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"Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles.
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Bike fitter for about 12 years, about 3000 fits. I'm decent at it. I've always tried to learn from those better than me and over the years, there have been a few tricky questions that I was having a hard time answering until I started experimenting with shortening cranks.

1. Seat too high! - Two angles are the primary drivers of the short crank movement. Knee flexion at the top of the stroke and, probably to a lesser degree, thigh torso clearance at the same point. Raising the seat opens both of these angles, so pedaling can feel better. It is not until later that we come to find that seat height may be causing us other problems.

2. Inability to rotate at the hips, or staying rotated rearward on the saddle, aka - posterior pelvic tilt instead of anterior. Also aka - "riding it like a road bike". Posterior rotation relieves thigh - torso pinching, and I have seen this tendency minimized or in some cases instantly and completely disappear once crank length was addressed. It doesn't really address the knee flexion issue directly, but it can move the overly flexed knee to an earlier portion of the stroke, which can be of some benefit, so perhaps a tertiary benefit to excessive knee flexion? Knee flexion is an issue because the knee can't be extended with close to max power from an overly flexed position. So if we can reduce the flexion or move the overly flexed knee back and away from the powerful portion of the stroke, we have made it better. Unfortunately, anterior pelvic tilt is not the fastest way for most of us to ride.

3. Excessive forward movement on the saddle You know the rider who no matter how far forward the saddle is moved, continually gravitates to the very tip of it, in some cases approaching an actual 90° of seat tube angle. IF everything else stays fixed, sliding forward will open the hip angle, at least the FIST defined "major" hip angle as I have come to refer to it, but other angles can become cramped. But IF we come forward AND raise the saddle (which we should), then it is more obvious how both thigh torso and knee flexion can benefit.

Anyway, just some quick observations that have been solidifying in my brain lately. I'm sure I was unclear about something and will be called out for my ignorance. I am not trying to dictate to the forum, as much as throw out some ideas and get some feedback on your experience as a rider or a bike fitter.

Finally, this is a rough range of crank lengths that riders have been selecting as a loose function of seat height.

<60cm seat height :: Crank 145mm or less. Really as short as you can find, maybe go custom. I’ve fit down to 135mm with custom cut BMX cranks.
60-65cm :: Crank length 140-145mm
65-70cm :: 145-150mm
70-75cm :: 150-155mm
75-80cm :: 155-160mm
80-85cm :: 160-165mm
>85cm :: 165-170mm, maybe 172.5 Keep in mind that of the tallest, strongest professional athletes I have fit literally ZERO of them have preferred anything over 165mm. These are 6’3” and taller athletes pushing wattage over 375 watts at threshold and upper 200s to 300 for IM races.


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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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As someone who rides at a very steep angle with a 155 crank I was actually contemplating this subject earlier today. I have some hip issues that only feel better when I'm able to keep that angle very open and riding very steep lets me do that however it also leads to me being on a very long bike IE I'm 5"11 and I ride a 58 da with a 120 stem. I would like to build a P4 next year in a 56 so could I just go to an even shorter crank and move the seat back to keep that same hip angle I know other things would change and it would take some time to get used to but I would love to hear your opinion.
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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I've not fitted as many people as you but I'm planning on studying this area soon.
I feel there should be a way of determining a narrow range of crank lengths and Q factor based on some simple anatomical measurements.
I'll need some small people on the ergo. I also need an engineer to help with and adjustable bottom bracket.
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [bluntandy] [ In reply to ]
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bluntandy wrote:
I feel there should be a way of determining a narrow range of crank lengths and Q factor based on some simple anatomical measurements.

What will be your basis for "determining"?

We know that optimal crank length is less a function of leg length than "something else". But there is a very wide range of crank lengths that will perform essentially the same for most people.

