So I've spent some time planning the past few days after long hard days at work and no motivation to work on house projects...
I got an angle finder so that I could prop the chassis up to a 24.5 to 25.5 degree rake angle and assess how much the jacked up rear and dropped front would really have be sliding into the tank forward and putting all the weight on my wrists on this aggressive riding position solo racer machine... 1.75" or so riser clipons ON TOP of the upper triple clamp yoke and angled down and back will really help out with the riding position and lessen strain. Couldn't believe the comfortable position on a 1st gen ninja I was on last year, angled down and back, riser clipons, same ones on the Rick actually, but not using that triple.
Reading an article about modern suspension designs, I ascertained that the ideal swingarm angle in terms of anti-squat powering out of turns is as much as 12.5 degrees from horizontal, but many vintage bikes will have trouble getting over 9 degrees. Somehow sprocket size plays into the equation as well, but I have not read that far to see how that affects things as far as chain pull trying to raise the rear end vs weight transfer trying to squat the rear end. With the swingarm between 9 or 12 degrees and horizontal, accellerating out of a turn will keep the swingarm fairly planted at a constant angle under power, but as it nears horizontal and goes beyond horizontal squatting the rear, the weight transfer increases greatly and gives you substantially more rake and trail, causing you to have to back off the throttle as you lose your good cornering steering geometry, and thus not being able to keep the tight turning radius exit under power. I am shooting for 10-11.5 degrees, and plan on YSS shocks with 10mm ride height adjusters so I can play around with rake/trail and swingarm angle changes, which will also work great with the two sets of shock mounts on the Rickman CR 2nd gen swingarm (MUCH more stout AND HEAVIER than the first gen CR arm). Moving the 13" shock that came on the bike from the rear to the front gives me 5/16" or 8mm higher ride height in the rear. The rear suspension will be slightly softer, but in terms of rear end lift under power, the leverage gain against the shock springs will help keep things in check in terms of allowing weight transfer to balance out the steeper arm's tendency to pull inward under chain pull force.
Porn, on the dining room table of all places (hope wife doesn't read this while she's away for 6 weeks training for the wall of death thrillshow!):
^^^^^^^ This is propped up in position with the rake at 25.4 degrees so that I could measure the frame pitching forward being a minor 3 degrees, not too terrible! No offset neck bearings needed after this discovery!
So I set this all up so that I could check out how much the seat would be sloping forward if I got the rake set where I wanted it, or rather needed to get it based on the triple clamp offset achieving a desirable amount of trail... Turns out that with approximately 25.48 degrees rake, the frame is only pitched forward 3 degrees, as in photo! Heck, I can offset that with differing seat and tail section rubber mounts, and level the the tank to match the body lines of the angle of the tail! May not even bother, seems pretty good to me. I could try undoing Corbin's job of reupholstering the seat and stuff some more foam in the front and stretch the vinyl out more with the help of a hair dryer... will try as is first before any of the above.
After the rake and frame pitch conclusion, I determined how I was going to arrive at that. 715mm was the original Rickman 38mm dual disc fork length. 94-97 43mm cartridge Suzuki RF900R forks are 730mm and run a common diamater rotor as with many 6 bolt 78mm pcd Honda floating rotors. Clipons on top will eat up at least 35mm of fork tube, so 695mm effective fork length drops the fork just a bit at 20mm to help reduce the rake and trail, but not too much to cause major clearance issues.
Then the biggie, Loooonnngggg shocks! $479-$999 range in whatever offering I can afford at the time from http://www.YSS-USA.com, shocks in the range of 360mm with their +10mm ride height adjuster to quicken the steering in the twisties when needed... With the angle finder, I didn't want to get all the way down to the modern ideal of 12.5 degrees, but I toyed around at 11.5-12 degrees, and looking at the exhaust mounting boss, not much clearance with a large bolt head there, figured I'd limit it below 12. 14-11/16" was the absolute max I could run in the forward shock mount position. This may require a larger front sprocket and rear sized in perspective, just to keep the chain off the swingarm... geometry update is worth it though. 520 DID chain and Vortex/SuperSprox cogs will save weight, a few more links will be offset.
So I didn't want to drop the forks any more, and I wasn't comfortable with any more swingarm angle or any longer shocks.... where else to go? Tires, of course! Sadly, my top pick Pirelli Sport Demons took the backseat... I have DID 2.50x18 front wheels and 3.50x18 rear wheels. Shinko and Avon say 140/70 fits best on a 3.75 rim, but acceptable on a 3.50. that tire is 26.2 diameter and looks not quite meaty enough on the rear of a vintage bike, but is a superb handler for sure (shredded 2 of them, awesome grip and profile). 150/70 looks right at home with a taller section at around 26.8" in an Avon Am26, but only comes in 17" in the Pirelli, bummer. 3.50 is the narrowest allowable rim, 4.00" is ideal. Now, my 3rd or 4th pick was the Bridgestone BattleAxe BT45V, and it comes in a rare 140/80-18, nearly the same width as the 140/70, but the same height as the 150! Now we're talking! I hate adding extra unnecessary rotating weight, but my only other option to get the geometry right on target was hassle around with custom offset steering bearing adapters to un-rake the front end, opposite of what most chopper guys use them for! real pain with alignment, and a hassle to calculate all the machining angles for the bearings. Only one flat track place advertises this custom service anyways. 1 degree steeper (less) rake for $120 and a nightmare of aligning the eccentric adapters.
The other bonus (cosmetic detraction though) was that the BattleAxe BT45V's 110/80-18 is smaller diameter than an Avon RoadRider, 24.8" vs 25.2"! smaller front tire means more help reducing trail with a limited choice in offset of only one good OEM swap triple clamp option! I was shooting for trail between 3.75 and 3.85, with hopes of adjustment options towards 3.85"-3.9" for long hauls and a steepened switcheroo for say when I arrive in the West Virginia mountains or in the Red River Gorge for the DoTheTon.com annual Spring Thaw campout...
I've heard great things from a very few about Continental Attack tires, or Attack 2's or something (they come in a 150/70-18 I was told), but I have not looked into them yet. The BT45V's get great reviews, but when compared to Pirelli Sport Demon's, the Pirelli always "Goes to Eleven."