Rim Repair & Runout Results

[benjamming]

I had an aluminum rim straightened (curb, pothole damage resulted in bent rim) by a local shop. The runout results after the repair as measured by Hunter RoadForce 9700 are:

Lateral:
left 0.004"
right 0.018"

Radial:
left 0.003"
right 0.020"

Is that pretty much spot on or am I kidding myself?

BTW, how do they straighten aluminum rims? I assume it is not by heat so some sort of machine, but don't know.

Thanks.

 

[chad8]

cheap shops use heat and beat. the right way is heat combined with a wheel straightener hydraulic rim machine.

http://www.rimandwheelworks.com/straighten.html

 

[mechanicx]

The max limit spec for radial and lateral runout for aluminum wheels is 0.030, at least for GM. So if you are at the measurments you listed you should be good.

How much does it cost to have a wheel straightened?

 

[CapriRacer]

Originally Posted By: benjamming
I had an aluminum rim straightened (curb, pothole damage resulted in bent rim) by a local shop. The runout results after the repair as measured by Hunter RoadForce 9700 are:

Lateral:
left 0.004"
right 0.018"

Radial:
left 0.003"
right 0.020"

......


So obviously it was the right flange that was repaired.

The problem here is spec comparison. The Hunter GSP9700 will give you runouts in terms of the first harmonic - since that is what the vehicle generally reacts to. The 1st harmonic is ALWAYS smaller than the total runout.

I am going to disagree with MechanicX that GM's wheel spec is 0.030" for both lateral and radial. These numbers sound like total runout - and even then they seem too large. I'm thinking the 1st harmonic runout specs would be in the 0.010" range.

But my experience says that the lateral runout is not nearly as important as the radial runout.

So I think your lateral number is marginal, and I think your radial numbers are going to cause a vibration.

But since you now know where the low point is (You did have them mark it, didn't you?) you'll be able to match mount the tire and then will likely bring the assembly down to a reasonble level - which is, by far, the most important item.

So I say, go for it. The worst that could happen is that you have a small vibration to live with.

 

[benjamming]

Capri,

Mechaninx is correct about the runout #s as shown below.

GM Service Manual Book 1 for 1994 Pontiac Grand Am

Section 3E
Measuring Wheel Runout on page 5 & Specifications on page 10 says:

Aluminum wheels:
Radial runout 0.76mm (0.030")
Lateral runout 0.76mm (0.030")

BTW, Steel wheels:
Radial runout 1.01mm (0.040")
Lateral runout 1.14mm (0.045")

However, I was certainly looking for an explanation on harmonics. I believe GM is only specifying for the 1st harmonic but don't know for sure. The instructions for measuring wheel runout says to measure it with a dial indicator on both the IB & OB rim flanges & rotate the wheel one revolution & record the total indicator reading.

We did measure & mark the wheel & tire & force matched them. 46# original to 28# final on the Roadforce machine. It required no weight to balance prior to force matching them but required 1oz on inside & outside after force balancing them. I wonder if the tire took a set to the bent portion of the rim since the weights were exactly opposite each other. The tire was badly flat spotted as well.

The bent portion was on the inside, but we measured & mounted it so that the old bent portion is now on the outside.

 

[mechanicx]

I believe the GM spec is the MAX spec from direct measurement of the rim with a dial indicator. So Capri might have a point about the difference of the RoadForce balancer measurement, but I'm not really familar with the how the Roadforce measures runout. But if that means the 1st harmonic then I think it would be equivalent to the GM max spec.

 

[mechanicx]

I meant to say 0.030 spec is the max total runout and not just the highest or lowest spot.

 

[CapriRacer]

Uh ..... Mmmmmmm ........ uh........

I thought max total runout was highest spot to lowest spot. (Peak to peak)

And I'll be careful what I say because the distinction is important.

The spec that GM has for wheels supplied to their assembly plants is specified in terms of both 1st harmonic and total runout. I think that spec is different - and tighter - than what they publish in their service manuals.

It's been my experience that the peak to peak value for runout is a bit larger than the 1st harmonic value. So a 0.030" peak to peak runout, would result in a 1st harmonic of about 0.025".

That number sounds way, way too large compared to the GM specs for tires - which is what I am familiar enough with to feel comfortable discussing this issue.

To give you guys a feel for this sort of thing, 1 pound of radial 1st harmonic force variation for a tire is like 0.001" (a thousandth). That is true for wheels as well.

So what force variation causes a vibration in a vehicle? Well, normally we use about 20# radial 1st harmonic as a threshold for passenger car tires and wheels. But very sensitive drivers in very sensitive cars in ideal situations can detect assembly 1st harmonic values at around 10 pounds.

The Hunter GSP9700 uses 26# as the dividing line for passenger car tires.

Based on GM's spec for tires, I can tell you that occasionally there will be assemblies that exceed 10#, but you will never get one that exceeds 20# - and just to be clear, I am talking brand new, properly mounted assemblies that have never touched the ground. Once a tire hits the ground, it develops flat spots and the original runout / force variation gets changed for the worse.

So I think the spec the GM publishes in their service manual is too high to assure 100% vibration free ride. I suspect that this spec - and a great more - are published with pretty wide tolerances to prevent warranty claims - although I admit that if a problem is not solved it still creates a lot of work. I wonder if GM compensates for diagnostic time even if the problem remains unsolved.

Nevertheless, I think the wheel in question ought to be tried.

 

[mechanicx]

As I said it was the total peak-to-peak run out with a dial indicator. GM I think has a tighter spec for tires. That's GM's spec and I don't see any reason to question that if you are within it the ride will be smooth.

 

[benjamming]

The "new" wheel has been tried & is much better than before. Of course, it resembled a Flintstone "wheel" before. I have bad rotors so that is contributing to vibration/shake. I also believe that the tires need to be balanced, badly.

 

[ewetho]

Over at ford we are down to 18 lbs road force on an F150 which also happens to be .018".

On cars the assembly should be down that low or less.As the other side is so low the .030 in the bead seat area may not be that bad overall. Still not ideal but may work out OK.

What did the tire and wheel assembly work out too?

Friend had tires that were not so good and the wheels were beat up too but properly indexed they were great. Sometimes it just works.