69 tires

[Gary Guthrie]

Curerently restoring 69 427/435 auto. Need to purchase tires. Obviously originals are pretty nonexistent. Suggestions needed for location of new repos. Would also appreciate any judging caveats.

[Dave S.]

Re: 69 tires

Gary, don't give up on original F70 X 15 nylon cord tires if that is your preference. They can be found in NOS or used condition if you look hard enough. The originals will be more expensive but not by a huge amount. The reproductions will cause you a slight deduct in NCRS judging. Kelsey tire deals in the Goodyear repros and I believe Coker deals in the Firestone. There may be others for Firestone but Kelsey(or Goodyear dealers) are the only source for Goodyear. You have a choice of white stripe, raised white letter or blackwall. Both the originals and repros handle poorly so I would be sure to have a street set of radials if you plan to drive the car. The F70 X 15, 1969-1972 nylon cord tires are DOT stamped and have plant and date codes debossed on the inner sidewall.

[Joe L.]

Re: 69 tires

Gary-----

The Goodyear Speedway Wide Treads available from Kelsey are the most correct reproduction tire available on the market today. These are bias ply, nylon cord tires, as original. The Firestone Super Sport Wide Ovals available through Coker Tire are a fiberglass belted tire. Although this type of tire was used on certain other 60s muscle cars, the fiberglass belted versions were never used on Corvettes. However, they are a better performing tire than the Speedway Wide Treads.

The Kelsey tires can be purchased through Goodyear dealers, if they're savvy enough to know that they can order them through Kelsey. You will pay the same price either direct from Kelsey or through a Goodyear dealer and you'll have to pay the freight either way. But, if purchased through a Goodyear dealer, they'll mount them for free. Once-upon-a-time, if not still, if you purchase a set of these tires through Corvette Central, they will pay the freight. However, then you'll likely have to pay a dealer to mount them.

[Juliet P.]

Just how poor is 'poor handling' ?

Dave & Joe, You both mentioned that the originals and the repro tires handle poorly. Can you describe in more detail what it is about the handling that is poor? Is it really that noticeable driving around town, on the highway, or are you referring to hard driving as in auto-crossing or really poor launching at the dragstrip?

I'm also in the market for 'new' tires for my shark, and I don't have the luxury of storage space for a spare set of street radials. I'm torn between taking a point deduction and getting current service replacments or taking the performance hit. I understand the point deduction, but I need to understand the extent of the handling degradation in order to make a decision. Is there a way to quantify it? I have only ever driven cars with 'modern' tires since I got my driver's license in 1984 so I can't really even imagine what you're referring to.... Even my old neon green '79 Ford Fiesta was fun to drive! LOL! ~Juliet


1970 Corvette Registry

[John H.]

Re: Just how poor is 'poor handling' ?

It's a personal opinion thing, but the old bias or bias/belted tires are pretty scary to drive on compared to current radial constructions; they're "squirmy" laterally, require constant steering correction, and react poorly to irregularities in the road surface. If you look at the standard deduction tables in the Judging Reference Manual, you'll see how much of a "hit" you'll take for different levels of deviation from the "non-DOT original tire" standard. The deduction is really minimal, IMO - certainly not worth ruining the pleasure of driving the car just for the sake of a few originality points if you don't have the option of having a "driving set" and a "judging set".

[Joe L.]

Re: Just how poor is 'poor handling' ?

Juliet-----

"Poor handling" is, of course, a relative term. It's very hard to quantify. I can tell you this, though: when I bought my 69 new it was equipped with Goodyear Speedway Wide Tread tires. I was very satisfied with the handling and performance although I was NOT satisfied with the longevity of the tires. BUT, THAT WAS 1969. I had not experienced the performance benefits of radial tires, so I had no frame of reference to compare to. Plus, I was a lot younger then and my overall state of "sophistication" with respect to appreciation of tire performance virtues was much different than it is today. However, if they provided acceptable performance then, they will provide acceptable performance today. They might not "feel like what you're used to" and they won't "perform like what you're used to", but their performance will fall within the "bounds of acceptability". I'm quite confident of that.

My first set of replacement tires was a set of Goodyear Polyglas GT tires of size F-60-15. I loved the handling qualities of these tires, although the ride was a bit harsh. I used 2 sets before I switched to radials of Goodyear Eagle ST model (I chose this model because it had the "closest to original" tread configuration, although it sure wouldn't fool anyone). I can tell you that I really felt that there was a noticeable REDUCTION in handling and performance when I switched from the Polyglas GTs to the Eagle ST radials. However, the ride qualities of the car were noticably improved, so there was a benefit in that regard. Plus, the bias ply, belted Polyglas GTs were no longer available (although they are now reproduced in certain sizes by Kelsey).

