16 inch tire question

[Jay McCook]

Please help with a 16" Pre-A tire problem. I have a '55 Speedster (#80920) after a recently completed 10 year total restoration. For the sake of originality I went with 500/525-16 Dunlop tube type BIAS PLY tires and am experiencing a 'wandering' above 50 MPH. After several thorough inspections by two highly experienced and qualified experts (One Porsche 356 and one suspension and alignment) they believe that they have corrected or eliminated all other front end (and rear) suspension, steering and alignment issues. This appears to leave the tall sidewall bias ply tires as the most probable cause. Since there are a lot of you Pre-A owners driving around with '16 tires without complaint, as well as anyone else experienced with this problem, I would appreciate your advice as to the brand/type of '16 tire you are using as well as the best tire pressure and/or any other solutions you may have.

[Martin Bruechle]

I would run a set of 15" with radials. Then if you go to a event/show put on the 16"

[Alan Hall]

Jim Liberty has recommended 165-16 Avon radials out of Longstone tires in England, I am planning to try these on my '53. But Martin's suggestion of running 15 inch radials on the street and saving the 16's for show is a good idea.

[Wes Bender]

Did the alignment shop give you any numbers? Wandering could very easily be caused by slight toe out of the rear suspension. When I first got my current C, the front was toed in excessively and the rear was toed out. The car wanted to drive in circles rather than a straight line at anything over about 50 mph.

[Craig Richter]

Very general rules for race cars (not just rear-engined cars) is a degree or so of front toe-out will help a car to go straight; the down side being more aggressive turn-in as toe-out increases. To minimize the "hooking" from aggressive front turn-in, a degree or so rear toe-in will stabilize the rear, and combined with a degree or two negative rear camber, the rear becomes "stuck". If you get it the wrong way around, it's a no-fun ride.
On my '55 Speedy, I had the 16" rims widened to 5" at a Bonneville race shop (so they would run true), and there are many modern 16x195 tires for cheap white knuckle rides.

[Erik Thomas]

What sort of tire pressure are you running?

Try 32 rear and 25 front, or possibly 32 rear and 28 front. I have run those Dunlops on MGs and they are pretty good, in my opinion.

[Steve Harrison]

Bias ply tires run kinda wandery,...that’s part of the nature of the beast. It has something to do with how the sidewall flexes with those interior belts going across the sidewall at an angle.
Radials track truer,..the belts radiate straight out. I’d say after checking the good suggestions, give a set of radials a try,...any brand. Far Far superior to Bias in handling.
I always suggest Coker and Universal. Mainly because they actually manufacture a lot of what they sell,...many of the others are merely markup resellers.

P.S. I also had the thought of using 15’s for average driving and keeping the sixteens for shows. But I found I never put the fifteens on. Once I got the sixteens on with radials I was happy enough with the handling that I just never bothered to fool with the efforts involved with switching back and forth.

[Jim Liberty]

I have just put a set of Michelin X 550R/16 tires on my '55. Look wonderful. Lucas Classic Tires. Jim.

[Alan Hall]

Jim, Can you install the 5.50R-16 Michelins on the rear inflated? Also same question for the 165-16's you have run on some of the other pre-A cars?

[Jim Liberty]

I have found every car a little different. The Michelins I just installed went on with no issues. It may be the fact the cars ARE hand built and different, or maybe due to accidents over the years. I have only installed 550 radials on my cars. Often the rears need to be deflated to get them past the fenders, and having a second set of hands pulling the lower lip of the rear fender is necessary. The good news is that if you get it in, everything else is OK.

[Al Zim]

In the OLD days when I started wrenching, we used Harley Davidson tires on the 16 inch rims. I have also seen 400MM diameter Michelin X stop tires used on 16 inch rims but they looked scary. Being 400MM was not 16 inches. Now 56 years have passed since those activities. I got a college education and all the adult things! My (still) gut feeling is that you should still look to the motorcycle tires. Paint the inside of your rims and use a short rubber large valve stem this will keep the air in the tire. My introduction to alignment in the early 60's was a board with a nail in it to put a scratch on the front tires so we could set the toe in with a tape measure (in inches metric was unknown) We used a scribe to scratch two sides of the on the rear wheels to set everything back to factory specifications. Move forward to the early 21st century. We spent a lot of money on alignment equipment that did not work! We now use a system from Hunter that is called the Elite. It works exceedingly well. If your car was not put on that system for alignment (which from us is usually a 3 hour job) your car is not aligned. I am sure there are other systems that can do alignment service, but Porsche uses Hunter. Making the assumption that the Porsche engineers knew what they were doing, we have to conclude that the specifications for their cars had careful scrutiny. We also know that the front edge of the tires move outward as the car is moving down the road. The faster the car moves the more pull outward. That is why there is toe in on the front end. Toe out will hurt you on the front and rear of the car. Those of us that grew up with the $19.95 alignment received a toe in adjustment because that is all that could be easily done. If you take your car in for a 4 wheel alignment, be sure you take the factory specifications with you, stuff for a 53++year old car is not in their computer. al zim

[Edwin Ek]

Al,

Very interesting. Why is there pull outward on the front tires, toe out, as you drive down the road? What forces are at work?

[Erik Thomas]

Edwin:

As the wheels move forward friction and mechanical resistance is pushing back on the front wheels. When you apply the brakes, it REALLY pushes back. So we set them toe in a bit at the front, so they are anticipated to move back into perfect alignment. Now it gets more complicated when the unequal tie rods change the toe in during cornering, more to one side than then other, as the left tie rod is shorter than the right tie rod. It is all a compromise. The goal in setting the toe in is to pick the best compromise.

[Steve Harrison]

One small trick to getting tires into the rear wheel well on Pre A cars is to take a look where that flat plate attached to the torsion bars hits on the body,...and grind just a tad off that small landing. That lets the plate drop (sag) just a smidge more,..and you’ll find that the tire is loads easier to get on the drum. No one will notice it after you body coat/paint it and you’ll be happy you did it when you find you need that extra sixteenth to clear the rolled fender bead. And like Jim said,..once it’s in, it’s fine from there on.