Bias Tires ?

[Glen C.]

Re: Bias Tires ?

Gary,
Not inexpensive by no means; I believe around $240.00 EA for 205-75-15 which should be a good look & fit for a C2 @ 6.20" thread X 8.0" section X 26.8" Dia. Note: Diamond Back also told me that If I want to see what the tire looks like to ask to see the Michelin "Defender" at any tire store that carries Michelin Tires which is identical to the Diamond Back MX only WITH the graphics and script which is not on the Diamond Back.
Ralph

Ralph, That is what I paid, just under a grand with shipping for the set of four P205/75R15. I went to a dealer that sells Michelin, to buy a spare tire, he said he could not get the Michelin X but that it was available at Sams Club. I took his suggestion and bought my fifth tire (the spare) at Sams Club, identical tire to the Diamond Back except un-shaved and a black wall at about half the cost.

[Glen C.]

Re: Bias Tires ?

Thanks Ralph, I'll give the higher pressure a try and see if I like the ride quality.

[Chuck G.]

Re: Bias Tires ?

had their part time Chevy mechanic do a computer alignment to later C-3 specs with radials - and have never looked back.
Stu Fox

You nailed the problem with the above quote, Stu. Most, if not all alignment shops have a "one size fits all Corvette" alignment spec, and that spec is the later C3 spec with radial tires.

The old spec for bias plies calls for much more toe-in.

THAT is why when you put bias ply tires on a car aligned for radials, it wanders and jumps all over the lane.

I have my cars aligned to the "old" toe-in spec, and can (and do) switch back between bias and radials without problems.

I don't have reference material in front of me, but I'm sure if someone checks the "old" Corvette bias ply tire alignment specs and compares it to the "new" Corvette radial ply tire alignment specs, you will see the difference, and the root of the problem.

Chuck

[Timothy B.]

Re: Bias Tires ?

Chuck,

The old TOTAL toe in spec in my 67 AIM is 3/16 for the front, my memory tells me the rear TOTAL toe in is 1/16".

I was at BJ's a few weeks ago and the tire man said the warehouse still stocks the Michelin 205/75 tire but I can't relate the speed rating of the tires.

[Chuck G.]

Re: Bias Tires ?

Chuck,

The old TOTAL toe in spec in my 67 AIM is 3/16 for the front, my memory tells me the rear TOTAL toe in is 1/16".

I was at BJ's a few weeks ago and the tire man said the warehouse still stocks the Michelin 205/75 tire but I can't relate the speed rating of the tires.

Hi Tim.

I was surprised at how long it took me to find alignment specs for midyears. I found this posted by none other than John Hinckley, aka JohnZ on many Corvette websites.

This is a cut and paste. Notice the difference in front toe-in between BIAS and RADIAL ply tires....

I've "been there, done that, got the tee shirt" trying to run bias ply tires with radial settings. It's a scary experience.



Rear camber = zero to 1/2-degree negative.
Rear toe = 1/16" total toe-in, split evenly across the thrust centerline (1/32" per side).

Front camber = zero degrees.
Front caster = 1 to 1-1/2 degrees positive (manual steering), 2 to 2-1/2 degrees positive (power steering).
Front toe = zero to 1/16" total toe-in.

The above assumes you're running radial tires, which require far less toe-in than the original bias-ply tires.

If you have bias-ply tires, front toe is 3/16" - 5/16" total, no change for rear toe.

Correct rear toe-in is critical to proper handling behavior, especially having it evenly split between both sides; make sure the alignment shop takes the time to do rear toe correctly (which is time-consuming, especially if the bushing bolts are rusty) - "close enough" isn't good enough. In the Detroit area, a proper 4-wheel alignment on a C2/C3 Corvette runs about $150, most of which is labor to do rear toe correctly.

BTW, saw your brother and sister in law last week in Florida. The old Bel Air Corvette Club guys went to the Twin 125's at Daytona. The girls went shopping. Imagine that.

Chuck

[Michael J.]

Re: Bias Tires ?

This is interesting about alignment. I have been switching back and forth from bias for shows and judging to radials for driving in my '67 for many years, every few months, and never changed a thing. I have no idea what the alignment is set at, but it drives just fine with either set, of course much better on the radials. I have not noticed anything amiss, and the tire wear looks even. I am curious, when you say: "I've "been there, done that, got the tee shirt" trying to run bias ply tires with radial settings. It's a scary experience.", I am wondering what you are feeling that is so different in the alignment settings that makes it a scary experience?

[Chuck G.]

Re: Bias Tires ?

