Saddle height versus sitbone position and saddle setback.
 

I'm setting up my recently re-assembled Mondonico, a 53 cm with typical Italian stage-race steep seat tube. I'm installing an older Specialized Toupe on it. Due to the steep seat tube I always set the saddle back, in this case about 7.5 cm based on measuring saddle nose to BB plumb line. I won't be doing any UCI racing, so the number is just fine while not race legal.

To set the height, I'm doing what I can do on my own, so I know my PBH (81.5 cm), have calculated frame size using the famed Lemond method (it's 53 cm, which just happens to match this frame, and the theoretical ideal nominal ballpark saddle height (720 mm). Since I am using a 172.5 crank arm, the target for saddle height is 717.5 mm. No, it is not convenient to measure that accurately. I used to have a cat as an assistant, but she passed away. Her assistance looked a lot like sleeping on my Allen wrenches, anyway.

Though I have done this dozens of times, I wonder if there is an additional rule. Since the saddle height is based on measuring my actual skeletal dimensions, it seems to me the 717.5 mm should be measured from teh BB center to the position where the saddle will support my sitbones, since those are the basis of the initial PBH measurement. The alternative and seemingly traditional approach is to measure the calculated distance along the seatpost regardless of setback. In this case when i do set the saddle slam factor (remember 7.5 cm) I would need to reduce the saddle height a few cm to account for the added length of the hypotenuse due to setback. If I do not correct by lowering the saddle a certain amount (being an engineer I can solve the triangles and find what the correction should theoretically be), I will have my legs over extending and risking back of knee pain, hamstring flexibility limitations, and dreaded and painful pelvic rocking. Other painful and personal problems can also occur.

So what's right? Set the saddle height to the 717.5 target value and then correct it by on the road iterative adjusting (driving my wife crazy!), or set the target value from BB axis to sitbone saddle contact point, and be closer to the ultimate target from the first ride?

Seems to me the latter approach is more correct. The purpose of the whole operation is to start riding with optimal leg extension, flexion, and power production, as well minimizing injury and fatigue. Therefore wherever I set my saddle (back for long-distance spinning, or foreward for time trialing), the extented length of my leg with crank arm should suit my calculated BB to saddle-top target length.

Unless pelvic geometry changes significantly with added setback?

https://www.stevehoggbikefitting.com...d-can-it-be-2/

https://www.stevehoggbikefitting.com...ard-can-it-be/

Thanks for referring me to Steve Hogg's pages on saddle height and positioning. It is far more interactive than I expected, but I should not be surprised. I take a lot of points from his sites, but they will be hard to use without his direct skill in the picture.

Would you please say a few words more about what you thought the key points were relative to my question? I don't have access to a dynamic strategy for fitting, but I can go out and ride, and feel for the smoothness of my pedal stroke under load and climbing.

Stationary pedaling with my position as I described it already feels pretty well, and the stiff old Toupe has not felt better on the ischials than it does now.

I do as you do, measure heigth to where the sit bones rest on the saddle.

If you feel great now, then fine. If not, then a more organic approach would be more helpful than angles and other measurements. Your goal is to be stable on the bike, efficient, and not induce injury. That can be better accomplished, generally speaking, though real world observational fitting, rather than formulae. Every person is different, and you may or not fit the formula, depending on flexibility and general fitness. You, may, and that is great. Engineering is an exact science when applied to a building, a product, or structure, but it does not translate well to the human body. The formulae are great to get you close, but after that, the minute adjustments are better accomplished, in my opinion, on how you feel and are performing on the bike. And yes, setback will affect seat height.

Saddle Height Tip - Get your seat height dialed to the millimeter

https://www.youtube.com/watch?v=IhcTPhERGiI&t=21s

Gents, thanks for your moral support, concurrence, and valuable information.

My current status is that I'm initially fairly comfortable on both bikes (the Mondonico steel roadie and light, flexy 650b Faux French bike) in brief trainer rides. Time now to ride more and watch more, keeping the two bikes at this height/setback combination for a week of 5 to 10 mile rides.

I never measure until after I have the fitting correct. I use the heel-on-pedal method. It works no matter saddle type, butt type, pedals, cranks, etc. Very quick and simple. Google if you haven't already.

I do know the method. From where I am right now, I should end up in a good place if I adjust it in small increments, if it needs any.

The UCI rule is a minimum setback of 5cm. More than that is fine. What the rule wants is that racers should be on fairly normal bikes, and safe bikes, and not be doing anything extreme. Your Mondonico would qualify easily.

As rules go, the UCI is kind of poor since it refers to saddle nose position, not some point that has something to do with comfort or leverage. It also doesn't accommodate a range of saddles.

99% of racing saddles in use are 27cm long. True, the UCI rule can be defeated by creating or locating aberrant saddles. What really defeats the intent and purpose of the rule is endless kvetching about nonsense. The signal to noise ratio on this thread is staggeringly low. Up above you stated the Mondonico has 7.5cm of setback and does not meet UCI rules. Either you have a unique and unstated method of measuring setback, or the Mondonico meets the rule easily. Mondonicos are good bikes. Most any good bike that has not been pushed into some strange configuration meets the rule easily.

Again, it is a simple rule. The purpose of the rule is safety. Bikes with saddles excessively far forward are not stable. It would be nice if there were some formula that would put center of gravity far enough back that pitchover would just not happen. The pushback against the simple rule is astonishing. Biggest part of that pushback is a peanut gallery that never stops talking nonsense. A good and comprehensive rule would never be accepted.

Chill, bud, I was trying to say that I don't care about the UCI rules, nor do I need them. In such discussions I have had people tell me 'just follow UCI.' I need a lot of setback due to my heavy upper body (no, it's not brawn), and can't get it with most road frames (including my Mondo's) without very set-back seatposts and long-railed saddles like Selle AnAtomica and Specialized Toupe and their other models. I hope you don't think I want to slam my saddle forward. I do not. Perhaps it would cause me to go over the handlebars, but I also have enough skill and experience to slide my weight backwards in a panic stop or other risky situations. Or by "pitchover" do you mean a wheelstand where the rider falls on his ass behind the bike? I guess I have not raced enough (meaning: not EVER) to have launched my ass off the back of the bike.

I never heard of racing bikes (road) being unstable based on going farther forward than the UCI limit, not have experienced anything like that. Can you describe the instability and in what situations it arises if its something other than going over the bars?

"It's a simple rule:" -- do you advocate it for all BF members? I don't think I understand your point. I should have said "it doesn't accommodate a FULL range of saddles." My bad.

Please, clarify your "peanut gallery" comment. If you mean me, let's take it offline. It's hard to understand if that pejorative phrase is meant for anyone in particular. I thought I was asking a sincere question.

One of my points was that with an S-A, the nose screw is supposed to be adjusted as you ride and stretch the saddle. This is unlike the other leather saddles: Brooks, Rivet, and vintage Ideale. This adjustment will elongate the saddle forward of the saddle rail clamps by maybe as much as 3 cm over time. No set criterion on saddle setback based on nose - behind - BB plumb can be reasonable, in that case. If a S-A rider was to follow the UCI constraint, he could easily and painfully end up with his sitbone contact points a few cm behind where they should be on those saddles.

Femur bone lengths vary by the individual..

Thanks for these. I have very long femurs and it seems to blow most recommendations out of the water