Saddle tip position in respect to bottom bracket ?

Serious Cat
Serious Cat Posts: 489
edited October 2013 in Road general
When I see some other riders bikes and pictures in the cycling press, I often see saddle tips that are considerably fore of the vertical centre bisection of the bottom bracket. When I installed my saddle I did take into account knee over spindle and used it as a starting point to be able to do long runs without suffering knee pain. As it happens the tip of saddle is behind the vertical bisection of the bottom bracket. I don't have long legs and I guess if they were longer the further back my saddle tip would be in relation to bottom bracket and vice versa. Is there an accepted chain of thought related to saddle tip / bottom bracket placement or is the whole set up directly related to leg length and those with saddle tip forward of bottom bracket do so because of their individual leg length ?
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Comments

  • kwi
    kwi Posts: 181
    Yes, the position of the saddle fore and aft is a function of leg length. (And crank length and frame size.) Some will slide back a touch if a lower cadence always climbing riding style and forward a touch for a higher cadence sprinter style.
  • buckles
    buckles Posts: 694
    When I see some other riders bikes and pictures in the cycling press, I often see saddle tips that are considerably fore of the vertical centre bisection of the bottom bracket.
    Are you sure? I don't think I've ever seen a saddle tip in front of a bottom bracket on a normal road frame. Are these people using layback saddles the wrong way around, and slamming their extra long-nosed saddles all the way forwards in the clamp?

    The seat tube angle on a large road frame would make it difficult to get the saddle tip anywhere near level with the BB without using a straight seatpost and ramming the seat all the way forwards (past the recommended 'safe' clamping area marked on the rails of some saddles). Maybe on smaller road frames, or frames with a more upright seat tube it's possible.

    For example the saddle on my 60cm frame is 10.3cm behind the centre of the BB. I have 2cm of layback on my seatpost but the seat it's as far forward as it's 'allowed' to be, within the marked clamping area, although there is about 2cm of rail left behind that. So even using a straight seatpost and ignoring the rail markings / death warnings in the user manual you could only get it 6.3cm behind the BB.
    Is there an accepted chain of thought related to saddle tip / bottom bracket placement or is the whole set up directly related to leg length and those with saddle tip forward of bottom bracket do so because of their individual leg length ?
    From what I was told by Adrian Timmis / read on Steve Hogg's website, saddle setback should be set to optimise your weight distribution over the bike, and not according to leg length measurements.
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  • kwi
    kwi Posts: 181
    Buckles wrote:
    From what I was told by Adrian Timmis / read on Steve Hogg's website, saddle setback should be set to optimise your weight distribution over the bike, and not according to leg length measurements.

    Yet all bike fit advice I have had is to get your knee over pedal positioning right while on the saddles 'sweet spot'.
  • johnmiosh
    johnmiosh Posts: 211
    UCI rules on saddle position 1.3.013

    The peak of the saddle shall be a minimum of 5 cm to the rear of a vertical plane passing
    through the bottom bracket spindle. This restriction shall not be applied to the bicycle
    ridden by a rider in a sprint event on track (flying 200 m, flying lap, sprint, team sprint,
    keirin, 500 metres and 1 kilometre); however, in no circumstances shall the peak of the
    saddle extend in front of a vertical line passing through the bottom bracket spindle.
  • MichaelW
    MichaelW Posts: 2,164
    Small bikes are usually fitted with medium rather than short cranks. To provide a knee over pedal spindle (KOPS) position, the seat-tube has to be very steep and the saddle quite far forward.
    Large bikes are usually fitted with medium cranks rather than long ones. To provide KOPS, the seat-tube has to be very slack and the saddle far behind the BB.
    Triathlon bikes use an alternative position whereby the whole rider is pivoted forward about the bottom bracket, bring the saddle up and forward and the bars down and forward. This provides time-trial-like aerodynamics with a more open hip angle. The UCI regs don't apply to triathlon races so it is OK for the saddle to be over the BB. UCI regs also make exceptions for very small riders
  • nicknick
    nicknick Posts: 535
    Buckles wrote:
    From what I was told by Adrian Timmis / read on Steve Hogg's website, saddle setback should be set to optimise your weight distribution over the bike, and not according to leg length measurements.

    Why does Adrian use that laser thing during the fit that seems to line the pedal axle with your knee? For a starting point? I never asked during my fit a year ago, but getting my fit done by him was the best £150 I've spent on cycling!
  • Buckles wrote:
    For example the saddle on my 60cm frame is 10.3cm behind the centre of the BB. .


    After reading this I took a tape measure out to my bike and measured that distance aft from the bottom bracket and then visualised where the saddle tip would be. Can I ask what your height is , you must be very tall or have legs like a heron :wink:
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  • themekon
    themekon Posts: 197
    Not long ago I was looking at a bike on this site with in line seat post and the saddle slammed all the way forward. Commented that it didn't look quite right the reply was it was set up as part of a bike fitting.
    There are some so called experts out there who know nowt.
  • buckles
    buckles Posts: 694
    Buckles wrote:
    For example the saddle on my 60cm frame is 10.3cm behind the centre of the BB. .


    After reading this I took a tape measure out to my bike and measured that distance aft from the bottom bracket and then visualised where the saddle tip would be. Can I ask what your height is , you must be very tall or have legs like a heron :wink:
    over 6ft
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  • JayKosta
    JayKosta Posts: 635
    No, there isn't a general rule about the location of the tip of the saddle in regards to the BB.
    The general rule is 'knee over pedal spindle' and adjust the saddle for comfort. Using that as a starting point works well for the vast majority of riders.

    For specialized riding such as time trials and triathelon events, having the saddle more forward is sometimes done to accomodate a very aero position on the bike. But that saddle position isn't usually good for other riding situations.

    It is best to setup a bike to achieve the best comfort and performance for the specific rider, and to not worry about how it looks.

    Jay Kosta
    Endwell NY USA
  • mikeeye
    mikeeye Posts: 162
    Buckles wrote:
    Buckles wrote:
    For example the saddle on my 60cm frame is 10.3cm behind the centre of the BB.
    After reading this I took a tape measure out to my bike and measured that distance aft from the bottom bracket and then visualised where the saddle tip would be. Can I ask what your height is , you must be very tall or have legs like a heron :wink:
    over 6ft
    I'm 6'2" and pretty long legged (inside leg 945mm measured with the book method). I had a bike fit by Adrian Timmis and my layback (i.e. saddle tip to bb center) is 11.0cm. That's with 175mm cranks on a 60cm frame.
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  • MichaelW
    MichaelW Posts: 2,164
    themekon wrote:
    Not long ago I was looking at a bike on this site with in line seat post and the saddle slammed all the way forward. Commented that it didn't look quite right the reply was it was set up as part of a bike fitting.
    There are some so called experts out there who know nowt.

    If the rider has oddly proportioned legs, esp short femur and long lower legs, it may be the position that fits.
  • keef66
    keef66 Posts: 13,123
    MichaelW wrote:
    themekon wrote:
    Not long ago I was looking at a bike on this site with in line seat post and the saddle slammed all the way forward. Commented that it didn't look quite right the reply was it was set up as part of a bike fitting.
    There are some so called experts out there who know nowt.

    If the rider has oddly proportioned legs, esp short femur and long lower legs, it may be the position that fits.

    I too remember this; IIRC the seatpost was also installed back to front to get the saddle even further forwards. Looked really odd, and I could only suppose the bike was too big and the fitter had been trying desperately to achieve KOPS rather than tell the guy he'd bought too large a frame.