A math error means I bought a set of spring that are stiffer than I was thinking.....which then got me thinking about ride height.
How low are you guys running your street or autoX cars?
A math error means I bought a set of spring that are stiffer than I was thinking.....which then got me thinking about ride height.
How low are you guys running your street or autoX cars?
My Miata is both a street car and an autocross car and it's pretty low. Like 22" from the ground to the highest point of the wheel arches. Not sure what the measurement is at the pinch welds, but it tucks 245/40R15 tires on 15x9" wheels inside the tops of the wheel wells. Last year I tried raising it up to be responsible and then a guy with a much faster and better set up Miata than mine went "What coilovers are you running? Xida Races? What's with the monster truck ride height? You should have it set on the ground." Say no more!
In reply to NickD :
I guess I was thinking measure clearance under the car so it would be the sameish comparison for everyone vs a model specific body point. any idea what you ground clearance is?
There's a lot of factors. If you've got multilink or strut suspension it's going to be equally or more important to get the geometry right as anything else. Too low on a strut suspension and the camber curve goes to complete crap. Multilinks can do even weirder stuff if you get them outside of their happy range. Double wishbone is usually a bit more forgiving but can still get into weird bumpsteer and other issues if you go too far.
dps214 said:There's a lot of factors. If you've got multilink or strut suspension it's going to be equally or more important to get the geometry right as anything else. Too low on a strut suspension and the camber curve goes to complete crap. Multilinks can do even weirder stuff if you get them outside of their happy range. Double wishbone is usually a bit more forgiving but can still get into weird bumpsteer and other issues if you go too far.
Roll centers get jacked up with wishbones, too.
you just can't compare ride height across platforms. A car that was designed to be low will be totally different from one you made low.
The MG runs 3" with a completely flat bottom. It's not really a street car but does get street use. Even at 3" there is a lot of scrapes on the bottom of the aluminum floor indicating that it has hit some things. That's about as low as I would ever go to see street use. The LMP360 is a full race car and will have ~2" ground clearance. Both cars have appropriately stiff suspension that keeps the chassis off the ground during normal suspension movements on roads.
nocones said:The MG runs 3" with a completely flat bottom. It's not really a street car but does get street use. Even at 3" there is a lot of scrapes on the bottom of the aluminum floor indicating that it has hit some things. That's about as low as I would ever go to see street use. The LMP360 is a full race car and will have ~2" ground clearance. Both cars have appropriately stiff suspension that keeps the chassis off the ground during normal suspension movements on roads.
3-4 is what I was expecting to hear was about the limit.....scapes on the bottom are fine but how does the front valance hold up? On an MG its not very far in front of the wheel is it? ...I'd guess that would also be a factor
as far as roll centers and what not, yes of course all that needs to be sorted. My question is more about what is a practical clearance number to sort at? Streets and paring lots are not flat 3" seems "Wow that's low!" for street use....at 8" its more like "wow, do you sleep under here when you're camping or use it as shade at the track?" :)
My Camaro is at 3" and when I drove it on the street it often scraped hard parts. I also had to angle driveways and avoid speed bumps. 4" is probably the minimum for a hassle free street car.
You also want to make sure nothing substantial will hit the ground if a tire goes down. The car is pretty much uncontrollable at that point.
Ride hight in New England is determined by how good the pothole crop is have in the spring. ;-)
It's going to end up being a trade of between lowering the center of gravity and screwing up the suspension geometry. I know there is a too low for my Alfa- I had been planning on running my car higher than others just to get better geometry.
Unfortunately, I have no idea for a Miata.
But I posted about the Alfa because I've been seeing APEowner for years, and every time I see that, I think Alfa Parts Exchange. Good opportunity to post that... ;)
MonZora is set for 4-1/2" to lowest point of front and rear crossmembers. I'll know in a few years whether that's a good value. 
