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  1. #1
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    Sorry, another dreaded tire psi question

    I have already read all the threads I could on the subject so I appoligize for this as I am still relatively new to mountain biking and looking for closure. Here are the specifics. Me - 142 lbs, maybe 145 with clothes and gear. The bike, new Blur XC Medium, 26 lbs. with 1.95 John Tomac Nevegals Kendas Stick E tires and ultralight tubes pumped to 30-31 psi. Sag is set to Santa Cruz recommendations. The situation - I was recently in a race, I flatted the rear tire after a fast long decent on a fire road. Everyone I showed the tube too thought it was a pinch flat although it did not look like a classic snake bite. The tube had a 1 cm slit around where the rim would line up but nothing on the other side.

    From everything I've been reading in these forums, it seems that I should've been ok at 30 psi. I'm sure all of you have come across these treads where guys that weight 160, 180, 210, are running air pressures such as 28, 30 32, 35 etc.etc...

    I originally started with a 40 psi when I got my new bike, and gradually reduced the tire pressure as I was l "learning" the bike and trying to set it up. The primary reason I gradually reduced the psi was because the bike felt "bouncy" when I was riding fast over trails. Secondary was that I was also trying to gain some more grip.

    I emailed Santa Cruz about my rear pinch flat and the details and the tech said that I should go to 45 psi and adjust the rebound. I guess that makes sense but I did not even think about it since I still learning about this mountian biking stuff. I feel like 45 psi is to much still and when I replied with that question the tech said that is what he uses. So now months later I'm back to square 1.

    A side note: All my future riding will include trails in So Cal, and cross country races. As far as my riding style, I don't know how to answer that since I'm too new to this. I can tell you that I am a roadie and just started to race this year. I've done a beginners race, a couple of Sports and may need to go to Expert as long as the races aren't too technical.
    My mountain biking/downhilling skills are definitley a beginner less but I am learning to go faster with everyride. My climbing is definitley at least Expert or better as far as I can tell.

    So....The question - Was 30 psi too low for me and should I be at 40,45??? What do you guys think given all the information I've provided?

    Sorry this was so long but I'm hoping for some good replies and therefore I felt I needed to provide you the best details I could. Thanks guys!!! I'm really liking mountain biking!
    Last edited by oscarc; 10-12-2006 at 02:58 PM.

  2. #2
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    35psi or tubeless

    30psi is a bit too low for tubed. My advice is run a few psi higher than required to prevent pinch flats - and it seems like you did get a pinch flat. So, you should go with about 35-45 if running tubes and adjusting the rebound is excellent advice because the Blur is sensitive to shock pressure and rebound (I like mine at nearly full fast rebound). If you run tubeless then the pressure is typically 28-35psi. You will not pinch flat running tubeless, you will get more traction and lower rolling resistance - but it pretty much requires that you have a compressor to mount tires. I don't know what rim you have, there are various ways to run tubeless - the simplest on a standard rim is to 3X wrap .25" wide kapton tape around the rim in place of the rimstrip to seal the holes and use Stan's latex (notubes.com) to seal the tire and of course you will also need a valve - like Stan sells.



    Quote Originally Posted by oscarc
    I have already read all the threads I could on the subject so I appoligize for this as I am still relatively new to mountain biking and looking for closure. Here are the specifics. Me - 142 lbs, maybe 145 with clothes and gear. The bike, new Blur XC Medium, 26 lbs. with 1.95 John Tomac Nevegals Kendas Stick E tires and ultralight tubes pumped to 30-31 psi. Sag is set to Santa Cruz recommendations. The situation - I was recently in a race, I flatted the rear tire after a fast long decent on a fire road. Everyone I showed the tube too thought it was a pinch flat although it did not look like a classic snake bite. The tube had a 1 cm slit around where the rim would line up but nothing on the other side.

    From everything I've been reading in these forums, it seems that I should've been ok at 30 psi. I'm sure all of you have come across these treads where guys that weight 160, 180, 210, are running air pressures such as 28, 30 32, 35 etc.etc...

