Tire Shaving

[mrpink]

Any one here do that? What's it cost?

[Bob In Ct]

I did! $20 per tire in Bridgeport, CT.

Eliminated most of my front end shake.

Bob

[mrpink]

Bob, that's what I'm trying to get rid of. Was this just a tire shop?

[Gordon Levy]

Jim, Chapman tire over by my shop can do it. The cost is around $20 a tire. Before you give that a try, give me a call. There may be a different explination or solution to your problem.

[Bob In Ct]

Retreading, took very little off my tires. A couple of other Cobra owners also had theirs done as well with similar results. I put a post under "shop talk" when I had it done.

Keep in mind that even a square tire can be balanced!

Bob

[mrpink]

Thanks Gordon, I will. I think when we get rid of the rag joint, we feel every little thing, I have had these road forced balanced 3 times and still get steering wheel shimmy.
Thanks, Bob. $40 is a small price to pay to get rid of that. I also know several others that have it. These BFG tires are crap!

[vettestr]

You can test roundness at tire store on balancer or on car by placing car on stands and rotating tire while marking with a tire crayon or even a nail to scribe lightly. hammer a nail in board with end sticking out and clamp baord agianst a jack stand. Push nail towards surface slowly and should be 100 % contact. Bent axles, out of round wheels etc. will all show up quickly as out of round but must then determine fault. If just out of round and remounting on rim does not fix then a good burn out will. If front wheels they will bolt up to rear for a good burnout to knock of the high spot ! Out of round on sidewall is another story Thank Goodness for warr.

[chopper]

Mrpink:

Before you do that, you might give this a try. The guys down at Discount Tire have a process which they perform called "road matching." It's an extra $15 per tire when you get new tires and it works like this. They mount the tire on the rim and then spin it slowly. The machine measures the radius of the tire and the rim separately and indexes the high and low spots of both. If the variation in the radius of the mounted tire exceeds a designated value, they de-mount the tire and rotate it on the rim to align the high spots from the rim with the low spots for the tire and then repeat the measurement process. Once the outer radius of the tire is uniform, then they spin balance it. I had this done to Jan's Miata when I replaced her tires a couple of months ago and the standard Miata steering wheel shimmy disappeared. I had it done at the Discount tire store down on Power by the Costco store. Not all of the Discount Tire stores have the machine. Hope this helps.

[mrpink]

Bob, thanks. I had them do it. They call it road force. I even took it to 2 different DT in case one machine wasn't right.

[SCOBRAC]

www.tirerack.com they will shave and heat cycle any tire they sell.

[Bob In Ct]

Do not confuse what tirerack does (taking off significant amounts of the tread for racing purposes) to what I'm talking about (very small amounts until the tire is dimensionally round).

Bob

[427 S/O]

I have about half the tread shaved off new tires, not for out of round
issues but for better grip and handling.
Works good......

[Big-Foot]

Hi Jim - Many tire places won't touch a tire for shaving once it has been run on the street due to all the crud (pebbles and such) that are stuck in the tread of the tires. It ruins their bits.

I have had pretty good luck in marking the tire and the wheel, breaking the bead and rotating the tire 180* from where it was and then re-seating the (well lubricated with soap) bead with high pressure air. Make sure that the valve core is removed from the valve stem when doing this so you can get the higher volume of air passing through the stem while inflating it.
The problem you are having is not just with the wider BFG T/A tires, but with any wide 14 or 15" tire that has a lot of sidewall and a lot of tread.

[mrpink]

Thanks, Randy. I'll give it a try.

[newmexico]

Mr. Pink

Give John Panfil at Anthem Motors in Phoenix a call. He is extremely knowledgeable about tire/wheel problems of the sort you speak of on Cobras. Sounds like you have done about everything you can. It won't cost you anything but the phone call. 623/879-0930

I know from experience that a good burnout doesn't get rid of "high spots". I guess it could but because of high rotational forces deforming the tire, it generally doesn't and can make it worse. Shaving in my experience just reduces the mass to be balanced, making the balancing more precise with a given machine. It can help in some cases. Shaving does work wonders for cornering traction on a race track.

