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So, let's take my own road bike Y and X to the handlebar clamp, which is 625mm and 505mm. Here's what I can do with that, and when you see this process you might ask why everybody doesn't use this process, whether the mechanics for pro cycling teams when setting up bikes for their riders, or bike fitters in shops, or people who just want to go in to test ride a prospective bike and want it set up to match their rider position. Yes, I wonder that. Honestly, I really do.
Let's say I'm a pro rider, and I've just come aboard the Trek Factory Racing team. I want to find out what Trek bike works for me. I go to that calculator referred to yesterday. When I plunk in my numbers (Y of 625mm and X of 505), and the front end I've got on my Cannondale Supersix EVO, you know what the output is already from Part-1 of this article. I'm looking for a bike frame with the following height and length:
Stack = 573
Reach = 396
But Trek doesn't have a bike with that stack and reach. Trek has three geometries, known as H1, H2 and H3. Let's look at the 58cm size of each geometry:
H1: Stack = 567 - Reach = 400
H2: Stack = 596 - Reach = 391
H3: Stack = 611 - Reach = 380
I start hitting the "back" button on my browser, on the page where my calculator sits, typing in different front end configurations until I come up with something that yields, as an output, the stack and reach of one of these Trek geometries above. The H3 geometry is not long enough, and is too tall. So I can "flatten" the front end by putting a minus-17° stem on the bike (versus the minus-6° that I have on my Supersix), and I can make up for the H3's frame "shortness" by lengthening the stem. But, even with a 130mm stem, angled at -17°, and only a 5mm headset dust cover, I'd need the following frame:
Stack = 611
Reach = 382
That H3 geometry is just too "Gran Fondo" for me. I can't get the bars low enough regardless of what stem/spacer combo I try (the head tube terminates too high above the bottom bracket) and I can't get the bike long enough, unless I put on a 140mm stem, and even then it's a few millimeters short.
H1 is on the other end. This is a Goldilocks and 3 Bears thing. The frame geometry is too low for me, and too long. I'm going to have to make the whole complex taller, and less long, by manipulating the stem and spacers. Let's start just with spacers. If I take that front end I've got on the Cannondale and just add an extra 10mm of spacers (20mm total), I'm now looking for the following frame:
Stack = 564
Reach = 399
Very close. So I can ride that H1 geometry. While the H3 was just too far away from what I ride to make it work, the H1, while a bit away from what I ride, is still usable.
But I can also ride Trek's H2 geometry, and I would do that just by, of course, manipulating the front end. But why do this in the shop, putting stems on and taking them off, measuring? Very time consuming! Why not do this virtually, using a calculator like the one on Slowtwitch? Much quicker.
Trek's H2 geometry is taller than the Supersix geometry, so, instead of a –6° stem I put on a –17° stem, which has a stem extension parallel to the ground. This makes room for the H2's taller geometry. If I want to "find" a bike yielding my rider position, and I'm looking for a bike frame geometry underneath a 120mm stem, angled at -17°, with 10mm total of headset dust cover and spacers, I'm looking for this geometry:
H2: Stack = 596 - Reach = 394
Almost a dead-on match with H2. And this is what I'd prefer, because I'd rather not have a big vertical component to my front end. I'd rather have frame take up most of that space. The vertical distance between the top of the frame's head tube and the center of the handlebar clamp is only about 30mm with the H2, and 60mm with the H1. Is either bike rideable? Yes. Is one bike materially better than the other for me? Debatable. Personal preference. Plus, maybe some other considerations. This process when applied to a small-statured rider might turn on other imperatives, like standover height. Maybe the lower frame geometry with taller front end is desired if extra standover height is needed.
The point is that this process above can be used for any frame, any bike, any contemplated front end, in the world of road bike riding. And that's because a stem is a stem. A spacer is a spacer. It's just a math problem. This even works for tri bikes, as long as they use standard stems.
Not so for triathlon superbikes. There's no 120mm or 90mm stem for a Speed Concept. There's no –6° or –17° stem pitch for a Scott Plasma Premium, or a Cervelo P5 Six. The calculator on Slowtwitch that makes the process so easy for road bikes can't be used for superbikes.
