Road force measurement balancing

[tamanaco]

I'm trying to fix a steering wheel shaking issue. Need to see if we have any tire balancing experts that can comment on the my results from a Hunter GPS9700 unit.

The before results on one tire was 33 lbs of force, but with force-matching they got it to 6 lbs. The service manager states this is really good, the before result would really shake a car. the second tire was at 3 lbs but it stated the wheel is marginal. What does marginal mean? btw, these are new Cooper Cobra tires 235 60 15 on team 111 wheels and they shake more then my old BFG.

What do the CC experts have to say the balance results?

Thanks...

[Power Surge]

Road force basically measures how out of round the wheel assembly is. First you measure the spinning tire, which measures the assembly. Then you use the sensor arms to measure the rim itself (while still on the tire). If you have high spots and low spot in both the tire and rim, the machine will tell you where to spin the tire on the rim so that the high spots and low spots cancel each other out, giving you the least amount of overall runout.

Typically we consider 15 and under acceptable for a car wheel. 33 is very high. I had huge shaking issues with my Cobra wheels and after I took the car to work and road force balanced the wheels, it was like a whole new car.

[flapjack]

Hi All,
This is my first post. I worked for an Audi dealer up until recently and now work for a Lexus dealer. Chances are that there is some runout in either the tire or rim. A Road Force measurement of 6lbs is exceptionally good. I would ask the service rep. for an explanation as to what is marginal. Chances are it will be fine at 6lbs. I would only suggest R/forcing a wheel assembly after a tire has seen some use. Tires take time to seat properly and to break in. I have done comparisons regarding this. Also make sure that when mounting tires that both the rim and tire bead are both lubricated and inflate to no less than 40 lbs. when seating. You would be surprised as to how many times a new tire shows poor Road Force measurements due to the fact it was'nt seated properly.

Good Luck,
Flapjack

[Bob In Ct]

Many tires are not dimensionally and/or dynamically round. You can fix the dimensional out of round by having the tires ground. If they're dynamically out of round there is little you can do. Since most Cobras do not have a "rag joint" the shake comes up to the steering wheel.

Remember, even a square tire can be balanced, but it will ride like crap.

Bob

[Rick Parker]

Road vibration and harsh steering input are real common in these cars IMO because of the wider wheels and tires, wheel offset, steering scrub radius, comparatively light weight and most importantly the lack of rubber bushings in most of the suspension pickup and shock mounting points. The tires "Talk" to you, often in a language you don't like.

[tamanaco]

Thanks for all the inputs.

did talk to the tech, 15 lbs is the max for a f150 truck, his comment on my 6 & 3 lbs was this is really good. even the most sophisticated race car should not feel anything.

interesting comment/observations about the seating of the tires...and the break-in before RF balancing.

The problem is it still shakes bad at 60 - 65 mph...and it not the road talking back to me because of solid supension.

[fastd]

does the shake go away at 65 mph+?

[cobred]

From a g.m. web site. Important:

• Before measuring tires on equipment such as the Hunter GSP9700, the vehicle MUST be driven a minimum of 16 km (10 mi) to ensure removal of any flatspotting. Refer to Corporate Bulletin Number 03-03-10-007C or newer -- Tire Characteristics of GM Original Equipment Tires (SI Document ID #1414757).

• Equipment such as the Hunter GSP9700 MUST be calibrated prior to measuring tire/wheel assemblies for each vehicle.


The purpose of this bulletin is to provide guidance to GM dealers when using tire force variation measurement equipment, such as the Hunter GSP9700. This type of equipment can be a valuable tool in diagnosing vehicle ride concerns. The most common ride concern involving tire radial force variation is highway speed shake on smooth roads.

Tire related smooth road highway speed shake can be caused by three things: imbalance, out of round and tire force variation. These three conditions are not necessarily related. All three conditions must be addressed.

Imbalance is normally addressed first, because it is the simpler of the three to correct. Off-vehicle, two plane dynamic wheel balancers are readily available and can accurately correct any imbalance. Balancer calibration and maintenance, proper attachment of the wheel to the balancer, and proper balance weights, are all factors required for a quality balance. However, a perfectly balanced tire/wheel assembly can still be "oval shaped" and cause a vibration.

If a vibration or shake still exists after balancing, any out of round conditions, of the wheel, and force variation conditions of the tire, must be addressed. Equipment such as the Hunter GSP9700 can address both (it is also a wheel balancer).

Tire radial force vibration (RFV) can be defined as the amount of stiffness variation the tire will produce in one revolution under a constant load. Radial force variation is what the vehicle feels because the load (weight) of the vehicle is always on the tires. Although free runout of tires (not under load) is not always a good indicator of a smooth ride, it is critical that total tire/wheel assembly runout be within specification.

