Well, i feel estupido.
Tried 75PSI on the rear. The bike on pedal power is within a hair of as fast as the 29er now ( at least on the flats ).
The ride quality didn't degrade as much as i thought it would.
The front is still ~40% bumpier than the rear.
I think the right PSI for the rear is 70PSI for the efficiency/comfort middle ground.
I looked at my previous Schwalbe Super Moto X 20" x 2.8" tire and noticed that it lists 50PSI as the max pressure. I'm very careful to not over inflate tires, so i knew i ran 50PSI.
I think that explains the mysterious rim dent as i went through the NVH hell-course. I've never had a rim dent on any bike. So this tells me 50PSI is way too little, even with a huge tire.
When i did ghetto weight measurement on this bike, approximately 70% of my weight sits on the rear, so it makes sense to have a roadbiker's PSI on the rear tire.
On to the next topic:
I'm a little concerned that these 180mm cranks might result in pedal to tire contact when i go from a 1.75" tire to 2.25-2.5". So i checked some angles:
The end of the crank lines up with the end of the crown but.. we've filed 2mm off the sides of the necessary areas to make it clear at all angles of rotation and have a 127.5mm wide BB ( the largest i can find for 68mm ), so, the 180mm cranks are working out fine.
It looks like foot to tire contact won't happen with the front fork uncompressed in any scenario.
Under maximum compression ( i'm sitting on the front! ), and an extreme turn angle ( more extreme than you would normally ride at ), it looks like tire to foot contact could never happen. In real riding, my foot is pointed upwards.. so it's pedal to tire contact that i have to worry about.
Looks like a good safety margin
I really want to remove this 10mm head spacer to reduce the angle of the fork, then max out the front tire size.
But i'm thinking if i add this pendulum pedal, i might enter the danger zone... not in terms of foot to tire strike, but pedal to tire strike:
I'm assuming that by removing the 10mm head spacer, due to the angle, i get the pedal 8mm closer to the tire
and the pendulum pedal gets the crank 12mm closer. To be safe, let's just say it's a 25mm reduction of the safety margin.
I think a good way to experiment with that would be:
- buy wider rim'd front wheel ( the 18mm internal maxarya rim is WAY too narrow )
- fit schwalbe 20 x 2.8" tire to it ( 13mm higher vs my existing 1.75" )
- take air out of the front shock until it's 60% compressed when i sit on it, to lower the height by at least 25mm versus where i normally ride at
- go hunting for bumps to make sharp turns on while pedaling
This is an intentional nightmare scenario to see what the outer edge of the safety margin looks like.
I know that even if i can't get away with this..
Moving weight forward > tire diameter > reducing excess fork angle... in terms of reducing front judder.
Thus if 2.4" is as tall as i can get the front tire, to make the pendulum pedal work.. so be it. But i'd like to see if we can get even bigger.
Ordered this front wheel with a 25mm internal rim for experimentation:
Front 20x1.75 Wheel Disc Brake with QR HUB