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Why use lower than Maximum tire pressure?(18 posts)

Why use lower than Maximum tire pressure?GeoCyclist
Dec 14, 2003 10:42 PM
I understand the advantage in reducing tire pressure while cycling offroad in sand (MTB). But I can see no advantage to cycling with less than maximum pressure when riding a road bike. Why would you want to use less than maximum tire pressure on a road bike?
Ride Qualityrussw19
Dec 14, 2003 10:59 PM
Riding on bad roads at 120psi while on a stiff aluminium bike and weighing 120 lbs will take a toll on your body. Lowering the pressure will allow the tire to give and absorb some shock. Otherwise we all might as well ride solid tires. Traction could also be an issue, but I think at the size of the contact patch for a road tire, I doubt that would make much difference.

Russ
re: Why use lower than Maximum tire pressure?Woof the dog
Dec 15, 2003 12:58 AM
Vredestein makes tires that go up to 145 psi in 23c and 160 in 20c. I have been in one race where I almost took out a teammate because I knew I wasn't making a corner at 145 psi. I had to straighten out, he then had a nice bent spoke from running into my rear der. I was being a dumbass with that kind of pressure for that course.

time trial is different story.

woof.
Get better tires or learn how to cornerspookyload
Dec 15, 2003 6:55 AM
Tire PSI should never have anything to do with how fast you can take a corner. Barring the fact you are not using a stupid tire not meant for crits, any high end tire should hold for TT or roadrace. People who try using supersonics or Vittoria ulraspeeds or any 20mm tire in crits deserve the dropping they usually get.

The only real reason for lowering PSI is for ride comfort. You do this at the increased risk of pinch flatting on train tracks and pot holes though.
NOOO, YOU get better tires or learn how to cornerWoof the dog
Dec 17, 2003 1:03 PM
I corner just fine, but at that time I was coming in too hot. Cyclists can't corner at the wrong speed because you run out of room and crash into fences and stones and trees. The decision to straighten out was the correct one, because I trust myself and I usually know the limits... well obviously not with tire pressure ;-) at that race.

Tires are perfectly fine, they are 23c. 20mm or 23mm tires do not make a difference, really, I've ridden both types in all kinds of weather and all kinds of races. If anything, everyone should use 20mm because they are faster. The tire pressure does make a difference in how tires corner though, so maybe in that regard 23 is a little bit better. You can tell me all this mumbo jumbo about the slipping point of the tire, and how it will slide out only if that point is crossed, but maybe, just maybe, in your reasoning you are missing the fact that you are not cornering on a perfect surface, there is sand and some oil and sometimes potholes...

Not to be a dick, but I think you are plain wrong here, because in my overall experience (racing and training), if you go into a corner with 145 psi, the chances are greater at sliding out compared with 120 psi. I just said why.

I stand behind what I just barked 100 percent because I, just like humans, can feel the bike and the point which we all better not cross. I've slid out enough times and hope not to repeat these experiences. So yeah, it was a dumbass thing not to expect dangerous turns like this in a race. It ain't a time trial, d'oh!

Woof the dog

P.S.

What are YOU talking about? Comfort my dog a$$!

:-O
re: Why use lower than Maximum tire pressure?alchemy
Dec 15, 2003 1:12 AM
I read an article by Uncle Al in Road Bike Rider (it's in the Uncle Al's Rant section). He recommended 95psi rear and 90psi front on the basis it would improve road feel and reduce the chance of pinch flats. I was sceptical at first but it's good advice. I get better feedback and I've hit a couple of things that I'm sure would have wrecked my tyres if they were at 120psi but caused no damage at all. I haven't noticed any increase in rolling resistance (which is an over-rated factor anyway from what I've read in some posts on here).
I read somewhere,...AJS
Dec 15, 2003 6:53 AM
...though I don't remember where it was now, that with any p.s.i. above about 90 there is no gain (or very little) in less rolling resistance. Don't know if that's true, but IME I used to run my Vitt tubulars at 120F/115R and the bike DID seem to roll easier than at <100 p.s.i.
I read the same articleDINOSAUR
Dec 15, 2003 8:54 AM
I read the same article and was rather skeptical. I had been running 120 psi on my tires for a couple of years (various brands). I gradually over a period of time reduced my psi and now run 108R and 105F (I weigh 195/200 with 700x23 tires). I noticed that the ride on both of my bikes is less harsh and the biggest improvement is tire wear. If I'm lucky I can usually get about 1500-1600 miles on a rear tire (usually Conti GP3000's). I have over 1K on my current Conti's and they are about half worn (if that). My next experiment will be to go to a 700x25's as I think that will increase my tire life. Another factor that I read is the silca compound used for tire casings has a limited stretch factor, so increasing your psi might do more harm than good. Tire wear was a big plus for me, plus a better ride. I think a 700x25 tire will make a big difference if you are a big rider. Unlike Uncle al, if I run below 100 psi I have to be very careful as I ride lousy roads and pinch flats are a problem. A lot of it has to do about the types of roads you ride, type of riding, body weight, tire manufacturer and so on. The key is to experiment. Also on the roadbikerider.com newsletter Fred Matheny said that the best thing you can do for winter riding (wet roads) is to decrease your psi as it puts more of your tire on the road for better handling and improves traction.
Lower pressure is way better...zero85ZEN
Dec 16, 2003 10:37 AM
...Uncle Al is right. Over inflation is rampant. I ride 90 front 95 rear (I'm light, 135 lbs) and my bikes perform better: more comfort, less pinch flats, longer tire wear, better traction. It makes sense, it works and it is good advice.

