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  1. #1
    Senior Member VT Biker's Avatar
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    What is the minimum PSI to run on standard clinchers?

    A complete newbie to cross here, so please bear with me. I am not yet ready to take the plunge to a set-up tubulars, and after hearing about the horror stories of trying to convert a standard rim to tubeless, I am going to go into this a low maintenance as possible.

    However, I have a few questions:

    A) What disadvantage will I have, when most of the courses here in the Front Range of Colorado are dry and dusty vs. muddy?

    B) What is the lowest PSI you typically run when racing on standard clinchers, and are there any special tubes/techniques with the tubes needed to achieve that low PSI?

    Thanks in advance

  2. #2
    Team Water Andy_K's Avatar
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    I've never used tubulars, so I won't comment on the disadvantages you'll see with clinchers.

    The lowest pressure you can get away with varies according to a lot of variables -- most significantly your weight, your riding style, the tire quality and the tube quality.

    I weigh ~200 pounds. I've run my 700x30 Michelin Mud2's as low as 30 psi without pinch flatting. I did bottom out a few times at that pressure. My only flat in a race came on 700x35 Schwalbe Racing Ralphs. I forgot to check my pressure before the race and had run them at about 30-35 psi the previous race, so it wouldn't surprise me if they were below 30. In that case, I think what happened was that the tire slipped during a fast turn on pavement.

    I use tubes that are listed for use with 700x35 tires, and coat both tire and tube with baby powder before installing them. I think this helps. I generally don't hit things in the course when I can avoid them, and when I know I'm going to hit something (like the lip on a transition from dirt to pavement) I usually hit it straight on and get out of the saddle to absorb the hit with my arms and legs.

    I should also say that when I use pressure this low it's generally on very soft, muddy ground. In the dry races I've done so far this season, with very hard ground, I've been running pressure closer to 40-45 psi. I tried ~32 psi on my pre-ride for the first race, but it felt too squishy for the fast sections, so I went up to about 38 psi. For the second race, with similar conditions, I tried pre-riding at 40-45 psi, but went a little lower for better handling on the singletrack bits.

    That is to say that while the general rule is to use the lowest pressure you can get away with, that isn't always the way to go. Higher pressure can be useful on very fast courses and on courses with a lot of thin mud.

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    Andy K is correct. The correct tire pressure will depend on such factors as your weight, the tire's size, the terrain you will be riding over and how muddy or dry the course is. Take your bike to a local park or anywhere where you can ride off road and experiment with different tire pressures. As a rule of thumb and notwithstanding all the variable I mentioned above, I wouldn't take standard clincher cyclocross tire below 30 psi. However, now that I've written than, someone is sure to come along and write that s/he does it all the time.

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    Quote Originally Posted by Andy_K View Post
    Higher pressure can be useful on very fast courses
    Pretty much spot-on until this. In general, the faster the course, the more hardpack it has, and that's where fat squishy tires (file-tread, if you're fancy) really shine.

    To the OP, you just have to find out for yourself, this is true of clinchers or tubulars. As you get too low, the chance of pinch-flatting increases, and also you'll start to fold the tire over and lose traction on corners. Better to be a little too firm than a little too soft, which incidentally is what she said.

  5. #5
    Team Water Andy_K's Avatar
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    Quote Originally Posted by flargle View Post
    Pretty much spot-on until this. In general, the faster the course, the more hardpack it has, and that's where fat squishy tires (file-tread, if you're fancy) really shine.
    I will humbly accept your correction here. But for the sake of my own learning, let me ask, isn't there a point if the course has a lot of pavement and the hard-pack dirt is smooth when lower pressure will be a hinderance? For instance, in the first pre-ride I mentioned above with low pressure during the pre-ride I felt like the bike was bobbing up and down with the cadence of my pedalling.

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    Quote Originally Posted by Andy_K View Post
    isn't there a point if the course has a lot of pavement and the hard-pack dirt is smooth when lower pressure will be a hinderance
    OK fair enough.

    Theoretically such a course could exist but not in my experience. Even a line that looks like this smooth dirt track through a nice grassy field almost always has a bunch of chop in there. And even on a very smooth course there's usually at least one power section that's bumpy grass or whatnot, so whatever time you gained in the rest of the course on high PSI, you give it up by bouncing around on this one section. I also think that good cross technique is about pedaling smoothly on pavement so you don't bob so much.

    But of course proof is in the pudding, "optimal" pressure comes from pre-riding and tweaking.

