TIRES and Road Force Variation
09-17-2002, 11:46 AM
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TIRES and Road Force Variation To make a long story short. I bought a set of Kumho MX's from discount tire. I immediately notice a bad vibration as soon as left the shop.
I went back. They road forced balanced the tires and found one to have a weak sidewall. They ordered a new tire. It took a month to get the new tire in from Kumho! Re-damn-diculous.
New tire installed, still vibrates, mirrors shake above 80 mph so bad cars in mirror's view are blurred.
Took tires back two more times to get balanced.
Road force is 16 lbs. for each front tire and 21 lbs. and 22 lbs. for the rear. I am told OE limit is 26 lbs.
Any suggestions? Any experts out there?
I just emailed the Kumho techs.
I am thinking the installer at Discount may not know what he is doing?
I went back. They road forced balanced the tires and found one to have a weak sidewall. They ordered a new tire. It took a month to get the new tire in from Kumho! Re-damn-diculous.
New tire installed, still vibrates, mirrors shake above 80 mph so bad cars in mirror's view are blurred.
Took tires back two more times to get balanced.
Road force is 16 lbs. for each front tire and 21 lbs. and 22 lbs. for the rear. I am told OE limit is 26 lbs.
Any suggestions? Any experts out there?
I just emailed the Kumho techs.
I am thinking the installer at Discount may not know what he is doing?
09-22-2002, 05:36 PM
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Re: TIRES and Road Force Variation Well, I'm no tire expert unlike the fine
fellows who work at discount tire shops.
But I do have a pretty good idea that
"road force" (pressure? No way 16lb of
force is holding your car up) has no way
of making a tire vibrate unless its
construction is uneven, and it's not
supposed to be uneven.
There's balancing, and there's balancing, and
there's out-of-round. You can have a static-
balanced tire that shimmies the wheel, and
you can maybe fix this with dynamic balancing
(if you put the weights on the right places).
You can have a tire that's oval out-of-round
and have perfect static and dynamic balance,
but bounce the wheel at 2X its rotational
rate.
Have to tell, also, whether it's tires or
maybe alignment. Tires are up/down and,
if out-of-round, torsional shimmy in the body.
Alignment is left/right (torsional can look
like this). And body / suspension dynamics
can make one look like the other.
If you can have somebody pace you, on the left
and then on the right, while this action is going on, they should be able to see if one or more
of the tires is turning abnormally (see the rim
bouncing up & down relative to the road). If
nothing like this is visible, then figure it's
more likely alignment.
Pretty surprising, how delivery on tires is
faster when they stand to make money than
when they lose it. My kind of vendor.
fellows who work at discount tire shops.
But I do have a pretty good idea that
"road force" (pressure? No way 16lb of
force is holding your car up) has no way
of making a tire vibrate unless its
construction is uneven, and it's not
supposed to be uneven.
There's balancing, and there's balancing, and
there's out-of-round. You can have a static-
balanced tire that shimmies the wheel, and
you can maybe fix this with dynamic balancing
(if you put the weights on the right places).
You can have a tire that's oval out-of-round
and have perfect static and dynamic balance,
but bounce the wheel at 2X its rotational
rate.
Have to tell, also, whether it's tires or
maybe alignment. Tires are up/down and,
if out-of-round, torsional shimmy in the body.
Alignment is left/right (torsional can look
like this). And body / suspension dynamics
can make one look like the other.
If you can have somebody pace you, on the left
and then on the right, while this action is going on, they should be able to see if one or more
of the tires is turning abnormally (see the rim
bouncing up & down relative to the road). If
nothing like this is visible, then figure it's
more likely alignment.
Pretty surprising, how delivery on tires is
faster when they stand to make money than
when they lose it. My kind of vendor.
09-22-2002, 06:18 PM
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Re: TIRES and Road Force Variation I had the road force ballance issue crop up on the last two sets of tires on different cars. One time it was solved with the replacement of the whole set of tires. The second problem they kept saying that the road force was OK. Finally I gave up on that Goodyear shop and went elsewhere to try for a solution and the Chevrolet dealership solved it all with simply a very good reballance. I've since wondered if the Goodyear shop simply needed better equipment or maybe better technicians. My point being that maybe it's time to try a different shop to get a second opinion. I have read a few of the guys having trouble with the Kuhmos.
09-23-2002, 12:35 AM
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Re: TIRES and Road Force Variation I guess i can sort of consider myself a tire expert, i deal with them all day long on lexus's. 26lbs is not the OE limit, that is what the machine recommends is the limit (im very familiar with the machine, the hunter machine), i know that on a GS300/430 with low profile tires and stiff suspension (similar to our cars), we cannot have anything in excess of about 11lbs of RFV, anything more will cause a vibration. Tires can be matched to a rim to reduce RFV however, usually turning is 180 degrees will greatly reduce the RFV, its possible that you got a bad batch of tires, we sometimes get that....
09-25-2002, 11:18 AM
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Re: TIRES and Road Force Variation The latest...
This past Sat. I went back to Discount Tire, AGAIN!
All this time I have been extremely patient and have avoided any yelling matches with the tire shop. Long story short, tire guy admits the Kumhos suck and I have them install 4 new BFG KDW tires for $63.
The RFV to 2, 6, 8 and 12 lbs for the new tire. I drive the car, run it up to about 120 mph on the freeway. Feels great, no more shaking or vibration.
Sunday I install BMR sfc's and take the LCA's loose to install BMR LCA brackets but decide not to due to poor fit.
I drive to work Monday and notice a vibration. I notice it's worse on Tuesday. I pull the car in the garage Tuesday night to have a closer look.
Front right tire has 15 lbs. of air! I pump it back up and determine the valve core is leaking. OK fine, the vibration must have been because the tire was low on pressure. Drive to work today, vibration is still there. Steering wheel shakes.
Maybe the tire threw a weight?
jimmyblue, you bring up some interesting ideas.
I haven't had an alignment in a while.
This past Sat. I went back to Discount Tire, AGAIN!
All this time I have been extremely patient and have avoided any yelling matches with the tire shop. Long story short, tire guy admits the Kumhos suck and I have them install 4 new BFG KDW tires for $63.
The RFV to 2, 6, 8 and 12 lbs for the new tire. I drive the car, run it up to about 120 mph on the freeway. Feels great, no more shaking or vibration.
Sunday I install BMR sfc's and take the LCA's loose to install BMR LCA brackets but decide not to due to poor fit.
I drive to work Monday and notice a vibration. I notice it's worse on Tuesday. I pull the car in the garage Tuesday night to have a closer look.
Front right tire has 15 lbs. of air! I pump it back up and determine the valve core is leaking. OK fine, the vibration must have been because the tire was low on pressure. Drive to work today, vibration is still there. Steering wheel shakes.
Maybe the tire threw a weight?
jimmyblue, you bring up some interesting ideas.
I haven't had an alignment in a while.
