Saddle Position

[aboylikedave]

(Sorry for a repost but I think in my last attempt it wasn't very clear)

Does frame size have any relationship with the position of the knee in relation to the pedal?

In other words with the saddle for example set as far back as it can go, and assuming the saddle height is set correctly and to the same height, will there be any difference in knee position with a small or large frame?

 

[Camilo]

(Sorry for a repost but I think in my last attempt it wasn't very clear)

Does frame size have any relationship with the position of the knee in relation to the pedal?

In other words with the saddle for example set as far back as it can go, and assuming the saddle height is set correctly and to the same height, will there be any difference in knee position with a small or large frame?

It depends on the angle of the seat tube. If the angle of the seat tube is the same between the two frames, the distance back from the pedal spindle would be the same, given identical saddle heights - the seat post is nothing more than an extension of the seat tube, going at the same angle.

On most frames, the seat tube (and head tube) angles change a little from one size to another in order to set the seat back further as the frame size increases.

You can probably find the geometry for the frames on the company's web site.

 

[aboylikedave]

On most frames, the seat tube (and head tube) angles change a little from one size to another in order to set the seat back further as the frame size increases.

Thanks, that what I was after. For whatever reason I always need the saddle back as far as possible, so a larger frame may help.

 

[capwater]

If you have to shove your saddle all the way back you are changing your body mass position relative to the pedals. While you can sometimes tweak a smaller frame with a longer stem, being too far back is definitely a sign of a too small frame.

 

[aboylikedave]

If you have to shove your saddle all the way back you are changing your body mass position relative to the pedals. While you can sometimes tweak a smaller frame with a longer stem, being too far back is definitely a sign of a too small frame.

Thanks for helping. But, according to the first reply, mass relative to pedals will be the same on either frane. I've checked the specs and the 17.5" (correct size for my inseam) and 20" (a bit big for a hybrid as it leaves only 1" of clearance) only have a 0.5degree difference in geometry. Can't make that much difference can it?

Every LBS says 20 " is a bit too big for me for clearance, but I always need to have the saddle full back. So what I'm really trying to find out is if I will be happy on a smaller frame.

 

[Camilo]

Thanks for helping. But, according to the first reply, mass relative to pedals will be the same on either frane. I've checked the specs and the 17.5" (correct size for my inseam) and 20" (a bit big for a hybrid as it leaves only 1" of clearance) only have a 0.5degree difference in geometry. Can't make that much difference can it?

Every LBS says 20 " is a bit too big for me for clearance, but I always need to have the saddle full back. So what I'm really trying to find out is if I will be happy on a smaller frame.

What measurement/criterion are you using for the fore-aft position of the seat? That's the first question.

Are you putting your seat so far back because it feels better with the handlebar position, or because it is what's needed to get the right pedaling position?

Pedaling (seat fore-aft) position should come first (using "knee above pedal spindle" or a a variation of that). Then you adjust the stem on your handlebars to fit the reach for comfort.

If your seat is back because it's necessary for pedaling position, maybe you nead a seat post with more "set back". That sets the seat further back without being at the end of the rails. They make various set backs; you might just need one with more than the one you have.

If the seat is so far back simply because you want a longer reach, you should set it according to pedaling position, then get a longer stem to achieve the comfortable reach.

As for the 1/2 degree difference in the seat post angle, it will make a difference - more of a difference the higher your seat is. It only takes an inch (2.5 cm) to be pretty significant on your seat rails.

It would be easy enough to measure the difference - set the seat height the same on the two bikes, and the fore-aft position the same. Drop a plumb bob (or use a level in the vertical position) from the nose of the saddle and measure horizontally to the pedal spindle.

It could also be calculated using the seat tube angle and seat height, but I'm way too far away from trig. to do it myself!

 

[aboylikedave]

What measurement/criterion are you using for the fore-aft position of the seat? That's the first question.

Are you putting your seat so far back because it feels better with the handlebar position, or because it is what's needed to get the right pedaling position?

Pedaling (seat fore-aft) position should come first (using "knee above pedal spindle" or a a variation of that). Then you adjust the stem on your handlebars to fit the reach for comfort.

Thanks - I appreciate your time. My seat-backness is 100% to do with pedalling position, and how my knees feel. If the seat's not back they feell too far foreward . I suppose the implication may be that I have long thigh bones relative to the rest of me. However getting my peddalling position correct ends to result in a frame which LBS says is too big. Fortunately its a hybrid so I don't need to worry about clearance too much. Reach feels OK.

Your seat post suggestion is therefore a good one.