66 big block

[Carol #46113]

I've recently tried to replace my 775-15 bias ply tires with 205/75R15 radial reproductions. Multiple merchants told me these are the correct tires for the car. My problem is that when the tires were put on the car , the front tires rubbed the fenders when the wheels were turned. I had to put the bias ply tires back on. Nobody can figure out why these tires don't fit. The car is completely stock with 15 inch knockoff wheels. Any information you can give us will be helpful. Thanks.

[Joe L.]

Re: 66 big block

Carol-----

205-75-R15 is one of the accepted replacement tires sizes for your car. However, there are a variety of reasons why there may be interference problems when using this tire.

For one thing, some 1966 Corvettes with big block may have received the GM #3851100 front springs. These were, basically, a small block spring that GM originally thought would work ok for big blocks. They're not really "up-to-the-task", though for the extra big block weight. Usually, though, if the car has these springs you will note a slight "rake" (i.e. the front of the car appears to sit just a tiny bit lower than the rear.

Another possible problem is that the car is equipped with F-41 suspension. Cars with F-41 tend to have a slightly lower ride height than those with standard suspension. You can most easily determine if the car has F-41 suspension by checking the REAR spring---it will have 7 leafs instead of the 9 used for standard suspension cars.

Yet another possible problem is that your front springs are the original springs and have "sagged" just a little bit over the years. That will causes a slight lowering of the front end, perhaps imperceptible to the eye but affecting tire interference.

My suggestion would be to use the alternate radial tire size of 195-75-R15. I think that will solve your interference problem.

[Carol #46113]

Re: 66 big block

Thanks Joe, I'm going to check the leaf springs tommorrow. The car does not appear to sit lower at one end or the other. It could be the springs are original and have sagged, but like you stated it isn't noticeable. I was also told the 195s would do the trick. Would you know who might carry them? and do they come with gold lines? Thanks again.

[Kent D.]

Re: 66 big block

I'm running 205/70R 15 on my '66 427 roadster. This is a little lower profile tire and may work for you.

[Joe L.]

Re: 66 big block

Carol------

It's a very difficult tire size to find these days (for that matter, so is the 205-75-15). Most of the major tire manufacturers no longer make tires in these sizes. However, you can get them from Coker Tire (www.coker.com). They have them in whitewall and red-line, but not gold line. I don't know of a source for goldline in this size.

[Carol #46113]

Re: 66 big block

Thanks Kent. We'll look into it.

[Mike McKown]

Re: 66 big block

Any possibility the tires were rubbing on the frame at full steering lock and not the fenders?

[Gerard F.]

Re: 66 big block

Carol,

I had the same thing when I put Coker P205/75R15 radials on my 67 small block and it was more pronounced on one side (drivers side) then the other.

There are three things to check:

1) Sag in the front coil springs.

2) Wheel alignment-camber and caster. Radials take a different wheel alignment.
Sorry I forgot the specs, maybe someone will chime in.

3) Check the flat bar front bumper braces for any bend. A slight hit in the front bumper will bend these braces. The braces act as a pivot point between the central part of the frame and the fender. A bend in the brace will actually move the fender back towards the wheel. Tension in the central bumper supports actually moves the fender forward at the wheel well.

I went through #1 and #2 above with new springs and a front suspension job. I found that #3 was the real culprit (and on the drivers side). A new bumper brace solved the problem.

The P205/75R15 are supposed to be the correct tire for your car and are closest to the 775-15s although slightly larger.

Hope this helps,

Jerry Fuccillo
#42179

[Gerard F.]

Also, Coker makes gold lines. *NM*

[Joe L.]

Re: Also, Coker makes gold lines.

Jerry----

Only in the 205-75-15 size. They do not offer them in the 195-75-15 size I was discussing.

[Carol #46113]

Re: 66 big block

No Mike, they weren,t. They didnn't clear the front fenders when turned by about half an inch.

[Carol #46113]

Re: 66 big block

Thanks Jerry. I've recently had the car checked out by the Vette shop in PA. They are an approved NCRS shop. They told us the car is right and recently did the camber etc. It's possible it might have to be adjusted differently for radials, but I'm at a point now where I'm just leaving on the bias ply tires until I really get sick of them.

[Clem Z.]

you will not want to hear this but

i fixed this problem by grinding off the inside lips of the front and rear fenders on brand new corvettes to install road race tires.

[Carol #46113]

Re: you will not want to hear this but

Your right Clem, I don't want to hear that. :-)

[Duke W.]

Re: 66 big block

The only difference in radial tire alignment is toe, which should be set to about 1/16" total for radial tires.

Like dwell angle and timing, caster and camber are "tuning" parameters and there is a wide range of values that will work.

For a road car I recommend front camber of zero to minus one degree, and the more aggressive your driving style, the more negative camber you should have.

Increasing negative camber also provides increased front fender tire clearance. I do all my own aligment with an inclinometer and tape measure on my flat garage floor, so get an inclinometer and simply measure front camber. If it's outside the above range, reset it to somewhere in that range. A one degree change in camber in the negative direction will increase fender clearance by about a quarter inch, so if it is plus 1/2 now, changing it to minus one half will likely solve your problem.

If you go to a shop don't accept "it's okay". GET NUMBERS - what it's currently set at then give them WRITTEN values that you want it set at.

Set front caster at 1.5 to 2 degrees and front toe as above.

Rear camber should be set at minus one half to minus one and rear toe should also be about 1/16", and it's CRITICAL to get the toe equally distributed between both sides or about 1/32" on each side.

Duke