Also, the optimal Q factor for most people tends to be quite a bit narrower than anything you can buy these days. So there isn't much point in exploring that for fit purposes.
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [rruff] [ In reply to ]
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I think it is a function of leg length / seat height, upper to lower leg ratio, foot size, preferred setback (which itself is a function of..?), strength (FTP) of the rider, degree of pelvic tilt, preferred reach, overall mobility, total lifetime duration of riding, and the "X" factor. If there is one angle that drives it, it would have to be knee flexion. I have found I can make pretty good predictions of what the rider will choose, or give good recommendations solely from seat height. I've also found that there is pretty much nothing really too short for steady state aerobar riding.


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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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Very.

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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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I am at 61" with a steep seat angle on my tri bike, 145 cranks. Right now 59.5" on my road bike and about to replace the 165 crankset. Thoughts on whether to make both bikes the same?
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
I think it is a function of leg length / seat height, upper to lower leg ratio, foot size, preferred setback (which itself is a function of..?), strength (FTP) of the rider, degree of pelvic tilt, preferred reach, overall mobility, total lifetime duration of riding, and the "X" factor.

Maybe preferring a high range of motion, lower force, and lower cadence... vs low range, higher force, higher cadence. Something to do with the muscles rather than dimensions.
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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Is this in the context of TT or road bike position? Or both?

I ask because, in the pro road circuit, teams like Sky are looking for every marginal gain they can possibly achieve (including choice of skin-suit material for group TT vs individual TT races) yet I don't see any of them racing on short cranks. It seems inconceivable to me that they haven't looked at this in the context of road racing, if not the TT.

That aside, I love your angle here to generate another high traffic thread. "Your seat is too high" to be replaced with "Your crank is too long"? Bravo!
Last edited by: bazilbrush: Jul 30, 18 17:32
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [bazilbrush] [ In reply to ]
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Always somebody who brings up world tour riders, Tour de France or Team whatever (usually Sky) to debunk the trend to shorter cranks. Most of them are just slow to change, bound by sponsorship parts (165mm and up), don't give a shit about time trialing, mired in the myth and lore of cycling and leverage, ride their ride bikes 40+ hpur a week and TT bikes less than 40 hours a year, etc, etc.


And most of them don't have a bike fitter that has taken thousands of riders to the limits of their existing crank length on a modern dynamic fit bike before changing lengths, thereby allowing the riders intuitive sense of "right" to dictate the fit instead of the fitters opinion or preconceived notions. But sure, I'm trying to generate traffic or business or whatever.

Time trial bikes in response to your question. Or triathlon bikes if you prefer. No difference really.


"WorldTour teams including Team Sky appear to believe that shorter cranks are more efficient..."


https://www.cyclingweekly.com/...cranks-better-188288



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Last edited by: FindinFreestyle: Jul 30, 18 17:59
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [Gee] [ In reply to ]
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I don't think you would be wrong to do that. I generally go about 5-10mm longer on a road bike. Why? I'm not actually sure. Thigh torso clearance is usually better, and there seem to be situations like out of the saddle climbing where the crank leverage takes precedent over all the other levers involved in moving the bike. One question I have is whether there is really a performance disadvantage in that situation, or if it is simply perception.

In your case, you would probably be even happier if you went less than 145mm on the tri bike, so 145mm on the road bike is probably just fine. There is no real need to make them equal on both bikes for any sort of "fit-symetry" reasons that I have noticed.


3 Months of Paradigm Shifting Swim Instruction for Cheap // Your Professional & Private “Critique my Fit”

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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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Hey,
I can jump in here since I just had one of those eye opening bike fits with David on Saturday.
My background unfortunately is not competitive cycling but road biking, I’m from Europe. Approx 3-4K km each year including training camps in Spain, half iron and a dozen short courses per year.
I got referred to David from a semi professional crit racer with the same result and the referral to shorter cranks. I guess she is like 5”4, had 165mm crank before.
I never felt comfortable on a tri bike in aero for more than 2hours and have multiple threads here open with questions.
However, after tweaking a little bit around with position and another different saddle the key was to go down 2cm in crank length which resulted into 20-30watt immediately and comfortable aero on top!
I can’t wait to get my bike now fit with the latest mods. I have never been that excited since years.
And yes, I have been to a couple professional fitters before! Never ever before someone paid attention to crank length. It simply was never discussed. I have had food scans with insoles, cleats adjustments in millimeters with scanner and all that shit. Spiro test with oxygen in combination with running. Name it.
Just saying, it is definitely one of the things no one really pays attention to!
Thanks again David, I’m very excited to share with you the progress!!
Last edited by: Spoili007: Jul 30, 18 19:23
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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Most of them are just slow to change, bound by sponsorship parts (165mm and up), don't give a shit about time trialing,

