Adjusting Geometry via seatpost ??

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hubba
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Adjusting Geometry via seatpost ??

Postby hubba » Tue Feb 05, 2013 16:44 pm

Hi,
i purchased a 2nd hand bike just because i liked it, it's a Cube SL pro road / cyclocross bike, has flat bars and 700c wheelset.

the issue i found was it's been ok when just crusing, when your head down and bum up style giving it everything i tend to get aches on teh tops of my legs near to the knee's. to the point now i did the plum line from knee cap to pedals and found that it's hitting the front of the pedal rather than middle of the pedal axel, this roughly translated is that it's around 40mm / 4cm to far forward, looking at the seatpost i have the seatpost with a slight layback (guessing 20mm max)

is there anything out there to get the geometry right for a full leg rotation or any other suggestions to get the knee above pedal distance more in line with the pedal axel ?? i'm hopeing here it's not a new bike solution and i've not bought a dud for my specs..

current seatpost is 300mm long and 31.6m wide something like this (http://www.cube.eu/en/equipment/bike-pa ... ht-316-mm/)
Cube Sl Road for sale
wanted Steel or titanium Touring / audax / sportif frame or complete bike.

dwanes
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Re: Adjusting Geometry via seatpost ??

Postby dwanes » Tue Feb 05, 2013 17:15 pm

I guess your seat is as far back on the rails as you can get?

hubba
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Re: Adjusting Geometry via seatpost ??

Postby hubba » Tue Feb 05, 2013 17:21 pm

unfortunately yes.., i see VK do a widget thingy but it don't look that good and is heavy from review, i really hope it's not yet another bike as i've already made a few purchases from what i call bike porn impulse buying and they are not really fit for the type of cycling that i do. this was suposidly a 56cm / 56cm frame from cube which should have been bolt on parts from old to new bike, giving me the touring bike i required. Just goes to show how different frames can actually be...
Cube Sl Road for sale
wanted Steel or titanium Touring / audax / sportif frame or complete bike.

trek_dan
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Re: Adjusting Geometry via seatpost ??

Postby trek_dan » Tue Feb 05, 2013 17:22 pm

If you need to dangle you ass cheeks off the back of the seat to get your knee comfortable you should probably try a layback post and a shorter stem.

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Monty Dog
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Re: Adjusting Geometry via seatpost ??

Postby Monty Dog » Tue Feb 05, 2013 18:46 pm

You can get seatposts with as much as 32mm layback - FSA do a K-Force version. Some saddles have longer rails too.
Make mine an Italian, with Campagnolo on the side..

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EPO Delivery Man
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Re: Adjusting Geometry via seatpost ??

Postby EPO Delivery Man » Tue Feb 05, 2013 20:24 pm

I would try the method mentioned above. Get a seatpost set back as far as you can and also shorten the stem a bit. Off the top of my head i think Cube stems are usually about 100mm or 110mm. So maybe try a 90mm or even a 80mm if you can get one. This will shorten your reach and not make you over-reach, therefore putting your backside a bit further back.

A few cm's might be all you need.

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smidsy
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Re: Adjusting Geometry via seatpost ??

Postby smidsy » Tue Feb 05, 2013 21:13 pm

You need to set your saddle to put you in the correct position relative to the BB, THEN you set everything from that.

Putting a large set back seat post on to compensate for fitting shortcomings elsewhere is NOT the answer.
Yellow is the new Black.

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passout
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Re: Adjusting Geometry via seatpost ??

Postby passout » Wed Feb 06, 2013 08:57 am

I'd move the seat back little a bit (using a regular post) and go for a longer stem.
'Happiness serves hardly any other purpose than to make unhappiness possible' Marcel Proust.

hubba
Posts: 211
Joined: Sun Nov 30, 2008 20:12 pm

Re: Adjusting Geometry via seatpost ??

Postby hubba » Fri Feb 08, 2013 16:19 pm

hi guys maybe i was not quite as clear as i thought.. i was thinking of slightly lengthining the stem to give more reach as i feel a little cramped.

my ideal is supposed to be around a 56cmtop / 56cm seat which this bike is, but i notice two differences as to why it's not 100% right.
1. the saddle to pedal/ BB ratio is out by around 4cm
2. having flat bars instead of drops means i don't get the additional reach i would with drops and sitting with hands on the hoods, more like i only get the position when climbing .

i think i'll look into the FSA K-Force to see if that will help and also i will look at the saddle position, i put the only spare saddle i had onto the bike which is a SDL Bel Air (mainly used for MTB style positioning, i will try changing for a slightly more road specific style and see if the rails add more distance further back.

will report back how i get on with it.
Cube Sl Road for sale
wanted Steel or titanium Touring / audax / sportif frame or complete bike.

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smidsy
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Re: Adjusting Geometry via seatpost ??

Postby smidsy » Fri Feb 08, 2013 16:25 pm

Not quite as clear.... you were totally misleading, your title even say via seatpost!!!!! :?

So yes, a longer stem is an option but gives a slower steering feel.
Yellow is the new Black.

hubba
Posts: 211
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Re: Adjusting Geometry via seatpost ??

Postby hubba » Sat Feb 09, 2013 21:54 pm

smidsy wrote:Not quite as clear.... you were totally misleading, your title even say via seatpost!!!!! :?

So yes, a longer stem is an option but gives a slower steering feel.


hi smidsy,
which in reality what i want to do as i don't think there is any other way to move the saddle back 4cm when i'm already at max adjustment to the rear as possible. the front stem increase is the second step i was going to take if the saddle movement back was not enough.

i'm still looking into the option of what saddle might work on there which has different or longer rails, and i'm looking into how much extra the FSA layback seatpost offers in comparison to teh cube standard fit ones (as to me it's a small layback seat post already.

i really hope i'm not nerfed on a second bike that i own and have to purchase a further bike or frame and move parts over.
Cube Sl Road for sale
wanted Steel or titanium Touring / audax / sportif frame or complete bike.

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smidsy
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Re: Adjusting Geometry via seatpost ??

Postby smidsy » Sun Feb 10, 2013 14:14 pm

I would reitterate that the saddle position is actually the first thing you should set and then adjust other things from that.

The saddle needs to put you in the correct position relative to the bb, so there is no room for 'moving it further back' as this then puts you in the wrong position for the BB.

If the stem does not put you where you need to be then you can also look at bars with longer reach to the hoods etc.
Yellow is the new Black.

ellj22
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Re: Adjusting Geometry via seatpost ??

Postby ellj22 » Sun Feb 10, 2013 14:40 pm

Hi Hubba

I'm no expert in bike fitting but I've always been taught that the plumb line should be from the base of the lateral meniscus and not the knee cap (I may be wrong but it works for me). this could account for up to 20mm of miss measurement. Another common error I've seen is when people try to set up on the turbo trainer and the bike is not completely level. Best way to check is a spirit level ran inline with the center on the axle on each wheel (on a hard level floor). I'm not suggesting you have measured wrong as I have no idea how you had it set up but this might be worth checking for peace of mind. It's also worth noting knee alignment is a guideline and a good place to start with a fit but a lot of riders tend to find a bit of adjustment either way suits their riding style better.


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