What’s actually happening when tyres go ‘off’ ?

As the citation offered by “gortnipper” explained, it is generally a one-way street with rubber tires, where upon aging (sun, light, heat, ozone) the rubber x-links further, becoming stiffer and the original tire modulus no longer exists. It is this stiffening of the rubber that would cause the tire to go “off”.

Standard protocol for preparing motorcycle ice racing tires here in MN is to throw your tire set up on a roof with a southern exposure for the summer, where they will see lots of heat and light. This advances the cure of the rubber via the means cited and provides an extremely firm tire that is ideal to receive ice studs and secure them rigidly.

NPeteN said:

I'm fine. Complete 360 degree separation from the sidewall at highway speed. Never seen anything like it.

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Reminded me of something that happened when I was a lad; At a nearby farm one of the hands was inflating a tractor rear tyre and it blew off taking his head with it. Be careful!

I bought a cheap Durometer so I could check the rubber hardness of different iso rubbers, but now use it to keep a check on the tyres of my bikes.
Whether you ride them or not the surface hardness of tyres increases with age. New Avon road riders measure around 55 on the hardness scale and even new car tyres are in the 55-60 range.
Earlier this year I bought a Commando to restore and the 20 year old tyres measured over 80 and were almost impossible to get off.
I now ride on the basis that if the tyres (especially the front) are above 65 then it’s time to change. Unfortunately, these days none of my tyres need changing because of tread wear.

NPeteN said:

I'm fine. Complete 360 degree separation from the sidewall at highway speed. Never seen anything like it.

Click to expand...

This tyre was not a remould was it?

WZ507 said:

As the citation offered by “gortnipper” explained, it is generally a one-way street with rubber tires, where upon aging (sun, light, heat, ozone) the rubber x-links further, becoming stiffer and the original tire modulus no longer exists. It is this stiffening of the rubber that would cause the tire to go “off”.

Standard protocol for preparing motorcycle ice racing tires here in MN is to throw your tire set up on a roof with a southern exposure for the summer, where they will see lots of heat and light. This advances the cure of the rubber via the means cited and provides an extremely firm tire that is ideal to receive ice studs and secure them rigidly.

Click to expand...

I was born in and grew up outside Minneapolis.

I remember pools for when a car parked on the frozen Lake Minnetonka would fall through the ice in the spring.

SteveC said:

I bought a cheap Durometer so I could check the rubber hardness of different iso rubbers, but now use it to keep a check on the tyres of my bikes.
Whether you ride them or not the surface hardness of tyres increases with age. New Avon road riders measure around 55 on the hardness scale and even new car tyres are in the 55-60 range.
Earlier this year I bought a Commando to restore and the 20 year old tyres measured over 80 and were almost impossible to get off.
I now ride on the basis that if the tyres (especially the front) are above 65 then it’s time to change. Unfortunately, these days none of my tyres need changing because of tread wear.

Click to expand...

Racers use nitrogen filled tires since they leak less than air and pressures are more consistent as the tire heats up.

Based on what I have been reading, I think I will fill mine with Nitrogen to help extend the rubber life.

WZ507 said:

As the citation offered by “gortnipper” explained, it is generally a one-way street with rubber tires, where upon aging (sun, light, heat, ozone) the rubber x-links further, becoming stiffer and the original tire modulus no longer exists. It is this stiffening of the rubber that would cause the tire to go “off”.

Standard protocol for preparing motorcycle ice racing tires here in MN is to throw your tire set up on a roof with a southern exposure for the summer, where they will see lots of heat and light. This advances the cure of the rubber via the means cited and provides an extremely firm tire that is ideal to receive ice studs and secure them rigidly.

Click to expand...

Is this before, or after you have inserted the studs for ice racing, may I ask?

Any rubber has a finite life post-cure, but track tyres (I'm told) can only tolerate so many thermal cycles before they go off, especially slicks.
I guess track compound road tyres will be similar. I know some guys have junked slicks in favour of Pirelli or Metzeler treaded track-based tyres for this reason (and the lethality of slicks once they're out of the temperature zone).

Hmmm... Perhaps I should upgrade from the thumbnail-in-the-tread technique. It's been ages since I had my thumbnail calibrated. Old tires certainly do get stiff though. I had the misfortune to remove a 20+ year-old Avon New Gripster a year or so ago. Did my hands no good at all.

