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  1. #1
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    Is it safe to overinflate?

    Do any of you guys overinflate your tires?

    I am running 25c gatorskins to max recommended psi (120) and still squish the rear tire quite a bit. I would like to reduce this squat, but am not sure how much to inflate it to, or if it would be safe.

    Any thoughts?

  2. #2
    Senior Member socalrider's Avatar
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    I usually go up to 130 with no issues on gatorskins.. It makes for a little rougher ride but it helps eliminate pinch flats quite a bit..

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    Senior Member Wogster's Avatar
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    Quote Originally Posted by ochizon View Post
    Do any of you guys overinflate your tires?

    I am running 25c gatorskins to max recommended psi (120) and still squish the rear tire quite a bit. I would like to reduce this squat, but am not sure how much to inflate it to, or if it would be safe.

    Any thoughts?
    Inflating tires beyond the recommended is usually okay. Most tire pressure limits are lawyer limits. Let me explain that the engineer designs a new tire capable of say 180PSI, the legal department, wanting to prevent lawsuits from exploding tires, want a low limit. Marketing wants a high limit because people have the idea that a tire with a high pressure limit is a better quality tire, better quality means you can get a higher price so accounting will ask them to negotiate. If 120 is the agreed upon amount, then that's what is on the tire sidewall.

    The problem we don't know as tire purchasers is who won the battle, if it's legal there could be quite a bit between the design limit and the moulded in limit, if marketing won the battle it could be fairly close. Pumps with guages could be a little high or a little low too. I wouldn't go above. Now realise something else, you actually want the tire to squish down a bit, if it doesn't then you could rattle your teeth out, especially on a stiff aluminum frame.

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    Quote Originally Posted by Wogsterca View Post
    Now realise something else, you actually want the tire to squish down a bit, if it doesn't then you could rattle your teeth out, especially on a stiff aluminum frame.
    I know you want it to squish some, but mine squishes a lot! I weigh 300lbs.

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    If you go too far, you'll blow out the sidewall on your rim. Though that's pretty darned high. I don't know how far you can safely over inflate those tires. If you don't mind experimenting and possibly having to replace a rim, experiment.
    -------

    Some sort of pithy irrelevant one-liner should go here.

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    You don't need to overinflate just because it squishes. Unless you are getting pinch flats, then you are inflating high enough. You could also try 28 tires if they fit in your frame.

  7. #7
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    Quote Originally Posted by hammond9705 View Post
    You don't need to overinflate just because it squishes. Unless you are getting pinch flats, then you are inflating high enough. You could also try 28 tires if they fit in your frame.
    cool deal. I do not get pinch flats, so I guess Im good. Thanks!

  8. #8
    Senior Member Wogster's Avatar
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    Quote Originally Posted by ochizon View Post
    I know you want it to squish some, but mine squishes a lot! I weigh 300lbs.
    It often seems to squish more then it does. Tire squish is caused by the fact that air pressure equalizes based on the load. Rider weight is distributed roughly 60/40 between the rear and front, At 300lbs that means there is roughly 180lbs on the rear wheel and 120lbs on the front wheel. With a skinny little 23mm wide tire the part of the tire that touches the ground is about 1" x 1" or 1 sq. in. With 180lbs on the rear tire, the contact patch needs to be 1 sq. in., the tire then squishes down to give you a contact patch that is 1 sq. in. To eliminate squish you need a tire that has a contact patch that is larger, a 35mm wide (or slightly wider) tire, that can be inflated to 120PSI should be about right

    A 35mm wide tire does not exist, so you could have 32mm with a bit of squish or slightly higher pressure or 38mm with a little less pressure. The problem is that many bicycle manufacturers have the idea that the only people who ride on the road are 120lb racers, so they make the frames only wide enough for a 23mm wide tire If your riding a road bike, ask your LBS or email the manufacturer to see how wide a tire you can use. Hybrids and mountain bikes take wider tires and many touring bikes can take wide tires. While this means you can use different width tires front and back, it's better to use the sane tire and if you like a lower pressure on the front.

    Tire pressure though is a compromise between two things the harder the tire the lower the amount of rolling resistance, the softer the tire the cushier the ride. If your going 35MPH trying to get the yellow jersey in a stage of the Tour de France then obviously you want a tire that is harder then the pavement. If your a Clyde going 9MPH trying to help your new diet along with some exercise, then all a rock hard tire is going to do is make riding uncomfortable, if it's not comfortable then you will not want to do it, and will quit. If your not getting pinch flats, it's okay, as I said you can always see if it's possible to fit a wider but still high pressure tire on there.

  9. #9
    member. heh. lambo_vt's Avatar
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    Good advice Wogster, but 700x35 tires exist. Here's one. There are also Paselas, Marathons, etc.

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    Quote Originally Posted by lambo_vt View Post
    Good advice Wogster, but 700x35 tires exist. Here's one. There are also Paselas, Marathons, etc.
    I think he meant that a 35mm tire that inflates to 120psi does not exist. I have no idea if that is true, but if it does I'm interested.
    __________________________________________________________________
    Shrinking steadily

  11. #11
    Senior Member Wogster's Avatar
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    Quote Originally Posted by lambo_vt View Post
    Good advice Wogster, but 700x35 tires exist. Here's one. There are also Paselas, Marathons, etc.
    stand corrected, didn't realise that there was anything between a 32 and a 38, unfortunately for our 300lb friend, the max pressure on the linked tire is 73PSI, so the weight limit without squish would be 109.5lbs a little short of the 180lbs (roughly) that we would require in this case. Effectively we need a 35mm tire that takes 120PSI.

