Here is an overly simple guide for making changes to either Saddle Height or Fore/Aft, and the related change in the other direction. Since The seat tube is inclined (around 73.0* on lots of road bikes), you are making a direct and indirect change.
Change Saddle Height and you are also changing the Fore-Aft position.
The inverse is also true, that if you change Fore-Aft, you are also changing Saddle Height.
This has a direct effect on the rider position over the pedals and bottom bracket, but also impacts the reach to the bars.
I am hoping this rough example can help people consider the direct change they want, and the indirect changes that come as a result of the primary change. The specific distances are for the 73.0* Seat Tube Angle. Differences will exist if you have a different STA, but anything close will be reasonable when considering the values below.
Saddle Height Change:
If you change the Saddle Height by 1mm [0.038in], you also get a Fore-Aft change of 0.3mm [0.012in].
Saddle move UP 1mm [0.038in] moves Saddle BACK 0.3mm [0.012in]
Saddle move DOWN 1mm [0.038in] moves Saddle FORWARD 0.3mm [0.012in]
I’ve been searching for the Perfect Fit since starting a TR Program. I think I’m making too many minor adjustments, and not letting my body adjust to each change. But I am constantly battling minor knee soreness so I’m always looking for a quick fix.
Anyway, this is interesting and a good reminder that one adjustment causes other indirect adjustments.
This makes a lot of sense. Basic geometry. I just made a huge (20mm) fore change to my road bike saddle. Finally have my position over the BB where it belongs. My quads are recovering slowly. Is this due to the position change? Please help
Note the Backward Shift of 25mm for the Saddle vs the Forward Shift of 25mm for the Saddle.
It is an extreme 50mm difference fore-aft.
Note that the Saddle Rail Height and Seat Tube Angle are identical for both sides.
And assuming the rider places Sit Bones on the same point on the saddle (top point about 1/3 from the end), the Effective Saddle Height for the rider is longer on the Backward Shift when compared to the Forward Shift.
This happens anytime you make a pure fore-aft shift change on the saddle. Again, assuming you follow the saddle with your position on it, the effective saddle height is altered every time.
The difference varies with the precise seat tube angle, but it is there in all cases since we pretty much never have a 90* seat tube angle (and even then, the Eff Saddle height would possible change, unless you made a perfectly even shift ahead or behind the seat tube angle, and also had dead level saddle rails… again pretty much never the case).
I see. In this case I’d say calling it “height” is a bit of a misnomer. Really what we are talking about is the distance from the sitbone to bottom bracket, which does effectively change how far the riders legs are relative to the pedals (or how stretched out the legs are). Thanks for the clarification!
So how do you work out what is ‘optimum’ in a lay-persons easy to understand and apply manner?
I had a bike fit (a good one) over two years ago but my body shape has changed a lot since then. I also recently changed saddle to one that has a different shape. Things feel a bit ‘off’ but I can’t explain how or why.
I can get the ‘knee bend’ about right in terms of how bent it is when the pedal is at the bottom but I’m not sure how to work out how far back or forward from the bottom Bracket the saddle should be.
Is there an easy way to sort this out without having to get another pro-fit?
That is the absolute perfect route to get you absolutely nowhere.
Additionally, your pain could be a result of something completely unassociated with your position and not solved by a position change.
You’re almost as well served by using my contact points on your bike — similarities/differences be damned!
Basically you just said, “I moved something. Now things feel different, is this normal?”
Probably need more context and information before we can WebMD your position. (FWIW it’s either a cold or its terminal).
Also, if your muscles are underdeveloped for this new position and you’re pushing hard (a la SSBII, Build, etc) you could be doing yourself some significant harm. A torn sartorius once taught me that lesson. How bout moving things 5mm at a time and giving yourself a week+ to adapt for each change.
Yes, you have two options:
Ride a lot. Assess the feeling. Make an adjustment. Ride a lot.
Make an adjustment. Ride a lot. Assess the feeling. Make an adjustment. Ride a lot.
Bike fits are not be-all-end-alls. They are not once and done. How fat you are, how old you are, what time of day you’re riding at, how hard you rode the day before, how flexible you are, etc all have an affect on your position. A “pro fit” is, at best, finding an approximate best position at a moment in time. As you change your fit will necessarily change.
The best thing you can do is really start to pay attention to how you feel on the bike now and then get a fit. Then pay attention to how you feel afterwards. Then you start to learn how you should feel on a bike. From there you can make educated guesses (which is what a fitter is really doing . . . sorry fitters, you’re not mathematicians… feel free to flame me.)
I figured out that the right fore-aft position for me can be determined by riding at tempo with my hands on the hoods. If I take my hands off the hoods and my torso doesn’t fall or roll backwards then I’m pretty close to the right position (or I have a stupid strong core). If I fall my saddle is too far forward. If I can do this at a lower speed/power my saddle is too far back.
The only problem with this is that it’s assuming that your rider cockpit is set up correctly — about the right drop + reach.
Steve Hogg is great. I have always gone back to his balance method of determining fore/aft…
Splitting hairs here probably, but, every fit and fitter has worked from the cleats to shoes/orthotics to saddle height then fore aft then cockpit. Not saying a really messed up cockpit can’t affect saddle height and fore/aft but, that is easier to figure out imo/e…