Ideal tire inflation pressure
Does anyone have thoughts on the ideal pressure for tire inflation, as I have heard some inflate to very high pressures? I have a zipp 808 in front and zipp disc in the back, thx!
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The short answer for clinchers is that very high pressures (you see people cite 180 lbs, for example) are perfect in the very limited instance that you are racing on a polished hardwood basketball court or other very, very, very smooth surface. Otherwise, you will never be FAR from optimal at ~100 lbs unless you are a very big guy.
For more realistic surfaces (read: roads), that uber-high pressure just makes your wheel bounce up and down (bad) when your tire should be deforming a bit (less bad) to let you ride along the road.
If you are a "generic" sized rider (under, say 180 lbs), then either follow the ratings on the tire (which can be looked up on google for most tires) or go to around 105-110 lbs. If you are using wider rims or are a lighter guy, you can get away with around 95 lbs. It turns out the wider rims have a little lower rolling resistance with the lower pressure and grip better as well. If you are very big, you need a bit more pressure...but surely not 180 lbs or whatever. :-)
FWIW, I'm 185lbs and run with Clinchers on FC808s and I usually race with ~110-115psi. When I used to roll with Tubulars, I would go a little higher at 115-120psi.
I often ride at 105/115 or 100/110; 5'10" - 155 lb
Personally, I'm not light, but I'm not heavy, I'm about 155 and I race on wide rims with latex tubes. Max I'll probably inflate to for a race is 105 psi, and that is mostly because I'll probably lose a few PSI throughout the day with the latex and probably sit closer to where I want to be, around 100.
The point William makes about high pressure and Crr is not an opinion, but rather something that has been validated through many Crr tests. If you were racing tubulars on an indoor track, inflate away, otherwise dial it back down.
Very high pressure "feels" fast because you feel the road more, which is due to all the bouncing I mentioned previously and others allude to. I race 145-150 lbs and do about the same as Trevor for IM. This year I got wider rims and I'm doing HIM, so I won't inflate to over 95 on race day.
Yes Joe, that's what I do. This will totally depend on what pump you are using. I'd be surprised if I lose more than 1 psi when I remove my pump on any given time... I have often stopped pumping and remove the pump at a given pressure, then decided that I wanted like 1-2 more psi. When I put the pump back on, it's almost always exactly where I had previously pumped to and have NEVER seen even 5psi lower unless I could hear it leaking out for a while like if I had trouble getting the nozzle out when my disc cover was on for example...
RE: rolling resistance -- The laymens reason a high pressure is good on a very smooth track is because there is nothing to get in the way of that tire/road interface, so the harder the tire is, generally the lower the crr and the faster it is... think of a bowling ball down a bowling lane. However, when you put a whole bunch of debris on the road, a hard, high pressure wheel will need to hit the pebble, then go up and over the pebble adding tiny vertical travels to your bike, thousands and thousands of times over 112 miles. When you have less pressure in your tires, your tire actually bulges in and simply absorbs these little bumbs so the pebble or crack essentially goes under your tire without your bike needing to climb over it. Think of a Mtn bike tire inflated to 30psi rolling over rocks or sticks. In this example, you will actually be able to see the tire compressing in the middle or sides to absorb these rocks or sticks without bouncing up in the air for every little bump. A shock on the fork of a mountain bike does the same thing, a front shock is like even lower pressure vs no shock which is like very high pressure. This example allows one to visualize the bars and frame of the mtn bike staying level as the tire and shock move up and down as you travel over small to medium sized debris. The problem with too low of a pressure is that you have much higher rolling resistance (crr) when you are actually on a smooth surface because your tire bends to compress a bit when it hits the road then extends back to the round shape again once the tire turns off of the contact patch (Imagine the bulge near the bottom of your car's tire when it is low on air). this is also why the rider's weight effects optimal tire pressure as well. Imagine that same car tire if it was just sitting there by itself without the weight of the car on it, this bulge near the bottom would disappear.
So you have to find the happy balance between too high and too low of pressure to optimize your crr over your entire expected race course. So at Kona with really smooth roads and minimal debris, you can ride higher pressure and at my recent Battenkill Road bike race with ~10 dirt/stone road sections, I actually ran about ~20psi lower than normal, but could have gone even lower.
My race wheels will probably be closer to 115psi.
Big Thanks from me too! (and fellow EN'er Cathleen!)
We raced last Sunday on TERRIBLE roads in TERRIBLE misty weather and saw lots of folks who flatted. Not us! We rolled with lower pressure and had decent bike splits despite the 22 turns, cruddy roads and bad weather on course!!!