jnbrown

So I have been riding 170 cranks on all my bikes forever and have no desire to change.
I have a 31" inseam.
FSA shows 170 Gossamer's on their web site but I was told they quit making them years ago.
I can get some old stock but its going to cost me around $150 more than the 172.5 cranks.
I think the 172.5 are an unknown, I might get used them or might not.
The front crankset is around $140 so if it didn't work it would not ba a great loss.
I am thinking maybe I should go test ride some singles with 172.5 cranks to see how they feel.
Anybody have experience with this?

rdtompki

My wife and I are new to tandeming, but I would think the variables associated with sharing the drivetrain would far outweigh the difference between 170mm and 172.5mm cranks.

lhbernhardt

Crank length is a non-issue. I go from 165 on my road fixed gear to 175 on the tandem and hardly notice the difference. (My inseam is 34") The key is to set the saddle height in relation to the bottom of the pedal stroke, so that your maximum leg extension is the same for any crank. This means that your saddle will be 10mm higher for a 165mm crank than for a 175mm crank.

Where crank length comes in handy on a tandem is when the pilot is very experienced and gravitates to a faster spin than an inexperienced stoker who is used to pedaling slowly. The longer crank results in faster foot speed for the equivalent rpm's, so the stoker - although spinning at the same rpm's as the pilot - will not feel the legs moving as fast.

Luis

jnbrown

It does seem 2.5mm is a very small difference. Although we have ridden tandems for many years, at times my wife feels we are spinning too fast which is when we hit around 95-100 rpm.
We currently have 170 on the back, but her new single back has 165. I am thinking she might feel better with 165 on tandem. So putting 172.5 on front and 165 on back should certainly help the spinning issue.

swc7916

Sorry, but too long of a crankarm can cause knee issues for some people. That 10mm of saddle height difference results in 20mm of knee travel difference. Our old tandem has 175/175 and they are just too long for my wife; she will develop pain in her knees if we ride this bike. We specifically ordered 170/165 crankarms on our "new" (2 years old now) tandem for this reason.

specbill

I have a 31" inseam as well. Ride about 5K miles a year most of that on Tandems for the last three. I found out that I was quite sensitive to Crank arm lengths when I started playing with then to help with our different spinning preferences. I quickly learnd that on long mileage days the 175's caused hip issues for me but then again I have a marginal right hip to begin with. 170's have always been the most comfortable for me in any situation. I have use 172.5' s and they are less problematic but still not quite as comforable as the 170's.
Performace wise, I could not tell that much difference with any of the three lengths so I stayed with the most comfortable set-up (170's).

Bill J.

jnbrown

Ok, so here is an idea maybe it is dumb.
I can buy a regular 170 Gossamer crankset really cheap.
Then I could switch the right and left arms and put in a helicoil to reverse the threads.
Or just leave the threads and make the pedals really tight.
So the next question is the bottom bracket on a tandem wider than a standard road bike?
How much wider? This is on a Calfee.
Will the spindle on the crankset be too short to fit?

bikeriderdave

YMMV of course, but not necessarily a dumb idea. I am like you: Used to 170 cranks and unwilling to compromise on our tandem(s). I have access to a small machine shop and have simply "cross-threaded" several cranksets for use on cross-over drive tandems over the years. I have not used Helicoils or inserts. Don't know how heavy one would have to be to experience problems, but I'm about 150 lbs and learned the trick from a slightly heavier/stronger engineer and former frame builder.

Chris_W

I had a similar issue. I run 170mm on all my bikes. The dealer told me that our tandem would come with 170mm front and rear FSA Gossamer cranks, but I was wary of this because I couldn't find such a combination available anywhere else. When it arrived, it was 172.5mm at the front. I can certainly tell the difference, and spent several rides playing around with my seat height without improving things much, and was expeciting it to be something that would always bug me.

After one year and several thousand kms on the bike, I've decided that it the slightly longer front cranks aren't too much of a problem. They do have one advantage: I like to spin the pedals a bit faster than my stoker, and the longer cranks makes my cadence feel a bit higher than it really is, so this makes a happy compromise in cadence easier to achieve.

I therefore recommend putting a decent amount of mileage into the bike with the 172.5's before deciding whether changing them would be worth the hassle.

osurxbiker

It was definitely 170's for me. Inseam of 28". I would probably be more comfortable on 165's, but then I would have to change my singles and fixie. Also I would probably spin too fast a cadence for my wife.