  7. #7
    Gears? CliftonGK1's Avatar
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    Quote Originally Posted by Andy_K View Post
    I will humbly accept your correction here. But for the sake of my own learning, let me ask, isn't there a point if the course has a lot of pavement and the hard-pack dirt is smooth when lower pressure will be a hinderance? For instance, in the first pre-ride I mentioned above with low pressure during the pre-ride I felt like the bike was bobbing up and down with the cadence of my pedalling.
    I think it depends on how smooth the hardpack dirt is, first off. Sure, pavement is pavement (mostly) and you might get some slogging and bobbing about on softer tire pressures (especially if you're like me and race singlespeed and have to keep a crazy cadence sometimes.) But the 3 races I've done this season have all been dry and dusty, but the hardpack has been like the freakin' craters of the moon. Seriously, the Midsummer Night's race had stuff that was like the rumble strips on the side of a highway. It was from the guy mowing with a brush-hog behind a big ol' tractor when it was wet out, then those v-shaped tractor tire chevrons all dried up like concrete. The LD/CX race was similar, but from truck tires and bulldozer treads at a gravel quarry. Last week the hardpack wasn't quite so horrible, so I felt better about running a higher pressure to compensate for the long straightaways and long pavement stretches.

    Now, my tire pressures are on the high side because I'm a big dude and I don't ride "light". I plow through stuff because I can.
    I ran 46 - 48psi in 34mm tires for the Midsummer Night's race and it was totally bone jarring on the rutted hardpack. It felt fine for the roadways and maybe a little high for the sections of woodchips, but at least I didn't flat out like the guy in front of me.
    I threw some monstercross 37mm WTB A-T tires on for the LD/CX race and went with 45psi. A little slow feeling on the roadway, but nice and cushy over the extensive choppy hardpack while still remaining hard enough that I didn't feel like I was going to mangle the sidewall in the tight turns.
    I went back to the 34mm PDX Crusades for this week's fast and flat race, and pumped those suckers all the way to 55psi. Lots of roadway, lots of hard and dry dirt, sections of rooty singletrack, not many tight turns and not much soft grass. It worked out really well for me and I didn't get much in the way of 'bounce' during the pavement straightaways even when I was spinning out my gear and sprinting. On the hardpack dirt it offered enough grip while keeping me from bottoming out on some of the ruts and divots, even when I just plowed into some high roots on the singletrack. In the softer grass I didn't get much 'float', but I didn't cut in and lose all momentum, either.
    "I feel like my world was classier before I found cyclocross."
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    Quote Originally Posted by VT Biker View Post
    A complete newbie to cross here, so please bear with me. I am not yet ready to take the plunge to a set-up tubulars, and after hearing about the horror stories of trying to convert a standard rim to tubeless, I am going to go into this a low maintenance as possible.

    However, I have a few questions:

    A) What disadvantage will I have, when most of the courses here in the Front Range of Colorado are dry and dusty vs. muddy?

    B) What is the lowest PSI you typically run when racing on standard clinchers, and are there any special tubes/techniques with the tubes needed to achieve that low PSI?

    Thanks in advance
    Fellow Front Ranger here. Following your theme, I'll keep it simple.

    You want the lowest pressure on which you will not pinch. As noted above, lower pressure = greater efficiency over rough ground, and most Colorado courses have a lot of rough ground. Lower pressure also = greater traction off-camber grass turns, and the very few courses here that are not very bumpy are grassy and fond of such turns. This far outweighs any benefits of higher pressure in other areas.

    Disadvantage to tubulars -the primary one is that they can safely be run at lower pressures, which means they will be ridden with greater efficiency over rough ground and have better off-camber traction. That said, as long as you have good, relatively high-volume clinchers, I don't think the difference is very big, and you will have plenty of clinchered company.

    For what it's worth, at just under 190lb, with 33mm tires (by label and in reality), I usually run about 36 on the rear and 32 on the front, although I'll lower both for the rare course with a low risk of pinching. A lighter buddy with the same tires runs a few pounds lower than me.

  9. #9
    Senior Member VT Biker's Avatar
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    As a follow-up,

    I am planning on running Stan's Sealant in my tubes, as I have been warned that the # of goat heads here increases the likelihood of a flat exponentially. However - I have seen little in the way of guidance when using Stan's Sealant as to:

    A) Amount to put in
    B) Tire pressure - they recommended a max of 40, but that was for the tubeless system. It seems to me that with a standard clincher/tube set-up, it makes sense to use a slightly higher pressure.

    FWIW - I am 144 pounds.

