Do I have a geometry problem?

[ultrazenith]

I've been reliving some of my old favourite routes on Dartmoor in the last few months, using Raleigh / M Trax titanium bonded frame based bikes, which has been fabulous, a real trip down memory lane, with some measure of sadness that my old riding crew have either gone off to other cities, or are deceased.

The frames in question are 19.25" centre to top (so around 18.5" c-c), which are probably a bit small for me at 6'3", but sadly the mid 90s bonded Raleighs didn't go any bigger. I've encountered a weird issue that I do not have when I ride my 21.5" Diamond back - I just can't get the normal full power at the end of each pedal stroke, my knees (or just above) feel like they are doing more work than the other leg muscles, and slip into a noticeably faster pedaling cadence than on my larger bike.

Could this be a case of incorrect positioning of my knees over the pedals?

My legs feel nearly straight when the pedal reaches the bottom, which makes me doubt that this is a question of the saddle being too low.

Any advice would be welcome, as I love these bikes, and would hate to have to part with them...

 

[suburbanreuben]

Re:

Sounds like your saddle might be too far back;it doesn't take much.
Are you running original length forks?

 

[ultrazenith]

Thanks, I'll try playing with the saddle positioning. Yes, original forks on both bikes.

 

[Bullpup]

Have you checked the crank length?

 

[PurpleFrog]

Re:

The best article I've ever seen on bike fit is this one by Keith Bontrager:

http://sheldonbrown.com/kops.html

..and it is mostly about getting fire/aft saddle placement right.

A whacky thought: if the the bike is too small that actually makes it ideal for a drop bar conversion.

 

[xerxes]

Re:

Could it be that you are no longer 17?

 

[ultrazenith]

Re: Re:

Could it be that you are no longer 17?

In fact, I'm certain that is part of the problem, yet on my larger framed retro bike I have no such problems, and have identical crank arm lengths.

 

[xerxes]

Re:

As others have said, try moving the saddle about and possibly even adjusting the stem length. Sometimes a small change in posture, seat height and position for and aft can make a big difference in comfort.

Try measuring the relative positions of the seat, bars and BB spindle and comparing them to a bike which you find comfortable.

 

[02gf74]

Measure the top tube horizontally.

Older frames pre 2000 ish would have shorter top tubes and even non sloping top tubrs so frame size as you measured it is not the important one.

You need to compare theriding posion of both framrs.

A modern 19.5 in frame should be just on the limit of 6 ft 3.