This is surely changing. In penultimate stage of the tour this year we saw that that the top 3 riders were also the 3 fastest in the TT. Additionally, Roglic lost 3rd place GC on the TT stage. If crank length can make a significant difference, these teams will be open to it. They have money on the line. If you are absolutely convinced that this can make a difference, you should be pitching to those guys any which way you can.

And the thread title was clearly designed to generate traffic. Nothing wrong with that, I liked it. Don't be so sensitive.
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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I don’t see my 175mm cranks on your chart 😂
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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I’m currently on 165mm.
Want to try 150-155mm but I don’t know where to find them. Any ideas?
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [bazilbrush] [ In reply to ]
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Sponsorships are a big barrier for TdF riders. Shimano, SRAM and Campy. Nobody makes a high end crank shorter than 165. Heck Campy Record's shortest length is 170 right now I believe. Gives you some insight into the myth and lore of cycling that really persists in that market. But yeah, the longer I fit, the higher level of athletes coming to me. A few years ago, I would have been scared to fit these guys. Not anymore. I'll fit any of them. And I intend to go after them. And pester SRAM and Shimano to at least make a 160.


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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
Sponsorships are a big barrier for TdF riders. Shimano, SRAM and Campy. Nobody makes a high end crank shorter than 165. Heck Campy Record's shortest length is 170 right now I believe. Gives you some insight into the myth and lore of cycling that really persists in that market. But yeah, the longer I fit, the higher level of athletes coming to me. A few years ago, I would have been scared to fit these guys. Not anymore. I'll fit any of them. And I intend to go after them. And pester SRAM and Shimano to at least make a 160.


The narrative isn't helped, though, by the fact that among those who really, really care about time-trailling at the very highest level, they tend to have longish cranks. Not saying that's optimal, or they shouldn't go shorter, or that we should listen to pros at all. They just tend to have longer-than-165mm-cranks. 175mm on Froome's Bolide. 170mm on Roglic' Bianchi. 175mm on Tom Dumoulin's Trinity. 170mm on Wiggins' hour record track bike.

Of course these are all pretty tall men too.
Last edited by: trail: Jul 30, 18 21:26
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
Always somebody who brings up world tour riders, Tour de France or Team whatever (usually Sky) to debunk the trend to shorter cranks. Most of them are just slow to change, bound by sponsorship parts (165mm and up), don't give a shit about time trialing, mired in the myth and lore of cycling and leverage, ride their ride bikes 40+ hpur a week and TT bikes less than 40 hours a year, etc, etc.


And yet they ride 32+mph on those TT bikes in races. There were several riders trying shorter cranks a few years back, but I don't know if any still are. Maybe like me they didn't find a benefit. It wasn't any worse either. Power and aero drag were about the same. I went from 172s to 150s for over a year, then to 167s. They always felt weird on climbs but ok on flat roads.

If a rider can acheive an optimal torso angle without any detrimental effects on power while using 170s or 175s, there really isn't a reason to go shorter. But there are a few guys in the pros who could probably benefit.
Last edited by: rruff: Jul 30, 18 21:56
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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Might be a stupid question but can´t figure it out myself: if I change to shorter cranks do I need to change gearing as well?

RPM stays the same, but given the shorter leverage it should feel lighter, thus calling for higher gears... or not? If so, is there a rule of thumb (e.g. 10mm shorter crank equals 53 instead of 52 chainring)?
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [Blabelzabel] [ In reply to ]
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I will add a data point.
For myself, before rules come in to prevent it, I rode 75mm in front of the BB nose riding a conventional Flyte saddle.
I rode 175mm cranks.
In that position there was very little weight on the saddle, I pretty much just floated on it using a cadence of 83rpm.

