C1 - Tire Size

[Jim K.]

I have a decent set of Cragar mags on my 61' with 215/65 tires on them. I have a set of 5" stamped steel rims ready to go on but think that the 65's may not work on them. Ultimately, I'd like the largest diameter tire that won't interfere with the rest of the car so it will do better on the highway. Other note is I have 3.70's in the rear end. So... Will the 65 series tires work on the 5" rims AND what is the largest tire I can put on the 5" rim (assuming the suspension is close to spec)?
Thanks!!!

[Mike Cobine]

Re: C1 - Tire Size

Here are some places to check.

Tire size comparison chart

http://www.turbinecar.com/tires.htm

http://www.angelfire.com/on/geebjen/tires.html

Available 15 inch tires - comparison chart

http://www.cristhomas.com/cars/tires.html

Tire comparison by Overall Diameter

http://www.musclecarclub.com/library/tech/tires.shtml

This is a neat little Tire Calculator for comparing tires and seeing what happens on the highway.
http://www.miata.net/garage/tirecalc.html

[Jim K.]

Re: C1 - Tire Size

These are great sites, I particularly like the last one, it graphically shows what the numbers do when they change, helps my understanding, thanks!!!

[Mike Cobine]

Re: C1 - Tire Size

I ran into a couple that were better a few months ago, but I didn't bookmark them and can't locate them right now. Figures.

[Christopher R.]

Re: C1 - Tire Size

I'll send you a 20+ page "Word" file of a collection of posts from this and other Corvette bulletin boards on this subject. If anybody else wants a copy, email me privately at cjr1@gte.net. I won't be able to do this until tonight.

To summarize:

1. If you want to use the standard 56-62 full size wheelcover (hubcap), you must use the standard 15" x 5" wheel rim. Or modify another wheel to add the 4 "bumps" that hold these covers on. If you use the 15" x 5" standard rim, you cannot go any wider than 205/75 or 215/70 (and that's at the extreme edge of the recommended spec.). Go to any of the major tire manufacturers Web sites, and see the recommended wheel size specs for their tires.

2. You can get 205/75s with a thin whitewall. You cannot get a performance tire in the 205/75 size. But it's still several magnitudes better than the standard bias plies that came on there originally. You can get a performance 215/70, but it'll be blackwall only. For wide whites, you need to go to a specialty manufacturer.

3. The 205/75 will cause the spare tire cover cover to sit up about 3/4" proud. Larger sizes are worse. You don't want to use a different size tire on the same rear axle if you have Positraction.

4. If you're going to use the RPO "dog dish" hubcaps (They're not "wheelcovers." They're definitely "hubcaps."), you could use another and wider Chevy rim with the same bolt pattern. If you used a wider rim, you could use a wider tire. Those wheels are relatively common. However, with the wider rim, you get into backspacing issues. I've seen relatively wide tires on the backs of C1s. But I know the owners spent some time experimenting and researching backspacing issues. The "Word" file has some posts on this.

5. Your speedometer will accurately read with the 205/75s. It'll be close enough with the 215/70s. Anything else, and you'll need to experiment and change speedometer gears. That's an easy job.

At some point below the widest that'll fit, it'll start to look funny. You won't need to go all the way to the limit. Wider means a lower aspect ratio. That doesn't fill wheelwells unless you go to 16" or 17" rims. A 205/75 will visually fill the wheelwell better than something wider.

[Mike Cobine]

Re: C1 - Tire Size- more info

Unfortunately, the tire manufacturers' web sites are not that easy to compare. Once you could get charts from the dealers with all dimensions listed and do a visual comparison. Now you have to page after page on a web site.

http://www.goodyeartires.com/goodyeartireselector/catalog.jsp

http://www.bfgoodrichtires.com/bfgapp/catalog/index.jsp

Work your way down through to the Sizes and Specs and you can frequently find a PDF file that has the charts like these:

http://www.bfgoodrichtires.com/assets/pdf/radial_ta.pdf

http://www.bfgoodrichtires.com/assets/pdf/gForceSport.pdf

Then you can find recommended rim widths. Usually the range is a bit wide, so the center is the ideal spot. The Radial TA P215/70-15 lists 5.5 - 7.0 for rim width.

