Hi, Currently I am running BFG 255/60/15s on all 4 corners of my 73, I like the look of the bigger tire. My question is with all the uneven roads here would a 70 series tire on the front help with the jumping around. Also kind of wondering what it would look like. Your thoughts
John

 

Hi John,
I'm not sure what you mean by "jumping around"? Those words seem to describe more of a suspension issue than tire issue.
When folks use a 70 series tire they typically select the 225-70 size.
This tire is similar to the 'original' tire on your car, but not as wide as the 255-60 you're using now.
It shows 'about' as much side wall as the original tires on your car so give the car a somewhat 'period' look.
Again, I'm not sure that any of this has any thing to do with "jumping around".
Regards,
Alan

 

Hi Alan,
After rereading this( jumping around) wasn't the best description of this issue, my car holds the road quite well but when coming across uneven areas the wider tire seems to exaggerate it more. My thought was would a 70 series tire on the front remove some of this. And has anyone tried this, and how did it look?
Thanks, John

 

I agree with Alan that what you seem to be describing is more likely a suspension issue. 78-82 Corvettes came with P255/60R15's as an option, and never caused issues with thee front of the car "jumping around".

To start with, you have to remember that the suspension under your 73 was designed over 55 years ago. Corvettes came with a fairly firm suspension, and any firm or stiff suspension will tend to jump or bounce around on rough roads. Suspension technology has advanced quite a bit in the last 55 years, improving handling on modern cars, without sacrificing ride quality.

What pressures are you running in your tires? 73 was the first year Corvettes came with radials. GM recommended very low tire pressures of 20 lbs front and rear, for the 73 Corvette. I don't think I would run pressures that low, but if you're running pressures in the 30-35 pound range, like recommended for modern cars, I would try dropping them to around 26-28 pounds, and see what effect that has.

If lowering pressures doesn't help, then I think I'd be looking at the shocks, ball joints and A-Arm bushings, before changing out the tires.

I will disagree with Alan over his statement that the 225/70 tire is wider than the original tire on your car. 73's came with GR70-15's, and the modern equivalent of that tire is the P225/70R15. A 225/70 is nearly identical in size, to the GR70's that were on it when new. The 255/60 you're running now are wider than the OEM GR70's, but are the same diameter.

 

tire width is not the problem, see any new corvettes with skinny front tires ?
I am sure GM spends plenty on tire and suspension research.
I would suggest reviewing your front suspension and steering.

 

Make sure front alignment provides a small amount of "toe-in" on those front wheels. If they are aligned 'true' (zero toe), the car will go hunting on un-flat roadways.

About 1/16" to 1/8" (max) toe-IN will solve your problem... IF you don't have other problems with 'loose' suspension components.

 

I was going to say alignment. If you run into ruts or any sort of directional surface or pot holes and the front of your car tracks onto them abruptly or jumps, I would check the front. If you hit an uneven surface and the back jumps then you rear needs an alignment. My rear on my car used to jump what felt like 6" to a foot either way after a good bump.

 

If this "jumping around" is caused by depressions on highways caused by trucks eroding the pavement and creating grooves there is no cure.

 

255/60/15 diameter is 27.05"
225/70/15 diameter is 27.4

So, you'd have a taller tire in the front, I don't think you want that.
The advice to try reducing the tire pressure a bit might be good, I'm going to try it! Also, a good alignment certainly can make a big difference.