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Karyn S.
Karyn S. Sendmail

Tire Pressure

posted about 1 year ago | Report

Hey guys, I've been pondering this for a while. I know that higher tire pressure can help speed but can also increase the likelihood of flats. I usually ride at about 105 psi, since my pump gives a range for road bikes of 90-120.

What do you guys do on race day? Pump up to the 120 max to get the most out of your speed, or play it safe and decrease the likeliness of getting a flat?

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13 posts

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  • Ryan
    Ryan Sendmail

    I max out based on the rated tire pressure as opposed to the pump. Some tires it's 100#, some its 110#, others are 120#, etc.
    I go to the max, figuring I lose a pound or two when removing the inflator valve.
    Any flats I've had have been because of debris that poked through, where anything but a flat tire would be pierced - so I don't consider that in my evaluation of how much air to put into the tire.

    posted about 1 year ago

  • Dan M.
    Dan M. Sendmail

    There are full essays written on this subject. Here is an excerpt from Sheldon Brown :

    A tire is supposed to deflect a bit under load. This deflection the whole purpose of pneumatic tires. When you sit on your bike, your tires should visibly bulge out at least a bit under your weight. If they don't, they're overinflated.

    Here is a calculator: http://www.dorkypantsr.us/bike-tire-pressure-calculator.html The lower Michelin calculator seems closer to me.

    Over-inflation can cause the tire to bounce over pavement irregularities and create a harsh ride. Combined weight of the bike and rider should be taken into account, my tires would be over-inflated for you, and yours would be under-inflated for me (unless we are ±15 pounds of each other, I doubt it).

    It seems the biggest drawback to under-inflation is pinch flats. If you would like to get a headache research MTB air pressures.

    Finally once you find your sweet spot for pressure keep your tires there for both training and racing. If you change tire models or brands plan on changing pressure, but use the old tire's pressure as a starting point.

    posted about 1 year ago

  • Karyn S.
    Karyn S. Sendmail

    Thanks, guys. It's interesting that I had a somewhat wrong impression of tire pressure and it's impact on my biking. I'm definitely going to try and figure out what's the best fit for me now.

    posted about 1 year ago

  • Tommy G.
    Tommy G. Sendmail

    Edited due to incorrect advice!

    posted about 1 year ago | edited about 1 year ago

  • Dan M.
    Dan M. Sendmail
    in reply to what Tommy G. said:Edited due to incorrect advice!

    I have to disagree. I ride both bikes with about the same pressure f/r 105/110psi. I have Vittoria Rubino Pro 700x23c (max pressure 145psi) on one bike and Maxxis ReFuse 700x25c (max pressure 120psi) on the other. When I'm on the Maxxis the ride is harsh and squirrely when it's just me and the bike, since it's set up for commuting with an additional 15# of crap. I cannot imagine how bad the ride would be on the Vittoria at or near the maximum pressure.

    posted about 1 year ago | edited about 1 year ago

  • Tommy G.
    Tommy G. Sendmail

    Your comparing two different sets ups. Where is your logic? That is like me comparing my set of Fulcrum racing 6's with specialized tires, to my full carbon Envy's with race tires.

    The Original poster seems like she is asking for when she is riding. Again, just fill the tire to spec. Unless she is racing, and willing to spend a couple grand on some rims designed for racing, there is nothing else she can do except fill the tire to max listed on the side wall.

    posted about 1 year ago

  • Karyn S.
    Karyn S. Sendmail

    Hmm, I think I will just compare what the calculator tells me is optimal with my max and see if I notice a difference. I am racing... But just at a very amateur level, so definitely no thousand dollar rims in my future.

    posted about 1 year ago

  • Morey B.
    Morey B. Sendmail
    in reply to what Karyn S. said:Hmm, I think I will just compare what the calculator tells me is optimal with my max and see if I notice a difference. I am racing... But just at a very amateur level, so definitely no thousand dollar rims in my future.

    Tommy's just wrong on this one. He probably fills his car tires to the max limit on the sidewall as well.

    that's OK, not everyone has an engineering mind. He's probably a really nice guy, that just doesn't understand the rather complex principles behind bicycle tire design.

    One of those calculators gave me some wrong numbers. But here is a pretty standard chart... direct from one of the world's preminant bicycle tire manufacurers.
    http://www.michelinbicycletire.com/michelinbicycle/index.cfm?event=airpressure.view

    posted about 1 year ago

  • Dan M.
    Dan M. Sendmail
    in reply to what Tommy G. said:Your comparing two different sets ups. Where is your logic? That is like me comparing my set of Fulcrum racing 6's with specialized tires, to my full carbon Envy's with race tires. The Original poster seems like she is asking for when s... read more

    OK, let's not get into a pissing contest.

    My logic is the wider the tire, the less air pressure needed. The maximum pressure listed on the sidewall has far less to do with the ride comfort and stability as the total weight of cycle, rider and additional weight that is added.

    I am at a loss as far as the difference the rim or wheel would make on this discussion, you will be maxing out the pressure regardless.

    If you would like to continue this dialog, feel free to PM me.

    posted about 1 year ago

  • Bryce H.
    Bryce H. Sendmail

    I used to run 125# on my Specialized. So when I got my Cannondale the Schwalbe tires maxed at 110# and found this to be smoother and less vibration and faster. So I started running all my bikes at 110#.

    I ride on Vittoria tyres so when went to their website the actually had a spread sheet on optimum pressure per type of tire and body weight.

    posted about 1 year ago

  • Tommy G.
    Tommy G. Sendmail

    Im not getting into a pissing contest. You compared two different rims in your original post. I didn't mean to confuse you. Sorry!

    posted about 1 year ago

  • Tommy G.
    Tommy G. Sendmail
    in reply to what Morey B. said:Tommy's just wrong on this one. He probably fills his car tires to the max limit on the sidewall as well. that's OK, not everyone has an engineering mind. He's probably a really nice guy, that just doesn't understand the r... read more

    How I fill my tires is dependent on what I am doing with my car. I use to race cars and owned a performance shop in Florida so Im a little versed with tire pressure on cars. But that is beside the point because we are talking about bicycles!

    But your right, I guess I don't understand "the rather complex principles behind bicycle tire design." When the OP asked what people fill there tires to when they race, I assumed filling the tire to the max PSI listed on the tire was somewhat "accurate" advice.

    No biggie, Im here to learn. Thanks for posting the chart!

    posted about 1 year ago

  • Ray G.PRO
    Ray G. Sendmail

    That's a great chart, Thanks for sharing the info! :)

    posted about 1 year ago

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