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Using a Wahoo Kickr bike as a fitting bike?

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Using a Wahoo Kickr bike as a fitting bike?

Old 11-23-22, 02:04 PM
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eddiepliers2
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Using a Wahoo Kickr bike as a fitting bike?

Hello all, Long ago I was here as just "Eddiepliers" but that email address has dissolved, so I'm here as the sequel.

I was curious for all the fitters out there who are using a Kickr bike to do bike fits on. It seems like it covers everything except for changing out handlebars.

Let me know what your thoughts are..
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Old 12-25-22, 12:32 PM
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How are you going to transfer your fit measurements off the Wahoo and to the rider's bike? This is harder than it sounds.
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Old 12-26-22, 03:57 PM
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I don't think there are any fitters out there using a Kickr Bike for fitting. But it's easy enough to transfer your own fit to and from a Kickr Bike. There is an App to help, but I just measure it directly.
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Old 12-26-22, 05:44 PM
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Given the level of error that even small changes in the floor level can make, I have never found it easy to precisely transfer things like saddle set back from one bike to another. At my last gig I built a special jig to do it.
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Old 12-26-22, 05:52 PM
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Much like what Pete had said, but I find it very easy find the initial X/Y from the bottom bracket to seatpost/saddle tip and take that initial measurement in relation to get the reach and stack, then measure to the bars. As far as setback and length of stem, then add those numbers to the Kickr since you can change the post length or setback. I feel as long as you get the initial numbers and go from there, you'll be good.
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Old 12-30-22, 02:58 PM
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Originally Posted by Kontact View Post
Given the level of error that even small changes in the floor level can make, I have never found it easy to precisely transfer things like saddle set back from one bike to another. At my last gig I built a special jig to do it.
How does the floor level affect saddle setback measurement? Even a 2 deg slope would only change your horizontal measurement by less than 0.5 mm per 500 mm.
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Old 12-30-22, 05:40 PM
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Originally Posted by PeteHski View Post
How does the floor level affect saddle setback measurement? Even a 2 deg slope would only change your horizontal measurement by less than 0.5 mm per 500 mm.
1 degree is worth 1cm over 57cm. Which means that if your floor has 2 degrees of slope your saddle setback is going to be at least 2cm off. And if you base your handlebar location off your saddle, your bars will be 2cm off horizontal and 2cm off vertically.

I imagine a lot of people think what you did, which is why they grossly underestimate how hard it is to measure and transfer fit data. The best way to fit is on the bike you're going to be riding. It has the right Q factor, the right bar and hood shape, the right seat post head and right top tube length. Because when you try to make data from a different bike work you start running into the tolerance stacking that occurs when the increments of the source bike's components don't match the increments of the final bikes.

And I've seen a ton of problem using Retul to do it. Without any sort of error messages you can get wildly erroneous results on equipment Specialized swears is adjusted correctly.
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Old 12-31-22, 05:27 AM
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Originally Posted by Kontact View Post
1 degree is worth 1cm over 57cm. Which means that if your floor has 2 degrees of slope your saddle setback is going to be at least 2cm off. And if you base your handlebar location off your saddle, your bars will be 2cm off horizontal and 2cm off vertically.


I have to disagree. 1 degree is only worth 0.15 mm over 570 mm in the horizontal axis. The 10 mm you are referring to is at 90 deg to the horizontal measurement you are making when measuring saddle setback. There will be a similar horizontal error tilting the seatpost 1 degree.

So the saddle setback error (measuring horizontally) with a 2 deg floor slope (most floors are typically way less than this btw) is likely to be less than 1 mm. You would get a similar error in saddle height measurement due to the 2 deg floor offset - this time measuring vertically with the same 2 deg error.

Your 2 cm error in both planes is totally incorrect as they are both at 90 deg to the measurement you are actually taking. The error in both cases is cos 2deg x measurement length.

Last edited by PeteHski; 12-31-22 at 08:51 AM.
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Old 12-31-22, 12:43 PM
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Originally Posted by PeteHski View Post
I have to disagree. 1 degree is only worth 0.15 mm over 570 mm in the horizontal axis. The 10 mm you are referring to is at 90 deg to the horizontal measurement you are making when measuring saddle setback. There will be a similar horizontal error tilting the seatpost 1 degree.

So the saddle setback error (measuring horizontally) with a 2 deg floor slope (most floors are typically way less than this btw) is likely to be less than 1 mm. You would get a similar error in saddle height measurement due to the 2 deg floor offset - this time measuring vertically with the same 2 deg error.

