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Triathlon frames and tire pressure(2 posts)

Triathlon frames and tire pressuremduell
Jan 9, 2002 5:15 PM
First question, why do triathlon bikes have the larger bottom bar on the frame?
Secondly, where do tires indicate their optimum pressure? On my MTB, its printed on the sidewall, but I cant find it anywhere on my roadie.

TIA

Mark Duell
re: Triathlon frames and tire pressurebrider
Jan 10, 2002 12:14 PM
By "bottom bar" I'm assuming you mean down tube, the one that spans the distance from the lower end of the head tube (the fork runs through this one) and the bottom bracket (the crank arm sindle runs through this). Usually, thay aren't necessarily larger, just have a deeper cross section for aerodynamic reasons. By making the axis parallel to the wind longer, the aerodynamic drag is reduced. If, in addition, the axis perpendicular to the wind narrower, aerodynamic drag is also reduced. For tire pressure on road tires, it depends a lot on your weight, the width of the tire, road conditions, etc... If you're fairly light (say about 150-160 lbs) on a 23mm width tire, road is smooth and dry, you can run them a little softer than others, say around 100 psi. If you're heavier, running narrower tires, or the road surface is rougher, you'll want to jack them up a bit higher, say 120-125. Myself, when I was racing (5'11", 155 lbs), I'd keep my 20mm tires at about 120psi all the time. I still use that pressure at 200+ lbs, but I occassionally run wider tires. Comfort is going to be a factor, as the harder tire will transmit more road shock and vibration into the frame (and thus into you). Of course, wheel comfiguration is going to contribute to this as well, and frame design. I use a Softride, so road vibration is a non-issue with me. Don't worry about blowing the tire off the rim -- burst pressures on most tires is well over 200 psi, something you'd be hard pressed to achieve with most pumps.