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    Senior Member Hank244's Avatar
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    Lowering the PSI / Pinch Flats a Worry?

    I've read several posts about lowering psi in tires (for better grip).

    I weigh 240lbs. I run maximum pressures on my road bike tires. What pressure should I run my Nokian Extreme 294 (29er)?

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    gbg
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    Quote Originally Posted by Hank244 View Post
    I've read several posts about lowering psi in tires (for better grip).

    I weigh 240lbs. I run maximum pressures on my road bike tires. What pressure should I run my Nokian Extreme 294 (29er)?
    Well I am north of 240 and run nokian mount and grounds, 160 studs. I run them at full pressure all the time.
    Not only does it greatly reduce the chance of a pinch flat, I do not want to try to change a tire in -20,
    it decreases rolling resistance, and it also lets the tire cut through the snow to hit solid ground.
    The worst thing to cycle in is that "car snot" brownish sandy slop that is just thick enough to
    stop your tire from getting through to solid ground, and your like flailing between full lock left, full lock right
    as you move at about 1 mile an hour.

    At 240+ I really don't know what "snow conditions" would be better at a lower psi. It would have to be
    real weird hard packed snow that could semi support 300lbs of bike and rider, and I can't see that happening.
    You need to get the tire to the ground, especially the studs to the ground.
    Studs are pretty useless unless they hit ice.
    Last edited by gbg; 12-10-11 at 04:36 PM.

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    AEO
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    going by this, I'd say around 55psi for 2.1" tires and upwards of 240lbs.

    http://www.livestrong.com/article/24...tire-pressure/

    lowering tire pressure for better grip is only when your tires don't bite all the way down to the ground, which usually happens on deep powder snow or slabs of ice hidden inside snow banks. By deep, I'd say more than 2" on the ground
    Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
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    gbg
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    Quote Originally Posted by AEO View Post
    going by this, I'd say around 55psi for 2.1" tires and upwards of 240lbs.

    http://www.livestrong.com/article/24...tire-pressure/

    lowering tire pressure for better grip is only when your tires don't bite all the way down to the ground, which usually happens on deep powder snow or slabs of ice hidden inside snow banks. By deep, I'd say more than 2" on the ground
    I don't think they are talking about riding on snow and ice.

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    AEO
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    Quote Originally Posted by gbg View Post
    I don't think they are talking about riding on snow and ice.
    it doesn't really change, because the ideas and concerns are the same.
    You want grip more so than low rolling resistance, but you don't want tire pressure so low that you pinch flat on the bumpy sections.
    With the tires being really fat, they don't pinch flat as much as narrow tires, even if they are under inflated.
    Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Hank244 View Post
    I've read several posts about lowering psi in tires (for better grip).

    I weigh 240lbs. I run maximum pressures on my road bike tires. What pressure should I run my Nokian Extreme 294 (29er)?
    With a 2.1" tires, you could run them between 40 and 50 psi without worrying about pinch flats on smooth roads. I'm a similar sized rider and I run a similar pressure on 2.1" mountain bike tires in off-road conditions where there's a lot more opportunity to pinch the tire and I've never had a pinch flat under those conditions.

    I would think that around 60 psi is the max pressure on a tire of that width anyway.
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    gbg
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    Quote Originally Posted by Hank244 View Post
    I've read several posts about lowering psi in tires (for better grip).

    I weigh 240lbs. I run maximum pressures on my road bike tires. What pressure should I run my Nokian Extreme 294 (29er)?
    Actually I was considering some 294's and from what I read I am surprised you are having traction problems regardless of
    the PSI. What conditions are you riding in?

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    Still spinnin'..... Stealthammer's Avatar
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    I don't know what a 240lb rider can get away with, but at 170lb I will only drop my Extremes down to 40psi. Any lower and I can feel the sidewall flexing too much on any kind of impact, and I worry about pinch flats. For what it worth, I would suggest that you not go below 50psi without some testing....
    Just your average 'high-functioning' lunatic, capable of passing as 'normal' for short periods of time.....

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    Senior Member Hank244's Avatar
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    Quote Originally Posted by gbg View Post
    Actually I was considering some 294's and from what I read I am surprised you are having traction problems regardless of
    the PSI. What conditions are you riding in?
    I just mounted the tires today. I haven't ridden them yet. (Much easier to mount than road tires!!)

    I've seen several posts in different threads about lowering PSI to get a better grip. I'm brand-new to winter riding (have owned my mountain bike for a month), so I'm asking questions as I go along.

    My only experience lies with sunny-weather road riding. With road tires, I always run maximum pressure. I wanted to know if that was best for the Nokians, too.

