My Hunter RFB Experience (Good!)

[JasonA]

Had all four tires RFB'd today. Car: 2001 STS with about 64,000 miles. Tires: Michelin Energy MXV4 Plus 235/60R16, unknown mileage.

He said that none of the tires were balanced correctly (static balance that is).

The L/F was WAY out. 38 pounds. He said the wheel itself was 16 pounds (of force). It was also .5 oz out of balance. They re-clocked the tire on the wheel and got it down to 28 pounds. I still wasn't satisifed with that, but it didn't seem like they wanted to do much else with it. He said that BMW's spec is 26 pounds, and anything under that is not detectable. I told him otherwise, but that didn't really go anywhere.

The R/F was very good at 11 pounds. It was .75 oz out of balance.

The L/R was excellent at 7 pounds. It was .5 oz out of balance.

The R/R was near perfect, at 4 pounds. I've never heard of a tire that low. It was .75 oz out of balance.

He swapped the L/F with the L/R, and I was on my way, $60 later. At 65-75 MPH, the imbalance was just BARELY detectable, and I was really feeling hard for it. The steering wheel now runs almost perfectly stable at those speeds. I can just BARELY feel that L/R in the seat, but it's really above my tolerance level, and I won't pursue it any further at this point. The problem may come when I want to rotate it back to the front eventually, but I guess I'll cross that bridge when I get there.

Question: if the wheel itself had 16 pounds of force, does that in itself mean it's necessarily a "bad" wheel? In other words, the wheel had 16, but the total assembly had 28 pounds. Does that mean the tire has 12 pounds, and the wheel has 16 pounds? If I wanted to "fix" this, should I look to a new wheel before I buy a new tire?

[Ranger]

The problem may come when I want to rotate it back to the front eventually, but I guess I'll cross that bridge when I get there.

I had mine road forced when I got it to get rid of a vibration. I know that two of the tires where replaced under warranty before I bought the car. After I did a rotation, the vibration was back. I put the tires back where they where and that is where they will stay till replaced.

[Cadillac Jim]

What you can do is have the tire skimmed. This makes the inflated tire and wheel assembly round about the axis of rotation. That, with good dynamic balance, should give you a good RFB reading.

This is recommended for new tires when you want really good RFB performance. Before RFB was available in smaller tire shops, skimming followed by dynamic balancing was the way to do really good balancing for luxury cars and high speed cars. If you don't like the RFB readings you are getting, get the tire skimmed. You won't lose tread life because the high spots wear faster anyway.

[Texas Jim]

Had all four tires RFB'd today. Car: 2001 STS with about 64,000 miles. Tires: Michelin Energy MXV4 Plus 235/60R16, unknown mileage.

The L/F was WAY out. 38 pounds. He said the wheel itself was 16 pounds (of force). It was also .5 oz out of balance. They re-clocked the tire on the wheel and got it down to 28 pounds.

Question: if the wheel itself had 16 pounds of force, does that in itself mean it's necessarily a "bad" wheel? In other words, the wheel had 16, but the total assembly had 28 pounds. Does that mean the tire has 12 pounds, and the wheel has 16 pounds? If I wanted to "fix" this, should I look to a new wheel before I buy a new tire?

JasonA,

Do any of your wheels have dirt / road crud built up on the inside?

My Dad was in the tire business for 40 years. (before Road Force balancing) When he had one that was hard to balance or took an excessive amount of weight... he would first clean it, if it was dirty, then if need be, break the tire loose from the wheel and turn it about 180 degrees. sometimes 90 degrees. It usually helped a lot. He claimed that some wheels and "MOST" tires have a heavy spot. He was trying to "NOT" have both heavy spots on the same side.

