mkhargrove

I have a bit of speed specific vibration and I suspect it that part of it might be due to out of round tires.

I jacked the car up and spun each tire and noticed that while the wheels were perfect, my tires are out of round about 1/8 each. I took each tire off and rolled them very slowly on a flat surface. The "high" spot is not distributed across the tread...it caused the tire to lean and change track when it rolled over that area.
The tires are fairly new (on the car when I bought it), and I'm considering having them shaved to true assuming I can find someone in DFW area who actually still does that.

I've never had that done to any tires, and I'm wondering if anyone else here has any experience and can tell me whether or not it's a good idea.

GregBBRD

What is the date on the tires?

If not over 5 years old:
Make sure you'be driven them several hundred miles and you'be gotten them hot, to "fix" any "flat spots" from sitting, before you do this.

If they are older than 5 years old:

Forget this idea.

mkhargrove

i am not sure how to read a date of manufacture on the tires...i'll google it.

i don't know how many miles....i'm guessing about 5k. i'm not sure if 1/8" is enough to cause vibration. but, watching how obvious the path was effected when rolling the tire slowly makes me think it has to be causing something noticeable at highway speeds.

i rigged up a router to shave tired for a vespa that were way out of round...like 3/8ths inches (router was stationary, and i slowly turned the wheel while on the scooter).. that's a lot for a small tire and even though my home made tool wasn't great, it made a HUGE difference in how the scooter felt at a whopping 30 mph

Adamant1971

Try having them road forced balanced and matched to the rims. And if you do make sure they get each tire down to at least 12lbs of road force, much more than that can cause vibrations. And always ask to see the report from the machine (hunter).

Bulvot

I have my own mounting and balancing equipment and have personally done a couple of hundred tires. Not nearly as many as a shop would see, but enough that I have a pretty good cross section of tires and wheels. I also probably take a lot more care with the process than the average shop does and I pay a lot of attention to the true of the wheels and tires.

My experience has been that it's only worth considering shaving a tire if the size makes it very hard to find tires that are true from the manufacturer. And I've really only seen that with very large off road tires. If tires develop a flat spot from sitting, you can usually get that to go away with some driving. But, not always. Assuming that that's not the issue...with the sizes common to 928's, I wouldn't personally waste any time or money on shaving the tires. I would just replace them.

Road force balancing is great if there are peculiarities to the car that make it necessary, or as a troubleshooting step. Some cars really benefit from it, and some really need it in order to be "right". But, it's not going to help an out of round tire.

Just my two cents.

Jeremy Mote

I've never seen a point in trying to save old tires. I'd just buy new ones.

mkhargrove

these are fairly new, low mileage tires.....just out of round.
as said above, pretty much every tired made is out of round to some extent. i understand the concept of road force balance, and i believe in it's benefits....but i don't see how out of round can be counteracted regardless of balance weights.
it might be a moot point because i don't know that there's anyone in the dfw area that has a machine....

SwayBar

My 993's front tires will develop flat-spots from sitting over winter, and will take several good drives to correct them and they're good the rest of the driving seaon.

Next spring, same problem with flat-spots, and, same cure.

Have you driven it enough to give them a chance to correct themselves?

mkhargrove

oh, for sure...i drive it all of the time. it's really more of a "high" spot on each tire, about 8 inches long, and it seems to be worse on one side of the tire (which is why they very obviously changed course when i rolled them slowly on a flat surface). i don't have a clue about how the belts are configured, but i am guessing it's just a junk tire. they were on it when i bought it. i think it's an ntb store brand.

i would rather use them up if possible, vs. investing in an new tire, and to be honest, i've always been curious about how much difference truing makes...

the suck part is that my dad's buddy races legends, and he has his own truing machine, but he's far removed in east texas.

dr bob

Often the "swollen" areas on a tire are the result of impact, where there is structural damage that allows the air pressure to grow part of the tire. Think in terms of air making the tire large and supporting the weight, while the cords in the carcass keep it from getting too big. While shaving to "true" the tire tread will solve an apparent static out-of-round, a road-force balance will help identify structural issues; if the road-force balance can mask it enough to make the car driveable, maybe OK. The numbers will tell you quickly. The aggravation factor for doing the research and finding the specialized balancing equipment and talent isn't worth it IMO, since the grinding and added balancing weight are band-aid cures for a tire that's damaged. The symptoms come back as the tire wears and the cord damage expands in normal driving.

My two sense.

mkhargrove

Dr. Bob, that's a very good point....the tires look pristine, so it never crossed my mind that it could be internal damage. I just assumed it was a belt overlap in cheaply manufactured tire. But it could be belt separation in a cheaply manufactured tire. Sadly, the car hit a tree yesterday. With no driver. It's out of commission temporarily....

soontobered84

OK, let's hear the story behind this little tidbit of information. You can't get off that easily! A caution: do not incriminate yourself to the point that your insurance claim might suffer. Alternatively, you can tell me about it at breakfast on Saturday. I can wait if need be.

dr bob

Ouch! "The car hit a tree yesterday..." doesn't sound like the beginning of a story with a fairy-tale ending, unless the tree was really a prince and it was just a gentle kiss. I suspect we all have similar stories buried in our personal archives. Hope this one isn't too serious.

jeff spahn

We shave the front tire on our Piper Cherokee when it gets out of round. Causes terrible shimmy that feels like the plane will come apart. Why not a car?

928 GT R

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