[Duke W.]

Re: C1 - Tire Size

The closest modern tire match to the OE 6.70-15 is the 205/75R-15. They are typically speced at 766 revs/mile versus 760 for the OE tire. The overall width is a little wider than OE, but not enough to be that noticeable.

The only issue with 205/75R-15s is that they are not performance tires. They have hard compounds and the highest speed rating is "T", but there are lots of them - at least four dozen listed at The Tire Rack, and many more cheap private brands. If you chose this size, buy what you think is the best quality. Price should not be an issue.

The best performance oriented tires are a select few 215/70R-15s and 225/70R-15 Revs per mile are 775 and 760, but the minimum recommended wheel width is 5.5" for 215/70s and 6" for 225/70s.

Duke

[Duke W.]

A WARNING!

You need to take these internet "conversion charts" with a grain of salt. They are often only a first cut approximation and other certain criteria are more important than other. Some are even flat out wrong!

I attempted to point this out in the two-part tire article for the Corvette Restorer last year.

The best way to match OE tires is to start with candidate sizes that are very close to the OE tires' revs per mile specification, AND have AT LEAST the same load capacity.

I noticed that one of the referenced charts listed revs/mile calculated from the inflated OD. THIS IS ABSULUTELY WRONG!!! Tires actually measure about 2-3 percent higher revs per mile than a "rigid body" due to deflection. Sites such as The Tire Rack and manufacturers web list list correct revs per mile for each modle and size tire.

If you want to read 4500 carefully composed words on how to select driving tires ,specifically for vintage Corvettes, dig up the Spring and Summer 2003 Corvette Restorer and get yourself an education.

Duke

[Jim K.]

Re: A WARNING!

Thanks Duke, very solid advice. Sounds like the 65 series tires are not a good choice for my stock rims. I was also hoping that someone may have done all the trial & error on the biggest diameter that will fit in the fenders on stock rims. I may just have to invest in some "may-pops" at the local garage to check clearances. ("may-pops" are the same as "bologna skins")

[Mike Cobine]

The Best Method

by far is to get the tire manufacturer's charts, like this on on the BFG T/A:

http://www.bfgoodrichtires.com/assets/pdf/traction_ta.pdf

http://www.bfgoodrichtires.com/assets/pdf/radial_ta.pdf

Comparing those to the calculators (most are wrong because like you said, they don't understand tires in dynamic motion) like this Miata one shows that the Rev/mi is definitely wrong.
http://www.miata.net/garage/tirecalc.html

The conversion charts are often just a linear same size designation, but the tires are rarely equivalent. These were often the results of competition bodies to regulate when someone had a stock size tire as to one that was not. Only a fool would think an F50-15, F60-15, F70-15, and so on were the same size. It states right in the designation that the aspect is lower on the 50 so it is a shorter tire. When you get to metric 225/60-15, 205/70-15, and 185/80-15 you can see the size is changing to accomodate the change in aspect. But yet the maker of the charts kept them on the same line as others.

However, you can take some information from one source, compare with a few other sources, and make your own conclusions as to what works, what doesn't, and what is real or not real.

But then, the ENTIRE INTERNET is that way. Anyone who takes one single source, even this site, as the complete truth, is bound to have a crash with reality.

[Joe Pennington]

Re: C1 - Tire Size

On my '56 I'm running stock 5" rims on the front with Goodyear Integrity 205/75-15's (27.1" dia) and on the rear I'm running '67 ralley 6" rims (with welded nubs) with GY Integrity 225/70-15's (27.3' dia). In these sizes, both WW and BW are available. I run the GY Interity tires on my '64 also and on my Buick LeSabre, which I drive faster and during 100*+ days driving on long trips in the Southwest. My life is just as valuable when I'm driving the Buick as it is when driving either of the vettes. If I felt a tire was dangerous to have on my Corvette, I sure wouldn't have it on my Buick. If you want to see what the car look like with these sizes, check www.vintagevettesoftheozarks.com and look under members cars (Joe P).