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Old Fox

The Sitting Posture on a Motorcycle

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by , 02-20-2014 at 08:37 PM (1575 Views)
The 'sitting' posture on a motorcycle is a compromise between either loading up the back or loading up the wrists. And this 'loading' is defined more by the relative position of the foot-pegs than the distance between the handlebar and the seat. The one other major contributing element is the front-end ride height.

The higher the speed at which a certain bike is expected to travel through most of its running life, the more is the torso rotated forwards and feet moved backwards. This is in no way connected to the power output of the engine or the ultimate performance capability of the motorcycle. Cruisers have powerful engines but the target cruising speed is low enough for the full-drag spread-eagle position to be viable. Ground clearence issues apart, try riding a cruiser through the twisties at a 150 kph and you'll understand it all. Sportsbikes are not just about fast acceleration, hard braking, quick direction changes and high speeds. Its all this with CONTROL. And so its about a very dynamic and aggressive riding posture with the rider ready for any body movement or control input done reflexively.


Most sportsbikes have riding postures that are like the rider is caught mid-way in a push-up. The forward leaning and tucked in position is not just for aerodynamic purposes as is usually thought. The purpose is to spread the rider's body-weight as much along the bike as possible and also keep him low so as to keep the resultant rider/bike C of G also low. A high C of G poses control problems both during hard acceleration/deceleration and quick direction changes, all the more exacerbated at high speeds that these bikes are meant to travel at. These bikes are NOT comfortable to ride. The ergonomics are not human friendly and yet they remain so for the benefits of handling and control they provide. Also because the rider in not expected to remain sitting in one position for long periods on such bikes. These bikes are meant for taking turns fast and when a rider does that, he hardly sits in one position for long. Weight shifts, foot-peg weighing and moving forwards/backwards on the seat for better control. All this movement doesn't highlight the discomfort of the posture. Use a sportsbike for touring and the 'painful' ergonomics come up front. As during touring, you sit in one position for long periods and any unusual muscle/ligament stresses get amplified.

The 'tourers' have the most rider friendly ergonomics. They follow the middle path between the sports-bikes and the cruisers. The rider is expected to cover large distances with little 'posture alteration' along the way. The 'direction change needs' are for a good response at reasonable speeds without compromising unduly on straight-line stability. The rider sits such that he doesn't need the support of his arms to stay sitting. A small test of 'long-time-on-saddle' friendly ergonomics is (with the bike on the centre-stand) to be able to stand on the foot-pegs and sit back on the seat without needing your arms for support. Try doing that with the rear-sets of a sprots-bike or the forward mounted pegs of the cruiser.

As for the proper (comfortable and control-friendly) arm position on a bike, it is with the rider's elbows level or a little below the handlebar level in a way that gets his forearms parallel with the ground. This is the unweighted position for arms i.e. the arms are there just for the task of steering and controlling the bike and not taking the load of the upper body. Loading with torso weight only happens under braking. And unloaded arms are a pre-requisite for precise steering inputs and feedback sensing. The cruisers do unload the arms but also place the feet so far forward that they no longer can play any role in taking any load off the back.The rider is like a sail catching all the wind at full stretch and this pushes his torso backwards at speed, making him hang on to the handlebars. The reason for large rake and trail with the accompanying long wheelbase is to give sufficient inherent directional stability to preclude a very active role from the rider. They are the 'easy' riders after all....aren't they.

There's an interesting bit of research in this 'research paper'. It is a downloadable pdf document. Just check out the body-position interrelation between various ergonomic/design configurations.

And here's the link to Tony Foale's works.

OF
lockhrt999 and Aaress like this.

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Comments

  1. lockhrt999's Avatar
    Sirji, big thumbs up for scientific observations.

    My case is a little different I'll always find a little leaned (little only) back posture of many sport touring bikes most comfortable for me. That's because I've got a week lumber but my upper body is very strong.

    You could wrap the blog article in . That will make it more readable.
    EDIT: wrap in QUOTES is what I wanted to write ^.
    Updated 02-26-2014 at 04:14 PM by lockhrt999
  2. Old Fox's Avatar
    Quote Originally Posted by lockhrt999
    Sirji, big thumbs up for scientific observations.

    My case is a little different I'll always find a little leaned (little only) back posture of many sport touring bikes most comfortable for me. That's because I've got a week lumber but my upper body is very strong.

    You could wrap the blog article in . That will make it more readable.
    @lockhrt999 - Thanks. The sport tourers do suit most of us ergonomically as they allow a more or less equal distribution of forces between both arms, the torso, the back and the legs. I too have a couple of ruptured discs (L4-L5 and L5-S1) from a decade and a half ago and so am partial to the likes of the Bonneville

    Will wrap it up. I just 'blogged' it from a post I had put in in one of the threads long back.
    lockhrt999 likes this.