Premise…I like wide tires for gravel, 2" or more
Problem…most gravel bikes don’t take tires that wide with good mud clearance
Problem…the MTB BB height is a pain in the neck on gravel and road
And…I have a 29" hardtail bike sitting around (have switched to a 130/130 bike for trail riding)
So…can you fit a shorter fork…like 20-30mm shorter…and put a 27,5" rear wheel on and just go to town? Or will the change in trail make it completely unrideable?
Highly bike dependent (depends what you’re starting with).
I’d probably say don’t bother changing wheel size. Look at fork length - if it’s a 120mm you might run a 100mm or rigid equivalent. That’s drop the BB a hair and steepen the HTA. Then run a 50mm or 2” tire.
I just did a quick hack using my “Sagged” suspension sketch. This was made for another user, and likely has dimensions that skew the results a bit, but this is a decent swag to start. If make one change and just drop the fork length by about 25mm:
Head Tube Angle & Seat Tube Angle steepen by about 1*.
It’s a 2018 specialized epic ht pro in XL. I’m not finding any 450-ish mm rigid fork options with boost and a tapered steer tube so now I’m thinking….just swap to 27.5” wheels front and rear. Drop the whole bike by 3/4”. But what will that do to the trail and handling? It should reduce the trail and make it ride like a low trail rando bike right? Which wouldn’t be a bad thing.
29" x 2.2" = 734mm Diameter = 367mm Radius (picked the middle between the stock sizes)
650b/27.5" x 2.2" = 696mm Diameter = 348mm Radius (matched tire size above for simplicity)
26" x 2.2" = 671mm Diameter = 336mm Radius (matched tire size above for simplicity)
Switching from 29" x 2.2" to 650b/27.5" x 2.2":
367mm Radius - 348mm Radius = 19mm
309mm BB Height - 19mm Wheel Drop = 290mm BBH
Switching from 29" x 2.2" to 26" x 2.2":
367mm Radius - 336mm Radius = 31mm
309mm BB Height - 31mm Wheel Drop = 278mm BBH
Consider those for a primer and see if one sounds like something you want to do. If so, I can take the extra steps into CAD, but you may know a bit from the above.
So incredibly helpful, thanks! I want to measure the bbh on my road bike trek domane 2021 60cm and then go from there. It says 80mm drop in the specs but I want bbh, would like my redneck gravel setup to be about the same.