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Old 09-11-2006, 09:36 PM
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How much runout is acceptable?

I just got a new tire for one of my wheels (17" Cragar S/S) and the guy at the shop told me that the wheel had quite a hop to it. I have noticed the vibration pretty well above 45 MPH and assumed it was the tire. I figured the tire had a permanent flatspot in it because of the long periods of sitting the car does. I've been reading in several places about wheel runout and have a few questions about it. Several things I read said most steel rims should have less than .050 inch of runout. Does that sound about right? I just got done reading a thread on this forum with a guy talking about how a "1/4 inch and more" wheel runout is not unusual. That seems like a *TON* of runout. Also, where exactly on the wheel should the runout be measured?

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Old 09-11-2006, 10:10 PM
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Yes, I would like to hear some recommendations as well. Here has been my experience. I hope Skizot doesn't think I hijacked his thread - it is relevant to the original question.

I use Weld Draglites on my Bucket. I have purchased four new wheels in the last year and believe me, it is hard to find straight wheels, new, out of the box. I have found that the wheels are not so much out of round, but there is some runout side to side. I purchased a set of 15 x 8s for the rear from Summit, and one had a side to side runout of .040, the other was much less. Summit's policy is once you mount them, they're yours, even if they're bent. So check them before you mount them, or Summit says you lose your hard-earned. I had them professionally mounted with new tires at a tire specialty shop, and the guy wouldn't even charge me the mounting/balancing fee on one of the wheels because he couldn't get it to come out right due to the condition of the new wheel. I feel that if you pay nearly $200 for a wheel, it should be straight when it comes out of the box. Some retailers see it differently.

I recently looked at a new set of 15 x 4 Draglites from Harlow for the front (one of my existing front wheels has a .035 side to side runout and I can see it from the cockpit going down the road). I traveled to their store At Norwalk and checked the new wheels before purchase - same runout. Needless to say there was no sale that day. Not Harlow's fault.

So now I believe I must get away from the Draglites and try to find a manufacturer who has consistently straight wheels out of the box.
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Old 09-11-2006, 10:24 PM
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Factory specs for steel rims say they can be as much as 3/16 (.1875) out and still be acceptable. Fortunately most are not.

Alloy wheels that have been machined should not have any run out; however, I would say that they allow some. One piece alloy rims should not (in my opinion) be more than .003 (three thousands) out in any direction. Two piece alloy would probably be as much as .030 (thirty thousands).

If memory serves me, Boyd Coddington allows as much as .060 on his wheels. Too much for those machined wheels in my opinion.

Tire run out can be much greater due to the manufacturing process. DON'T accept any new tire with more than 3/16" run out as it will always need to be rebalanced. Shaving the tire OD used to be a common practice and removes a lot of tread life from the tire. It does not cure having to have the wheel/tire combo to be re-balanced often. This process should be avoided for street applications.
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Old 09-11-2006, 10:41 PM
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Quote:
Originally Posted by skizot722
Also, where exactly on the wheel should the runout be measured?
Radial run out (up and down variance) is measured on the outer edge of the rim where the tire mounts.

Lateral run out (in and out variance) is measured on the outer edge of the rim where the bead seals.

I've seen steel wheels with 0.050" run out and machined aluminum with 0.001" - 0.003"

Of course the less run out the better. If the tire / wheel combination needs little weight and the steel rim has 0.050", then 0.050" is ok in this situation. Also, using the appropriate tire balancing equipment (ie Hunter 9700) the tire and wheel can be match mounted reducing the effect of any rim radial run out.

Another tire element that can contribute to vibration is radial force variation. Radial force variation is a variance in the stiffness of a tire sidewall from one point in it's rotation to another. Think of many coil springs radiating out in a circle from a center point. These represent the tire sidewall. Now imagine one of those coil springs is stiffer. As the tire rolls, the stiffer point will force the vehicle upwards, resulting in a vibration even though the tire / wheel has been balanced. Radial force is measurable and somewhat correctable with the correct equipment ie Hunter 9700.
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