Clyde1820

Have got some leg weakness that likely will only marginally improve, due to old injuries in the muscles that cannot be fixed. Add onto that the aging process ...

Anyway. I am looking for crank, crank arm length, chainring and cluster recommendations under a 9-gear setup, for being capable of handling hills of up to 20 percent grade. (Some longer half-mile climbs, on my routes.) About 95% paved streets and paths, though some rougher streets, with occasional jaunts on hard-packed dirt. Hills a part of every ride, which are unavoidable.

Goals:

• Crank arm length of 150-160mm, based on my shorter leg length.
• Gear-inches on the low end of ~13-15in, give or take.
• Want to be able to stay seated, keep pedaling along, and easily make it up these hills. (Not loaded with more than 15lbs on the rear trunk bag.)
• Works on a Trek DS, ideally. Though, not utterly averse to a different frame if that becomes absolutely necessary to achieve the gearing changes.

What I've currently got: a 9spd Shimano Alivio triple, with 48/38/26T chainrings, and a 12:36T cluster. Most rides, I have troubles finishing the climbs. And strength hasn't improved this past year. Gear-inches currently at ~22in, give or take. (Discussions on fitness and strength improvements should be left for another discussion thread. This one's on the components.)

What I'm considering: a 9spd Thorn Short Triple, with 44/32/22T chainrings, and a 12:36T. Perhaps even a custom cluster, one with a stouter "granny" gear or two, one with tighter gearing on the low end so it's easier to add a little more "oomph" when I find myself challenged by a steeper hill. Have yet to decide on crank arm length.

Question for the group: given the circumstances of shorter legs, injuries that I've been unable to fix (through strength training or medical) in 40yrs, and lower gearing options via judicious component selection, what practical combination of components might you choose to fix that problem?

Thoughts and suggestions?

BlazingPedals

I think you're planning what I'd do given your circumstances. I actually have a Thorn 153mm crankset and it's surprisingly nice considering the relatively low price. If that doesn't give you a low enough climbing gear, you could go to an IGH solution such as the SRAM DD3 or the Sturmey-Archer CS-RK3; although that'd be a lot more money. Eventually though, you get such a low gear that you can't go fast enough to balance.

FlamsteadHill

Lightening the load (bike, components, rider and accessories) will also help.

On a related but somewhat different note, I have been very confused since seeing posts/articles about crank length.

To my mind, the longer the crank, the less effort it should take to operate it, based on simple leverage. As Archimedes is presumed to have said "give me a place to stand and I shall move the earth". Yet everything I've read seems to indicate the opposite...??

tyrion

I just happened to be looking at this page for the Marin Pine Mountain and saw it used a Deore derailleur and 11-42 10 speed cassette:

https://www.marinbikes.com/bikes/pine-mountain

I don't know if they had to do something tricky to get that derailleur to work with that big cassette, or if it just happens to work. In anycase, I think you're going to need a cassette bigger than 36t if you want to get to 15 gear inches with 700c wheels, so you might examine the Pine Mountain to see how they got that big cassette to work.

FlamsteadHill

There's an option. Get 20s...

Stormsedge

IRD has an 11-42 cassette...I'd do the gear calculations to see if that yields a little more "oomph" to your proposed crankset replacement where you are wanting it. I ran across a 10-50 on the internet the other day, believe it a SRAM for a 1x set. My buddy put a rear derailer extender on his road bike to accommodate the 11-42. I think you are on the right track. I won't comment on crank length other than to say I have 175s on two bikes and 170 on one...the shorter 170 is easier for me to maintain a higher cadence and proved useful in that regard in mountainous countryside (were I to do it again, I'd have 170s on all my bikes...gotta save my $$).

Retro Grouch 

13 to 15 gear inches is pretty low. Are you going to be able to balance while grinding uphill that slowly?

OldTryGuy

Think I'd rather walk or motorize.

fietsbob

+1, at a 13" gear you need 3 wheels, or your momentum will be insufficient to stay up.. on 2.. [tested 35 years ago with mountain-tamer quad on the crankset 16,26, 36, 46 ..]


Best then to get off and walk.






.....

Clyde1820

That's an 11spd cassette. Prefer 9spd (and my bike's current config is 9spd).

IRD does have a 12-40T 9spd cassette, though it's got huge jumps between the last three cogs: click.

Thanks for the reference to IRD. I'd missed them, in my poking around.

Clyde1820

I've done 17in, before. Though 13-15in would be new territory. Uncertain if balancing would be a problem. It wasn't at 17in, even up hard-packed and somewhat-rutted dirt trails. Of course, that was some years ago, but still.

Good point. Something to consider. But there aren't many choices, here, other than cycling or walking up the hills.

BlazingPedals

Short cranks are all about limiting knee flex. The idea is, you can apply more power through more of the pedal stroke if your knees aren't bent as far at the top. You make up for loss of leverage by spinning a lower gear.

FlamsteadHill

I see. Very interesting. I think I understand the fundamental premise.

