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  1. #1
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    Max tyre pressure

    When working out your max tyre pressure should the weight of the rider and extra equipment such as bags be taken into consideration? Or can you pump up to the max pressure specified by your tyre without this extra load?

    My tyres say max 35-65psi - I'd like to pump up my tyres to the max. Will this mean I can pump up to 65psi with no additional weight in the bike?

  2. #2
    Clyde on a mission!
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    I think you're looking at it the wrong way, on a mountain bike it's normally about how low pressure you can get away with without getting that wobbly feeling. On tarmac high pressure is good as it lowers rolling resistance, but on anything that's not smooth as a pool table, you're better off with low pressure.

    Lets say you ride a gravel fire road with your tires inflated to the max. Every time the tire hits a small rock the tire doesn't deform much so the whole bike has to make a small upwards motion to clear the rock. If you run your tires at a lower pressure, the tire will deform and absorb the small rock while the rest of the bike remains at the same height. Having a lot of pressure in the tires will actually increase the rolling resistance unless the surface is silky smooth.

    So try with a low pressure. If the bike starts feeling wobbly then add some air. Low pressure makes it roll better over rough terrain and you get more grip as a bigger part of the tire is in contact with the ground, it's win-win. Personally I run 30-35 psi which seems to work well for a 250# clyde like me..

  3. #3
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    yeah it really depends on where you ride. if you are riding on concrete, it doesn't matter how much you weigh, the max psi is for the tire itself.

  4. #4
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    I usually run 35psi for off road however I'll be using my MTB for commuting which will mainly be on paved bike paths. That being said I'd like to run a high psi and given the tyre says 65psi is the max, I was wondering whether this is what I should inflate the tyres to or whether I should inflate lower than this to accommodate body weight and bags.

  5. #5
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    the max psi is fine, the tires will still sag from the weight. if you're running paved, you're probably better off running street tires on it.

    Amazon.com: Kenda K838 Slick Wire Bead Bicycle Tire, Blackwall, 26-Inch x 1.95-Inch: Sports & Outdoors

    i have these and love them. they're pretty cheap too, totally worth it.

  6. #6
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    Those tyres are cheap! But unfortunately I'm at a stage where I don't want to be switching tyres between offroad and bike path rides so will stick with the full knobby tyres for now. I'll be slower but I can live with that for now.

    I'll just pump up my tyres to 65psi - thx for everyone's help.

  7. #7
    Flow like water
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    Just for fun, try different tire pressures. The roadies are even discovering that high pressure is not always lowest rolling resistance. Since you are going to be commuting, you are in a good position to do some testing. If you keep some records of your commute, with travel time recorded, you can compare highest with lowest pressure.

    The reason I suggest this is that high pressure feels faster because there is more shock and vibe. A more compliant tire at lower pressure is smoother. Check the travel times and note the feel to see actual results. The roadies have found that a 115psi tire feels fast, but a 90 psi tire may actually roll easier.

  8. #8
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    DavyRay, where did you hear this info? It's all news to me...

  9. #9
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    Quote Originally Posted by podoco View Post
    DavyRay, where did you hear this info? It's all news to me...
    This has been common knowledge to mountain bikers for quite some time podoco. As Sandrenseren noted, unless the surface that you are riding is very smooth, think new asphalt, it is very likely that any tire that you chose will roll faster and smoother at less than maximum pressure. When searching for the right pressure there are plenty of variables, rider+gear weight, riding style, tire size/volume, road/trail surface conditions, etc. It's just take our Roadie brethren a bit longer to catch on. Anyway, there are limits of course. Go to low and you'll pinch flat all the time. But running max pressure can be uncomfortable and a slower as well.

    In answer to your original question. No maximum pressure is not limited by rider and gear weight. The maximum pressure listed on bike tires is the max that the tire carcass will withstand and still stay on the rim. There is a bit of wiggle room there though. When tire manufacturers test for max pressure, they inflate the tire until the carcass fails or the tire blows off the rim. This is done several times and failure pressure is averaged. From there they set max pressure by a healthy percentage below average failure pressure. There are other test done as well, but that's the biggy.

    But do experiment with your pressure. I commute on a converted 26" MTB quite regularly. I'm running pavement tires that are 2.0" wide, and that have a pressure range of 35 to 65 psi. For the road and path conditions that I ride and my weight and load, I've found that 40 psi is the sweet spot for my current tires. At 65 psi I could feel every crack in the pavement and every pebble that got in the way. And the bike is faster, because the tires "give" a little and allow me to maintain control at higher speeds over rougher sections of pavement.

    So experiment a bit. You may find that running less than max pressure is both more comfortable and a little faster as well.

    Good Dirt
    "I do whatever my Rice Cripsies tell me to!"

  10. #10
    Fat-tired Roadie
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    OP - I'm lucky enough (and it probably says something about my priorities too) to have a few bikes. So it's very rare for me to ride my mountain bike on the road for long enough to consider messing with the tire pressure. But IME, max. pressure is probably too high, even for riding fat tires on the road. There's a certain amount of deformation you want the tire to have when you're sitting on the bike. Supposedly 15%, but I have no idea how I'd go about measuring that. Given how big a mountain bike tire is, and how big the contact patch becomes with even a very small amount of deformation, it doesn't take as much pressure to prevent that amount of deformation as it would in a road tire.

    Play around with it. Try adding 10 psi or so from your off-road pressure and keep going up until you get good manners from your tires - no squirming or wallowing. I bet it happens at less than 65 psi, and it's probably going to be pretty close to your optimal road pressure.

