Setback question

[Guitars and Bikes]

The length of my san Marco rolls saddle is 282mm, in order to achieve my setback of 32mm (short legs) I simply measure from centre of bolt that tightens the headset to tip of saddle, 388mm and its bang on. I tried this with a bontrager verse comp saddle which is 270mm long and my bum took a beating. If I adjust my setback to 32mm + 12mm =44mm, would this place my sit bones in the correct position ?

 

[OldShep]

Forget about saddle length just measure to the point your sit bones are at.

 

[wafter]

Forget about saddle length just measure to the point your sit bones are at.

Indeed; although defining that point often isn't straightforward..

 

[Sharky]

I doubt if the saddle set back is causing the problem.
A "Rolls" saddle has a reputation for comfort. Your new saddle is just a different shape.

I took a similar route. For years, my saddles were San Marco Regal. Had no real problems with them, but wanted to try a "cut out" saddle. It was agony and I quickly went back to the "Regal"

 

[fossyant]

As you know some saddles are different, and I really doubt a few mm makes much difference - it's the saddle itself, very different from a Rolls.

 

[mickle]

Setback is horsesh!t. Chuck it on there, ride it and adjust it as necessary.

 

[rogerzilla]

Setback is relative to the BB, not the handlebars, so use a plumb bob from the saddle nose, mark the point it intersects the seatstay, and measure from there to the BB.

It is quite critical for pedalling efficiency. I have the opposite issue and I need at least 85mm of setback, preferably a bit more, so modern frames with steep seat angles are a problem. I have to seek out seatposts with a lot of layback.

 

[MichaelW2]

Setback is relative to the BB, not the handlebars, so use a plumb bob from the saddle nose, mark the point it intersects the seatstay, and measure from there to the BB.

It is quite critical for pedalling efficiency. I have the opposite issue and I need at least 85mm of setback, preferably a bit more, so modern frames with steep seat angles are a problem. I have to seek out seatposts with a lot of layback.

Assuming all cranks are the same length. If you are setting up a bike with different length cranks, then the reference for height is the 6.00 position and for setback, the forward 3.00/9.00 position.
You can mark the BB plumbline point with tape on your top tube. You then measure forward and back from this point. Using [X, Y] coordinates eliminates using angles of tubes, which are hard to measure.

 

[wafter]

The core issue here is that the only position on the saddle that matters is where your arse actually goes; which, across a range of different saddles could be almost anywhere relative to arbitrary positions like the saddle nose.

Of course if you run the same saddle on all your bikes then using some arbitrary point as a reference won't be a problem. As @rogerzilla suggests saddle position should be dictated relative to cranks, then reach set as necessary using the bars. I too apparently have long femurs so require a lot of layback, which usually results in fitting shorter stems to keep reach comfortable.

 

[Guitars and Bikes]

You don't think adding 12mm to the 32mm rolls setback is the way to go about it ?

 

[mickle]

Setback is relative to the BB, not the handlebars, so use a plumb bob from the saddle nose, mark the point it intersects the seatstay, and measure from there to the BB.

It is quite critical for pedalling efficiency. I have the opposite issue and I need at least 85mm of setback, preferably a bit more, so modern frames with steep seat angles are a problem. I have to seek out seatposts with a lot of layback.

If saddle set back is so very critical for pedalling efficiency how do you explain recumbents?

 

[rogerzilla]

If saddle set back is so very critical for pedalling efficiency how do you explain recumbents?

You can compensate for it with saddle height, or whatever it's called on a recumbent, but if you ride several normal bikes you want the seating position relative to the pedals to be the same across various seat angles, or it just feels really uncomfortable.

Recumbents need a learning/acclimatisation period anyway, because the legs don't hang naturally. You could probably get used to the "wrong" setback on a normal bike too, but that's only ok if it's your sole bike.