Capacity of tires to withstand standing out-of-shape


#1

Dear Click and Clack,
I was listening in San Antonio when you conversed with John Blaha as he hurtled back to Earth–what a riot! My wife and I belonged to the church where his mother belonged at the time. I mused that you probably already knew he was calling ahead of time before he stated his Rockwells burned for a few seconds and then cut off. Did you?
My questions to you at this point are about tires. One, are they affected to a significant degree by being set against curbs and other barriers for hours? For example, I see cars parked against curbs with tires held in that position–out of round–for who knows how long. Would that cause them to perform improperly afterward? Two, would turning tires by power steering while a vehicle is motionless every day after backing from a parking place before driving forward cause premature wear or improper performance later? I always move away from curb-like obstructions and only turn wheels/tires when my vehicle is moving.
Thank you.
Daniel in Mason, TX


#2

Most automotive tires use rayon for the basic structure of the tire and rayon does not seem to take a “set” under normal driving conditions. Nylon tires were notorious for “setting” a flat spot when driven until hot and then parked to cool and several miles of thumping were endured before the carcass heated and lost the “set.”

FWIW, when tires are manufactured they require that the rubber be cured at temperatures above 250*. Immediately after the tires are removed from the hot mold they are inflated for 20 minutes or more to cool and ‘set’ to the finished shape. That ‘setting’ is critical but the tire will never be heated to curing temperature in even severe use so it can withstand being parked against curbs, etc., with no problem.


#3

p.s. The brothers Grime rarely post here. I hope they won’t be offended that I replied to your post, dess.


#4

Hitting a pot-hole at 70 MPH puts FAR more stress on a tire than ANY low-speed abuse you can dish out…If they can endure the high-speed impacts and side-loads encountered during normal driving, parking-lot distortions are NOTHING…


#5

Don’t believe it hurts them much but sure doesn’t do them any good. Back to drivers training class in 1964, don’t turn the wheel unless you are moving-it is hard on the power steering not the tires. Of course that was with a 1964 Ford Galaxy so times might have changed but I still don’t turn the wheels much unless I’m moving so it stuck with me. Me wonders what they are teaching in drivers ed these days.


#6

First, nowadays most passenger car tires use polyester body plies (not rayon!) and steel belts. The term “steel belted radial tire” is, for practical purposes, redundant!

Tires can and will be permanently distorted when they are compressed against something. The simple act of letting a car sit still will generate a flat spot. The question is how long was the exposure and how severe was the compression. We’re talkinmg weeks of exposure and high loadings. Also high ambient temperatures encourages flat spots.

But for practical purposes, no one needs to worry about tires being placed against or sitting on top of curbs.


#7
Parking against the curb can break the seal and give you a flat tyre or can damage the rim.

#8

Well, hitting a curb can do that, JEM, but the normal parking, where you slowly roll up to a curb and stop won’t damage anything, right?


#9

Well, hitting a curb can do that, JEM, but the normal parking, where you slowly roll up to a curb and stop won’t damage anything, right?

It will not case a problem every time, but it can. I have had two cars that did not like being parked close to the curb. It can bend the valve stem and cause a leak or damage. It took me six months one time trying to figure out why I kept getting flats.


#10

Modern tires will not be affected by being pressed out of shape for “hours”. Eventually the materials wil “cold flow”, but it takes years, or at least many months, for that to happen.

Turning the steering wheel while the car is sitting still will not affect the parameters (radial runout, roundness, coaxiality, concentricity) anywhere near the tolerances of the tire itself. You’d have to sit in one spot and turn the wheel back and forth through an entire season of “American Idol” to feel the wear.

The danger with rubbing curbs is tearing a hole in the sidewall, especially with granite curbs. Been there, done that. Twice.


#11

Excuse me Capri Racer. I stand corrected. Polyester is the most common fiber today. My mind drifted off to long ago and far away. I seem to recall when nylon tires were the most highly rated but they were prone to flat spotting while rayon tires never had such a problem. Believe it or not, Sears had a difficult time selling the public on radial tires. And tubeless tires were somewhat slow to catch on in their first few years.