Your 2 cm error in both planes is totally incorrect as they are both at 90 deg to the measurement you are actually taking. The error in both cases is cos 2deg x measurement length.
Why do I love bikeforums? Because even the underlying mathematical nature of the universe is up for debate.

So, you're wrong: This is a simple rise over run problem. We measure the location of handlebars horizontally and vertically. If you put the bike on a slope of 1 degree and measure 57cm horizontally from the saddle nose, that line will intersect the drop to the bars with a 1 cm error. And if you have a 1 degree slope and you measure vertically from the BB straight 57cm up to the setback number, your saddle nose will now be 1 cm horizontally closer or further than it should be.

If I had to guess, you are mistaking the vertical drop of a line tilted 1 degree back from vertical. But we measure bike stuff perpendicular to horizontal and vertical lines, not too them.

There is no arguing with basic rise and run: https://www.inchcalculator.com/rise-...es-calculator/ The end of a 57 cm vertical line tilted 1 degree back from vertical moves 1 cm horizontally, and the end of a horizontal 57cm line tilted up 1 degree moves 1 cm vertically.

Small angles produce big errors at the distances we measure fit references to. Doesn't matter if you are measuring from the saddle nose or from the BB for stack and reach.

Last edited by Kontact; 12-31-22 at 04:18 PM.
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Old 12-31-22, 03:42 PM
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Yikes guys, lets calm down on the BS... Admin can you shut this down?
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Old 12-31-22, 07:07 PM
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Kickr Bike, measuring

When measuring my Kickr bike I use a 4' T-square.

If the floor under the kicker is off by 15 degrees it won't matter...... The T-square resting on the floor will also be off 15 degrees.
A level floor only matters if you are using a plum bob.

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Old 01-01-23, 09:18 AM
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Originally Posted by Kontact View Post
Why do I love bikeforums? Because even the underlying mathematical nature of the universe is up for debate.

So, you're wrong: This is a simple rise over run problem. We measure the location of handlebars horizontally and vertically. If you put the bike on a slope of 1 degree and measure 57cm horizontally from the saddle nose, that line will intersect the drop to the bars with a 1 cm error. And if you have a 1 degree slope and you measure vertically from the BB straight 57cm up to the setback number, your saddle nose will now be 1 cm horizontally closer or further than it should be.

If I had to guess, you are mistaking the vertical drop of a line tilted 1 degree back from vertical. But we measure bike stuff perpendicular to horizontal and vertical lines, not too them.

There is no arguing with basic rise and run: https://www.inchcalculator.com/rise-...es-calculator/ The end of a 57 cm vertical line tilted 1 degree back from vertical moves 1 cm horizontally, and the end of a horizontal 57cm line tilted up 1 degree moves 1 cm vertically.

Small angles produce big errors at the distances we measure fit references to. Doesn't matter if you are measuring from the saddle nose or from the BB for stack and reach.
Now you've completely changed the goalposts. One minute we are talking about measuring saddle setback horizontally and now you are talking about bar drop. I'm not arguing about rise over run. That's not the error in the horizontal measurement due to the floor slope. The error is simply cos (1 deg) x horizontal measurement i.e. the difference between a measurement directly along the slope vs the true horizontal distance. The rise over run i.e. sin (1 deg) x horizontal is not relevant in this measurement as I'm not measuring the rise at all.

Similarly when measuring bar drop, the error is equally small if you measure the vertical height from the floor at both the bar and saddle. The fact that the floor may be on a slight angle is trivial and will not lead to the magnitude of error you are stating.

Anyway believe what you like. I'm confident in my own basic maths skills that this 20 mm error in both horizontal and vertical measurements you discussed is laughable. We can draw it out if you like and apply SOHCAHTOA. It's only a triangle and the maths is set in stone.

Edit: Reading again I do see where you are coming from if you are relying on a plumb bob to project the saddle nose position down to the BB.

Last edited by PeteHski; 01-01-23 at 09:43 AM.
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Old 01-01-23, 01:02 PM
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Originally Posted by PeteHski View Post
Now you've completely changed the goalposts. One minute we are talking about measuring saddle setback horizontally and now you are talking about bar drop. I'm not arguing about rise over run. That's not the error in the horizontal measurement due to the floor slope. The error is simply cos (1 deg) x horizontal measurement i.e. the difference between a measurement directly along the slope vs the true horizontal distance. The rise over run i.e. sin (1 deg) x horizontal is not relevant in this measurement as I'm not measuring the rise at all.

