New Member
Hi all,

I'm looking for a bit of tyre advice.

My Marathon +'s have begun to crack on the walls. The rear is the worst, with a large number of 1/2 inch cracks all around the tyre. The bike is stored outside in all weathers.

My question is whether this is a sign that the tyres need replacing? There are no other problems with the tyres, tread is fine, no sign of the tyre inner pushing through, etc.

Any advice would be much appreciated.


jonny jeez

Legendary Member
Hi cornelius, sorry I cant help, but hang in there someone will come along in a moment.

hopefully this reply will bump the post a little

oh and Welcome!


Über Member
It is possible that they're from a bad batch but I suspect that you've been running on them at much too low a pressure. I've used SMPs for years and my bike lives outside all year round and I've never known the sidewalls to crack.
Without seeing them I think they'd be fine Cornelius going by the words of the great Sheldon Brown:

Tire Wear-When should you replace your tires?

Many cyclists waste money replacing perfectly functional tires simply because they're old, or may have discolored sidewalls. If you just want new tires because the old ones look grotty, it's your money, but if you are mainly concerned with safety/function, there are only two reasons for replacing old tires:
  1. When the tread is worn so thin that you start getting a lot of flats from small pieces of glass and the like, or the fabric shows through the rubber.
  2. When the tire's fabric has been damaged, so that the tire has a lumpy, irregular appearance somewhere, or the tube bulges through the tire.
Cracks in the tread are harmless. Small punctures in the tire such as are typically caused by nails, tacks, thorns or glas slivers are also harmless to the tire, since the tire doesn't need to be air-tight. Gum-wall tires sometimes get unsightly blistering on the sidewalls from ozone damage. (This is frequently caused by storing the bike near a furnace--the powerful electric motors in typical furnaces can put a fair amount of ozone into the air.) This blistering is ugly, but doesn't actually compromise the safety/reliability of the tire in the least.


New Member
Thanks for all your replies.

Looks like the best bet is to get the tyres off and have a look inside.

I do check the tyre pressure every couple of weeks or so (when I remember), so it could be a possibility that they've not been properly inflated when I've ridden. The tyres have probably done around 2k miles or so and have been used daily through most weathers.

Thanks again for your help.


Noting the comment made by HLaB from Sheldon. I must add that the thinnest part of a tyre the sidewall. If it is cracked, that further reduces the thickness. You should then consider the consequences; worst case, best case and most likely.

Worst Case; Blow at speed leading to injury.
Best Case; Tyre lasts a further 2 months and deflates at home.
Most Likely; You get a puncture on the road and your spare tube cannot repair the damage because it is a sidewall blow.

In summary - replace now
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