SteveC said:

I bought a cheap Durometer so I could check the rubber hardness of different iso rubbers, but now use it to keep a check on the tyres of my bikes.
Whether you ride them or not the surface hardness of tyres increases with age. New Avon road riders measure around 55 on the hardness scale and even new car tyres are in the 55-60 range.
Earlier this year I bought a Commando to restore and the 20 year old tyres measured over 80 and were almost impossible to get off.
I now ride on the basis that if the tyres (especially the front) are above 65 then it’s time to change. Unfortunately, these days none of my tyres need changing because of tread wear.

Click to expand...

Tyres on a race bike can be hard, but as soon as they heat up, they become soft again. You just have to be careful on your first few laps, It is the reason some guys use tyre warmers. They get nervous when they get a bit of slip. These days, during races most bikes are out on the ripple strips at full lean and totally tyre dependent. In the old days we had shit tyres, but the bikes were more vertical in corners. My Seeley has a lot of trail in its steering, so it stays more vertical. The tyres can have less grip and the bike can still be gassed very hard. The faster you get out of corners, the faster you will be towards the end of the next straight. If I used better tyres, I would not be any faster. Nobody can beat you when you are hard on the gas from the point just after you have entered the corner. The guys on full lean cannot do that. I just turn tighter early and ride under them.
TRY IT, but be careful the first time you do it. Playing with steering geometry is dangerous. I think my trail is about 106mm, but it is difficult to measure. If your bike does not tip into corners very easily as you brake, don't do this. If you don't have enough trail, the bike will understeer both going into the corner and when coming out of the corner.

B+Bogus said:

Any rubber has a finite life post-cure, but track tyres (I'm told) can only tolerate so many thermal cycles before they go off, especially slicks.
I guess track compound road tyres will be similar. I know some guys have junked slicks in favour of Pirelli or Metzeler treaded track-based tyres for this reason (and the lethality of slicks once they're out of the temperature zone).

Click to expand...

In the old days we used to use Dunlop T1 compound race tyres, but it did not matter because the bikes stayed more vertical, It is almost impossible to lean a Manx Norton as far over as you can a 1970s two-stroke. These days modern road tyres are immensely better than anything we had in the old days. However, these days I do not play their game . I don't follow other riders at full lean on the high line in corners. I always turn under them early. If you ride an original Manx, you find that if you get off-line, you just gas them harder and they will come back. It is the reason they were much faster than other bikes of their time.
If you have really sticky tyres, you can apply more power when the bike is on full lean. But if the bike stays more vertical, you can be much more heavy-handed.

I was taught when I worked in the M/C tyre trade that with a race tyre it will slightly change its composition with every heat cycle.

In 2007, NHTSA's Research Report to Congress on Tire Aging presented clear evidence of both tire aging failures and the outsized effect of sustained heat on the aging mechanism.

• “This trend was observed in NHTSA’s analysis of data provided by a large insurance company... It reported that 27 percent of its policyholders are from Texas, California, Louisiana, Florida, and Arizona, but 77 percent of the tire claims came from these states and 84 percent of these were for tires over 6 years old. While tire insurance claims are not necessarily an absolute measure of the failures due to aging, [they are] an indication that a large number of tire failures are likely occurring because of the effect of sustained high temperature on tires.” - NHTSA Research Report to Congress on Tire Aging

When NHTSA conducted further testing in Arizona, they found not only that tires did show an increasing failure rate with age, especially at around 6 years, they also found that the rate of aging was only slightly less for spare tires.

• “DOE analysis confirms that mileage was a relatively unimportant factor in [failures due to] aging compared to time. Thus time, not mileage, is the correct metric for tire aging... Besides variations from manufacturer to manufacturer, tire size, or more specifically, tire aspect ratio seems to effect the tire aging rate. Tires with higher aspect ratios age faster than tires with lower aspect ratios.” - Rubber Oxidation And Tire Aging - A Review.
• “...the results support the hypothesis that spare tires could degrade while stored on the vehicle. This is a particular concern when coupled with the inflation pressures of full-size spare tires at retrieval. Over 30% of the passenger and light truck tires at the spare tire location had inflation pressures below the T&RA Load Table minimums.

Higher speed rated tires degraded less – even on spare tires.

• “Results indicated a strong correlation to the speed rating of the tire, with the higher speed rated tires losing the least capability with increasing age and mileage.” - NHTSA Tire Aging Test Development Project: Phase 1