[Cadillac Jim]

Texas Jim's suggestion of rotating the wheel on the tire to get better dynamic balance before weights are put on is a very good one. Any tire and wheel should be clean before you begin the balancing process. If you do have a problem wheel, then

• Do a dynamic balance and RFB, with or without skimming. If you like what you see, you're done. If you need over 3 oz or the RFB fails, continue with the following steps.
• Separate the tire and wheel, marking the valve stem location on the tire. Remove the balance weights but mark their location on the tire and the wheel.
• Chuck the bare wheel up on the balancer and rotate it slowly. If you have a dial gauge with a wheel, use it to measure the roundness of the bead where it centers the tire. If it is significantly out-of-round, straighten the wheel or replace it.
• Spin the bare wheel and dynamically balance it. If it needs more than an ounce or two, mark the locations of the weights, remove them, and mark the locations opposite the weights as virtual wheel balance weights inherent in the wheel.
• Look at the virtual weights on the wheel and the marked first-cut weight location(s). Subtract the two to get the virtual tire wheel weight values and locations. If you have trouble with this, ask your kid in college to do it using vectors or complex variables. Or, visualize the virtual weights on the wheel and tire separately and use your common sense.
• Find the rotation of the tire that cancels out the virtual weights as much as possible. Mount the tire there.
• Skim the tire at this point if you want guaranteed RFB performance. Re-balance the assembly. Skim the tire and repeat if you didn't skim it and don't like the RFB performance.

My dad's shop did a seat-of-the-pants version of this with premium tires and luxury cars in the 1950's and 1960's, as Jim's father apparently did also. He never had a complaint or a comeback. His biggest problem was the tire dust, which was considered hazardous waste by the Fire Department, and, my college buddies found, was violently explosive when disturbed or any attempt was made to use it in rocket fuel. We used it for blasting. This was in Texas, too.

[JimD]

....If I wanted to "fix" this, should I look to a new wheel before I buy a new tire?

Yes. Or have your wheel straightened/repaired.

That wheel has hit a curb or a hole and you will always "feel" the out of balance/out of round even though the RFB can meet Hunter's or Michelin's guidelines.

Been there, done that; twice. Cardiodoc fixed me right up with wheels.

[JasonA]

Thanks guys.

I asked him if the lateral runout was okay with all the wheels...ie, if all the wheels were straight and true. He said they were. He said it was probably due to casting differences or porosity. I think 16 pounds is quite a lot of "casting" error.

They did re-clock that tire on the wheel -- and that brought it down from 38 to 28 pounds of force. Again, it's on the back, and just BARELY perceptable when driving. I'm taking the car on a business trip this coming week, so I'll get a good chance to feel for it then. Interstates around here are either 65 MPH or 70 MPH for the speed limit -- perfect for feeling the vibrations for which these cars are known.

I was going to ask if the wheel can be balanced on its own. I thought it might, and from what you guys are saying, it can. I may take it to a different shop (my Cadillac dealer also has a Hunter GSP9700) and see if they can work on just that one wheel/tire. I have a feeling that something's up with the wheel with that much force. But again, he DID say that it was laterally straight. No curb rash on any of them (wheels).

Thanks again. I'm still really impressed with the other three. I haven't seen many assemblies in the single digits, and I've never seen one at 4 pounds.

Edit: interestingly, at only 4 months old and at 170 miles, the original owner had the tires balanced at a Cadillac dealership. 13 days and about 700 miles later, a re-balance was done AGAIN. 2 months and 2,000 miles later, ONE tire was replaced. I wonder if this one wheel has been the culprit the entire time.

[JasonA]

Let me ask you experts one final question. I imagine that inflation pressure can have SOME effect on a tire's road force, correct...especially if that force is due to variations in sidewall structure/stiffness? I suppose that a higher inflation pressure can help mask some types of road force (and maybe amplify others). This particlar tire was inflated to about 39-40 PSI at the time (it was on the front), and now that he moved it to the rear, I deflated it to about 32 PSI, which is what I tend to like in the rear. Thoughts on inflation pressure as it relates to measured road force?

[JohnnyG]

Somebody's just not getting it.

OK, I'll give you this much, I've never heard of Road force balancing JUST the wheel. This is a very original idea, TOO original in fact, and one that opens up a whole new can of worms. I agree with JimD on this one, that wheel is garbage. But before I'd totally scrap it, I'd need to know what the other wheels were measuring. Something could be wrong with this theory, and ALL wheels may exceed 20 pounds of road force!!! After all, they are hard material, and don't give a bit. Any wheel with a slight runout may measure excessively high under these conditions. This sound like a question for HUNTER, and I really doubt that their machine was ever designed to test just a bare wheel!

