Tuesday, August 19, 2014

Stack-Reach smackdown: Trek vs Specialized

Last time I compared Trek to Cervelo for stack-reach. The Madone H1 and the even more aggressive Domane Race were much longer/lower than the Cervelo H1, and even lower than the more race-geometry Cervelo R-series from 2008. The Madone H2 and Cervelo R5 were comparable. The Trek Domane 6 was substantially more relaxed than the Madone H2. It's really designed more as a century bike than a race bike, although it may provide a good fit for some racers.

Here I compare the Specialized line to the Trek line. I already looked at the 2015 Tarmac. In the following plot, I add in the Roubaix endurance bike as well as the Venge aero road bike:

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The Venge is basically identical to the Tarmac. The Roubaix is fairly close to the Trek Madone H2, not nearly as relaxed as the Roubaix: around 2.5 cm spacer difference. The Madone H1 is more aggressive than the Tarmac, however: with two lines of Madone they can afford to be more aggressive on the longer/lower version. This suggests for racing the Roubaix may well be the better choice than the Domane, unless you want to spring for the super-low, super expensive Domane Race.

Monday, August 18, 2014

Stack and Reach of Trek Madone, Domane

Previously I plotted the Trek Madone stack-reach. Consistent with using "race bikes" from other manufacturers, I used the more aggressive of the two geometries, the H1. The H1 used to be called the "pro" geometry, in contrast to the more relaxed "performance" geometry, but Trek decided, apparently, that this implied the more relaxed geometry was a lower standard, compelling weekend warriors to buy bikes which didn't fit them well. So the "pro" became H1, and the "Performance" became H2.

In addition to the Madone, the Domane is also a legitimate race bike, sold for comfort at some cost in mass. The standard Domane, as is the standard with "endurance" bikes, has relatively relaxed stack. To compel professional riders, most notably Fabian Cancellara, to ride the frame a lower-stack model needed to be developed. Since the UCI requires bikes given to professional riders be made available to the public, Trek made available a "Domane Race" version, with low stack. I must say this looks to be a very attractive bike.

Here's how the stack-reach numbers compare on these frames:

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I show for comparison Cervelo geometry, 2008 and 2014.

The Madone H2 is very similar to the H1 with 4 cm of spacers. They also have an additional size in the H2: 8 versus 7 for the H1. This is very impressive. A lot of bike models are sold in only 6 sizes. Cannondale sells 8. The Trek Madone has 15. But even if it's relatively relaxed versus the H1, the H2 is within 1 cm of spacers within the Cervelo R5. So it's hardly endurance category.

The Domane Race is even more aggressive than the Madone H1, which should make Fabian happy. Obviously with Trek selling only one model, at over $10k each for the full bike, the intent isn't widespread distribution on this one.

The Domane is more relaxed still. A Domane with slammed stem is like an H2 with between 2 and 3.5 cm of spacers on the stem, depending on size.

All of the bikes are clearly designed to a stack-reach standard, since the parameters sweep out nice smooth curves in stack-reach space. They're not straight lines, like Cervelo pioneered, but then perhaps straight lines aren't optimal.

Sunday, August 17, 2014

stack-reach comparison: Specialized, Colnago, Felt, Parlee, Cervelo

More stack-reach comparisons, retaining the tall (Cervelo R5) and long (Trek Madone H1) winners from last time:

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First, there's a new obvious "tall" winner, and that's the Parlee Z5 tall model. Of course this isn't a fair comparison, as it would make more sense to compare the Parlee tall geometry to the endurance geometries of other bikes, but I put this here for comparison since I recently test-rode a Parlee ESX. The regular Parlee Z5 geometry corresponds to around 2.5 cm less spacer height, and has more traditional road racing geometry (clearly not designed to a stack-reach spec, however, since the curve zig-zags).

