DWPC

My CTT has developed an irritating wheel vibe at 75-80 mph, probably the front since I fell it more in my hands than backside. I have plenty of local tire franchises who could do a "road force" balance. Anything unusual about balancing Cayenne wheels?

Dennis C

They are morons. I wouldn't take any of my cars there, especially a Porsche.

I bought tires there once and they scratched two of my wheels. They then told me that I needed an alignment, but they couldn't do it because I needed to have suspension components replaced. They offered to order the parts and fix my car. I politely asked them to put the tires on and give me the keys.

I'll never go to Big O again.

DWPC

I mentioned Big O because I had a great service for ten years from their store in the CA town where we used to live.

Mike in CA

There's probably a lot of variation between individual franchises. In my area Big O is one of the Tire Rack's recommended installers.

JohnnyBahamas

Humbly, I opine, when it comes to balancing tires, it is all about the skill of the technician and the time they put into the effort.

I've been unable to get a balancing job that is smooth over 75mph anywhere but Porsche or, better, a pro-race shop.

spooltime

Couldn't agree more. Properly used by a qualified technician, a Hunter GSP-9700 and their newer road force balancing machines that followed, will all give the best available balance in the automotive aftermarket. Period.

The problem is that the GSP is a complex machine with lots of capabilities that are ignored by tire shops due to time and profitability considerations. You'll be told you got a Road Force balance, but I guarantee that they took short cuts. There's a lot of steps that are simply skipped in the quest to generate high volume production off the GSP9700. Most average tire shop technicians have never been properly trained on the full capabilities of the machine, and likely never will be. If this matters to you, ask to see the technician's Hunter GSP9700 certification certificate. Very few will have achieved it.

So what can go wrong or be skipped? Well, for starters, find out when the last time they actually did either a full calibration or even a simple weight-check calibration of the machine. It's probably been way longer than you suspect. Out of calibration = inaccurate weight placement and possibly inacurrate balance.

Did they use the correct mounting cone and flange plate adapter for your wheels? If your wheel bolts are the ball style, then they shouldn't be using cone shaped studs on the flange plate, and vice versa.

Did they bother to do a centering check of the wheel on the balancer? There's a procedure for that, and it makes sure the wheel is properly affixed to the balancer.

Next, did they take the time to do actual bare rim lateral and radial wheel runout measurements before mounting your tires? Without doing this, you simply cannot do the most accurate Road Force balance because you don't know for sure whether the wheel has out of round problems or has any sort of lateral bend in the lip from a prior pothole encounter. Porsche specifies that the maximum permissible lateral or radial runout permitted on a rim is less than .7mm. Make sure they confirm your bare rims meet this spec.

After doing the measurements and initially mounting the tires, did they take the car out for a short drive (maybe 10 minutes) to warm up the tires for final balance work? Immediately after returning to the shop with the tires warm, the car needs to come up off the ground immediately to eliminate any possibility of temporary flat-spotting prior to the final balance. Once again, they need to confirm the centering check and mount of the wheel on the machine. Then, did they adjust the air inflation to spec? After all of this, they can then take the initial Road Force measurements of the tire, and having correctly marked the wheel, can rotate the tire to the precise spot on the wheels to have the combined wheel/tire assembly yield the lowest possible road force variation.

Another step that shops will never do, if all of your wheels and tires are the same size, is to match code the tires to the rims. This is a process which measures all of the bare rims (lateral and radial runout), measures the RFV of the four tires, and then assigns each tire to a particular rim to optimzie the RFV of the entire set.

And how many shops, after telling you they did a Road Force measurement, will actually place the balanced wheels in the proper location on the vehicle? Virtually none. Wheel with the lowest final RFV value goes on driver's side front. 2nd lowest goes on passenger side front. 3rd lowest goes on driver side rear. Remaining wheel goes at passenger side rear.

Did they place the wheel locks bolts in the correct location on the hub? There's a definite location the locking bolts should go.

There are a few other tips and procedures as well, but I can't spill everything.

With all of these extra steps that can be taken for optimization, it's easy to see why the average shop selling it's "Road Force" balancing is really just selling a minimally glorified balance and actually wasting most of the capabilities of the machine. Problem is, the averrage car owner doesn't want and won't pay for the time it takes to do it right. And frankly, the tire shop is about staying in business and making a profit; so they'd rather not take the time either.

JohnnyBahamas

^^^ Oh, this is great information! Thank you! Spill more!

In your opinion, what are the key questions to ask a shop over the phone before you decide to go in?

Things like...

- "Do you have a tech or techs with full Hunter GSP certification documentation?"

- "Does your certified tech offer a full ground up balancing that includes match coding of the tires to the rims?"

billyg

The S pig, just traded for that new sweet diesel delivered a week ago, actual was in that Big O shop in Sedona. Their service was second to none!

LexVan

Wow. Great post. Best wheel balancing post, ever! Thanks.

spooltime

Do you have a Hunter Road Force tire balancing machine?

Do any of your tire techs have a Hunter training certification for using the machine? But don't get too hung up on this one. There are plenty of knowledgeable techs who can adequately use the machine without having had the benefit of formal training at a Hunter training center. The way the industry works, there's usually a guy that sells the tire equipment and a different guy that services the equipment. If they've both been in the business awhile, then each could, and normally do offer "training" to the shop's staff on the new machine they just sold. The problem related to training is that the shop owner won't have them come back in to train the "new" guy; instead he'll direct the previously "trained" tech to show the new guy how to run the machine. So if a shop has turnover (and these tire shops certainly do), at some point the overall level of training of the staff becomes seriously diminished. That's why stuff like the time I took a nearly new Michelin Pilot Sport tire in for a minor patch repair and ended up with the tire tech severely tearing the tire bead with the mounting equipment happens. Because they're inadequately trained on how to use the equipment. So at a minimum, try to find out who trained them on the equipment and how much experience they have. You don't want a newbie working on your expensive wheels and tires.

