Author Topic: What determines whether you go in line or laid back with your seat post?  (Read 3499 times)

PH


Knee-over-pedal-spindle isn't a rule either. 

Not a rule, but it works for many people so probably worth trying as a starting point.

Porkins

  • Formerly Nick H. And a long time ago etc, Eurostar
What if, like me, you have a custom touring frame with relaxed angles but still need lots of layback?  People have told me that this means 'your frame must be the wrong size'. But the bloke who measured me (a Serotta-trained bike fitter) insists that layback must be part of my equation. And the bloke who chose my frame dimensions (Dave Yates) seemed to agree. I can't remember the reason - it was complicated and I just accepted it because these people are experts and the idea that they would spec me a wrongly sized custom frame is a nonsense. Could it be something to do with me having long thighs and a short torso? 

I think of myself as an averagely proportioned cyclist and would have thought that if I need layback even for a custom touring frame then many, many other people must need it too..so why are there so few layback posts on the market? I could only find two silver ones - the kinked Thomson and the beautiful VO, which I imagine is only sold in tiny numbers. It seems odd that decent looking seat posts with layback are not in every manufacturer's range.

What if, like me, you have a custom touring frame with relaxed angles but still need lots of layback?  People have told me that this means 'your frame must be the wrong size'. But the bloke who measured me (a Serotta-trained bike fitter) insists that layback must be part of my equation. And the bloke who chose my frame dimensions (Dave Yates) seemed to agree. I can't remember the reason - it was complicated and I just accepted it because these people are experts and the idea that they would spec me a wrongly sized custom frame is a nonsense. Could it be something to do with me having long thighs and a short torso? 

I think of myself as an averagely proportioned cyclist and would have thought that if I need layback even for a custom touring frame then many, many other people must need it too..so why are there so few layback posts on the market? I could only find two silver ones - the kinked Thomson and the beautiful VO, which I imagine is only sold in tiny numbers. It seems odd that decent looking seat posts with layback are not in every manufacturer's range.

Layback posts are everywhere.  It is the inline posts that I find few of and therefore wonder if layback is taking over.

In my view an ideal frame would mean a seatpost with medium set-back. An in-line, or one with extreme set-back are a compromise for a less than ideal frame geometry (except for TT bikes where in-line may often be used)

In the old days, Belgian and French frame builders only used set-back behind bracket and top-tube klehgth, along with size, as the measures.

Just watching the TdF hightlights and I saw Menchov's Giant TCR with the integral seat post.
So that would be inline then?

Here is Gesink's from last year:  looks like there is a bit of lay back in the top.


In my view an ideal frame would mean a seatpost with medium set-back. An in-line, or one with extreme set-back are a compromise for a less than ideal frame geometry (except for TT bikes where in-line may often be used)

In the old days, Belgian and French frame builders only used set-back behind bracket and top-tube klehgth, along with size, as the measures.

That makes sense, you view the bottom bracket as the pivot point, I just find it easier to see the top tube in two length, behind BB and forward of it.

I know that my saddle, when at the correct height, wants to have the nose about 80mm back of the BB. There are several combinations of seat tube length/angle and seatpost setback that can achieve this. I think this is the essence of the OP, as in what combination is best and does it differ for different styles of riding?
Nuns, no sense of humour

Here's a link to the Cervelo website and the way they show their geometry, their 'reach' measurement is what I was on about:-

2010 - Aero Road Bikes - S3 - Geometry
Nuns, no sense of humour

David Martin

  • Thats Dr Oi You thankyouverymuch
Ignore the set back completely until you have determined where you want your saddle to be relative to the BB. I like mine too far forard for the UCI's liking (short legs don't help) so I have an inline seatpost. I have also used a 'fast forward' seat post and a modest layback with the saddle pushed forward to the limit.

My preference. On another frame I would get the saddle where I want it then get a seatpost to suit.