Similarly when measuring bar drop, the error is equally small if you measure the vertical height from the floor at both the bar and saddle. The fact that the floor may be on a slight angle is trivial and will not lead to the magnitude of error you are stating.

Anyway believe what you like. I'm confident in my own basic maths skills that this 20 mm error in both horizontal and vertical measurements you discussed is laughable. We can draw it out if you like and apply SOHCAHTOA. It's only a triangle and the maths is set in stone.

Edit: Reading again I do see where you are coming from if you are relying on a plumb bob to project the saddle nose position down to the BB.
Hilarious edit!

The way virtually everyone measures bikes involves setting setback with a vertical level or plumb bob, and then setting the handlebar drop and reach from the saddle also using a level. They do it that way because almost no one owns a 4 foot framing square that reaches from the floor to the saddle or bars. And if you use a framing square you'd need to put reference marks on the floor so you can move the square around, and you still won't be able to directly measure things like handlebar angle or saddle angle. And the floor has to be evenly not level - which they rarely are - or the framing square will keep changing what it shows as vertical.

But then you still haven't solved the problem of transferring fit off the Kickr bike because that fit is actually level, despite the slope of the floor it is sitting on. So you're going to be collecting those numbers with a level and applying them with a framing square.

All of which are doable, but involve a lot of problematic steps where measuring and arithmetic errors can come in because there are two techniques using two different sets of tools.


After seeing all the different ways my colleagues could mess it up, I built a level track for the bike's tires with a moveable grid board that centers on the BB location without losing level. Then you can observe setback, stack and reach directly for each component and even mark those locations on the grid with chalk. Pull the source bike out and you can read off the numbers or put a second bike in and move the components to match the marks.

Last edited by Kontact; 01-01-23 at 01:15 PM.
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Old 01-02-23, 09:45 AM
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Originally Posted by Kontact View Post
Hilarious edit!

The way virtually everyone measures bikes involves setting setback with a vertical level or plumb bob, and then setting the handlebar drop and reach from the saddle also using a level. They do it that way because almost no one owns a 4 foot framing square that reaches from the floor to the saddle or bars. And if you use a framing square you'd need to put reference marks on the floor so you can move the square around, and you still won't be able to directly measure things like handlebar angle or saddle angle. And the floor has to be evenly not level - which they rarely are - or the framing square will keep changing what it shows as vertical.

But then you still haven't solved the problem of transferring fit off the Kickr bike because that fit is actually level, despite the slope of the floor it is sitting on. So you're going to be collecting those numbers with a level and applying them with a framing square.

All of which are doable, but involve a lot of problematic steps where measuring and arithmetic errors can come in because there are two techniques using two different sets of tools.


After seeing all the different ways my colleagues could mess it up, I built a level track for the bike's tires with a moveable grid board that centers on the BB location without losing level. Then you can observe setback, stack and reach directly for each component and even mark those locations on the grid with chalk. Pull the source bike out and you can read off the numbers or put a second bike in and move the components to match the marks.
Well I'm glad you are amused, but this has actually been a useful thought process for me. I do now realise you are right about the potential issues with using a plumb bob to measure saddle setback if your floor happens to be on a slope. So I will eat some humble pie for you there and thank you for explaining your reasoning. It does make sense now.

The method I actually use for transferring a setup is pretty simple. I use a floor and wall as a reference and for saddle setback I rest my back wheel against the wall, measure the distance of the BB and saddle to the wall and subtract the two. But I do happen to have an inclinometer to check that the floor and wall are actually square. I also measure my road bike and Kickr bike on the same floor and against the same wall to minimise any reference error. I have also measured the saddle setback with a plumb bob on various floors around the house and get the same answer within a mm. So I guess my floors are flat enough, as I would have thought most hard screed floors are.

For bar drop I measure the saddle height and bar height vertically from the floor and subtract. I'm sure you would agree that a slight slope would not really matter using this method.

For reach I simply measure directly from saddle to the hoods. So the floor doesn't matter at all.

Saddle height I measure directly from BB centre to centre of saddle. Again floor slope is irrelevant.

I therefore have 4 simple measurements to transfer and only saddle setback requires a consistent reference plane. So I don't think it's very hard to accurately transfer a setup from my Kickr Bike to road bike. The biggest mistake I've ever made in this process is not having my Kickr Bike set to zero deg tilt before measuring!

