zze86

Finally had the chance go for a decent ride on my bike with a shortened crank (155mm) and I love how much more comfortable it is. I actually prefer being in the drops now, my knee doesn't swing out, less cramping.

I kept the stock gearing on though, 52/42/30 with a 11-26 10 cog in the back, and I was struggling quite a bit. Used the whole range on the 42/30 rings. Didn't even touch the 52.

My crankset is a 130/74 BCD triple so I'm thinking maybe a 48 or 46/38/24 but wondered what other short crank users are using for chain rings.

McBTC

Using the typical 11-spd compact (50/34 x 11/32) setup with 165mm cranks. I'd like to have a 1:1 gear but it wasn't possible in '15 on a 105-equipped road bike. I was able to swap out the OEM 175s but nothing less than 165 are available in 105 components. However, if I had the option I'd enjoy trying out 155 cranks. My bike frame size is 61.

rgconner

Praxis Alba 48/32 165mm and SRAM 11-36 in the back on the CX.

That gives me better than 1:1 low gear.

I also run a 155mm on a Touring bike I turned single speed. Running 36:15 on that one. 155mm is a little short, I can definitely feel it in the small climbs (overpass sized) and it is definitely snappy.

Main road bike is 172.5, I so wish it was 165... but Campy does not make anything shorter.

Iride01 

I run 165 mm cranks with 52/36 chainrings and a 11 spd 11-32 cassette on the back for road biking. I find the gearing works.very well for me and my ride conditions. Now that my legs have gotten over their winter vacation, I don't even use the 36 ring anymore. In fact the only time I needed it recently was on a ride that had a very long hill that had a short section of grade exceeding 10 to 12%.

I'm thinking of trying shorter too. There are studies that indicate it works for some. I'm sure it depends on your discipline and how you like to ride. Lots of stopping and starting in rugged terrain off a paved surface might favor longer cranks with their leverage benefit. I just know it's more comfortable for me sitting and spinning 80 to 90 rpm up a hill than chugging out 45 to 60 rpm standing.

When they start making a 12 speed rear inexpensive enough for me, I'll consider just a 1x front and have something similar in range to my current 11-32 for the last eleven speed. First would be more of a bailout gear in the 36 to 40 tooth range.

Of course your specific riding conditions and physical capability make a difference. So my experience won't be yours and no chart or guide based on old thinking is going to help. However it's going to take a lot before changing the mind of those clinging to the belief that anything outside a 12-28 isn't a "road" bike cassette. That was a different day and time many years ago.

fietsbob

a double from the triple, replacing the outer,
with a toothless disc, chain/trouser guard gives you a single ring
with a granny gear,
Yes, a short crank is easier to spin,

12 : 42 should be high enough.. difference of 16t ; 42, 26,
gives you 3 or four more lower gear ratios..
below overlap of ranges..




....

Retro Grouch 

Is the 30/26 adequate with the 155 mm crank arm to get you up the hills?

If it is, I doubt there's a lot of benefit to be had by screwing with your gearing.

McBTC

Good point and... I guess the question is, was gearing ever adequate? if so, going to the shorter crank probably is irrelevant.

While there may be the temptation to think going to a shorter crank will decrease leverage such that additional pound-feet of torque at a given rpm will be required to go the same speed, we know that at the same foot speed the rpms increase when going to a shorter crank and, greater horsepower can result from an increase in rpm, even when torque falls, so... there probably is little if any actual change in horsepower involved such that changing gears would be required due to a loss of torque due to shortening the crank arm.

My experience with shorter cranks go along with what I've read, which I think boils down to foot-speed being a key albeit overlooked factor in maximizing power to the pedal. Within some relevant range there may exist the potential of increased performance coming more from the human factor and doing more of what feels more natural-- i.e., getting more from what power you have (and some research indicates that going even as low as 145mm for crank length could be optimal).

u235

I went down to a 165 last year as part of my overall transition from dieseling along at ~70 RPM for years to the mid 90's. I saw no need to swap gears for my typical rides which is a compact and 11-34. I do now change gears a LOT more than I ever did before. Strange how much comfortable RPM range I lost in the down size. I couldn't imagine a 155, I'd probably have to change gears for every 0.2 mph 😁
I'm keeping 175 on my MTB

catgita

McBTC

you are ~7.3'...

rm -rf

Your 155 mm crank arm is about 5% harder than the usual 162.5 mm arm. ( 155/162.5 = 0.954, or 4.6% )

That's somewhere between a half rear shift and one shift. (depending on the tooth counts, a rear shift is usually somewhere between 4% and 12% or more. A lot of them are around 8%. Examples: 12/13 = .92 or 8% ; 16/17 = .94 or 6% ; 25/28 = .89 or 11%)

A 50 chainring is 4% easier than a 52. (50/52 = .96) A 48 chainring is about 8% easier. So that would work.
But your new crank arms have only moved everything less than one rear shift. I'd ride it some more before changing anything.

That makes a lot of sense. And the cadence would only need to increase slightly, since the crank differences are much less than 10%.

rm -rf

I have a 52/39/30 on one of my bikes, with a 162.5 crank. And either a 12-25 or a 12-29 cassette. I rarely use the 52, mostly on long downhills.
The 39-12 gear is 23 mph at 90 rpm. I really like the 39 (or your 42) for it's wide range of speeds at cadences in the 90s -- that's a speed range from about 12 mph up to 24 mph.

For steep hills, I'd like a lower small chainring, but my crankset won't go below 30 teeth. A 28 or even a 26 would be great for steeper climbs.

Kapusta

zze86

Thanks for the perspective and sharing all. That 42/26 "compact" idea of @fietsbob is one I didn't even think of and merits further consideration.

I think part of the problem is I haven't quite got my summer legs back yet as @Iride01 suggests. My winter riding was non-existent this yeat and the crazy weather around here has limited my riding time.

I am finding I have to shift much more often now. Up-down, up-down front and rear. Maybe the combo of the two - noodle legs and constant shifting - is mentally affecting me as well.

I do think the 30 ring may not be low enough so I may switch it out with a 26 I forgot I had. I'll give it a couple of weeks and see. I think I'll start with the rear cassette as everyone suggests before buying new rings.

Thanks!