Author Topic: Tire Inflation Pressures  (Read 4112 times)

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cyclesafe

  • Guest
Tire Inflation Pressures
« on: January 11, 2006, 10:34:34 am »
OK, we know that rolling resistance and a higher incidence of pinch flats are inversely proportional to tire pressure.  In other words, the higher the pressure, the lower rolling resistance and the fewer pinch flats.

However, lower tire pressures mean a more comfortable ride and in the absence of suspension seat posts, suspension stems, or suspension shocks at the either end of the bike (a touring bike), having a lower tire pressure may be the only remaining means of smoothing out the ride.  I am assuming that the rider wears cycling gloves and will stand in the pedals to distribute her weight more evenly when anticipating bumps.

Tire width is dictated by the load the bike must carry and the worst road conditions that will be commmonly encountered during a tour.  So, given 35 mm tires with recommended tire inflation of, say, 50 to 85 psi, what is your experience / recommendation for rear and front tire inflation pressures that will work best for sustained rough surfaces such as those generally found in double track?  Would there be any significant improvement if, assuming they would fit the frame, a wider 40 mm tire were used?  50 mm?


Offline driftlessregion

Tire Inflation Pressures
« Reply #1 on: January 14, 2006, 07:32:58 pm »
The tire pressure stamped on a tire is the MAXIMUM pressure for that tire. Higher pressures do not give significant reduction in rolling resistance, especially for a tourist, to justify the reduction in safety that a stiffer tire provides. Lower pressure allows a tire to grab the road better and contrary to popular belief does not increase the possibility of flats. Al Ardizone of roadbikerider.com also claims that tires last longer at the lower pressure. I've forgotten what I ride touring with the 35's but when I ride 25's I put in 90# front and 95# rear despite being able to put in 120#. Some riders are using 85#. The handling is also far superior at the lower pressure.


cyclesafe

  • Guest
Tire Inflation Pressures
« Reply #2 on: January 14, 2006, 10:14:22 pm »
Thank you for responding.

Are there any heuristics that would help understand the optimum tire pressure versus maximum and the best relative pressure between the rear and front tire?  I would think that a 5% difference between the rear and the front would be unnoticeable.  I know there's no science here.....


Offline driftlessregion

Tire Inflation Pressures
« Reply #3 on: January 23, 2006, 12:29:42 am »
I'm sorry but I don't know. There is lots of discussion on other websites such as roadbikerider.com and I think Sheldon Brown weighs in as well. Basically, we have been fed bad information for years about tire pressure. I used to run my tires ABOVE the maximum to get that added rolling benefit. But it was an illusion. The difference just wasn't there. Harder tires are more prone to cut because they can't give and are too hard to grip on tight turns, not too mention the comfort factor.


Offline Dan

Tire Inflation Pressures
« Reply #4 on: January 26, 2006, 12:28:50 am »
Another thing to keep in mind is the psi rating on the rim.  While riding the GDMBR a few years back I started out using Mavic 517 rims(fairly narrow)with Specialized Armadillo Crossroads tires (max psi rating of 85).  About 2000 miles north of the Mexican border (riding north) I had a buldge on my rear rim.  I rode 80 miles to Kalispell,MT with the rear break released and it turns out the rim had a microcrack in the inside center the whole way around.  The bike mechanic in Kalispell said most rims have a psi rating and that the mavic 517's are only rated for 55psi.  I bought a sun Rhynolite and had the hub re-spoked with the new rim while I ate lunch across the street and was on my way in a few hours.  The front rim was still fine so I lowered the psi on the front tire and had no problemes the rest of the ride up to Jasper.  The Sun Rhynolite is much wider than the 517's and can handle the greater psi.  I feel the Rynolites are bette suited for off-road touring than the 517's which are more for XC mountain biking.


Offline Beep!Beep!

Tire Inflation Pressures
« Reply #5 on: May 19, 2006, 10:47:23 am »
In the days before tyre gauges was told if you can push your thumbs into the sidewall then the tyre is too soft. Another trick is to to bike on an uneven pavement with sticking up slabs or a raised drain cover, if the tyre is too soft you will feel the edge or worse bang the rim, of course cycle slowly. Another trick is to sit on your bike and see if you can see the sidewalls of the tyre, if too much shows then the tyre is too soft-hope this helps.