I have been working on a build like this:
https://www.cyclingabout.com/custom-...ing-bike-2019/
I was originally going to do 29 x 2.15" Almotion wheel set. I am thinking I might want to throw on a 27.5" wheel set instead last minute. I am trying to understand BB drop and what that truly does to the setup of the bike in relation to peddle strike issues.
The bike is a Surly Ogre. The author of the article personally rides 27.5" x 2.4" with
Schwalbe Super Moto-X MTB Tyre. I was thinking of doing a similar wheel build, but 2.4" is too small for BB drop. The current BB drop of the bike is 68mm. In conversation with the author, he mentioned to me:
27.5x2.4" = 706mm wheel diamter
27.5x2.8" = 726mm wheel diamter
29x2.15" = 730mm wheel diamter
If you swapped in 27.5x2.8" tyres onto the Ogre I've suggested it'd drop the BB by 2mm.
I don't totally understand the math and just starting to now. If I understand this correctly, if I go from a 29x2.15" that means the wheel diameter is 730mm, and I want to do a 27.5 x 2.8" at 726mm, then I do 730-726mm = 4 mm.
I am not sure where the author got "2mm" from. How actually do I figure this out exactly?
So does that mean if I want to do a 27.5 x 2.4" instead, I subtract 706 from 730, and come up with 24mm difference. Does that mean that the Bottom Bracket then drops an additional 2.4 centimeters closer to the ground?
That sounds like a lot and I don't have a bike to test it on, so can folks tell me if that is a lot. That is too much correct?
So if the BB is 68mm pre-change, then I take 6.8-2.4= 4.4cn=44mm?
Am I doing this right?