Measuring change in geometry

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Measuring change in geometry
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Posted: Jul 29, 2021 at 13:45 Quote
I recently changed the the fork travel on my YT Jeffsy from a 150mm to 160mm. I am curious how to calculate the changes to the geometry of the bike. Head tube angle maybe even the BB height. what else might have changed?

Is there an equation that I can use? I am not very strong in math (I get by) so it would need to be pretty simple Big Grin

Posted: Jul 29, 2021 at 14:12 Quote
If you're not good with math then why bother?
Just use the angle measuring app on every iphone. Open the app and lean the phone against your head tube.

Measure BB height with a ruler or use the measure app on the iphone instead.
What else changed? Seat tube angle, down tube angle, every tube angle. Just use simple tools to measure or use your smart phone.
Hope that helps.

Posted: Jul 30, 2021 at 10:07 Quote
Thanks @BenLow2019, I didn't think about this option...
My experience with angle measures apps is that it's ain't too accurate and in cases where 1-2 degree makes a big difference I'm a bit skeptic. But I'll give that a try

Posted: Jul 30, 2021 at 11:02 Quote
You probably have something there.
My only other idea is to start doing the math - bust out the trig and solve the for the angles that way - I'd have to do a quick review on Khan Academy personally.
https://www.khanacademy.org/math/algebra2/x2ec2f6f830c9fb89:trig/x2ec2f6f830c9fb89:radians/v/introduction-to-radians

Posted: Jul 30, 2021 at 12:40 Quote
https://bikegeo.muha.cc/

Posted: Aug 3, 2021 at 0:29 Quote
Ye old rule of thumb.

20mm change in travel up front changes the head and seat angle aprox 1degree.

Posted: Aug 3, 2021 at 19:07 Quote
outerculture wrote:
I recently changed the the fork travel on my YT Jeffsy from a 150mm to 160mm. I am curious how to calculate the changes to the geometry of the bike. Head tube angle maybe even the BB height. what else might have changed?

Is there an equation that I can use? I am not very strong in math (I get by) so it would need to be pretty simple Big Grin

Do you notice a difference?

I just changed the travel on my Capra from 170 to 180… couldn’t tell at all physically but my mind kept wandering. Ended up lowering the stem 10mm (spacers) so my riding position is back to “normal”.
Pretty sure it’s all in my head.

Posted: Aug 4, 2021 at 13:32 Quote
Thorjensen wrote:
Ye old rule of thumb.

20mm change in travel up front changes the head and seat angle aprox 1degree.

That's pretty much what I'm seeing. 10mm changed the angle by 0.5 degree

Posted: Aug 4, 2021 at 14:20 Quote
outerculture wrote:
Thorjensen wrote:
Ye old rule of thumb.

20mm change in travel up front changes the head and seat angle aprox 1degree.

That's pretty much what I'm seeing. 10mm changed the angle by 0.5 degree

I'm not sure either... I made the change while I was sidelined by an injury for 6 weeks, and returned to ride the bike with the modified fork. I attribute most of what I feel right now for being out of shape and confidence due to that injury. I'm not back to ride my rowdy and steep trails yet to really see any benefits.
I'm keeping the 150mm shaft so I have the option to revert back in the future. I'm doing it mainly because I love tinkering with this stuff

Posted: Aug 5, 2021 at 0:41 Quote
outerculture wrote:
Thanks @BenLow2019, I didn't think about this option...
My experience with angle measures apps is that it's ain't too accurate and in cases where 1-2 degree makes a big difference I'm a bit skeptic. But I'll give that a try

The 'Angle pro' app for ios is free and shows tenths of a degree. The measurement is probably not for mission critical stuff. The floor the bike is standing on could be not perfectly level though.

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