Tyre Sizing Guidance- Max Tyre Width

Maximum Tyre Size

One of the most often asked questions about any of the bikes that we sell is “What’s the biggest tyre that I can use with that bike?” Unfortunately, there’s not a simple answer to that question for the following reasons.

• 1. Not all manufacturers size their tyres the same way, so two tyres from two different brands that both have 700 x 28c written on them might not be the same actual size. One might measure-up slightly undersized (because that brand likes to give the appearance of having lighter tyres) and the other might come up slightly oversized because that brand like to give you more tyre for the money. Either way, the size range between those two tyres could easily be 4mm in total, (+/- 2mm from the nominal value).
• 2. Tyres are generally measured around the carcass, not around the widest point of the tread. This could easily make your knobbly tyres larger than the stated width.
• 3. Stretched or loose spokes and buckled rims can cause the tyre to wander with each revolution, this can reduce the clearance between tyre and frame.
• 4. Heavier riders tend to flex their wheels more than lighter riders and this can reduce the maximum safe tyre size.
• 5. The width of the rim affects how wide a tyre is when fully inflated. If you place the same 32mm slick tyre on a rim with a 17mm internal width and another with a 23mm internal width the tyre will measure almost +2mm wider on the wider rim.
• 6. Older tyres increase in size as the threads stretch and they increase slightly with increasing tyre pressure. This is especially true of lightweight clinchers.

So, with all that in mind it’s apparent how difficult it can be answer the “What’s the biggest tyre?” question. To simplify the process for all new bikes we intend to give you two measurements.

• The actual measured width of the widest tyre that we have test fitted to a bicycle and the total frame width at the closest point between tyre and frame. In those cases where the height of a tyre may foul a fork, we will give separate measurements for fork and frame.

Advice

• Always buy slightly undersized tyres, they might stretch out with use.
• Keep your wheels trued and spokes tight.
• Try to leave at least 4mm between the tyre sidewall and any part of the frame.