    I never wanted to deal with swapping tires either. A complete road bike from the late '80s or early '90s is cheaper than a complete wheelset, especially since you'd need a new brake rotor and cassette too, not just the wheels and tires, and doesn't require messing around. I actually have something a bit more expensive for commuting now, but another thing I like about having a bike that's for commuting is that I can leave commuter stuff on it - a rack and fenders, different pedals - and not have to do a mode switch. I also don't have to leave my mountain bike, which I care more about, locked outside at school or work.

    Of course, your MTB will get you where you're going fine. But this is something to think about if you start thinking about spending some money on improving its utility.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  11. #11
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    not sure about that - on the road - the harder the faster UNLESS it compromises traction (rain etc) and UNLESS riding on cobblestone most of the time or similar roads, which do not belong to "road" category any more...

    for off road - yes - the philosophy is "as soft as possible without burping"... i am kinda sitting on the fence on this - would not go this low, but DEFINITELY would not go high as well... High - to me with tubeless setup - is anything over 32-ish psi.

    The sweet spot that i found is around 26-28 psi, using tubeless 2.20 tires, for my 200# riding weight...

    when not racing - i may even go lower...

    Schwalbe has a nice write up on one of their websites about why hard tires do not work as well as soft tires off road... it is very logical...

  12. #12
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    i swap my tires all the time... takes me 5 minutes. its really not hard to change a tire lol.. i don't know why people would invest hundreds of dollars on a new wheel set just for a set of tires when it reallyi doesn't take long at all.

  13. #13
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    Quote Originally Posted by podoco View Post
    When working out your max tyre pressure should the weight of the rider and extra equipment such as bags be taken into consideration? Or can you pump up to the max pressure specified by your tyre without this extra load?

    My tyres say max 35-65psi - I'd like to pump up my tyres to the max. Will this mean I can pump up to 65psi with no additional weight in the bike?
    Yes it means you can pump it up to 65 psi not matter what the load...(if the load is too heavy the tire will flatten out and get squirmy)...

    Please note some rims have inflation limits that are often lower than the tires...

    Mostly UST rims Mavic, Shimano, Stans.
    Last edited by jeffscott; 09-25-2012 at 01:21 PM.

  14. #14
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    Quote Originally Posted by ou2mame View Post
    i swap my tires all the time... takes me 5 minutes. its really not hard to change a tire lol.. i don't know why people would invest hundreds of dollars on a new wheel set just for a set of tires when it reallyi doesn't take long at all.
    I have three different wheel sets one for slicks, one for knobbies and one for studs....

    I ride 5 to 6 days a week....it gets old changing tires.
    Last edited by jeffscott; 09-25-2012 at 01:17 PM.

  15. #15
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    Quote Originally Posted by ou2mame View Post
    i swap my tires all the time... takes me 5 minutes. its really not hard to change a tire lol.. i don't know why people would invest hundreds of dollars on a new wheel set just for a set of tires when it reallyi doesn't take long at all.
    Because some people run sealant.
    No, YOU don't understand. You're making an ass of yourself for all of eternity.

  16. #16
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    Quote Originally Posted by jeffscott View Post
    I have three different wheel sets one for slicks, one for knobbies and one for studs....

    I 5 to 6 days a week....it gets old changing tires.
    Agree about the max psi on the rim my ears still ringing from the tire exploding in my face

    I have 2 wheelsets for my XC Full suspension when I want to do a road ride on my Mt bike since I have a spare 29er disc wheel, why not?

  17. #17
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    Quote Originally Posted by ou2mame View Post
    i swap my tires all the time... takes me 5 minutes. its really not hard to change a tire lol.. i don't know why people would invest hundreds of dollars on a new wheel set just for a set of tires when it reallyi doesn't take long at all.
    I used to do this on my 26" bike. Then I got some free wheels and was so much easier. And once I went tubless I didn't even think about switching tires. Now I have a 29er tubless but can't afford another set of wheels. It sucks swapping tires back and forth and getting sealant everwhere. That reminds me, I gotta put my street tires back on tonight

  18. #18
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    Quote Originally Posted by osokolo View Post
    not sure about that - on the road - the harder the faster UNLESS it compromises traction (rain etc) and UNLESS riding on cobblestone most of the time or similar roads, which do not belong to "road" category any more...
    As someone else said, this has been proven wrong. even the roadies are dropping tire pressure and going faster. They're also moving to larger tires, and going faster.

    The max pressure your tire will take isnt necessarily the fastest. Its almost always not actually.

  19. #19
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    i always forget about tubeless setups lol.. i just don't see the benefit of tubeless, esp for my specific needs since i swap tires a lot.

  20. #20
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    Quote Originally Posted by One Pivot View Post
    As someone else said, this has been proven wrong. even the roadies are dropping tire pressure and going faster. They're also moving to larger tires, and going faster.

    The max pressure your tire will take isnt necessarily the fastest. Its almost always not actually.
    Agreed. I've dropped the psi on my road bike about 15 psi over the last few years...much nicer.

    Think of the knobs on your knobbies as bumps that a lower psi will help smooth out...or just pump em up to 65 psi and "enjoy" the buzz.

  21. #21
    Fat-tired Roadie
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    I kind of enjoy the way my knobbies hum when I ride the road with them. Not enough to do it often, which is probably part of what I enjoy about it.

    I only use 80 psi in the front tire (23 mm) of my nicer road bike. It's enough that it doesn't pinch flat or do anything weird, but low enough to much better compliance.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  22. #22
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    Quote Originally Posted by ou2mame View Post
    i always forget about tubeless setups lol.. i just don't see the benefit of tubeless, esp for my specific needs since i swap tires a lot.
    The reason I went tubeless is when I switched to light weight tires I would get flats every ride sometimes 2 a ride. Went tubless and haven't had any flats except a sidewall cut which I was able to ride back to the car just stopping to add air every 15 min. If flat tires wasn't an issuse for me then I would still be on tubes.

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