When I get my car back on the road, I intend to install a set of Kelsey's Custom Wide Tread Polyglas tires in size F-70-15. These tires were never used on a Corvette, but they are "period-correct" and I like the handling of fiberglas belted tires. I'll also keep a set of Eagle STs mounted on a spare set of rims for the "long drives".

[ken sieloff]

Re: Just how poor is 'poor handling' ?

In my most recent experience, I'd describe the handling one experiences with a bias ply tire as "nervous". At cruise speed you can feel the car wandering side to side causing you to respond with more frequesnt slight corrections to stay on course. Under braking, the same sensation is somewhat amplified. It takes some getting used to. I found it difficult to adjust from bias-ply to radials on a daily basis from car to car.

[Clem Z.]

Re: Just how poor is 'poor handling' ?

never tried this on a corvette but after removing the radial tires from my truck and putting the B/P back on to sell it i thought i had forgotten to tighten the wheel nuts. i stopped on the road to check to see if they were loose. the difference was outstanding.i know there was big difference between the factory B/P tires on corvettes and goodyear blue streaks we use back in the 60s for autocrossing and road race tracks.

[Duke W.]

Re: Just how poor is 'poor handling' ?

I installed a set of Michelin X radials on my SWC in 1964. Back then radials were said to be like "riding on rails". This is because the had greater "cornering power" - defined as cornering force divided by slip angle, and they were much more linear i.e the plot of cornering force versus slip angle is nearly linear (and much steeper than a bias ply tire) up to about 80 percent of available cornering force.

On the car the steering felt much faster and much more precise. The downside of early radials was their tendency to break away suddenly at the limit. This was evident in cornering force plots in that peak cornering force would typically drop away quickly beyond about a six degree slip angle.

For this reason, Pirelli only made fabric belted radials claiming their breakaway characteristics were more benign, and my first set of Pirellis to replace the Michelins proved this to be true.

Modern steel belted radials do not have the sudden breakaway characteristics, though the low performance radials are much poorer in this respect than high performance radials.

One you experience radial tires on any vintage car that has bias plys, you won't want to go back.

Duke

[Juliet P.]

Re: Just how poor is 'poor handling' ?

Thanks everyone for the feedback. I think you all have me convinced that the radials are better suited to my situation. Duke, I understand the cornering under load issues based on your explanations. Thanks. But that would not explain the dartiness and nervousness when going in a straight line (I don't think)??? Would the straight line instability be related to the tread pattern or perhaps even the alignment settings? ~Juliet

[Dave S.]

Re: Just how poor is 'poor handling' ?

As usual Joes explanation is on "target" and I sentiment his comments. I have the polyglass redline Firestone reproductions on the 67 Camaro and they are pretty good. Certainally a lot better than the Nylon cord originals and reproductions. "Flip a coin and go with result"

[Duke W.]

Re: Just how poor is 'poor handling' ?

Straight line stability/dartiness is effected by many things. Certainly alignment can be an issue, but the OEM specs should be okay as long as you reset toe-in to about 1/16".

Radial tires have more self aligning torque that bias plys, so they tend to be less darty such as following road ruts and rain grooves than bias plys, but tread patterns can have an effect, too.

A big contributor is tire width and profile, which determines contact patch aspect ratio. A narrow tire will have a relatively long contact patch, which provides high yaw damping for good straight line stabililty. A wide tire with a short, wide contact patch will tend to be more responsive, but not as stable. Ths can usually be compensated with more positive caster.

If you compare a radial and bias ply that have about the same width and profile, the radial will have a longer contact patch and will be more stable in straight line driving, but this won't tell you which one has the best cornering grip. Then it's primarily the tread compound along with details of the internal construction.

Duke

Duke

[Chuck G.]

Re: Just how poor is 'poor handling' ?

Duke mentioned what I've heard for years. An old expert "alignment" man here in my town told me that the reason bias ply tire feel "darty" when compared to radials is that the toe-in setting is not correct. Apparently when they align your car today for radials, they don't put as much "toe-in" setting in their alignment. When you switch to bias ply tires you should increase the toe-in back to factory specs to prevent the wandering, darting, that is common with bias ply tires on a car that is "set up" for radial tires. I run Michelin radials on my 63. I have a set of repro Firestone bias plys on the original wheels. When I switch, it's an adventure to drive that car. BUT....I've never changed the alignment back to compensate. Chuck