    What is really needed in cycling is a touring tire, comes in a variety of widths (28,32,35,38,42mm), 700mm, 27", 26" and 20" sizes. It must be long wearing, puncture resistant, take pressures from 90-120PSI and comes in both folding and non-folding versions. Think about it, take a 150lb rider add 30lbs of bicycle and 50lbs of gear thats 230lbs, well into Clyde territory.

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    I'm 220lbs, and I run about 130psi in the front and 140psi at back. That's on Vittoria Rubino Slick's, 60TPI, 120 max psi. So far no problems, though I also run deep-v rims for strength. In my opinion, the biggest thing that's going to slow you down is rolling resistance (for clydes who like to go fast).

  13. #13
    Senior Member rdtompki's Avatar
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    Here's a link to what appears to be a credible article on tire pressure:

    http://www.adventurecycling.org/reso...SIRX_Heine.pdf

    I'm headed toward putting 32mm on my tandem versus the 28mm Ultra Gatorskins that I'm running now. Our full-up weight including tandem I would estimate at 380 lbs which is clearly clyde territory. I'm wondering if the tandem isn't closer to a 50/50 weight distribution since I'm considerably heavier than my wife which helps some
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  14. #14
    member. heh. lambo_vt's Avatar
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    Quote Originally Posted by Servo888 View Post
    I'm 220lbs, and I run about 130psi in the front and 140psi at back. That's on Vittoria Rubino Slick's, 60TPI, 120 max psi. So far no problems, though I also run deep-v rims for strength. In my opinion, the biggest thing that's going to slow you down is rolling resistance (for clydes who like to go fast).
    When I started on my road bike with 700x23 Rubinos I was about 210-215; 130/140 psi seems very high to me, and those seemed like especially harsh tires.

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    I'm running slicks on a 2" wide mountain bike tire. Even at 65 lbs pressure, there is minimal squish.

    I find the rolling resistance is suitable for commuting. My speeds don't match the fast bikes, but I'm ussually riding alone.

    I've also noticed that my ride averages 90 minutes, no matter what my riding speeds are. The route and traffic lights must regulate my time more than I figured.

  16. #16
    Senior Member socalrider's Avatar
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    Quote Originally Posted by lambo_vt View Post
    When I started on my road bike with 700x23 Rubinos I was about 210-215; 130/140 psi seems very high to me, and those seemed like especially harsh tires.

    60tpi tires are going to be a little harsh especially at max pressure.. If you had run the rubino pro II they would have a more comfortable feel at the high pressure.. They wear much quicker though..

  17. #17
    Serious Newbie Aleforge's Avatar
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    I posted a similar question in the off topic thread as I had no idea this one existed.

    http://www.bikeforums.net/showthread...=1#post9062463

    I don't want to double post so I thought I would chime in on this topic.

    I have cheap tires that came with a cheap bike, the PSI range is 40-50. Obviously by reading above its usually ok to push it a little higher if needed. How high would you guys think would be ok to try on such a low rated tire?

    Thanks and don't mean to hijak!

  18. #18
    Senior Member bbeck's Avatar
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    i run 700x25c on mine and have been inflating to 130 psi on any day with no problems.......until i aired up at the tour de cure here a week ago. i aired up at 6:00 am to 125 psi and i blew the tube out from under the tire @ 12:00 noon. the temp had went from 55 degrees or so to over 80 degrees. after talking to the lbs we came to think the pressure rose with the temps to the point it was way over pressured and blew. so if you go to 130+ psi on a cool morning you may want to watch your tire(s) as the temps progress through the day. i am now experimenting with 115 front and back to see how that does.
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  19. #19
    FNG destikon's Avatar
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    Be careful peeps. One time I eye-balled my mt bike tire at the convenient store are compressor (before I actually had tools and air). Everything was good. I made it home, took out my tire to put on my bike and BOOM!! It sounded like a *** shot. It blew out the sidewall of the tire as well. I'm thinking it wasn't just over inflation that did it. I had 2.2 tubes in 1.5 tires. Yeah, that's before I knew what the hell I was doing. That would be the *hits blowing going down a hill about 30mph.
    Quote Originally Posted by powers2b View Post
    time's up

  20. #20
    Senior Member DieselDan's Avatar
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    Quote Originally Posted by ochizon View Post
    Any thoughts?
    How about getting over the fact the laws of gravity, chemistry, and physics are against you. When you put weight on a tire, you will have deflection and deformation, no matter how much air you put in it. Get over your OCD and ride your bike.
    Bikes use brakes to stop.

    If your bike has breaks, don't ride it.

  21. #21
    creaky old bones FZ1Tom's Avatar
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    Aye, it's probably almost impossible to totally eliminate squish unless you happen to be a 120# female or Marco Pantani's ghost and ride tubulars at 200psi. At that point, sure

    As for me, I give my pump a couple extra strokes and run 85psi which is only 5psi over the recommended limit (Bontrager Select Inverts, 700x35 with 80psi max recommended on the sidewall). I can see a little bit of squish on the front and presumably the back has more (hard to see while riding), but it's not so much as to bother me.

    Just don't go whole hog - I'd say 10 percent over is probably safe, any more than that and you might be taking your chances

    Tom

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