How to reliably replicate the same fit on different bikes

[cyan]

As most people here probably have more than one bike, short of getting a bike fit for each individual bike (assuming for the same type of riding, so not trying using the road bike fit on a gravel bike), I wonder what is the best way to replicate a fit (done by professional) from one bike to another. What are the tools and steps involved?

Case in point: trying to replicate a fit done on one bike to another which has an extra 0.5-deg STA and an extra 0.25-deg HTA, but 3mm shorter fork length, 15mm shorter HT, 9mm shorter frame reach. Assuming I'm adding 10mm in total in stem+handlebar reach, how do I determine the saddle height and fore and aft, as well as the stem height? Is there a calculator that takes into account of all these variables? And once I have the numbers on paper, how I implement them reliably on the bike?

EDIT: just to add, same stem angle, same crank length, same pedals, same seatpost (so same post setback), 5mm shorter saddle length

[weisan]

http://gearinches.com/blog/misc/bike...try-comparator

https://forums.thepaceline.net/showthread.php?t=234437

[colker]

There used to be stems in 0.5 cm increment..

[wallymann]

Originally Posted by cyan

what is the best way to replicate a fit (done by professional) from one bike to another. What are the tools and steps involved?

start with BB center axis as your reference.

measure saddle height and setback.

then measure saddle-to-bar reach and drop.

lastly, buy parts and install so as to replicate those numbers on your other bikes.

[Mark McM]

If you're using the same pedals, saddle and handlebars (plus the same crank length and shifters), then you don't need much more than a ruler and plumb bob to duplicate a fit. For saddle height, measure from the center of the BB shell to the top of the saddle. For setback, use a plumb bob to find a vertical line through the center of the BB, and then measure horizontally from the tip of the saddle to the plumb bob line. For handlebar reach, measure from the center of the handlebar clamp to the plumb bob line.

There are some specialized tools that do essentially the same things as above, such as the Fit Stick, but they're a bit spendy:





Trying to figure out new "fit" dimensions from frame dimensions is prone to error. Firstly, it involves using multiple dimensions in the calculation, allowing multiple errors to creep in; and secondly, published geometry charts aren't always accurate to start with. Its better to use direct measurements from a common reference point (which is typically the BB shell).

Sadly, it becomes more complicated if you've changed components that directly contact the rider (pedals, saddles, handlebars), because these affect how you sit on the bike. If these components have changed, transferring dimensions from one bike will only give an approximate duplication of the fit - for a true duplication, you'd have to go through another bike fit process.

[jtbadge]

Instead of using some contraption like above, it's easy to measure saddle setback by putting your wheel against the wall, then taking the difference of the wall -> center BB and wall -> saddle tip measurements.

Saddle -> bar drop can similarly be measured by comparing distances from the floor to the top of saddle and floor to top of bars.

[-dustin]

Originally Posted by cyan

As most people here probably have more than one bike, short of getting a bike fit for each individual bike (assuming for the same type of riding, so not trying using the road bike fit on a gravel bike), I wonder what is the best way to replicate a fit (done by professional) from one bike to another. What are the tools and steps involved?

Case in point: trying to replicate a fit done on one bike to another which has an extra 0.5-deg STA and an extra 0.25-deg HTA, but 3mm shorter fork length, 15mm shorter HT, 9mm shorter frame reach. Assuming I'm adding 10mm in total in stem+handlebar reach, how do I determine the saddle height and fore and aft, as well as the stem height? Is there a calculator that takes into account of all these variables? And once I have the numbers on paper, how I implement them reliably on the bike?

saddle height - tape measure, center of bb to top of saddle at a repeatable, defined point

setback - plumb bob and tape measure, center of bb to very tip of saddle

reach - tape measure, tip of saddle to bar center, consider the bar reach between the 2 bikes

drop - long level and tape measure, position the level on the nose of the saddle and measure at the bar.

for saddle angle, a clipboard and angle finder, clipboard on the saddle.

you must put each bike in the same location when taking measurements. also remember that your measurements will mean very little to anyone else trying to replicate fit of your bike, so use reference points that are easily remembered and replicated by you. i won't even swap tape measures when i'm replicating fit.

https://www.parktool.com/blog/repair...itioning-chart

that's pretty handy, as well.

[raven]

https://www.velonews.com/2012/05/bik...tically_216035

[vincenz]

I use bikegeocalc.com and make a model of each of my bikes.

[jpritchet74]

Plumb line to get the saddle set, and then just a tape measure. With stems now mostly in 1 cm lengths, you can get reach just right with bars of varying reach.

[Mzilliox]

this comes up every so often, here is what respected builder Dave Kirk has to say on the topic.
https://forums.thepaceline.net/showp...&postcount=534

you always put your saddle in the same place relative to bottom bracket and work from there.

there are also online bike compare thingies like this:
http://www.bikegeo.net/

then there is just eyeballing it and getting real close and riding and saying yes or no or maybe so

[MikeD]

Originally Posted by Mark McM

If you're using the same pedals, saddle and handlebars (plus the same crank length and shifters), then you don't need much more than a ruler and plumb bob to duplicate a fit. For saddle height, measure from the center of the BB shell to the top of the saddle. For setback, use a plumb bob to find a vertical line through the center of the BB, and then measure horizontally from the tip of the saddle to the plumb bob line. For handlebar reach, measure from the center of the handlebar clamp to the plumb bob line.



There are some specialized tools that do essentially the same things as above, such as the Fit Stick, but they're a bit spendy:











Trying to figure out new "fit" dimensions from frame dimensions is prone to error. Firstly, it involves using multiple dimensions in the calculation, allowing multiple errors to creep in; and secondly, published geometry charts aren't always accurate to start with. Its better to use direct measurements from a common reference point (which is typically the BB shell).



Sadly, it becomes more complicated if you've changed components that directly contact the rider (pedals, saddles, handlebars), because these affect how you sit on the bike. If these components have changed, transferring dimensions from one bike will only give an approximate duplication of the fit - for a true duplication, you'd have to go through another bike fit process.

That fit stick is an improvement over my wooden one. Glad to see someone picked up where the old company left off.

[Mark McM]

Originally Posted by MikeD

That fit stick is an improvement over my wooden one. Glad to see someone picked up where the old company left off.

Yeah, it looks pretty nifty. I've seen a few competitors as well, such as the VeloAngle:



There's even an iPhone App that supposed to be able to take a video of a person riding a bike on a trainer, and figure out the angles and distances of the bike fit. DCRainMaker posted a review of it.

[pdmtong]

For setback forget the plumb bob. just level measure (as previously mentioned) 1) center BB to wall and 2) tip saddle to wall then 3) subtract.

since its hard to measure to the center of the BB hole, just measure to the edge. separately measure the hole width (typically around 24mm) and then add half that to the measure from the wall to the BB hole edge.

[jtbadge]

Originally Posted by Mzilliox

this comes up every so often, here is what respected builder Dave Kirk has to say on the topic.
https://forums.thepaceline.net/showp...&postcount=534

you always put your saddle in the same place relative to bottom bracket and work from there.

QFT, DK's post contains everything you need to know.