Is having the seat directly over the rear axle not optimum?

[amator]

If u set back your seat post such that the rear edge of the seat protrudes slightly past your rear dropouts (axle), Is this bad for 1)power transfer and 2)weight distribution.
This is assuming u drop a plumb line from the rear lip of the seat downwards.

Conversely,where is the optimum for the hoods to be in relation to the front drop outs (plumb line again).

[Ken Robb]

the farther away you can get the saddle from being directly over the rear axle the less you will feel bumps.

[Dave]

Whether that saddle position is "bad" would depend a lot on the rider's size, but for the most part, the saddle would rarely get that far back.

With a saddle height of 73-74cm and my saddle nose 6-7cm behind the center of the BB, the back of my saddle is about 3.5cm ahead of the rear axle. If the saddle was raised 10cm, it would also move back about 3cm, so a rider with much longer legs might approach the setup you've mentioned, particularly with the more slack STA common to larger frames.

A lot of fit experts still maintain that the most efficient pedaling will be achieved with the knee joint approximately 90 degrees to the crankarm at the 3 O'clock position. I prefer my saddle a little further back to keep the weight off my hands. That allows me to use a 12cm drop from the saddle to the bars.

For the best handling, you want the F/R weight balance to be no less than 40/60 and probably no more the 45/55. What affects that weight balance most is the saddle fore/aft position and the torso angle. The lower the torso, the more weight on the front.

As for stem length, it has little effect on weight balance. I judge adequate stem length by the lack of knee to arm interference when I'm pedaling with my hands in the hooks and my upper back nearly horizontal. With a 12cm drop to the bars, I can do that with almost no bend in my arms, so it doesn't take an extremely long stem to eliminate knee to arm interference.

[Tobias]

With a saddle height of 73-74cm and my saddle nose 6-7cm behind the center of the BB, the back of my saddle is about 3.5cm ahead of the rear axle. If the saddle was raised 10cm, it would also move back about 3cm, so a rider with much longer legs might approach the setup you've mentioned, particularly with the more slack STA common to larger frames.
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As for stem length, it has little effect on weight balance. I judge adequate stem length by the lack of knee to arm interference when I'm pedaling with my hands in the hooks and my upper back nearly horizontal. With a 12cm drop to the bars, I can do that with almost no bend in my arms, so it doesn't take an extremely long stem to eliminate knee to arm interference.Maybe that’s when the chainstays should be made a little longer for such large riders. It's not the current fashion since one size seems to fit all. ;)

IMO knee to elbow interference has a lot to do with femur to torso lengths, not something easily adjusted. Some riders with short torsos and long femurs (made even worse by long arms) will likely have problems no matter what they do.

[Dave]

Maybe that’s when the chainstays should be made a little longer for such large riders. It's not the current fashion since one size seems to fit all. ;)

IMO knee to elbow interference has a lot to do with femur to torso lengths, not something easily adjusted. Some riders with short torsos and long femurs (made even worse by long arms) will likely have problems no matter what they do.


That depends on the weight balance. If more weight is needed on the front, then longer stays will do that. If the unavoidable increase in setback results in too little weight on the front, then shorter stays or a shorter F-C are needed. A lot of larger frames have relatively steep HTAs to keep the F-C as short as possible.

I have a very short torso with a 169cm height and 83cm inseam. I manage to avoid knee to arm interference, but I don't think my femurs are long.

[WadePatton]

the further back one moves the saddle, the easier it is to initiate wheelies.http://forums.thepaceline.net/images/smilies/banana.gif

[Ken Robb]

the further back one moves the saddle, the easier it is to initiate wheelies.http://forums.thepaceline.net/images/smilies/banana.gif

I have a post with 13cm of setback and a 5mm stem and I still can't get a wheelie. Maybe I need more power?

[Tobias]

That depends on the weight balance. If more weight is needed on the front, then longer stays will do that. If the unavoidable increase in setback results in too little weight on the front, then shorter stays or a shorter F-C are needed. A lot of larger frames have relatively steep HTAs to keep the F-C as short as possible.Dave, what I was trying to get to in order to address the OP question is that bicycles are not made proportional to rider size. For whatever reason (and I’d rather not question it or defend its wisdom, but rather address what actually is) typical bicycle wheelbase is not in proportion to riders’ height.

