New bikes, steeper seattubes, inline posts.....

[Sketchyxup]

:? What's the deal with this shift in position on modern bikes, loads of new stuff is moving towards steep seat tube angles (74deg ish) and not only that but they're being sold with inline posts.

I was always under the impression that you had an ideal seatback decided by your own physical factors and that was that, but this looks like a deliberate move by the manufacturers to get you forward, surely it's just going to cause discomfort, reduced peddling efficiency and knee pain?

Or am I missing something?

On my new 2017 Focus raven which is at the xc race bike end of the scale, even with the seat slammed back to the limit im a good 35-40mm in front of my seat position on my old bike. Before I try and find a post with a crane like set back am I missing a trick?

 

[mattr]

Longer wheelbases, more relaxed head tube angles (Some XC bikes are in to the high 60s now!!) more travel (both ends.

Trying to compare an "old school" geometry with current stuff is an exercise in futility.

And it's not setback that's ideal, its relationship between pedals, saddle, bars, hip/knee/ankle/back angles and so on.
Setback seems to be more road specific.......

Just have to look at the WC XC, almost everyone is using a more forward position these days.

 

[Sketchyxup]

Just have to look at the WC XC, almost everyone is using a more forward position these days.

That's what I mean, it seems a deliberate move to position like that. To stray even more away from mtb for a moment they set the seat like that on TT bikes for increased power and lower drag, but this is at the expense of loads of weight on the front and dodgy handling. Neither of those trade offs are desirable on a mountainbike.

You could argue that the roadie seat position will be the most efficient for peddling, it's basically the top middle and bottom of road riding so it should be sorted to the highest degree. On my roadbike the seat nose is 100mm behind the bb, the most i can manage on the xc bike is 60mm before running out of adjustment. Seems like a massive difference.

 

[mattr]

but this is at the expense of loads of weight on the front and dodgy handling. Neither of those trade offs are desirable on a mountainbike.

Except that with the longer front centres/wheel bases and slacker head angles and shorter stems etc you don't actually get the negatives. You just get a more stable bike on which you can put more power down. It just feels odd.

On my roadbike the seat nose is 100mm behind the bb, the most i can manage on the xc bike is 60mm before running out of adjustment. Seems like a massive difference.

it is a massive difference. It's also one i don't like either. But i can see the reasoning.

 

[Sketchyxup]

By my dorky workings out and assuming my roadbike is in a reasonably good position to start with then to get the same bb to hip position if the seat is 30mm further forward it also needs to be about 10mm higher.

That is going by my bb to seat dimension to the middle of the seat being 830mm, if you maintain position then you are effectively rotating your entire body around the bb.

See image if it works, big dot is my road seat position, the curved line is part of an 830mm radius circle around the bb. In theory you should be able to put seat anywhere on that line taking into account the horz/vertical movement to hit the line?

 

[mattr]

Yup. That looks about right.
Further forward and higher. Should open up your hip angle too, which in theory is good for power. Might also need some tweaking based on changes to ankle motion and the changes to hip position.

Not looking forward to setting up my next new bike. Current one has 72.5 seat tube angle. One I'm eyeing up is built around a 74 point something. Plus all the related front end changes. Including a wheel size change. :|

 

[Sketchyxup]

Re:

That's roughly what im doing now, had a Saracen Kili Ti as my xc race bike, 26" wheels fully rigid etc. Bought a 29er Focus Raven and it came with 74deg seat angle, inline post etc etc... Still a bit baffled what to do with it.

Might try it with the higher forward position rather than fight it to mimic my old bikes.

:?

 

[gradeAfailure]

Re:

Thing is, old school MTBs were based around Road bike geometry - which is fine if your off-road riding is mostly seated and on terrain that doesn't really vary.


The current school of MTB geometry says "Hey, actually, these aren't road bikes!", and attempts to set the geometry appropriately.

Have a read of anything written by Chris Porter (of Mojo), Leo Kokkonen (of Pole Bikes), Cesar Rojo (of Mondraker) or Ben Pinnick/Dan Hodge (Bird Cycles) on the subject. It's quite interesting..

http://geometron.mojo.co.uk/Geometry.html
https://m.pinkbike.com/news/the-intervi ... -2017.html

For starters..

 

[GrahamJohnWallace]

Re:

Correct me if I am wrong, I probably am, and feel sure that you will, but:

*isn't bio-mechanics concerned with getting the best possible power output from the human body, and the influence of riding position is well understood and does not change with fashion?

*aren't very slack steering angles to do with avoiding unstably steep steering angles resulting when the front end dives on long travel front suspension bikes during heavy braking? (With anti-dive front suspension systems we wouldn't need such steep angles and the long wheelbase that goes with them.)

*that according to the physics of inverted pendulums, (ie the physics of how top heavy things balance) the bicycle is a form of inverse pendulum that falls sideways more slowly the taller and top heavy it is? (Therefore, with lower bikes you have less time to regain balance when it is lost)
https://en.wikipedia.org/wiki/Bicycle_a ... e_dynamics

*that lower bottom bracket heights increase the chance of pedal grounding and mean the pedaling cannot be maintained through corners, inverse cambers etc?

*that increasing the weight over the front wheel also increases the risk of that wheel skidding in slippy conditions? (far better if the rear wheel slides as it is much easier to control)

*that long rear ends result in less weight over the rear wheel, less traction and so poorer hill climbing ability?

https://en.wikipedia.org/wiki/Bicycle_a ... e_dynamics

 

[FluffyChicken]

So what you are saying is, they are moving back to retro seat angles and retro inline posts? (of course back then it varied with frame size, at least on decent bikes).
(for example my 92/3 ish Rockies).

Nowt wrong with that, good to see they've seen the light.