Had a question for anyone who knows a bit about rim/wheel construction:
I am well versed (more than I'd like to be) in tire balance and road force and all that goes with it.
But I've always wondered, how many out of balance tire/wheel assemblies can be attributed to the rim being imperfect, and is there any advantage to trying to balance a rim? If there is, how would one go about it?
I have a pair of 08 Jeep alloys that I'm planning on experimenting with soon, but thought I'd ask around before I began. I wasn't able to find any information on this anywhere, as the internet is flooded with tire balance info
The biggest issue would come from a wheel tire assembly balanced together and then the tire slipping on the bead. If the balancing was even partially due to wheel imbalance, the result of tire slip would be an imbalance. So, if you balance a wheel before mounting a tire and then balancing the assembly, you would get the best combination, until/if the tire slips. You would want to mark the 'wheel balance' weights so that when rebalancing or mounting new tires the 'tire balance weights are the only ones to come off. Then you probably have to check wheel balance again to make sure it is still good (should not change, but variation in balance machines and/or process could give different results).
Although most wheel are made through automated processes, there is still room for out of balance situations. Coating the wheels comes to mind, I had friend get wheels powder coated and they left a pile of powder at one side of the center to barrel, which threw off any chance of balancing properly. The variation in material and/or weld should be small enough that the manufacturers consider it good enough for most users.
Two years ago I did an experiment to see how well balanced race tyres were. I took all of my 15" race wheels, peeled the rubber off of them, balanced them all on a spin balancer, mounted tyres afterwards, and checked their balance again. I found that there was surprisingly little change in balance between a bare wheel and one with a Hoosier R7 or BFG R1 on it.
As expected, the higher quality brands seemed to be better balanced from the get go. At one point I did this with a set of (rather pricey) Hankook F200 race slicks and found that all four tyres perfectly balanced, down to 1/4 of an ounce. Street tyres tended to need a lot more weight to balance, even on a perfectly balanced wheel. Which made sense, since most street tyres are mass produced with looser tolerances and have more tread.
Nowadays, I balance the wheel and tyre together if the tyre is new. However, if I'm installing takeoffs (which usually comes with some uneven wear and with rubber clag stuck to it), I will balance the wheel by itself, mount the tyre afterwards, and go.
I had figured that wheel balancing wouldn't make much of a difference, but still curious anyway. And of course tire and wheel assembly would get balanced each time either way.
I'm mostly curious about this for those times when an assembly is out of balance by more than an ounce on each side. I don't like adding a lot of weights to correct balance issues, as you always run the risk (however slight) of a weight coming loose over time.
I usually will break the bead and rotate the tire on the rim by 120 degrees or so to see if it helps (it's 50/50 that it does). I can only imagine that the rim is out of balance when rotating a tire to different position on the rim changes how much weight is required to balance the assembly. If this can be corrected by balancing the rim, I would think the preferable thing to do would be just that.
Naturally, this curiosity is for personal use and not general shop practice lol
Sorry if I wasn't clear, I actually meant to imply that balancing the wheels CAN make a difference. I found that, because decent race tyres are so well balanced from the factory, most of the imbalance in the resulting assembly was down to the wheel itself.