I'm now curious how much on the piss your floors must be? I've just been checking all our floors with an inclinometer and they all level within the 0.1 resolution of my inclinometer.

I would also genuinely like to hear some critique of my above method and what errors would arise.

Last edited by PeteHski; 01-02-23 at 09:49 AM.
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Old 01-02-23, 02:20 PM
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Originally Posted by PeteHski View Post
Well I'm glad you are amused, but this has actually been a useful thought process for me. I do now realise you are right about the potential issues with using a plumb bob to measure saddle setback if your floor happens to be on a slope. So I will eat some humble pie for you there and thank you for explaining your reasoning. It does make sense now.

The method I actually use for transferring a setup is pretty simple. I use a floor and wall as a reference and for saddle setback I rest my back wheel against the wall, measure the distance of the BB and saddle to the wall and subtract the two. But I do happen to have an inclinometer to check that the floor and wall are actually square. I also measure my road bike and Kickr bike on the same floor and against the same wall to minimise any reference error. I have also measured the saddle setback with a plumb bob on various floors around the house and get the same answer within a mm. So I guess my floors are flat enough, as I would have thought most hard screed floors are.

For bar drop I measure the saddle height and bar height vertically from the floor and subtract. I'm sure you would agree that a slight slope would not really matter using this method.

For reach I simply measure directly from saddle to the hoods. So the floor doesn't matter at all.

Saddle height I measure directly from BB centre to centre of saddle. Again floor slope is irrelevant.

I therefore have 4 simple measurements to transfer and only saddle setback requires a consistent reference plane. So I don't think it's very hard to accurately transfer a setup from my Kickr Bike to road bike. The biggest mistake I've ever made in this process is not having my Kickr Bike set to zero deg tilt before measuring!

I'm now curious how much on the piss your floors must be? I've just been checking all our floors with an inclinometer and they all level within the 0.1 resolution of my inclinometer.

I would also genuinely like to hear some critique of my above method and what errors would arise.
When you do a fit on a Kickr, "level" is whatever the position it has that comes out of fit. So if you move the Kickr from the fit area to a wall, you've changed the level.

When you use a wall with a floor you are adding floor level error to wall plumb error. If your floor is sloped up 1 degree and the wall is sloped in 1 degree, your saddle setback will have a combined error of 2cm too far forward, since the floor pivoted the saddle back and the wall is pivoted forward toward the saddle. The problem isn't just simple slope - walls and floor curve in ways that are hard to measure.

For drop, if the floor isn't level, your method for bar drop will definitely be in error. If the floor sloped by 1 degree, your drop will be off by about 1 cm because the saddle is close to the rear wheel and the bar close to the front. So they will have a large slope built into them from the floor.

Saddle height and saddle-to-bar are just point-to-point distances, so those are fine. But when you change setback, saddle height changes enough to matter to many cyclists, so it is not set and forget.


Without special equipment, I would zip tie the rear wheel to a vertical post and the front wheel to the downtube, then level the bike with 4 foot carpenter's level between the axles using cards under the fully inflated tires. Then I would do set back with a plumb line, recheck after saddle height, and then use the level again with a ruler to set drop from the saddle nose to the bar. Measure reach from the saddle nose to the bar, or (better yet) to the center of a stick placed across the hoods (if your bars or hoods aren't identical between bikes). Use saddle to floor and handlebar to floor to confirm that you haven't introduced an error with the spirit level. Use a cell phone inclinometer app and a board to copy saddle tilt and bar slope.

All the same applies to the Kickr, except you never move it or reference the floor.

These methods can be very precise, but suffer a little bit from the accuracy of a bubble level, which is why I like to use a plumb line for setback instead of holding the level vertical. If you are at all sloppy with the level, nothing is going to work well.
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Old 01-02-23, 08:49 PM
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A bubble level is monster accurate. 1 over 3' is a little over 1/2". If your house or place of business is that far out, you have some serious issues. My workshop was built in the late 40's and sits on concrete blocks. Its floor is pretty much dead on as shown with a 3' bubble level and thus out maybe 1/32" over 3'. I don't get the problem.
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Old 01-02-23, 09:21 PM
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Originally Posted by Carbonfiberboy View Post
A bubble level is monster accurate. 1 over 3' is a little over 1/2". If your house or place of business is that far out, you have some serious issues. My workshop was built in the late 40's and sits on concrete blocks. Its floor is pretty much dead on as shown with a 3' bubble level and thus out maybe 1/32" over 3'. I don't get the problem.
Many concrete floors, wood floors and sheetrock walls are not so level - especially in older buildings. My point is that you don't know your floors or walls are level until you check, and that small errors compound. The methods PeteHSki mention makes error compounding relatively easy. I used 1 degree increments to illustrate the problem, but when you have measurements based on other measurements, even 3mm mistakes add up.
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Old 01-03-23, 09:24 AM
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Originally Posted by Carbonfiberboy View Post
A bubble level is monster accurate. 1 over 3' is a little over 1/2". If your house or place of business is that far out, you have some serious issues. My workshop was built in the late 40's and sits on concrete blocks. Its floor is pretty much dead on as shown with a 3' bubble level and thus out maybe 1/32" over 3'. I don't get the problem.
Out of curiosity I just measured saddle setback on 3 different hard floors around the house using a plumb bob. They are all within +/- 1 mm measuring with a steel rule. I checked the floor level with a metre long beam and digital inclinometer. All 3 floors were level within 0.1 deg.