I ended up there because at my prefered rpm, I needed to be that far forward to oppose the push down from the legs.
At that stage my threshold was in the region of 370 watts and my seat height 87cm.

When the 5cm rule come in I simply rode further on the nose.
Even now, my prefered TT revs is 83 and crank length 175mm at a time when I ride 180mm on the road bike.
But now at a reduced power level and few KG too much body fat, I can now ride much further back as I no longer need full body weight to balance the leg thrust.

So I think you need to add body weight to leg thrust ratio into your fitting equation.
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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I changed from 172.5mm to 160mm myself about 6 or 7 weeks ago. I needed new cranks to go with a new PM and felt I would probably prefer shorter cranks due to slight knee discomfort at the top of the stroke and a vague sense of pinching at the hip. I've been riding fairly well with the existing cranks and if I couldn't find an improvement it wouldn't be a disaster. Unfortunately, I didn't have the opportunity to try various crank lengths before purchasing so spent a while musing on what length to go with. 165mm seemed a bit conservative but 160mm seemed a bit risky. I changed my mind back and forth a few times before saying to hell with it and going with 160mm. On my first ride with them, i thought I'd made a mistake. I rode alright but it felt a bit odd. Like I wasn't able to stretch my legs properly. A certain lack of physical satisfaction if that makes any sense? I thought, dammit, I should have gone with 165mm. Next time out I an hour on the road before I suddenly realised "Oh wait, I'm on short cranks today. I never noticed, but I do feel smooth!"

My seat height was about 750mm on 172.5mm cranks. I initially raised it about 11-12mm when I installed the new cranks and after the first ride it's felt very good there. I'll likely play around with it a little to be sure. Based on your ranges I picked about right and 155mm would have been a likely candidate too. I'm happy with the change albeit I haven't got a convenient objective way to verify if I made the right choice!

P.S. Still happily using 172.5mm on the road bike and will probably leave it alone. I wouldn't bother changing that length unless I was changing the cranks anyway for some other reason. If so I might go with 170mm, but unsurprisingly I can't tell any difference between 170, 172.5 and 175mm all of which I've used before on road bikes.
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [FindinFreestyle] [ In reply to ]
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FindinFreestyle wrote:
I think it is a function of leg length / seat height, upper to lower leg ratio, foot size, preferred setback (which itself is a function of..?), strength (FTP) of the rider, degree of pelvic tilt, preferred reach, overall mobility, total lifetime duration of riding, and the "X" factor. If there is one angle that drives it, it would have to be knee flexion. I have found I can make pretty good predictions of what the rider will choose, or give good recommendations solely from seat height. I've also found that there is pretty much nothing really too short for steady state aerobar riding.

Thanks.
It would be nice if I could take a few simple measurements. Let's say seat height, leg length, clear position, torso angle and then come up with a simple formula.
It won't be that simple as I'm sure that using shorter cranks will then enable a change in all of the other variables.
Aarrgh!
I've got two years to figure it out.
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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [rruff] [ In reply to ]
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rruff wrote:
FindinFreestyle wrote:
Always somebody who brings up world tour riders, Tour de France or Team whatever (usually Sky) to debunk the trend to shorter cranks. Most of them are just slow to change, bound by sponsorship parts (165mm and up), don't give a shit about time trialing, mired in the myth and lore of cycling and leverage, ride their ride bikes 40+ hpur a week and TT bikes less than 40 hours a year, etc, etc.


And yet they ride 32+mph on those TT bikes in races. There were several riders trying shorter cranks a few years back, but I don't know if any still are. Maybe like me they didn't find a benefit. It wasn't any worse either. Power and aero drag were about the same. I went from 172s to 150s for over a year, then to 167s. They always felt weird on climbs but ok on flat roads.