  10. #10
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    Quote Originally Posted by VT Biker View Post
    As a follow-up,

    I am planning on running Stan's Sealant in my tubes, as I have been warned that the # of goat heads here increases the likelihood of a flat exponentially. However - I have seen little in the way of guidance when using Stan's Sealant as to:

    A) Amount to put in
    B) Tire pressure - they recommended a max of 40, but that was for the tubeless system. It seems to me that with a standard clincher/tube set-up, it makes sense to use a slightly higher pressure.

    FWIW - I am 144 pounds.
    The goat heads aren't as often a problem as they used to be, because more promoters are making effort to stay away from them. That said, they still come into play on some courses, and are flat machines. I use Stan's becuase of them, and I think most Colorado crossers use sealant. The bottle says how much to put in.

    I don't know about the interplay of tire pressure and Stan's effectiveness. Since you still seem troubled by the low pressure concept, I suggest you go out to the cross course in Golden. Put your tires at 45 psi and ride a lap hard. Each lap drop it 5 psi until it feels too low. Then put 5 psi back in the rear only and do another lap. You'll probably be surprised where you wind up.

  11. #11
    coprolite fietsbob's Avatar
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    Seems to me,
    At some point the rolling resistance will outweigh the advantage to increased traction.
    I know from My Touring bike on a tour, Tires quickly lets me know
    when the PSI in them falls lower..

  12. #12
    TWD
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    Quote Originally Posted by colobrio View Post
    Fellow Front Ranger here. Following your theme, I'll keep it simple.

    You want the lowest pressure on which you will not pinch. As noted above, lower pressure = greater efficiency over rough ground, and most Colorado courses have a lot of rough ground. Lower pressure also = greater traction off-camber grass turns, and the very few courses here that are not very bumpy are grassy and fond of such turns. This far outweighs any benefits of higher pressure in other areas.

    Disadvantage to tubulars -the primary one is that they can safely be run at lower pressures, which means they will be ridden with greater efficiency over rough ground and have better off-camber traction. That said, as long as you have good, relatively high-volume clinchers, I don't think the difference is very big, and you will have plenty of clinchered company.

    For what it's worth, at just under 190lb, with 33mm tires (by label and in reality), I usually run about 36 on the rear and 32 on the front, although I'll lower both for the rare course with a low risk of pinching. A lighter buddy with the same tires runs a few pounds lower than me.
    precisely what I ride as well, same pressure, me at 193, Hutchinson Bulldogs on stiff Rovals. I might hear them bottom once or twice a race. I tried tubeless and couldn't keep tires from burping at the same volumes. Given unlimited finances I would buy tubies but thats just not he case

  13. #13
    Team Water Andy_K's Avatar
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    Quote Originally Posted by CliftonGK1 View Post
    I think it depends on how smooth the hardpack dirt is, first off. Sure, pavement is pavement (mostly) and you might get some slogging and bobbing about on softer tire pressures (especially if you're like me and race singlespeed and have to keep a crazy cadence sometimes.) But the 3 races I've done this season have all been dry and dusty, but the hardpack has been like the freakin' craters of the moon. Seriously, the Midsummer Night's race had stuff that was like the rumble strips on the side of a highway.
    I've raced on stuff like that, and it can be painful. I definitely agree that low pressure and fat tires are the way to go there. I'm expecting conditions like that this weekend as we'll be racing on flat pasture land and it hasn't rained in almost two months. I'm toying with the idea of dragging my mountain bike along just in case it's really bad, even though the course looks flat as a pancake.

    At the other end of the spectrum, at David Douglas CX two weeks ago even most of the singletrack was smooth as a baby's bottom. That's what I had in mind when I made my comment about using higher pressure on faster courses.

  14. #14
    Senior Member VT Biker's Avatar
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    Hey everyone,
    thanks so much for the advise. Going to put the tubes/tires on this evening, and take my first ride tomorrow on them at Valmont. I am going to try 50, see how they do, and then lower by 5 as you suggest.

    VT Biker

  15. #15
    Tiocfáidh ár Lá jfmckenna's Avatar
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    Quote Originally Posted by flargle View Post

    But of course proof is in the pudding, "optimal" pressure comes from pre-riding and tweaking.
    Yup it's all in the pre ride. I've done race pre rides on my Tubular wheel sets only to change to file tread (Ritchey Speedmax) clinchers because the conditions were more like a dirt crit. Tubs are ALWAYS better, thats the general rule. I now have a tubular set of file tread if in the event this ever occurs again. Happens rarely..

    But if it's dry where you are then clinchers are fine, but honestly, for a few years I disagreed with friend of mine and a Sachs team racer( who taught me a lot about cross) that tubs are not all that great till i tried them. World of difference in any condition...

    I never went below 35psi front and 40 psi back on clinchers FWIW and when I was in good shape I was weighing in at 190lbs
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