Thursday, October 6, 2011

CX or 29er?

I'm on the fence here. I first raced Ironcross on a 26" hardtail MTB in 2003. I did well (5th overall), but it was a smaller field back then and the course was quite brutal for a CX bike. Numerous guys multiple flatted that year and complained about the quantity of terrain not compatible with a cross bike.

The last two times I raced Ironcross, I've used my Ridley CX bike with knobby 35mm tires pumped up super hard. The course has been tamed since the first couple years. There is less bony ATV track and more gravel road. An aero position with drop bars can be a real bonus on many sections of the course. I managed to podium the large masters field in 2009, the last time I raced here.

So why mess with success? The risk of pinch flatting on this course is very high. I run 60-70psi in my CX tires to help mitigate that risk. But that increases other risks, like losing control on a loose, washboardy turn at 40mph. There's also that two mile singletrack descent. I've never cleaned the bottom portion on a CX bike. I don't even try. It is all ledgy drops and loose rocks. With my skills, I'd go over the bars and need dental reconstruction. On a MTB however, I can fly through that section.

I now have a carbon 29er hardtail. It is a little lighter than my 26" titanium Dean that I raced in 2003, but much heavier than my cross bike. The tires are also about 60% wider and can only go half as high in pressure. So I'd increase the rolling resistance in most places, have no aero position, carry an extra five pounds around, for what? Minimal time is usually lost or gained on descents, about the only opportunities for a mountain bike to excel. The MTB comes with lower gears, which can be useful when cramping occurs in the 4th hour. Both bikes have Schwalbe Racing Ralph tires, my new favorite tire that I have on three bikes now.

I'm still curious though, curious enough to risk experimenting. The Ironcross organizers threaten to heckle anybody that brings a MTB. I saw lots of them last time. I don't think any of the podium finishers were on MTBs, unlike the first couple years. The race could certainly be more fun on a MTB. Winning once and a while is fun too. Help me out here. For once, I might get to race in my definition of IDEAL conditions!


Chris said...

So, put skinnier tires on the Gary Fisher, say 1.9" or so. Run more pressure. Put aero bars on the MTB. There you go. completely bastardize the whole thing.

DaveP said...

I'm rubbing my crystal balls.....what will the future hold.....will he cramp?, will he whine about the food stops?, will the hotel room smell like carpet cleaner?, will he forget his endurolytes again?, will some body part reel it's ugly head?

Hahaha, looking forward to reading your post race report.

Anonymous said...

Why not run a nice fat pair of tubular cross tires? Low pressure and low weight. You'll be much more comfortable and be able to handle much more the a pair of clinchers at 60 PSI.
A 35 c tubular would be a great set up. Just bring Vittoria pitstp just in case you puncture.

CB2 said...

I with Chris on the tire front. You could run Karma 1.9s, Stan's Raven or Crow, or Maxxis Aspens @ 35-40 psi.
Flip your stem or get a flat bar for a more aero position.

Hill Junkie said...

I have set of Raven's, a narrowish 2.0" tire. They are wicked fast but a little too scary light for my comfort level. One of them weighed less than 400g for a 29" MTB tire! My 35mm cross tires with tubes weight over 500g. Point is, the sidewalls are thinner than Michelin Pro3 Race sidewalls. First ride out on them they spewed Stan's twice from sidewalls but sealed up nicely after that. Might consider swapping the Ralph's out and take the risk. It could give DaveP entertainment if I flat twice and whine a lot about it.

I have brand new set of Ultegra tubeless wheels I haven't mounted tires on yet. I wanted to put tubeless CX on there, but tubeless-ready tire selection is still extremely limited. Next year...

bikesmith74 said...

Remember who told you to bring your hard tail for the 100! I usually choose reliability over potential speed gain. Mentally you'll prob be wanting to push the bike harder if you choose the S-Fly. You'll feel validation when you pass the first racer with a pinch flat. I like the Bonty XR1's also about 400g. They were also my tire of choice last year at the pinnacle when I beat the now legendary Alby King. Good luck with your decision, and with the race.

Mr. Speer said...


I say ride the cross bike, slow the hell down for hours 2 and 3 (by that, cut 2 or 3% perceived effort) and then put the hammer down the 4th hour. Make sure you don't forget your electrolyte shit this time either! I say if you didn't cramp that would be the biggest gain over any fricken bike or wheel setup you choose.

good luck,

j speer