Yet Another Cycling Forum
General Category => The Knowledge => Topic started by: GruB on 15 July, 2010, 07:41:24 pm
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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?
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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.
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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.
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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.
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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.
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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.
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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!
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I found the Neuvation method very interesting, they assume a static saddle to BB relationship:-
Bike Geometry (http://www.neuvationcycling.com/bikegeometry.html)
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.
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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.
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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. :)
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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.
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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?
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Yes, but you may be overestimating how much leeway the rails give you.(might be a problem, might not).
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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.
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With modern frames you might need a layback post *and* the saddle pushed right back on its rails, just to feel comfortable.
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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Presumably using lay-back makes a mockery of 'racey' steep seat angles?
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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.
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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.
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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.
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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.
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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.
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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.
(http://autobus.cyclingnews.com/photos/2009/tech/probikes/robert_gesink_rabobank_giant_tcr09/Gesink_Giant_TCR_saddle.jpg)
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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?
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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 (http://www.cervelo.com/en_us/bikes/2010/S3/geometry/)
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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
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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!
(http://farm5.static.flickr.com/4077/4818219970_08b215485c_o.jpg)
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 (http://farm4.static.flickr.com/3026/2817796028_c6b2113f3e.jpg?v=0)
www.corridori.co.uk (http://www.corridori.co.uk/gbu0-display/Touring_Tips.html)
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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?
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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.
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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 (http://farm4.static.flickr.com/3026/2817796028_c6b2113f3e.jpg?v=0)
www.corridori.co.uk (http://www.corridori.co.uk/gbu0-display/Touring_Tips.html)