Q. How do I know when an off-road mountain bike tyre needs replacing? What's the minimum tread depth or does it differ from tyre to tyre, and is it different for mud than for dry tyres? >David Roberts, email
A. There's no hard and fast rule because tread depth from new varies from tyre to tyre and from tyre type to tyre type. Semi slicks, for instance, have a very low tread profile, whereas mud spikes are the opposite.
In terms of grip, that's pretty much down to when you deem the tyre is no longer behaving as it should. But if you can see the weave of the tyre coming through the sidewalls, it's time to replace it. Also, when you take the tyre off the rim, when changing tubes for example, inspect the inside of the casing. If there's any sign of wear or of the tyre carcass coming apart, again, it's time to change it. Also, if the rubber is dried out and flakey, replace the tyre.
You should never use any tyre to the point where there's no longer any central tread or where there's an excessive imbalance in the profile. For example, if the tyre has been heavily skidded on, there's likely to be a weak spot where it's been worn down, which could then prove to be susceptible to failure.
