Shimmy / Road Force Balance

skizot722

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This year has been the year of fun and money pit action with the LS. Earlier this Fall I had all of the frontend suspension replaced. But I still had a bad shimmy in the front end between 75 - 85 MPH. I took it back to that shop and they balanced the front wheels. Said each wheel was right about 1.0 ounces off. So they added the weight. This barely changed the shimmy. It's definitely still there and you can see the steering wheel oscillating back and forth when you take your hand off the wheel.

Talked to the shop owner and asked him if they road force balanced the wheels. He said they don't own one of those machines and he doesn't believe in them. Basically said that it's just a marketing gimmick. Needless to say, that's the last time I take my ride back into that shop. Guy who doesn't understand the difference between static/dynamic imbalance and radial force variation doesn't get my business. No idea why people aren't interested in educating themselves these days. There is zero substitute for road force balancing. A rotating assembly can be perfectly in balance, both statically and dynamically, but if it has too much RFV, it's still going to vibrate.

Anywho, I found a shop that has a road force balancer and took it in today. The guy claimed he couldn't give me a print out when I asked him up front to print off the before and after. All Hunter 9700's are capable of printing this, but he acted like it wasn't possible. Said they would write down the force measurements by hand. They didn't match mount any of the wheels. I asked why not, and they said they were all fine with regard to RFV. They showed me the numbers the tech jotted down. They were: 0.015, 0.017, 0.018, and 0.024. So I'm guessing the tech really meant: 15, 17, 18, and 24?

If we assume he just wrote the numbers down with the decimal in the wrong place, the first three numbers aren't horrible. But 24 is getting to be too much for a passenger car. I told them that was too high for me and that the whole reason to go with road force was to get the RFV as low as possible. They claim the machine wouldn't even show them how to rotate the tire unless it was over 26. I know this isn't true. Also, to give some perspective of cars these days, 12 is the _max_ for Cadillac passenger cars. Even for Chrysler the max is 13.

What's your guys' opinion on what I should do here? Just be happy with the wheel that's at 24 and learn to live with the shimmy. Or make the shop match mount to get the RFV lower. I paid $90 for the balance and feel like they should have done something with that wheel.
 
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skizot722

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Actually, these values might be in inches. Which makes the RFV even higher (0.015in = 25 lbs, 0.024 = 40 lbs). So it's looking more to me like the shop just didn't want to mess with actually dismounting the tires and match mounting. It's a place called Big O Tires (national chain) and guessing they just want cars in and out as quickly as possible.
 

milehighmikey

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If your steering wheel is oscillating, and the balance looks pretty close, it's possible that it is not your tires. Did you move the wheels/tires fore and aft to see what changes?
 

04_Sport_LS

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In all practicality... the tires should be rotated every oil change (5k miles). This will help reduce NVH. Especially with the negative camber on the rear.

Are you using rims with a high offset (40mm or more). If so... the wheel that measured 24 might be due to a bad/worn wheel hub if it's on the front.

You could also try another shop that has a low speed spin balancer... and have them check the rim balance separately for a heavy spot... and have them mount the tire accordingly.

If that doesn't work... then the tire may have a lateral balance issue.
 

04_Sport_LS

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If your steering wheel is oscillating, and the balance looks pretty close, it's possible that it is not your tires. Did you move the wheels/tires fore and aft to see what changes?

Even though all of the suspension components have been replaced... this doesn't mean that there may not be an issue with the steering rack... or the mounts/bolts that hold the rack in place (or the rack bushings).

Over the years... a few members on here have found the rack bolts loose... or the bushings bad.
 

clubairth

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Go to Discount Tire. That's ALL they use now. I never got the print out but then again I have always been satisfied with the balance job Discount Tire does.

They will also price match anybody so I don't have to bother shopping for tires anymore either.
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04_Sport_LS

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Disount Tire is good... but not fully a national chain. However... they are in the midwest.

To the best of my knowledge... the one near me does not have an RFB machine.

As an afterthought... with cooler weather now... and most shops using "sticky" weights... is it possible one fell off?

I have had that happen in the past.
 

SultanGris

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Discount tire comes back the highest prices of any tire store I've ever been to in my entire life, they add on so much bullshit it's ridiculous! You got to watch those crooks and definitely make them price match and remove the extra bs charges if you're going to go there otherwise you'll be paying more than anywhere else I guarantee you that, lol
 

04_Sport_LS

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I think that can vary state to state... and store to store.

The one near me has always treated me good... and their prices and quality work are better than most other tire stores in the area.

They definitely beat Belle tire.

When I had Belle do tires on my truck... I somehow had misplaced the key socket for the tamper resistant lug nuts.

2 and a half hours later... They sent me out the door with 4 lug nuts per wheel... cause they didn't have replacements.

I went right over to Discount... and told them what happened... and they gave me 4 new tamper resistant lug nuts... and the socket... even though I didn't buy the tires from them. (Belle had the tires in stock ... and Discount didn't).
 

SultanGris

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I think that can vary state to state... and store to store.

