'14 Trek Domane WSD 48cm - Help, shorter cranks!

[j0oftheworld]

So my GF's bike is a 48cm and came w. 170mm cranks.
She has some knee pain when riding, hiking, running so feel this could be alleviated on the bike at least w. a crank adjustment.
She's only 5'3" and has an inseam of 27" so most calculators I've found online list her anywhere from 144-155mm ideal crank length.
Obviously going from 170 to 165 from the major brands probably won't be much of a change so I was wondering if anyone has any places we could go for a crankset in the ~150mm area that'll work on her BB90 Trek?

Mini-bike in question:

[cajer]

Cobb cycling has cranks all the way down to 145mm. However they will likely need a BB adapter or something. Also I also ride a 48 and am using a 170mm. Though she is 2 inches shorter than me

[hornedfrog]

Check out Cobb cranks, they have plenty of options.

[j0oftheworld]

I think he biggest issue is her short legs @27"
As her bike is now at the top of her pedal stroke her thighs are perpendicular to the ground w a huge dead spot in her stroke!

Is anyone familiar with what fitting techniques are used to determine optimal crank length?

Cobb's site list GPX bb's.. what would we need to adapt those to her internal BB90?

[rijndael]

See the chart on this page:
http://www.slowtwitch.com/Tech/Short_Cr ... _2862.html

[shimmeD]

Check out Rotor

[spdntrxi]

my wife is 3 inches shorter and uses 165s on her 47cm Madone WSD

[wingguy]

Out of that list Rotor looks like the definite winner. TBH though crank length would be low on my list of potential sources of knee pain.

Also, I would get that stem as low as possible. If you can get her even a cm or two of drop it should be much nicer to ride.

[spdntrxi]

^^ that's what I am thinking too.. crank length is pretty low on my list for knee pain as well. I've had knee surgery and have used 165-175 and really notice nothing different. Ended up sticking with 172.5

[j0oftheworld]

She's 2 spacers lower now..
Her knee pain is from a crash w some scaring on her patella region so reducing any shearing leverage on that knee was my train of thought. The same exact cranks from shimano in 165mm might be the first step but if there was some way to do this during a fit I wanted to be open to even shorter options.
Thanks guys for all the input.. riding w your significant other is a luxury for most so I want to get her comfortable!

[wingguy]

Any modern fit bike (Guru, Shimano etc) should have adjustable cranks.

[dogg]

TA Specialties does down to 155mm as well.

[sanrensho]

I'm 5'5" and ride 170mm cranks. I have also ridden 165mm on my trainer/winter bike and felt it was easier to spin.

[FIJIGabe]

To go from her current crank to a GXP crank, she only needs to swap out the non-drive side BB bearing to a GXP bearing. Any Trek dealer should have the part in stock. Go with the steel bearings and it's <$20, plus labor. The drive side bearing is the same (24mm), so she won't need to swap that out, but the bearings come as a pair, so you',ll have an extra bearing. Keep them, and use them on your bike (if you have a BB90 shell).

[Mr.Gib]

There is always a chance that a shorter crank will make the difference but the real key to avoiding patella related pain is to make sure you are familiar with all of the physio protocols designed to promote proper tracking of the patella. For some people the slightest difference in muscle balance and connective tissue tightness can mean the difference between being unable to walk and being able to run a marathon, ride all day, etc. pain free.