Kirk Pacenti said:
Derby,
I am not sure this is the case... According to the frame drawing / geometry chart on the Ibis web site, both the Mojo and HD are designed with 0mm of BB drop. That means the static BB height will always be equal to the wheel radius.
The HD was obviously designed for large (2.4"+???) 26" tires. If the drawing is accurate, the wheel radius is almost exactly the same as a 2.3" 650b tire, resulting in a 352mm BB height. There should be very little if any rise in the BB.
This is the very reason I am so excited to pick up an HD frame. It seems perfectly suited for a "Plus 1" type 650b conversion
Cheers,
KP
The WTB Mutanoraptors are unusually tall for their width, the Race version I used on California trails measured only 3/8 inch less in diameter compared to your excellent 650b x 2.3 Pacenti neo-moto tires. The UST AM Mutanoraptors appear even taller, but the thicker AM tread may be deceiving.
After looking closely at the published BB height numbers the BB height at sag is within .35 inch across all models of Mojo C, SL HD 140, and HD 160. (See "Numbers" for calculations, below)
The Ibis geometry graphic is just a reference map, not to scale. The C/SL frame has no BB drop at top-out, the HD 160 has .5 inch negative BB drop, the HD 140 .25 in negative drop.
Conclusion...
650b will bring the sagged BB height up 1/2 inch with same width tires to about 12.5 on any Mojo model. Very little difference in BB height when sagged.
I'm very happy to see the BB height HD when sagged is no higher than the Mojo C/SL, and ideal for 650b. My plan is to swap my 650b x 2.3 wheels over for most uses, and also build some much heavier 26 inch DH wheels using 2.5 Minions for ski park use.
Numbers....
BB height w/o sag::
HD 160mm BB height at top travel front and rear is listed at 352mm (13.8″) I presume with 2.4 WTB tires as demoed.
HD 140mm BB height at top travel front and rear was announced at 343mm (13.5″)
C and SL 140mm is listed as BB height unsagged: 336 (13.23") with 2.1 Kendas as sold.
But sagged is what really matters for CG and pedal clearance.
BB height sagged:
HD 160/160mm posted BB height at sag: 304mm (12″) @30%
(HD 150/140mm BB height at 25% sag: 308 mm (12.12")
C/SL 140mm BB height at sag: 314 (12.36") Presuming @25% (and 2.1 tires)
http://www.ibiscycles.com/mountain/mojohd/geometry/
http://www.ibiscycles.com/mountain/mojo/geometry/
Your sag may vary. I use at least 25%/30% front/rear sag on my C.
Edit: corrected mistake in Numbers