 You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
Bear with me .....
I have a 26" frame designed around using a 2.4" tyre. It's currently running a pair of 700 X 35 cross type wheels.
This has increased the BB height. No biggie.
Now I've been offered some 650b wheels.
From a quick Google it suggests that a 26x2.4" wheel will have a very similar overall diameter to a 650b X 40 with the 650b wheel being marginally shorter.
Having a bit of a brain fart moment this morning......
Do I have this right?
Obviously a lot depends on the height profile of a given tyre, but on the assumption that the carcass width leads to a consistent height (not a great assumption, but Im going with c.75% of width for tyre height) and that:
700c bead diameter = 622m,
650b BD = 584mm and
26" BD = 559mm
your 700c would be c.622+(2 x 40mm x 75%ish) = 682mm
Your original 26" would be c. 559mm+(2 x 2.4" x 75% x 25.4mmish) = 650mm
Assuming fatness fit at c.670mm, a 650b at 584mm, would leave up to 86mm, or somewhere between 2.0" and 2.25" of 650b tyre (50+mm) I reckon.
Hmm.
Thanks Stoner
If I'm reading this correctly [url= 
?efg=eyJpIjoidCJ9&oh=72fead226c616f5c7dcee9dbbc28ba4f&oe=57DC4D58]Linky[/url] then it shows a 26x2.35" tyre as having a circumference of 2083mm compared with a 650b X 1.5" as 2079.
Allowing for a variation in tyre height and coupled with the reality of running the 26" tyre softer than the 27.5" the two would be very similar.
I appreciate 1.5" is only 38mm (ish) and not 40mm but what's a few MM between friends .......
seems about right.
are there many 40c 650b tyres out there?
[img] 
[/img]
I may have meant 42mm ... 😕