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  #21 (permalink)  
Old 11-11-2021, 04:53 PM
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Quote:
Originally Posted by SBSerpent View Post
Came on at 60 MPH. Did it get progressively worse as your speed increased (I imagine that it would with an out of balance wheel).

My shake is only at around 60. Above that it smooths out.
55 mph became noticeable.
60 mph pronounced steering wheel shake left-right-left.
70 mph it progressively smoothed out.

I took camera photos of the wheel weight locations after balancing.
That culprit wheel was suppose to have (5) 1/4 oz adhesive
backed weights on it. When compared against the photos
I noticed there were only (4). Those photos saved me a ton
of time and aggravation. Instead of taking wheels off for re-balance
check, just stuck a new 1/4 oz weight where the missing one
should have been. Problem solved.

Last edited by Unique427; 11-11-2021 at 04:56 PM..
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  #22 (permalink)  
Old 11-11-2021, 05:23 PM
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My wheels and tires have no more than .50 oz per wheel, 1 has no weights after road force. If tires and wheels are good then you should be ok. But remember you can balance an egg, and it will still vibe when rolling
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  #23 (permalink)  
Old 11-12-2021, 10:36 PM
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What tire pressure is everyone running?
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  #24 (permalink)  
Old 11-13-2021, 09:40 AM
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Street driving, 22 lbs.
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  #25 (permalink)  
Old 11-13-2021, 10:00 AM
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I have about 9000 miles on my car,I found sticky tires nitto nt05 245 wanting to grab everything was the cause. I will say tires are the problem remember the car is very light. you should leave the car up off the tires when not driving this will help.If I drive about 50 miles the car will drive better [less shake].Others have told me to use less of a performance tire but I can not bring myself to do so. Put a new set of tires and you will be amazed how much better the car will drive.At least that has been my experience.I have owned my 2013 backdraft for two years and put about 6500 miles.
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Old 11-14-2021, 10:12 AM
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Default alignment

Shes now in shop getting alignment. Name:  091B7904-4225-40D9-8643-422E3DC1E419.jpg
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  #27 (permalink)  
Old 11-15-2021, 08:38 AM
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Wide tires on a light car with a manual rack and pinion steering is very susceptible to polar imbalance.

Imagine there is a heavy spot on the outside edge of a tire, and they try to fix the imbalance with a weight on the inside edge of the wheel, but opposite side. A static balance will look good, but as the wheel spins, the 2 heavy spots will try to move the wheel so that the 2 heavy spots are in plane and make the wheel wobble. At the perfect resonant frequency of the steering system, it will become a very obvious left right shake.

ALSO, if the other wheel has a similar polar imbalance, when the wheels are synced, it'll be more pronounced, then you make a slight turn and they become antisynced and the 2 shakes will cancel.

Most heavier cars with narrower tires and power steering are far less susceptible and most shops are not that picky about the polar balance. The only way to see the polar balance is with spin balancing. The old bubble thing won't show it.
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Old 11-15-2021, 09:57 AM
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Quote:
Originally Posted by Luce View Post
Wide tires on a light car with a manual rack and pinion steering is very susceptible to polar imbalance.

Imagine there is a heavy spot on the outside edge of a tire, and they try to fix the imbalance with a weight on the inside edge of the wheel, but opposite side. A static balance will look good, but as the wheel spins, the 2 heavy spots will try to move the wheel so that the 2 heavy spots are in plane and make the wheel wobble. At the perfect resonant frequency of the steering system, it will become a very obvious left right shake.

ALSO, if the other wheel has a similar polar imbalance, when the wheels are synced, it'll be more pronounced, then you make a slight turn and they become antisynced and the 2 shakes will cancel.

Most heavier cars with narrower tires and power steering are far less susceptible and most shops are not that picky about the polar balance. The only way to see the polar balance is with spin balancing. The old bubble thing won't show it.
Very interesting concept indeed! I have had some similar thoughts along this line in trying to understand my wheel shake that comes and goes at speed.

