Newbie here..

Stock tires on a 86 Z28 that i'm looking at is 215-65-15 and they are
dried and cracked and i was wondering if a set of 235 70 15 would fit
without any problems like striking the fenders etc..in order to drive it home 300 miles ?

TB

 

those are truck tires, 29 inch tall. they "may" barely work on the rear, but dont count in it, not a chance on the front

 

They're 28". If the car isn't lowered, and if you don't turn tight, ( even if it means making 12 point turns instead of 3-point ) Then it should work. I've done 215/75R15s, and they're 27.7".
Your speedometer should show 51 when you're really doing 55.

 

you are right, i must have punched in a wrong number on the chart, came up with 28.9" diameter

28 is still really tight on the front, you will really have be be careful turning.

 

Is there anyone who can tell me whether I will be able to fit 295/50 R15 on the back of '91 Z28 without any modification? Or are they gonna be too wide?
If it's not possible I will go for 275/60 R15...

Good choice? Bad?

 

In the rear? Depends on the backspacing of your wheels. Yes, if your bs is good. No if it isn't.

 

What is the biggest i could fit on stock crosslace rims in the rear and the widest in the front

 

15" or 16" crosslaces?

The 16" wheels are 8" wide and the BFG 295/50R16 will fit just fine in the rear (been there, done that myself). And for a street 16" tire, 255 is the biggest they make except the 295, which will not fit up front.

IIRC, the 15" crosslaces are only 7", so I (personally) wouldn't go more than 265/275, but those aren't real common widths & the aspect ratio has to be kept in check, not to get too large in overall diameter.

275s will fit up front, but you really have to get the backspacing of the wheel just right, which would be hard on a 15" wheel clearing the strut & spindle.

 

The 295 rear and 255 combo I think would be perfect. Its what I plan on running on my IROC wheels for the street. Just keep in mind that the 295 tire is taller than stock so you will be going faster than what your speedometer says.

 

I have the 16x8, Well could the speedo gearing be accounted for, if not what is the largest tire that wont affect the speedo gear. It is a mechanical speedo. Also i dont wanna use wheel spacers.

 

255/50/16 is stock height. You could get different gears to account for the tire.

 

Look for a 245/50r15 or something. If your spending the money, make it look good at least. You don't want tall skinny tires on a Z28 do you?

 

i got that but i dont understand how a wider tire would affect the gearing i thought if it was taller that the height would affect the gearing

 

Just wider won't. But 50% of 295 = taller overall than 50% of 245. (295/50 & 245/50)

 

The first number in a tire size is the width in milimeters. So a 295 is about 295 milimeters wide. The second number is the aspect ratio. What that means is that whatever the number is, say 50 for this tire, the tire sidewall is 50% of the width. So a 295/50's sidewall is 50% of 295 milimeters tall. Thats why its taller than a tire that has a sidewall that is 50% the height of 245 milimeters.

 

oooooo will the difference be noticable or if im doing 50 will it say 52.

 

Here is a calculator you can play with. Just put in what rear gear you have, the ratio of whatever gear you will be in for the trans, and your tire size and it will give you rpm.

http://www.fbody.com/calc.htm

 

It is a differnece of about 100 rpms, which is not significant, i jsut cant find a tire that they make in 295/50/16 and in 255/50/16.

 

BFG has the ONLY 295/50R16 that I know of.

 

Yea the only 295's I've found for 16's are the BFG's and Mickey Thompson drag radials.

 

yea and it is my dd so the drag radials are no good for rain, and the BFGs dont come in a 255

 

235/60R15 firestone makes a good tire

 

Finally fitted new wheels and tyres.
So I can now confirm that the 275/60 R15 will fit at the back of 1991 Z28 with stock suspension but they will rub on the wheel arch on every little bump on the road.
That's how they look:

21092010260.jpg?t=1285271398

21092010255.jpg?t=1285271423

BTW the front ones are 225/60 R15
Wheels are Cragar S330 15x7 front, 15x8 rear.

I had to cut a bit of the wheel arch lip to be able to drive... I'm gonna to put adjustable shocks at the rear as well to minimise the bounce.

 

Here's a handy calculator that i have been using alot lately:

http://www.miata.net/garage/tirecalc.html

It doesn't tell you tire clearance at all, but it will help you keep your profile close to Original when you're using different size wheels and tires. Really handy tool.

 

Hey, thanks.
I used it before I bought the tires but never took account of car bouncing up and down on uneven surface. Stiffer shocks should sort that out tho.