I was at a car show last weekend and saw two '71 vettes with different size tires on stock 15x8" rims. (Both had raised letter BFG Radial TA''s). The first car had more "stock looking" P235-65R-15's which had about a 7-8" tread width. The second car had P265-50R-15's which had about a 8-10" tread width. The second car looked a lot more aggressive with the wider tread but the car also looked like it had been lowered about an inch front & rear. My question(s) are threefold; (1) are there any rubbing issues with the 265's? (2) Without lowering the car do the 265's look too small for the wheel-well opening? and (3) How troublesome and permanent is lowering a C-3? Are there any issues with getting over speed bumps and entering dirveways?

Thanks!

 

I would stick with 255/50/15 in the front, rear you can go 275/40/15 but you should check you vette first. 255's all around look good. Lowering is permanent at least in the front becuase you have to cut/replace your springs but you could reverse with different springs if needed. Rear lowering depends on your type of spring - metal or glass

 

Correct sizes are either 225/70R15 or 255/60R15 both of which are 27" tall.

I have 255/60R15 on all four corners with no rubbing.

BTW: A 255/50R15 is only 25" tall and a 275/40R15 is 23.6" tall. IMHO, that would like terrible.

 

i have front 255/60/15 and rear 275/60/15 on white minilite alloys and they look really good...i've been trying to lower the '77 vette i have but with little success, i have front transverse glassfibre monospring and rear composite monospring too, for the rear i've already fix 8'' bolts but even at minimum it won't go further down, what can i do there?? front i have gimcana coils, harder but NOT hard enough for my type of drive, i'd like to drop fron too even if permanent i dont bother.

could you pls advise what to do? also what stiffer coils could i fix there (i like sharp bends at high speedddd...... ) thanks...

 

Looking to buy 4 tires - 255-60-15 but I can not find any speed rated H or above. Whose tires do you have?

 

15" high speed tires are almost now non-existent. BFG are only rated to 110mph, if you exceed that speed the tires start to "crown" in the middle,lessening your contact patch with the road. this is true any time you exceed the speed rating on a tire. I take my 79, with 255/60/15 BFG ta's, up to 105 mph once in awhile, the problem I have is with my 700r4, at a little over 105 mph the tranny automatically downshifts and all of a sudden I'm way over the red line. I did this twice, the first time I wasn't exactly sure what had happened, the second time I cautiously approached 100mph and over, and that's how I know not to exceed 105. both times I quickly lifted on the pedal and hit neutral, I'm glad I had my rebuilt L-48, blueprinted and balanced, no damage and the motor is fine.

 

Where do you find these bastard tire sizes?

 

I run the BFG's all around, 245/6015's in the front and 255/6015's in the rear. I've also lowered the front with VBP springs 460's I cut. In lowering the rear with a mono spring you can use longer bolts and cut off the excess, however keep your half shafts level or you may have problems with the u joints and other components.....

 

Pirelli Scorpion Zeros. . . They are V-rated 255/65/R15 SUV tires. I'm happy with mine. Tire rack has them for $90 each right now, which is less than what I paid from Sears a few years ago.

Also, remember, if you are driving at high speed for extended periods of time, you have to inflate the tires to a higher pressure to keep them from heating up too much. Look at the specs carefully for whatever tire you buy. . .

-dath

 

I've been wondering and maybe one of you has the answer. Will a 255/60/15 on a stock 15x8 rim still fit in the spare tire carrier?

 

Does NOT on my '75.

I have been running without a spare for 3 years now. Driven cross country that way. Can of Fix-a-Flat and a cell phone.

 

hmmm.....just had a thought.....

instead of going bigger gears in the rear (at the moment) - I was going to change the 3.08 to 3.7 gears....

could I change the tyre profile - so instead of 60 profile - go 50 profile? do you know what Im saying?
my bf said he was going to work out the ratios tonight.
its all ratios!

 

front 255/60/15 and rear 275/60/15

 

73jst...how much did you cut fm the coils? with what result, how much lower front? isnt better use the 550? maybe stiffer aren't they? thanks Giu

 

[QUOTE=Carl Granquist]I've been wondering and maybe one of you has the answer. Will a 255/60/15 on a stock 15x8 rim still fit in the spare tire carrier?[/QUOTE


Stock OEM tires for a 73 are 225/70R15 is 27.4" Dia., 255/60R15 is 27.1"dia. so it should fit the carrier, you would need to adjust the carrier bolts which may not be long enough and hang too low.... now I just carry a can of fix a flat, no problems here for 4 years now and loose around 58lbs. with it removed........I think alot of the Forum members don't carry a spare.....

 

I have never been able to get a 225/70-15 to fit into my spare tire carrier. I even have a brand new Goodyear I purchased from Ecklers just for this purpose… won't fit. The 255/60-15's on the car, I wouldn't even try. I finally purchased a 225/60-15 and it fit's in there snugly. The problem isn't the diameter; it is the width of the tire when mounted on the rim. The 225/70-15 sidewall bulges enough that it will not allow me to close the carrier without extending the bolts well beyond stock.

The GR70's that came on these cars must have been significantly narrower.

GUSTO

 

Me too, but they are actually a bit big.....but they don't rub with the stock '78 alum wheels.

 

Yeah, you can put smaller tires on and end up with the same kind of advantage you get with a different gear ratio. The problem is that it will also lower the car and they may not fill up the wheel well and look as good. Look up the tire diameter for whatever tires you are considering, that is the number that will really matter (actually circumference, but the formula I'll give uses diameter in inches). You can easily calculate the RPM of the car at a given speed:

RPM = (mph * tgear * rear * 88) / pi * (d / 12)

tgear = transmission gear ratio
rear = rear gear ratio
pi ~= 3.14159
d = diameter of tire in inches

I made a chart for my car with different gear combinations as I'm thinking of swapping out my gears. The gear ratios for all of the transmissions I was considering are:

TH350 TH400 200-4R 700-R4
1st 2.52 2.48 2.74 3.06
2nd 1.52 1.48 1.57 1.62
3rd 1.00 1.00 1.00 1.00
4th ---- ---- 0.67 0.70

So for example, with a TH400 in third gear at 55 miles per hour with a 3.08 rear end and the tires I have (27.1" diameter) the math looks like:

RPM = (55 * 1 * 3.08 * 88) / 3.14159 * (27.1 / 12)
RPM = 2101.157

In other words, I'm screwed with my 2500 RPM stall torque converter that I'm currently running! That probably explains my 4.6 MPG

Hope that helps!
-dath

 

Panic, check some of my other posts on this topic, I went into detail on what I did with the VBP 460 springs and how much I cut. Remember if you change front springs and start cutting every vehicle is differant with weight/accessories, cut alittle off at a time until you get the height your looking for....

 

Thanks Dath...that helps for sure.