Listen to Uncle Al. He's a wise old man.
Or, Why ride higher than 110 PSI?Spunout
Dec 15, 2003 4:58 AM
If you weigh 230, you shouldn't be on 19mm tires, so that should solve the pinch problem.

Rolling resistance improvements are negligible. Handling deteriorates, danger, high tire wear, blowouts, and death.

I race 23s at 105 front 110 rear and weigh 160.
I agreeThe Human G-Nome
Dec 16, 2003 4:11 PM
I weigh 145 and race 105 rear, 100 front. I've never felt like I needed higher pressure. It does your cycling good not to feel like your jumping all over the road every time you hit a crack or rough patch. I think that alone negates the advantages you might have had for running slightly higher pressures.
Wet road conditionsSpoiler
Dec 15, 2003 2:04 PM
BTW, I also run less than 100 psi for comfort reasons. You have to take your body weight into consideration. At 140 lbs, 90 psi is the happy medium between comfort and no pinch flats. If I weighed 200, I'd use much more pressure.
Thanks for the feedback...GeoCyclist
Dec 15, 2003 3:57 PM
and confirming my suspicions that low psi is a comfort issue. For those who posted about reducing psi to improve handling on wet roads; I wouldn't count on this. There have been millions of dollars spent by the pro auto racing groups to test this theory. Reducing the tire pressure results in an increase in hydroplaning as a softer tire will not cut through the water as well as a hard tire. MTB sand riding is the only place where I reduce the psi to achieve a float on top of the sand.

Thanks again!
Foolishness on hydroplaningKerry Irons
Dec 15, 2003 6:25 PM
You're right about hydroplaning with auto/truck tires but it is virtually impossible to get a bicycle tire to hydroplane at any speed, any water depth, or any tire pressure that you would sanely contemplate. The reason for lower pressures is to increase traction, improve comfort (tied for first place, depending on personal preference) and reduce wear (a distant third). A larger contact patch is the reason for lower pressures in the wet. You will NEVER hydroplane.
mmm it dependsWoof the dog
Dec 17, 2003 1:13 PM
think of it this way:

Dry: little bumps and valleys in the road that your tire's rubber graps onto. In the corner, its probably better to corner on the asphalt, not a painted sidewalk line because it is smoother.

Wet: same thing, but there you got water in those little valleys. Almost like a librication for condoms. It is not like your tires magically dry out at those contact patches as the wheels rotate. There will always be some water between the tire and the asphalt. So, I guess hydroplanning, a microscopic one, is possible then, even if it has no real effect. Unless your idea of hydroplanning is something rediculous like in cars. On the other hand, wouldn't you think that the reason why people slide out on wet painted lines is because of hydroplanning: i.e. there is enough water between the tire and the road to cause loss of friction.

I agree on the larger contact patch. So if you ride harder pressure, you do reduce contact patch.

mmmm

woof. the dog.

let me know what you think.
Accurate Terminologyasgelle
Dec 17, 2003 4:31 PM
The effect you describe

"There will always be some water between the tire and the asphalt. So, I guess hydroplanning, a microscopic one, is possible then, even if it has no real effect."

Is lubrication. Hydroplaning is when the pressure at the leading edge of the tire contact patch is sufficient to lift the tire above the road surface. Given the shape of bicycle tire contact patch (like a canoe) this is virtually impossible.
There's a difference between hydroplaning and less frictionKerry Irons
Dec 17, 2003 4:41 PM
Hydroplaning, by definition, is where the combination of enough water and speed makes the tire literally separate from the road, leaving a layer of water between the tire and the road surface. You can't brake or steer because the tire is not in contact with the road. This is a completely different phenomenon than the reduced friction caused by a damp or wet surface. In the latter situation, the coefficient of friction between the rubber and road surface is reduced due to a thin film of water acting, just as you said, as a lubricant. This is NOT hydroplaning.
i see (nm)Woof the dog
Dec 18, 2003 1:04 AM