Ask them if they will perform force matching for you, using bare rim runout measurements. Ask them if they'll let you observe the process. They'll likely tell you that safety regulations and insurance requirements won't permit you in the shop's working area, and that's a reasonable reply. But some places are more customer friendly, especially if you're a good customer.

Ask them what RFV value spec they have their balancer set at as "acceptable". It's better to have lower RFV results on sensitive cars (I want a RFV of 15 or less); SUVs can ride very smoothly with somewhat higher RFV measurements (RFV of less than 24 on a SUV will get you a smooth ride, but always go for as low as can be achieved given the condition of the wheel and tire). Unscrupulous shops will set the RFV specs high, give you a fast lousy job, and then tell you the measurements met "spec."

Another factor often overlooked in achieving a good balance and low RFV values is the quality of the actual tire mounting job. It is critical that the tech use enough tire paste to enable the tire beads to seat fully in place on the rim. This is even more important when your rims have AH safety humps (these are the humps next to the bead seating area that hold the tire in place in the event of a blowout). The tire bead needs plenty of lube during the mounting process to slide over the hump. A bad mounting job will always prevent attainment of favorable RFV results because the balancer is applying pressure against the bead during the measurement process. If the bead isn't seated correctly as the result of a careless mount job, there will always be too much RFV.

The actual optimization of each tire to each rim in the set is probably overkill for any but the most obsessive because it can requires two complete mounts and dismounts and measurement after each - who wants to do and pay for that? A skillful force matching job done on each wheel assembly should yield sufficiently low RFV measurements.

With a well-done Road Force balance, you'll be rolling smooth.

mudman2

Wow so its not like just mounting the tires then, lol

Thanks

JohnnyBahamas

Awesome stuff! Thank you very, very much!

May I ask, is the RFV value spec something that can be requested?

For example, after asking a shop what RFV value spec that they set as acceptable, is it a legitimate request for a customer to ask for a lower RFV spec value for their balancing?

spooltime

The machine is set up such that when the measured actual RFV for a wheel/tire assembly exceeds the limit set on the machine, the machine will reports to the operator the out-of-spec measurement, and instructs the operator to measure run-out of the rim in order to determine if rotating the tire on the rim will sufficiently reduce the RFV to an acceptable level. The problem at this step is that some of the wheels today are designed such that the machine can't make an external runout measurement of the rim, and even if it could, if the RFV is close, the tech may not want to screw around breaking the beads and rotating the tire on the rim to optimize. That's why it's always better to start with a bare rim runout measurement and to mark the wheel accordingly (which also requires marking the wheel to machine mounting position for repeatability of the runout reading for the rim).

So you don't really need to ask them to change the setting on their machine; what you need to request is the actual RFV value for each of your wheel/tire assemblies and tell them what level of RFV is acceptable to you. I promise you, if you go in and ask these types of questions, they'll think you're some kind of freak or something, because the average customer doesn't know or understand the significance of RFV and certainly doesn't ask for a specific level to be achieved. My guess is they simply don't get too many requests specifying a "target" RFV goal.

The simple answer is that you would, in ideal circumstances, like to have the lowest possible RFV measurements you can achieve on all of your wheel/tire assemblies. But it's harder to get there than you might think for reasons I mentioned in my earlier post - poor mounting, tires with issues, bent or out of round wheels. When the Road Force balancers first came out, the tire manufacturers weren't happy because in lots of cases, the machines revealed the lack of uniformity in tire manufacturing quality control. I think they've now achieved some sort of truce, realizing that some new tires are indeed duds, while other out of spec measurements resulted from conditions not related to the tires. In addition, there was also some concern about repeatability of the Hunter machines - measuring the same assemblies with no change and coming up with different measurements. It's not a perfect science or process, but for a smooth, vibration-free ride, give me a lower RFV wheel/tire assembly over a higher one any day of the the week.

From the factory, the GSP9700 came programmed with the passenger car RFV setting for P metric tires at 26 lbs., and for light truck tires at 39 lbs. But every vehicle has a different sensitivity level and tolerance to RFV and imbalance. So far a high performance car, I say shoot for a RFV of 15 lbs. or less, and I'll stick with my 25 lbs. or less RFV for a SUV. If they can get it even lower, so much the better.

That's why you're better off going for a target RFV that is dependent upon your vehicle type than just saying it's got to be "this" or else. The shop ought to be willing to share with you the measurements for each assembly. In fact, the balancers can be equipped with printers to provide print-outs of before and after measurements as a sales tool. So tell them what sort of RFV for your wheel/tire assemblies you're seeking and ask them to meet or exceed it if possible. They ought to be willing to try, and to show you the results; after all, you're paying for the premier balancing experience.

Cole

FWIW......You may want to take a very close look at the lower control arm bushings on a CTT. They are known to fail. The vibes you are feeling could be caused by one going bad.

Edit for a picture.

Here is a stock CTT lower control arm bushing that is toast. You may see cracks in the rubber before they get to this point where they clunk going over "some" bumps. This is next to the CTTS arms I put in that have a different bushing set up in them. Cost of the CTTS arms is the same as the CTT arms.

USMC_DS1

Tag... great posting re road force balancing equipment. Thanks.