Seat tube angle vs less offset

GrasB

Veteran
Location
Nr Cambridge
What are the advantages/disadvantages of increasing the seat post angle rather than using a seat post with less offset. Eg. what's the difference between a 73 deg seat tube with no offset & a 74 deg seat tube with a 12mm offset seat post if both put the saddle in the same position relative to the BB?
 
If I'm reading your post rightly, the advantage of less offset is your position is more over the BB therefore you can get more power and comfort. A disadvantage would be that in being more upright you are less aero. So I guess it what works for you what you feel is most optimum.
 
OP
GrasB

GrasB

Veteran
Location
Nr Cambridge
Yes you're reading it correctly but the original post is the wrong way round. It should be 73 degrees with a straight seat post or 74 degrees with 12mm offset. The difference of 1 degree at my seat post height from the BB is about 12mm so the saddle will be in the same position.
 

Ian H

I am an ancient randonneur, & I stop often for tea
Location
East Devon
The relative position of saddle to bottom bracket is important. The metalwork (or carbon) that connects them is not, except that a steeper seat-tube allows a shorter wheelbase.
 

jimboalee

New Member
Location
Solihull
Ian H said:
The relative position of saddle to bottom bracket is important. The metalwork (or carbon) that connects them is not, except that a steeper seat-tube allows a shorter wheelbase.
This answer is correct.

Steeper seat angle allows shorter chainstays.

To a point where the seat tube starts out pointing forward and curves round the tyre; and the seatpost has 8" of horizontal, like a polo bike.
The arse is almost directly above the rear axle so a wheelie turn is incredibly easy and a 'J' turn is possible because the bikes are usually fixed wheel and can be ridden backwards.
 

e-rider

crappy member
Location
South West
I think to answer your question, the answer is that there is no difference in riding position but changing the seat tube angle will affect other characteristics of the bike.

So frame makers try these things out before deciding on the best all-round option depending on what the bike will be used for and the size of the rider.
 

MartinC

Über Member
Location
Cheltenham
As the others have said the difference to your riding position is nothing. Ideally you'd want the saddle to be clamped by the middle of the rails when it's in the right position so you'd try and get a combination of seat angle and seat post with the right amount of set back to put the clamp in the middle position on the rails. Normally seat post set back varies from 0 to about 30mm depending on the model but there are odd ones around that have bigger or even negative set backs.

It's not a big deal - even (heavy) riders like me who normally have the saddle set back as far as it goes very rarely break good saddles.
 

jimboalee

New Member
Location
Solihull
Many years ago I went to see two friends in Coventry about building me a 'retro' frame using the existing dropouts in my Pug.
You see, I bought the Pug when I was fifteen and my LBS man assessed I had another two inches to grow. The Pug was sized to the French fit and it has always been 2cm too big for me.

I had a crazy notion to get LA Cycles to reproduce the frame to my ideal size.

After a discussion, it was agreed that the 2cm only makes the standover height a bit tight, and the 74 deg seat tube angle means the saddle is a little rear of centre. ie, sod all advantage in having a custom £550 frame built.

If 2cm and 1 deg makes such a difference to bike performance, I'm sure they would have happily taken my £550.
 
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