Flee103
Im a 5'4" male rider interested in trying a couple gravel races next year. I'm riding a 47cm niner rlt steel. The top tube is basically almost touching now but though I've never been professionally fitted everything feels good. I was thinking of going to a 650b wheel for better mud clearance and a little extra stand over. I realize this would drop the bb a little and wondering if that should be a concern. And would I benefit from a 650b wheel in general? Would they be slower? More of my riding is road (lots of hills)or rail trail mix. I'm trying to currently find more gravel riding in the western PA area. Thanks for any advice.
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ljsmith
My wife is 5" 1" and is on a 41cm Ridley.  I converted in to 650b to lower standover, but also get rid of bad toe overlap.  It works great on the Ridley because the BB drop is 55mm.  Your bike has a 70mm bottom bracket drop which is a bit lower, but honestly if you aren't riding singletrack (on singletrack pedal strike is an issue) then the lower BB height will benefit you and have no downsides.  On paper 650b is going to be very slightly slower overall because they will not have the same inertia of the larger wheels, so once up to speed they will need a little more input to keep rolling.  But, assuming the wheels and tires will be lighter and smaller, they should spin up faster for better acceleration and hill climbing.  But it also depends on what tires you use.  A fast 650b tire is going to make the bike faster than a slow 700c tire.  Other things to consider are that it will speed up your steering a bit because it will change the trail, but the lower BB will also offer a little more stability.  On my Lynskey GR250 and switch between 29 x 2.0 and 650b x 2.0 wheels/tires.  My BB drop is 75mm, so lower than yours.  It rides great with either wheelset, but the 29 x 2.0 is far superior for rough trails and singletrack.  I use the 650b x 2.0 on the road and easier crushed limestone rail trails.  
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Flee103
Thanks! Great information. On that sidenote of your wife I'm glad to learn of the 41cm Ridley. I'm just getting started to look into a bike for my wife who's just a hair taller then yours.
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drwelby
I live pretty close to Niner HQ and I've seen employee RLTs with WTB Horizon 650 x 47 tires.

What you gain in standover you lose in pedal clearance, and the RLTs are already pretty low. From your description of your riding it sounds like you could make that tradeoff if you really want more standover.  

Since you have one of the smaller RLT sizes it looks like the bottom bracket drop is 75mm. So if you do the math, 584mm rim / 2 + 47mm tire minus 75mm drop gives you 264mm bottom bracket height, which is pretty average for a road racing bike. 
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Laeljon
I'm 5' ...ride a 46 Moots PsychloX Had some toe overlap. But later on decided to shorten the cranks. Went from 165mm to 135mm....no regrets...will never go back to longer cranks. Breathe better, less hip and knee flex, and still able to ride with friends.
No such thing as bad weather....just bad clothing...
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Flee103
What cranks are you running? I didn't even know I could get down to 135mm. I had always thought something like a 150mm would be nice. What I should do is pay up and get a professional fit.
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drwelby
These short cranksets popped up recently:

Dixna Crank

They appear to be 110/74 subcompact doubles like the Sugino OX601d and are available in 5mm increments from 140mm to 170mm. They look a little ugly in my opinion but at around $120 that's forgivable. No idea about shipping. With a shorter crankarm you probably want to drop your chainring size a similar amount, so this chainring pattern lets you do that.

Otherwise there's a bunch of short cranks in the BMX market in 110 and 102 bcd which doesn't let you get quite as low but might work as a 1x.

Rhythm Expert Crankset
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Laeljon
Gearing has nothing to do with shorter cranks....Your still doing the same cadence, just with less effort. Running custom 125mm on road bike. Had a machinist drill and tap my 170's and 165's down to 135mm. $100 for both pair. DSCN3367.jpg  DSCN3369.jpg 
No such thing as bad weather....just bad clothing...
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drwelby
Laeljon wrote:
Gearing has nothing to do with shorter cranks....Your still doing the same cadence, just with less effort.  


A shorter crank means less leverage, which means a higher pedal force over a shorter power stroke. If one wanted to keep the pedal force the same (say for standing climbing), then a smaller chainring would keep that the same. 

That's only one piece of the whole puzzle, so if your old chainring and gearing range still works for you then I'm not going to tell you you're doing something wrong. Dropping your crank length from 165 to 135mm is a 20% reduction which is 1 1/2 gear shifts so it's not a big deal, especially if you get a similar improvement in power output from the better ergonomics.


