The Bike Fitting Mega-Thread

As I said, I’m completely failing a geometry, but how can these two statments both be true:

  1. If I increase my sadddle heigth by 1cm, saddle goes back 3mm.


  1. If I change my aft by 3mm, saddle goes up by 1mm.

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.

  1. If you Raise or Lower the Saddle, the Fore-Aft distance change is roughly 1/3 that height change.

    • Raise Saddle 10mm = Fore-Aft changes 3mm
  2. If you move the Saddle Fore-Aft, the Height distance change is again, roughly 1/3 that height change.

    • Shift Saddle Aft 10mm = Height changes 3mm

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.

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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.

Here is a more exaggerated example to illustrate the point:

Height is 4 units.
Your butt is back 2 units.
Length from butt to foot is 4.47 units.

Move your butt back 0.5 units
Length from butt to your foot increases from 4.47 to 4.72.


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:


I didn’t finish the 2nd diagram, because the seat moves along the seat tube and length increases by the amount you raised it (assuming measurement marks are on seat post):

@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.

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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 :wink:

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I’ll be moving from a 42cm handlebar to a 38cm one.

I heard that you have to increase your stem by 0.5cm for every 2cm you go narrower upfront to match your reach.

Is that true?

Just a quick CAD sketch to demonstrate. This shown as a simple top view, bottom is the tip of the saddle.
Top is the bars in fixed position, only changing width.

683mm - 677mm = 6mm delta

So, that rule of thumb is quite reasonable IMO. As ever, many factors are at play here and the above assumes everything other than bar width remain the same.

Depending on the actual reason to change bar width, it may or may not be appropriate to adjust reach via stem or otherwise.

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Great visual represantation. Confirms what i was thinking. Much appreciated.

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Ideal postion for a short TT vs a long one varies, and triathlon fits aren’t identical to either. Aero is important, but comfort and saving your hamstrings for the run is as important - plus you’re not restricted by the UCI on saddle and aero bar positioning.

Does anyone have recommendations for a bike fitter in/near Chattanooga, TN? Looking to get a bike fit done, but I want to get someone who is very experienced, understands physiology, and can dial me in.

Come up to Brevard and check in with FitByReid


I probably need to double check and link these in the OP, but here are some ways to find fitters:

I recently flipped my stem to have a bit more of an upright position which seems to have been helping with some back pain. The additional benefit is that the drops are more comfortable for longer periods now. It’s hard to get super aero when I carry my extra weight around my midsection :rofl::grimacing::man_shrugging:

My wrists are comfortable on the hoods, but feel a bit awkward in the drops. I haven’t had a fit on this bike but tried to carry forward measurements from my last bike and fit. The fitter mentioned having your wrists in a “handshake” position, and in the drops it feels like my hands are tilted up too much.

I’m trying to figure out if I should rotate by bars forward to straighten my wrists in the drops then bring the hoods back a bit as needed. Figured I’d ask the experts for their thoughts on the position before messing with everything.

I usually have a little more bend in the elbows but it was hard to stand still so my wife could take pics!