While I agree you have to be careful, I don't believe it is THAT difficult to measure with reasonable accuracy.
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Old 01-03-23, 09:43 AM
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Originally Posted by Kontact View Post

For drop, if the floor isn't level, your method for bar drop will definitely be in error. If the floor sloped by 1 degree, your drop will be off by about 1 cm because the saddle is close to the rear wheel and the bar close to the front. So they will have a large slope built into them from the floor.
I still don't get this. I am just measuring the saddle and bar heights vertically relative to the floor plane. A 1 deg floor slope may lead to an error of approx 1 mm over a metre if I measure vertically at 89 deg rather than 90 deg . But my floor is much less than 1 deg out anyway. This is not the rise over run error discussed earlier when measuring setback with a plumb bob.

Actually the error would be tiny as both height measurements would be at 89 deg, so the error would be their difference i.e. bar drop x cos 1 deg

In practice using this method to measure bar drop I find that the important thing is to make sure the bars are level in the front view, which I do by measuring their height at both ends.

Last edited by PeteHski; 01-03-23 at 09:54 AM.
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Old 01-03-23, 12:43 PM
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Originally Posted by Kontact View Post


Without special equipment, I would zip tie the rear wheel to a vertical post and the front wheel to the downtube, then level the bike with 4 foot carpenter's level between the axles using cards under the fully inflated tires. Then I would do set back with a plumb line, recheck after saddle height, and then use the level again with a ruler to set drop from the saddle nose to the bar. Measure reach from the saddle nose to the bar, or (better yet) to the center of a stick placed across the hoods (if your bars or hoods aren't identical between bikes).

Use saddle to floor and handlebar to floor to confirm that you haven't introduced an error with the spirit level.

Use a cell phone inclinometer app and a board to copy saddle tilt and bar slope.

I get this method apart from the part in bold. If say you have shimmed the front wheel up to level the axles then the distance to the floor is not directly relevant anymore as you have effectively moved the bike to a virtual level floor reference.
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Old 01-03-23, 01:15 PM
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Originally Posted by PeteHski View Post
I get this method apart from the part in bold. If say you have shimmed the front wheel up to level the axles then the distance to the floor is not directly relevant anymore as you have effectively moved the bike to a virtual level floor reference.
If your drop should be 3", a quick measure to the floor will confirm you didnt get something wrong.
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Old 01-03-23, 01:36 PM
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Originally Posted by Kontact View Post
If your drop should be 3", a quick measure to the floor will confirm you didnt get something wrong.
But didn't you just shim under the wheels to level the axles? In which case measuring directly to the floor for bar drop will introduce a larger error than you would have got simply by ignoring the slope in the first place. Now you will be measuring a rise over run error across the wheelbase.
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Old 01-03-23, 01:53 PM
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A 48" drywall T-Square is about $15, why would you bother to level the bike.

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Old 01-03-23, 03:13 PM
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This is the exact method I use:-

https://www.myvelofit.com/fit-academ...ry-rider-needs

I do check that the floor is level and the wall is perpendicular - which only really affects the saddle setback measurement. The other 3 measurements are not sensitive to floor level.
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Old 01-03-23, 08:02 PM
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Originally Posted by PeteHski View Post
But didn't you just shim under the wheels to level the axles? In which case measuring directly to the floor for bar drop will introduce a larger error than you would have got simply by ignoring the slope in the first place. Now you will be measuring a rise over run error across the wheelbase.
You would measure to the shims. But this isn't for being super exact - it is to check that your previous work isn't wildly out of wack.
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