    I originally started with a 40 psi when I got my new bike, and gradually reduced the tire pressure as I was l "learning" the bike and trying to set it up. The primary reason I gradually reduced the psi was because the bike felt "bouncy" when I was riding fast over trails. Secondary was that I was also trying to gain some more grip.

    I emailed Santa Cruz about my rear pinch flat and the details and the tech said that I should go to 45 psi and adjust the rebound. I guess that makes sense but I did not even think about it since I still learning about this mountian biking stuff. I feel like 45 psi is to much still and when I replied with that question the tech said that is what he uses. So now months later I'm back to square 1.

    A side note: All my future riding will include trails in So Cal, and cross country races. As far as my riding style, I don't know how to answer that since I'm too new to this. I can tell you that I am a roadie and just started to race this year. I've done a beginners race, a couple of Sports and may need to go to Expert as long as the races aren't too technical.
    My mountain biking/downhilling skills are definitley a beginner less but I am learning to go faster with everyride. My climbing is definitley at least Expert or better as far as I can tell.

    So....The question - Was 30 psi too low for me and should I be at 40,45??? What do you guys think given all the information I've provided?

    Sorry this was so long but I'm hoping for some good replies and therefore I felt I needed to provide you the best details I could. Thanks guys!!! I'm really liking mountain biking!
    M

  3. #3
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    I agree that 30psi is too low for tubes. That's one of the advantages of going tubeless is that you can run low pressure. I've used stan's, successfully on many different tires and have not had a flat yet (knock on wood). Oh, and I have not had any problems mounting any tires with stan's using a floor pump.

    Rob
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  4. #4
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    Another thing you should think about is that you only need to lower the pressure if you are looking to gain some traction (eg wet roots and rock). I smoother terrain, you will notice 35psi or less will feel spongy if it is an aggessive race where you stand up often (tire will flex as you push down). Under dry grippy conditions, you can run 40-45psi. Those nevegals are pretty grippy, and even with stan's tubeless conversion I run the front at no less than 32psi and rear 34psi...even in wet rooty slippery conditions. With tubes I simply cannot go under 35psi without pinch flatting at some point. Btw, I weigh 140lbs too...and also ride a blur xc. Hope that helps abit.

  5. #5
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    Thanks guys!

    Thanks for the advice guys. It really helps me a ton!

    I've read alot that riders are putting a few psi less in the front and more in the back as GSpot states. Should I be doing that or the same on both front and back? What will be the difference, will I turn better if I have less in the front for example? What do you recommend?
    If I'm not climbing, I'm not riding.

  6. #6
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    I run more in the rear because the rear tire supports more of your weight, especially while seated. Since you (and I) are riding FS bikes, we are more likely to be seated when riding over imbedded rocks and such, so the chances of pinch flatting the rear are higher. Also, as far as people running lower psi who are heavier than you, chances are they are running fatter tires. Fatter tires support more weight per psi (pressure x area = force) than a skinny tire (hence road tires need over 100psi). If you were running 2.1's or 2.25's or whatever, you could run lower pressures. I run 2.1's mostly, sometiems a 2.25 in the front, and generally run 32 in the front, 38-40 in the rear. Any less with tubes and I pinch flat consistently, and less with Stan's and I'll roll the bead and burp air. For reference, I ride a large Blur XC and I'm 6'2" - 190~195lbs.

    BM
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  7. #7
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    If you've got the resources and the time, I really don't understand why you would use tubes??? I will purport that traction is far more important than any other factor or reasons you may have for using tubes, cost being no object. You ride a Santa Cruz, a fairly expensive frame compared to foreign-produced moels, do you really have a good excuse why you are still using tubes?

    Time has passed tubes by. How many automobiles are still using tubes? The stronger sidewalls of UST tires allow you to run pressures of 30 psi or lower. I weigh 30 more pounds than you and run 30 psi on trails that are most definitely technical and rocky. I ride the Ozark mountains with my hillbilly friends. I love rocky, technical trails. I've flatted every tire I have ever ridden, tubes or no tubes. I've flatted Stan's setups with tubed tires so many times I've lost count. I've flatted UST tires sealed with Stans, no problem, but much less often. If I had ridden smarter, it wouldn't have happened. They are the best possible setup you could use to run the lowest pressure and avoid flats.
    As regal as a Buick!

