What determines whether you go in line or laid back with your seat post?

[GruB]

I am in the market for a new seat post.
I have always been laid back but when I got the USE Alien in line post it felt great ( but the design and Wiltshire's shite roads let me down ) so I am looking again.

What determines whether in line or laid back is the best option?

[pixieannie]

I think the size of the frame makes a difference.  I had a laid-back post on the Sunday but the frame is slightly too big so opted for an in-line post to get me closer to the bars.  I had already popped a shorter stem on and didn't want the handling to be affected further.

[PH]

What determines whether in line or laid back is the best option?

Trial and error.
There's a theory that having your knee directly over the pedal spindle when the crank is at 3 o'clock is ideal.  There are theories that this is complete nonsense.  What many people find is there is a position saddle to bottom bracket that they prefer.  You can't change a frames geometry, you can achieve the same set up on different bikes with a change of saddle and/or seatpost.

[hubner]

It's your saddle position and the frame seat tube angle.

Eg, if you have a steep frame and a saddle that's quite far back, then you probably need laid back seatpin, and vice versa.

[Ian H]

Saddle rails have been known to break if not clamped fairly centrally. Find the right position for your saddle, then buy a seat pin to suit.

[Biggsy]

My backside is just not comfortable in the long run with the saddle in line, even with a longer stem to provide the same reach as otherwise.

That doesn't apply to everyone.  You've just got to experiment to find what suits you, or perhaps go for a bike fitting service if you believe in that sort of thing (ie that someone else can know what's right for you).

Remember that putting the saddle back effectively extends your legs, so it's somewhat (but not completely) the same as putting the saddle up, and vice versa.

[giropaul]

It's your saddle position and the frame seat tube angle.

Eg, if you have a steep frame and a saddle that's quite far back, then you probably need laid back seatpin, and vice versa.

Exactly. There is a right place for your saddle, height and distance back from bracket. Getting this right may mean getting a seatpin with the right offset. I recently got a new frame, and bought a very bling seatpin - unfortunately this had too much offset and I had to buy another with less setback to get my position.

If you can't get the right seat setback, and right reach, you've got the wrong frame and it's time for e-bay!

[MacB]

I found the Neuvation method very interesting, they assume a static saddle to BB relationship:-


Bike Geometry

They class reach as BB to HT measured in the same way as you would measure effective top tube. Put another way a vertical line from the BB that bisects the effective TT line and use the measurement from there to HT rather than ST to HT.

So, if you measure that on a bike that fits you well then you can apply that measurement to other frames to see what size works. It's just a shame that all the little geometry charts don't include this. Say you had an ideal of 385mm reach and looking at their geometry chart. You could go with the any of the frames and just add/subtract the difference to your existing stem length. Obviously you'd be more likely to choose one of the closest matches, above or below, but it does give you an easy reference point for comparing frames.

Thought I'd share that, probably old hat to a lot of you, but I found it much easier to understand than other methods.

[Crepello]

Isn't there a risk with the in line position of putting more weight on your wrists and the handlebars? My impression is that when I've got the seat further foreward that it is a more powerful riding position, but the laid back position helps achieve the upper body's centre of gravity in the fore/aft plane. Ergo, less wrist ache. Put another way, it's not so much a question of KOP as ABS (Arse Behind Seatpost)*.  However, too much lay back found me lifting off the seat unexpectedly when I put the power down.

*Obviously this depends on a relaxed or aggresive seatpost angle.

[bikenerd]

All down to seat tube angle and top tube length as stated above.
For example: my geared MTB, seat tube angle 72.5 degrees - inline post, my single speed MTB, 73.5 degrees - lay back post.

If I put the lay back post on the bike with the 72.5 degree seat tube angle then I'm pulling wheelies on the climbs and the front wheel washes out on loose surfaces.

On a road bike it probably doesn't matter as much.

[Biggsy]

Isn't there a risk with the in line position of putting more weight on your wrists and the handlebars?

The handlebar stem should be changed if moving the saddle back or forwards to maintain the same reach, unless you want to change that as well.

[GruB]

I am very comfortable at present so I think I will get another laid back post.
However, if we take as given that my stem is correct and that my saddle is the correct distance back from stem / bars - then would not a new in line post just mean the saddle would need to sit back further on the rails?

[mattc]

Yes, but you may be overestimating how much leeway the rails give you.(might be a problem, might not).

[GruB]

If there is sufficient distance in my saddle rails to enable that shift, what it does mean is there is more saddle behind the post central axis.  This could put more pressure on that axis point and might cause the nose to shift up more?

So using the laid back design incorporates the gap in the design of the post rather than putting extra pressure on the rails.