Specialized is interesting, as the smallest 3 models are essentially constant reach, changing only in stack. This is because top tube length is directly canceled by seat tube angle. This keeps the reach the same as the top tube is lengthened. The bikes still fit bigger riders, however: adding spacers to the smaller frames would bring them to a shorter reach for the same stack as the larger frames (see dotted blue lines). The smallest Specialized is a good fit to riders who want a relatively low stack with what is still a moderate reach. Note for the same stack, it's 2.5 cm more reach than the small Cervelo R5.

The Canyon AeroRoad is another bike, like Cervelo and Swift, which is apparently designed to a stack-reach curve. The largest Canyon wins the "long and low" award for this comparison, beating out the Trek Madone.

Overall, though, the Felt F1 is lower than the Canyon. It covers a significantly longer reach range than Madone for essentially the same stack range, going from shorter in the small sizes to longer in the longer sizes.

Colnago has two models, a sloped top tube and a parallel "traditional" top tube, for its C60. The geometries are very similar, although the traditional model has fewer sizes. Colnago, like Specialized, is also constant-reach for part of the size range, with four having essentially the same reach. With the limited reach range, Colnago goes from Canyon-like in the small sizes to Cervelo-like in the large. Colnago's sloped model has the most sizes of any model here: a remarkable 9. Colnago's are pricey, but they want to make sure you get a good fit. They actually used to run even more sizes. Cannonondale is another range with a closely spaced size range: I showed them last time. But even Cannondale only has 8.

Saturday, August 16, 2014

Trek Madone, Scott Addict, Cervelo R5, BMC SLR01, Swift Carbon geometry comparison

More bikes added to the stack-reach plot I showed last time. It's tempting to add more and more but I run out of colors, and humans have only 3 color receptors so there's contrast only between so many...

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Again the mostly vertical blue lines indicate points which can be matched to fit with the same stem but with more spacers on the lower stack, longer reach frame. Spacers reduce reach and increase stack. I additionally added mostly horizontal blue lines, which are spaced by 1 cm spacer height apart, again assuming a 73 degree head tube. These lines would correspond to points which you could reach with the same spacer height, but different length of 0 degree stem. Of course stems aren't typically 0 degrees 6 degrees, 10 degrees, and 17 degrees are popular, and these can be flipped positive or negative. But the spacing between these lines is the key point.

For small riders, Cervelo and Swift rule, Swift providing less stack, the Cervelo geometry at this size only relatively unchanged from the 2008 Cervelo. For big riders there's several contenders: Cervelo, Trek, BMC, with Trek providing the lowest stack. It would take around 2.7 cm of spacers to bring the Trek up to the bar height of the Cervelo.

In the mid-range, Trek is the low-stack king of this group, with Cervelo the big-stack leader by far. Note the difference between the Trek and the Cervelo here is around 5 cm of spacer. This is why among the pro riders you see so many slammed Cervelo stems with riders on small frames.

Cannondale clearly is not designing to stack-reach. Personally I don't care: I only need to fit one bike, so for a given point on this chart which would be my best fit, all I care about is which bike is closest. The shape of that bike's curve doesn't matter. If I were fitting a team or running a bike shop I'd feel differently. In contrast both Swift and Cervelo are clearly designed to stack-reach: their ranges form essentially perfect lines on the plot.

Wednesday, August 13, 2014

Swift Carbon, BMC SLR, Cervelo old and new: geometry comparison

Last time I noted that Adam Blythe when he switched from the BMC Pro Tour team to the NFTO continental team his stem went to something truly disturbing: a giant horizontal protrusion from the front of his otherwise very nice looking Swift Carbon frame. The obvious explanation is frame grometry: the BMC allowed a lower, longer position than the Swift. So I decided to check this.

Here's a plot of reach (x-axis) versus stack (y-axis) as reported by various frame brands (I need to be careful not to say "manufacturers"). I compare the BMC SL01 with the Swift Ultravox Ti, along with two favorite references, Cervelo old (2008) and new (2014).