  8. #8
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    Quote Originally Posted by oscarc
    Thanks for the advice guys. It really helps me a ton!

    I've read alot that riders are putting a few psi less in the front and more in the back as GSpot states. Should I be doing that or the same on both front and back? What will be the difference, will I turn better if I have less in the front for example? What do you recommend?
    Some mtb riders would say get the front wheel to go where you want and the rear will follow. Lowering the pressure in the front allows the tire to conform to the terrain and get more grip over bumpy stuff. When you are on the edge of grip you will feel the difference between ...say...35psi and 32psi in the front tire. The front end won't feel so skitterish in bumpy corners, front will be more planted and will resist washing out better, front end will feel smoother like the fork is working better (since the tire acts like additional suspension as it compresses)...Since the rear handles most of the rider weight and tends to be the one that pinch flats the most, many riders will sacriface some additional grip and use more air pressure than the front to 1) try to reduce rolling resistance on smooth surfaces 2) reduce chance of flatting (pinch flat with tubes...or with stans conversion...reduce rock casing slicing) 3) reduce chance of burping a stans converted tire (for me can happen under 33psi in the rear under the right circumstance). Most riders will be able to handle rear tire slides as long as the front has good grip.

    Tire pressure does depend on the rider. I ride with some that weigh the same as me, but love 45psi...all the time. They ride great. The get on my bike and think I have set it up as a couch (DH past has me liking 30+% sag and soft compression settings and soft tire psi). Soft setups aren't for everyone so do experiment. I tend to ride the suspension soft but use the lockout/propedal settings to stiffen it up for smooth parts of races. I use soft tire psi in wet rooty conditions; more pressure in predominantly smooth fast conditions. As you might have guessed it, my style favors ugly conditions. You have to gauge what suits your style of riding and the race course. Since you are new to the dirt, it will take some time for you to see what works best for you. Experiment.

  9. #9
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    Is the tire pressure the issue?

    Might be your technique. With a FS at 40psi and nice suspension set and wheels (which I'm sure you have it if you are riding a Blur) you should be fine.

    When I have raced in FS I even used 50-60psi to go faster. With both front and rear suspension it won't affect that much your riding because the rear shock will absorb. In HT I ride between 35-40psi depending of the terrain and the tires size (tubeless in both cases).

    Try to move your body away of your bike in fast sections, kind of separate yourself from the bike. Let the bike to receive all the toughness from the ground, not your body. Maintain your arms and legs relaxed and always remeber to breath like you were in a yoga session.

  10. #10
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    [QUOTE=kingfurby]You ride a Santa Cruz, a fairly expensive frame compared to foreign-produced moels, do you really have a good excuse why you are still using tubes?/QUOTE]

    When I bought the bike, it came with DT Swiss hubs, spokes and rims for tubes. At the time I didn't even know about Stan's and has only heard of tubes. Still when I read posts here about going tubeless and Stan's, it seems that about 65% people are extremely happy with tubeless and Stan's and about 35% are not sure or have gone back to tubes for various reasons. If 98% we're pro and 2% against then I would immediatly jump on board. So for now I'm not totally prepared, if I ran 30 psi again it would be to take some of the bouncyness out of the ride. But now that I know I can reduce the rebound I would prefer a higher tire pressure as I would like to minimize rolling resistance. I still run tubes in on my Trek Madone and can't even remember the last time I had a flat on my road bike, even having gone over glass, pot holes and other debris. Also my down hill speeds on my road bike get up to 45 mph every weekend and it would be scary or fatal to have a tire go down if it were a sew up. With that thinking, it kind of also scares me to have tubeless tire go flat at high speed, especially since I'm not a very good mountain bike handler yet.
    If I'm not climbing, I'm not riding.

  11. #11
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    Quote Originally Posted by josech77
    Might be your technique. With a FS at 40psi and nice suspension set and wheels (which I'm sure you have it if you are riding a Blur) you should be fine.