This is interesting about alignment. I have been switching back and forth from bias for shows and judging to radials for driving in my '67 for many years, every few months, and never changed a thing. I have no idea what the alignment is set at, but it drives just fine with either set, of course much better on the radials. I have not noticed anything amiss, and the tire wear looks even. I am curious, when you say: "I've "been there, done that, got the tee shirt" trying to run bias ply tires with radial settings. It's a scary experience.", I am wondering what you are feeling that is so different in the alignment settings that makes it a scary experience?

I would venture a guess that your car is aligned to the bias ply setting, which is OK for both.

What do I mean by "scary experience"?

The car won't track straight. It'll move 2'--3' within a lane without turning the steering wheel. If you take your eyes off the road for a micro-second, you won't be going straight anymore.

Very sensitive steering with NO road "feel". You have to keep both hands on the wheel at all times. You're constantly "correcting" your course.

I have both my 63 and my 69 aligned to the "old" bias spec, and have NO problems. As a matter of fact, I now have repro bias/belted tires on my 69, and can drive it anywhere with ease.

I currently have radials on my 63, but I have my repro belted tires on original rims ready to put on at any time.

Now, it would be a fools argument to say that bias ply tires are better than radials....... That's not the point I'm trying to get across here.

I drove these cars when they were new back in the mid to late 1960's and the "dart-like" steering and lack of road feel was NOT an issue back then. It's the front end alignment.

Chuck

[Michael J.]

Re: Bias Tires ?

OK, thanks I got it. I thought it would be incredibly expensive and a PITA to have to change alignment every time I change tire sets unless there was something really dangerous, glad to know the bias setting is the way to go for both. Back in the day, I do remember how much of an improvement the Polyglas tires were over the old Power Cushions for handling and road tracking though.

[Timothy B.]

Re: Bias Tires ?

To ad to Chucks comment, the bias tires have you constantly steering the car while driving down the road, if you find a groove in the pavement, "hold on".

With radials you can relax and keep the woman closer to you while driving with one hand on the wheel. :-)

[Chuck G.]

Re: Bias Tires ?

To ad to Chucks comment, the bias tires have you constantly steering the car while driving down the road, if you find a groove in the pavement, "hold on".

With radials you can relax and keep the woman closer to you while driving with one hand on the wheel. :-)

Tim has mentioned the REAL reason to use the bias ply alignment........ keepin' your gal closer.

Chuck

[Joe C.]

Re: Bias Tires ?

I went through a set of beautiful Kelsey Goodyear Power Cushion 7.75-15 Goldlines. There is NOTHING that looks as good, or gets as much attention as a set of original looking tires. The change to modern radials completely changes the "look" of the car, and at shows, etc., it now garners much less attention, as experience has shown me.

Reproduction bias ply tires are obviously not made exactly the same as originals, and I believe that the rubber compound used on repops is quite a bit softer. They do grip better than the originals, I think, as it was quite difficult to get the car to break away around turns. When these tires were installed on the car, I wasn't driving it very hard at the time. I had the air pressure carefully monitored at 28 psi. The tires showed a wear pattern that suggested overinflation.........................all 4 tires wore out in the center with good and even tread thickening as you approached the edges! I tried underinflating them for awhile, to even-out the wear, but there was no difference.

On the rare occasions that I smoked the rear tires (again, back then I was driving the car with kid gloves on), tread chunked off, big time. Pieces of rubber the size of raisins came sloughing off!

As far as safety, I'd have to say that there were no issues. I'd cruise at 75-80 MPH with occasional runs up past 130 with nary a shudder or shimmy. Toward the end of their life, I began racing the car at Raceway Park, in an effort to quickly burn off the last 1000 miles or so of tread. There were no issues.

They lasted for about 10,000 miles, with most of that being normal driving. Back in the day, I remember that many tires would last between 18,000 and 25,000 miles, depending on how often they were rotated, and if they were installed on Chrysler products with torsion bar front suspensions.

[Michael J.]

Re: Bias Tires ?

I am now thinking about replacing the BF Goodrich bias ply polyester redlines I have on my '67 as show tires, they are pushing 7 years old. I always lose points for being a non-OEM redline and being polyester. I am thinking about the Kelsey Goodyear PowerCushion full nylon bias plies, and thinking I want white walls instead of redlines, since my tank sticker says it came with white wall. I know the tank sticker is immaterial for judging, but just want to take it back to original setup, it is a Rally Red car. This will be a tough decision, as I like the look of the redline, and the tracking/handling of polyester, but think I should go ahead and bite the bullet and put up with the cold flat-spotting of the nylon and get the original look of the old girl back.