shopping advisor

Tyre Properties

Rolling Resistance

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What influences rolling resistance?

The tread compound and tread pattern have the most influence. The width is a very terrain specific factor and a wider tyre will be faster in some conditions.

Road: Given the same inflation pressure, a widertyre is faster. If you have 120psi in both a 20mm tyre and a 23mm tyre, the wider tyre will be faster. The contact patch of the wider tyre will have rounder shape while the narrow tyre will have an elliptical shape. The elliptical profile means that the tyre casing is distorted along more of its length and this distortion of the casing is what creates rolling resistance. A wider tyre is a heavier tyre though.

Mountain: In smooth hardpack with a gravel surface a narrow tyre inflated to a higher pressure will be faster but in rocky terrain a wider tyre can be faster because it absorbs more of the bumps that would otherwise slow you down.

TPI Count

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What are the pros and cons of a high or low TPI (threads per inch) casings?

Lower TPI tyres have thicker cloth and the gaps between the threads are bigger. These take on more rubber as the tyre is made, making a heavier tyre but with sturdy, abrasion resistant sidewalls. A low TPI count is good for a downhill tyre.

Higher TPI tyres take less rubber to fill the gaps so give a lighter tyre with lower rolling resistance as a result of having more flexible (thinner) sidewalls. Also the smaller gaps between the threads make it harder for a thorn to penetrate the casing. For racing, touring, or any performance oriented tyre, a high TPI count is good.

Tyre Compound

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Is a soft compound MTB tyre always better for grip?

When the tread knobs fold over, or "squirm", when cornering on a hard surface, the surface area in contact with the ground can increase, giving better traction, despite the unnerving feel.

In mud a hard compound can be good when the tread blocks become stiff paddles. But you might be wishing for a soft compound when you go over wet tree roots.

Tyre Grip

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For grip, is tyre size, tread pattern or rubber compound most important?

Tyre volume and rubber compound are the most important. The tread pattern, though important, is not as important as size & compound. A large tyre with a good compound and very little tread can give remarkably good grip.