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  1. #1
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    Tire pressure for the heavy rider

    Hi there,
    I figure right now that since I own a mountain bike it might be worth tryint to start riding it that way, if even for a bit of fun. Now mostly I ride on roads and I have have the original set of MTB tyres on there. I do own a set of slicks but it seems a waste not to use the tyres that came with the bike - plus it's a pain to switch them over,

    Now I tend to run my tyres at the maximum written on the sidewall but I know for offroad you should decrease that for better traction. However, that of course increases the risk of pinch flats from my heavier weight. So, what would be a good pressure value to start at? I'm currently about 215lbs riding a Trek 3900. As for riding, it won't be anything too exciting since I am really starting out, you know...walking up and down the scary hills. I've already ridden around the flatter firetrack type areas OK with the max pressure but even on this style of track I am thinking a reduction would be good.

    That leads to another question. If riding on roads at the same (reduced) pressure you would offroad does it increase the risk of a pinch flat compared to riding offroad? The places I would ride offroad are pretty close to where I live, so I would just ride there, on the roads.

    Thanks for your help and sorry or being long winded.
    I want to live.

  2. #2
    Air
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    Destroyer of Wheels Air's Avatar
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    Get the Topeak Road Morph, pump up the tires when you're on the road, decrease it a little when you go offroad, pump it up again on the road

    In terms of pressure - what does the actual sidewall say? You won't be going as fast offroad as you would onroad (probably) so you have less to worry about with pinchflats, but you shouldn't ride them so low that you need to worry about it. I'd say experiment but about 30% less may be about right.

  3. #3
    The Site Administrator: Currently at home recovering from a couple of strokes,please contact my assistnt admins for forum issues Tom Stormcrowe's Avatar
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    I'd start out at about 80% of max rather than 70, other than that, I agree wholeheartedly with the carry a pump and vary the pressure between 100% for road and reduce for offroad.
    on light duty due to illness; please contact my assistants for forum issues. They are Siu Blue Wind, or CbadRider or the other 3 star folk. I am currently at home recovering from a couple of strokes. I am making good progress, happily.


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  4. #4
    Amateur stunt driver D0ugB's Avatar
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    for some reason I like to use 45# as my minimum (I have seen snakebites below that) with MTB tires I try to stay at 50 - 55 # on my Cyclocross tires when racing. Just my observations
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  5. #5
    Senior Member jboyd's Avatar
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    Sounds like you are using your bike like me. I have a Giant Rainier and primarily use if for road, but probably one ride a month has been a single track trial, with drops and hair pins :-)

    I changed my tires out to allow this hybrid use. The bike came with knobs, so I switched them out for a tire that has a couple rows of cleats on each side, but are slick on top. The slick is great for the road and the cleats do their job on curves.

    The range on these tires are 40 - 65 psi. When I road ride, I actually pump them up to 70psi. For the trails, I operate between 40-50 psi. So far this has worked OK.

    Good Luck
    Jay

  6. #6
    Gravity Is Yer Friend dirtbikedude's Avatar
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    I will not tell you what to use. Rather I will give ya a suggestion and let you know what I use for pressures.

    Suggestion, if you have stiff sidewalls on the tire I would say drop the psi 25%. If the tires have a soft sidewall then I would say 20% drop in psi. This would be a starting point and riding style/terrain would dictate where to go from there.

    These are current psi readings, I am at 285 right now and when I get back to race weight (235-245) I will drop the PSI 3 more pounds. The terrain I ride varies from hardpack with loose top coat and some slick rock with deep gravel in some of the creek beds. Oh yeah, I have not had a pinch flat in 6yrs.

    My 2.1 xc tires are run at 34fr/36rr (suggested 50psi/MAX 65psi)

    My 2.5 freeride tires are run at 30fr/32rr (suggested 29/MAX 36)

    My 2.3 DH tires are run at 26fr/29rr (suggested 36/MAX 65)

    How I determine those pressures, I start at 25% of max and ride a section. I then adjust the pressures accordingly, meaning, if the front pushed to much or the rear drifted I would lower the psi. If the bike railed through the corners but would not roll well on the flats I would raise the psi. Then just do the procedure over and over until I was happy with the results.

    Granted, I did this years ago and still run the same type of tires so I know what I need when I swap 'em out.

    DBD

  7. #7
    Downtown Spanky Brown bautieri's Avatar
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    My tires max out at 80lbs. I usually run them about 60lbs when I'm off road so a reduction of 25% does the trick for me. Usually there is just a bit of sag in the tire at 60lbs, enough to maximize the tires surface area without pinching over rocks and other fun stuff. When I'm in commuter mode I generally run them about 75lbs. I personally wouldn't worry about running the miles on road to the trails at a reduced pressure, but if it irks you you could always get a frame pump and adjust as needed.

    Bau

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    Mine max out at 60PSI... I ran them at 55PSI and it wasn't enough; I'm going to put in 60PSI and leave it at that as most of my driving is urban.