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Slight digression: Cervelo decided to take a fresh look at geometry back in those days by setting a seat tube angle of 73 degrees for all frames. They reasoned that the human body when it's shorter or taller is still optimized by the same seat tube angle: the desire for steeper seat tubes in smaller geometries is more driven by the desire to avoid foot-to-toe overlap. But skilled riders don't worry about foot-to-toe overlap, they decided: if there was contact, then it was at such slow speed that it wasn't a problem anyway (turning at such a radius at higher speed would result in a crash, overlap or no). Their point was it was reach which mattered, and while a steep seat tube would allow for a short top tube without overlap, the fit advantage of a shorter top tube was squandered when the seat needed to be jammed back on the rails. So they advocated for stack and reach being the two dimensions by which geometry should be primarily judged.

I like Cervelo: I don't always agree with them, but they are dogmatically engineering-driven: everything on their bike designs except for paint job is justified by sound functional reasoning. It's no coincidence it's on paint and graphics that they tend to go terribly, terribly wrong. But I digress.

Anyway, they complemented their R-series frame, which tended to follow a low trajectory in reach-stack, with an RS series, which allowed for a more "relaxed" position. But they subsequently determined that shorter riders benefitted most from the R-series geometry, while taller riders more from the RS-series, and so they redesigned their geometry to follow a straight line in reach-stack. At shorter reach, the stack was close to the original R-series. At longer reach, it became similar to the RS.

An additional big change they made was to go to longer rake forks and slacker head tubes on the smallest sizes. The combination of a slacker fork and more fork rake increases the front-center while allowing for the same trail. Thus the toe overlap problem is minimized while retaining responsive handling.

Another change: they increased the chainstay length from 399 mm to 405 mm, the minimum recommended by drivetrain manufacturers. With 10 or 11 speeds in the rear, the chain deflection angle becomes large the shorter the chainstay length. With 399 mm, there could potentially be chain rub against the big ring on the small-small cross-gear. The change was just 6 mm, but at some point the next mm makes a difference.

Anyway, digression over. The point of this post was Swift versus BMC.

Of the four bikes on the plot, the Cervelos offer the widest range of reach. It appears from the plot that the 2014 R5 has less than the 2008 geometry, but this is misleading: the angle between the coordinates of the top of the head tubes, which determines stack and reach, is 82.6 degrees between the two frames. That means if you added spacers on the old bike to bring the bars up to the same level on the new bike, with the same stem, the bar on the old bike would actually be further back.

For supporting long-and-low, however, both the BMC and the Swift are well ahead of the Cervelo 2014. Compared to each other, the Swift is lower at short reach, while the BMC is lower at around 40 cm reach, the longest the Swift offers. BMC's largest frame is a full cm longer than Swift's, but this isn't relevant to Adam, since he doesn't ride a large frame.

One thing is clear, however, which is that Swift Carbon followed Cervelo's "new" model of designing to stack and reach. However, they did so using a "lower and longer" trajectory. Those who find the Cervelos too upright might find a better fit with these bikes.

How to reconsile this with the photo of Adam's bike remains a mystery.

Tuesday, August 12, 2014

NTFO win in London

Adam Blythe, 2013 BMC, 2014 Continental team NFTO, won the London-Surrey Classic this past Sunday in a remarkable upset, beating the World Tour riders otherwise dominating his winning breakaway. I watched the final 10 km on youtube, although that video seems to have since been pulled. Too bad -- it was an impressive final.

Adam was there with 5 pro tour riders including Sky's Ben Swift and BMC's former world champion, Philippe Gilbert. Although Blythe was on BMC last year, obviously his preparation for this race was handicapped by the lack of top caliber race opportunities available to his team, NTFO. Despite this, he took his share of the pulls, longer pulls than some of the others. Surprisingly there were no attacks in the final kilometers, the group instead working together until the end game began well within the final kilometer. Adam went from relatively long, not wanting to get jumped by Swift, and it worked. He held his gap to the finish, winning his home "classic".

Good stuff.

The NFTO bikes and kits look really good. The jersey and shorts are well-fitting and make good use of color, mostly black and red, a distinctive combination. The bikes are Swift, a small company which also sponsors the Drapac team in Australia. Their frames aren't particular light and are certainly not aero, but they look good and delivered Adam to the win in the race.

