assume that the roof is a 100 lb point mass on the centerline of the car at a height of 57 inches. By rotating the car forward 0.554 degrees, we move this point mass forward by:

57 * tan 0.554 = 0.551 inches

We'll simplify this to 1/2". This move changes the weight distribution by:

103.3/2 = 51.65 <--- distance from center to front wheels
.5/51.65 = .00968 <--- fraction of that distance that is 1/2"

Since if the weight were directly over the front wheels (i.e. 100% distance) the front would see a change of +50 lbs and the rear would see a change of -50 lbs, you can calculate the change in weight by multiplying your % change in distance by your weight:

0.00968 * 100 lbs = 0.96 lbs

So by raking your car 1" you've managed to transfer 1 lb of weight from the rear wheels to the front wheels.

So if it doesn't transfer weight front to rear (or the other way), how does it have an effect on the car's handling?

It works by changing the suspension geometry and weight transfer in a turn. With the car raked, the front tires are deeper into their camber curve (what little we have in a McStrut car) and they will add camber more quickly than the rears under compression. It also changes the roll centers and the CG of the front vs. the rear. The higher CG in the rear should result in more roll force. This will increase the amount of weight transfer on the rear tires when the car starts turning. More weight transfer = less grip.
(/Pasted Text)

[CaptainSquirts]

rebound damping controls how fast the tire returns to the ground and compression controls how fast weight goes onto a tire.
here is a poorly adjusted vs well adjusted shock
https://www.gtplanet.net/forum/proxy.ph ... 7d02703c81

ahhhh the link doesn't work

[jmdoc66]

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.

[CaptainSquirts]

Don't forget about your tires. Have you done any testing to find the correct psi?

Only thing I've really done is set it up to make sure the fronts don't roll over which is like 39psi cold. I've up'd the negative camber so I can probably drop that. The rears, I usually just have them like 4 psi less than the fronts. I haven't done anything else much/not sure what else to do to get a good test in.

[Rpwolf]

that looks like a calculation for static weight, but when you drive a car the weight is no longer static.
suspension and weight can be dynamic.

1 lb at 60 mph is going to have more energy than at zero, especially with 3k lbs behind it

I'll get the pic when I get home tonight.

[Carracer]

12166317754_61bf2713e4.jpg (17.94 KiB) Viewed 13502 times

Here is Rpwolf's image.

[CaptainSquirts]

Is it easy to tell if it's doing one or the other?

[twistedwankel]

Dan I think you should be in charge of the yearly points chart after looking at those calcs

[CaptainSquirts]

Dan I think you should be in charge of the yearly points chart after looking at those calcs

uhhhh, i just copied and pasted that

[Rpwolf]

Is it easy to tell if it's doing one or the other?

in more extreme cases, yea. otherwise, you gotta know what to look for in the given situation (ie: rear end chatter during hard braking = probably speed up rear rebound)

but there is more than one way to make a car oversteer:
more front camber than rear, stiffer rear bar than front, higher rear compression....

or you can do the the opposite of all of these to the other end of the car. which is thw right answer? that's the fun part.

start with the right tires, then springs, then damping, then bars. in my situation I'm limited to scca stock rules so I can only adjust a single sway bar, so I have to make due with what I got. the true optimal setup depends on tires, driver, weather, and course. the true optimal setup can always change. a good base tune is what you need, so adjust one thing at a time and test. it's the labor of tuning.

when I was racing motorcycles the best setup changed by a few clicks throughout the day at a particular track as the shocks, track, and tires heated up . don't over think it, just do the basics because without telemetry and a team it can take a while.

surprised the evo forums don't have suggestions. there is a wealth of info on shock development on S2k pages. but again, there are many variables.