sobe_death
sobe_death Dork
10/9/19 12:50 p.m.

I picked up a set of General AT/x yesterday and started to get them mounted up on the wheels, when I realized that none of them have red OR yellow dots on the sides!  The previous Altimax Arctics had them, the Dunlop/Hankook 200TW tires on the other cars have them, so is this an A/T thing?  In any event, these are heavy tires that I could see taking a lot of weight if they aren't mounted right, so how would a GRM'er go about finding the radial force/light point on these tires?

collinskl1
collinskl1 Reader
10/9/19 2:44 p.m.

Most of the time, those dots are required by OE car manufacturers. The replacement tires having the dot is a carry over function from them being produced on the same equipment as OE tires, and the dot markers not being turned off.

The dot is just there to be able to match it (the high spot of the tire's radial force) up with the wheel's low spot - typically called "match mounting." What you really care about is the force variation and balance of the mounted tire and wheel assembly. Any tire shop with recent equipment can road force balance the tire after mounting. If the tire is highly non-uniform (think big mud tires) they might dismount, clock the tire, and re-mount in a different orientation to optimize the mounted assembly.

 

Vigo
Vigo MegaDork
10/9/19 3:01 p.m.

OEMs also do silly things like mark pistons/bearings etc ABCD based on tiny tiny variations in measurements and then match their slightly non-uniform parts to whatever slightly non-uniform other part matches it best. 

In terms of those tire dots, they depend on the wheel being imperfect to have any meaning. If a wheel is truly perfect you can spin the tire any which way on it and you will still have the same problems. So while it may be considered a 'good practice', it's still something built on assumptions that might not always hold true. The real way to know is to do 'road force balancing' where you mount the tire to its wheel, and then spin the whole thing with a roller against it to measure stiffness variation and in some other way measure wheel runout to figure out if A. there's enough variation to warrant doing anything, and B. If the wheel is imperfect enough that you could use its imperfection lined up with the tires imperfection in a way that 'cancels out' some of the effect.  Sometimes the machine will say yes your tire AND wheel are screwed up and if you line it up this way it will fix it. Sometimes the machine will say your tire is  screwed up but you can't do anything about it because your wheel is perfect. In that situation if it were a new tire you could probably pester your retailer to warranty it out for a different one, but you'd have to be privy to the actual readings they got via a printout or something or have some kind of symptom they could observe. 

dps214
dps214 Reader
10/9/19 4:48 p.m.

If you really think it'll make that much of a difference, balance the wheel alone and note the heavy points, then put the tire on and balance it. Compare the heavy spots and relocate the tire to balance it out. But realistically just slap the tires on and go with it. I'm usually happy if I get the tire mark anywhere on the opposite half of thw wheel from the valve stem, if I even remember to find it.

collinskl1
collinskl1 Reader
10/10/19 6:42 a.m.
dps214 said:

If you really think it'll make that much of a difference, balance the wheel alone and note the heavy points, then put the tire on and balance it. Compare the heavy spots and relocate the tire to balance it out. But realistically just slap the tires on and go with it. I'm usually happy if I get the tire mark anywhere on the opposite half of thw wheel from the valve stem, if I even remember to find it.

Balance (weight) and force variation are two different things, but both contribute to vibration. The dot is not related to balance or heavy spots around the tire.

sobe_death
sobe_death Dork
10/10/19 7:18 a.m.

Seems like the solution is to just make sure the shop is using a road force machine.  Thanks for the replies!

Our Preferred Partners
YOu0wJmO8SVr74tGu1PxDd6Y10zmKreKghIGNhw80v641Q6ZA1gg8TChN7jPddLA