It takes state of the art balancing equipment and a patient operator who is more artist than technician to get rid of the problem you describe. This assumes the problem is balance and not one of a dozen other things that could cause the problem.

I'm spending just over $800 on the new SPF to have John go through the suspension, wheels and tires with a microscope and gram scale just to preclude any problems. I consider it money well spent. Call it proactive if you like. Good luck.

[TButtrick]

Mr.Pink,

I've chased the same problem for two years. I've changed much if not all suspension parts. I've had three sets of tires on the car, two sets of BFGs and lastly a set of Yokos. I've had the tires/wheels dynamically balanced, statically balanced and road force balanced on a Hunter at Moroso's speed shop. None of which cured the problem. I've had anywhere from 15-25 ounces of weights on my wheels and every time they seem like they get put in different locations. I've had the weights installed on the inside and outside of the rim. I've had the wheels trued round within .001" then reinstalled the tires, balanced again and STILL no luck. I've checked the wheels ON the car to confirm that the rotors/wheels are true.

I put my car on jack stands and put it in gear and let it idle while I checked the OD of the tire. My vibration in fact came from the tires. You can see the videos here and here

The ONLY thing that I've found that cured my problem was having the tires shaved. Bob in CT found a place that will shave the tires even if they've been on the road. I only had the fronts done and 90% of the vibration is gone. I went from needing 20 ounces on one tire to needing only 1 ounce. I was so happy that I never took the time to take the rears to have done as I've been enjoying the car much more. I'll take them to have them done this winter.

Some tires may be better than others but most fat 15" inchers have the potential to cause problems as our cars are so light. A dampener will help but your masking the problem. My thinking was that if F1 cars can get by without a vibration, why shouldn't mine? They run a solid link steering as well so why don't they have a problem? Yes, our cars feel every little bump and given the same tire on a 3500 pound car, you probably wouldn't even notice it. Any amount of bump-steer will amplify the problem so make certain you've got that under control as well.

My $.02 worth

[newmexico]

Have you tried on-car balancing? Used to be the only way to go.

[TButtrick]

Bob,

I've never found anyone who could balance a wheel on the car. If the tire balances on a machine and not on the car, then you most likely have rotor/axle problems. Balancing really isn't the issue here. You can balance a square tire but it ain't gonna ride very nice. With these cars they have to be balanced AND round. I've also heard that even if you have all things perfect, you may still feel a small vibration from where the plys overlap/join inside the rubber.

[newmexico]

I've always thought that on-car balancing was a way to cancel the balancing tolerances. Even if the rotating parts of the axle and disc are finely balanced and the wheel and tire are also, they are still not perfect. Unless you are willing to remove and replace the wheel assembly, moving one pin (or lug stud) at a time, on-car balancing is the only method to offset the errors. Having said this, I don't know if modern on-car balancing equipment has the ability to do this with the required precision thereby gaining you anything.

BTW, this thread apparantly uses the terms rounding, truing and shaving interchangeably. I think shaving is used to reduce thread depth and thus flex and improve cornering. Truing/rounding takes off only the high spot(s) and hopefully leaves maximum thread for the buck. Either method improves on what comes out of the mold but since rubber has plastic and elastic properties, it will never get TIR's with great precision or even repeatability. I once read that F1 tires are hydro-pressurized and then trued. I dunno for sure.

As for ply overlap, it would seem that would cause a bump sensation, not indicate an out of round or balance problem. Unless running on glass, it would be hard to pick out.

Naw, you can't balance a square tire. Good point.

[TButtrick]

I don't want to mislead anyone here. There are MANY things that can lead to a vibration in the steering wheel. If your doing all the normal checks, I would add the test that vettestr recommended and do a quick visual on the tire as it's spinning on the car. I eliminated one possible cause at a time which lead me to tires. I just wish I started there first!

In my case I "believe" the out of roundness of the tire manifested itself as a harmonic vibration at 65 MPH and 75 MPH. One harmonic was the front tires and one was the back tires transmitted though the frame. It may be a bit worse in the fronts for FFRs as they seem to have inherent bump steer problem.