Let's say I'm a pro rider, and I've just come aboard the Trek Factory Racing team. I want to find out what Trek bike works for me. I go to that calculator referred to yesterday. When I plunk in my numbers (Y of 625mm and X of 505), and the front end I've got on my Cannondale Supersix EVO, you know what the output is already from Part-1 of this article. I'm looking for a bike frame with the following height and length:
Stack = 573
Reach = 396
But Trek doesn't have a bike with that stack and reach. Trek has three geometries, known as H1, H2 and H3. Let's look at the 58cm size of each geometry:
H1: Stack = 567 - Reach = 400
H2: Stack = 596 - Reach = 391
H3: Stack = 611 - Reach = 380
I start hitting the "back" button on my browser, on the page where my calculator sits, typing in different front end configurations until I come up with something that yields, as an output, the stack and reach of one of these Trek geometries above. The H3 geometry is not long enough, and is too tall. So I can "flatten" the front end by putting a minus-17° stem on the bike (versus the minus-6° that I have on my Supersix), and I can make up for the H3's frame "shortness" by lengthening the stem. But, even with a 130mm stem, angled at -17°, and only a 5mm headset dust cover, I'd need the following frame:
Stack = 611
Reach = 382
That H3 geometry is just too "Gran Fondo" for me. I can't get the bars low enough regardless of what stem/spacer combo I try (the head tube terminates too high above the bottom bracket) and I can't get the bike long enough, unless I put on a 140mm stem, and even then it's a few millimeters short.
H1 is on the other end. This is a Goldilocks and 3 Bears thing. The frame geometry is too low for me, and too long. I'm going to have to make the whole complex taller, and less long, by manipulating the stem and spacers. Let's start just with spacers. If I take that front end I've got on the Cannondale and just add an extra 10mm of spacers (20mm total), I'm now looking for the following frame:
Stack = 564
Reach = 399
Very close. So I can ride that H1 geometry. While the H3 was just too far away from what I ride to make it work, the H1, while a bit away from what I ride, is still usable.
But I can also ride Trek's H2 geometry, and I would do that just by, of course, manipulating the front end. But why do this in the shop, putting stems on and taking them off, measuring? Very time consuming! Why not do this virtually, using a calculator like the one on Slowtwitch? Much quicker.
Trek's H2 geometry is taller than the Supersix geometry, so, instead of a –6° stem I put on a –17° stem, which has a stem extension parallel to the ground. This makes room for the H2's taller geometry. If I want to "find" a bike yielding my rider position, and I'm looking for a bike frame geometry underneath a 120mm stem, angled at -17°, with 10mm total of headset dust cover and spacers, I'm looking for this geometry:
H2: Stack = 596 - Reach = 394
Almost a dead-on match with H2. And this is what I'd prefer, because I'd rather not have a big vertical component to my front end. I'd rather have frame take up most of that space. The vertical distance between the top of the frame's head tube and the center of the handlebar clamp is only about 30mm with the H2, and 60mm with the H1. Is either bike rideable? Yes. Is one bike materially better than the other for me? Debatable. Personal preference. Plus, maybe some other considerations. This process when applied to a small-statured rider might turn on other imperatives, like standover height. Maybe the lower frame geometry with taller front end is desired if extra standover height is needed.
The point is that this process above can be used for any frame, any bike, any contemplated front end, in the world of road bike riding. And that's because a stem is a stem. A spacer is a spacer. It's just a math problem. This even works for tri bikes, as long as they use standard stems.
Not so for triathlon superbikes. There's no 120mm or 90mm stem for a Speed Concept. There's no –6° or –17° stem pitch for a Scott Plasma Premium, or a Cervelo P5 Six. The calculator on Slowtwitch that makes the process so easy for road bikes can't be used for superbikes.
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So we reluctantly bypass this process above entirely, and in its place we just measure your Y and X distances from the bottom bracket to the armrest, and then each bike company gives you its own prescription via its own system (I spent last week walking you through these systems, bike company by bike company, the links to these articles are just below this article).
Remember how in Part-1 I could have fit aboard either a 56cm, 58cm, or 60cm Supersix EVO, just by making the front end longer and taller as the frame got smaller; or by making the front end (stem length and pitch, and spacers) shorter and flatter as the frame size got larger? Same thing with these superbikes.
