Bent wheels that still balance

[bull]

A while back I found a good used Cooper Cobra tire that matched my new front tires and had it mounted to my extra Magnum 500. During that time I asked the tire shop to rebalance my rear wheels because I suspected they did not balance them correctly. I was getting a vibration that seemed to come from the rear of the car and at the time they were mounted I didn't emphasize the fact that these repro wheels are lug centric (need to be balanced at the lug holes, not the hub).

So while balancing them the tire tech calls me over to show me that one of the rear wheels has a wobble. He then tells me that the wheel was able to be computer balanced but we both could plainly see that it was out of whack. I worked a brief stint at a tire shop so I've seen this myself but being young at the time I pretty much shrugged it off. After all, computers are never wrong, right? So I have to ask, how can a wheel be "balanced" and yet not be balanced? Is it that they can only achieve a certain balance at a certain speed? I still feel the vibration most at around 45-55 mph and I imagine the balancing machine probably only turns at something like 15-20 mph.

Your thoughts?

[Ghoste]

My first thought is, what the hell is "computer balanced"?

[bull]

My first thought is, what the hell is "computer balanced"?

Just pne of those newer style wheel balancers that every tire shop has these days. Everything has some sort of computer in it now.

[Dino]

You pretty much got it.  At certain speeds an unbalanced wheel will be within balance range, but it will only feel right within that range.

Find a motorcycle shop with spoke wheel repair experience and they will true up that wheel for you in no time.  Without using a computer...   

[Ghoste]

Okay I misunderstood.  I took it to mean that according to the computer it was balanced but in real life it wasn't instead of the machine used to calculate the balance.

[Troy]

I have a wheel like that! I just use it as a spare.

Balancing generally doesn't have anything to do with "straight" or "side to side". The idea is to make sure there is an equal amount of weight (pull) in all 360 degrees from the hub so the rotation will be smooth. If one part of a tire/rim (say, at the 90 degree mark) is heavier it causes acceleration/deceleration which is felt as a "hop". Tape some quarters to a hula hoop and watch it roll. The old style balancers were basically just a pivot with levels in a couple directions. You laid the wheel on there horizontally and added weight until it stayed flat. It did NOT matter which side you stuck the weight on the weight was equal at all points. A dented rim shows an imbalance right away because of this (metal has been pushed closer to the center).

Your vibration could lateral movement I guess. Is it more pronounced in a turn. Is this wheel on the front or back of the car? It will be more noticeable on front.

When I was in high school my girlfriend's dad said he had all his tires "balanced at 100 mph". I have no idea how as I don't know of any tire machines that spin them that fast. I assumed he was full of it. So yeah, just because the tire doesn't excessively vibrate at 30 mph I don't believe it will be perfect at 70 mph.

Troy

[bull]

I don't know that it's more pronounced in a turn because all my turns have been made at slow speeds so far. When I notice it it's when I'm going straight, usually on the freeway, at around 50 mph and it seems to come from the rear.

[Bob T]

Bull, I have had my wheels balanced previously but still had a noticeable vibration at 106 km/h, it would shake the rear view mirror to the point of no rear vision. I swapped the wheels left to right and the vibration nearly disappears, this after a second balance as well. The vibrations disappear by the time I hit 115 km however, a bit oddball
I would expect a wheel balance to produce the same result for either side but that is not the case.

[bull]

Thanks, I'll give it a shot. Gotta pull the LR wheel anyway to check on a leaking axle seal.

[Stretch]

You can balance an egg but it still won't be round! 

[Back N Black]

Bull, I have had my wheels balanced previously but still had a noticeable vibration at 106 km/h, it would shake the rear view mirror to the point of no rear vision. I swapped the wheels left to right and the vibration nearly disappears, this after a second balance as well. The vibrations disappear by the time I hit 115 km however, a bit oddball
I would expect a wheel balance to produce the same result for either side but that is not the case.

Check you Caster, if you have to much negative caster you will get the shopping cart effect.

[Bob T]

Bull, I have had my wheels balanced previously but still had a noticeable vibration at 106 km/h, it would shake the rear view mirror to the point of no rear vision. I swapped the wheels left to right and the vibration nearly disappears, this after a second balance as well. The vibrations disappear by the time I hit 115 km however, a bit oddball
I would expect a wheel balance to produce the same result for either side but that is not the case.

Check you Caster, if you have to much negative caster you will get the shopping cart effect.

Ok, will do, cheers. The wear pattern on the fronts after around 7000 miles here is normal though, no sides chewing out.

[Ghoste]

You can balance an egg but it still won't be round! 

I can't. 

[Dino]

You can balance an egg but it still won't be round! 

I can't. 

Try smacking it on the table a bit harder, I can assure you it will no longer roll.   

[bull]

Bull, I have had my wheels balanced previously but still had a noticeable vibration at 106 km/h, it would shake the rear view mirror to the point of no rear vision. I swapped the wheels left to right and the vibration nearly disappears, this after a second balance as well. The vibrations disappear by the time I hit 115 km however, a bit oddball
I would expect a wheel balance to produce the same result for either side but that is not the case.

Check you Caster, if you have to much negative caster you will get the shopping cart effect.

Ok, will do, cheers. The wear pattern on the fronts after around 7000 miles here is normal though, no sides chewing out.

This could be my problem too (or something similar) because although the front end got aligned the ride height got screwed up in the process and I had to fix it. When I get the front end realigned I'll be having it done at a shop where they know how to align the steering wheel and make sure they get everything dialed in at once.