seatpost setback?

[kellym]

Could someone please explain setback in regards to a seatpost? I am interested in switching out the stock aluminum seatpost on my Giant TCR3. I located Token carbon seatposts on ebay but the description says 20 mm or 22 mm setback. Is there really any difference between a one bolt or two bolt design?

Thanks

[bcipam]

Since this is not a visual medium I would recommend you go to a bike shop to check this out but setback refers to the post angle. Imagine 90 degrees from the ground straight up and down and then angle the post away from 90 degrees - that is your setback. Some seatposts are setback more than others affecting your reach etc. If you switch out for a more setback post, you may have to adjust your handlebar stem (make it shorter).

As to 1 vs 2 bolt. I use a 2 bolt - its a safety issue but I've never had a problem with a one bolt. Setback has nothing to do with the bolts.

Now I have had the saddle rails break - that's a whole other issue!

[kellym]

thank you.

[mellic]

If you are happy with your current riding position on your bike you should really try to find a new post with a similar setback to your current post. Find out the setback angle on the TCR3 post and work from there.

In regards to one and two bolt systems, I have used both and snapped both. From my own personal experience the one bolt system is a lot easier to manage, but the bolt can loosen over time causing the seat to slip back. The two bolt system is a little more fiddly but once you have it right I think it distributes the clamping force a little more evenly over the seat rails.

The post I am currently using is the thomson masterpiece and I have had no problems as yet.

[madisongrrl]

If you switch out for a more setback post, you may have to adjust your handlebar stem (make it shorter).

You don't want to necessarily do this or assume that you can make the stem shorter to compensate for the increase in setback. If you get a setback you need to examine how this saddle position change affects your knee-pedal position (the position will vary with body structure, pedaling style, and types of events in which you compete).

[SadieKate]

A 2 bolt system can also allow more adjustments to the saddle angle.

I'm going to second the advice that you make sure you do not change the fore and aft position of your saddle unless you know what you are doing. You need your knees and hips in the proper position in relationship to the cranks.

Lastly, be sure that you get a saddle with the proper min and max insertion points. A mtbike post can be farther out of the down tube that a road post.

Just a hint, when you are looking at a seatpost you can see the setback in usually two ways. The post itself will have an angle (such as the LH Thomson's) or the head of the seatpost (the clamps) will be designed to sit behind the post. If the clamps are directly above the post, there is no setback (Thomson's also has a model with no setback).

[kellym]

Okay, thanks for everyones patience.
I went out and measured my stock Giant post. I measured the back of the seatpost tube to the back of the actual seatpost head. I came up with 25 millimeters. Does that make sense? If I buy a 22 mm (setback) post will that work?

The length of the post is 330 millimeters. I can't even see the numbered adjustment marks on the post where I have it set at for my height. Should I go with a 250 mm post or 300 mm post?

One of the websites advised that the more seatpost inside the frame the more stable and strong the post.

I've read alot of good things about the Thompson posts but I wanted carbon for a smoother ride.

[madisongrrl]

Okay, thanks for everyones patience.
I went out and measured my stock Giant post. I measured the back of the seatpost tube to the back of the actual seatpost head. I came up with 25 millimeters. Does that make sense? If I buy a 22 mm (setback) post will that work?

It depends on how your bike was initally set up. Did you have a bike fit? Do you like your current position? Measure your current saddle setback position (provided that you like it and it is the correct position for you). You can do this 1 of 2 ways.

Method 1 - Drop a plumb line from the nose of your saddle. Measure the horizontal distance from your crank center to the plumb line.

Method 2 - Take yard stick or a similar object that is perfectly straight and line it up (vertically) to your crank center. Measure the horizontal distance from the yard stick to the nose of your saddle.

The length of the post is 330 millimeters. I can't even see the numbered adjustment marks on the post where I have it set at for my height. Should I go with a 250 mm post or 300 mm post?

One of the websites advised that the more seatpost inside the frame the more stable and strong the post.

That website is correct....the more seatpost inside the frame = more stability. That is why manufacturers mark the limit of the seatpost. If you exceed that mark, you could ruin your bike frame. So it is important to get one that is long enough (but not excessively long because it adds needless weight to your bike). If you are not sure if a 250 or 300 will work, you might want to bring your bike in to your LBS and ask them. Also remember that changing the saddle setback will change the saddle height (for example less setback would mean an increase in saddle height) as well as changing the saddle height will change the saddle setback.

It really comes down to how much you like your current position. If you are happy with it, get a seatpost enough setback and the proper height. If not, then you will have to figure out what your new position is and take the appropriate measurements.

Good luck,

[kellym]

decided to go with the thomson masterpiece after reading great things about it and not so good things about carbon posts. thanks for all the info.