If a rider can acheive an optimal torso angle without any detrimental effects on power while using 170s or 175s, there really isn't a reason to go shorter. But there are a few guys in the pros who could probably benefit.

You need to understand something.. Either you're an outlier or you went about it wrong. Don't get me wrong... I think you are smarter and know more than me about most things cycling. But if you pulled your existing cranks and pressed in shorter cranks and took it for a ride, that is not the best way to evaluate shorter cranks. Even if you kept t hem for months. I think crank length needs to be changed quickly, like in under 2:00, on a fit bike, after the rider has been optimized and taken to the limit of drop on their existing crank length. I don't prescribe cranks as a general rule. I take riders to a place where their intuitive sense of correct selects the cranks.

As far as TdF riders, 32mph is a stretch if we are talking aggregate. Some of them sure, but it would be more accurate to say they ride 30mph. And it might be more accurate to say some people succeed because of what they do, and other succeed in spite of what they do. So rather than holding up 30mph as some testament that they are doing everything right, maybe we should look at amateurs who are riding close to 30mph on a 'mere' 350 watts, and ask ourselves why aren't these riders going faster?

Those riders make upwards of 400 watts at threshold and some of them upwards of 450. I think there is a pervasive belief that TT positions cause a substantial power loss, and I think many of those riders are very pleased to "only" give up 10% on their TT bikes. So they still make 370 - 420 watts or whatever, and they still go really fast, but to be honest, I am not really seeing the speeds, in the aggregate, that I would expect to see, based on what I know about their power, again, in the aggregate. I think it is time in the saddle of those TT bikes, and sub optimal fits including addressing crank length, that hold them back.

There is definitely a large swath of fans who beleive that these guys are thoroughly tweaked, optimized, and know every trick in the book to go fast on TT bikes. I used to to think that. I don't any more.


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Re: "Maybe your seat is too high because your crank is too long" and other interesting bike fit puzzles. [trail] [ In reply to ]
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trail wrote:
FindinFreestyle wrote:
Sponsorships are a big barrier for TdF riders. Shimano, SRAM and Campy. Nobody makes a high end crank shorter than 165. Heck Campy Record's shortest length is 170 right now I believe. Gives you some insight into the myth and lore of cycling that really persists in that market. But yeah, the longer I fit, the higher level of athletes coming to me. A few years ago, I would have been scared to fit these guys. Not anymore. I'll fit any of them. And I intend to go after them. And pester SRAM and Shimano to at least make a 160.


The narrative isn't helped, though, by the fact that among those who really, really care about time-trailling at the very highest level, they tend to have longish cranks. Not saying that's optimal, or they shouldn't go shorter, or that we should listen to pros at all. They just tend to have longer-than-165mm-cranks. 175mm on Froome's Bolide. 170mm on Roglic' Bianchi. 175mm on Tom Dumoulin's Trinity. 170mm on Wiggins' hour record track bike.

Of course these are all pretty tall men too.


No, it is definitely not helped by that. But yeah, they are tall, and one of the things I think might mitigate the need to go shorter is being super FTP gifted, and riding your bike rotated rearward at the pelvis....as Froome and Dumoulin clearly do. Roglic is more rotated and maybe not coincidentally, riding 5mm shorter. I don't think these guys are too far off the chart I posted in the OP to be honest. A world tour rider over 6 foot on 175s is not going to be nearly as screwed up as a 5'9" age group triathlete pushing 200 watts of FTP on their stock 172.5s or whatever.

But there is still some stuff to be learned about this phenomenon. I really want to get about 20 of those guys on my fit bike and see what happens. At this point I've had some version of the "holy crap, that is the most profound change I have ever felt on the bike!" reaction upwards of 500 times. So it is going to take more than "Dumoulin rides 175s" to convinicie me there is not something profound going on.


3 Months of Paradigm Shifting Swim Instruction for Cheap // Your Professional & Private “Critique my Fit”

The Swim Help Compilation Thread

Last edited by: FindinFreestyle: Jul 31, 18 5:39
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