Flatspotting tires

[Big Block 69]

I have a 90 Blazer that is all stock except for 7 inches of lift and 18.5X44in. tires. The tires feel like square blocks. After driving a little bit, this straightens out a little. It is much worse in colder weather. But even in the summer it doesn't go away enough to drive over 25 mph. Trying to speed up, it will get violent. Can anyone advise me? I had this issue with 12.5X38's, but it goes away after about a mile, winter or summer.

Thank You for any help!
Rick
Big Block 69

 

[PrairieDrifter]

Check your tire pressures, best bet is to drive them around every couple of months at least.

 

[78C10BigTen]

Are they old bias ply???

 

[Grumpy]

Number one: Are you driving the truck regularly? Tires will have mild flat spots after sitting for a few weeks or more.

Number two: What is the quality level of the tires? Higher-end tires will be less prone to flat-spotting than say an "economy" tire; with even some of the lesser tires taking dozens of miles to pound out.

Number three: Cold weather is also a contributor when the vehicle remains stationary for weeks - this is very common in the colder climates such as Canada and the American Mid-West.

Frankly, I would look at tire quality first.

 

[Big Block 69]

They are old bias ply Ground Hawgs. I do not go in the mud, I just like the look. I will try pumping the air pressure up and see if that makes it any better. I also have an old set of Super Swamper 12.5X38's (also bias plys) that do this, but not nearly as bad and they will clear up completely after about a mile. I live in south east Ohio and it does get cold here.
Thank you for the replies.
Rick
Big Block 69

 

[Memaloose]

Don't forget to check the balance.

 

[78C10BigTen]

They are old bias ply Ground Hawgs. I do not go in the mud, I just like the look. I will try pumping the air pressure up and see if that makes it any better. I also have an old set of Super Swamper 12.5X38's (also bias plys) that do this, but not nearly as bad and they will clear up completely after about a mile. I live in south east Ohio and it does get cold here.
Thank you for the replies.
Rick
Big Block 69

Im 99% positive the problem is simply the bias ply, the composition isnt the same as radials.

 

[HotRodPC]

Are they old bias ply???

That was going to be my exact question. Otherwise, I'd say bad shocks or not strong enough shocks for your lift and tire size. People do not understand the main purpose of a shock. It doesn't carry weight, and yes it does control body bouncing, but it's main purpose is to hold the tire to the pavement. You ever seen a car going down the freeway and a tire is dribbling like a basketball? That's bad shocks and will cause flat spots in tires from pounding the pavement.

 

[AuroraGirl]

also the more plies and heavier the truck it will accentuate the behavior even more

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Dont mind this absolute low-effort paint job this wheel was incredibly rusty and I hit it with rusty metal primer and then when I had a white rustoleum "pro" can in hand I decided the brown would be white. that tire is older than the OP and me put together probably, and its also pretty heavy duty one. that thing I can park it for a few hours and it will move its flat spot and no matter how slow you crawl forward THUD THUD THUD for a solid moment or two but this is an old, worn, OLD, bias ply. Its only on the front because the bf goodrich has a broken cord and looses air.

then if you have a wheel which is not round, oblong one could say, you may see more pronounced issues as you have. Im only sayingthat to covers what ifs here, its 85% likely its your tire and hotrod was good to point out what may cause an otherwise fine tire to start behaving that way.

 

[bucket]

They are old bias ply Ground Hawgs. I do not go in the mud, I just like the look. I will try pumping the air pressure up and see if that makes it any better. I also have an old set of Super Swamper 12.5X38's (also bias plys) that do this, but not nearly as bad and they will clear up completely after about a mile. I live in south east Ohio and it does get cold here.
Thank you for the replies.
Rick
Big Block 69

I'm super jealous of your old Ground Hawgs. Good lord I'd sure like to find a set, lol.

Jack the axles up and give the tires a spin to check for excessive runout. I'm betting that you find a bunch. But for a realistic test, make sure to do it after driving it around for a while. If they aren't too awful out of round, it may be worthwhile to break them down and toss 16oz of BB's into each tire to help with the balance.

Also, if they are crazy out of round and shaped more like eggs, I find that running LOWER air pressure will actually help with reducing the shake. I'm talking running 10-12 psi.

 

[Big Block 69]

Thank you all for your suggestions! I will start with the air pressure. I have been at the tire shop and saw a machine working that had a brand new 22.5 truck tire on it. The tire turned slowly while a small blade that looked like it was off of a can opener cut off what was out of round. I never considered that might be my problem.

 

[bucket]

Thank you all for your suggestions! I will start with the air pressure. I have been at the tire shop and saw a machine working that had a brand new 22.5 truck tire on it. The tire turned slowly while a small blade that looked like it was off of a can opener cut off what was out of round. I never considered that might be my problem.

I didn't realize any tire shops still had those machines. That's pretty cool.

 

[Big Block 69]

I want to thank you all for your replies. I pumped the pressure up to 30 and that seemed to have cured most of it. When I put them back on, I lowered each tire to just off the driveway and turned them. They seem very round. If this continues, I will try the BB trick.
Thank you again for all your suggestions.
Rick
Big Block 69

 

[AuroraGirl]

I'm super jealous of your old Ground Hawgs. Good lord I'd sure like to find a set, lol.

Jack the axles up and give the tires a spin to check for excessive runout. I'm betting that you find a bunch. But for a realistic test, make sure to do it after driving it around for a while. If they aren't too awful out of round, it may be worthwhile to break them down and toss 16oz of BB's into each tire to help with the balance.

Also, if they are crazy out of round and shaped more like eggs, I find that running LOWER air pressure will actually help with reducing the shake. I'm talking running 10-12 psi.

would running that much lower pressure, assuming he has no load or trailer of course, cause any issues with the tires getting too hot or wearing excessive on the shoulders? Or is the idea to run them that way so they are warm and encourage it to a more "round" shape and eventually air back up? That may not make sense but I would be concerned using old tires at a large drop in psi especially if more weight is in the truck. do we know the ply rating? A higher ply would prob get hotter doing that than a lower.

 

[bucket]

would running that much lower pressure, assuming he has no load or trailer of course, cause any issues with the tires getting too hot or wearing excessive on the shoulders? Or is the idea to run them that way so they are warm and encourage it to a more "round" shape and eventually air back up? That may not make sense but I would be concerned using old tires at a large drop in psi especially if more weight is in the truck. do we know the ply rating? A higher ply would prob get hotter doing that than a lower.

Most of those old bias ply tires were designed to run at a much lower psi than we are all used to now. Ground Hawgs have a very tough carcass and really don't flex that much, compared to a modern type of tire. Most people actually ran too much psi in them, even for the street, which is why most of them go bald in the center of the tread. The trick is to find the right psi setting that gives you a nice even contact patch on the road, and that is different with every truck.