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Thursday, July 9, 2015

Technical FAQ: Minimum tire pressure and more

Photo: Caley Fretz | VeloNews.com

On minimum tire pressure


Dear Lennard,
I read with interest your reply to Manny with regard to 25mm tyre pressures. I recently purchased 25mm Vittoria Open Corsa SC tyres, and these are clearly marked with “Clincher MIN to MAX pressure: 115 to 145 PSI.” This seems quite unreasonably high to me, so I’m wondering what is a safe minimum pressure to use with 25mm clinchers (would be interesting to hear from your contacts at other tyre manufacturers), and why does Vittoria see the need for such a high minimum pressure?
— Simon
Dear Simon (I sent this answer directly to Simon),
Here is the response to your question from Vittoria:
According to ETRTO, bicycle tires are allowed to deflect 30% of its height at maximum load only. We respect the ETRTO, but we do not limit the body weight of our customers. 115PSI minimum air pressure is the consequence for our high-end 25mm tire with its very flexible casing; the minimum air pressure is related to the worst case: heavy load, rear wheel, aged tire.
We will address this matter more precisely on our MY16 new models.
— Christian Lademann – Product Manager
Vittoria S.p.A.
I’m not going to tell you to do anything differently with your Vittoria tire than Vittoria’s product manager just told you. However, since you’re asking generally what minimum pressure you can with 25mm clinchers in general, I can answer it generally. The safe minimum tire pressure is certainly a function of rider weight, and you’ve not given me yours. I, at 174 pounds, have ridden safely for extended periods on many different 25mm clinchers, both standard clinchers and open tubular clinchers on smooth roads, at as low as 75 psi in the rear and 65 psi in the front. I haven’t measured to see if I get over 30% tire drop at those pressures, but tire squirm is not an issue for me at those pressures...

Read more at http://velonews.competitor.com/2015/05/bikes-and-tech/technical-faq/technical-faq-minimum-tire-pressure-and-more_369794#FiC6P8I2FuHcyQeE.99

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