So when I change the for-aft of my saddle by 3mm, the saddle heigth goes 1mm up or down respectively, right?
Is the opposite also true? If I go up 1mm, my saddle effectively goes back 3mm?
I recently increased my saddle heigth by 2mm, does this mean my setback changed by 6mm and I should move my saddle 6mm forward?
You have the concept right, but the actual numbers you are citing seem extreme (3:1 ratio)
I’ll defer to @mcneese.chad or those who are better at math, but I always used more of a 1:1 ratio.
Assume a 700 mm vertical seat post height and a seat angle of 73.5 degrees
700 x cos(73.5)=198.8
Raise the saddle 9 mm to 709
709x cos(73.5) = 201.3
i.e. a 2.5 mm difference in the horizontal position.
But wouldn’t that mean a 2.5mm change in the horizontal position would amount to a 9mm difference in saddle heigth? I’m pretty sure I’m completely missing something, but can’t figure out what it is.
Correct. Your initial post was the wrong way round. You raised your saddle 2 mm so you need to move it forward <1 mm to keep your leg extension the same.
Why did you increase the height? If it was to increase extension don’t adjust the fore and aft.
The Fore and aft position is about balance and postural stability (or terrain compensation). Are you balanced? Steve Hogg’s website is worth a read to find out more.
I think you all have this covered well. For future reference, here is the separate topic I wrote a while ago. It contains a graphic that might help with the visualization too.
So if I move my saddle 3mm back, it goes up by almost 1cm? This sounds extreme too me, but maybe thats just how physics work?
Take this example:
700mm saddle height at 73*, then shift 3mm directly rearward horizontal. It effectively lengthens the saddle height (all else being equal) about 1mm (not 10mm / 1cm like you said)
As I said, I’m completely failing a geometry, but how can these two statments both be true:
However
I would have thought that only one of these statements and the according inverse could be true.
I think my mistake is that I apply the same ratio to both changes, but basically a for-aft change doesn’t change saddle heigth on the same ratio as a saddle heigth change does change for-aft. Right?
This is about “who’s driving the bus” sort of thing.
If you Raise or Lower the Saddle, the Fore-Aft distance change is roughly 1/3 that height change.
If you move the Saddle Fore-Aft, the Height distance change is again, roughly 1/3 that height change.
I am probably not explaining well, and as a visual learner, the graphic above is easier for me to understand. So I am likely failing in a verbal definition, but see if this most recent attempt in text helps at all.
In short, the primary change you make only impacts the related value by a smaller proportion of that primary change.
Are there resources on fitting cleats. I have a sensitive knee and I got new shoes and can’t quite get the clear in a comfortable position. I could find tidbits on some adjustments based on what I’m feeling but not enough to get them set properly.
this is helpful. I think that you really need two diagrams to illustrate the two cases raised by @pnzr .
for case 1, the effective angle of the seat tube does not change.
For case 2, the effective angle of the seat does change (which is what @WindWarrior has shown).
this may be where (some of) the confusion stems from.
I don’t have a single resource, but here are some random ones referenced in some of the cleat topics here, in no particular order:
@pnzr I think to help us explain the relationship you still need to answer the question about why you increased your saddle height?
The ratios that we’ve been discussing are for maintaining the same leg extension when making adjustments.
When fitting we tend to look at saddle height first to find the most effective position for power production. When we come to consider the fore and aft position we’re looking to find the best postural stability and balance. So if we find optimum height first but then we adjust fore and aft to improve stability, we adjust the height again using that ratio to keep the extension the same.
I had some knee issues, but I’m not sure it’s saddle heigth related. Might have been too wide of a Q-factor, but have to see how the long weekend ride goes the day after tomorrow.
OK, what are the knee issues that you’re experiencing? Pain behind the kneecap is associated with height being too low. Lateral and Medial pain can be associated with the lateral cleat position i.e. Q factor.
Have you previously had a bike fit (if so, how long ago) and have any changes occurred since then e.g. new cleats, new shoes, saddle, shorts, had a crash, health changes?
Since you are adjusting saddle height due to knee pain if you alter the fore and aft at the same time too, you’ll not alter your leg extension, therefore if you’re too low now you’ll still be too low if you move the saddle forward.
I always thought pain behind the knee is associated with saddle being too high (since you are overextending the knee) and not the other way round.
At any rate, in my case it’s lateral pain. I had widened my q-factor since my thighs were rubbing a bit on my saddle, not in a painful way, but I noticed that my bibs were a bit roughened up on these locations. I’m pretty narrow, but have big thighs. Considering switching to a narrower saddle, altough the Romin Evo Mirror in 143mm is already a pretty narrow saddle I think.
Behind the kneecap is different to the back of knee. Behind the kneecap might be too low, back of the knee, yes, might be too high.
I think you’ve found the cause then, you’ve widened your stance and knee pain occurred. Keep the saddle height as was and move the stance back to where it was.
The only true way to find the right saddle is to sit on them. Pelvic tilt, your flexibility, saddle to bar drop and width all have an effect on comfort, as does fore/aft position. 143 isn’t narrow. The Pro Turnix 132 mm is popular with flexible people with narrower sit bone widths.
My recommendation would be to see a fitter with saddles that you can try and have a proper fit. The cost of buying saddles that don’t work for you and the discomfort on your bike exceeds the cost of a professional fit in the long term. A bike fit is better value in the short, medium and long term 