Equipment such as the Hunter GSP9700 loads the tire, similar to on the vehicle, and measures radial force variation of the tire/wheel assembly. Note that the wheel is affecting the tire's RFV measurement at this point. To isolate the wheel, its runout must be measured. This can be easily done on the Hunter, without the need to set up dial indicators. If the wheel meets the runout specification, the tire's RFV can then be addressed.

After measuring the tire/wheel assembly under load, and the wheel alone, the machine then calculates (predicts) the radial force variation of the tire. However, because this is a prediction that can include mounting inaccuracies, and the load wheel is much smaller in diameter than used in tire production, this type of service equipment should NOT be used to audit new tires. Rather, it should be used as a service diagnostic tool to minimize radial force variation of the tire/wheel assembly.

Equipment such as the Hunter GSP9700 does an excellent job of measuring wheel runout, and of finding the low point of the wheel (for runout) and the high point of the tire (for radial force variation). This allows the tire to be matched mounted to the wheel for lowest tire/wheel assembly force variation.

The machine will simplify this process into easy steps. The following assembly radial force variation numbers should be used as a guide:

P-Metric tires of passenger cars
18 lbs or less

P-Metric tires on light trucks
24 lbs or less

LT-tires on light trucks
35 lbs or less


If match mounting tires to in-spec wheels produces assembly values higher than these, tire replacement may be necessary. Replacing tires at lower values will probably mean good tires are being condemned. Because tires can sometimes become temporarily flat-spotted, which will affect force variation, it is important that the vehicle be driven at least 16 km (10 mi) prior to measuring. Tire pressure must also be adjusted to the usage pressure on the vehicle's tire placard prior to measuring.

Most GM vehicles will tolerate radial force variation up to these levels. However, some vehicles are more sensitive, and may require lower levels. Also, there are other tire parameters that equipment such as the Hunter GSP9700 cannot measure that may be a factor. In such cases, TAC should be contacted for further instructions.

Important:

• When mounting a GM wheel to a wheel balancer/force variation machine, always use the wheel's center pilot hole. This is the primary centering mechanism on all GM wheels; the bolt holes are secondary. Usually a back cone method to the machine should be used. For added accuracy and repeatability, a flange plate should be used to clamp the wheel onto the cone and machine. This system is offered by all balancer manufacturers in GM's dealer program.

• Any type of service equipment that removes tread rubber by grinding, buffing, or truing is NOT recommended, and may void the tire warranty. However, tires may have been ground by the tire company as part of their tire manufacturing process. This is a legitimate procedure.

[tamanaco]

Hey Cobred...great info. the good new is my tires had about fifty miles on them before road force balance.

Fastd...It almost goes is gone at 68 -70 ish.

I spent 5 hours today, measuring wheel runout, checking for loose, bent, not looking correct items on the front supenion and talking to a few people and Reg at Backdraft on what could cause this. The car alignment was checked and a slight toe in adjustment was made. What I have found was the right front tire showed much more wear, the small tits (the air vent holes that fill with rubber) were gone and edges on the forth tread rib were worn. The left front tire still had it tits and looked good. The tires only have 200 miles or so. Further inspection (by luck) showed the right strut (w/o spring loading) moved freely at the bottom inch of travel. Don't think a strut which is shock it should now do it. So, a new strut is going to be installed. I hope this solves it.

I've be chasing a tire and balance issue, now it looks like it be a bad front shock/strut. WOW

I'll keep

[fastd]

I had a similar shake in mine; I have seen so much written about shakes at 60-65 mph on Club Cobra and elsewhere. Mine started at 60 and went to about 90! I changed the tires; shake range tightened a little from 70-90 mph. Road force balancing didn't really help but it turns out it wasn't really done right; ultimately I got them balanced 3 more times after other things were fixed until everything came together.

The major reason for my shake was unbalanced brake rotors (the thickness of the vanes were much different from vane to vane and top to bottom). I think each situation is different; need to check shocks, tie rods, steering rack, etc. until it gets sorted out. Unfortunately, no one answer.

[cobred]

Good, I hope it works out. When they say drive it 10 miles they mean just before you do the checking on the machine. This is to remove flat spots from sitting.

[DMXF]

How much wheel runout will typically start to cause a vibration?