The one near me has always treated me good... and their prices and quality work are better than most other tire stores in the area.

They definitely beat Belle tire.

When I had Belle do tires on my truck... I somehow had misplaced the key socket for the tamper resistant lug nuts.

2 and a half hours later... They sent me out the door with 4 lug nuts per wheel... cause they didn't have replacements.

I went right over to Discount... and told them what happened... and they gave me 4 new tamper resistant lug nuts... and the socket... even though I didn't buy the tires from them. (Belle had the tires in stock ... and Discount didn't).
Ya, discount will rotate or balance or something for free too cause they try and get your business, but if you don't question them on buying the tires they always add road hazard insurance and other crap you don't need\want that jacks up the price. If you go through the hassle of making them price match and take all that crap off then they're decent prices, but they will get you if you're not paying attention. If you called five tire stores and ask the price on the same tire I bet discount would be in the top two for most expensive if not the top one.
 

04_Sport_LS

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but if you don't question them on buying the tires they always add road hazard insurance and other crap you don't need\want

Again... my experience has been different. The one near me has always asked about road hazard... but never tried to sneak it (or anything else) on the bill.

Don't make generalizations based on your experience alone... or just one shop in your area. I've nothing but positive experiences with Discount tire near me... for over 10-15 years.

YMMV... literally. :)
 

SultanGris

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Again... my experience has been different. The one near me has always asked about road hazard... but never tried to sneak it (or anything else) on the bill.

Don't make generalizations based on your experience alone... or just one shop in your area. I've nothing but positive experiences with Discount tire near me... for over 10-15 years.

YMMV... literally. :)
I live in ND in the summer and NV in the winter, one year az, one year Floridia, I've talked to 50 tire stores from here to there to Floridia when i was looking for 35 Toyo open country tires. The cheapest was 1600 and the most expensive was 2300 and change, at multiple discount tire stores. Now if you tell them that Joe blow down the street said 1600 and prove it then they'll match that but if you say nothing you get all the extra bull crap 9 out of 10 times let's say.
you might have the only good discount tire that exists, go call 5 more in random states if you get bored, you'll see that I'm correct.

Unlike most people on the internet I generally don't say things unless I know what I'm talking about, been there, done that, got the t shirt, lol :D
 

SultanGris

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Then you have no frame of reference if you've only talked to one store, I've talked to many in many states and those are the results i got.
 

skizot722

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Sorry for the delayed response here. Been dealing with a few things, and actually went through this same balancing mess with my wife's car as well since she recently got new tires and the balance job was horrible.

In all practicality... the tires should be rotated every oil change (5k miles). This will help reduce NVH. Especially with the negative camber on the rear.
Not sure what you mean by "NVH". What we're discussing is RFV, which is Road/Radial Force Variation. It's the amount of force, measured in lbf in the US, exerted by the rotating assembly (rim+tire) against the suspension of the vehicle. Rotating tires has nothing to do with RFV. It's a fixed amount of force which is based on the runout of the rim plus the radial force of the tire. Every tire has what's known as a stiff spot in the sidewall. It's a byproduct of the way tires are manufactured. The following image will give you an idea of this stiff spot when you envision the side wall being comprised of springs.

A4159T-06.jpg


Each time there's a transition between the softer springs (in yellow) and the stiff spring (in red), a force is created by the rotating assembly and exerted against the vehicle.

Road Force Balancing in a nutshell aligns the tire and rim together such that the low spot in the rim matches the stiff spot in the tire. This cancels out the force created to an extent by reducing the difference between the yellow springs and red spring. This is why reducing RFV as much as possible will give you the smoothest ride as possible. Remember, you can have static and dynamic balance absolutely perfect, but if there's too much RFV, you're guaranteed to experience vibration at highway speed.

Here's an example (taken from the Hunter GSP9700 manual, which is by far the most common road force balancing machine used):

Given a RFV of 30 lbs and a speed of 50 MPH, this is the equivalent of being out of static/dynamic balance by 0.50 ounces. Some of us will be able to detect this vibration.

Given a RFV of 30 lbs and increasing the speed to 70 MPH, this is the equivalent of being out of static/dynamic balance by 2.50 ounces! Everyone, even non-ethusiasts, will notice this level of vibration.

That paints the picture of how important RFV is, as it just gets worse / exerts more force the faster you go, aka more rotations your tires are making per given amount of time. With static/dynamic balance, being off by 0.50 ounces doesn't change with speed. Off by 0.50 ounces at 50 MPH is still off my 0.50 ounces at 85 MPH.

Now on to the topic of which big chain tire store is better. They all stink. They all have the exact same goal in this world of capitalism. Get the customers in and out as quickly as possible to maximize profit margin. Sure, they'll be friendly with you. And some will work with you on price matching, etc. But back on the floor where the actual work is being performed, they're all cutting corners. I'll give examples below of what I learned after speaking with managers at both Big O Tire and Discount Tire about road force balancing.

