Road Force Balanced Explained
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From: Concord, NC
Road Force Balanced Explained
I have been doing some digging as I am really really leaning towards the 08 Harley 22's. My tire shop would be Town Fair Tire in North Attleboro, MA. I did a google search to see if they would do Road force Balancing and I got this. A VERY informative read by someone who helped design the road force machine. I think it clears up a lot of questions many of us have. Plus he said Town Fair does it properly 
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From: Olive Branch, MS
I had my tires road force balanced when I got them. The first shop had the machine and didn't have a clue how to use it they told me my tires were out of spec. They did not know to index/rotate the tire on the rim. The second shop I went to knew their stuff. The owner was pretty proud of the machine he had said it was state of the art and cost $25000. He took me back and let me watch the whole process. It was like the machine used by Chip Foose on Overhaulin. It measures the road force and then the machine will spin the tire on the rim to the correct spot. All the tech had to do was mount the tire on the machine, press a few buttons and then put the weights where it told him too. It was a pretty cool deal and the ride is great. This shop handles large wheels and tires so I am pretty sure it can do over a 33" (mine are 32") tire so you may have to ask around to find a shop with that ability.
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From: South Bend, IN
I really like his last thought:
The GSP9700 is a complex and sophisticated machine, and the whole process is subtle and ingenious. Some people understand it and some don't. The problem is that those who don't understand it often don't know that they don't understand it. You should not necessarily conclude that they are trying to cheat anyone, rather you should simply identify them and go elsewhere.
It reinforces my periodic comment that it's important to find an installer who knows how to USE the machine, and more importantly is willing to take the time to use it correctly. Many times a tire can be made to balance better on the rim, but the shop has already spent a half hour on the corner and isn't willing to spend any more time on it. It may be a blanket statement, but shops who charge the same price to road force balance a tire may not be spending the time they should to do it, because it isn't uncommon for it to take 1.5-2 hours to roadforce balance a set of stubborn wheels.
The GSP9700 is a complex and sophisticated machine, and the whole process is subtle and ingenious. Some people understand it and some don't. The problem is that those who don't understand it often don't know that they don't understand it. You should not necessarily conclude that they are trying to cheat anyone, rather you should simply identify them and go elsewhere.
It reinforces my periodic comment that it's important to find an installer who knows how to USE the machine, and more importantly is willing to take the time to use it correctly. Many times a tire can be made to balance better on the rim, but the shop has already spent a half hour on the corner and isn't willing to spend any more time on it. It may be a blanket statement, but shops who charge the same price to road force balance a tire may not be spending the time they should to do it, because it isn't uncommon for it to take 1.5-2 hours to roadforce balance a set of stubborn wheels.
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From: Columbus
yes some wheels can be a pain to balance, like if you need to spin it on the rim
but the road force balancer, the one i started to learn on before moving to a new shop, you also number the tires also and it would tell you where to mount them on the car for best wear and not to pull
road force balancer link http://www.gsp9700.com/
but the road force balancer, the one i started to learn on before moving to a new shop, you also number the tires also and it would tell you where to mount them on the car for best wear and not to pull
road force balancer link http://www.gsp9700.com/
Last edited by redfx4150; Apr 8, 2010 at 07:55 PM. Reason: add more
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From: Nebraska
I really like his last thought:
It reinforces my periodic comment that it's important to find an installer who knows how to USE the machine, and more importantly is willing to take the time to use it correctly. Many times a tire can be made to balance better on the rim, but the shop has already spent a half hour on the corner and isn't willing to spend any more time on it. It may be a blanket statement, but shops who charge the same price to road force balance a tire may not be spending the time they should to do it, because it isn't uncommon for it to take 1.5-2 hours to roadforce balance a set of stubborn wheels.
