Now totally confused about tyre pressures

by edd23   February 8, 2014  

Hi

This link was posted in another thread and I now have no idea what tyre pressures to run Thinking

http://janheine.wordpress.com/2010/10/18/science-and-bicycles-1-tires-an...

I weigh 62kg, my winter bike is 10kg and summer bike 7.5kg, according to the chart my tyre pressures (winter bike) should be approx. 75 psi front and 90 psi for the rears and summer bike pressures should be less.

Both bikes run 23mm tyres.

I have always been told 95 psi for the front and 110 psi for the rears.

I ride on mainly poorly maintained scottish 'B' roads.

Am I over inflated!! Rolling Eyes

12 user comments

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Probably.

harman_mogul's picture

posted by harman_mogul [121 posts]
8th February 2014 - 18:14

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So many people overcomplicate things. Vary pressures by 10 psi and find a setting that works for you.

You are the same weight as me. I never run more than 80 psi except for my time trial bike. I use lower pressures (and wider tyres) in winter, not higher, and don't bother with different pressures front and rear or on a lighter bike.

Simon E's picture

posted by Simon E [1941 posts]
8th February 2014 - 19:52

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What "you have always been told" is irrelevant. Most of people overinflate their tyres (thinking it makes them faster) or use too narrow tyres for their weight and road conditions.

A 15% tyre drop method described in the article is a pretty good starting point and sounds about right for your weight. If it works fine for you you can try dropping the pressure even more untill you start having getting pinch flats/rim strikes or handling issues.
On most of roads in the UK you're likely to be faster by dropping quite a few PSI.

P.S. One could also ask why you're using 23mm tyres on crap roads... They don't offer any advantages.

I don't follow trends. Trends follow me.

posted by BBB [178 posts]
8th February 2014 - 22:38

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Honestly I am not sure if I can tell the difference unless my tires are half inflated, I run 10psi less in winter but it all feels the same to me. But you are supposed to get more grip, don't complicate things and just ride.

pants's picture

posted by pants [73 posts]
9th February 2014 - 13:31

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Does it not depend on what tyres you are using?

I know the Michelins have a graph on the box, which suggests I run them around the 90-95 psi mark. However IIRC, my Onza tyre has a minimum of 110 and max of 140, the Specialized Roubaix are 100-120 psi, yet the Bontrager is 80-110.

posted by Yorkshie Whippet [289 posts]
10th February 2014 - 13:53

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Well I'm no expert, but I much prefer the feel of the tyre at near it's max pressure, it's not freezing in London.

Lower pressures have higher risk of pinch flats and god knows I get some nasty bumps off of potholes from time to time.

Aren't lower pressure tyres more effort because you're losing energy to the flex of the tyre?

And pressure depends on the tyre itself, the max for mine is already low at 115psi.

posted by kie7077 [451 posts]
10th February 2014 - 13:59

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kie7077 wrote:
Aren't lower pressure tyres more effort because you're losing energy to the flex of the tyre?

Yes, that is why wider tires at the same tire pressure have less rolling resistance. They deform less. But high pressures cause the bike to jump over bumps sooner and spin more quickly when there is grit. The worse the roads are, the less advantageous high pressures are. Having the tires absorb some of the road bumps reduces fatigue.

Weight is also a major factor. A 100 kg rider will put almost twice as much weight on a tire as a 50 kg rider, so obviously that 50 kg rider gets way less tire deformation at the same pressure. So it would be silly for both riders to have the 'same' tire pressure, since the tires will behave differently for these riders even if they run the same tire pressure.

posted by Aapje [167 posts]
10th February 2014 - 16:24

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For your scenario 80-90psi front and rear is fine. Do consider going to 25mm or larger tyre (25mm will fit nicely on your rim) for comfort.

Simple Rule of Thumb Regarding Tyre Pressures
If the tyre 'squirrels' when your riding or the rim touches the floor - Put more air in.
If you can tell the brand of the cigarette butt you ran over - Take air out.

posted by levermonkey [358 posts]
10th February 2014 - 22:15

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120psi front and back, one-twenty just sounds pro. Ninety-five sounds like the pressure a sucker fool would ride.

posted by Nick T [792 posts]
10th February 2014 - 23:10

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Nick T wrote:
120psi front and back, one-twenty just sounds pro. Ninety-five sounds like the pressure a sucker fool would ride.

damn tootin mate, like me, it's just not hardcore enough unless its over 100 psi

Summer, winter, raining, shitty roads, anything else to us older guys feels like a puncture!

Then again, I ride tubulars 8 months of the year at mega pressures, always have since I was at school and told in no uncertain terms that anything less was for the likes of John Inman.

Can't get the hang of lower pressures, too stuck in my ways.

All Campag

posted by Flying Scot [522 posts]
10th February 2014 - 23:41

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My perfect tyre pressure is when I pump them to 120 psi and I have a week of teeth rattling. After that I have a window of about a week where the tyres are bouncy and the bike feels amazing. And then I have to pump em up again. Ive tried getting the perfect PSI but I never seem to get that sweet spot

posted by dunnoh [172 posts]
10th February 2014 - 23:47

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A week? I have to pump my latex lined tubs up before every ride.

posted by Nick T [792 posts]
11th February 2014 - 8:09

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