53-11_alltheway

Now measurement to the "sit bones" sounds more legit, but most people are not using it this way it seems. Can you show me in print where it says that? That almost sounds like something you added in (after the fact) because you know how important that is. LOL!

Still doesn't take into consideration crank length and how that changes biomechanics.

I just realized it doesn't take into account pedal stack height or sole thickness also.

Yeah, lots of problems with this formula.

biker7

What you will likely find out on the web is measurement from BB to the highest point on the seat...which is theoretically where your sit bones sit...which is not in the middle of the seat as most seats even positioned nose up a bit have a concave curvature slightly downward from where the sit bones contact. This is how I measure for example.

As to the crank length not being in Lemond's equation...true. Most don't run 180mm cranks like you do however...I am about your size and run 175's for example and most cyclists run this length or slightly shorter. Agree his formula does not take into account crank length but for most they are near nominal or 170-172.5mm. I didn't move my seat position much when I changed crank length by 2.5mm.
I hear what you are saying about crank length but set back is in the mix my friend if you measure correctly. Perhaps your broader thesis is all formulas are flawed...I agree but no formula should ever be used as an absolute but more as a guideline.
George

53-11_alltheway

This sounds too general (top of saddle height). I mean most people will not interpret "sit bones" into this equation from that description (though you obviously understand what I'm talking about).

Also I forget to mention (in addition to crank length) the effects of pedal stack height (which can vary from ~5mm TIME to ~22mm SPD-SL) as well as shoe sole thickness have on this equation.

P.S. I like how the equation is .883!! Like the accuracy is spot on to the .001 decimal spot. LOL!

pigmode

Agree with B7. If needed go with a calculator/rule of thumb, but just to get in the ballpark. After that, if you're not secure in your own intuitive adjustments, go to the trainer and knee-angle protractor. As mentioned, the trainer will account for cleats and saddle (seat butt) position. As you adjust for knee angle you will be adjusting saddle height, and saddle position fore and aft (while maintaining your prefered knee/spindle preference). The trainer and a good helper/observer will not only allow you to make these adjustments fairly accurately and quickly, but you will also be able to try out different combinations and styles at the same time. By this method you might also be able to determine whether you are a high or low heel spinner and then factor that into the process. After this is all said and done, you will be able to fine tune your position with appropriate road time.

The theories of one pro and another are fine and good, but the first priority is a good position that will allow for health and longevity of the knees.

Patriot

I can see 55/Rad saying, "Yeah, I feel like homeboy today." He then drops his saddle all the way down to the top of the seat tube, and rides like a low rider with his knees blocking his forward veiw.

53-11_alltheway

Everything you said that I quoted above is correct. The formula is so rough in accuracy it is almost ignorable.

".883 x inseam" would be lucky if it even got you within +/- 5 % of your ideal saddle position.

pigmode

Yeah, I agree. A noob might have better luck studying a wide variety of pics of pro riders, coming up with an average knee angle, and starting from there. That and checking yourself out in every plate glass window you pass. All of these mathematical ratios and formulas border on being ********.

53-11_alltheway

You are right about the knee angle being one of the more critical factors. If it closes up too much at the top of the stroke it's gonna be murder on that joint.

The hip angle is important as well for overall power.

pigmode

By hip angle I take it that you are now adding the factors of reach and bar drop into the equation? In reality, they all affect each other and it is difficult to deal with any one in isolation.

53-11_alltheway

Yeah, I agree it's all interconnected.

supahjew

I just went to get my seatpost cut as it wouldn't go down further past ~74cm. My inseam is 81cm, recommended saddle height is 72cm with a 172.5mm crank, I've got it set at 67cm with a 30 degree leg angle on the downstroke (center of bb to top saddle). I'm 5'8". Screw you online calculators. Using the Hamley method, which is center of pedal axle to top saddle (inseamx1.09) is much mor reliable than what the online calculators use (inseamx.833). It's more reliable because it consistently produces knee angles of around 25 degrees, which is optimal for reducing risk of injury and increasing efficiency.

Source: https://72.14.209.104/search?q=cache:...ient=firefox-a