Saddle forward = saddle up or down?

[rodneycc]

Hi All, I read something recently that contradicted what I thought was the usual practice and need some clarification.

I recently moved my saddle fore-aft more forward on the rails which I always thought that meant it drops the saddle height by a couple of mm. But I read somewhere its the reverse where if you set it back further it drops the saddle height. So what is it really?

I'm having a few lower hamstring (where it meets the knee) issues. I think the saddle is too high but I need to play with the fore/aft as well.


Edit: From Neil's Bike fit:

"Remember that as the seat setback is adjusted, so too does the seat height. Move the seat 10mm back and you will likely need to drop the saddle around 3mm to account for this effect. After any major setback change, saddle height should be re-assessed and fine-tuned"

This is what is confusing me as I always thought it was the other way around...

[Derny Driver]

If you slide your saddle forward, you need to raise the seatpost height slightly.
If you slide the saddle back, you need to lower it.
Usually 3-5mm.

[rodneycc]

Thanks Derny, I had to re-read that a couple of times before it got through my thick head. So both of those statements and my understanding were right. I was just reading it wrong. So moving the saddle forward gets you closer to the spindle so it reduces the saddle height (which is what I was trying to achieve). Good.

There are other factors here with my setup like the ISP has two offset pivot positions that I have been playing with and with the Selle Smp has those angled rails but its more about the theory that I was after so thanks again. Time to have a bit more of a play I think. Got a feeling I need to cut that ISP a bit more too, darn it.

[Duck!]

Saddle design can play a part in whether or not you need to tweak the height; if the rails are a considerable angle off horizontal (lower at the back) then sliding the saddle one way or the other will alter the height automatically, but may still need a fine tweak.

To illustrate how it works, try some rudimentary geometry. You will need a bit of paper, a ruler & maybe a protractor & compass:

On your sheet of paper, scribe a straight line vertically. Length isn't critical, but longer helps. From the bottom end of your first line, scribe another of identical length, but at an angle (17 degrees represents a typical seat tube angle from vertical ). You could use a compass to scribe an arc between the other ends of the lines to show your constant distance. Now mark a line at a right angle to your original one, at a height that intersects with the end of your angled line, and extends past it. See where this is going? Moving along this horizontal plane toward the vertical axis reduces the distance from the base point, ergo lower seat height. Sliding back increases the distance.

[rodneycc]

Thanks Duck, I didn't go as far as the compass and protractor but I got a piece of cardboard out and a ruler and tape measure and kind of got the idea with measurements from saddle to stem and BB to top of saddle and did the same comparison on my other bike as well (with the same selle smp saddle). I don't know how much the compact geometry plays a part but I kind of just imagine a straight line on the top tube and get an idea where abouts in the ballpark it needs to be. Verdict is I need more seatpost cut.

[Tim]

Got a feeling I need to cut that ISP a bit more too, darn it.

Rodney, I can lend you a clamp-on cutting guide for the TCR aero seatpost if you don't already have one. It'll make the cut nice and properly square and I think helps avoid a frayed edge.

[rodneycc]

Got a feeling I need to cut that ISP a bit more too, darn it.

Rodney, I can lend you a clamp-on cutting guide for the TCR aero seatpost if you don't already have one. It'll make the cut nice and properly square and I think helps avoid a frayed edge.

Thanks Tim but I have already paid my lbs to cut it once so should be no probs to take it back there and get a little more taken off. Just painful I didn't get it right the first time. Thanks for the offer though and will look you up if I have any dramas with them.