Well I have been lurking here on the forums for some time, but finally have come across a question I have having difficulty in finding an answer.

Its time to replace the tires on my 77. it has 235 60 r15 on it now. I see a lot of people using 255 60 r15. I was going to put the 225 70 r15 on.

how much of a difference in fuel economy will I see between the 225 and the 255?

 

You won't see much difference in fuel mileage. The 225 70 15 is only 3/10" larger diameter than the 255 60 15. The 255 60 15 is over an inch wider than the 225 70 15.

 

Not much to notice.

The question is wether or not the 255 will fit ok. Some cars were modded by the factory after 1978 to fit the 255 and some of the earlier cars have clearance issues with the 255. Your best bet it to have a set mounted and see how they fit.

 

They have the same diameter so I do not think there will be any significant difference in mpg. They are about 1" larger in diameter than what you currently have.

255X60 255 x .6= 153mm, 153/25.4=6.02362inch (6.02 x 2) + 15 = 27.04 diameter

225X70 225 x .7= 158mm, 158/25.4=6.02007inch (6.02 x 2) + 15 = 27.04 diameter

 

MPG's not much difference,but looks No rubbing on my 76:
[IMG][/IMG]

 

Those are the 255 60 correct? Looks pretty good. This is my 77, just doesnt sit right with the 235 60. I have a brand new set of 235 70 which if my calculations are correct is just a smidge taller than the 225 70 and obviously wider. I'm certain I would probably run into issues with turning if I used them though.

here it is as it sits now.

 

Yup, 255-60-15 Firestones they are good tires for the price.Not sure if they are available anymore.Costco had the BF Goodrich if you do search by size on their website.Another view:[IMG][/IMG]

 

one last question. with the 255 width, what type of clearance do you have at the back side of the front fenders where it wraps around under the car.

Just for kicks today I put two of the 235/70 on the front to see what type of clearance issues I would have, and they do rub at that spot.

now the 235/70 have an overall diameter of 27.95 with a width of 9.25.

the 255/60 have an overall diameter of 27.05 with width of 10.04

so they are like .8" wider than the 235. so even though they are .9" smaller in diameter wouldnt the extra width still cause problems with the front? where mine are getting caught is right on the outer edge of the tread.

here is where I'm talking about. It looks good otherwise and no other clearance issues, so before I went out and bought the 255/60 i just wanted to confirm that I wouldnt run into the same issue. you can see where the paint rubbed off from the tire. oddly enough it only has this issue on the passenger side. the drivers side clears by about 1/4"

local tire shop has the Firestone but only in 235/60 but they do have the BFG Radial T/A in 255/60. worst case scenario I can just put on the Firestone 235/60 I know those will fit, its just that the 255/60 looks better. And to top it off, nobody will put 225/70 on the car even though that is what it came with from the factory. everything lists 7.5" as the widest you can mount it on.

 

Run 225/70-15 on the front and 255/60-15 on the rear. That's what I decided to do with mine to prevent rubbing issues.
I can't rotate them that way, but it is likely that the tires will need replacement due to age before they need it for loss of tread.

 

No rubbing issues on my 76 with the 255/60/15 but each car may be a little different.I would like to lower my car a little but the roads here suck so it's a no go.You could trim a little off the inside fender to gain more clearance.The 255/60/15 tires do give the Vette a meaner look....Good Luck!

 

I'm still learning about tires....but....255s are NOT 10 inch wide tires, so far as I know it...I thought you had to 295s or higher for ten inch wide tires?

 

I see where my problem is, I was looking at my friends 82 today he has 255/60 on his but I also noticed that the area that I'm having contact issues on his car is contoured differently, its cut back at an angle where on my 77 its just straight across.

 

255 are in fact 10.04" where the 235 are 9.25"

 

Well, I've got 275 eagle run flats on mine, and they are 9.5 inches wide.

What PSI are your tires at? Maybe they "balloon" out more under the weight, than lower profile tires, resulting in a wider footprint, on the pavement?

 

I'd do that except every tire manufacturer I have looked at specs the 225/70 tires to no bigger than 7.5" rims and the vette has 8"

 

The car was originally spec'ed for 225/70-15's (actually GR 70-15s old numbering system which may have been 215/70 15's?) when I look up tires for 77 corvette on tirerack it comes up with 225/70-15 and that is what it had on it for ten years. They looked good and handled fine. I noticed the tire manufactures stated 7.5 inch rims too don't know why that is.

 

The 275 is millimeters. 275mm = 10.8 inches. Where are you measuring to get 9.5"?

 

this is where I get my info from, they spec a 250 at 9.84" and a 255 at 10.04" for your 9.5" you would need a 240 or 245. They list the 275 at 10.83". I'd repectfully ask that you remeasuer your tires.

http://www.ajdesigner.com/fl_tire/tire.php

 

I was watching this thread last week as I was planning on getting new tires and just had 225/70/15 installed on the 72 this past weekend.

 

Nice looking tires. I like how the 225/70-15 fills up the wheel well not leaving a big gap between the body and top of the tire.
I settled for the Cobra radial GT, which I think is essentially the same tire under a different name. The 255/60-15 is .30 inches smaller diameter wise, not really noticable. I wanted the T rated tire for that extra 6 MPH. LOL!