My Dad was in the tire business for 40 years. (before Road Force balancing) When he had one that was hard to balance or took an excessive amount of weight... he would first clean it, if it was dirty, then if need be, break the tire loose from the wheel and turn it about 180 degrees. sometimes 90 degrees. It usually helped a lot. He claimed that some wheels and "MOST" tires have a heavy spot. He was trying to "NOT" have both heavy spots on the same side.

This is EXACTLY what RFB is, but in a scientific, measurable way. On this machine, it tells you EXACTLY where to "clock" the wheel to, by providing marks on the rim, then on the tire which then are matched up.

Next is the tire skimming thing. This used to be common, but my thoughts are that if you think finding a Hunter RFB machine with qualified operators is tough, just try to find somebody willing to grind rubber off of your tires!

And finally YES, tire pressure will affect RFB, and so will a lot of other things, which is what I've been saying for the last two years on this board.

[JasonA]

OK, I'll give you this much, I've never heard of Road force balancing JUST the wheel. This is a very original idea, TOO original in fact, and one that opens up a whole new can of worms. I agree with JimD on this one, that wheel is garbage. But before I'd totally scrap it, I'd need to know what the other wheels were measuring. Something could be wrong with this theory, and ALL wheels may exceed 20 pounds of road force!!!

I asked him that and he said that the other three wheels' forces (the wheels themselves) were negligible. I don't know how/if the machine separates the forces of the wheel from the tire if they're balanced as an assembly, but with only 4/7/11 pounds of force on the other ones, I really don't care about those. I agree that it seems that the wheel itself is probably the issue vs. the tire. Maybe I'll contact Hunter and/or my local Cadillac dealer and see what they say...if it would help to dismount the tire and balance the wheel itself...if only to get a real good look at radial/lateral runout of just the wheel. With a history of balance issues since this car was new, and with just a SINGLE tire replaced earlier on in this car's history, I do believe there's a physical problem (probably radial runout) with this one wheel.

Fortunately, it's not bugging me anymore like it used to (when it was at 38 pounds, and mounted on the front). At 28 pounds and mounted on the rear, it's really not a problem (to my perception, anyway). I'll know more about it after my 600 mile trip later this next week.

[JohnnyG]

Edit: interestingly, at only 4 months old and at 170 miles, the original owner had the tires balanced at a Cadillac dealership. 13 days and about 700 miles later, a re-balance was done AGAIN. 2 months and 2,000 miles later, ONE tire was replaced. I wonder if this one wheel has been the culprit the entire time.

Has anyone ever tried to spin balance just a rim? Forget RFB for now, I'm just talking plain old spin balance. It seems to me (and probably every wheel maker out there) that given the light weight and the small diameter and density of an aluminum rim, its effects would be negligeable. I've never tried it, but you can bet it'll be on my wish list NEXT time I go to the tire shop! And those guys ALREADY think I'm crazy!

[JohnnyG]

asked him that and he said that the other three wheels' forces (the wheels themselves) were negligible. I don't know how/if the machine separates the forces of the wheel from the tire if they're balanced as an assembly, but with only 4/7/11 pounds of force on the other ones, I really don't care about those.

WAIT A MINUTE! This is a totally different story now. Do you mean to tell me that these wheels/tire were tested as an assemby? That's not what I got from your original post.

The wheels are ALWAYS tested for runout on the RFB machine, but this has nothing at all to do with the "road force" of the rim!

[Cadillac Jim]

The rims are heavier than the tires, and aluminum wheels are heavier than equivalent steel wheels. Most high quality aluminum wheels are trued and dynamically balanced as part of the manufacturing process. If you see lathe marks in the tire bead and drill marks or more subtile indications of weight shaving in the metal underneath, that is the case for your wheel.

Tire pressure can make a difference in the shape of the tire. So, shaving, blanancing, and RFB work should be done at the inflation pressure to be used on the road.

[Ranger]

WAIT A MINUTE! This is a totally different story now. Do you mean to tell me that these wheels/tire were tested as an assemby? That's not what I got from your original post.