  10. #10
    7-speed doomsday prepper ThermionicScott's Avatar
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    This article has some recommended minimum pressures for MTB tires based on bodyweight: http://www.bccclub.org/documents/Tireinflation.pdf
    Quote Originally Posted by chandltp View Post
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    gbg
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    Quote Originally Posted by Hank244 View Post
    I just mounted the tires today. I haven't ridden them yet. (Much easier to mount than road tires!!)

    I've seen several posts in different threads about lowering PSI to get a better grip. I'm brand-new to winter riding (have owned my mountain bike for a month), so I'm asking questions as I go along.

    My only experience lies with sunny-weather road riding. With road tires, I always run maximum pressure. I wanted to know if that was best for the Nokians, too.
    The problem with riding snow/ice it can go from rideable to impassible very quickly. Nothing like riding on a dry trail, unless
    you get a downpour and all of a sudden your are in 4 inches of mud.
    If you are riding in the city on packed trails etc I would say max pressure for the speed,
    and for guys like us will still compress the tires pretty good. One thing to consider is that 60psi at 75 degrees indoors
    is not 60psi at -20 (fill em up outside), but I don't know how cold you will be going. I would hope those 294's would hook up real well.

    If you want to start slogging off road and break your own trails good luck. Snow is a funny thing it really is only
    enjoyably rideable to a few inches, and you need a solid base below it. They didn't make snow shoes for nothing.

    Your studs really won't help in deep snow either, they help on ice and only ice.
    I would even say with that aggressive tread pattern to be very wary on the pavement as well.
    That's why I choose the ground and mounts, they are more forgiving on pavement.
    Last edited by gbg; 12-10-11 at 07:26 PM.

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    Quote Originally Posted by Hank244 View Post
    I've seen several posts in different threads about lowering PSI to get a better grip.
    I don't bother with that, and don't understand the point of it. On ice (I don't use studs) it won't make much of a difference. In snow, it's not like your rear tire starts spinning and you're helpless because of that. (not like a car)

    I run the same pressure winter and summer. My favorite size is 700 32. I'm 150 lbs and keep it at about 60 psi.
    mainlytext.com/bike.html Bicycling in winter, the entertainment version

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Closed Office View Post
    I don't bother with that, and don't understand the point of it. On ice (I don't use studs) it won't make much of a difference. In snow, it's not like your rear tire starts spinning and you're helpless because of that. (not like a car)

    I run the same pressure winter and summer. My favorite size is 700 32. I'm 150 lbs and keep it at about 60 psi.
    A lower pressure on a studded tire, especially on with knobs, would put more of the studs in contact with the pavement. A knobby tire pumped up to maximum pressure is going to ride on a very small foot print. Letting some air out allows more of the knobs to contact the ground and be more effective. That's one of the reasons why mountain bike tires are run at lower pressures.

    Look at this picture of the Nokian tire that Hank244 is using



    At high pressure, even the studs that run near the middle are going to have minimal engagement. Lowing the pressure will bring the side studs into play. And there are several studded tires that have no studs down the middle of the tire.

    The other reason that mountain bike tires are run at lower pressure is for control. A tire that is pumped up to 60 psi will bounce all over the place when it hits something. Without suspension, that becomes a problem of keeping the bike rolling where you want it to roll. A high pressure makes mountain biking a game of pinball rather than a bike ride as you bounce off each rock while riding. A similar event could happen on a snowy or icy street.
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    At lower PSI there is the possibility of torque creep of the tire on the rim.
    the inner tube sticks to the inside of the tire , and shifts with it.

    the hole in the rim will not move, and shearing at the stem can happen.
    letting the air escape entirely ..

    the recommendation to use sew up tire glue to stick down one tire bead of the tire to the rim
    seems a reasonable prevention of that , tried and proven my far north bike riders. apparently.


    Mount and ground W. myself the 160 stud tire is fine, none down the center,
    so bare pavement and black ice patched roads make them suitable.

    studs down the center , perhaps..
    if the roads are not scraped dry, and remain icy
    and a packed snow surface edge to edge..

    local conditions are not like that..
    Last edited by fietsbob; 12-11-11 at 11:15 AM.

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    gbg
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    Quote Originally Posted by cyccommute View Post
    The other reason that mountain bike tires are run at lower pressure is for control. A tire that is pumped up to 60 psi will bounce all over the place when it hits something. Without suspension, that becomes a problem of keeping the bike rolling where you want it to roll. A high pressure makes mountain biking a game of pinball rather than a bike ride as you bounce off each rock while riding. A similar event could happen on a snowy or icy street.
    I don't think a 240+lb rider on a 60PSi 2+" tire riding on snow/ice is going to bounce anywhere. At least is hasn't happened to me in
    1000's of snowy/icy miles. And I ride a Full rigid in the winter since I don't want the possibility of suspension problems/maintenance in very cold temps.
    Speeds on studs in the snow are a lot less than on dry hard pack.

