Short Cranks, Compact Chain Rings, Advantages?

I have been running 165s for a few years. I am on 50/36 but will probably go to 52 at one point.
The 165s do open up your hip angle in aero position.

Love short cranks. I use a 162.5mm. I use a 54t up front however, but yes compact rings are great for most people.

I used compacts on all my bikes (which is really 2 road bikes and one tri bike, but I do have a few other bikes in different stages of build or use). A typical 53/39 is over geared for me, I don't have enough of a low end to climb the way I want (we do have some seriously steep climbs around me... right outside of my door I have a 26%, which granted is fairly short, ~600', but anything that steep and you run out of gears in a hurry).

I do like mid-compacts a lot for tri's, right now I have a 52/38 with 11-27 on my tri bike. That seems to be a sweet spot between enough low end and high end gears. For both my road bikes I have 50/34 with 12-29 cassettes. All bikes have Q-rings.

As for shorter cranks... I've been using 170mm cranks for as long as I can remember. I tried to use 165's on my tri bike, but it just felt strange and unfamiliar. It did open up my hip angle slightly so definitely a positive, but in the end, I traded that for the familiarity of my trusted 170's. Nothing but personal preference.

Yes I understand, I do think the compact are what the majority of triathlete should be on.

agree with others, compact chainrings for the vast majority are a good thing.

I had some thoughts on crank length, but I'll keep them to myself instead of rocking the boat too hard in a thread like this.

come on, that's no fun....tell us what you think

Rock the boat, no teasing allowed!

 

Thank you to everyone who responded. I should have them next week and am really looking forward to getting used to them. I am a little scared of going so short at 155mm. They are custom drilled to length so there is no returning them and they did cost quite abit. 

I think these are going to be the ticket to the big hills out here in Tehachapi area, not to mention St. George in just a few months and Auburn, Ca right after that. 

For anyone who might be interested:

Bike Smith Design, Short Cranks

Edited by rjcalhoun 2017-02-09 9:33 PM

Haha of all the people you know what I think!

Honestly, I do think that for triathletes in general shorter cranks *can* certainly be the right choice, mainly because it lets you run more drop with an open hip.
The question is... is more drop synonymous with "low" and/or "aero."

In some cases yeah, it probably is. But I don't think it's clear cut across the board. At least not in my experience. Longer cranks would mean a lower saddle height, which may or may not be a big(ger?) determiner in lowering drag. Also with shorter cranks you see more of the upper leg (a big cylinder) throughout the pedal stroke, and also (generally) more of the foot. Unfortunately there are (yet to be...hint hint) not too many people who have been looking at this (at least outside the UK) closely so we don't have tons of info to draw from. Certainly not in triathlon.

The question might then be, can you run afterwards riding like that. (to make it applicable to triathletes) My gut says you can with adaptation, but I'd guess it takes a while and unfortunately I gave up running :D But now we're going to run into effective seat tube angle, etc..etc... haha.

Still, I don't think OP wanted this devolved into n=1 aero theory about crank length... but it might be something to think about for some of the other nerds on here.


TL;DR - I don't have a problem with somebody running any "reasonable" length cranks (just me, but I judge that around 150-180 for "normal" proportioned people) if they feel like it's a benefit (I never noticed the difference between 155's and 175's so long as I adjusted the rest of the bike to match) but I think since John Cobb started pushing shorter cranks there has been an overwhelming amount of belief that they make you more aero... I just think that in certain scenario's that's true, but maybe not for the exact reasons people think. (You never make *just* one change in fitting without it effecting other stuff)

PS: I'm not claiming to know more than John Cobb (or anyone else) just my own opinions (and data)

We should test you in March at Girodana with two different crank lengths.

My bet : if you slam front end to the lowest. short cranks seat up vs long cranks seat down = 0.000x difference aero wise.
But many people will generate less power in the long crank position. Some guys, it will make no difference. Lionel was an example of someone that made a big difference from a power production/muscle recruitment perspective.

When we tested those guys in the blue uniforms, we could have put their pads at the front skewer and they would have been fine. Yet they are experimenting with short cranks. But it's to produce power, not go lower.

