Shorter crank arms for my [FSA SL-K Light BB30 11sp 50/34] or new crank ?

ToiletSiphon · May 27, 2015

I will probably be going with this, which is BB30:

FSA Omega Compact Road Bike Crankset BB30 165mm 50 34T N10 Speed NEW | eBay

It states 10 speed, but does anyone knows if it also fits 11 speed systtems?

deviousalex · May 27, 2015

ToiletSiphon said:
I will probably be going with this, which is BB30:

FSA Omega Compact Road Bike Crankset BB30 165mm 50 34T N10 Speed NEW | eBay

It states 10 speed, but does anyone knows if it also fits 11 speed systtems?

It should work. I have a DA7900 crankset on my 6800 11 speed setup right now and shifting is fine.

rm -rf · May 27, 2015

165 mm is 6.49 inches
172 mm is 6.77 inches.

That's about 1/4 inch shorter on the downstroke, and another 1/4 inch at the top.
So you can drop your seat 1/4 inch and you'll raise your leg 1/2 inch less high at the top of the pedal stroke. Is that enough to make a difference?

ToiletSiphon said:
I do have a specific physical problem. The conversion to a short crank arm is something my PT / fitter wants me to do. I'm on a bike break until I do it. I realize it will be expensive and a real pain in the... I currently have a 172.5 mm and preferably would like to go shorter than 165mm, which is the lowest most "big names" go.
.

Does your fitter have one of those adjustable fitter trainer bikes? Some have shorter cranks to swap in.

Crank arm shorteners are sometimes used on tandems with a smaller stoker. They screw into the pedal hole, then extend back toward the spindle with more pedal holes. They do move the pedals outward, which might cause it's own fitting problems.

For example:
Ride2 Crank Arm Shorteners

Tandems East - Crankarm Shorteners

~~~~~~~~~~~~~
or a do-it-yourself project: drill and tap the solid aluminum arm.

That looks kind of sketchy. He cut off the arm way too close to the drilled hole, and also says that the arm is hollowed out on the backside. So there's not as much threading as the original hole.

ToiletSiphon · May 27, 2015

rm -rf said:
165 mm is 6.49 inches
172 mm is 6.77 inches.

That's about 1/4 inch shorter on the downstroke, and another 1/4 inch at the top.
So you can drop your seat 1/4 inch and you'll raise your leg 1/2 inch less high. Is that enough to make a difference?

I don't know if 1.5 cm (7.5mm x 2) will be enough

. I certainly hope so.

rm -rf · May 27, 2015

ToiletSiphon said:
I don't know if 1.5 cm (7.5mm x 2) will be enough . I certainly hope so.

Try raising your saddle 1.5cm temporarily. You'll have to stretch down to the bottom of the pedal stroke, but the top will match the 165mm cranks. See if it helps.

ToiletSiphon · May 28, 2015

I saw the shorteners, but I'm not going that route first because I currently have a carbon crankset and it will probably mess it up but also because my fitter is trying to keep my Q-factor to a minimum.

MMsRepBike · May 28, 2015

Go to a different bike fitter.

crit_boy · May 28, 2015

MMsRepBike said:
Go to a different bike fitter.

I am having an difficult time trying to figure out OP's problem and how anything other than child sized cranks would make much impact.

Problems: tight achilles tendon; tight quads. Achilles causes foot to point down, which causes knee to go too high, which causes too much shear force on knee.

My thoughts:
1) if your foot can go perpendicular to your lower leg (like when you walk), then why can't it go perpendicular when you pedal?
2) assuming the same cadence range, a shorter crank is going to require relatively more force to generate the same power/bike speed. Won't more force make the shearing force on the knee a bit worse?
3) OP called the person recommending this a PT/fitter. I have a great amount of respect for PTs. But, does the person really know cycling in particular? The thing they are vaguely suggesting (shortest crank you can get) does not sound like it is coming from a person that understands bicycle component availability.
4) if the problem is simply right tendons and muscles, will continued quality stretching improve the condition over time? If so, why not dedicate yourself to regular stretching - like multiple times throughout your day.

Father Guzzi Obrian · May 28, 2015

I'm a red suspenders and corn cob pipe Moto Guzzi restorer, so I always look at the least expensive way when experimenting. Drilling, tapping for a helicoil and trying the shorter crank distance on your existing cranks is at most a ~$100 at any local machine shop, likely cheaper. If you like it, you can proceed with a final solution, if not, you now have a lighter bike. Let us know how things work out.
Cheers,

crit_boy · May 28, 2015

Father Guzzi Obrian said:
I'm a red suspenders and corn cob pipe Moto Guzzi restorer, so I always look at the least expensive way when experimenting. Drilling, tapping for a helicoil and trying the shorter crank distance on your existing cranks is at most a ~$100 at any local machine shop, likely cheaper. If you like it, you can proceed with a final solution, if not, you now have a lighter bike. Let us know how things work out.
Cheers,

You can't drill and tap hollow carbon crank arms.

Shorter crank arms for my [FSA SL-K Light BB30 11sp 50/34] or new crank ?

ToiletSiphon

deviousalex

rm -rf

ToiletSiphon

rm -rf

ToiletSiphon

MMsRepBike

crit_boy

Father Guzzi Obrian

crit_boy

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