I'd assume it isn't as simple as just moving things in proportion, because you aren't just rotating, but you're extending your arms forward. It'd be easy if you just rotated; you'd just move things forward and down and you'd end up facing down towards the road.

Get a proper bike fit. That's pretty much the answer to your question. If you start moving things around, you might be able to lower your front end but that may result in a smaller hip angle, which would possibly result in a loss of power.

I think talk of rotating around the BB is more applicable when you're already quite low and looking to go lower without closing up the hip angle. If your position is as upright as you say then just start dropping the front little by little so that you can adapt to a lower position. Once you think you've reached the limit of this approach, get a proper bike fit. If you get a bike fit straight away before you've adapted to riding lower then either they'll fit you in an upright position, or they'll fit you in a low position that you can't hold.

There is a heap reading here from a few years ago http://www.slowtwitch.com/...techctr/bikefit.html.

Slowman has progessively refined his writings as the world and bikes have changed but it's always good to go back to basics. These articles have served my well, take the time to read through them.

See, this is where I think you are wrong. I want to "rotate around" not just drop the front. I feel like if I drop the front it closes down that hip angle and makes everything less comfortable. That is why I am interested in the process of changing my position on the bike without substantially changing my body position.

Do I move the seat forward 2 cm, down 1 cm, pads down 2 cm?

I have been fitted several times in the past. It is amazing to me how completely different two (or more) different fitters can set up the same person. It leads me to believe that there is a little bit of voodoo that goes in to any fit session. How do I know that 'this' fitter is going to set me up the 'right' way. I am very comfortable with my current position. I have done two IMs with my current set up. I would like to chase the holy grail of comfort while getting more aerodynamic on the bike (flatter back, lower head......) I have my current fit coordinates so I can always return to this position but wanted to get some basic idea of how to start tinkering with the fit.

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Jason
None of the secrets of success will work unless you do.

Thanks for the link. I have been wading through Dan's fitting references. I think I am getting a start point to start experimenting but wanted to know if there is a rule of thumb when it comes to the concept of rotating around your bottom bracket (with out substantially changing your body's relationship to itself, instead changing your relationship to the bike without closing the angle of your hips, etc).

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Jason
None of the secrets of success will work unless you do.

If you just want to purely rotate around the BB, and I get your point, you could get the iPhone/iPad app "Bike Fast Fit" and measure angles in current position, then start moving seat forward and up maintaining the hip/knee/ankle angles, and adjusting stem length/height to maintain whatever hip and shoulder angle you think you like from current. Seems like it would be pretty easy to just rotate.

Now whether that's a good idea is another question altogether. If your angles are good now, they'll be good then. A fitter might make this easier, but you could always try yourself first and then impress them with your history if you cave and pay for a fit.

Measure and document where everything is on your bike now.

Take a pict from the side with your leg extended.
Measure:
Hip Angle
Knee angle
Upper Arm to body angle
Lower arm to upper arm angle

Drop front end as much as you like:
Move the seat forward to get the same hip angle
Move the seat up/down to get the same knee angle
Move the pads/bars forward/back to get the same Upper arm to body angle
Adjust the aerobar tilt to get the same Lower arm to upper arm angle

If you screw it up just put it back where it was in the first place and start over.

You'll have to purchase a protractor, that may run you as much as $5 (or whatever currency equivalent you use)

You may have to learn how to sit on the saddle differently.
You may find that it's comfortable without moving anything other than the height of the bars.
You may not ever get any lower.

jaretj

Just in case anyone cares (and almost no one does based on replies to this thread ;-) ), last night I decided that the easiest way to experiment with this would be to remove the block from under my front wheel while riding the computrainer. This lowered my front end close to 4 cm (will have to measure tonight) while not changing my position on the bike at all. It isn't really rotating around the bottom bracket but rather rotating around the rear cassette but I thought it would give me a reasonable starting point.

I found that I was able to ride comfortably in my new lower position for 1:10, leading me to think that I can get more aerodynamic while maintaining my body's position in space. The faint reflection that I get from the glass in the picture in the next room suggests that my head was lower and my back flatter (very scientific, I know). The one problem I had was feeling like I was sliding off the nose of the saddle which shouldn't be a surprise as my experiment had the nose of my saddle at a significant downward angle.

Now for me to take some pictures and start tinkering to try to replicate the fit coordinates of last night while the wheels of my bike are level. I'm doing this all on my backup bike and leaving the race bike alone until I am confident that I can make it work.

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Jason
None of the secrets of success will work unless you do.

I don't think you've understood how rotating around the BB to maintain all your current angles will do very little to get you any lower if you are in an upright position at the moment.

To get an appreciation of the limitations of this approach, print out a picture of yourself on the bike and then using a protractor with the point on the BB, draw an arc from the top of your head, contact point on the saddle and contact point on the bars. If you move each of these through the same angle you will find that your head mostly moves forward rather than down as you rotate from an upright position. You will then find that stem length becomes the major limiter.

I've had a similar question for many years, and never had a good answer like you've got from others here.

I have some particular issues that affect my comfortable position on any bike. I'd love to ride in a good comfortable power position. However, the arthritis in my hips, my two broke back accidents plus a broken neck (among many others) means even on a road bike, I have to sit up quite a bit. This makes riding liveable, but certainly reduces my aeroness and power output. I have found a position I can live with. I would love to take that position on my road bike and rotate that forward, but a wrist bone graft and arterial transplant a few years ago means I can't handle that much weight on my hands. I generally ride my road bike for commuting or pleasure (not speed) so not a biggie. I can live with the limitations my body forces on me....grudgingly.

On a tri bike, with the weight being on my elbows, I can tolerate a much more rotated postion. I'm still limited by hip angle (I need to be quite open) but I can still rotate to get not toooo bad a position. With being rotated forward, and my busted neck vertabra, I get even more neck issues than regular trigeeks.

I have found that fitters in the past have always set me up too cramped (too tight hips) to get comfortable. Until now and the iPhone app noted above, I've never been able to check and therefore modify my position dependably.

Being forced into a fairly open hip angle, when I rotate forward I end up moving my seat really far forward and that puts even more weight on the front wheel which makes life tricky. Luckily I'm heavy so even with twitchy handling, cross winds don't bother me too much.

Of course, by rotating forward, your angles should stay the same but seat and bars will move. Let us know what you find out re forward, up/down rules of thumb, assuming you're of average build. I'm sure I'm not the only one that wants to know what you find out.

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"