Flat spots & modern tyres


#1

I am old enough to remember when leaving a car sit for a week would result in a flat spot. I can also remember when tyre design progressed to the point when the tyre manufacturers believed they had beat that problem (at the time I was in the manufacturing facility and personally talked to the engineers).



How many of you have actuarially had flat spots on tyre in say the last five years? I have had flat spots, but that was many years ago on my Sunbeam IMP with 12 inch tyres designed for a house trailer.


#2

Yokohamas and Falkens are prone to it on heavier cars. Had both on my TL, and they’d both flatspot overnight. Terrible. Never thought I’d pay for overpriced Michelins, but at least they don’t flatspot.


#3

I last experienced flat spots on the bias belted tires my '72 Duster used, 1980 or so. Since then, never, all radials, all brands (including my current Yokohamas), all climates (Anchorage to Dallas).


#4

The last flat spots I experienced was on a set of nylon cord tires in the 70s. Since that time, even at -40F, I do not recall any flatspotting, even when the car sat at the airport for 2 weeks in the winter.


#5

I remember the debate back in the 1950’s and 1960’s as to whether nylon cord tires or rayon (tyrex) cord tires were better. In cold weather, sometimes it would take a mile or so of driving for the nylon cord tires to smooth out. One remedy we used to use if the car sat for a couple of weeks or more was to inflate the tires 10 psi over the specified pressure, drive a couple of miles, and then let the excess air out to reduce the pressure to specifications. Back in those days, I thought that superior sidewall strength of the nylon cord made up for the inconvenience of temporary flat spotting. On my limited budget, I bought recapped tires on a good nylon casing. I felt this was better than a third line new tire running rayon cords.


#6

Today, especially on “performance tires”, a NYLON “cap ply” has been added which greatly aids adhesion between the tread rubber and the steel belts. Tires with this feature can indeed “flat spot” for a few minutes after sitting overnight.


#7

My 79 chevy pickup sits for weeks or even months at a time ( 71,000 total miles ).
The three year old Firestones will give some degree of vibration for a few miles until they heat up enough to even out, then all is fine.

With this truck I don’t go fast enough for it to be a big bother and they correct themselves anyway.

But the flat spots are there initially, sure enough.


#8

Modern tires do indeed flat spot - even with only polyester and steel as reinforcing materials. However, they don’t flat spot nearly as much as the old nylon bias ply tires did.

HOWEVER, many modern tires come with nylon cap plies (sometimes called overlays). These tend to flat spot more than tires without - BUT - tires with overlays are much more capable. That is, they have much more speed capability and are therefore less prone to failure than tires without.

Nevertheless, EVERY tire will flat spot. It’s just a matter of how long, how much inflation pressure, how much load, and how hot it gets.


#9

“Nevertheless, EVERY tire will flat spot.”

I guess theoretically, OK, but it must be very rare in practice.


#10

I’ve experience out of balance tires due to ice build up on the rims, and once mud on the rims. The last time I experienced a “flat spot” on a tire was sometime in the early '70’s. This was a real issue at one time, but tire manufactures changed the materials in the tires and the design and have virtually eliminated the problem. Perhaps all tires have flat spots after sitting for a few hours, but they quickly round out in a few revolutions and most driver’s will never notice.


#11

In cold temperatures I find my ultra high performance Bridgestones do it for the first few miles of driving in the winter. Annoying but small compromise for an incredible tire otherwise.


#12

Thanks for all the replies. I guess we can say, flat spots are no longer a problem, but still exist.


#13

Been driving since the early 70s and know what a flat spot feels like. I have a number of rarely driven cars, trucks and trailers with various tire types. None of them exhibit any flat spotting. I have a 1700 lb bass boat rig on single axle trailer w/bias ply tires. Sat for over a year outside on asphalt never moved only pressure adjusted periodically. There were depressions in the pavement but the rig pulled as smooth as ever right out of the driveway.


#14

I think you meant, that it is largely undetectable in normal conditions - and that is true. But when tire manufacturers conduct flat spotting tests - where they purposely produce conditions conducive to flat spotting (high loads, high temperatures!) - they will always find them.

So do not be surprised to find folks complaining about flat spotting - even on tires that are not really prone to this. It’s all a matter of how severe the conditions are - and some tires are more prone to this than others.