Many older, less flexible, with a little beer belly AG athletes could benefit from shorter cranks. The tooth pick youngsters like yourself can't appreciate it like us old fat guys :-)

Edited by marcag 2017-02-10 5:45 AM

^ agree... like everything "it depends" :D For my n=1 raising the front (to keep a relatively sustainable hip angle) was better than raising the saddle. But I also sit very far back on "top" of the saddle instead of rotating the hips. Very Joe Santos fit for those who know who that is... changing too many things at once it is tough to see exactly where the change came from.

There is efficiency as well which takes it even further down the rabbit hole. (San Millan's aero/metabolic ratio etc etc) Then you have to figure out if you can train that (d)efficiency (likely a lot harder for a triathlete than a focus'ed cyclist, and then less likely for a stage racer than a specialist tt'er or trackie)

I'll see what kind of cranks I have laying around the house. May need to borrow a longer octalink

(Btw, probably not the place to discuss, but if you are going to be around the weekend of the March 11th by chance, I'll be at A2 that Friday-10th- and then going to Girodana afterwards... would be neat to compare tunnel to track back to back. Plus selfishly as many sharp eyes in the tunnel as possible is a bonus in my book :D )

Edited by Leegoocrap 2017-02-10 5:56 AM

FB message sent on that "btw" point

You are so correct on the it depends. We tested 8 pro riders including a grand tour winner. Most benefitted from going as low as possible. But some did not. There as one really skinny guy that we could have had sitting up and his CDA would have been the same it seems
Arm tilt was very important. All riders saw a very significant improvement based on tires. I can't name brands but the point is tires are as important as anything.

IMO, super low vs low is less critical than power production which is where I find short cranks make a difference.

I switched my tri bike to 165mm cranks 3 years ago with a 52/34 chainring. I was using 172.5 cranks and when I changed over it was very noticeably. I was able to breath easier, stay aero going up moderate incline like 4-6%, stay smooth turning my legs over faster. As for the gearing, that depends on your power, but most people are better off on a compact crank. You need to adjust fit to the new cranks, and is entirely for fit. So some people may not see any benefit from it.

My road bike has a standard crank (53/39) which is a lot harder on the hills around here. On the "three Sisters ride" last summer where I am in the middle of the pack for the group, I was dropped on each sister because of my road bike gearing. The middle sister is a 1/3 mile hill that varies between 17% and 24%.

I switched to a 150 length crank in 2012 and noticed a very big difference right away. I am pretty short, 5'5", with very short legs, 27" inseam.

1. Raised seat a bit which resulted in more aero position.
2. More comfortable when in aero because my knees where not coming up as high
3. Decreased pressure on my diaphragm, which made breathing easier.
4. Increased lung capacity meant I could stay in aero while climbing steep hills for much longer.
5. RPM's increased based on feedback from Garmin by 5-6 on average.
6. Average speed over distance on same courses increased dramatically (example of race below).
7. Did I mention comfort?
8. BTW, it is much more comfortable and for me that trumps all of the other stuff. If I can maintain a comfortable position for 3-6 hours I can ride a lot faster.

It just so happened that I had raced a course in Feb of 2012 with the longer cranks and a month later in March with the shorter cranks. Weather was almost exactly the same. The course was 2 X 6 mile loops with rolling hills and 1 long steady climb, 1/2 mile, on each loop. The result below show the difference between both. I wen't from a 170 (50-34) to a shorter 150(53-39). Even turning a big set of gears up front I was able to maintain a much higher speed than the longer cranks with smaller gears. My run was also faster in the second race by about 20 seconds 25:50 vs. 25:30

Date Crank Length Front Rear Distance Time Speed
2/19/2012 170 50-34 11-28 12 38:00:00 18.95 MPH
3/25/2012 150 53-39 11-28 12 34:13:00 21.04 MPH

I just bought a new Cervelo recently and I am shopping again for a set of 150's that I can fit on it.



Edited by Batlou 2017-02-10 8:13 AM

There's folks who are more knowledgeable and experienced than me on this chiming in, but I've always been under the impression that shorter cranks are the solution to a problem, rather than something that is necessarily going to result in some sort of improvement for everyone.

If you want to get lower, and find that hip impingement is preventing you from doing so, then shorter cranks should help solve this problem. I'm not sure there's any real compelling reason for shorter cranks otherwise, but I may be wrong on that. There seems to be this idea floating around that triathletes should be on shorter cranks, and I feel like that's too much of a generalization. If you're experiencing the problem they solve, great. But I feel like a lot of people who are doing this aren't actually in that camp.

