Originally Posted by
Andy_K
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.