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Rear tires on a T-Bucket

11K views 7 replies 5 participants last post by  rrmccabe 
#1 ·
Had the rear tires on my T-Bucket spin balanced today. As I suspected ,the tech told me that the tires appear to be out of round. Wheels are fine. The rear tires are Pro-Trac S375/60D15. I understand what the tire size spec is saying with the exception of the 'S' in the 'S375' portion of the size spec.

So my first question is what does that 'S' mean. Secondly, can any tire pros out there recommend a proper replacement tire? I would like to replace these diagonal-belt tires with a radial unless there are reasons that argue against that. Any comments are appreciated.
 
#4 ·
Thank you, 1ownerT. I also looked on Coker's web site before making my initial post and could not find anything. I followed up on your suggestion and contacted their tech support for an answer. I'll post their reply when I receive it.

And thanks to you as well, Henry. I have not heard of a process that will true a tire back from an out-of-round condition. But I will follow up on that and see who may be able to do that. I am surprised the tech did not mention that when he balanced the tires today. I realize that slinging around tires with this much rubber / cross section, they will not be perfectly round. However, in this case, you can feel it in the car as a vibration occurring at about the same frequency as the tire rotation, and that is not right in my book. That's why I took them in to determine if it was merely a balance issue or something else. If I can find a place that does this, then your suggestion takes the brass ring.

Thanks to all.
 
#5 ·
The problen could also be with your rims and not your tires. Boyd Coddington rims for example are notorious for being untrue. A good dial indicator should be able to verify your rims. If the rim centers are not perfect the rim will wobble some. When this occurs it really cuts up at certain speeds.
 
#6 ·
Well, since I started this thread, I'm obligated to post a follow-up.

I tried contacting Coker Tire via their website to ask the original questions I posted. Although their website says they will get back to you quickly, it has been 5 business days and no reply. Read into that what you may, but it speaks volumes to me.

I finally hooked up with Harlow Tire. After discussing what's going on with my car, they helped me out with the following:

1) Spin balancing a bias ply tire does not do much good. The bias ply tire will develop a flat spot on the tread after sitting a period of time. This flat spot does not get 'rolled out' until the tire either heats up or is driven a considerable distance. Taking your bias ply tire off of the car and then spin balancing it only accentuates the flat spot, causing the spin balancer to think the tire is out of balance. Yes, you can balance it, but when you put it back on the car and it sits overnight or longer, a flat spot will develop at a different location on the tire and the balance job is no longer doing what it is supposed to do. The question was, do you drive on long trips (yes), and after a while on that trip, does the out of round vibration seem to lessen or go away (yes). Bingo. Bias ply tires should only be static balanced after you are sure there are no flat spots in the tire tread from sitting a while. Still, that balance job is somewhat less effective after the car sits awhile.

2) Radial ply tires do not have a tendency to develop flat spots in normal use. Further, the sidewall of the radial tire has more flex, allowing for a smoother ride over that bump in the road. They can be both effectively spin-balanced and static balanced.

As a result, today I had a set of Hoosier Pro Street radials put on the rears. This is a different car now. Tracks straighter, handles better, no vibrations, and a lot smoother ride. Worth every penny.
 
#8 ·
I used to be a technician that worked on spin balancers for COATS tire machine company. Just thought I would chime in on a couple things and comment.

Yes, I agree on flat spots. Even some radials did that as well. Nylon belts come to mind. The material in the tire takes a set and has to get warm before it comes back to what we will call a normal state.

That said, its still a good idea to balance them because 99.9% of the time they will be better than they were before. The rare exception is if the tires happened to be a perfect balance (and it does happen) before you balance and then you balance the flat spot into the weight job.

Electronic balancers are nothing more than a vibration sensing device that pegs the location of the vibration. So yes, an "temp" out of round condition will action like a balance issue because it really is :)

The main reason I chimed in was because you used the word "static". When given the opportunity always dynamic balance and not static. Static is on a single dimension. Dynamic balancers can sense not only how out of balance the wheel is radially but they sense where it is across the tread. Inside, outside or middle and have you add weights on the inside and outside at whatever location to make sure that assembly is balanced completely.

I always take a car in for balance and call ahead so I can bring it in with warm tires. Never in the winter !

Sounds like you have moved on to radials. Probably the best thing you can do anyway. I play with old muscle cars that are running original Firestone Bias plies to be correct and.. They suck !

Rich
 
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