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by gbg View Post
    I don't think a 240+lb rider on a 60PSi 2+" tire riding on snow/ice is going to bounce anywhere. At least is hasn't happened to me in
    1000's of snowy/icy miles. And I ride a Full rigid in the winter since I don't want the possibility of suspension problems/maintenance in very cold temps.
    Speeds on studs in the snow are a lot less than on dry hard pack.
    60psi tires and my heavy carcass aren't my favorite ride on rutted ice filled streets because they bounce all over...and that's with suspension (although I do have lock out on the shock). Overinflated tires bounce all over on rocky trails and icy roads aren't a lot different. On fresh snow without a lot of car traffic it wouldn't be an issue but once things get icy, control is a lot more difficult.
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    Still spinnin'..... Stealthammer's Avatar
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    Quote Originally Posted by cyccommute View Post
    A lower pressure on a studded tire, especially on with knobs, would put more of the studs in contact with the pavement. A knobby tire pumped up to maximum pressure is going to ride on a very small foot print. Letting some air out allows more of the knobs to contact the ground and be more effective......The other reason that mountain bike tires are run at lower pressure is for control. A tire that is pumped up to 60 psi will bounce all over the place when it hits something......
    My experience exactly after four years riding all winter here in Indy, I drop the pressure from 60psi to 40-45psi in the snow. I get better traction both in driving forward and turning, and it is MUCH easier to hold a line especially across ruts at an angle, whether on-road or off. It doesn't matter if I am using my Nokian Extreme 294s or my Mount and Grounds W160s. Lowering the pressure increases both traction and stability, as well as rolling resistance, but at least I am rolling and stable. Also, I have never experience any "creep" at 45psi. I would guess that I would need to drop the pressure to at least 30psi before "creep" would be an issue.
    Last edited by Stealthammer; 12-11-11 at 08:31 PM.
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  18. #18
    AEO
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    I can't give a solid number, but tire creep only happens at about 25psi or lower.
    Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
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  19. #19
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by AEO View Post
    I can't give a solid number, but tire creep only happens at about 25psi or lower.
    Both you and Stealthammer are correct if a little high on the pressure where tire creep occurs. Whether or not a tire will creep on the rim depends on a number of factors including the pressure, whether or not the tire is used in a high torque application, how tightly the tire fits to the rim, etc. At 45 psi, I doubt you could get a tire to creep under any conditions (I never have) At 25 psi, you might be able to get a tire to creep if you didn't pinch flat first but I have heard of riders using that pressure off-road. You could probably run 25 psi without pinch flats if you rode the bike light (even big guys can do that) and worked carefully to lift the bike over stuff that might cause a pinch flat.

    Riding 'light' means that you ride the bike while floating over the saddle rather than like a sack of cement sitting on the saddle. 'Lifting' the bike means that you use the bounce in the tires and/or suspension to lift the tires over hard edged stuff that can pinch the tire. For example rather than letting the bike slam into a curb, you do a small wheelie to lift the wheel over the curb and then hop the rear wheel up over the curb. It's pretty easy to do with a little practice as is riding 'light'. Both should be how you ride the bike to begin with.
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  20. #20
    Mad bike riding scientist cyccommute's Avatar
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    After my experiences yesterday and today with rides on 10" of fresh snow (yesterday) and car packed snow today, I thought it might be illustrative to revisit the tire pressure issue. Yesterday, I left my house with the tires at the same pressure I use them for riding on dry pavement...about 60 psi. The snow had some tracks in it so I had the choice of plowing through the fresh stuff (not easy) or trying to follow the tire tracks. I tried both but following the tire tracks is just easier with that much snow. However, as I rode down the tracks, my bike kept sliding off the side of the tracks and down into the snow. Keeping going was very difficult and going in a straight line almost impossible. The tires do indeed want to punch all the way through the snow to the ground but that's not necessarily a good thing.

    After struggling with sliding off the tire tracks, I decided to let air out of my tires and see what that would do. The difference was like night and day. At around 20 psi, the tires started to float across the car tracks instead of driving through them. Staying up on the packed part of the tracks became much easier and the bike tracked better. The tire tracks were no wider than before, however. And in snow pack you are very unlikely to run across anything hard edged enough to cause a pinch flat.

