1977 Corvette GR70-15

[chris1977]

Hi Everyone,

Thanks for your help with the brakes questions and suggestions last month. The cars original front rotors with 32k on them cleaned up great and the car took its first short spin around my neighborhood since it went off the road in 1987.

Next question for the PRO'S. Since being off the road for almost 20 years the original tires have staken on a shape of their own. They are not saveable and I need to get her some new shoes. I want the original tires but Coker does not reproduce the GR70-15. From what my father told me, GM recalled his new tires in 1980 and put the GR70-15's on. I dont know what the car came with originally since I dont have the recall paperwork in my hands yet.

What is acceptable to the judges? What is going to work? and What is going to look period correct for my car?

Thanks everyone.

Chris

[Duke W.]

Re: 1977 Corvette GR70-15

Tire sizing switched to metric in '78, and the GR70-15 was superceded by the 225/70R-15 (with a 255/60R-15 optional), which has similar dimensions to GR70-15 and the same revs per mile, so 225/70R-15 is the modern functional equivalent to the GR70-15.

The old alphanumberic sizing system is long obsolete, and I'm not aware that any alphanumberic radials are reproduced - just a handful of bias types like E70-15 and F70-15.

Most of those early radials produced by American tire manufacturers were very poor quality and subject to tread separation. None had nylon cap belts like modern high speed rated radials.

The best current 225/70-15s are the V-rated "police pursuit tires" produced by Goodyear, Firestone, and General. See the Spring and Summmer 2003 Corvette Restorer.

If you have what you think are "original" GR70-15s and you want to have your car judged, consider keeping them for that purpose only and buying a new set of wheels to mount modern 225/70-15s for driving. If you review the '77 JG and score sheets you will be able to determine the points deduction for modern tires and decide whether buying another set of wheels is worth it.

Duke

[Doug F.]

Re: 1977 Corvette GR70-15

I just replaced my 28 year old original tires on my 78' pace car with close originals from the internet,, try www.tirerack.com,, is where i got mine, good luck,, doug

[Paul B.]

tires...

You'll get the "most" points by showing up with the "correct" replacement size as posted earlier and also the same BRAND as was available on your car. Firestone & Goodyear were the two suppliers from '73-'77, so to get the most points stick with either of these two "brands". Michelin's, B.F.GoodRich, etc., all "used" to be a 100% point deduction on both originality & condition(I believe it was 30pts for "originality", 30pts for "condition"). If I remember correctly, these tires get about 60% to 80% in points with a 40% to 20% total deduction out of 60 points.

[KEN BUTCHER]

Re: 1977 Corvette GR70-15

Original tires for your car back in 77 was firestone 721

[mike cobine]

Re: 1977 Corvette GR70-15

Be glad yours were recalled.

I knew a guy that had a set on his and was running down the road one night when his rear tire decided to cut off his fender.

[Bob B.]

Re: 1977 Corvette GR70-15

Ken
The correct OEM tires were Goodyear Steelgards or Firestone Steel Radial 500's the 721's were the replacement for the 500's.
Bob Beck

[Chris1977]

Re: 1977 Corvette GR70-15

I agree the car had Firestone 721's and you bring up a good point. GM recalled the Firestone 721's and the current GR7015'S were put on. We still have the recall letter and what they were replacing the original tires with. Do you still lose points for that?

[Chris1977]

Re: 1977 Corvette GR70-15

OK Ken so either way the tires were recalled and the recall replacements are what the car rides on today.

are these still going to get me all the points for judging or will I lose points because there was a recall? I cant see why I would but I am new to this so who knows.

[Bob B.]

Re: 1977 Corvette GR70-15

Chris
You will take a hit on points with the replacement/recall tires, the car is judged as how it left the factory.
Bob Beck

[Jack H.]

See the book...

Recall modifications are addressed in the NCRS Judging Reference Manual. I don't believe this rule was modified in the 7th Edition of the book, but from the 6th Edition, Section 4 Standard Deductions, Rule 9:

"Factory Recall Modification

Owners able to document Chevrolet notice for a 'factory recall' modification to their vehicle and which appears to have been perofrmed by a Chevrolet Dealer to factory specifications, will receive a minimum originality deduction."

[Gregory G.]

Re: See the book...

If that is true why do you loose all points for a factore warentee replacement engine??????

[Michael W.]

Re: See the book...

You don't. Please read the book.

[Jack H.]

It wasn't a 'factory recall' situation...

and you don't lose ALL points for a proper service replacement engine. Where did you get that piece of information?

The deduction(s) for Engine Block Cylinder Cases are defined in the NCRS Judging Reference Manual, Section 4, Rule 1 which has been discussed pretty well on this board in prior threads. You start with the casting number of the block and if it's a "Correct, normally configured casting number and case configuration", you get at least HALF credit for the replacement block.

The rule goes on to define the other criteria (casting date, information on the stamp pad, and broach marks) that take you up to full credit for the car's factory original block OR a properly done 'restoration' block (sometimes referred to as a 'restamp').

[Gregory G.]

Re: It wasn't a 'factory recall' situation...

You are right. It is only a loss of~6%. Since it is a warentee replacement the casting date is wrong and you loose everything after that. If everything else is prefict I could still get top flight. But it is a huge loss for one item when it was a factory replacement. I would get more points with a junkyard engine from a truck that had the right casting date and part number. Just does not maks sence to me.