Font vs. rear tire pressure

Discussion in 'Cycling Equipment' started by RC2, Aug 17, 2004.

  1. RC2

    RC2 New Member

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    I'm wondering what the conventional wisdom is on this. I've always used ~max PSI to minimize rolling resistance, 120-130 in the tires I'm currently using as trainers (Rubino pro's). Recently I've been using 20-30 PSI less pressure in the front to soften the ride -- my current bike is a bit more jarring, al frame, and I've had a bit of issue with hand numbness.

    I haven't noticed any effects to bike handling, but my local training rides are pretty tame w/r/t twisties and descents, and I've never really pushed cornering limits with the uneven pressures.

    Is this common? Downsides (other than a small increase in resistance)?
     
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  2. dhk

    dhk New Member

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    Not sure where the idea got started that running the max tire rating was the thing to do, but I did the same thing for about 20 years. Believe conventional wisdom is all wrong here.

    I weigh 170 lbs, and have used 95-100 psi front, 100-105 rear for the last couple of years now. I've found lower rolling resistance on most road surfaces, plus a much better ride, roadholding and grip. Also believe you'll have fewer tire cuts and flats.

    Now that you've discovered 100 psi in front, try the 100-105 in back. If you're under 160 lbs, I'd take another 5 lbs off these pressures.
     
  3. squidwranglr

    squidwranglr New Member

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    A tire inflated to a higher pressure (within its maximum rating, obviously) will always make less contact with the road (ground) than an equal tire inflated to a lower pressure. That results in a lower rolling resistance under all circumstances, I think.

    As far as flats are concerned, it's a bit harder to use intuition. On the one hand it seems obvious that once again, if less of your tire is making contact with the ground, the less likely it is to get punctured or cut. Furthermore, the firmness would allow it to "deflect" debris that might otherwise cause a flat. However, it's also logical that a slightly softer tire has a better chance of deforming as it rolls over debris than a firmer tire, therefore avoiding a puncture.

    I keep both of my tires close to maximum inflation, ever so slightly lower in the front to reduce vibration a bit.

    Berend
     
  4. dhk

    dhk New Member

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    I'd say it depends on the road surfaces you ride. Believe the conventional logic on rolling friction applies only to perfectly smooth surfaces, like a track or very smooth asphalt. On roads with texture, high pressure will cause more energy to be transmitted up the forks and frame, where it turns into frame buzzing. The articles I've read, and actual on-the-road experience with coasting against other riders, tells me lower pressures aren't slower at all.

    Going downhill at higher speeds, the correct pressures will give you better roadholding when you encounter bumps or course surfaces, so you can descend with less braking and more confidence. Just my experience, but suggest you give lower pressures a real try and for yourself.

    Have you noticed that Michelin Pro Race tires show a "Pressure Range" on the sidewall, from 87 to 116 psi? Believe if all tires had this, rather than just a max pressure rating, more people would run the correct pressures.
     
  5. cachehiker

    cachehiker New Member

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    Save for my first, rather naive year of road riding, I've always run my tires between 10 and 20 psi below the maximum recommended pressure. Unless I'm riding on roads as smooth as glass, I don't see a noticeable difference past 100 psi. The lower rolling resistance seems to be offset by the decrease in rear wheel traction on marginal road surfaces. I also attribute my luck with flats to my anal-retentiveness about having the pressure just right. I'm under 155 lbs. too, and I'm sure that the 100 psi threshold changes with rider weight.

    On smoother roads, I use Hutchinson 700x23's at 105 psi front and 115 psi rear. When they've been doing chipping and sealing, I switch from Michelin Pro Race 700x23's at 95 psi front and 105 psi rear to Michelin Carbon 700x25's at 85 psi front and 95 psi rear. They're noticeably slower but half of that is carrying the extra 120 grams of rim weight. I can ride a lot longer than my friends on such roads before the hands and shoulders start feeling hammered as well. Trying to keep up on better road surfaces also makes for great training.

    Typically, numbness in the hands results from too much weight resting on the handlebar. Moving my saddle forward just 3mm a couple of months ago let me go almost twice as far without numbness. When I move back to the top of the bar, I get the feeling back much quicker too.

    Bri
     
  6. lokstah

    lokstah New Member

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    A lot of folks seem verrrry particular about their tire pressure; something I never completely understood for cyclists not trying to shed a few seconds time-trialing.

    For high-performance tires and rims, anything in the 100psi ballpark is likely to be plenty fast. If varying between, say, 95psi and 130psi gives you differences in feel that are meaningful to you, then by all means, have a favorite setting -- but does it really make much sense to insist that 10psi below max is better than 30psi below max?
     
  7. RC2

    RC2 New Member

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    Good inputs from all and good point lokstah. I'm going to try out different pressures, and lower the back. I'm 180 lbs, so I don't think I'll drop much below the 100 psi range.

    My key take-away here is to ask my wife what she's using. I'm pretty sure she's using 100-110 psi, and as a 140 pounder, that's probably way too high for her in most circumstances. Now I'm wondering if any tire manufactures have some kind of guideline on rider weight vs. PSI.... probably beating a dead horse...
     
  8. Wurm

    Wurm New Member

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    Optimal tire pressure depends on several factors: rider weight, tire size/width, road conditions (wet/dry, smooth/rough), even the design of the casing and rubber compound, front or rear tire, etc.

    I weigh around 198 lbs. and on road tires sizes 25c & 28c I usually run no higher than about 107 psi F/112 R. I've found no real benefit to higher pressures with them.