It reinforces my periodic comment that it's important to find an installer who knows how to USE the machine, and more importantly is willing to take the time to use it correctly. Many times a tire can be made to balance better on the rim, but the shop has already spent a half hour on the corner and isn't willing to spend any more time on it. It may be a blanket statement, but shops who charge the same price to road force balance a tire may not be spending the time they should to do it, because it isn't uncommon for it to take 1.5-2 hours to roadforce balance a set of stubborn wheels.
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From: Statesville, NC
Road force is the way to go, if done by some one that knows there stuff. When I bought my BBS wheels, I had teh tires mounted and balanced at teh Infiniti dealer, and they did an excellent job, two of the wheels took multiple attempts to get the tires indexed. When I bought my Expd wheels, I had them done at Discount. All 4 cme up correct teh first time. Just put tires on my girls van, and all four required reindexing.
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From: Fishkill, NY
I had the tires on my truck RoadForce balanced. It took a little less than 2 hours. The guy let me watch the whole thing. I had one tire that wanted almost 6 oz. of weight prior to the RoadForce, and took just 1.25oz after the RoadForce indexed the tire / wheel combo. The guy said he could ask the machine for better ride (less vibration) or less pulling, and it would tell him where to put each tire on the truck. It cost me $65 including tax, WELL worth it! $10 each to balance, and only 2 needed the tire / rim indexed at $10 each.
Last edited by copcarguy; Apr 10, 2010 at 12:53 AM.
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From: South Bend, IN
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From: Wisconsin
That was a good read. Bookmark. That explains why my Scorpions cause the front end to vibrate when they are cold, but it goes away as they warm up. Here is the heart of it:
So, let's look at just what the GSP9700 measures, shall we?
A tire is not necessarily round. Its tread surface does not necessarily describe a perfect circle. What is most important is, "Is it round while rolling?" The first step in using a GSP9700 is to measure just that.
A tire/wheel is mounted on the shaft of the GSP9700 and a roller is pressed against the tire as the shaft slowly rotates. The roller presses with a constant force of about 700 lbs (early version) or 1,400 lbs (later version). If the tire is perfectly "round while rolling", then the roller will roll with the tire but will not move otherwise, i.e. there will be no measured "runout" of the tread surface. If the tire is not "round while rolling", then the roller, which is mounted on an arm, will move back and forth, toward and away from the shaft of the GSP9700, as it rotates, i.e. it will measure the "loaded runout" of the tire.
Now, how significant is that runout?
Here is what happens: Suppose the tire rolls along a perfectly flat surface (i.e. a really good road), and suppose its axle is mounted to an assembly that keeps the axle at exactly the same distance from that surface. If the tread surface is perfectly round while rolling, then the force exerted by the axle on the wheel (which, of course, is the same as the force exerted by the tire on the wheel), will be constant as the tire rolls along. As a "high spot" in the tread circumference, i.e. a "high spot" in the loaded runout, rolls into contact with that surface, then the tire pushes upward against the axle with a little more force than average, right? As a "low spot" in the tread circumference, i.e. a "low spot" in the loaded runout, rolls into contact with that surface, then the tire pushes upward against the axle with a little less force than average, right? That variation in the upward force the loaded tire exerts against the axle tries to make the axle move up and down as the tire rotates. In a vehicle, it does make the axle move up and down. It feels like an out-of-balance tire/wheel assembly.
Interesting, huh? The nominal scale factor is that a measured runout of 0.001 inch corresponds to about one pound of "road force". That's where the term "road force" originates.
It isn't enough to just measure the loaded runout of the tire, though. Why not? Because the wheel isn't perfectly round at the bead seating surface, either. You could mount a perfect tire on a wheel that isn't round and you would get the same effect as mounting a tire that isn't round on a perfect wheel.
So, what's a feller to do?
The GSP9700 can also measure the runout of the wheel. It uses a small roller against the rim on each side to measure its runout. Then, with a bit of arithmetic, it can determine how much of the loaded runout at the tread is due to the wheel and how much is due to the tire.