    When I have raced in FS I even used 50-60psi to go faster. With both front and rear suspension it won't affect that much your riding because the rear shock will absorb. In HT I ride between 35-40psi depending of the terrain and the tires size (tubeless in both cases).

    Try to move your body away of your bike in fast sections, kind of separate yourself from the bike. Let the bike to receive all the toughness from the ground, not your body. Maintain your arms and legs relaxed and always remeber to breath like you were in a yoga session.
    Yes, I think you are partially right...I am still learning the proper positioning when riding down hill which is where I experience all my weaknesses. Well...it sounds like I'm pretty satified with all the responses I've gotten here. Thanks all! I'm gonna go to 40 psi and dial in the rebound and just try to continue to improve my positioning on the bike.
    If I'm not climbing, I'm not riding.

  12. #12
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    [QUOTE=oscarc]
    Quote Originally Posted by kingfurby
    You ride a Santa Cruz, a fairly expensive frame compared to foreign-produced moels, do you really have a good excuse why you are still using tubes?/QUOTE]

    When I bought the bike, it came with DT Swiss hubs, spokes and rims for tubes. At the time I didn't even know about Stan's and has only heard of tubes. Still when I read posts here about going tubeless and Stan's, it seems that about 65% people are extremely happy with tubeless and Stan's and about 35% are not sure or have gone back to tubes for various reasons. If 98% we're pro and 2% against then I would immediatly jump on board. So for now I'm not totally prepared, if I ran 30 psi again it would be to take some of the bouncyness out of the ride. But now that I know I can reduce the rebound I would prefer a higher tire pressure as I would like to minimize rolling resistance. I still run tubes in on my Trek Madone and can't even remember the last time I had a flat on my road bike, even having gone over glass, pot holes and other debris. Also my down hill speeds on my road bike get up to 45 mph every weekend and it would be scary or fatal to have a tire go down if it were a sew up. With that thinking, it kind of also scares me to have tubeless tire go flat at high speed, especially since I'm not a very good mountain bike handler yet.
    There is nothing wrong with sticking to tubes.
    When riding you need to look for sharp edges (ledgy rocks) or even things like rain drainage ties (2x4")...On local races, tons of people get flats going over wooden bridges if there is a step up 3+" high. These sharp bumps can compress the tire easy and cause pinch flats.
    Ride lots of dirt and you will learn what to avoid and find the lines that are fastest and those that are smoothest (important if you are worried about flatting). For objects that you are worried about flatting against, bunny hop them...or you can slow down. You can pull up the rear and then when the rear gets to the object you can lift the rear.

    Good luck!

  13. #13
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    Interesting. ALL this talk about too low pressure and yet NO ONE has even asked ..... what tubes are you running???????? Wow!

    So, Oscar - what kind of "ultralight" tube was this????

    My take - I gotta harp a bit here. Anyone that says something like "you shouldn't run below this psi on a tubed tire" makes me wonder (not ina nice way, either). I run tubes - always have, always will. I run a pair of Nokian NBX 2.3's (which supposedly have weak sidewalls ). I run Bontrager Superlight tubes. Psi? How about 25. I can run to my heart's content at 25 psi all day, whatever the terrain and I don't flat on nothing, no matter the speed, angle, prep into the obstacle ..... no problems. Guess what? I can do the same thing with it at 20 psi. Oh, and I weigh 165 loaded.

    Anyone know why? C'mon, take a stab.

    Okay, more. Same tire. Same tube. Running 37 psi. I can pinch flat riding over a 1" thick root. WTF?!?!??!?! SURELY more psi means you're better protected from flatting, RIGHT????????????????????

    Not when you're on a different frame with very different suspension settings.

    Example #1 is The Bastard (San Andreas). VERY soft suspension front and rear.

    Example #2 is my old NRS. NOT soft suspension in the rear. Ask me about the two consecutive rides I had on that bike using a Continental Explorer SS with those Bontrager tubes and how I had two consecutive flats. I can run those tires on The Bastard juuuuuuuust fine ..... at 25 psi nonetheless.