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Laeljon
The only time leverage is in play, is if your standing on the petal, and only a fourth of a revolution. When UR knees are at 90 degrees or up in UR chess, less power. Science says the power band(or wattage) between 140-180mm is no difference. However less effort during the spin with shorter cranks. For instance, put a dot on the tire, and another one half way down on a spoke. spin the wheel an keep a finger on the dot. which on take more effort to keep spinning? I'm done...been there, done that....never know, unless U try...

No such thing as bad weather....just bad clothing...
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drwelby
Laeljon wrote:
However less effort during the spin with shorter cranks. For instance, put a dot on the tire, and another one half way down on a spoke. spin the wheel an keep a finger on the dot. which on take more effort to keep spinning? I'm done...been there, done that....never know, unless U try...



Which position on the wheel makes it easier to get the wheel started if you're trying to spin it with your finger? It's two sides of the power equation, force times velocity, and you trade them off. If you can spin a shorter crank faster (more velocity), you can run a lower gear(less force) at the same power.

I've done it too. I spent a year running 170s on my single speed mountain bike instead of 180s. I had to drop the gearing ~5% to still climb about the same. But I could spin those cranks faster to make up on the flats. 

So all I'm saying is that if someone were to buy a set of new cranks, my personal recommendation based on my personal experience would be to gear down. I also recommend this based on that almost nobody ever asks here "how do I put a bigger gear on my gravel bike?".

If you're going to mod some cranks, sure, start with your old chainrings, and if you find yourself struggling on the hills then do what everyone else does in that situation and gear down. If your old gearing still works, then awesome, keep on pedalling!


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Smale Rider
I am in a similar situation. I purchased 160 cranks from rotor. Switched gearing to 46/30 with their direct mount chainring. 170 is standard crank length, every 7.5 mm change in length there needs to be a 2 tooth count change in chainring to maintain same feel. 50/34 with 170 cranks feels like 48/32 with 162.5. Additionally when people talk of gearing they don’t account for tire size. Going from a standard 25 mm road tire to a 40mm gravel tire adds effectively more “teeth” to the chainring and more effort is needed.
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bnystrom
"The only time leverage is in play, is if your standing on the petal, and only a fourth of a revolution."
Really? This is one of the most ridiculous statements I've ever seen. If leverage didn't matter, you could just take off the crank and kick the spindle with your foot.

Seriously, while it's true that maximum leverage occurs within a limited section of the PEDAL stroke (it's not "petal", unless you have flowers on your crank), a longer lever still provides more leverage at all angles. Furthermore, the force vector applied to a crank is not the same throughout the stroke; in an efficient pedal stroke there is a significant forward component at the top of the stroke and a rearward component at the bottom. Consequently, there is no point in the stroke where you won't get more leverage with a longer crank than a shorter one and this is true whether you're seated or standing. More leverage means less force needs to be applied to the pedal for a given power output

"When UR knees are at 90 degrees or up in UR chess, less power."
Of course there are practical limits to crank length, but the taller the rider, the longer the cranks they can use efficiently. Not everyone benefits from shorter cranks. The fact that you are only 5' tall is a significant factor here. I'm a foot taller and have long legs for my height. Short cranks simply do not work for me.

"Science says the power band(or wattage) between 140-180mm is no difference. However less effort during the spin with shorter cranks."
Not without lowering the gearing and increasing the cadence, assuming that you intend to go the same speed. How low do you have to go to compensate for the shorter cranks and how fast can you spin your legs? There are practical limits to these things, too.

I know from my own experience that while I can comfortably spin on the flats and downhills at 110+ rpm, I simply cannot climb at a high cadence without my legs seizing up. Shortening my cranks, lowering my gearing to compensate for the decreased leverage and having to increase my cadence is simply not an option for me. I strongly suspect that this is more the norm than the exception.

Contrary to your (apparent) assertion, short cranks are not a panacea. Perhaps they work for you, but they're not going to work for everyone. If you feel more comfortable on 135s, that's great, but you haven't discovered some "magic bullet" that will benefit every rider.

Although competitive cycling is still somewhat bound by tradition, if there was a significant advantage to shorter cranks, everyone would be racing on them. Professional cyclists are some of the most studied athletes on the planet and are always looking for an advantage. The fact that they're all riding cranks within a limited range of lengths belies the theory that shorter cranks are more efficient or effective at putting human power to the ground. This is not constrained by the component manufacturers either; if there was a demand for shorter cranks, manufacturers would make them for their sponsored riders. There isn't, so they don't.
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