Need help with tire sizes for wheels on an AE, slighty lowered.

my eibachs settled a good 3/4" over the first couple months so you might wanna drive it a bit and see where they end up. do you have poly rear subframe bushings? That won't affect stance but it sure as hell affects ride quality. you may want a slightly bigger tire to absorb some road shocks depending what roads are like where you live…

This thread may be pertinent…

https://z31performance.com/forum/ann…mma#post536525

Stockers were 215-60r15 or 225-50r16 (thank you z31.com). So, I'd say 50's or 60's on 235's or 255's will be WAY too tall.

I was reading about how they settle in most cases. i am hoping they don't settle as low as they were before. I installed the bushing kit from the Zstore, but it didn't come with the rear subframe bushings, so don't got 'em on the car. i'm surprised they don't include those, but yet they include other bushings that don't belong to the Z31. strange.

I am thinking of going just a size bigger, say 45/40. unless they really settle, could just stick with the 40/35 too. so hard to tell. i will post some pictures of how the low the car was before. I live in the UAE and the roads here are very nice. flat and solid, no potholes. however, there are speed bumps. thousands of them. my car could barely squeeze by before.... barely.

Bon

thanks. i was reading up on that yesterday. there are some cars that have the 235's with 40s and 45s. don't look too bad. the problem is you can't tell if some of them have been lowered even slightly or if they had aftermarket springs and they don't list it.

I was thikning the same thing, that those would be just too big. 50's and 60's. maybe I should just stick with what I have?
I have the stock wheels and tires as well and indeed they are 225-50r16 all around. I have thought about just throwing those on and seeing how far it settles and they handle it, at least temporarily until everything settles and I can figure out what to do with the aftermarket wheels. would they be too big even though they are only 16" ?

one thing I don't really understand is why alot of folks have smaller tires in the rear and bigger ones in the front. and some keep the same size all the way around. is this wise for me to do in my case?

Thanks

Hi Bon,

First thing to look at is how much distance you have in the front between the top of the tire and the strut housing. You can only go as high as clearance allows there.

The stock 225 60 16 are around 25" tall. These measurements are approximates, tire tread, air pressure, wheel width, etc could all have an effect.

Front
The tires you have on now 235 40 18 should be around 25 to 251/2" tall.
235 45 18 will be a little over 26" tall, 235 50 18 will be a little over 27" tall and 235 60 18 will be around 29" tall.

Rear
255 35 18 are around 25" tall
255 40 18 about 26" tall, 255 45 18 about 27" tall and 255 55 18 about 29" tall.

The reason for the wider tires in the rear (255 vs 235) is because the 255's would most likely hit the struts in the front without adding spacers or lowering the aspect ratio. The 255 are 20mm wider than the 235s and 30mm wider than the stock 225.

If you don't need the wider tires in the rear, you could put the same all around and be able to rotate the tires.

Remember if you go to a taller tire, your speedo will be incorrect, so GPS your speed to figure out the difference, the faster you go, the more it will be off.

That's some pretty good info, Dunkine, sounds like you really know your wheels! it gives me a pretty good visual perspective on the wheel comparisons, though it would be best if I measured them on the car.

that's interesting about the bigger tires. i never really thought about that. but I was also wondering about the height… i understand the width. but the aspect, 40 vs.35. why is it smaller than the fronts?
personally I like to be able to rotate all four tires around, prolonging the their life or at least making them wear evenly.

i really don't want to go too tall on the tires. don't want to mess with the speedo readings, and don't want them to rub up against wheel-well liner, but I do want to make more clearance for the wheels and the bottom of the car. the whole reason for changing out the lowered-butchy hack springs was to be able to have more clearance underneath so its not always hitting and scraping everything. maybe i should have went stock springs? but the stance does look pretty cool lowered like it was. rough ride though when hitting any bumps at all. i just figured the Eibachs would be better than the "modified" springs that were on before. the passenger side was completely sagged down, there wasn't even evenly spaced areas in between the front spring rings!

also it should be noted here that in addition to the previously "modified" springs, the struts were KYB gas-adjust all the way around with NO BUMP STOPS or RUBBER BELLOWS on them, NO BOOTS or DUSTCOVERS..... just struts and metal. everytime i hit a big bump going at high speeds, it felt like and sounded like anti-aircraft-artillery tearing into the chassis bottom, i kid you not!

now I have installed the bump stops, bellows, and boots on all the KYB struts like they are supposed to have. the poly-urethane bushing kit, new tie rods, ball joints, engine mounts (one was worn severely) and the new Eibach pro springs. I think this will be a definite improvement on the road. just hope it sits a bit higher so I can at least clear all the damn speed bumps, barriers, and curbs on the street. if it goes all the way back down to its previous lowered state, then I'm back to square one
if that turns out okay, I then just need to figure out the new tire sizes. I already mentioned that the rears are gone… I'm surprised they lasted this long without blowing.

here are the pics of the previous lowering:

thanks,

Bon

You usually see a smaller aspect ratio in the rear (40's vs 50's for example) when there is a wider tire in the back. Aspect ratio is a measure of how wide the side of the tire is, but it's always a proportion of the width. If you go taller at all than factory, then speedo readings will be affected. You may be able to change the speedo pinion gear to compensate, but there's only so many teeth you can add or remove before it just won't fit. There's some online calculators readily googlable that will tell you how much the speedo will change.

I think what you're wanting to do is change ride height using a stock size wheel.. Unless you go a custom route (adjustable height coilovers, for example), the only way you'll be able to do that is to change springs. As for bottoming out, as long as your not driving on Mississippi's crappy roads you'll probably be fine. If you are in Mississippi, get a lift kit.

Like Mwolvinm said, it's a proportion or percentage of tire width. If you have a 255mm wide tire and an aspect ratio of 35 it's 35% of 255mm.
255 x .35 = 89.25mm or 3.5"
So if your rim size is 18" and you have sidewall on top of the rim and on the bottom of the rim 18 + 3.5 + 3.5 = 25" tall

for the fronts
235 x .40 = 94mm or 3.7" so 18 + 3.7 + 3.7 = 25.4" tall

If you ran the same aspect, 235 35 18 would be 235 x .35 = 82.25mm or 3.24" so 18 + 3.24 + 3.24 = 24.48" tall (which isn't too much smaller, may have to factor in engine weight)

You can do that with any size rim. 235 40 15 would be 15 + 3.7 + 3.7 = 22.4" tall