Team Fj Racer Suspension Ideas???

[andyoutandabout]

Peeps,
If you haven't heard already, Ron Oort is pushing Fj performance boundaries on the track. He's many ideas about suspension upgrades, but I'll just focus on swing arms. I know Pat favors the thunder ace and Tim Minns has gone the R1 route.
Question is about clearance. Can anyone with knowledge of these upgrades comment on tire / swing arm clearance. The idea is to run slicks and use tire warmers at the track, but we are not sure there's enough room to fit them.
Additionally he runs the 5.5 gsxr rear wheel, so not sure if that will fit and line up with the front sprocket without offsetting that.
Lots of angles and fitment puzzles.
Can anyone shed some light?
Thanks in advance
Andy

[Pat Conlon]

Hi Andy & Ron, the problem isn't the swing arm, it's the chain to tire clearance.
T-ace swinger with 180/55-17 with Michelin PR-4's, 1.2" clear between tire and side arms, 1.5" clearance from tire to front of swinger box..... however....
The clearance between the 530 chain and edge of tire is tight...only 1/4"....no way a blanket will fit between the tire and chain.
You can move the chain away from the tire by:
1) installing a longer XJR countershaft
2)  getting a 1/4" offset countershaft sprocket. You will lose the cover on the countershaft sprocket.
You want to keep the back tire centered so you have to move the back sprocket out to match the front sprocket.
3) removing the sprocket studs from the cush drive and use a countersunk machine head bolt that sits flush with the face of the sprocket. By removing the oem sprocket studs and nuts and using a low profile machine head bolt this will get the back sprocket as close as possible to the swingarm (away from the edge of the tire)
4) add spacers as needed between the cush hub and sprocket to line the back up with the front.
5) use a narrower 525 chain.
This should net you about 3/4" to 1" clearance between chain and tire.

I suspect the wider R-1 swinger will present the same problem, clearance between tire and chain.

This assumes Ron will be using a tire with the same width as the 180/55... if he could use a slightly narrower 170 racing slick, perhaps the chain clearance would be improved?

Cheers guys, Happy New Year....  Pat

[Millietant]

The FJOC here in the UK supported a number of FJ Racers with mods to their bikes to improve handling.

All of them ran race spec tyres and sometimes, depending on the class, slicks - some were very successful championship winning bikes, and pretty much all of them used a FJ swinging arm. Some of them used either a XJR 1300 output shaft, others used a shouldered countershaft sprocket (from a range of bikes) to get the extra tyre clearance for the wider tyres & slicks.

One option is to use a Hionda VF 1000 countershaft sprocket, with some slight machining, as detailed in the Thunderace swinging arm conversion by Marc Rittner - there are plenty of others.

Here's a link to the FJ Racer pages by Phil "Doc" Hacker - lots of great info there for anyone thinking of racing a FJ 

http://www.fj-racer.com/

[Millietant]

Posting about this made me look through photo's of the FJ racing - here's a one of Phil racing against much more modern bikes and showing the FJ was still a force to be reckoned with 

[andyoutandabout]

Pat - Ron and I spent ages on the phone trying to figure out why offset sprockets were necessary, thinking washers would do it. Of course, chain clearance. Doh - my poor brain.
Yep = sounds like a bunch of work for little gain. I would say the narrower tire would do, but Ron is on a mission.
Millitant - have eyeballed Doc's UK racer page and reviewed his weight saving mods etc. If they managed with standard Fj swingers, I suspect it'll do for us.

Mods to the Fj seem to run the spectrum of making a real world difference.
Front end forks with valves and braces or USD replacements make a huge improvement - fact
I wonder if changing the rear swinger would make any noticeable improvement anyway.
I can see how a nice shock would be advantageous (he's already got that)

Exciting times

Happy New Year to you both

Andy

[Millietant]

Pat - Ron and I spent ages on the phone trying to figure out why offset sprockets were necessary, thinking washers would do it. Of course, chain clearance. Doh - my poor brain.
Yep = sounds like a bunch of work for little gain. I would say the narrower tire would do, but Ron is on a mission.
Millitant - have eyeballed Doc's UK racer page and reviewed his weight saving mods etc. If they managed with standard Fj swingers, I suspect it'll do for us.

Mods to the Fj seem to run the spectrum of making a real world difference.
Front end forks with valves and braces or USD replacements make a huge improvement - fact
I wonder if changing the rear swinger would make any noticeable improvement anyway.
I can see how a nice shock would be advantageous (he's already got that)

Exciting times

Happy New Year to you both

Andy

Swapping to a shorter swinging arm (like the Thunderace) will take about an inch off the wheelbase of the bike.

This means that you'll need less lean angle for any given corner radius at any given speed - so ultimately, as long as you don't run out of grip (or talent), you can corner faster than you ever could on a standard FJ.

I'm just not sure anyone less talented than a National level professional racer would be able to make use of that extra lean or achieve the extra corner speed. 

[fj1289]

Andy - my landspeed/dragbike uses a 1st gen FZ1 swingarm.  It also runs a 6" R1 rear rim.  To get the R1 rim to fit with no mods on the sprocket side, the rim ended up offset 4mm to the right in the swingarm.  I countered this by taking all 8mm off the left side of the swingarm - so the tire ended up centered in the frame.  (Normally the FZ1 - or thunderace - swingarm gets narrowed by 4mm on each side). 

I think a talented enough rider exploiting the grip available from slicks is going to find some flex in the stock swingarm.  Probably less so in the newer swingarms.  I'll bet if some of the faster UK race bikes (and riders) had improved swingarms, their limits would be even higher!

The drawback could be changing the rear linkage setup.   I don't have all my old notes, but when I swapped the FZ1 swingarm on the street bike, I modeled the rear linkage in some software Tony Foale sells (motochassis.com).  The FJ (like most early rising rate suspensions) has a VERY progressive rate - probably best for pure street riding (more adaptable to varying road conditions and motorcycle loads).  Later progressive suspensions are a lot less progressive - and much better suited for track use.  As I recall, on the street bike I used the FZ1 swingarm, FZR1000 "rocker", and custom length dog bones to gear the ride height I wanted.  Pretty sure the analysis showed a less progressive rising rate like a more modern design (sometimes you just get lucky!). 

Any writeups of his project and racing anywhere?  Awesome!