Huh? Aren't they supposed to be? Anytime I had mine done, they where spun up as an assembly. That is why I could never understand how the hunter could tell where the tire should be clocked in relationship to the wheel. I could understand it if they where spun separately.

[JohnnyG]

Huh? Aren't they supposed to be? Anytime I had mine done, they where spun up as an assembly. That is why I could never understand how the hunter could tell where the tire should be clocked in relationship to the wheel. I could understand it if they where spun separately.

No, No, No, They are ALWAYS tested as an assembly. From Jason's first post, I got that somehow they could tell the RFB numbers FOR JUST THE RIM. This would only be possible if the rim were tested by itself, no tire on it! THAT IS NOT (APPARENTLY) WHAT REALLY HAPPENED.

The rim is only tested for runout, Jason was mixing his metaphors by saying it was an RFB number for the rim.

OK, on a Hunter machine, the little arms go onto the rim of the wheel, and are usually held in place while the operator slowly rotates the tire/rim assembly. This registers the high and low spot of just the rim, in the machine's memory. It marks a place in its revolution, where, say, the HIGH spot is. THE BIG ROLLER, at the same time, presses down on the tire while IT is slowly rotated. This finds the place on the tire with the MOST deflection (soft spot). It marks that place according to the axel position too. The operator them marks both of these spots on their respective parts, in the proper location. The tire guy then "reclocks" the tire to match those two spots up, and VIOLLA! the soft spot on the tire is at the high spot on the rim.

End result? Low RFB numbers. This is why I was saying that testing just the rim was TOO original an idea, but I'm going to keep it in mind.

In the end, all Jason needs to do is find the worst tire, and match it to the worst rim. The two major differences should cancel each other out. Or he could get rid of the worst tire.

[JasonA]

WAIT A MINUTE! This is a totally different story now. Do you mean to tell me that these wheels/tire were tested as an assemby? That's not what I got from your original post.

Yes. That's how I've always seen it done. All four tires/wheels were RFB'd as an assembly. The one showed 38 pounds, as an assembly. The machine told them how to re-clock it, and they did, then re-balanced as an assembly, to get 28 pounds.

The wheels are ALWAYS tested for runout on the RFB machine, but this has nothing at all to do with the "road force" of the rim!

Won't a wheel with radial runout have some element of "road force"? Maybe I use the term too loosely. At least that's how the operator explained it -- the WHEEL had 16 pounds of force by itself, and the best they could get the wheel/tire is 28 pounds as a package.

Yes, I want to (out of curiosity) have the wheel itself even just spin-balanced, to see where it sits. Because of the nature of the GSP9700 machine (with a metal "road force" drum), I don't imagine that a wheel itself could be RFB'd...but I sure would like to know what is causing that alleged 16 pounds of force. I imagine that I could also chalk it up to a poor job by the operator, but the other three were dead-on, so I assume he knows how to use the equipment.

[JasonA]

From Jason's first post, I got that somehow they could tell the RFB numbers FOR JUST THE RIM. This would only be possible if the rim were tested by itself, no tire on it! THAT IS NOT (APPARENTLY) WHAT REALLY HAPPENED.

The rim is only tested for runout, Jason was mixing his metaphors by saying it was an RFB number for the rim.

That IS what they told me. He said that on the tire/wheel that originally measured 38 pounds of force, the wheel itself measured 16 pounds of force. I did not witness the job being done. I know the tire was re-clocked. So for all I know, they COULD have somehow RFB'd the wheel itself. Again, all I'm going on is what the guy was telling me. He showed me the operator's notes. He indicated 16 pounds for the worst one, for the wheel. I asked what the other WHEELS themselves were, and he said that if the tire/wheel wasn't bad, he didn't get a separate WHEEL force.

So maybe that IS what happened. Maybe the guy RFB'd the bad wheel itself, and got that number. That would mean that the wheel is necessarily slightly out of round, wouldn't it?

[JohnnyG]

You won't lose tread life because the high spots wear faster anyway.

Or, Jason could run it a while, and have that one assembly RFB'd again, who knows, it might level itself off after a few hundred miles.