When I drive along a smooth, straight road keeping a constant throttle and maintaining a constant speed (lets say 65 MPH), I have a wheel shake that comes and goes as I drive. Roughly speaking, its cycling every several seconds.

I have 255/40s on the front and 315/35s on the rear (17" wheels). The diameters of these tires are 25.0" and 25.7" respectively, which comes out to a difference of 2.2" between the tire circumferences. What this means is that both front and rear will not remain constantly in synch when you travel in a straight line. Based on some rough calculations, after about 18 revolutions, the tires will be 180 degrees off from each other. Another 18 revolutions and they will be back to where they were with respect to each other 36 revolutions ago (again, approximate).

So I'm thinking that there is some sort of harmonic going on where, depending on where the tires are with respect to each other, i am getting a pronounced shake or nothing at all since whatever imbalance there is is cancelling itself out. Hmmmmmm.

Last edited by SBSerpent; 11-15-2021 at 01:26 PM.. Reason: incorrect dimensions on tires initially reported
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  #29 (permalink)  
Old 11-15-2021, 05:40 PM
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Ill get it back tomorrow ��
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Old 11-15-2021, 10:45 PM
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Quote:
Originally Posted by SBSerpent View Post
Very interesting concept indeed! I have had some similar thoughts along this line in trying to understand my wheel shake that comes and goes at speed.

When I drive along a smooth, straight road keeping a constant throttle and maintaining a constant speed (lets say 65 MPH), I have a wheel shake that comes and goes as I drive. Roughly speaking, its cycling every several seconds.

I have 255/40s on the front and 315/35s on the rear (17" wheels). The diameters of these tires are 25.0" and 25.7" respectively, which comes out to a difference of 2.2" between the tire circumferences. What this means is that both front and rear will not remain constantly in synch when you travel in a straight line. Based on some rough calculations, after about 18 revolutions, the tires will be 180 degrees off from each other. Another 18 revolutions and they will be back to where they were with respect to each other 36 revolutions ago (again, approximate).

So I'm thinking that there is some sort of harmonic going on where, depending on where the tires are with respect to each other, i am getting a pronounced shake or nothing at all since whatever imbalance there is is cancelling itself out. Hmmmmmm.
A front imbalance cannot be cancelled out by a rear imbalance.

Two front wheels can cancel each other out, and so the steering wheel can shake at around 50-70 mph typical, and then cycle on/off.
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Last edited by Gaz64; 11-15-2021 at 10:49 PM..
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  #31 (permalink)  
Old 11-16-2021, 06:13 AM
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I agree with Gary. I think it is more likely the unbalanced tire(s) at the front is out of sync with your front suspension components at some speeds and the shake comes and goes as those two resonant frequency patterns come and go into phase with each other.
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Old 11-16-2021, 06:34 AM
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Sean,

From your earlier posts (when you had 17" wheels) you've had this issue it appears back to 2017.

That said this thread may be of help if it's your pin drive hubs causing the issue.
BDR vibration issue finally fixed
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  #33 (permalink)  
Old 11-16-2021, 08:57 AM
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I agree with Gary. I think it is more likely the unbalanced tire(s) at the front is out of sync with your front suspension components at some speeds and the shake comes and goes as those two resonant frequency patterns come and go into phase with each other.
How would the front wheel go in and out of phase? If traveling in a straight line and with the same tire size and identical pressures in the front tires, wouldn't the front wheels (in theory) be rotating at the same speeds and as such, always be 'in synch' with each other? And, if the road surface is ideal with no bumps, ripples or undulations, then how do the suspension components go in and out of phase with the rotating wheels?

Last edited by SBSerpent; 11-16-2021 at 06:01 PM..
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Old 11-17-2021, 02:18 PM
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Quote:
Originally Posted by SBSerpent View Post
How would the front wheel go in and out of phase? If traveling in a straight line and with the same tire size and identical pressures in the front tires, wouldn't the front wheels (in theory) be rotating at the same speeds and as such, always be 'in synch' with each other? And, if the road surface is ideal with no bumps, ripples or undulations, then how do the suspension components go in and out of phase with the rotating wheels?
The first time you turn a corner the inner wheel rotates slower than the outer wheel. This is why rear tires squeal when you use a locked rear axle on the street.