My Ae86 sat with the frame rails about 3.5" off the ground. Suspension was super stiff and it still scraped quite abit, sure was good at autocross though!
Autox vs street are two very different scenarios. Autox parking lots are smooth - yes, yes, there can be some bumps but generally the courses are set up to avoid them and you're not having to deal with speed bumps or 3" deep potholes - so you can get away with compromising the car in order to maximize performance. Street use is the wild west, there's always something unexpected and the surface varies widely. My Miata runs about an inch lower in track/autox mode than it does in performance street mode, and tarmac rally mode is at least an inch higher than that.
We once had a car in our shop with a Nationals-winning suspension. We couldn't get it out of our shop lot because it would hang a wheel crossing the gutter and the Torsen diff would send all the torque to the wheel in the air.
depends on wheelbase, shorter cars can run a bit lower and don't get beached as much as longer ones. 5" at the lowest for me now. After running lower and having to pinball around obstacles all the time...i'm too old for that now. My mini had less ground clearance than a can of WD40 on it's side, and if you didn't see a manhole cover coming at you it'd be a few heart stopping seconds to see if it took the gearbox off on the way
My splitter is about 2 inches off the ground. Engine crossmember is about .5 inches higher than that. Not really a street car though.
I can tell you that a stock Renault 5 has almost but not quite enough ground clearance to clear a coconut. The car will dribble it like a basketball for a few moments before spitting it out the back.
The wheelbase thing is a big one. My E38 has 6.5" under the front end of the rocker panels (a little more further back) and I have to stance crawl the steep, awful end of my driveway. If I drive straight in or out, it'll hit. And that's at stock ride height, but on a fairly long car. I honestly bought the thing not knowing if I could get it into the driveway at home...
We used to glue a bit of foam to the bottom of the front crossmember on the super late model. If it was about half worn off after practice, we knew the bumpstops were about right.
gonna say the front of my F500 is something like 1.5 inches... I kinda need to raise it a smidge, its scraped on bumps a bit at some lots. I got a cone stuck under it once and one of the front wheels was lifted off the ground...
For a dual purpose car 5" is about the limit, otherwise you start bashing everything under the car. If you live in area with no sharply peaked drives or speed bumps you could probably get away with 4".
In reply to mke :
The tires determine that for me. When I build a chassis The normal ride height is even with the rim of the wheels. So with tires of 2&1/2 inch sidewall I have 2&1/2 inch ground clearance. 5" sidewalls 5" ride height etc.
It's a math challenged way of designing a happy car. I think bumps etc are deviations from a chassis plate and if you set your suspension so you are there normally. Camber change and bump steer are as sweet as it can be.
My Locost is about 2" or less at the oil pan. There are some driveways I cannot get into. The chassis clears -most- speed bumps if I creep over them - too fast and the chassis will tag with the falling momentum.
My '77 Silverado is 3.25" at the front control arms. It clears all speedbumps, but sometimes the collector flanges hit parkinglot berms.
The Nissan Hardbody I had previously was low enough to scrape the plastic undertray under heavy braking.
For the street: clear most (not all) speed bumps.
For autocross: tag the at least ground once on course.
All of these are a potential answer to the question posed at the beginning of this thread. All are correct for their use.
Autox height (this varies, it's sometimes a bit lower):
Street height:
Go fast on the street height:
Slamming a car just to make it lower is not something that should be done lightly. It may negaively alter the roll center height and cause bump steer issues.
There is a point at which a drop spindle is needed, extended ball joints, or control arm mounts need to be relocated to fix the geometry.
dean1484 said:Ride hight in New England is determined by how good the pothole crop is have in the spring. ;-)
The wife's @stilettoss TT is terribly low for here. I bet there is 2.5" to the cat's skid. I had to drive it to work a couple times this winter and I destroyed a ball joint and a tie rod end on a frost heave. -1.5" eibachs and koni yellows.
I have also taken out the plastic aero for the tire on my stock Cayman S on a frost heave crack.
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