[Ranger]

When I had mine done, I came back because it still had a little vibration. The guy told me to run it and it may smooth out after a few hundred miles. I thought, Yeah right . Sure enough it did.

OK, on a Hunter machine, the little arms go onto the rim of the wheel, and are usually held in place while the operator slowly rotates the tire/rim assembly. This registers the high and low spot of just the rim, in the machine's memory.

I thought that was to measure runout as opposed to high & low spots.

[JasonA]

I thought that was to measure runout as opposed to high & low spots.

In my understanding of the term, high and low spots are expressed as radial runout. Radial runout is the difference between the highest and lowest spot (again, as I understand), and lateral runout is the variation in side-to-side movement (lateral "wobble").

Thinking further, expressing radial runout as a force in pounds doesn't really make sense on a wheel. A tire has a spring rate, which may and does vary around the tire. That's one of the objectives of a RFB -- to move either the highest point of the tire, or the stiffest portion of the sidewall, to the lowest spot on the wheel. A tire's spring rate is expressed in pounds of force. But a wheel's spring rate is infinity. I would imagine that if you applied a force to the wheel (1400 pounds from the drum in this case), and attempted to measure a wheel's "force", it would be 1400 pounds (equal and opposite to the force applied). So I don't know where he got 16 pounds from "just for the wheel".

I will wait and see what happens over the next few weeks... My driving is relatively easy and miles accrue relatively slowly, so it takes a while for tire wear to even out for me on this car.

[JohnnyG]

I'm sorry Jason, I didn't mean to get on this subject as hard as I did, but I've been posting on this subject for better than 2 years here, and that "road force of the rim itself" took me by surprise. I had just returned from my bi-weekly 300 mile trip to Pittsburgh (yes, I'm still doing that.) and was a bit tired.

You're in good shape, and apparently have some concept of the forces at work here, so I'm going to drop the issue. Thanks for straightening out Ranger on the radial runout thing.

One thing that did occur to me is that the wheel may show excessive runout due to a hard hit across the entire rim, (pothole) or that the rim center was not exactly right when it was made, drilling the center and the bolt holes off center just slightly. This may be an unlikely scenario though. More likely, the operator MIGHT have had the wheel in the machine incorrectly. They still use the old hub cone/adapter on these things, which I never felt really comfortable with.

Thanks for the great post, I'm glad you finally will get to enjoy the true capabilities of your car! I'm sorry that it took 6 years for this to happen, I'm going to blame BMW and their stinkin' 26 pound limit for that!!! Next time you're driving down the road at 72 MPH, think of all the wear on the suspension parts that you have just eliminated, as well as the steering column bushings, etc.

[JohnnyG]

So Jason, what did you do about the stick-on weights?

[JasonA]

I didn't even ask about them (the tape weights). I'd prefer them cosmetically, but would feel sore if they couldn't get them balanced just right, and I'd always be wondering if I just threw that 60 bucks away, because I made them use the tape weights.

It made sense to me to put the wheel by itself on the machine, if only to see where you are with the wheel itself. Even if runout is perfect all around, I suppose you could still identify some weird imbalance in the wheel, if one exists. If that one wheel bothers me (I'll ALWAYS know it's sittin' back there at 28 pounds), I'll take it to a different shop and have 'em look ONLY at that wheel/tire, and even give them the specs from this balance I just did and see what they think.

Sorry I haven't followed this forum too closely in the past year or so. Had I, maybe I'd have been more up-to-date on the ins and outs of the RFB.

Cheers, Jason

[JasonA]

Followup: I'm in Savannah right now. Wonderful ride down here. Absolutely solid and vibe-free on the road. I'm thinking the guy maybe had the one wheel mounted to the machine wrong or something. I don't even think I'll waste money addressing that other wheel...unless it shows up as a problem after a rotation. For now, the sucker is FLAT SMOOTH.

[Logan]

Hmmm..

I can scratch another shop off the Hunter list...went and had mine RFB today. Now its worse.

That being said, I'm going to swap the fronts back to the back (tire shop had rotated them to the fronts). I know those rims had a few issues...hence why they were mounted in the back.