In addition to Shimano Di2, which is hard to argue against from a functionality perspective, the team has wheels and bits from Enve Composites. Enve stuff looks really good, is well made, but is heavy for carbon. In this case, however, with the UCI 6.8 kg rule, this wasn't much of a handicap.

The bike looks really good. Here's a photo from the team blog:

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And here's NFTO rider's Russell Downing's bike (BikeRadar article). Note the Enve stem. Russell runs only 49 mm saddle-to-bar drop, not much for a pro (I have 80 mm on my Ritchey Breakaway):

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One notable thing about Adam's bike is the stem: a truly impressive demonstration of SlamThatStem.com :

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Whoa! Is that a stem on your bike or are you just happy to see me?

One thing of note is the stem isn't Enve: it looks like an FSA to me. This is because the NFTO philosophy is fit first, sponsorship second. Pro Tour teams could learn something. Enve doesn't make a stem like that: it may be FSA, but I'm not sure.

His BMC last year wasn't quite so extreme. Here's a photo of his 2012 BMC from Cycling Weekly:

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And here he is racing in Qatar last year. Unlike Andy Schleck, for example, Adam can reach his drops. He seems reasonably comfortable, although the mutant bend in his back allows his rather exceptional saddle-to-bar drop.

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You'd think the Swift Carbon must be some sort of endurance bike geometry, but it doesn't seem so. The geometry is described here. The head tube lengths seem quite reasonable. The trails are slightly long in the middle frame sizes, but otherwise I see nothing exceptional. In contrast, BMC seems longer. Did Adam's position change?

As nice looking as the NFTO set-up is, there's nothing to replace doing the big races with a Pro Tour team, and hopefully Adam makes it back to the top level next year.

Friday, August 8, 2014

Specialized puts a 1980's Allez in the "Win Tunnel": the Venge beat it, but what about the Tarmac?

For a long time I've been alarmed by the trend in carbon bikes to go to fatter and fatter tubes in a never-ending quest for higher stiffness-to-weight ratio. Indeed the trend predates carbon fiber: it goes back far further, to Cannondale, and before that, Klein with their fat-tube aluminum bikes. To save a relatively small amount of mass, giving up a large amount of wind resistance.

But then as the quest for lighter carbon frames started approaching a limit, there was an effort to gain performance elsewhere. So wind resistance got renewed interest. Starting perhaps with the Kestrel Talon, there were a series of "aero road" frames which, at the cost of around 200 grams more or less, performed much better in the wind tunnel.

These frames had a hard time catching on with professional riders, however. Road cycling is performed mostly in packs, with fatigue and avoiding crashing both major factors, so optimizing the bike is a lot more than optimizing speed at a given power: it's about positioning yourself within a pack, of reacting to attacks, of confidence at speed. For whatever reason the aero frames didn't provide these things, and the majority of riders remained with the fatter-tube bikes designed for stiffness and handling.

This led to a compromise: bikes like the Scott Foil, Cervelo R5 (and RCa), and the Trek Madone incorporated aerodynamic features like truncated foils into their frame designs in order to split the difference aerodynamically between the "aero" bikes and the bikes designed without any consideration to aerodynamics. These, I thought, had hit the sweet spot.

But they were basically working to undo the damage which had been done going to fat tubes in the first place. What of the lowly steel bikes with their relatively narrow one-inch tubes? How would these do in the win tunnel? Tony Rominger set an impressive hour record in the 1990's on a steel tube frame, going more than 53 kph. This is fast by any standard. Of course, Rominger used EPO, which helped, but nevertheless it was clear his steel round tubes didn't handicap him too badly. Nobody has much of a financial interest in showing whether standard steel tubes do compared to, for example, a Specialized Tarmac or Trek Emonda.

Finally Specialized, ironically, delivered. Specialized built their own wind tunnel in Morgan Hill, California, which allows them to investigate a lot of questions which become harder to justify if you're using a commercial facility with a high cost/hour. But for some reason they compared an old steel-tube Specialized Allez bike with a state-of-the-art Specialized Venge, an "aero road" bike designed to be on the leading edge of UCI-mass-start-legal frames.

