High performance racing bicycle technology and technique
Richard’s Blog

 

Fine-tuning tyre pressure

 

Just 5psi may be enough

 

Posted 23 August 2012

 


First time out on Fulcrum’s new Racing Quattro clinchers I found the ride to be “fast and responsive but firm”. No real surprises there; the substantial deep-section rim is bound to be relatively inflexible and, when laced up using high spoke tension, is equally bound to give a ‘firm’ ride.

 

There are, for sure, circumstances in which ‘firm’ itself is a fine thing for a wheel to be: on a velodrome, for example. On regular, variable British tarmac, however, firmness can prove fine one moment and not so fine the next. Firmness does not provide much by way of shock absorption. And so, by the time I got home after some three hours of riding on Surrey’s least cosseting tarmac, my hands were tingling from road vibration.

 

Bicycle tyre pump gauge

 

Transmitted through the handlebars, the vibration had been generated through vertical movement of the wheel as it rolled over irregularities in the road surface. The rim of a less radially-stiff, less ‘firm’ wheel rolling on tyres inflated to the same pressure would have deflected a little more, soaking up – along with the spokes – some of the movement before it reached the hub. For sure, the Fulcrum ride proved noticeably more ‘vibey’ than that of the previous outing on the same bike, with the same tyres at the same pressure fitted to Shimano WH-7850 Dura-Ace wheels.

 

But then, there is nothing that says tyres have to be inflated to the same pressure for every wheelset. If a particular pair of wheels rides a little more firmly, then the obvious step is to let the tyres down. They, after all, are the primary suspension system in any lightweight road bike.

 

Adjustment is easier if you know how hard the tyres were when you found the ride too harsh. It’s one good reason to inflate tyres before every ride; not only do high-pressure cycle tyres lose perhaps 5psi overnight – depending on inner tube spec – but keeping them inflated to a specific pressure means they can be inflated accurately to a different one if desired.

 

In this case, that meant lowering front tyre pressure by 5psi to 90psi while leaving the rear at 105psi since there was no reason to change. All this assumes access to a pump with an accurate gauge, of course. Otherwise, it’s a case of letting a tiny bit of air out if the ride feels, well, overly firm.

 

In this case, 5psi was just right; result, no tingling of the hands at the end of the next ride while retaining the ‘fast and responsive’ feel of the previous one. It’s the tyres that do almost all the work of deciding ride comfort, after all.





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