Turbo trainer tyre pressure

On the road, softer is faster. On a turbo, it is the opposite — and getting it wrong quietly changes every power number you record.

## This is the opposite of road tyre pressure advice

Everything written about tyre pressure in the last decade has pushed in one direction: lower. Wider tyres, less pressure, better grip, lower rolling resistance on real roads, more comfort. That advice is correct, and on a turbo trainer it is exactly wrong.

On the road, a slightly soft tyre deforms around bumps instead of lifting you over them, and you lose less energy. On a trainer there are no bumps. There is a perfectly smooth steel roller, and every bit of deformation in your tyre is energy turned into heat and rubber dust instead of resistance.

So on a trainer you want the tyre hard: near the printed maximum. A hard tyre runs cooler, lasts longer, makes less noise, slips less and — the part that actually matters — gives a resistance curve that stays the same from one session to the next.

## The three things that change your numbers

A wheel-on trainer does not measure your power. It infers it, from how fast the roller is turning and a stored curve of how much resistance it should be producing at that speed. Anything that changes the contact between tyre and roller changes what that inference produces.

Tyre pressure. A tyre twenty psi down will read noticeably low and will drift further as it heats up. Tyres lose pressure on their own — several psi a week is normal — so a pump before every session is not fussiness, it is calibration.

Roller tension. How hard the roller is pressed into the tyre. Too little and it slips, especially when you stand up or sprint. Too much and you are adding resistance the trainer does not know about, so you work harder for the same reported watts. The fix is a routine rather than a number: wind it in until it just touches the tyre, then exactly the same number of turns past that every single time. Two is a common choice. Write it on a sticker if you have to.

Temperature. Rubber and steel both expand. A trainer calibrated cold will read differently once everything has warmed up, which is why every manufacturer tells you to spin down after ten minutes of riding and why almost nobody does.

Get all three consistent and a wheel-on trainer is perfectly good for training. Change them at random and your power numbers mean nothing week to week.

## Trainer tyre or road tyre?

A trainer tyre is made of a harder compound designed to survive being pressed against a hot steel roller for hours. It will last a very long time indoors, run quieter, and shed far less of itself onto your carpet.

An ordinary road tyre works perfectly well and will be destroyed. The roller wears a flat band into it surprisingly quickly, and the black dust everywhere is your tyre leaving.

If you ride indoors more than occasionally, a trainer tyre on a spare wheel is the answer: no swapping, no compromise, and your good tyre stays on the bike for the road. If you only ride indoors in bad weather, a road tyre is fine and you will simply replace it sooner.

Never ride a trainer tyre outdoors. The compound that makes it survive the roller gives it almost no grip in the wet. They are usually made in a lurid colour for exactly this reason.

## If you are shopping for a trainer

The honest summary: all of this is why direct-drive trainers took over. Take the wheel off and the tyre, the pressure, the tension, the slip, the noise and the dust all stop being your problem, and the power figure becomes far more repeatable.

A wheel-on trainer is still a perfectly reasonable way to train, and it is a great deal cheaper. It just needs a routine. The routine is: pump it hard, tension it the same way every time, warm up, spin down.