Seat position relative to Bottom Bracket

Discussion in 'Cycling Equipment' started by ecandl, Jul 22, 2008.

  1. ecandl

    ecandl New Member

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    I know there is no definite number here but I am curious to the average distance from the tip of the seat to the center of the bottom bracket on a traditional racing bike?

    If I understand correctly, for a TT or triathlon, the tip of the seat is supposed to be 5cm behind the center of the bottom bracket - minimum.

    Also, what is the benefit of having your seat back further? Is there a difference in power? I heard another racer at a hillclimb saying that he had put this seat back further for the race.

    The reason I ask is that I am getting ready to do the swim/bike leg of a triathlon and when measuring the tip of my seat to bottom bracket, I was around 7cm back already. I don't know if I forgot to move it back after a series of TTs or not. After this tri, I will be messing with my seat position and was wondering the reasoning of where to place your seat. Thanks.
     
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  2. dgregory57

    dgregory57 New Member

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    Usually for a competition the specification is that it must be at least 5cm behind the BB, and I beleive it is to make sure the bike is a conventional geometry and not some sort of prone geometry.

    Even at that, if you look at some professionals while riding a time trial, they are barely riding on the tip of their saddle in order to be as far forward as possible.

    The bottom line is to be as aerodynamic as you can while still applying enough power to get as much speed as you can with a bicycle that meets the requirements. For the professionals this is accomplished in wind tunnels while hooked up to power meters, how you accomplish this is probably not going to be as precise.
     
  3. ecandl

    ecandl New Member

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    That makes sense. Any ideas on seat positioning for a normal race bike - road race, hillclimb, crit... I assume positioning is not as regulated. Any ideas on average setback and why?
     
  4. alienator

    alienator New Member

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    Saddle setback is a function of your body geometry, bike fit, saddle, and what twists your nads. There's no real way to say what is average. Two riders with the same body dimensions, same weight, on identical bikes might have two different seating positions, and both positions could be absolutely right for the same event. While in general bigger saddle setback tends to favor more power delivery and less saddle setback favors a higher cadence, those are only rules of thumb, very, very general statements.
     
  5. scirocco

    scirocco New Member

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    Well, you could measure everyone's bike and calculate the average, but I agree, the idea that the average must be the right position for person X doesn't make much sense. No more sense, anyway, than checking your saddle with a spirit level and assuming that must be right for you.

    Personally I find that I generate more power the further back I set the saddle. Too far back, though, and I get knee pain. So my perfect position is as far back as I can go without creating problems.

    How is that 5cm behind the bottom bracket regulation defined, anyway? Is it measured from the tip of the saddle?
     
  6. alienator

    alienator New Member

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    Yup. It's measured from the nose of the saddle, which is where saddle setback is typically measured from. If you look through piccies of Pro TT setups, you'll see that in a fair number of cases, the riders are using saddles whose nose has been chopped so that the seat can be moved farther forward without violating the 5cm barrier.
     
  7. ecandl

    ecandl New Member

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    The last two mornings I have been riding with aero bars with my seat about 6cm set back and I am more comfortable with the seat further forward In the aero positon. I have noticed that I do better sitting on the end of the saddle. Of course the contact point isn't too comfy but I can breathe better and my HR stays lower for the effort. (all perceived)

    After this weekends race I will experiment with the seat much further back and see if I can feel the power.
     
  8. daveryanwyoming

    daveryanwyoming New Member

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    I agree with all the posts above that ideal saddle position varies quite a bit between individuals, but FWIW I get a lot more sustainable power by sliding back in the saddle on my road bike but get my best power on the TT bike in the aero position by riding as far forward as I can tolerate.

    My saddle is right up against the UCI setback limit (which by the way is only enforced for national level events in the US) and it's about one cm lower than my road bike. I tried to match saddle height between bikes but my power (measured with a PT hub, not perceived) dropped by ~10% in long time trials and training unless I dropped the saddle height a bit on the TT frame.

    The further I push the aero bars down (greater vertical drop between saddle height and elbow pad height) the more I have to ride forward with a bit lower saddle. When I was first getting used to the aero bars and I had the bars set fairly high I could generate my normal power with a saddle height and setback similar to my road bike but my aerodynamics sucked and I worked pretty hard for mediocre speed. I've been moving the aero bars down over time (an adjustable stem is really helpful) as my flexibility improves and my times are getting much better but I can't run with my normal road saddle height and position when I'm that low.

    Good luck,
    -Dave
     
  9. longfemur

    longfemur New Member

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    Leaving aside UCI rules...

    There is no way that any on bike measurement without your body on it means anything whatsoever to you as the person riding it.

    You may or may not feel a little more power a bit further back, but it depends so much on the proportions of your upper/lower legs, the position of your foot on the pedals, your pedaling style, your weight distribution on the bike, how high or low your handlebars are, etc.

    Racers in sanctioned races have to abide by the rules. The rules are intended to prevent extreme positions and extreme bike designs, but if you look closely, most riders end up sitting quite forward on the saddle anyway. Plus, there's no standard length for a saddle. They vary, so where the nose is in relation to anything doesn't mean a darned thing.

    You can't really just go by what anyone says. If you don't happen to have a pro coaching team and equipment on hand, all you can do is to experiment for yourself on long enough rides with both flats and hills, and see what works for you. Personally though, I wouldn't go forward of KOPS on a road bike, at least not on a stage racing bike or a touring type bike. Right on it or a bit behind should be fine for most people.

    PS I know KOPS is frequently debunked by various debunkers, but I'm using it only as a point of reference.

    I've always found that whatever rules or methods you want to follow or not follow, there is NO substitute for going out on the road and bringing your set of Allen keys so you can try different combinations of fore-and-aft and saddle height.
     
  10. Russ Reynolds

    Russ Reynolds New Member

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    I can only agree with other here. I am the same height and weight as a mate from work, yet for me to ride his bike or visa versa is a struggle. We both look about the same shape but apparently his trunk dimension ( neck to groin ) is longer than mine so the bikes are setup completely different.
     
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