That's what Michelin wants measured. They want to know the loaded runout (measured in thousandths of an inch or in pounds) of the tire. If it's too much, then the tire is defective. Michelin understands this quite well.
So far, all we've discussed is how road force is measured. What, then is a "road force balance"?
Once the operator has measured the loaded runout of the tire and the runout of the wheel, the GSP9700 computes how to minimize the net loaded runout of the assembly. The operator makes a chalk mark on the outer sidewall of the tire and another on the rim, as directed by the GSP9700. He then removes the assembly from the shaft, deflates the tire, breaks the beads loose from the wheel, and rotates the tire on the wheel to align the two marks. Then he re-seats the beads, re-inflates the tire, and re-mounts the assembly on the GSP9700.
What this does is mount the "high spot" of the loaded runout of the tire at the "low spot" of the runout of the wheel, which minimizes the net runout of the whole assembly as measured at the tread. The proof is in the puddin', as the saying goes. The GSP9700 re-measures the loaded runout, at which time the operator can see just how much better it is.
It is not necessarily going to be perfect, because the loaded runout of the tire does not necessarily equal the runout of the wheel. The procedure is more correctly described as a "compensation" than a "correction", as one defect is used to compensate for another.
That procedure is called a "road force balance". Note that a road force balance has nothing to do with mounting weights on the wheel. Once the road force balance is completed, then the whole assembly has to be spun by the balancer, its imbalance measured, and weights applied to correct the imbalance, in the usual manner.
The result is that you can have a wheel/tire assembly that has significant road force imbalance but is in perfect weight balance, and you can have a wheel/tire assembly that has significant weight imbalance but is in perfect road force balance. Either condition can cause vibration that you can feel. You gotta get 'em both right, and it takes a separate procedure for each one to do that.
But, you can't get road force balance perfect, as I noted above. How good is good enough? Usually about 25 lbs of road force imbalance is a threshold above which you can begin to feel vibrations from it.
Is this real? Damned right it is. EVERY wheel and tire put on new vehicles is road force balanced at the factory.
A tire is not necessarily round. Its tread surface does not necessarily describe a perfect circle. What is most important is, "Is it round while rolling?" The first step in using a GSP9700 is to measure just that.
A tire/wheel is mounted on the shaft of the GSP9700 and a roller is pressed against the tire as the shaft slowly rotates. The roller presses with a constant force of about 700 lbs (early version) or 1,400 lbs (later version). If the tire is perfectly "round while rolling", then the roller will roll with the tire but will not move otherwise, i.e. there will be no measured "runout" of the tread surface. If the tire is not "round while rolling", then the roller, which is mounted on an arm, will move back and forth, toward and away from the shaft of the GSP9700, as it rotates, i.e. it will measure the "loaded runout" of the tire.
Now, how significant is that runout?
Here is what happens: Suppose the tire rolls along a perfectly flat surface (i.e. a really good road), and suppose its axle is mounted to an assembly that keeps the axle at exactly the same distance from that surface. If the tread surface is perfectly round while rolling, then the force exerted by the axle on the wheel (which, of course, is the same as the force exerted by the tire on the wheel), will be constant as the tire rolls along. As a "high spot" in the tread circumference, i.e. a "high spot" in the loaded runout, rolls into contact with that surface, then the tire pushes upward against the axle with a little more force than average, right? As a "low spot" in the tread circumference, i.e. a "low spot" in the loaded runout, rolls into contact with that surface, then the tire pushes upward against the axle with a little less force than average, right? That variation in the upward force the loaded tire exerts against the axle tries to make the axle move up and down as the tire rotates. In a vehicle, it does make the axle move up and down. It feels like an out-of-balance tire/wheel assembly.
Interesting, huh? The nominal scale factor is that a measured runout of 0.001 inch corresponds to about one pound of "road force". That's where the term "road force" originates.
It isn't enough to just measure the loaded runout of the tire, though. Why not? Because the wheel isn't perfectly round at the bead seating surface, either. You could mount a perfect tire on a wheel that isn't round and you would get the same effect as mounting a tire that isn't round on a perfect wheel.
