Thursday, August 21, 2014

Trek Emonda: geometry comparison and other comments

I'd left the Trek Emonda out of my previous comparisons for two reasons. One is it's technically a 2015 bike. Note, however, I'd included the Specialized Tarmac 2015, but that was an iteration on an existing bike. But more importantly I left it out because I don't like it.

You'd think I would, as it's marketed as a weight weenie special. But, unlike another weight weenie special, the Cervelo R-Ca, the Emonda is designed with down tubes which show an utter contempt for wind resistance. And for what weight savings? 30 grams. Yes -- 30 freakin' frams: the claimed weight for the Madone Vapor Coat H1 is 720, the claimed weight for the vapor coat Emonda H1 is 690 grams. There's a lot of ways to save 30 grams. 30 grams will save around 0.35 seconds up Old La Honda.... which I'm pretty sure will be squandered to wind resistance by the Emonda's bulbous down tubes. If the CdA of a rider on a Madone is 0.35, and if the Emonda is 100 grams equivalent of force more wind resistance at 30 mph (according to the Cervelo RCa white paper, the RCa is 102 grams more and the Madone 76 grame more than the Cannondale Evo, and the Emonda is almost surely more than the Cannondale Evo judging by the bulbously eccentric down tubes), then that's a CdA difference of 0.009. If you're going up Old La Honda in 16.5 minutes, that's 12.2 mph. That speed reduces the force difference to 16.5 gram-equivalents. That's 869 joules of work up Old La Honda. If you're riding at 300 watts, that's 2.9 seconds.

So weight savings is great, but paying 100 grams-equivalents of added drag at 30 mph for 30 grams of mass reduction saves you 0.4 seconds but costs you 2.9 seconds for a net time which is 2.5 seconds slower, assuming 300 watt power.

Note I assumed the wind resistance difference is 100 gram-equivalents at 30 mph. This is my best guess. But even if I'm off by a factor of two, and it's only 50, then it's still a full 1 second slower despite the mass advantagr.

So, you say, 30 grams? But what about the 4.6 kg weight? Madones are least 1 kg more.

This is really a matter of marketing by Trek. The reason the bike is so light starts with the mutant-light wheels which stock on the $14k Emonda. They are over 100 grams lighter than my Mount Washington wheels, which are already crazy light. There's a bunch of other similarly weenie-special parts on that top end Emonda. If you were to put those parts on the Madone, you'd have a bike which was very close in mass to the Emonda, with the possible exception of the semi-ISP on the Madone. The frame itself plays relatively little role in this impressively low mass. And indeed, Trek have priced the top-end Emonda so high, I'm fairly sure you could set up a Madone with that part list for less.

And if you look beyond the SLR, the top-priced Emonda frameset, the bikes aren't even remotely light. It's 1050 grams for the SL version, and 1200 grams for the S version, according to Trek. For comparison, 1050 grams is the same weight as this late 1990's Trek 5500, repainted. That's progress. My 2008 Fuji SL/1 is 860 grams for a size small.

Anyway, back to geometry. The top end Emonda comes only in the H1 geometry, according to the web site, but you can still get the SLR frame built to a more conservative part spec with the H2. The H2 Emonda is basically the same as the H2 Madone, but on the H1 Emonda Trek went a bit taller. Since a number of pro riders have adapted the Emonda over the Madone, this doesn't seem to be too much of an issue.


Note the H1 is slacker now, but it's still more aggressive than the Specialized Tarmac and Venge. If you slam the stem on your Tarmac, your fit on the Emonda H1 would have around 1 cm of spacers with the same stem, and your fit on the Madone H1 would have around 2 cm of spacers for mid-range sizes. In the smallest geometry only the Tarmac is close to the Madone and longer than the Emonda. Curiously the largest Emonda goes super-long, an apparent attempt to capture more of the statistical tail of tall riders, which makes sense.

Other aspects of geometry are similar to the Madone, which is a good thing. Bottom bracket drop is size-dependent, which makes sense since smaller bikes have shorter cranks and so can have a lower bottom bracket without cornering clearance penalty. Trail is relatively low, around 5.6 mm except for the smallest size which is only up to 6.1 cm in the Emonda (5.8 cm in the Madone). The moderate trail is due to the heat tube angle dropping to only 72.1\v{0.3}\-\-o\N on the Emonda (72.8\v{0.3}\-\-o\N on the Madone). Cervelo uses long-rake forks (> 5 cm) on the smallest R5's, but Trek uses a 4.5 cm fork on the smallest Madone and Emonda. Overall I think every aspect of the Trek geometry makes sense. Indeed the Emonda H1 would fit me better than the Madone H1.

So it's not really lighter, and it's obviously a lot less aerodynamic: why would any of the pro riders choose the Emonda over the Madone? One possibility is they didn't choose: the choice was made for them based on marketing. Another possibility is they fail to appreciate the importance of aerodynamics, which has strong historical precedent. Pro cyclists aren't necessarily more sophisticated than weekend warriors. But a third possibility is they've considered the aerodynamic cost, and balanced it against a benefit in ride quality. Indeed, Peloton Magazine in its latest issue reviewed the bike and said it was the "liveliest" Trek yet. Does this translate into better race results, despite the parachute-like aerodynamics? I can't say. Racing is an extremely complex dynamic. But I'd guess not.

1 comment:

Angry Bald Guy said...

An excellent example of making assumptions that support your obviously biased preconceived notions. Bravo,