..d
"By creating we think. By living we learn" - Patrick Geddes

Paul Smith SRCC

  • Surrey Road Cyling Club
  • 37+ years a club rider, 27+ years in cycle trade
    • www.plsmith.co.uk
For sure some have different theories as to bike set up, but generally a road/sportive/audax bike will use a layback pin, this is because normally these bikes are set up in the neutral position for a variety of roles, climbing, general riding at 60% effort right through to flat out effort etc. On these bikes as general rule you are  looking to have a saddle set back so that if you drop a plumb line down from your knee when the cranks are horizontal, the line should be touching or near the pedal axle. This is not the Holy Grail though; we wouldn’t exactly stick a broom handle in the top of the seat pin clamp if we can’t get it back far enough!



On a road/sportive/audax bike the seat tube is generally at such an angle that we can struggle to get the saddle back far enough; vice versa can apply to MTB bikes, it is these bikes where straight pins are more common place. Straight pins are often used on Low pro TT bike for a different reason, as these bikes have a much narrower focus interms of type of use, they are normally used for high level effort over more level terrain than a road road/sportive/audax bike and the rider may want the plumb line to be more over the BB as a result.

Paul_Smith
www.corridori.co.uk

but that's not really answering the question as to whether there are pros and cons to saddle position in relation to seatpost. If you have an ideal saddle setback then that would apply for all bikes for general riding. This will also produce the same knee to pedal realtionship assuming equal cranks. Say for example someone is best suited by 75mm of saddle setback, measuring saddle nose to BB center, vertically. This can be achieved in a variety of ways depending on saddle position on rails, inline/setback seatpost and seat tube angle. The steeper the seat tube angle the further forward the saddle needs to be and vice versa. So what's best?:-

slacker ST angle and inline seatpost saddle in middle
slacker ST angle and laid back seatpost but saddle right forward
steeper ST angle and inline seatpost saddle right back
steeper ST angle and laid back seatpost saddle in middle

As the same riding position is being created then doesn't it come down to saddle/seatpost interface and weight dispersion? Or whether one option is comfier than another, or is there no difference?
Nuns, no sense of humour

Manotea

  • Just 1 sob, Vassily
but that's not really answering the question as to whether there are pros and cons to saddle position in relation to seatpost. If you have an ideal saddle setback then that would apply for all bikes for general riding. This will also produce the same knee to pedal realtionship assuming equal cranks. Say for example someone is best suited by 75mm of saddle setback, measuring saddle nose to BB center, vertically. This can be achieved in a variety of ways depending on saddle position on rails, inline/setback seatpost and seat tube angle. The steeper the seat tube angle the further forward the saddle needs to be and vice versa. So what's best?:-

slacker ST angle and inline seatpost saddle in middle
slacker ST angle and laid back seatpost but saddle right forward
steeper ST angle and inline seatpost saddle right back
steeper ST angle and laid back seatpost saddle in middle

As the same riding position is being created then doesn't it come down to saddle/seatpost interface and weight dispersion? Or whether one option is comfier than another, or is there no difference?

Tourers have slacker seat tube angles than racing bikes for comfort, and maximum comfort will be achieved with a slacker seat tube and the seat post interfacing with the saddle rails at their mid point to allow for maximum flex of the saddle rails to provide a cushioning effect.

However more to the point, you need to use a seat post that will allow  the saddle to be positioned correctly relative to the BB. This might entail an inline or layback post depending on the frame geometry and your preferred riding position. I don't believe selecting an inline or layback post has any inherent impact on comfort per se and its only worth changing if you cannot get the the saddle into the correct position right with your current setup.

Paul Smith SRCC

  • Surrey Road Cyling Club
  • 37+ years a club rider, 27+ years in cycle trade
    • www.plsmith.co.uk
but that's not really answering the question as to whether there are pros and cons to saddle position in relation to seatpost..........

I was simply replying to the title; “What determines whether you go in line or laid back with your seat post?” and for most what’s determines this is what they need to use to get the correct height and setback; providing that the saddle ends up where it needs to be and then it doesn't matter that much if you have a straight/inline or laid back seatpin.

There are other contributory, layback may offer slightly more comfort for example, some prefer the look of inline, but in reality the main influence would normally be achieving the correct position.

Paul_Smith
www.corridori.co.uk