[Cobra #3170]

I don't know if this is still the case but OEM's were offset boring aluminum wheels about .006" and using the valve stem hole as a reference point. That offset was used to help cancel the spring rate variation in the tire which was supposed to be within certain specified limits. When tires were mounted at the assembly plant the machine used a paint mark on the tire that indicated
where the high point for Force variation was, it was then indexed to the "low run out point" on the wheel. Tires that did not meet OEM specs went to the aftermarket. My understanding is that Force variation or spring rate variation is due to overlapping components and other inconsistencies in both the tire sidewall, tread and belts. If it is way off, the only fix is another tire. Balancing cannot solve this problem nor will it show as run out in every case.
The GM web site explanation is very good, after watching tires being built at various manufactures I was amazed that they work as well as they do.

Originally Posted by cobred

From a g.m. web site. Important:

• Before measuring tires on equipment such as the Hunter GSP9700, the vehicle MUST be driven a minimum of 16 km (10 mi) to ensure removal of any flatspotting. Refer to Corporate Bulletin Number 03-03-10-007C or newer -- Tire Characteristics of GM Original Equipment Tires (SI Document ID #1414757).

• Equipment such as the Hunter GSP9700 MUST be calibrated prior to measuring tire/wheel assemblies for each vehicle.


The purpose of this bulletin is to provide guidance to GM dealers when using tire force variation measurement equipment, such as the Hunter GSP9700. This type of equipment can be a valuable tool in diagnosing vehicle ride concerns. The most common ride concern involving tire radial force variation is highway speed shake on smooth roads.

Tire related smooth road highway speed shake can be caused by three things: imbalance, out of round and tire force variation. These three conditions are not necessarily related. All three conditions must be addressed.

Imbalance is normally addressed first, because it is the simpler of the three to correct. Off-vehicle, two plane dynamic wheel balancers are readily available and can accurately correct any imbalance. Balancer calibration and maintenance, proper attachment of the wheel to the balancer, and proper balance weights, are all factors required for a quality balance. However, a perfectly balanced tire/wheel assembly can still be "oval shaped" and cause a vibration.

If a vibration or shake still exists after balancing, any out of round conditions, of the wheel, and force variation conditions of the tire, must be addressed. Equipment such as the Hunter GSP9700 can address both (it is also a wheel balancer).

Tire radial force vibration (RFV) can be defined as the amount of stiffness variation the tire will produce in one revolution under a constant load. Radial force variation is what the vehicle feels because the load (weight) of the vehicle is always on the tires. Although free runout of tires (not under load) is not always a good indicator of a smooth ride, it is critical that total tire/wheel assembly runout be within specification.

Equipment such as the Hunter GSP9700 loads the tire, similar to on the vehicle, and measures radial force variation of the tire/wheel assembly. Note that the wheel is affecting the tire's RFV measurement at this point. To isolate the wheel, its runout must be measured. This can be easily done on the Hunter, without the need to set up dial indicators. If the wheel meets the runout specification, the tire's RFV can then be addressed.

After measuring the tire/wheel assembly under load, and the wheel alone, the machine then calculates (predicts) the radial force variation of the tire. However, because this is a prediction that can include mounting inaccuracies, and the load wheel is much smaller in diameter than used in tire production, this type of service equipment should NOT be used to audit new tires. Rather, it should be used as a service diagnostic tool to minimize radial force variation of the tire/wheel assembly.

Equipment such as the Hunter GSP9700 does an excellent job of measuring wheel runout, and of finding the low point of the wheel (for runout) and the high point of the tire (for radial force variation). This allows the tire to be matched mounted to the wheel for lowest tire/wheel assembly force variation.

The machine will simplify this process into easy steps. The following assembly radial force variation numbers should be used as a guide:

P-Metric tires of passenger cars
18 lbs or less

P-Metric tires on light trucks
24 lbs or less

LT-tires on light trucks
35 lbs or less


If match mounting tires to in-spec wheels produces assembly values higher than these, tire replacement may be necessary. Replacing tires at lower values will probably mean good tires are being condemned. Because tires can sometimes become temporarily flat-spotted, which will affect force variation, it is important that the vehicle be driven at least 16 km (10 mi) prior to measuring. Tire pressure must also be adjusted to the usage pressure on the vehicle's tire placard prior to measuring.

Most GM vehicles will tolerate radial force variation up to these levels. However, some vehicles are more sensitive, and may require lower levels. Also, there are other tire parameters that equipment such as the Hunter GSP9700 cannot measure that may be a factor. In such cases, TAC should be contacted for further instructions.

Important:

• When mounting a GM wheel to a wheel balancer/force variation machine, always use the wheel's center pilot hole. This is the primary centering mechanism on all GM wheels; the bolt holes are secondary. Usually a back cone method to the machine should be used. For added accuracy and repeatability, a flange plate should be used to clamp the wheel onto the cone and machine. This system is offered by all balancer manufacturers in GM's dealer program.