    Oscar - use sag as a starting point for your suspension settings - not the goal. Even then there's no rule or law that says you have to use that number.

    One last example - The Bastard uses about 10% sag in the rear (just what it happens to be!). The NRS is designed for, and was used, with NO sag. There's more to be thought of in your suspension than you think. (not bashing - I know you're new)
    I ..... need ..... DIRT!!!!!

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  14. #14
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    Andrew, I find your post inflammatory. We are talking about 2.0" and narrower tires for xc racing. Sure technique, suspension, line choice, tire choice, tube choice, terrain, etc all have an effect on when one might experience a pinch flat. But we are talking about racing here. To loose 1-3min on a flat is killer. So we are talking about what tire pressure we run during races due to our experiences: these numbers are bound to be on the high side. It is because we want extra protection against flatting. Better reliability is generally favored on xc races. We rather give up abit of handling to avoid flatting.




    Quote Originally Posted by AndrewTO
    Interesting. ALL this talk about too low pressure and yet NO ONE has even asked ..... what tubes are you running???????? Wow!

    So, Oscar - what kind of "ultralight" tube was this????

    My take - I gotta harp a bit here. Anyone that says something like "you shouldn't run below this psi on a tubed tire" makes me wonder (not ina nice way, either). I run tubes - always have, always will. I run a pair of Nokian NBX 2.3's (which supposedly have weak sidewalls ). I run Bontrager Superlight tubes. Psi? How about 25. I can run to my heart's content at 25 psi all day, whatever the terrain and I don't flat on nothing, no matter the speed, angle, prep into the obstacle ..... no problems. Guess what? I can do the same thing with it at 20 psi. Oh, and I weigh 165 loaded.

    Anyone know why? C'mon, take a stab.

    Okay, more. Same tire. Same tube. Running 37 psi. I can pinch flat riding over a 1" thick root. WTF?!?!??!?! SURELY more psi means you're better protected from flatting, RIGHT????????????????????

    Not when you're on a different frame with very different suspension settings.

    Example #1 is The Bastard (San Andreas). VERY soft suspension front and rear.

    Example #2 is my old NRS. NOT soft suspension in the rear. Ask me about the two consecutive rides I had on that bike using a Continental Explorer SS with those Bontrager tubes and how I had two consecutive flats. I can run those tires on The Bastard juuuuuuuust fine ..... at 25 psi nonetheless.


    Oscar - use sag as a starting point for your suspension settings - not the goal. Even then there's no rule or law that says you have to use that number.

    One last example - The Bastard uses about 10% sag in the rear (just what it happens to be!). The NRS is designed for, and was used, with NO sag. There's more to be thought of in your suspension than you think. (not bashing - I know you're new)

  15. #15
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    Quote Originally Posted by GspotRider
    Andrew, I find your post inflammatory. We are talking about 2.0" and narrower tires for xc racing. Sure technique, suspension, line choice, tire choice, tube choice, terrain, etc all have an effect on when one might experience a pinch flat. But we are talking about racing here. To loose 1-3min on a flat is killer. So we are talking about what tire pressure we run during races due to our experiences: these numbers are bound to be on the high side. It is because we want extra protection against flatting. Better reliability is generally favored on xc races. We rather give up abit of handling to avoid flatting.
    Sorry you find it inflammatory, Gspot. It was not my intention when I posted to do so, despite my agressive manner.

    Please allow me to ask of you one question;

    What's the difference between ride that is a race and a ride that's not a race?

    Please understand that while i'm not a pro (or otherwise) racer, MY goal during my rides is none different than yours or any other racer's. I don't like to flat. I don't know a single person out there who get's a flat and say's "oh, goody, I got a flat" or anything even remotely positive about the experience.

    My goal while riding is to have the best ride I possibly can. This entails not flatting, not crashing, passing people if there's anyone else using the same stretch of trail I am and having fun.

    Hmmmm, sound familiar?