There are probably a lot of AGers that could benefit from getting lower or produce less power when they are in aero. Shorter cranks are one of several tools their fitter can use to improve things. People should not rush out and buy shorter cranks without understanding if they need them. But if someone is about to buy a new bike or a PM it is right to explore this option.

Agreed. Seems most bikes come standard with 172.5mm cranks and for those folks who have the motivation and physiology to get as aero as possible, 172.5 may be too long for them, so shorter cranks should definitely be explored. But there's also a lot of AGers riding around with almost zero seat-armpad drop, and they aren't going to be going any lower, whether that's for comfort, back issues, flexibility, etc. Shorter cranks aren't doing anything for those folks.

It's an opinion, not fact, but this is where I disagree. Of those with little drop, many are due to flexibility and shorter cranks could help. Proper rotation around the BB and cracks could help them. But that's do be explored with their fitter.

Well your opinion is an educated one, so it carries some weight. Looking at the folks I see at races riding with zero drop, it never seemed to me like it was a hip impingement issue that was the cause of their position (the handful of times I've discussed this people tend to say back issues). Whatever the reason they have for their position, it may very well be that shorter cranks would open up new possibilities to them, for some other reasons unrelated to hip impingement that I don't understand. I've never sat in on a fit session with someone like this so I don't know all the ins and outs.

One set of candidates are the people that say "I can generate 20 more watts sitting up than in aero".

That makes a lot of sense. And, anecdotally at least, it seems like maybe most people describe some loss in power when going aero. Maybe not 20W, but something. I think there is something to be said for just general adaptation to a particular position (ex: I actually experience a loss of power when sitting up, but I train in aero almost 100% of the time, so that's the position I'm adapted to), but I think the point you're getting at is that short cranks aren't just for solving "hip impingement prevents me from getting lower" issues, but also for "significant loss of power when in aero" issues, which are obviously related but not exactly the same thing.

I've thought about trying shorter cranks, but haven't gotten to the point where I've perceived a need for it. I've heard some people talk about noticing instant improvement, while other people talk about taking months and months to adapt (and then of course others for whom the switch is detrimental). It would be interesting to see what effect, if any, they would have, but for now I don't feel limited with my current crank length.

I think the reason cranks are not changed out more is because of the "fitter". Most that I have seen or talked to do not consider this an option. Maybe this is changing recently but just a few years back almost everyone was saying shorter cranks helping is just myth.

There is also a lack of parts to work with, the shops tend to have 0 extra cranks laying around in various sizes. It's a shame because when I went down to 165 it helped my a lot, I may be better off going even further down to 160 or 155. But the availability of parts in those sizes just a couple years ago were slim. The ones that were available seemed to be very expensive.

From most of the studies I read changing cranks tend to help shorter people more than tall people. Since the standard sizes are 170, 172.5, and 175 Someone up around 6'-2" already has a "short crank" when using a 175.

I got a high level professional bike fit and they sized me down from 172.5 to 165mm cranks. (for reference, bikes in my size usually come with 175mm cranks)
Helped me a lot.
It decreased the "dead spots" at the top and bottom of the pedal stroke.
With the same perceived effort, I got about 5 rpm and 5 watts "for free."
Also contributed to a position with more open hips, and I feel that I am breathing a lot easier in the aero position.

No experience with compact chainrings on my Tri bike. I like them on my road bike. For the same ratios, you get a smaller lighter chainring set and smaller lighter cassette. You can also change cassettes and get a more "granny gear" without having to change to a medium or long chain rear derailleur. If I was riding and racing in a more hilly area, I'd be very tempted to put compact chain rings on my tri bike.

I got my fit on one of those Robo-Fit-Bikes, where they can change everything - including changing to different crank lengths - without having to get off the bike or bolt different parts on.

If I hadn't had the experience of physically feeling how much better the shorter cranks were, I'm not sure I would have done it.

But having an immediate comparison between longer and shorter, it was glaringly obvious the bike fitter was right.

I do understand why they don't go this route in a routine everyday LBS fitting session. When I got my first road bike fit, I was slightly disgruntled to have paid for a new bike, and then told I needed to buy a different length stem to make it fit (this despite the fact they give a 50% discount on anything you buy for fitting). If they told me I needed to pay upwards of $200ish or whatever to put a new crank set on the new bike I just bought, my head would have probably exploded.