Here's the video:

So the result is the Venge was 50 seconds faster per 40 km. What do I do with this number? First, I need to make some comparisons.

The test rider in the video has a relatively relaxed position compared to most pro racers. Tour magazine did a wind tunnel test with a dummy rider and got a CdA of 0.32 m2. Analysis of rider speed-power data has shown a good match for climbs of a CdA = 0.35 m2. I'll assume this rider is more like the pro racer climbing position than the more aggressive Tour magazine dummy.

I'll then assume that the 40 km time is at an assumed speed of 40 kph. This is an excellent time on a road bike with drop bars.

Then I'll assume that the time comparison is under the assumption power is proportional to speed cubed. This is a standard approximation which neglects the effect of rolling resistance, but it's commonly used.

I start with the fractional time savings: 50 seconds out of 1 hour is 1.39% time saved.

I assume power saved is three times speed saved, so the power difference, and therefore the difference in CdA, is 4.17%.

Given the baseline CdA value of 0.35 m2, I then get an absolute difference in CdA of 0.0146 m2.

There's a common standard, especially in the US, that tests on wind tunnels are done at 30 mph (Specialized echews imperial units and uses 50 kph = 31.1 mph, but plots with 30 mph are common). Assuming 30 mph and an air density of 1.2 kg/m3, this difference in CdA corresponds to a difference of 21.1 watts, or a difference in force of 1.57 Newtons, which is 160.4 gram-equivalents of force, or 0.353 pounds less retarding force on the Venge versus the steel bike.

This isn't at all surprising, as was described in the video. Round tubes aren't close to optimal for wind flow, while the shaped tubes on the Venge, along with the hidden cables, are. Additionally the downtube shifters on the steel frame add some wind resistance. The other components are probably a wash.

But my interest isn't so much in the pure aero road frames, but rather in the middle-ground frames like the Madone and the Cervelo R5, and even more so in the bikes like the Emonda and the Tarmac. Is is possible my humble steel Ritchey Breakaway is actually faster on the flats than these super-expensive carbon bikes?

For comparison of results, it's best to compare with other tests which included a rider on the bike, since some parts like the seat post or handlebars may affect wind resistance more on a naked bike than with a rider. Both Cervelo and Tour magazine use dummies: Cervelo uses its dummy of Dave Zabriskie in his CSC days, while Tour used a clothing mannequin. I don't have good data from Cervelo, but I'll show some 2012 data from Tour.


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Recall I concluded the CdA difference between the steel bike was 0.0146 m2. The horizontal lines on the Tour magazine plot are 0.0100 m2. A difference of 0.014 is thus comparable to the spread in values from the Tour test for moderate yaw values from 0 to 10 degrees. Curiously the Cervelo and the Venge both have issues at zero yaw, but move to the front of the field at 5 degree yaw. This was also seen by Tour in their 2011 test of the Cervelo S3. In any case, the Venge is 0.011 m2 better than the "reference bike" with the same wheels at 5 deg, and 0.029 m2 better at 10 deg, 0.027 m2 at 15 deg. Whatever the reference bike, the Specialized test of the steel bike seems to be doing a bit better, depending on what sort of yaw angle averaging Specialized used in the 50 sec/40 km number quoted in the video.

The next plot is from Bicycling magazine showing bike-only data, no rider.

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The bikes here are the Cervelo S5, the Specialized Venge, the Felt AR1, the Blue AC1, the Scott Foil, and the Specialized Tarmac, all with the same wheels. The difference between the Venge and the Tarmac is approximately 250 grams equivalent force at 30 mph. Recall I calculated 160 grams equivalent foce between the Venge and the steel frame. This suggests, the steel frame is around 90 gram equivalent force less than the Tarmac.

This isn't a fair comparison: different tests and one with and the other without a rider. But it makes sense: narrower tubes = less wind resistance. But I'd love to see a straight-up head-to-head time trial comparison.