• Any type of service equipment that removes tread rubber by grinding, buffing, or truing is NOT recommended, and may void the tire warranty. However, tires may have been ground by the tire company as part of their tire manufacturing process. This is a legitimate procedure.

[jhv48]

I've tried road force balancing on my SPF but the front end vibration is still there. I'm having the entire rotating assembly balanced while the tires are still on the vehicle on Friday. Will let you know if this cures the problem.

[Power Surge]

Originally Posted by Dcmgt

How much wheel runout will typically start to cause a vibration?

Mike, we usually see vibration complaints from customers over about .020 Roadforce.

[fastd]

Originally Posted by jhv48

I've tried road force balancing on my SPF but the front end vibration is still there. I'm having the entire rotating assembly balanced while the tires are still on the vehicle on Friday. Will let you know if this cures the problem.

Where are you getting that done? I didn't think that was done anymore...

[tamanaco]

I had mine checked via spinning the tires on the car. The guy had to dig the unit out of his home stuff. we just spun them. this showed very little vibration on the car. but the car still was shaking bad...car body movement bad.

I totally agree with you, Fastd, on the cause of front end shaking/vibration. I also have read many threads and talked with many people about this subject. I do believe that each will have it's own cause. And it can be caused by any of the items I'm reviewing below.

What a mechanic by profession and a home car bulder friend told me to do was, check and study everything in detail. It can be like not seeing the tree because of the forest. So, this means, checking all nuts, bolts and fastners, checking all joints for looseness while loaded and unloaded, Rotate the steering wheel while tire are loaded and feel the joints for motion, wheel bearing, steering rack, Rack to steering wheel for tighness...rotational and axial movement, front alignment, shocks/strut (this may be my cause ), brake rotors (balance if you can & run out on mounting surface of wheel), wheel run out, tire balance and mounting...flapjack & cobrad seem to have the best insight here...while mounting the tires lube the tire and rim, seat at 40 PSI, I like this! The road force balance seems like the best approach. Don't over look anything! Did I miss anything?

Just an note on what confused me on my vibration issue. I had a mild steering wheel shake at 60 - 65 MPH, got the tires balanced, just a slight vibration at 65. However, at spin balancing noticed one tire was pretty out of round. So, decided to get new tires...the car after the new tires was 10X worse than before. almost not driveable at 55 - 65 mph. Now if the strut shock solves my problem, then the question is why did the old brand X tires (9k miles) not shake, while the new Y brand ones did? my view is...the tires had different springeness(sp)?

New parts are on the way...I'll update once replaced.

[MaSnaka]

I had similar shaking in the car at 30-35 and then again at 60-70 mph. After Hunter Roadforce balancing several times, adjusting air pressure, alignment, I even had the tires balanced while mounted on the car (now there is a lost art). Nothing seemd to eliminate it to an acceptable level although it would seem to improve slightly. All the tire guys kept saying "get rid of the bias-ply tires". I started thinking all kinds of mechanical things were to blame and disliked driving my car so much it sat. I finally replaced the tires with new radials and woah that made all the difference. It was like driving a different car. I can's say for sure but that might be all you need to do.

[tamanaco]

Originally Posted by MaSnaka

I had similar shaking in the car at 30-35 and then again at 60-70 mph. After Hunter Roadforce balancing several times, adjusting air pressure, alignment, I even had the tires balanced while mounted on the car (now there is a lost art). Nothing seemd to eliminate it to an acceptable level although it would seem to improve slightly. All the tire guys kept saying "get rid of the bias-ply tires". I started thinking all kinds of mechanical things were to blame and disliked driving my car so much it sat. I finally replaced the tires with new radials and woah that made all the difference. It was like driving a different car. I can's say for sure but that might be all you need to do.

Thanks for the feedback. My car tires are radials. 235 60 15's started with BFG (9K miles), then INDY 500 Firestones (50 miles), and how Cooper Cobra. I my viewing of the 6 tires the Cooper Cobra have been the best. This is based looking at the tires spinning on the balancer, roundness and tread side to side movement the Coopers handsdown the best. I do want to say it's only been two of each tires.

[jhv48]

Originally Posted by fastd

Where are you getting that done? I didn't think that was done anymore...

Very few shops do it any longer. Luckily, I've got a couple of them nearby that only balance tires this way. One charges $80 per wheel, the other $17.95 per wheel. Guess which one I'm trying first!

Call around to the hot rod shops or the specialty alignment shops. They will either do it or know someone that does.

If mine fails, then the tires are the next to go.