Saddle Positioning

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M.G
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Saddle Positioning

Postby M.G » 3 Aug 2007, 10:30am

Have a problem setting up my Orbit Helium Audax bike. been riding it for a year now, but i have never been able to get the seat far enough forward. Due to being 6"3 the seat has to be up high which positions it further back. Recently i tried turning the seat post round 180degrees and fixing the saddle that way round, only problem being is the micro adjuster doesnt allow the saddle to be angled down enough to make it hozirontal.

Hope that makes sense.

Any ideas?

Mario

Postby Mario » 3 Aug 2007, 11:30am

Hi,

I spotted a funny set up the other day. I believe it was a BMX seat post angled to lean forward at the top. Hope this helps. M

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Mick F
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Postby Mick F » 4 Aug 2007, 8:59am

MG.
It sounds to me like the frame is the wrong size and shape for you. The seat post shouldn't be extended so far that you're too far back.

Ah, the joys of Made to Measure .....
Mick F. Cornwall

M.G
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Postby M.G » 4 Aug 2007, 9:28am

Quite right, ive only had two frames that fitted one a 25 1/2" raleigh sprint and a 25" peugot frame (which got smashed by a car within an hour of riding it and was replaced by my orbit). I assumed when i got it that because it was the largest size it should fit me, but its still a semi compact frame so not really.

Any other options than new bike?

Michael

reohn2

Postby reohn2 » 4 Aug 2007, 9:36am

MG
I think the problem you have is quite unique.Forgive me for this but at 6' 3" your thighs must be quite short or you have a very unusual riding position.I'm 6ft tall and usually have the opposite problem in that I can't get the saddle far enough back on the rails so the saddle is pushed as far back as it can go and due to the cantilever effect created by this position break saddle rails on a regular basis (about every 18months).
Have you tried an inline seat post or does that not get you far enough forward?also have you looked for a saddle that the rails extend nearer to the back of the saddle?
Just a final thing,what distance behind the bottom bracket would the nose of the saddle be to be ideal?

M.G
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Postby M.G » 6 Aug 2007, 2:25pm

Thanks,

I didnt know you could get an inline seat post, so will look into that. I havent looked into saddles as the one i have is quite comfortable and i dont wont to forfit that.
I base saddle postioning on having my knee over the axle at 3 o clock and being able to touch the handlebars while my elbow is touching the end of the saddle. I have not come accross the reasoning of the rlative positions of the saddle and BB, could you explain it?

M.G

reohn2

Postby reohn2 » 6 Aug 2007, 6:18pm

MG wrote:-
I have not come accross the reasoning of the rlative positions of the saddle and BB, could you explain it?


With the saddle in your ideal riding position and the bike on level ground, if you hang a weighted string (pumbline)from the nose (front) of the saddle,what is the measurement from the string to the bottom bracket(BB) spindle,in other words how far(if any) is the front of the saddle behind the BB spindle.Most people ride with the saddle nose further back than the BB.
This measurement and the distance between pedal (measured when the pedal is at the bottom and the crank is in line with the seat tube)and top of the saddle are crucial for comfort.The distance between nose of saddle and handlebars can be adjusted with differing stem lengths but the saddle/BB relationship is the most important for comfort.

PS millimetres can make a lot of difference to comfort.

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towedhaul
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Postby towedhaul » 6 Aug 2007, 7:46pm

reohn2 wrote:This measurement and the distance between pedal (measured when the pedal is at the bottom and the crank is in line with the seat tube)and top of the saddle are crucial for comfort.The distance between nose of saddle and handlebars can be adjusted with differing stem lengths but the saddle/BB relationship is the most important for comfort.


I've always measured by sitting on the saddle. Then, with the pedal horizontal, a plumb line from the front of my knee should go through the pedal axle.


reohn2 wrote:PS millimetres can make a lot of difference to comfort.


Absolutely! When I tried it first I moved my seat about 1/4 inch forward & the difference was amazing :shock:

M.G
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Postby M.G » 6 Aug 2007, 11:06pm

Hmm, currently my saddle nose is most obviously in front of the BB, I have a 90mm stem riser (reduced from the ridiculous 180mm that was fitted on it), so anything shorter could affect steering, with the saddle in the position it is now my forearm reach is still only just to the headset.

Thanks for the advice,

Michael.

reohn2

Postby reohn2 » 7 Aug 2007, 8:14am

M.G wrote:Hmm, currently my saddle nose is most obviously in front of the BB, I have a 90mm stem riser (reduced from the ridiculous 180mm that was fitted on it), so anything shorter could affect steering, with the saddle in the position it is now my forearm reach is still only just to the headset.

Thanks for the advice,

Michael.


It is a fallacy that short stems affect the handling/steering of a bicycle.

M.G
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Postby M.G » 7 Aug 2007, 1:13pm

You would be quite right if the steering force was always being applied perpenducular to the handlebars.

As you steer, the handlebars are no longer perpenduicular to the applied force because they are not perpendicular to your arms.

Due to geometry the lever arm becomes longer as you turn the hadlebars away from perpendicular. If the handlebars are closer to the pivot (i.e shorter stem), this lever arm increases less with the amount you turn the handlebars, than if you had the handlebars further away from the pivot.

[The lever arm is the distance to the pivot perpendicular to the applied force. If the lever arm is longer a greater moment can be applied for the same amount of force.]


If you dont believe me try it with a piece of paper, considering what would happen if the handlebars were directly attached to the pivot.

It is actually more complex than the above.
Last edited by M.G on 7 Aug 2007, 4:50pm, edited 2 times in total.

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horizon
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Postby horizon » 7 Aug 2007, 2:08pm

Hi M.G. I had the opposite problem to you and wanted the saddle further back. You can get it back or forward a further 2" by using the VK adaptor (SJS Cycles have them). This shouldn't be necessary - next time I will have a bike with a longer top tube but in the meantime this little device has transformed my comfort level and, if that is the problem, will transform yours too.

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georgew
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Postby georgew » 7 Aug 2007, 2:13pm

A "Layback " seatpost would also do the trick.

reohn2

Postby reohn2 » 7 Aug 2007, 2:35pm

M.G wrote:You would be quite right if the steering force was always being applied perpenducular to the handlebars. (and the hadlebars always being perpendicular to the frame).

But: as you steer, the handlebars are no longer perpenduicular to you and therefore the applied force.

Due to geometry the lever arm becomes longer as you turn the hadlebars. If the handlebars are closer to the pivot (i.e shorter stem), this lever arm increases less with the amount you turn the handlebars, than if you had the handlebars further away from the pivot.

The lever arm is the distance to the pivot perpendicular to the applied force. If the lever arm is longer a greater moment can be applied for the same amount of force.


If you dont believe me try it with a piece, considering what would happen if the handlebars were directly attached to the pivot.

It is also much more complex than the above.

Michael


In reality there is no difference between a long stem or a short one,as most of the steering on a bike is by leaning unless travelling very slow.
The only difference is that with a longer stem the leverage is greater say with say the hands on the hoods than with the hands in the same position with a shorter stem,due to the radius between steering column centre (centre of fork steerer) and hoods(hand position).

M.G
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Postby M.G » 7 Aug 2007, 2:51pm

Quite, that is the essence of my explaination. I shall look into that adapter, then prob make one!
Last edited by M.G on 7 Aug 2007, 4:51pm, edited 1 time in total.