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    Senior Member Not the Slowest's Avatar
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    First : Topeak road Morph has higher PSI for Road bikeas and a smaller barrel. A good choice , but they have one for MTB, Hybrid with lower PSI. Either way its a GREAT pump.

    Next:
    On the road, use the higher suggested PSI or a bit lower on rainy days for more grip.
    If you run too low you can get pinch flats or the tire will square off on the bottom.
    You also will not have the same grip on turns.

    I weigh 210 and always pump to the suggested PSI on the rear and maybe 10 less on the front, but one rule that helps. Make sure your WHEEL can take a HIGH PSI. Some road wheels max out at say 120-125, but tires can go 135-160.

    Rob
    Robert
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    I have a somewhat different issue with tyre pressure - I don't seem to be able to keep the air in the tube. I always seem to finish my ride 15-20PSI down from where I started. I'm riding a pretty bog standard 26" rim Trek mountain bike. Can anyone recommend any high-pressure tubes that can actually take high-pressure (50-60PSI)+my weight (around 230lbs)? Thanks in advance.

  11. #11
    Air
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    You have a slow leak. If you've tried changing the tire for a new one and that didn't work examine the inside of your rim really, really carefully - there might be something that's causing that or you might be pinching. Also closely examine the inside of the tire and see if there's a tiny piece of glass sticking through - you have to pinch and squeeze the tire to find it.

    Take the tube off the tire, fill it with air (t should get huge, wait till it's about 3" in diameter) and submerge it in the bathtub - you should see some air bubbling up).

  12. #12
    On my TARDIScycle! KingTermite's Avatar
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    I almost always run my tires at (or close to) MAX PSI. If I were smaller, I'd probably ease off a bit.

    Don't you guys that are big and run the PSI lower see low wheels when you ride? Traction has got to be too high....and what is it doing to your rims?
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  13. #13
    Senior Member Not the Slowest's Avatar
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    Quote Originally Posted by zultan View Post
    I always seem to finish my ride 15-20PSI down from where I started. I'm riding a pretty bog standard 26" rim Trek mountain bike. Thanks in advance.
    ditto on the leak or, if using presta tubes, make sure you close the valve.

    Check the tubes, or just put new ones in and then patch the oldies,
    FIRST, inspect the tire slowly for something embeded in it. Take it off the wheel, bend it on the outside so you can see if a staple, glass etc is embedded, then do the reverse on the inside.

    I do that EVERYTIME, I get a flat.
    Also check your tires after you get home. If you remove anything on or in the tire, its one less thing to deal with

    Rob
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  14. #14
    Air
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    I usually run my tires at 110% of max in the rear, don't have flat issues.

  15. #15
    The Site Administrator: Currently at home recovering from a couple of strokes,please contact my assistnt admins for forum issues Tom Stormcrowe's Avatar
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    Quote Originally Posted by Air View Post
    I usually run my tires at 110% of max in the rear, don't have flat issues.
    I think I know why you trash rear wheels now! Try dropping to 100% The tire needs SOME flex to ease shock to the spokes.
    on light duty due to illness; please contact my assistants for forum issues. They are Siu Blue Wind, or CbadRider or the other 3 star folk. I am currently at home recovering from a couple of strokes. I am making good progress, happily.


    . “He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you.”- Fredrick Nietzsche

    "We can judge the heart of a man by his treatment of animals." - Immanuel Kant

  16. #16
    Air
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    There's still plenty of bulge when I sit on it.

    Quote Originally Posted by 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.

    <snip>

    Most tires have a "maximum" pressure, or a recommended pressure range marked on the side of the tire. These pressure ratings are established by the tire manufacturers after consultation with the legal and marketing departments.

    The legal department wants the number kept conservatively low, in case the tire gets mounted on a defective or otherwise loose fitting rim. They commonly shoot for half of the real blow-off pressure.

    The marketing department wants the number high, because many tire purchasers make the (unreliable) assumption that the higher the pressure rating, the better the quality of the tire.

    Newbies often take these arbitrary ratings as if they had some scientific basis. While you'll rarely get in trouble with this approach, you will usually not be getting the best possible performance with this rote approach.

    Savvy cyclists experiment with different pressures, and often even vary the pressure for different surface conditions.

    Optimal pressure for any given tire will depend on the load it is being asked to support. Thus, a heavier rider needs a higher pressure than a lighter rider, for identical tires.

    Since most bicycles have substantially more weight on the rear wheel than on the front, the rear tire should almost always be inflated to a higher pressure than the front, typically by about 10%.
    By the time I take the valve off with the pssshhht of air being released it's probably just the right amount.

    (I run the same amount on the front too - sshhhhh! )

    [ed - The first wheel was tensioned so poorly that when I sat on the bike the spokes bowed out and rubbed the deraileur! Hard to argue that air pressure had something to do with that.]
    Last edited by Air; 10-25-07 at 04:04 PM.

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