SPF TIRE Problem

[Allan A]

I drove a 351 SPF today with Goodyear Eagle #1 tires (yellow lettering) with the Trigo rims. The car had a slight steering wheel woble. The owner said he had it balanced before to correct, but it only lasted 7-8 months. The car has 8000 miles and is in very good condition.

Is this typical for the tire or is there a problem somewhere else. If it is inherent with the tires what would be a better tire to use.

Thanks,

Allan

[Bob In Ct]

Allen:
I have the same problem with my SPF. I'm running Goodrich T/As however. The tires are perfectly balanced (spin balanced), and the steering rack is tight. My local dealer says all SPFs do it and I'll have to live with it. Great!

Since the problem only happens at certain speeds (in my case 60 to 70) I feel the problem may be in a resonance setting up in the front springs at certain speeds. It could be due to the tires not being perfectly round (few are). I would like to find a tire shop that grinds tires to eliminate high spots. I used to work for a major tire company as a Rubber Chemist and I can tell you that most top shelf tires are ground to eliminate the high spots.

Bob

[Rick Parker]

If the tires are correctly balanced it's possible that there is unacceptable runout in the hubs or wheels themselves. That fact is evidenced by the fact that the symtoms reappear after a few thousand miles. It may indicate an underlying problem unassociated with the tires themselves. Just a thought....


.......Rick

[Mr.Fixit]

SPF's often do this between 65 and 70 mph. Goes away after that. And it only happens on the freeway, not surface streets. I have pondered that it was becuse the ripples on the freeway expansion joints were hitting the tires one before the other, causing an occilation back and forth. Just guessing as to the cause.

[Allan A]

Thanks for the help, what does a set of new tires run? Assuming that I replace all four tires. I can always set the rims up on a lathe and check the possible defect. If that is the case, Trigo would need to replace.

Thanks

[webebob]

I've heard of well over a dozen Goodyear owners on SPF's with this complaint (Friends, carshows, track events, internet threads).
I've heard of 2 Goodrich / SPF complaints.
I've never heard of a SPF with Dunlops wobble.
I'm on my second set of Dunlops. Never had a wiggle.
Bob


ps...any unhappy Dunlop GT Qualifier owners out there?

[Lumberman]

My car just developed this same problem. I experience problem right at 70 mph and have BF Goodrich tires. Wobble started immediately after I adjusted tire pressure lower. According to the manual tire pressure cold is to as low as 18#. I set mine at 20. Wobble showed as soon as I hit the highway. Planned on having front wheels rebalanced but sounds now like this is not the problem.

[Mr.Fixit]

Since webebob mentioned it,
It was always on BFG's or Goodyear's, they're the same thing.

[jrichard]

tire pressure is very important and 20 is awfully low. make sure both front tires are balanced and inflated to the exact same pressure. even a 1/2lb can make a difference. of course, if you've been driving on under-inflated tires you may never get rid of the wobble. go with what the tire is marked minus -5lbs or so. NOT what the manual says- how do they know what tire you're running...

My SPF doesn't have the wobble problem that I can feel, but I had a guy pull along side me once and indicate the rt front rim was wobbling a little. Maybe the knock-offs aren't tight enough...

I have Dunlop GT Qualifiers on my SPF. Not a "top-shelf" tire. I plan on replacing them soon with kumho or a better, lower profile tire. Be careful with the GT's sidewalls. don't catch a curb or you're likely to rip the sidewall.

[stevewrm]

new spf/bfg's ---smooth for first 3-400 miles then shakey steering wheel and vibrations at 60+mph. had re balanced by tire shop that does lots of street rods and 20-22 inch wheels. perfect now.

he said were out of bal by as much as 2 3/4oz--best was 1 1/2 off
i also noted that the placement of the weights is in way different locations of the wheels.

my advice is to find a shop that does lots of work for the street rodder guys-----

steve

[427sharpe]

Any wobble between 60-70 mph that dissapates above or below is tire balance! Make sure that the guy balancing your tires is competent, and that the machine he is using is calabrated...yes, they do have to be 'trued' every now and then! Also, if you are static balancing, which means using weights on the inside of the rim to avoid putting a weight on the external edge, you will have a lot harder time getting a good balance. Another help is to mark the tire and rim ass'y with a ink crayon (like a junkyard uses) on the inside to make sure the tire is not 'walking' around the rim during hard acceleration / braking...not that you'd do that in a Cobra! If you want the best balance but not the ugly weight on the outside of your pretty rims, have the technician do a dynamic balance. He will put one weight on the inside edge of the rim, and another (usually stick-on) weight as close to the outside edge as possible. this will be the most accurate, as long as the machine is in tolerance and the operator knows his a$$ from a hole in the ground.

[Lumberman]

Assuming there is an operator that can find his a$$ from a hole in the ground and I can find him. Once balancing is done properly how would one go about determining appropriate air pressure? Tires and manufacturers information provide maximum air pressure. However isn’t it correct that actual cold tire pressure will depend on weight of vehicle, estimated increase in air pressure as tires heat up, driving style and type of driving? My Cobra is used as a weekend driver that occasionally accidentally slips over the speed limit but is normally driven well below the car’s potential. Your thoughts would be appreciated.
Thanks,
Lumberman

[Bill Wells]

SPF tire pressure for street use: between 18 and 22 psi cold. for track , 25-26 psi. Play with the pressure, everyone seems to have a different magic number with their SPF, but 90-99% of em are between 18-22 . Some set fronts lower than rears, say 18f and 22 r. I keep mine at 22 f/r but i have tried them all. Minimal tire at those settings wear as attested to by Hal Copple with his 40,000 miles of daily driver SPF experience. Bill.

[Mr.Fixit]

I like the big 60 series tires closer to 35 psi, the sidewall doesn't move around so much. According to my burnouts, the contact patch looks good too. They're just more predictable when they're inflated.

[Lumberman]

Thanks for the info gents.