    For 23c I go with 115F/120R. For 32c width I'm usually going to be off-road or on rougher dirt roads, (cyclocross) so it's about 43F/48R on the low end (soft or mud conditions) and no higher than 90F/95R (hardpack/pavement).
     
  9. cachehiker

    cachehiker New Member

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    I had this nut job buddy who insisted in running 130 psi in his Michelins. I forget which ones, but they were most likely the ones replaced by the Pro Race. He always complained about never having a set of tires last through a season. The tread would start splitting after the smallest of cuts and was always pretty worn after 800 miles. Granted I split miles between three sets of tires on two sets of wheels, but I'm guessing I'll get be getting close to 1500 miles out of my Pro Races at 105 psi.

    When I first started riding, I didn't pay much attention and was suprised with a few pinch flats after my tires lost more air in a week than I expected. At 80 psi, I had to be delicate with RR tracks and potholes. Then this buddy comes along and insists that I should be running my 700x25 Conti Sport 1000's at 120-125 psi. I never had so many flats in my life! Everything would suddenly puncture the tire, the cheap plastic rim tape tore, and then I blew a sidewall. I quit listening to him at that point.

    The guy isn't the sharpest tool in the shed but he is fast. Placed in the top 10 at Sea Otter a few times. He's been in jail for a while now for being a dumba** and blowing off a judge. Not a good idea. Instead of 60 days for another DUI, they threw the book at him this time.

    Anyhow, tire companies put a lot research into what pressures their tires work best at. Yunno, at what psi the sidewalls blow, what psi gives the best treadlife, rolling resistance, etc. My experience has dialed me into the 105 psi range, and I assume the recommended pressure provided by the tire company's research is generally 10 or 20 psi below the maximum. I therefore shop for tires rated to give me 10 or 20 psi of headroom. Another riding partner who comes in around 220 lbs. has switched to Vredesteins so he can have the same headroom at 125 psi. He's seems to be having better luck in spite of adding 50g of tire weight.
     
  10. lokstah

    lokstah New Member

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    Good points, cachehiker. The very best PSI setting for any rider is what seems to minimize flats, and feels right at the same time. I suspect for most folks, this is a little over 100 PSI, but you never know.

    Those who enjoy 130 PSI, more power to ya.
     
  11. Wurm

    Wurm New Member

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    I'm tellin' ya cachehiker, Vredestein's are The Sh!t. They're the ONLY road/CX/commuter clincher tires I use now, and I've spent way buck$ in the past on all of the major brands/models, and some of the less known ones. If I ever get the urge to go back to sew-ups, I won't be searching for Dugast's and Vittoria's anymore either - it'll be the Vred's.

    People whine about a dozen or so extra grams with comparably-sized Vred's - well I don't feel it at the pedals. All I can tell is a damned fast, comfortable, and great handling tire that doesn't get a flat with every pebble I hit.

    What, me worry?? :D
     
  12. lokstah

    lokstah New Member

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    Word. I use the Fortezza TriComps on my hotrod, and I've had nothing but great luck with them. I'd heard mixed things about their training/commuter-level tires, but the Fortezzas are more than tough/fast enough for me.
     
  13. cachehiker

    cachehiker New Member

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    I like the Vred's too. I use their tubes almost exclusively. When the big guy asked about the Fortezzas, mainly because he likes to run higher pressures, I recommended he try them. I myself haven't had a reason to try them. After all, I've had good luck with my three good sets.

    I've never had a flat on the Hutchinson Carbon Comps or the Michelin Pro Races, but I'm sure it will happen eventually. After over 4000 miles, I've only had two flats on the Michelin Carbons. Both of those came from riding in the dirt. I do more of this than I should which is why I keep them around.
     
  14. Wurm

    Wurm New Member

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    cachehiker -

    On the tube deal: I haven't yet tried the Vred's, (can ya believe it!?) but I'm going to. I've been running the Vitt UltraLite's for the past 1 1/2 years and they've been great until I put on my new Zondas. All of a sudden, I started getting the valves pulling out from the tube AND the valve pins leaked air!!! :mad:

    Probably because the Vitt's valves are only 36mm, and the Z's rims are 30, I dunno - it's hard to get a grip on them with the air chuck. I probably damaged the valves somehow along the way.(?) I didn't have any of the long valve numbers because I was using box rims before the Z's. Tried to get away with it for awhile, but "Yeah RIGHT"!

    Anyway, went to the LBS and picked up my other choice - the Specialized lightweight 48mm valves. So far, no sweat, but it's going to take some miles on these wheels before I can yelp too much about these tubes, because they're thinner than the Vitt's: 25-23c .7 or .8 Vitt's vs. 18-23 .6 Spec's.

    The Spec's have always done me right in the past, just like the Vitt's have. But before a puncture can get to the tubes they gotta go through the tire somewhere. That's why I like the Vred tires so much. If you have good rim strips and run the right air, you've got no worries there.

    lokstah -

    Like I said somewhere else (?), I use only the Campo, Fortezza Road, or Fortezza Tri-Comp. All 3 have the exact same casing & excellent rubber compound, (except as U know the Tri's have the harder rubber in the center). For the price I'm paying there's no reason to go to the Volante, Ricorso, Flex Sport, or Spider Extreme just to save a few buck$. Those last 4 models might be the ones you're hearing mixed reviews about? I've heard generally good things about ALL of the Vred's, except I know the Flex and Spider are a bit on the heavy side.

    As always - YMMV!
     
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