2x2 Build

W

wardog

Member
#21
#21
I ended up cutting 6" sections off of long u bolts from a block lift kit for a pickup. It has virtually no runout and pounding on it with a dead blow hammer did not create any runout. I still want to replace the inner nuts with coupling nuts, and of course some locknuts. I think this will be strong enough, but time will tell.



 
W

wardog

Member
#23
#23
I have been exercising my geometry skills trying to figure out this front end geometry. I believe I have a decent grasp of the principles, but I am having a difficult time finding real numbers to at least give me a starting point. Super wide tires and front drive make it even more a shot in the dark. I wish I could find the rake, trail, and offset of a Rokon.

This is what I have come up with. Please tell me if these numbers seem ok.
25" dia tire
2" offset
3" trail
23° rake

This will obviously be a low speed bike where maneuverability is key.
 
Motra

Motra

Active Member
#26
#26
Very cool idea! If you could center the hubs within the wheels you'd get more even bearing loading and better transfer of forces placed on the chassis, which would make it much stronger. With the hubs that far offset you'll have very uneven bearing loading and extreme and uneven vertical forces placed on the stubshaft which will cause a twisting of the frame where the axle attaches. But it's probably too late for that so just four more words..........................lots of frame bracing!
 
W

wardog

Member
#27
#27
Motra said:
Very cool idea! If you could center the hubs within the wheels you'd get more even bearing loading and better transfer of forces placed on the chassis, which would make it much stronger. With the hubs that far offset you'll have very uneven bearing loading and extreme and uneven vertical forces placed on the stubshaft which will cause a twisting of the frame where the axle attaches. But it's probably too late for that so just four more words..........................lots of frame bracing!
Click to expand...

I agree with the bearing loading which is why I used 1000 lb high speed trailer hubs with tapered roller bearings. However, centering the hub would not change the twisting forces on the frame all else being the same. Any single sided swingarm/fork will create twisting forces, mine is just multiplied by the extreme width. I am using 1.25" schedule 80 which has an o d of about 1.7" and .180 wall and also a 1" sch 80 support. Bending the big stuff almost maxes out my 12 ton bender, so Im not too worried about strength..... mostly just weight.
 
W

wardog

Member
#28
#28
Little bit of progress. Squaring up this frame is turning out to be fairly difficult. Once I get the pivot tacked in square I should be home free.




Got the steering pivot figured out. I couldn't decide on the rake angle so I made it adjustable.




Thinking about using this old CZ tank.

 
W

wardog

Member
#33
#33
That would be awesome if you can get the fork pivot rake and fork offset. I believe they have a 25" tire, so I can calculate the trail with the other numbers.
 
FordGalaxy

FordGalaxy

Member
#34
#34
Ok front fork is @ 75 degrees.
Center of pivot bolt to center of fork tube at the top of the pivot is 3/4 inch
Center of pivot bolt to center of fork tube at the top of the pivot is 1 3/8"
pivot length 5 3/8"
 
F

firebirdparts

New Member
#36
#36
Nice work! I also have a 69 Mark 3 Rokon. I thought it had some trail on the 15" wheels, but FordGalaxy may be right. If you look at pictures you can put a ruler down on a picture and it's close to zero.

I wanted to mention the Rokon is extremely maneuverable at really low speeds due to the near-vertical steering angle. You can ride at 3 mph without putting your feet down (most people don't, ha ha). However, high speed stability is a tradeoff. You may want to use more rake if you are thinking about riding at higher speed.

I was real curious about whether you were planning to run 2 right angle gearboxes. The old trail partner avoided the expense of that by running the front drive sideways through the steering head. One side (the right) swiveled with the forks and the other side was mounted to the frame. Good luck!
 
W

wardog

Member
#37
#37
FordGalaxy said:
Ok front fork is @ 75 degrees.
Center of pivot bolt to center of fork tube at the top of the pivot is 3/4 inch
Center of pivot bolt to center of fork tube at the top of the pivot is 1 3/8"
pivot length 5 3/8"
Click to expand...
Thank you so much. This info helps with my steering setup tremendously. And sorry it took so long to reply, I have been on vacation in Oregon..... it was great.
 
W

wardog

Member
#38
#38
firebirdparts said:
Nice work! I also have a 69 Mark 3 Rokon. I thought it had some trail on the 15" wheels, but FordGalaxy may be right. If you look at pictures you can put a ruler down on a picture and it's close to zero.

I wanted to mention the Rokon is extremely maneuverable at really low speeds due to the near-vertical steering angle. You can ride at 3 mph without putting your feet down (most people don't, ha ha). However, high speed stability is a tradeoff. You may want to use more rake if you are thinking about riding at higher speed.

I was real curious about whether you were planning to run 2 right angle gearboxes. The old trail partner avoided the expense of that by running the front drive sideways through the steering head. One side (the right) swiveled with the forks and the other side was mounted to the frame. Good luck!
Click to expand...

I have reduced the trail significantly from what I was planning. I am shooting for 1.25"-1.5" of trail, not so much for high speed stability, but because of the extreme width of my tires. I think that on uneven terrain or when leaning into a turn the effective rolling diameter gets smaller as the contact area moves up the sidewall. I believe this could potentially result in a negative trail situation which is why I would like a little extra positive trail built in, even if I have to give up a little slow speed maneuverability.

I am doing the front drive similar to the trail partner and also the arctic cat cub. Mine will have the front disc brake mounted on the steering jackshaft also.
 
You must log in or register to reply here.
Top