So, what's a feller to do?
The GSP9700 can also measure the runout of the wheel. It uses a small roller against the rim on each side to measure its runout. Then, with a bit of arithmetic, it can determine how much of the loaded runout at the tread is due to the wheel and how much is due to the tire.
That's what Michelin wants measured. They want to know the loaded runout (measured in thousandths of an inch or in pounds) of the tire. If it's too much, then the tire is defective. Michelin understands this quite well.
So far, all we've discussed is how road force is measured. What, then is a "road force balance"?
Once the operator has measured the loaded runout of the tire and the runout of the wheel, the GSP9700 computes how to minimize the net loaded runout of the assembly. The operator makes a chalk mark on the outer sidewall of the tire and another on the rim, as directed by the GSP9700. He then removes the assembly from the shaft, deflates the tire, breaks the beads loose from the wheel, and rotates the tire on the wheel to align the two marks. Then he re-seats the beads, re-inflates the tire, and re-mounts the assembly on the GSP9700.
What this does is mount the "high spot" of the loaded runout of the tire at the "low spot" of the runout of the wheel, which minimizes the net runout of the whole assembly as measured at the tread. The proof is in the puddin', as the saying goes. The GSP9700 re-measures the loaded runout, at which time the operator can see just how much better it is.
It is not necessarily going to be perfect, because the loaded runout of the tire does not necessarily equal the runout of the wheel. The procedure is more correctly described as a "compensation" than a "correction", as one defect is used to compensate for another.
That procedure is called a "road force balance". Note that a road force balance has nothing to do with mounting weights on the wheel. Once the road force balance is completed, then the whole assembly has to be spun by the balancer, its imbalance measured, and weights applied to correct the imbalance, in the usual manner.
The result is that you can have a wheel/tire assembly that has significant road force imbalance but is in perfect weight balance, and you can have a wheel/tire assembly that has significant weight imbalance but is in perfect road force balance. Either condition can cause vibration that you can feel. You gotta get 'em both right, and it takes a separate procedure for each one to do that.
But, you can't get road force balance perfect, as I noted above. How good is good enough? Usually about 25 lbs of road force imbalance is a threshold above which you can begin to feel vibrations from it.
Is this real? Damned right it is. EVERY wheel and tire put on new vehicles is road force balanced at the factory.
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Joined: Dec 2005
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From: Nebraska
I just took my 05 Screw in last week and had the dealership (only place in town with a roadforce machine) do my 35's on 20" rims. It took them about two hours but it drives like the day I bought it, absolutely no wobble at any speed. The best thing is that they only charged me $25.00.
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From: Green Bay, WisconSIN
Okay I have a question, I can get the 275/60/R20 Cooper Zeon LTZ's for $178 a piece without tax for my stock 20's on my 2009....now for the question, I'm calling around and to mount and balance the tires some shops want anywhere from $24 to $30 each. Then I called a shop with a road force machine and they only want $15 each (plus weights)...What gives? I thought road force was a bigger PITA than balancing regular? Am I missing something here? I didn't want to say, "NO!, that's too low of a price" to the salesman on the phone. 
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From: Olive Branch, MS
Okay I have a question, I can get the 275/60/R20 Cooper Zeon LTZ's for $178 a piece without tax for my stock 20's on my 2009....now for the question, I'm calling around and to mount and balance the tires some shops want anywhere from $24 to $30 each. Then I called a shop with a road force machine and they only want $15 each (plus weights)...What gives? I thought road force was a bigger PITA than balancing regular? Am I missing something here? I didn't want to say, "NO!, that's too low of a price" to the salesman on the phone.
Seriously though ask them what machine they use and if they know how to index the tire and rim. If they sound like they know what they are doing then I would not hesitate. Some shops look at big tires as a pain to deal with and charge more. Others that are used to handling them and know what they are doing tend to charge less in my experience.