I had a bike fit recently and was wondering about transferring the fit data to my other bike.

I realise that some things such as bar height are going to depend on the bike's geometry and I'm not going to replicate an endurance bike fit on a race bike, but I was wondering about saddle set-back. I've been told that this is a "fixed value" for a given rider, once they've worked it out via their preferred method (KOPS, balance test, gut feeling...). Much like saddle height that is determined by your cycling inseam (at least on road bikes). Reach variations should be done only by changing stem length & angle, or getting a frame with a different top-tube length.

It this a good rule, even if you change between bike sizes or geometries? I'm assuming that the set-back can be measured from some agreed reference point on the saddle (e.g. sit-bone position).

Thanks!

Technically, you can transfer all of the measurements from one bike to another using very specific measurements and an infinite number of stem lengths and saddle setback posts.

I think if you use the same saddle between bikes, you can measure from the tip of the saddle.

If you're really good and use the same saddle and handlebars between bikes, you can use tip of saddle to clamp of handlebar as a measurement for how long your stem should be.

Setback, however, I think is generally measured by hanging a plumb line from you knee when your petal is horizontal and measuring the distance between the plumb and pedal spindle.

Personally though, I always go by feel. Ride the bike for 20-30 miles, make a few adjustments, take it for another ride, etc. My butt sits where it wants to sit, and I move the saddle in response to that. On flat saddles, it's a bit harder, but if you ride with a curved saddle, it's VERY obvious where you have to move the saddle.

I duplicate my riding position as close as possible on all my bikes, road or off road. No two have the same saddle, so setback has to be done by feel, but when I check, it usually works out to 1cm behind KOPS, even after switching from 175mm cranks to 200mm. Reach is a little less sensitive, plus or minus 1cm, and bar height least important at plus or minus 2cm.

KOPS (knee over the pedal spindle) was discredited in the nineties - this article by Keith Bontrager was published in 1998 https://www.sheldonbrown.com/kops.html
There are others.

The saddle set back is adjusted to balance you on your bike properly and thus will vary depending on bar height, how stretched out you like to be, etc.

Certainly, with a new bike, you could transfer your numbers across as a starting point, but to be honest, I think you're better off starting from scratch. It's not hard to get a basic set up and no matter how you start, it has to be fine tuned on the road anyway.

Where are you measuring saddle set back from on the saddle? A more normal figure as I understand it is for the tip of the saddle to be about 60-90mm behind the BB. I'm not sure where are measuring your 1cm behind KOPS from...unless you mean your kneecap. I'm asking about the saddle position - which is of course related to where your knees end up!

I could probably transfer the fit from the bike I ride the most, but I don't find my other bikes any less comfortable than it, so perhaps I'm already there. I haven't checked the measurements.

Yes, I'd agree that KOPS is not ideal for all cases - I use the "balance test" method myself. It's interesting that you mention that this is affected by bar height, which has been one of my issues. I'm a new cyclist and found it uncomfortable to have too much bar drop, so I was playing around with all sorts of fit changes. I finally got a professional fit and moved my saddle forward and up a fair bit - I thought the increased drop was going to make things worse, but it didn't.

It sounds like there isn't really an absolute value of saddle set-back then, even for an individual, and that the ideal position could be altered by the bike's geometry and usage (e.g. race or endurance etc.).

The ONLY absolute in bike fit is that it has to be fine tuned on the road. Getting it close to right to start with helps of course.

Yes! Ultimately, it's all about making it comfortable and efficient for long rides. If it still hurts after you've followed all the guidelines, then you're "holding it wrong" to quote Steve Jobs....

From the point where my sitbones hit the saddle, horizontally to a plumb line passing through the BB.

This way I can (and do) use different saddles on different bikes and set them up relatively close to each other. Been practicing this for the last 16-17 years.
The only bike I have set up differently is my fixie/singlespeed, where the saddle is a bit fore compared to the other bikes, resulting in a relative offset of knees only 20-25 mm behind the pedal spindle. The other bikes are closer to 25-30 mm.

This replicates what I have found as my "best fore-aft" balance point, resulting in ability to carry negligible body weight via my hands.
I don't use KOPS as a directive, and only measure the KOPS offset for my own reference.

Once I drop the plumb over BB on a new bike of mine, I mark the location with a Sharpie on its top tube. Then it is a child's play to correctly position a new saddlle from this reference anytime if needed.

With a little variance aside for differences in saddles, my saddle setback is roughly the same from bike to bike relative to the bottom bracket. I wouldn't be able to measure or visualize it relative to the seatpost or seat tube since I have frames with different seat tube angles.

No, the way you set the set back on a saddle is by starting with the saddle pushed forward, then slowly moving it back until you can take your hands off the drops and you don't fall forward. That's the correct seat setback.

Bicycle positioning is all about feel, you have to ride a bicycle, you have to know how the bicycle should, feel. following some moronic computer program is just wrong.

My allez with 8cm saddle-to-bar drop is much more forward (relative to bb) than my Fuji. Although my Fuji has a good bit of drop compared to most endurance bikes. It is, however, a good bit longer. One has a romin and the other a romin evo which is longer.

The only bike in my arsenal that has a different setback is my Triathlon bike.
But of course a Tri bike is unique and the ride is VERY different than a normal road bike.

So I think the answer to my question is that set-back can depend on bar drop, and ultimately depends on the correct balance point for a particular bike and individual.

I would definitely agree that getting balance correct has more impact on riding comfort than trying to blindly follow KOPS (although it might be a reasonable starting point).

Set the seat set back first. Once you get that balance right everything else will fall into place. You can easily fine tune the seat height, the handlebar drop, the stem legnth.

Try it.

Everything is relative, and all rules of fit are nothing more than a starting point. There is no objective point on a saddle to determine height or position. 60-90mm behind the BB would be totally wrong for me with my 37" (94cm) inseam, and because I ride an ISM saddle, which has no nose. Measuring the saddle position directly only applies when you are duplicating your position from one bike to another with an identical saddle.

When setting up a new saddle, ride the bike to figure out the sweet spot you like to sit in, set the saddle height, then use the KOPS to find the front/back position. KOPS is "Knee Over Pedal Spindle". It always gives the same result regardless of saddle design or bike. It is measured by dropping a plumb bob from the bony part of the knee just below the kneecap (the height of the kneecap itself is variable) with the crank horizontal forward. It is a good starting point, but most riders will adjust from there. I measure back 1cm from the pedal spindle and make sure the plumb line touches that line. Remember to adjust saddle height and check again.

Saddle height is more vague. The flexibility, padding and shape change, as does the spot you sit in. So basically you need to choose a spot in the middle of the saddle and always measure to the same spot. But the only way to determine saddle height in the first place for each saddle is by experimentation.

Not for me! I have a triangle between the BB, the seat and the handlebars I like. HTet triangle gets rotated roward of back depending on what that bike is for. Fix gears it gets rotated forward (bars forward and down) to get a position that is easier going up wind. I have a bike that is more of a comfort bike and the triangle is rotated back. I have real weight on my hands in all but the comfort bike. With comfortable hand positions, seeing that weight isn't an issue. (But it does mean staying far from most of the newer handlebars and brake levers. Old fashioned handlebars with near horizontal drops and the brake levers half way down the bend work really well for me and have for the past 45 years.)

Ben