Saddle Height Discrepency

starockets

This maybe a bit of a bizarre question but has anyone out there had a similar problem to the one I'm having at the moment.

I have just pulled out the winter bike for a ride today, which has been dimensionally set up as near as i can to that of my good bike. After about an hour into the ride I had to drop the saddle by nearly 10mm to get it comfortable to ride. (Which is where it ended up after last winter as well).

Saddle to bar drop is a bit more on the winter bike 5-10mm.
Cranks are 172.5 on good bike and 170 on winter bike.
Good bike has 50/34, winter bike has 52/39.
Good bike is carbon and light, winter is ally and quite heavy ( maybe not relevant but it feels like it needs a bit more grunt to keep it going)

Do you think this is just an accumulation of small dimensional differences between the two bikes or do I need to see a shrink?

Bobbinogs

Is the height from saddle to pedal axle the same? That's the thing that really matters, IMO. I cannot feel 2.5 mm of crank difference.

starockets

Bobbinogs wrote:

Is the height from saddle to pedal axle the same? That's the thing that really matters, IMO. I cannot feel 2.5 mm of crank difference.

The saddle height to the bottom bracket was the same at the start of the ride but I dropped it by 10mm during the ride to make it more comfortable. That is the thing I can't understand, it should feel similar between the two bikes, maybe because my saddle to bar was now similar to the other bike when i dropped the seat, I didn't think about the legs too much :?

StillGoing

Personally I believe crank length does make a difference although you seem to be suffering with shorter cranks as opposed to longer ones. If your seats were both set at the same height from bottom bracket to seat top, with the differing length crank arms, one would be 2.5mm shorter at the bottom of the stroke and 2.5mm lower at the top of the stroke. There is in effect a 5mm difference between your pedal rotation on both bikes as you're obviously 2.5mm higher at the bottom of the stroke and 2.5mm lower at the top of the stroke. The measurement from pedal spindle at the bottom of the stroke to the top of the seat is presumably where your fitter took the measurement from and not bottom bracket centre to seat top? If so, your seat in theory should be going up 2.5mm to maintain the same length as with your longer crank arms. The difference is that your leg at the top of the stroke won't be compressed as much because of the 2.5mm shorter crank length at the top of the stroke and therefore there would be 5mm difference between bikes at the top of the pedal stroke. Is the problem you experienced from the top of your pedal stroke in that you feel you can't get the power down as well as on your good bike? If so lowering the seat by 2.5mm might be a happy medium so that your leg at the bottom of the stroke isn't too bent. Alternatively, take the measurement from BB to seat top off your good bike and make the winter bike the same, you'll then be in the middle of the range with the 170mm crank arms.

starockets

philthy3 wrote:

Is the problem you experienced from the top of your pedal stroke in that you feel you can't get the power down as well as on your good bike? If so lowering the seat by 2.5mm might be a happy medium so that your leg at the bottom of the stroke isn't too bent. Alternatively, take the measurement from BB to seat top off your good bike and make the winter bike the same, you'll then be in the middle of the range with the 170mm crank arms.

I think the main problem is that the saddle to bar drop is about 10mm more on the winter bike and I am running out of options to raise the bars. This puts me in a slightly diffeternt position and by dropping the saddle I felt more comfortable on the saddle and with the arms, saying that my legs hurt like something else the next day so I am going back to a setting the seat position similar on both bikes.

I have re-positioned the saddle to be identical to the good bike like you have suggested, both the saddle height from the bottom bracket and the saddle fore / aft. Going to give it a go on the rollers tonight, I think it might be a case of putting up with the bar drop difference and maybe just raise the hoods a bit.