Seat Posts - Straight vs. Set Back (angled)

[Chuck Hammer]

Why the differances and when would you use a set back? ...thanks all

[malcolm]

Assuming you don't need the set back for saddle position, it is aesthetic.

[AndrewS]

There is some confusion on this topic, so here's some pictures:
This is a set back seat post:
http://www.evanscycles.com/product_image/image/8ff/466/893/28410/small/thomson-set-back-seat-post-410mm.jpg?1227121549
This is also a set back seat post, because they both have a clamp that is not centered over the post:
http://s.wiggle.co.uk/images/pro-vibe-mono-carbon-post.jpg
This is a straight post:
http://www.evanscycles.com/product_image/image/7ae/982/273/26251/product_page/thomson-seat-post-250mm.jpg?1227115933

Set back seat posts are usually necessary to get your seat in the correct position over the bottom bracket for you leg length on a road bike. Unless you have very short thighs or a very relaxed seat tube angle, the straight post will prevent you from sliding the saddle back to where it belongs for good fit.

Straight posts were first made for mountain bikes, and are often the lightest posts, which is why they are too often seen on road bikes. They are usually a bad idea because of saddle position. Under normal circumstances, they shouldn't be used on road bikes.

[rugbysecondrow]

Your saddle choice might dictate as your decision as well. Brooks have less travel along the rails, so you might need a setback to accomodate it.

[1centaur]

A long-time road racer truism is that to get your powerful glutes involved sufficiently in the production of power, given the typical distance from hips to knees and the typical range of bike geometry, you need a set-back post.

[ergott]

The seatpost you choose is the one that puts your saddle where it should be. Most frame designers I've talked to suggest about a 60%/40% weight distribution (60% over the rear wheel, give or take a few %) for good handling. Most of the time this is done with a setback seatpost. You can then adjust your reach with the bar/stem combination to achieve this and a position you are comfortable with. If not, the frame isn't for you.

You can design a frame around a seatpost with no setback if you prefer those aesthetics.

You can check your weight dist. easily if you can put your bike in a trainer and weigh the front wheel while in your riding position. Be sure to weigh the total weight of you and the bike before when doing this to get an accurate weight distribution.

I would probably leave off any bags or other add ons for this, but a more qualified frame designer/builder could correct me if I'm wrong.

[torquer]

Your saddle choice might dictate as your decision as well. Brooks have less travel along the rails, so you might need a setback to accomodate it.
True dat!
My Thompson no-setback post only works with my Sella Italia SLR saddle, which has a longer flat rail segment than my other saddles (SI TA Max). So that's my super-light setup, which is fine for up to an hour of racing, which is all I do these days anyway. But I wouldn't get another one. (And the setback version always brings to mind "bent-nail syndrome." But that's just me.)

[AndrewS]

Eric,

Which position should you be when you weigh yourself? For fractions of an inch on the seat position to matter, it seems like a movement of even an inch in hand position between drops and hoods would shift the weight fairly noticeably.

[Charles M]

Bike fit = Required setback

The post set back (for most people who dont prefer the spring effect of having their saddle slammed forward or back) should allow the clamp to be in the center of the saddle rails for a given position and will depend on the seat angle and shape of the saddle and rails.


That's it...

[ergott]

Eric,

Which position should you be when you weigh yourself? For fractions of an inch on the seat position to matter, it seems like a movement of even an inch in hand position between drops and hoods would shift the weight fairly noticeably.

I measure "on the hoods" because that is where I spend most of my time.

I would also make sure you are in a relaxed position like you ride (you ride relaxed right?;-) Checking this after riding outdoors for a while would be best so you loosen up.

If your scale is too difficult to look at this way, then get someone to help. An alternative is leaning up against a wall, but I think it's hard to sit naturally if you are concerned with falling over. Keep the bike lever as possible. A typical bathroom scale might not be as high as a riser block for the trainer. If your floor is level, measure the height of the front and rear axles if your top tube isn't level.

[ergott]

should allow the clamp to be in the center of the saddle rails for a given position

This is why frame builders will work with the saddle in question. If you are constantly swapping things you probably shouldn't be committing to a high ticket custom until your contact points are sorted out (not you, Pez, but the collective reader).

[rugbysecondrow]

This is why frame builders will work with the saddle in question. If you are constantly swapping things you probably shouldn't be committing to a high ticket custom until your contact points are sorted out (not you, Pez, but the collective reader).

I agree with this. When I got fitted, I should say before I got fitted, I had to have my bars, saddle, brifters and pedals. All of these were then mounted on the size cycle so we could work with the real parts I was using on the bike.

[AndrewS]

I think most road saddles are more alike than different in terms of rail position. Even after receiving a custom frame built just for you, it is most likely set up to have the kind of seat tube angle that will work with an average set-back post and popular saddle. If not, the builder probably has a specific post designated to use.

It is important to remember that seat tube angle is also used to adjust ride characteristics, not just adjust position. So a builder may include a rather slack or upright seat tube and then spec a seat post to position the rider counter to this angle to get position.

That being said, a normal set back post is usually the right choice with a road bicycle and standard saddle. If departing from this, there is an important and unique reason for the change. Liking the looks of a zero set back post is not a good reason. Having a bicycle or body that is outside the norm is.


Thanks, Eric!

[Chuck Hammer]

Thank You All.... some great feed back. I am looking at the Thompson with the set back. Any thoughts on this?

[rugbysecondrow]

Thank You All.... some great feed back. I am looking at the Thompson with the set back. Any thoughts on this?

It works, the two bolt design is highly adjustable. Some folks don't like the way they look, I do though. It is a seatpost, so not much to say really.

[gone]

Thank You All.... some great feed back. I am looking at the Thompson with the set back. Any thoughts on this?
I've got a Thomson on a couple of my bikes. Personally, I like the look and the adjustability is great, easy to get the angle of the saddle exactly right.

[AndrewS]

I buy into Thomson's philosophy about aluminum being a more practical post material. I think you can find other light and adjustable alloy posts for slightly less money, but the quality is good, and if you like the look, there you go.

[Dave]

The only time that the front to rear weight balance makes a lot of difference is in serious cornering. With that in mind, I measure the weight balance with my hands in the hooks and my upper back nearly horizontal (or as low as you'd ever intend to ride). The lower torso position increases the weight on the front. I shoot for 42-45% on the front, in that position.