Tony_G

Thanks for your reply. It helped me to understand the root cause of the tires cracking.

The tires did not crack on the seams. The balm is not for flexing, but for UV and ozone, which is known to degrade rubber.

Yes, I do think that safety critical items like tires should not fail in their expected useful life. For tires in general, that life is generally defined as: manufactured less than six years ago, no road hazard damage, no abuse, and safe tread remaining.

That said, after considering your mention of flex, I now realize that more than likely the cause of failure is that I probably ran these tires underinflated.

Here’s how that happened. The tire size in question is 700 x 28C. I like 85 to 90 PSI, and I maintain it carefully. The max stamped into the rubber sidewall on the removed GP 4000’s say “max 116 PSI”, and oddly, the painted on decal says “115 PSI max”. Maybe the 1 pound difference is a rounding error when converting from Bar, but it is unusual to see a tire sidewall disagree with itself. More importantly, unlike most tires, there is no minimum PSI on the sidewall.

I found out about these tires on bicyclerollingresistance.com, where they were tested at 60, 80, 100, and 120 PSI. Their review is the reason I bought the tires.

https://www.bicyclerollingresistance...0s-ii-23-25-28

I checked the Continental website, and the regular folding GP 4000 tires are already removed since the new GP 5000 is out. Checking the GP 5000 700 x 28C, the inflation is listed at 95-115 PSI.

https://www.continental-tires.com/bi...rand-prix-5000

From having read the review at rollingresistance, I got the idea that 80 to 90 PSI would be no problem at all.

I think that was wrong. The rubber splitting on the tires at the edge of the tread is consistent with under inflation, and I now consider that to be the likely cause. I previously discarded that possibility because I mistakenly thought that 85 PSI was well in the safe inflation range for these tires.