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G'day all. im still in the process of learning as much about suspension as I can but one thing I have learned is there is no "perfect" suspension that works for every car (if only it was that easy)

So im turning to you who have infinately more experience with these style of cars for what are some good design criteria to aim for.

Quick rundown of my build design (in my head) so far

4ZE1 inline 4cyl, R154 5-speed gearbox, Miata Diff, Suspension will use Miata parts mainly the knuckles, coil overs, brakes possibly the suspension geometry if it matches with the design criteria we set out in this thread but ill be making my own A-arms and happy to change any and all of the geometry as needed.

I am undecided if I will keep the motor naturally aspirated with about 200rwhp or Turbo for an adjustable 250-350rwhp with boost pressure. One day I think keep it simple and lightweight the next morning I wake up and think, no the more power the better!

Use will be for amateur track days and for runs around the lovely twisty roads we have around here. (Tasmania, Australia)

From my research these are the parameters I need/want to obtain But please offer your opinion on all of the points!

Scrub Radius: Between zero and -ve 19mm (for a slight amount of toe-in under braking/accel)

Bump steer: Zero or as close to it as possible

Ride height/Ground clearance: As low as possible but If I want to road register the vehicle local rules are a minimum of 100mm but Im happy to design the ride height to a lower height for optimal handling for the track but wind up the coil overs for street driving accepting less then optimal in those situations. What would be your suggested ride height/ground clearance be?

Wheels/Tyres: This sort of depends on if I go Turbo or not I think, For non turbo Im thinking 15x7.5" wrapped in either 205/50/15 or 225/45/15. If Turbo and expecting i'll need more grip and larger brakes then 17x8.5" with 225/45/17 or 235/40/17. All these sizes are available in Nitto NT01's or Nankang AR-1

Roll Center: This is one I really need help with, I understand there is no right answer and a higher roll center means less body roll and I always thought one of the main aims of suspension is to reduce body roll BUT now im learning that without body roll you don't have as much weight transfer to the outside wheel??? So what is a good compromise for a Locost7?

Anti dive/Anti Squat Not sure what I should be aiming for here?

Ackerman Steering Not sure what to aim for here either.

Suspension Travel How much jounce and rebound should I aim for?

Steering Angle How much steering angle do most aim for?

Track Width Does everyone aim for? equal width front to back?

Anything else you can think of?

Long post I know, if you made it this far thank you and really appreciate the help!

These are my opinions, and are worth what you paid for them...Maybe less.

Scrub Radius: Negative scrub is for FWD. Some people talk about 0, but I'm more in the positive 5-15mm camp.

Bump steer: Zeroish, erring to the side of toe-in under compression.

Ride height/Ground clearance: I wouldn't bother with switching ride heights on a street/track toy. If it's just for fun, just run it at street ride height. I'd probably be a little over 100mm for that.

Wheels/Tyres: Totally reasonable. Although if going 15's, I'd try to keep it 17's capable for future proofing.

Roll Center: Roll center doesn't change how much total weight transfer occurs, but rather how it occurs. I'd keep the front RC low, just high enough to not cross the ground plane under full compression. Then generically set the rear a little higher, maybe 25-50mm. This also leads directly into looking at instant center lengths and camber gain.

Anti dive/Anti Squat: Better to err on the side of too little than too much.

Ackerman Steering: Your variable is the rack location. For front steer, set it to stay aft of the outer tie rods.

Suspension Travel: This is mostly the byproduct of how stiff you choose the suspension to be.

Steering Angle: As much as the rack travel will allow.

Track Width: Rear will be similar to Miata. These usually end up rear weight biased, so a bit narrower front wouldn't hurt.

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Ride height / Ground Clearance:
Don't adjust coilovers for switch between track and street. Use different wheel tire sizes with about a 2" difference in OD. Four inches clearance with the "street set" goes to 3 inches clearance with the "track set".

I do fine with 4" clearance on a slammed mustang street/track car and the "speed table" speed bump design that's popular in my area. You'll need to check the ones in your area in advance.

Also a smaller wheel and tire combo for the track will reduce your gearing some (if by "gearing" one means "engine revolutions per mile of road squirted out the back.").

_________________
Locost builder and adventurer, and founder (but no longer owner) of Kinetic Vehicles

Thanks guys, another question which I know you cannot answer specifically as it depends on springs and anti-roll bars But what amount of body roll should I be designing around? 0-3degree's?

Still not sure on tyre width as I know it depends on final weight and use.