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  • Frame geometry question
  • davidtaylforth
    Free Member

    Does anyone find it easier to pedal if the sit right towards the front of the saddle?

    I know its easier for uphill stuff, but on the flat it seems like I can put more power ‘down’ for some reason.

    I dont use SPD’s but tend to try and pedal with the ball of my foot

    buzz-lightyear
    Free Member

    yes.

    davidtaylforth
    Free Member

    A useless response (or maybe a well suited response) to a useless question.

    Ok, why is it easier? and why dont frame manufacturers make frames with steeper seat tubes so you are sat further forward?

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    Onzadog
    Free Member

    maybe the same reason why I can gte more power riding on the hoods than the drops.

    Onzadog
    Free Member

    not that I know what the reason is mind!

    brant
    Free Member

    Ok, why is it easier? and why dont frame manufacturers make frames with steeper seat tubes so you are sat further forward?

    Some of us do.

    http://www.shedfire.com/2009/03/27/the-numbers/

    davidtaylforth
    Free Member

    Yeh I noticed your frame has a steeper seat angle on the larger size, which makes sense since the seat will be further back the more you put the saddle up.

    Im 6foot2 so I guess running alot of seatpost showing puts the seat further backwards (the bike is specialized stump jumper)

    brant
    Free Member

    Yeh I noticed your frame has a steeper seat angle on the larger size, which makes sense since the seat will be further back the more you put the saddle up.

    Yes. For the same saddle height, a rider on a larger frame of ours will be further forward of the back wheel.
    Which will make the bike climb better when seated (without wheelieing).
    Stood climbing will be essentially the same (as distance from BB to rear wheel is same).
    It’s only quite a small difference, but half a degree on the seat angle is about the same as 6mm of movement on the saddle. But 6mm movement on the saddle does make a difference in making the front end stick down on climbs (or not).
    Setting knees over pedal spindles or trying to get a longer seated position by running a layback post just throws weight too far back.
    To my mind seated position should be optimised towards steeper climbs which on a long travel bike will give a “seat forward” feel.
    Riders trying to duplicate seated length from bikes of ye olde days, or heaven forbid, their road bikes on a long travel bike will end up with something that won’t work well in rumpy bumpy terrain.

    Of course for singlespeeds, it makes no odds at all, and infact rearward weight bias is good (especially for offroad fixies), as climbing is not affected, as you can’t really climb steep stuff in the saddle on a singlespeed.

    So if that layback post if for a singlespeed, it has my blessing 😉

    Onzadog
    Free Member

    While we’re on the subject of geometry, I had an odd one the other day. The wife (5’9″ is looking for a mountain bike on the ld ride 2 work scheme) we looked at a Rockhopper for her. My guess would have been the 17″ but the angle between arms and torse looked very acute and I noticed she was sitting right back on the saddle. On the 19″ she looked a lot happier. Closer to a right angle between arms and torso and sat in the middle of the saddle. It looked right but the little voice in my head says you can’t put a 5’9″ female on a 19″ mens Rockhopper.

    Reading Brants post above about knees over pedal spindles made me wonder what guides people use for picking toptube length/reach on a bike.

    brant
    Free Member

    My guess would have been the 17″ but the angle between arms and torse looked very acute and I noticed she was sitting right back on the saddle. On the 19″ she looked a lot happier. Closer to a right angle between arms and torso and sat in the middle of the saddle. It looked right but the little voice in my head says you can’t put a 5’9″ female on a 19″ mens Rockhopper.

    Sounds like that’s more to do with relative saddle/bar height and reach.

    buzz-lightyear
    Free Member

    “yes”

    Sorry it was all I had time for before bed last night. I think that if you are over the pedals then you can apply your body weight more effectively with each stroke (although you are sat in the saddle, you’re not slumped into it). With the the pedals in front more, you really pushing more with leg muscles.

    And as Brant says, controlling the front of the bike while sat down is possible if the saddle is positioned reasonably forward – you still have to shufty toward the nose but at least you can semi-sit and it’s less tiring and more balanced than honking.

    james-o
    Free Member

    worth remembering that saddle position and post type can make the equivalent of 1-2 degrees effective SA difference so don’t get bogged down over half a degree or so unless on the edge of the set-up variables already. Brant’s right, a degree on the seat angle is worth about 10-15mm in saddle fore / aft position for an average 700-800mm seat height and seat rails can adjust this far usually so if your bike feels wrong for your shape / ride style it can usually be adjusted here.

    C of G is about rider geometry too – a guy with a bulky upper body will have a more forward c of g than a guy with big legs and slim upper body for a given overall rider weight and bike geometry. There is a good article by Keith Bontrager titled “KOP-Debunking The Myth” that is worth looking up if you are interested in why knee-over-pedal is wrong for MTBs and doesn’t always work on road bikes. Rodies will also point out that more power is developed by sitting further back, but how applicable this is to MTB’s is debatable.

    brant
    Free Member

    Rodies will also point out that more power is developed by sitting further back, but how applicable this is to MTB’s is debatable.

    Though time trialists like to sit forward, and it’s not to do with aerodynamics. Wayne Randle once said to me “I don’t matter how far forard yer is, you’ll always sit on’t rivet when yer gowin forrit”.

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