[rogerzilla]

With modern frames you might need a layback post *and* the saddle pushed right back on its rails, just to feel comfortable.

[Rapples]

My backside is just not comfortable in the long run with the saddle in line, even with a longer stem to provide the same reach as otherwise.

I find exactly the reverse. With layback I find myself sitting too far forward on the saddle to be comfortable, and consciously pushing myself pushing myself back.

When changing to an inline though as you say you need to lenghten the stem.

Try putting the saddle forward on the rails for a ride and see how it feels.  If you don't feel more comfortable in the nether regions, sort of more balanced and in one with the bike, it's not for you, stick with a layback post. As stated above the ideal is the saddle in the right place clamped in the centre of the rails.

FWIW my favourite saddle is a Toupe, or Flite trans am.  I think the choice of saddle can affect what seatpost feels best.

[GruB]

Roger's post got me to thinking about modern frame design so I have gone onto Cyclingnews.com and looked at the tech pictures for pro bikes at the tour.

Back = no gap in the rails at the front.
Middle ish = gap either side of saddle rails.
Forward = loads of saddle rails showing to the front.

Tyler Farrar - Felt F1 - laid back with saddle pushed right back ( not much gap at the front ).
Thomas Voeckler - Colnago C59 - laid back with saddle in the middle ish.
Ivan Basso - Cannondale Super6 - laid back with the saddle in the middle ish.
Mark Cavendish - Scott Project F01 - laid back with saddle pushed all the way forward.
Carlos Sastre - Cervelo R5 - laid back with saddle in middle ish position.
Thor Hushovd - Cervelo model - laid back with saddle in the middle position.

From looking at the Enigma site and the geometry tab for the Etape, my seat angle is 73.

[Cudzoziemiec]

This is a technically fascinating discussion, but at a level too detailed for me. However, I'm sure there is an element of fashion in the present popularity of laid-back posts, just as with steeper frame angles. At some time the fashion will come round again and we will be riding frames with shallower angles and in-line posts.

[Domestique]

At one time wouldnt all seat posts have been in-line?
I am lucky in a way as I nearly always need the smallest frame in the range so frame size choice is limited, but it must be almost possible to fit the person to a frame, rather than frame to person given the sheer number of stem lengths and seat post designs available.

[inc]

What determines whether in line or laid back is the best option?

Where your bum needs to be in relation to the pedals, everything else is secondary. Modern frames tend to be compact in just a few sizes S,M,L,XL so seat posts now come is various degrees of setback from zero to 60mm and some saddles with longer rails. This works fine for most people unless you have  a Brooks with short rails and a design from the birth of cycling where getting enough setback can be a problem.

[rogerzilla]

Yes, Brooks saddles are the usual problem.  With racing bikes a 73 deg seat angle is OK because few people use Brooks.  On a tourer 70 or 71 deg are better to accommodate the shorter rails of the tourist's favourite "ass hatchet"*.


*(c) Jobst Brandt

[MacB]

What determines whether in line or laid back is the best option?

Where your bum needs to be in relation to the pedals, everything else is secondary. Modern frames tend to be compact in just a few sizes S,M,L,XL so seat posts now come is various degrees of setback from zero to 60mm and some saddles with longer rails. This works fine for most people unless you have  a Brooks with short rails and a design from the birth of cycling where getting enough setback can be a problem.

Agreed, I think the frame dictates the seatpost as you need to fit whatever will allow you to achieve your usual saddle to BB relationship. My understanding is:-

steeper seat tube means less top tube behind the BB and therefore more likelyhood of needing a set back seatpost and vice versa.

If you go for a smaller frame then a setback post is more likely to be required. I have frames up at the top end of my size range so inline works better for me. It wasn't an option for my bike with the Brooks, I needed it to get the saddle to fit right and still get a saddle pack fitting on the rails.

[rogerzilla]

My understanding is:-

steeper seat tube means less top tube behind the BB and therefore more likelyhood of needing a set back seatpost and vice versa.

That is, indeed, the beginning and end of it.

Knee-over-pedal-spindle isn't a rule either.  Simply, you need more setback (which means a layback post if pushing the saddle back as far as possible isn't enough) if you find yourself constantly trying to wriggle backwards in the saddle.

ISTR that nearly all seatposts were layback until USE came out with their superlight inline design in the early 1990s for MTBs.  It's an easy way to make your seatpost a few grams lighter than the competition.

[mattc]

Presumably using lay-back makes a mockery of 'racey' steep seat angles?

[Ian H]

Presumably using lay-back makes a mockery of 'racey' steep seat angles?

Seat tube angle is more to do with wheelbase, or shortening the rear triangle. You'll see old bikes with very shallow angles often had seat pins that put the saddle forward.