Yet I'm guessing there is a point of diminishing returns or we we'd all be using 20MMs...

Is this one of those scientific things, where you can calculate an ideal based on inseam or upper/lower leg length kind of thing, or is it more rider preference?

jefnvk

I'll jump on RGs side here. I know I am projecting my own abilities, but my lowest goes down to 19GI, and when I need that I'm on the fence of just walking. Can't imagine trying to ride 13GI.

Stormsedge

Duoh! 9 spd...sorry wasn't paying attention. 🤦*♂️

Cyclist0108

You are talking about some seriously short cranks, which will effectively make your gearing higher (i.e., it will make it considerably harder to climb in your 26/36, so you will be cancelling the advantage of lower gearing). How short are your legs? (I have a 29" inseam and 172.5 mm cranks have been fine in my case.) Spinning fast in a really low gear on a 20% grade would make me fall over or be a quick ticket to the coronary care unit.

Clyde1820

Yes, sub-160's are shorter. But with a ~27" inseam ...

I've done short-crank bikes before, though have not yet owned one. I appreciate the difference in cadence, reach, and the relative change in leverage. The crank-arm length change would be more for accommodation of my shorter legs than anything else. Since I'd be altering the chainrings anyway, it makes sense (to me) to get 'em on a new crank set where the pricing is better. Thorn has that, among others.

Don't get me wrong. I've always had either 170mm or 175mm cranks on all bikes I've owned as an adult. And they've "been fine" too. But with the leg power vastly down over what it has ever been (and not likely to improve, given the condition), a few changes are needed to accommodate it.

Clyde1820

Well, now the IRD website is showing the 12-40T cluster in 9spd: click. (Wasn't showing up for me, this past couple of weeks.)

Anyway, thank you for the reference.

Given the leg/power issues I've got, I would much prefer closer spacing on the lower-end cogs ... say, 40T, 38T, 36T, then jumping 3-4 through the mid-range. Still, a good option. Paired with 22/32/42T chainrings, it'd offer quite an increase in cadence at the low end.

Current ability (with 26/38/48T and 12:36T cluster): 20.1 g-i.
New ability (with 22/32/42T and this IRD 12:40T cluster): 15.4 g-i.

fietsbob

As the gears are a % of the next higher gear the Lower Range gears of the Rohloff (1~7) are closer together than the 8~14

Same thing with the 2 speed Mountain drive Gear Box Crank , the low range gears are closer together than the high range..



Do the Math..

Jean_TX

Based on my experience, I agree with those above who indicate that 13 to 15 GI is too low to be able to balance. I find that the slowest I can ride stably ride is about 4 mph. That would require a cadence of over 102 RPM at 13 GI ... which would be difficult to maintain on a 20% slope. (Note: mph = GI * cadence * 0.003)

Clyde1820

As a percentage, it wouldn't surprise me.

Irrespective of the "math" however, from personal experience, in terms of effort I have found (on various bikes) the jump from 36->32 to be tougher than the jump from 14->12. Just the way this bum leg's power range works. A 34-36T (or I'm assuming 38-40T) "granny" gear change would be fairly subtle for most people, sure, but the difference for me is pretty solid when on a hill. No clusters seem to be available with such tighter jumps at the "low" end, though.

No big deal. I'll cope.

fietsbob

one thing you're probably on the flat to have the 14~12 shift
, working against gravity when needing the 32, 36

Technique: speed up get some momentum, then shift, taking tension off the chain with that surge and coast,

and the forcing it off one cog onto the other will meet with less resistance, from gravity..



...

Clyde1820

If I could generate more power (with the bum leg), I'd certainly use the momentum thing. But on the hills I deal with during commuting, plenty of spots are tough enough I can't do that. Steep enough there's no room for surging+coasting. Long enough that I peter out in a given gear before reaching the top. So, the best option I've got is to head into the lower/lowest gears early. A little frustrating, I suppose, but far better than being caught in too tall of a gear.

Anyway. If I can get the gearing low enough, it'll be the best option available.


Thank you for everyone's input, so far.

Likely setup: Thorn Short Triple crankset, with 44/32/22T chainrings and 150-155mm crank arms; IRD 12:40T cassette. About a 28% improvement in gearing over current.

CliffordK

Origin 8 also has some shorter cranksets, 140, 150, 155, 160, etc.

https://www.amazon.com/Origin8-Alloy.../dp/B00R6R3ZPM

Origin 8 also has a triple in 155 length.
https://www.niagaracycle.com/categor...et-155mm-130mm

Browsing the bike co-op and used bike sources, one can often find triple cranksets from kid's bikes, usually with integrated sprockets, and sometimes in lenghts around 152mm. Anyway, it might be good if you just wanted to test it out.

You're talking about some mighty low gears. You might at least try to hit parts of the hills hard, in higher gears, then shift down when you're wiped out. Maybe try to go further each day in the higher gears.

philbob57

Rather than going to extraordinarily low GI, how about electric assist?