Therefore, if we assume a given set of required contact points, and start from the BBKT to define the location of the saddle and bars, we almost guarantee that very tall riders will end up with the back of the saddle closer to being over the rear wheel and the hoods closer to being over or beyond the front axle.

I don’t see how this can be avoided when a rider that is 6’-6” tall versus a rider 5’-5” (that is, 20 percent taller) will likely end up with a bike that is only marginally longer in wheelbase. If the bikes are not made much longer (which they are not), and the rider doesn’t sit more upright (some tall riders are actually flexible), then what choice is there other than push the saddle and bars closer to the axles?

[WadePatton]

I have a post with 13cm of setback and a 5mm stem and I still can't get a wheelie. Maybe I need more power?
longer cranks!

lever that bugger up!

[WadePatton]

Okay, silliness and wheelies aside, here's my current method of locating a saddle. It is derived from Peter White, David Kirk, and Steve Hogg's advice-at least that's where I got it. It is based on getting the pelvis far enough behind the feet to balance your torso. Nothing to measure and it automatically compensates for body dimensions and cleat placement. (Cleat placement is a study in itself.) All three of these guys likes for the rider to be able to lift his hands just off the bars and not fall forward or strain to keep his/her upper body in position with the hands off.

Peter White does it with hands on hoods feet stationary at horizontal, Dave Kirk-pedaling moderately up a gentle rise with hands near stem, Steve Hogg-pedaling a little harder on a trainer with hands in the drops. They want the saddle just far enough back for this balance point, but no further.

Then re-check saddle height, and finally reach. Reach/bar height is then set according to the rider's flexibility and purpose.


Worked for me and I'm just starting to work with others on this.

[L84dinr]

Kinda...

I have a Colnago CX bike with crank brother pedals. Anyway this is one of the wheelingest (that a word) bikes i have owned in a while, but having my feet locked in inhibits the wheelies. I am thinking of installing my old record toe clip pedals just to impress the childrens with my wheeling prowess lol ;>)

stay hard!

[Dave]

I also follow the idea that the saddle needs so be back far enough to balance the rider over the saddle and keep weight off the hands, but I do like to check my bike's F/R weight balance, when I'm in an agressive position, just to be sure that it's not way off the ideal. If you have the saddle way back and sit very upright, I could see the weight on the front going below 40%.

I'd like to know if any large riders out there have ever checked their F/R weight balance. I have no clue whether the added torso length balances out the effect of the further back saddle.

[flickwet]

If u set back your seat post such that the rear edge of the seat protrudes slightly past your rear dropouts (axle), Is this bad for 1)power transfer and 2)weight distribution.
This is assuming u drop a plumb line from the rear lip of the seat downwards.

Conversely,where is the optimum for the hoods to be in relation to the front drop outs (plumb line again).
But I seem to remember an old fit chestnut about looking down when in the drops and the bar should align with or obscure the axle/dropouts, sounds real technical don't it.

[WadePatton]

But I seem to remember an old fit chestnut about looking down when in the drops and the bar should align with or obscure the axle/dropouts, sounds real technical don't it.
I know zero current builders/fitters who advocate such silliness. Let it go.

[zap]

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I'd like to know if any large riders out there have ever checked their F/R weight balance. I have no clue whether the added torso length balances out the effect of the further back saddle.

If by large you mean someone over 6' then yes, I have. Riding in drops or the end of bullhorns (TT) I have 43-45% up front.

I've been a fan of Lemond's and Hogg's position guidelines for quite some time.

[Tobias]

I have no clue whether the added torso length balances out the effect of the further back saddle.I think yes for “most” riders because we tend to set up our bikes so that our center of gravity is very close to being over the BBKT regardless of rider size or how upright we sit. That seems to place about the right amount of weight on the hands.

And if the CG is kept relatively close to being over the BBKT, then the weight distribution will be determined by chainstay and front center horizontal dimensions; which on most bikes fall on approximately a 40:60 ratio.

If you recall a while back I think Dave Kirk started a thread about weight distribution, and most respondents were within a relatively tight range. I think that to get outside of a normal range a rider would have to have a whacked fit or a bike built with unconventional dimensions.