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Old 11-17-2021, 02:54 PM
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Quote:
Originally Posted by SBSerpent View Post
How would the front wheel go in and out of phase? If traveling in a straight line and with the same tire size and identical pressures in the front tires, wouldn't the front wheels (in theory) be rotating at the same speeds and as such, always be 'in synch' with each other? And, if the road surface is ideal with no bumps, ripples or undulations, then how do the suspension components go in and out of phase with the rotating wheels?
I couldn't find a good picture to illustrate this concept so I'll try with words alone. All systems have a natural resonant vibration frequency. For a front suspension, that means that when the spring is compressed as it passes over a bump (or reacts to the up force from an out-of-balance tire), it will compress and then extended in predictable cycles until the damper (shock absorber) stops it. If you have an out-of-balance tire attached to that suspension, it too has a natural up and down motion (vibration) determined largely by the speed and diameter of the tire. Most of the time those two vibrations will not be in sync and tend to cancel each other out to a degree. But over time, the up motion of the tire will coincide with the rebound up motion of the suspension to produce a larger deflection of the suspension. The same occurs in the down direction. Such a phenomenon might account for your shake coming and going.
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  #36 (permalink)  
Old 11-17-2021, 04:11 PM
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I found that balancing the tires at your normal tire pressure made a difference. They usually run them up to 32psi when balancing and you run them at 22/24psi maybe?

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Old 11-17-2021, 05:18 PM
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Got the Cobra back, they did an alignment and its much better. They checked everything bolt and nut on the car. Im going to look into that post where he upgraded the steering. I think they should have made a more robust steering system. I do relize the Billboards will effect the driving but i love the look of them. If i do the upgrade ill post some pics. SPM
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Old 11-17-2021, 07:08 PM
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Quote:
Originally Posted by Tommy View Post
I couldn't find a good picture to illustrate this concept so I'll try with words alone. All systems have a natural resonant vibration frequency. For a front suspension, that means that when the spring is compressed as it passes over a bump (or reacts to the up force from an out-of-balance tire), it will compress and then extended in predictable cycles until the damper (shock absorber) stops it. If you have an out-of-balance tire attached to that suspension, it too has a natural up and down motion (vibration) determined largely by the speed and diameter of the tire. Most of the time those two vibrations will not be in sync and tend to cancel each other out to a degree. But over time, the up motion of the tire will coincide with the rebound up motion of the suspension to produce a larger deflection of the suspension. The same occurs in the down direction. Such a phenomenon might account for your shake coming and going.
Shocks are the original Gabriels that came with the car (2011 build). Wonder if swapping out the shocks to the KYBs will help matters.
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Old 11-18-2021, 10:41 AM
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Default Vibration

Depends on the severity of the shake and vibration. I own #383 and the Cobra does not drive anything like my C7 Corvette or even my '65 Mustang. Wear of the tires on Cobra are good and in perfect road conditions, Cobra is smooth sailing. However in my opinion, the vibration and shake you may be experiencing is because you are in a short wheel base car with big wheels and tire. Lots of rubber on the ground and you are picking up road conditions. I would suggest having a reputable shop check out condition of the front end, steering, and look for tire wear issues. If a reputable shop states all looks good, then it really might be an over reacting.
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Old 11-18-2021, 05:43 PM
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[ATTACH]Name:  A2C34CA2-D3C0-4BE7-812E-0EAC478F9E7E.jpg
Views: 71
Size:  86.9 KB[/ATTACH] Anyone know how to tighten this upper steering shaft. Its loose at the mount but i cant figure out how to get it tighten up. I cant get to it from underneath or inside the car. Theres got to be a way to tighten that mount Thanks SPM
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