    Really, i'm not trying to be sarcastic or anything negative. PLEASE don't read me like that. My original post was done so with a level of frustration of seeing sooooo many people recommending something that they really can't, or at least shouldn't be. If I may, a quote, one of my fave's;

    Quote Originally Posted by Dougal
    I'm afraid commenting on other peoples setup numbers is a little like commenting on their shoe size. It's impossible from numbers to tell how well something fits someone else.
    While Dougal was referring to fork settings, I don't believe and know that it doesn't end there.

    Anyways, hopefully this post clears things up enough for yourself and others to see where I was coming from and read my post with some form of positive information. Apologies to all.

    I'm still puzzled as to why no one has asked about what tube was being used, though?!?! Any thoughts Gspot? Soooo many questions not asked with this one.
    I ..... need ..... DIRT!!!!!

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  16. #16
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    Quote Originally Posted by AndrewTO
    I'm still puzzled as to why no one has asked about what tube was being used, though?!?! Any thoughts Gspot? Soooo many questions not asked with this one.

    Andrew, to answer your question. Since that was the first rear flat on this tire since it was new, I believe it was the Kenda superlight tube with which it should've come with. How ever I bought a Continental Ultralight tube that really seems much thinner than the supposedly Ultralight Kenda. I'll have to take a second look at the cut Kenda since I saved the piece with the cut in it. Some how if I remember correctly it seems like it might be a regular tube, but I'll check. Maybe it's in between a regular tube and a Continental Ultra Light. Are you suggesting that maybe a thicker tube would have allowed a lower psi?
    If I'm not climbing, I'm not riding.

  17. #17
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    Quote Originally Posted by AndrewTO
    What's the difference between ride that is a race and a ride that's not a race?
    My goal while riding is to have the best ride I possibly can. This entails not flatting, not crashing, passing people if there's anyone else using the same stretch of trail I am and having fun.
    My original post was done so with a level of frustration of seeing sooooo many people recommending something that they really can't, or at least shouldn't be. I'm still puzzled as to why no one has asked about what tube was being used, though?!?! Any thoughts Gspot? Soooo many questions not asked with this one.
    Andrew, you have answered it on your own. You ride to have fun. During a race it is the fastest from point A to B. eg, fun? hit the jump but risk a crash. race? skip the jump and keep pedalling. (I would still be tempted to jump). And as for making suggestions to a fledgling racer, you are right, you should have some race experience before you diss other's responses.

    Yes some tubes flat easier than others: but with tubeless or Stan's conversion, debating different tubes is moot for many racers as many are choosing tubeless as it is a huge step up in pinch flat resistance, whereas the differences between tubes are relatively small.

    Rip it up dude...and give a dh and xc race a try....I'm sure you will like it. Fun in a different way.

  18. #18
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    First, sorry for bumping an old thread.

    If I may, I'd like to ask a question about tire pressures and racing.

    I've read here and other places online that lower tire pressures are better because the tire conforms better to the terrain, provides some cushioning, and offers lower rolling resistance. Obviously you don't want to go low as you don't want to pinch while out on course.

    During the one race I participated in last year, I was told to run high pressures (55-60psi). I was extremely new to mtb at that time, and I still have a lot to learn today. At the time, the guy mentioned only a lower rolling resistance.

    Reading this thread, it appears people run higher pressures to give extra protection against pinching and that they do so willingly at the expense of rolling resistance and handling. Is this true?

    I have entered in to a racing series in my area that runs 12 races. First race is next week so I want to be as prepared as I can. I'm riding in the beginner class because, well, I'm a beginner . Can you guys give me some general rules regarding why higher pressure vs. lower pressure is preferred in a racing situation? I'm not asking for specific psi recommendations (unless you want to ..), rather, just a "higher is better because x" or "lower is better because x".

    Thanks.
    :wq

  19. #19
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    On new tyres I'll run around 55-65psi, depending on the tyre and tube; as they get older I'll drop towards 45psi. That's on a 13kg bike with a 64kg rider.

    But that's all due to preference and the fact that I don't want to destroy tire sidewalls with rolling. I went BMX as a kid and road until I was early 20s so I'm used to running high tyres at high pressures.

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