do any of you guys know how much an 18" wheel will raise the car off the ground? also, same question for 17" wheels.

 

The idea is to keep the same diameter of wheel + tire as original. So you have to choose a tire that will keep this diameter.

 

That depends on the profile of the tire.

Stock tire (16", 225/50 I believe) has a total diameter of approximately 24.9 inches, which means the distance between the ground and the center of the wheel is about 12.4 inches.

On my car: front - (17", 235/45) = 12.7 inches; rear - (17", 275/40) = 12.8 inches.

I created a simple little excel model that calculates this for you. Although the numbers might not be exact, it gives a good relative picture for comparative purposes.

So in theory, one can get a tire/rim combo that would actually sit lower than stock with larger rims.

 

Go to www.tirerack.com and go to the wheel and tire tech sections. Read everything.

 

as a general guide, for everyinch you go up from stock, lower the sidewall width of the tire by 5 EX: 16" wheel with a 205-50-16> 17" wheel 205-45-17

 

ahh, gotcha, thanks guys. so then the middle number is the tire side wall height(xxx-45-xx)??

but then for tire rubbing, I'm sure that width also plays a big part, and I guess offset does too.

I guess it's a matter turning the stock tire to the left as far as it will go, then measure the clearance I've got there, then look at the width (figure out what the hell offset means), and outer diameter of the would be new tire and see what will match up.

thanks for the help guys, this does clear things up quite a bit.

 

You don't have to do any of that. There are well established size/offset combos for the FD that have been researched over the years. Do a search and look in the archive sections. You'll find all you need to know.

 

You basically got the right idea. Just to clarify, the middle number is actually the profile height as a ratio of tire width. i.e. 245/45/16 interprets to a tire width of 245 mm, a profile height of 45% of 245 = 110mm, and a rim size of 16 inches.

 

oh, so the middle number is actually a percentage of the overall width of the tire interpreted as the height??? I dodn't know that, good to know. Yeah, I did a search, and I could find the sizing and all (I think 18"x8.5 for the front and 18"x9.5 for the back should be ok from what I saw, I forget what the offset was, will have to take a look again).

see, the real reason I'm asking is I've been talking with an importer for a front bumper, and I think the bumper will sit about an inch lower, which means I'm gonna be scraping it left and right, if that was the case, I'm just not going to get the bumper and go 99 spec, but I'd like to check out all of options first and see if the wheels raised the car enough then I'd be fine.

So let's see, the stock tire is 225/50/16, with a 16" wheel, that gives a height of 16+4.43= 20.43
20.43/2 = 10.215" distance from the center of the wheel to the ground

Now for a 18" with a wheel of 245/40/18 (took this size off the http://www.scuderiaciriani.com site) :

18+3.86 = 21.86
21.86/2 = 10.93

10.93-10.215=0.715" height difference

Hmm, not much, and I don't think that might be enough to satisfy the bumper. Guess I may have to go with the 99 spec cause at least that sits a little higher than the other bumper and I don't mid the scraping as much on that (if it's anything like the R1 bumper, it's pretty resilient)

Ok, thanks a lot for all of the help guys. This really helped a lot.

Thanks

 

Trying to raise the ride height of the car above stock height to give an aftermarket body piece clearance is a really, really dumb idea.

Your math is also a little off, 225/50 16 is ~25" in diameter, not 20.4"! We don't have BMX wheels...

 

You only added the side wall height once to the dia. of the wheel.....you have to add the side wall height twice since there is rubber all the way around the wheel man. And yeah don't raise the car just to fit a bumper on it, you are hurting the handling of the car.

 

My Junx is correct...you would need to multiply the profile width by two to get the overall height of the tire/wheel combo...or you could just cut the rim diameter by half and add the profile height x 1 to get the distance from the ground to the center of the wheel...same thing.

 

gotcha, just realized my mistake guys, thanks for that.

one question about the bumper thing though. would that really change the handling of the car. I mean, the car is going to be a little higher off the ground, but since the suspension setup is the same as well as the alignment, how will that change the handling characteristics? I mean, the force being displaced to the wheels when cornering is the same, and shouldn't the spring rebound rate be the same as I am retaining the same springs and suspension??

 

Raising the ride height raises the center of gravity = the car will not handle transitions as well and will also suffer poorer aerodynamics.

It's silly to do this just to fit an aftermarket front bumper. Either drive carefully and deal with the occasional scraping or go with a different bumper.

 

yeah, guess you're right. ok, cool, thanks guys.