rosinante25

billydonn, when i "mirrored" the two bikes i measured the length from the bars to the seats, etc.so i don't think this is the problem. that's why i was mystified as to what it could be. i'm surprised the lbs guys never mentioned the cranks when they worked on the bike. i'm guessing since i never mentioned it they didn't consider it either. in their defense i was more concentrated on getting the cockpits to match. i'm bringing her in to the shop today & will know more. i wonder if i need expensive cranks or r they all about the same??

10 Wheels

Rowan

Good one, 10Wheels. I know a guy who theft-proofed his bike by painting with a brush dots all over it in yellow. It looked ugly as can be, and those dots served their purpose.

The thing is, you might not need to replace the cranks. you just need to lower the saddle slightly and measure from the pedal at the bottom of the stroke to the sitbone position on the saddle to ensure that measurement virtually matches that on the other bike. The issue then becomes knee-over-pedal spindle, hence the suggestion about the plumb bob, and as stated by others, it then becomes a matter of moving the saddle forward or back as need be.

Actually, I was expecting a bit more of a discrepancy in the crank length -- say, 165 compared with 175. A few millimetres in seat height adjustment can make a difference to knee or achilles tendon soreness... that I do know.

FanaticMN

Also check that your pedals are the same distance apart. Are the bottom brackets the same width?

Do you use cleats?

indycar

Like your response Rowan. So...what are we drinking at this pub anyways?

Road Fan

Need a two-column proof for that ...

Road Fan

I dunno how big a project you want right now, but I'd start with the small one of making sure the pedal to saddle top distance is the same for the two bikes, with the crank arms aligned with the seat tube. This would have you raising the saddle 2.5 mm for the bike with 172.5's. At the same time the two bikes need the same setback.

The consequences are that with the longer crank, your leg will rise an extra 5 mm at top center, with a tighter hip closure angle resulting. This can be uncomfortable, or perhaps you have enough flexibility that it's no problem.

Essentially, geometry can cause injury, but only if it requires a compromised fit - in other words, if the frame is just plain wrong for you.

Chainring, I dunno.

BTW, I've found the difference between a low saddle that causes knee pain and high enough not to cause it, can be less than 5 mm.

lphilpot

Well if I still had my 9th grade algebra and 10th grade geometry grades, I'd be glad to put them in two columns and prove beyond any shadow of a doubt.

rosinante25

will do the above. it's just that in aligning the bikes i've moved that darn saddle up & down & back & forth a hundred times and it didn't fix the problem altogether. my understanding is that the smaller crank creates a shorter pedaling circle and that many riders report that even the difference between the 175 & the 172.5 has alleviated knee and hip problems. but i will try measuring again including using the plumb line and then readjust the saddle accordingly. by then i hope to find the right crank set in case that is the last resort.

cranky old dude

Algebra just blew my mind but Geometry was a breeze...well at least until I droped the Geometry book on my foot. At that point Geometry hurt.

lphilpot

Kinda my experience as well, but I never studied either beyond the classes I had to take. Geometry seemed to be more intuitive, but I later developed an interest (if not great ability) in computer programming, which would seem to relate more to algebra, possibly. At least, I've enjoyed the logical side of what little programming I've done.

Then again, this was all more than 35 years ago and my 'revisionist' memory may be enhancing erstwhile abilities.

bradtx

rosinante25, Generally riders can cope between different crankarm lengths, of course a few may not. Before spending any money, make sure that the saddle is as close as possible to the better bike's WRT KOPS. Don't adjust your saddle fore and aft to compensate for reach, change stems for that. Saddle height is adjusted for leg extension with the pedal at BDC. Adjusting the height of the saddle may require a fore and aft adjustment.

Brad

rosinante25

it took some searching but i found a set of moderately priced 172.5 fsa cranks ($70. at bikeisland.com) that work with my 9 speed chain. the rings start at 50t and altho the big ring on the bike is a 52t i understand that it should work ok. the big mystery seems to be whether i will need a new bottom bracket to go with the cranks. well so here goes. over the next few days i will be experimenting away in the basement mad scientist style measuring and plumbing, fore & afting. then i'm going to ship the moto to florida to take a week long vacation for a family get together. my family lives along the pinellas bike trail and i hope to do 5 early morning 60 milers to test the moto. if this doesn't work i'll get the new cranks. if that doesn't work is anybody interested in a 2 yr old modified red cafe sprint with drops & brand new cranks?

Road Fan

rosinante25, make small changes as you adjust, sometimes just 2 millimeters or 1/16 inch at a time. This applies to fore/aft, saddle height, and to the height of the nose above the top tube (saddle tilt). If your seatpost forces you to tilt the saddle in jumps that are too big, you need to get one that microadjusts, a two-bolt type.

You're going by feel, so one of the tasks is to learn the feeling of a saddle too high/low, forward/backward, or tilted wrong nose up or nose down.

The order of adjustments should be: saddle height with saddle centered on rail clamps, incrementally move saddle fore/aft to see which direction you need an dhow much (readusting height every few adjustments to restore proper leg extension), and then saddle nose height (saddle tilt).

rosinante25

i don't use cleats. i ride with clips & a pair of lake cycling shoes. will measure the pedal distance & width of bottom bracket when i work on matching the bikes again. thanx everyone for the great advice. this has got to work this time. i 'd hate to give up on my moto. time will tell.