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Newbie Racer - CX vs road

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Newbie Racer - CX vs road

Old 01-12-15, 04:27 PM
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Newbie Racer - CX vs road

I'm a newbie racer, with one season of road racing and a whopping 2 CX races under my belt, so please excuse my ignorance, but -

Why is there no peloton in CX? With the exception of early season cat 5 races, nearly every road race I've been in or watched has a pretty tight peloton, and even breakaways and stragglers tend to be clumped in 2-6 rider packs. But in every CX race I watch, regardless of level, the pack explodes by midway through the first lap to the point that racers appear to be randomly distributed around teh course by 30 minutes in.

Is it simply that the speeds are slower, offering less benefit to draft and hide in the pack? Are skills more unevenly distributed in CX?

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Old 01-12-15, 04:38 PM
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I think it has more to do with the technical nature. It's more difficult to ride a wheel, and the efforts are more violent. If you watch a technical criterium, or a race with a lot of wind, a similar dynamic happens. Gaps open, and once they're open they tend to spread.
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Old 01-12-15, 04:44 PM
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What gsteinb said. There's no drafting advantage when you're shouldering your bike up stairs, for example.
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Old 01-12-15, 05:12 PM
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Riding on someone's wheel in a CX race is a great way to tangle up your bike and meet a tree. There are too many starts and stops, with unanticipated complications in the course many times. I don't trust anyone else on a cross race - only myself - and sometimes that's a stretch.
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Old 01-12-15, 05:19 PM
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I've never done a cross race but I did some mtb races. The big difference is the "minimum power required to move" bit, i.e. rolling resistance. On the road it's a negligible number; when on dirt or on foot it's a significant portion of your total energy output. Therefore once you reach your "I am going as hard as I can" level for a given surface then you're going to be limited to that speed, regardless of the draft etc.

On the road rolling resistance is relatively insignificant. The biggest limiter is wind resistance and drafting goes a long way towards eliminating a huge portion of that resistance.
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Old 01-12-15, 05:56 PM
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What @gsteinb and @carpediemracing posted

You still save 33% by drafting, but when the aero resistance isnt great to start with, the saving is even less.

In a 25mph race, it takes ~250w on the road to overcome aero resistance and 40w for rolling resistance. You save about 80w by drafting. Quite significant watt saving.

in a CX race where the average is 15 mph (and more dominated by stretches when you go quite a bit less), aero drag at 15mph is 60w whereas the remainder, as CDR mentions, goes to rolling resistance. You save 20w by drafting, which barely makes a difference.

as a tangent, also shows how a cobbled race affect things. Instead of saving 100w or more when sitting in while on good tarmac, roughness of cobbles increases rolling resistance and dips your speed down to the low 20's. You save 50w by drafting compared to the usual 100+, thus reducing effect of draft. Ditto for tailwind, when effect of drafting is reduced.

in someways it's interesting that tactics only comes into play b/c the speed gets high enough for drafting to be significantly advantageous. If we could run at 20mph, i'd bet running would be just as interesting
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Old 01-12-15, 10:35 PM
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Originally Posted by echappist
What @gsteinb and @carpediemracing posted

You still save 33% by drafting, but when the aero resistance isnt great to start with, the saving is even less.

In a 25mph race, it takes ~250w on the road to overcome aero resistance and 40w for rolling resistance. You save about 80w by drafting. Quite significant watt saving.

in a CX race where the average is 15 mph (and more dominated by stretches when you go quite a bit less), aero drag at 15mph is 60w whereas the remainder, as CDR mentions, goes to rolling resistance. You save 20w by drafting, which barely makes a difference.
On top of that, the technical component is very important and most of the ways that you would optimize your fit for aerodynamics actually penalize you technically. For example, you really need a much more upright position on a cross bike or you just won't be able to turn.

Things like rider weight also play out very differently than they would on the road. Compared to the road, being light and having less power as a result is much less of a weakness on the flats in cyclocross. I'm pretty sure that's down to greater weight correlating to greater rolling resistance over the rough terrain. If you're light, you "float" more across the bumpy stuff. Being light also is also a major advantage for cornering on cyclocross tires, the tires will resist folding and slipping away at higher speeds when there's less weight on them, and of course you can run lower pressures period. So differences in power are equalized a bit compared to the road, which further reduces the emphasis on drafting.

Still, none of that means that drafting doesn't matter in cyclocross, and I would disagree a bit with chappy that tactics only come into play because of drafting. On the road, yeah, drafting is the biggest reason for the importance on tactics, but while that dimension shrinks a lot in cyclocross, the technical features of the course and changing terrain introduce a different dimension for tactics and strategic application of strengths. I would say that the difference is that drafting makes small technical differences mostly unimportant in road racing, while the reduced draft in cyclocross makes small gaps introduced by differences in technical ability tougher to close. Really, I think it's the technical features that make for the biggest difference between the disciplines. For all that we like to talk a lot here about cornering skills, technical ability just doesn't usually amount to major differences in most of the road racing we do. Even in criteriums, the technical element pales to its significance in cross, where being able to go through a bumpy corner a little faster than someone else can very quickly add up to seconds or even minutes per lap. Things spread out so quickly because the spread of technical skill is so wide in a (amateur) cyclocross race.
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Old 01-12-15, 11:32 PM
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yes. you are right. i was exaggerating a bit. after all, we can have tactical stuff in uphill racing, another situation where effect of drafting is minimized.

also agreed on your point re: weight and rolling resistance as those are directly correlated.
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