QuestionDick, I have my grandfather's '66 Mustang coupe, and like you want, to keep it as original as possible and within reason. It is not my goal to make this car show quality, just cruising quality.
My question deals with the original tires and manufacture that were standard when the car was new. I have not been able to find a definitive answer. If memory serves me correctly, Firestone was the original manufacture and a bias ply tire used. Uniroyal 185/75R14s are on it now. I was thinking about going to Firestone 205/70R14s (their model number FR380). This was one recommendation I found on the web. What would you recommend and your thoughts about using radials vs. bias ply.
Another question I have deals with the profile look of the car. Mine "appears" to sit lower than other Mustangs of this era. I do not see the clearance from the top of the tire to the fender. To the best of my knowledge, the car has not been modified at all. Would shocks, springs or the tires I am thinking about address this situation?
AnswerThe original tires, the ones the car was designed for, were 695X14 bias ply. These have a taller cross section than the tires that are on it now, because all radials have a low profile design. That accounts for the difference in ride height somewhat, since the 185/75R14s are 185mm wide and 75% of that high (from rim to road) or 139mm. That is the distance from the inner bead seating surface of the rim to the tread surface. Contrast that with the 6.95" width times the 88% profile height of the original bias ply tires, giving a rim to road distance of 6.12". Converting the 139mm to inches gives only 5.5", so the tires that are on it now let the car down almost 3/4". It also makes your speedometer and odometer read way high, and makes you think you are getting better performance and MPG than you are.
The 205/70R14s would be much wider than what is on it now at 205/25.4 or 8.1 inches - The ride height would be 70% of that or 5.7" - a little higher than what is on it now, but I would be very concerned about clearance for the wider tire - in sharp turns (at the front) and for roadside repairs if you have to change a flat (at the rear). They would also look way out of era for the design of the car.
The argument about bias ply tires versus radials is raging on and on, for the last 40 years. You will get a different opinion from every one you ask. My thoughts on it are as follows:
In favor of Radials: They give a better grip on the road, and a better handling feel to the car for high speed driving, and they last much longer. Also, you can buy very high quality tires with radials; the currently available bias ply tires are not as good quality of manufacture as the best radials. This can lead to balance, appearance (white wall quality) and roundness problems with some brands of bias ply tires. I can't mention supplier names here, but ask around with your old car buddies - you'll hear the horror stories!
The downside of radials is: They lower the car, which makes it look inauthentic. They are harder to steer at low speed, which makes them almost unbearable to park if the car doesn't have power steering. They transmit road imperfections to the passengers much more than bias ply tires, this is especially noticeable at low speeds on less than perfect pavement surfaces. Radial tires place more stress on the original wheels, which were not rated for use with radial tires. If you go to radials, you should obtain a set of wheels that are designed for them. The car has to be re-aligned for use with radials, in particular, the toe-in specs are different, and ignoring this will result in rapid and uneven wear. The shock absorbers should be changed to radial tuned shocks from the old bias ply shocks - that will help with the road harshness mentioned above.
The bottom line of all this for me is: For those cars that I want to take to shows and have them appear as close to the original as possible, I put the original bias ply tires on them. These are cars that may not have power steering, so they would be tough to drive with radials, and these cars are not usually used for long trips, although I have sometimes taken very long trips with them and felt very much like I was really experiencing the way it was (my show cars are older - 40s and 50s cars). For one of my cars, (a 1947 Packard Limousine) which I like to use on long trips, I actually bought two sets of wheels, one for modern radial tires and one with the original bias ply tires on it - and I found I never used the radials, even on very long trips (over 3000 miles) because the difference wasn't that significant to me. It is a bear to park, but I just make sure to pick parking spots where I don't have to do a lot of wheel winding. For my 55 Hudson, I just put the original Firestone 7.10X15 bias ply wide whites on it and drive it everywhere on them.
For my later restored cars, those from the era when radials were coming on the market (late in 1968), I use radials of the closest appearance to original that I can find.
There is a company called "Diamondback Classics" that will make you just about any tire appearance you want, starting with a radial tire of your choice, including very high quality tires. I had them make me a set of 3 inch wide whitewall tires for my 56 Packard (which we use on very long cross country trips) on some good quality radial tires - they came out perfect - with exactly the right appearance for the car almost hiding the fact that they are radials -the car drives beautifully with those tires - smooth, quiet and no vibrations at all. For that car, which came with 8.20X15 tires originally, I used 235/75R15s, so they are a bit wider than the originals, but the difference isn't causing any trouble. That car has a very heavy engine, but the power steering masks the effect of radials, so there is no problem parking it.
As for brands of tires, I agree your car probably came with Firestones, but the auto manufacturers actually bought tires from any of the major tire companies, depending on which ones they could get for the best price, so you will find Goodyear, BFG, U.S. Royal etc. as original tires also. But, Ford always has had a good relationship with Firestone (until the Explorer roll-over fiasco), so probably the majority of 66 mustangs came with Firestones. By the way, the "Firestone" tires you can buy to day from the classic car tire dealers are not the same tires as in 1966 - the tires are made in the old molds so the appearance is the same, but the methods, materials and procedures are not necessarily the same; most of the reproduction tires come from New Zealand - where the old molds were shipped when Firestone quit making bias ply tires way back in the dark ages.
This discussion doesn't explain why your car seem to have less gap between the top of the tire and the fender lip - the tires are in fact almost 3/4 of an inch less in height from the wheel to the fender lip. The springs are the only car part that affects the ride height on the Mustang - if the car is not riding at the right height (measuring from the wheel rim to the fender lip), the problem has to be that the springs have sagged with age. You can buy replacement springs to correct this if it really bothers you. The shock absorbers have nothing to do with ride height - they are simply dampers to keep the car from bouncing after a bump, and they cushion some road harshness, but they do not lift or lower the car at all. (Unless they are the variety sold by the el-cheapo parts stores that promise added load carrying capacity by incorporating a booster spring around the shock absorber - for the rear of the car only. These are junk, don't do it!)
If you are comparing the stance of your car to the showroom brochures, remember that the brochures were probably air-brushed to make the car look as good as possible, and in fact actual photographs of cars in service after a few months of use (to let the springs settle down to their normal height) would be a much better picture to compare your car with. See if you can find a copy of one of the automotive magazines that did a road test of a 66 Mustang, and compare the stance of that car to yours.
Good luck with it, and thanks for keeping it original!
Dick