    On today's ride, I did notice that even at a low pressure, the packed snow had enough soft spots that it kept throwing me off my line. Several times, it threw me off enough that I had to pop out of the pedals (another aspect of riding in snow is that clipless aren't difficult to get out of but that's a different thread) and stop. It took a while for my mountain bike brain to kick in and start riding the packed snow like sand, instead of like a harder surface.

    When you ride in sand, it's best to sit up and even lean back on the bike. The idea is to pull your weight off the front wheel so that it doesn't dig in as bad and floats over the sand while your rear wheel - which is going to dig in anyway - provides the drive. Get into a lower gear (but not too low) and spin your way along through it. Works the same with snow and packed snow. Try to float the front wheel over the snow as best you can. Again, a lower pressure in both tires causes them to float rather than dig into the snow. Front suspension (perhaps even dual suspension) allows the tire to float more and dig less.
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  21. #21
    Dog is my co-pilot 2manybikes's Avatar
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    170 lbs rider, 34 lbs steel hardtrail 16 lbs panniers. Worst bumpy conditions with Nokian 294s. 15 lbs in the front tire, 22 in the back. No tire creep, no pinch flats. I use the same presure (15 front, 22 rear) on trails so rocky there is no dirt, only rocks. No problems. I have probably posted 10-15 photos of rough ice riding and the bike on the forums by now.
    The old ice bike site had plenty of photos of double wide rims with 5 psi tires. They glued one bead to prevent tire creep. This is not unusual for Iditabike racers.
    Starting about 1968 - 69......... 18 front, 25 rear.....40 mph on hiking trials on a motorcycle, dirt bike. No tire creep, no pinch flats. Some time in the early 1970s I hit a sharp rock about 50 mph on the dirt roads that are under the power cables. Dented the rim, sent me 3 feet in the air, the tire held and I kept on riding. Later I did replace the rim. I have no idea why the tire was OK ??????
    That taught me to scan the ground more, never happened again. About 42 years total. No tire problems. One needs to scan the ground and back up in front and even the sides as fast and with as much concentration is possible. I'm not special, I had the faster experience of the motorcycle first. I became used to the speed over the years. That made not hitting any thing on an MTB very easy. The last few years I am now losing the conditioning I had from the motorcycle. Still no tire problems but, it's more work. Or maybe being 60 years old is slowing me down.
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    Still spinnin'..... Stealthammer's Avatar
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    Wow, you guys are running really low psi and not having any issues with pinching, and you are also finding that you have even more control down at 20-25psi. I have been reluctant to dropping the pressure on the Mount and Grounds below 40psi on the road (but I will drop to 30psi off-road with the Extremes), but now I am looking forward to some good hard snow this year so I can test road traction of the Mount and Grounds at 25-30psi. I appreciate the input.
    Just your average 'high-functioning' lunatic, capable of passing as 'normal' for short periods of time.....

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    Dog is my co-pilot 2manybikes's Avatar
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    In the really soft deep power on the road, I can tell the difference between the rear tire sliding out at 40 psi, and a small improvment at 15 and 22. It's small, but I'll take any improvement possible. On the flat surfaces the loaded panniers help a little with traction too. Just a little.

    Here you go, look around the site. http://icebike.org/ lotsa good stuff
    Last edited by 2manybikes; 12-23-11 at 06:41 PM.
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  24. #24
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Stealthammer View Post
    Wow, you guys are running really low psi and not having any issues with pinching, and you are also finding that you have even more control down at 20-25psi. I have been reluctant to dropping the pressure on the Mount and Grounds below 40psi on the road (but I will drop to 30psi off-road with the Extremes), but now I am looking forward to some good hard snow this year so I can test road traction of the Mount and Grounds at 25-30psi. I appreciate the input.
    I went a little lower than I had planned but it was cold, it was snowing and I didn't want to dig out a gauge. I only found out how low I had gone after I got home and pumped the tires back up.

    That said, you can run lower pressures on the road than you can off-road because the surface is smooth. And the snow softens everything even more.
    Stuart Black
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  25. #25
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    Steathhammer, I use the nokian mount and grounds 26x 1.95 on my rockhopper. I'm 235 lbs + gear. For the worst of bumpy, rutted snow and ice, I run 30 psi front and rear with good results. My side wall are really thick and heavy, I'm not worried about pinch flatting at that pressure. It has more traction than at 40 psi. which I run them for less crappy stuff. One thing not mentioned here is rim width, wider is better. Not too wide but enough to spread out the tread some. I like to do the sit test. Sit on the bike, tire should squish out a little. Tire gauge helps too.

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