Is there a specific reason why most road bikes tend to use a layback seatpost? Is it a comfort thing?

I find it easier to get more power through the pedals when I sit further forward on the saddle, why is this?

Is it sacrilege to use an inline post on a road bike?

Use what ever fits, I do.

looks weird..

the seatpost is irrelevant, what matters is the seat tube angle, which at c73degrees works better for most people with a layback post. slacken the seat tube to 70degrees? which would mean a inline would work best for most and the back end would probably have to kicked out to give wheel clearance. steepen it to 76, and you might find a bit too much weight on the front end.

I am only guessing at numbers, but roadbike geometry has been reasonably sorted for years, why mess with something that works?

I think mrmo is right!! I guess that with a slight setback on the seat post you’ll be pushing over the top of the pedal stroke & down giving more smooth power rather than “chopping” down on the pedal stroke. It is all about the angles & traditionally set back posts are the norm so I’m guessing that if you need an inline post the frame could be a bit on the large side for your natural/comfortable riding position.

‘cos it looks best innit 😆

Both seat angle and layback are relevant.

For me, with a bb-seat dimension of 80cm, 2.5cm of layback makes ~1 degree difference.

Most folk feel a steeper seat angle gives more power – I think it’s about how you train your body to pedal and what you are used to – triathletes ride steep bikes, maybe because they can’t specialise their bodies to cycling.

Slacker angles are thought to be more comfortable. Greg Lemond liked them

The bike is a planet x carbon, this has a 72.5 degree st angle on the XL (my frame) compared to a 74 degree on the small.

I also run alot of seapost showing (cos Im 6’2″ and have long legs) so it feels like Im sat quite far back. It was the same on my last road bike aswell, just feels like I can push down on the pedals better whan sat a bit further forward. Abit like when you sit on the nose of the saddle for climbing.

Slacker angles are thought to be more comfortable.

I dont find it uncomfy at all with a layback post, it just seems like Im losing out on the power!

Most, if not all road frames will be designed for a lay back post (plus most mtb frames). I think the penchant for inline posts is a fashion thing from the mtb world.
The correct fore/aft position for the saddle is when the crank arm is horizontal the bony protrusion below the knee is vertically above the pedal axle.
Here endeth the first lesson!

Well I have two road bikes, one with inline post, one with lay back post, the difference between the two? The seat tube angle.

just feels like I can push down on the pedals better whan sat a bit further forward.

Learn to Sit properly on the bike and pedal correctly, therefore using more than just your quads for power!

The correct fore/aft position for the saddle is when the crank arm is horizontal the bony protrusion below the knee is vertically above the pedal axle.

I thought this was just a guideline with little physiological reasoning.

The inline post is fitted

Dont plan anything for tomorrow night because Im going to go for a ride and then post a very dull report about my findings

If you think about things in a logical fashion, and accept that Knee Over Pedal Spindle (KOPS) is a reasonable starting point, then the amount of saddle setback will be proportional to the length of your femurs.

Saddle height is set by referring to leg length; but set back is more influenced by femur/tibia ratio.

It’s also going to be influenced by the way you ride in terms of toes down or flat foot at the bottom of the pedal stroke.

As a wise man noted earlier; Use what ever fits, I do.

😉

angle & distance between bb/arse/bars is all that matters in terms of comfort/power surely (ie you could ride a super slack seat tube or big layback post as long as your bars were a bit higher and not as far forwards or else super-steep with a low & forwards stem). (or you could ride upside down, or on a recumbent).

I suppose the “traditional” angles (that work well for most) are what delivers that, plus a nice aerodynamic angle of your torso. They also stop you having to support lots of your weight on your hands, which will tire your shoulders/back.

TT and triathletes presumably mostly ride shorter durations so don’t need absolute comfort (they also rest on their elbows, so can prob tolerate more weight on the front to get a very aero postion)

I don’t ride long distances so bike fit isn’t crucial for my comfort. I suspect my position is also shite – something is sho’ making me slow 😥

As a wise man noted earlier; Use what ever fits, I do.

But, would it be wise to tailor my bike to a suit bad pedalling technique, or improve my pedalling technique to suit my bike?

It would be wisest to just ride the thing. There is no ‘optimum’ position for pedalling, no optimum position for power output; it’s about riding the thing.

If you are comfortable, that’s 90% of the battle won.

Them scientisters done a study about the way power is applied around the pedalling cycle; they found that everyone pedals the same, except the pros press harder…

I’ve got a bike with an in-line post, and a bike with a set back post, and to get my comfy position I ride with the saddle a bit back on the in-line post and a bit forward on the setback post. See?

Alot of positioning “rules” are good starting points, but no more.

I have various seat angles, top tube lengths, stem lengths and KOPS-misses on all my bikes. And I ride everyone fast, hard and like a God.

Sorry I started off being serious. My point is my stem occludes the front hub every time, but lots of other things are different, and I conclude the “rules” matter not a jot.

There is no ‘optimum’ position for pedalling, no optimum position for power output;

Hahahahahaahahahaahahahaahahaahahahaahahahaha, thats a good one! Thats so wrong I’m not even going to try and explain.

Hahahahahaahahahaahahahaahahaahahahaahahahaha, thats a good one! Thats so wrong I’m not even going to try and explain.

Oh good. Have a nice Christmas then.

Hahahahahaahahahaahahahaahahaahahahaahahahaha, thats a good one! Thats so wrong I’m not even going to try and explain.

Did you teach me Physics A-level?

Blimey, thedoctor really knows his stuff.

Most bike geometry is to do with the manufacture of the thing, then humans get on and adjust everything so it fits 🙂

Mines online on my race bike, but that due to the almost TT style of circuit racing.
I was coached from an early age to move along the saddle to suit the terrain/effort.

triathletes ride steep bikes, maybe because they can’t specialise their bodies to cycling.

International Triathlete friend of mine says it’s because it allows for a better run – use of slightly different muscles with a more forward position which then makes it easier to swap from bike to run.

Though I wonder if flexibility is part of it – like TT riders, a more forward position makes it easier/more comfortable to achieve a flatter/lower position because you’re stretching the hamstrings less.

Interesting though that traditional cyclocross geometry would be the opposite of Tri geometry; slack at the back, steep at the front, and yet they run/ride/run more in a shorter time.

Like I said, no real optimum, just whatever works is best.

Yeah but I think if you’re doing run/ride/run/etc quickly as in CX it’s less of an issue than if you do an extended period of one then swap to the other.

Cross is messy, normal rules on geometry go out of the window. Coleman might disagree? you start out with an idea of optimum geometry, but cornering with your leg out or bunny hopping sleepers is unaccountable.

oldgit – Can’t argue with that! Geometry is the least of my worries whilst hooning around a typical cross course.