The place I took my car for road force balancing was Big O Tire. After getting it back from them and realizing they did zero force matching (to correct/lower RFV), I called up the manager. It turns out that they do not actually force match unless the RFV is over 26 lbs. This is the default setting for passenger vehicles on the Hunter GSP9700s. 26 lbs is the absolute max before *failing* the balance, but that doesn't mean there won't be vibration below 26 lbs. Anything over 12 lbs RFV on a passenger vehicle can be felt, especially more sensitive vehicles. The LS would be considered a more sensitive vehicle, even though it's a heavy passenger car, due to the fact that so much of the road is transmitted to the steering wheel.

So, here you have Big O Tire skipping force matching, even when you've paid for it, because dismounting the tire and rotating it to the optimal spot on the rim takes time. Time is money. And these days profits are more important than doing things the right way.

That brings us to Discount Tire. We just had new tires put on my wife's passenger vehicle a couple months ago. It's got a really annoying vibration at highway speed. So I took it back in this week to get them to check the balance. They are one of the chains out there that do road force balancing, and that's what they sell you when you purchase the tires. Get the car back, and no chalk on the tires. So I know they didn't do squat with road force. Ask them what's up, and they tell me that they don't do any force matching unless the road force is above 35 lbs. 35 lbs! That's the equivalent of almost 3 ounces of imbalance at 70 MPH. I asked the kid what the force measurements were, and one was 29 lbs! I convinced him to do what they are supposed to be doing from the get-go. He was able to get it down to 17 lbs, which isn't great, but on my wife's vehicle it eliminated the vibration.

Lots of text above. The TL;DR is make sure you tell the shop you want your tires force matched with road force balancing, regardless of what maximums they have their machines set to. The machines come with an optional printer, but of course none of these big chain shops have them, because then the customer would be able to easily identify that they are cutting corners. So if the shop can't give you a printout, ask them to take before and after pictures of the screen on the balancer.

Edit: wanted to make sure and give credit for the image above. It came from the Hogan Tires website, which has some really good info on RFV: Road Force | Hogan Tire & Auto
 
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skizot722

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NVH = Noise, Vibration, and Harshness. The LS shop manual mentions it... but it is a general term for all vehicles... and has been around for a while.
Gotcha. Thanks. The one being discussed in this thread is vibration. Rotating your wheels doesn't eliminate vibration or reduce RFV.
 
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04_Sport_LS

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If you say so. Keep in mind the rear wheel on the LS have a decent amount of negative camber... and with the passive rear steer (and driving style) it is possible since the rear wheels will change toe angle.

Unusual tire wear can affect balance.

Also... a bad/worn shock may exacerbate rfv... a worn wheel bearing can throw the balance off when RFV balancing... and bad rack bushings can affect it too when driving.
 

skizot722

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If you say so. Keep in mind the rear wheel on the LS have a decent amount of negative camber... and with the passive rear steer (and driving style) it is possible since the rear wheels will change toe angle.

Unusual tire wear can affect balance.

Also... a bad/worn shock may exacerbate rfv... a worn wheel bearing can throw the balance off when RFV balancing... and bad rack bushings can affect it too when driving.
If I say so? Ok.

Worn wheel bearing, nor worn/bad shock, has absolutely zero to do with RFV. The force measurement is performed with the rim+tire off the vehicle. RFV is for the rotating assembly *alone*. If you want to go read up on RFV and then come back to have further discussion about it, then I'm happy to continue the discussion.
 

SultanGris

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If I say so? Ok.

Worn wheel bearing, nor worn/bad shock, has absolutely zero to do with RFV. The force measurement is performed with the rim+tire off the vehicle. RFV is for the rotating assembly *alone*. If you want to go read up on RFV and then come back to have further discussion about it, then I'm happy to continue the discussion.
Take this guy with a grain of salt, he's very knowledgeable about lots of mechanical stuff on these cars but he thinks he knows everything and loves to argue about stupid little things that don't even matter, like my discount tire experience above for example. I love to argue about stupid little things too so we get along great, haha!
 

04_Sport_LS

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but he thinks he knows everything and loves to argue about stupid little things that don't even matter

Now you are describing yourself SG.

I DID find something a while back that mentioned that RFV balancing issues can be caused by a bad wheel bearing... but can't find it now.

Your still a (dangerous) hack.
 

SultanGris

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Now you are describing yourself SG.

I DID find something a while back that mentioned that RFV balancing issues can be caused by a bad wheel bearing... but can't find it now.

Your still a (dangerous) hack.
I may have ninja edited ya if you didn't see it, but i admit i like to argue about stupid shit as well, after all it takes 2 to tango, ha. I'm not dangerous at all, you're just jealous that I'm way more ingenuitive than you are, it's all good bud, no worries.
 

04_Sport_LS

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And your Discount Tire story is anecdotal evidence at best.

I checked some cutomer review sites on the web... and DT actually gets pretty high reviews.

While most of the time people only leave bad reviews on such sites (which is normal... and very few take the time to leave positive reviews... DT is one of the nations highest rated tire stores.
 

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