Remember how in Part-1 I could have fit aboard either a 56cm, 58cm, or 60cm Supersix EVO, just by making the front end longer and taller as the frame got smaller; or by making the front end (stem length and pitch, and spacers) shorter and flatter as the frame size got larger? Same thing with these superbikes.
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Look at the images above. This is a Speed Concept owned by Chris Legh. Note that for this bike the front end uses a "stem" (what passes for a stem in the Speed Concept) that is tall, and it is long. The SC has 6 available stems: two lengths, three heights. What you're looking at here is a pretty tall stem, and a pretty long stem. And a pedestal on top of it all as well. Furthermore, the pads are pushed out pretty far. Same thing with Rebecca Keat's Speed Concept in the 2 images below.
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I think for Chris's bike, and maybe from Rebecca's as well, one could make the case that a larger frame size could have easily been chosen. In this case, more frame would have filled up that space, and less front end. You use a frame the next size up, and a stem that's less long and less tall. It's analogous to me riding a 56cm road bike with a 130mm stem pitched up, and with spacers under the stem, versus riding a 58cm road bike with a 120mm stem, angled flatter, with fewer spacers.
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Dirk Bockel's Speed Concept (below) probably could have been a size smaller than it is, most likely. If so, it would have had a front end that looks more like the one on Chris Legh's bike. Dirk's bike has the lowest of the 3 stem heights that Trek offers for its Speed Concept.
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Meanwhile, pro cyclist Matthew Busch (below) has a nice position, bike looks good, but it's pads are quite a bit above and out in front of the frame. He also could have opted for one size up. But it would have brought his pursuit bars up accordingly, and this smaller bike, pedestaled, might be more aerodynamic than a larger frame size unpedestaled (I don't know).
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I'm not arguing that any of these frame sizes is wrong for the athletes riding them, rather this explains how, when you look at a Cervelo, Felt, Trek superbike sizing chart, you can either be a M or a L, or a L or an XL. It just depends on what front end you stick on that bike. This is why, when you look at Trek's chart for its Speed Concept, there are 2 or even 3 sizes you could choose. You either opt for less frame and more front end (stem length, stem height, and pedestal), or you opt for more frame and less front end. What should you choose?
Weight Displacement
The higher you sit off the ground (saddle height) and the more forward you sit (the steeper your seat angle; or the more forward your saddle position versus the bottom bracket), the more front/center your bike needs in order to give you a good base of support. A bike's front/center is (remember Part-1 of this series) the distance from the bottom bracket (where the crank attaches to the bike) to the front wheel axle. How much front/center do you need? For tri?
Weight Displacement
The higher you sit off the ground (saddle height) and the more forward you sit (the steeper your seat angle; or the more forward your saddle position versus the bottom bracket), the more front/center your bike needs in order to give you a good base of support. A bike's front/center is (remember Part-1 of this series) the distance from the bottom bracket (where the crank attaches to the bike) to the front wheel axle. How much front/center do you need? For tri?
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The Take-Away
When you reach forward with your hands and grab the handlebars, or lay your elbows down in the cups, the handlebars or cups got to where they got because a number of sub-assemblies were bolted, slid through, slid over, screwed down, that created an entire assembly. Those sub-assemblies are like Tinker Toys, or an Erector Set. The frame can be low or tall, long or short. If the frame doesn't project out far enough, get a longer stem. If it's not tall enough, spacer it. Or pitch the stem up. It's all just a compendium of parts that get you to the same position, just as this simplistic rendition of a road frame + spacers + stem. (In this very simple and not very precise drawing, these are two frames a size apart in the size run, but each can be used to achieve the same position for a rider through mating the frame with a front end that is either taller and longer, or less tall and less long.)
When you reach forward with your hands and grab the handlebars, or lay your elbows down in the cups, the handlebars or cups got to where they got because a number of sub-assemblies were bolted, slid through, slid over, screwed down, that created an entire assembly. Those sub-assemblies are like Tinker Toys, or an Erector Set. The frame can be low or tall, long or short. If the frame doesn't project out far enough, get a longer stem. If it's not tall enough, spacer it. Or pitch the stem up. It's all just a compendium of parts that get you to the same position, just as this simplistic rendition of a road frame + spacers + stem. (In this very simple and not very precise drawing, these are two frames a size apart in the size run, but each can be used to achieve the same position for a rider through mating the frame with a front end that is either taller and longer, or less tall and less long.)
