CBX Racing

[swarrans]

Hi Rick,. The ratio of shock length to ride height on the Prolink is definitely not 1:1
I recently replaced my shock and wanted to increase the ride height because the only Bridgestone tyre available in the UK was lower profile and made the side stand precarious - ie the bike wanted to stand too tall and not lean over enough.
Unfortunately I can't remember exactly the numbers but i think the ratio is more like 1:4 - so if you add 5mm to the shock length you will get something like 20mm at the rear wheel.
Hopefully someone will have exact numbers - although it is unlikely to be a linear relationship anyway because of the linkage geometry

You might want to check how the chain tension changes over different geometries too as i seem to remember it was quite dramatic when i looked at it when changing mine

Simon

[Syscrush]

I was not scraping anything at the limits of adhesion on the old high profile 130/80x18" Conti's but I know that Trevor Manley on 'the Beast' with the same sized slicks that I am now running but with a raised motor (the Dr Tom mods) was wearing through his crank end caps and occasionally lifting the front wheel off the ground on them mid corner. This makes me a bit trepidatious about tipping it in too enthusiastically in my track testing in a month's time. I think I will need the full practice day b4 the races to work out how to ride it with the reduced ground clearance. I expect it will also have a more nervy front end with the reduction in trail from the smaller diameter front wheel. I certainly won't be going gangbusters, that's for sure.

It might be a good idea to do your practice runs with some GoPro (or similar) cameras mounted such that they can watch the clearance on the end caps so you get some concrete feedback on just how much of a margin you have.

Good luck getting this stuff sorted out - it seems like it should be a lot of fun once you're over the trepidation!

[Warwick Biggs]

We travelled over 4,000 klms for our first trophy on the CBX. Third overall in the over 500cc Period 5 class at the Mac Park Seniors or ‘Old Farts’ in Mount Gambier in May 2017 run over 3 days and multiple legs. This could be the first CBX podium for some years, unless Bill Brint has enjoyed any recent success in the AMA Historic series and now that Roly Skate has retired his racers.

That is the best part. The other good part is that the new wheels and brakes all work OK and nothing was scraping as a result of 40mm loss of ground clearance in the conversion to 17” slicks. And I did have some really good dices. There was some excellent high class racing, particularly in the mixed classes where riders were gridded based upon the combined age of rider and machine. My 100+ Cup class winner Mark Lithgow on a 600GPZ had a phenomenal battle with John Snoad on a modern GSXR1000 in the 60 and over 500 and over race. The big Suzi was wheelying past Mark down the straight only to have Mark reel him in the bends with the 600 first over the line by a hair’s breadth.

The not so good part is that I generally finished in loneliness, well behind the leaders in mixed classes, including modern works Superbikes only scoring my class trophy on points. The worst part was the bad rear wheel chatter reappeared after last experiencing it at the Island Classic. On that occasion I put it down to the too soft and skinny 130/18 Avon. But this time I was running a 165/17 YCY Battleax slick on the rear. Upping rear wheel tyre pressure from the mid 20’s to the mid 30’s helped but I could not carry a trailing throttle at all and had to focus hard to have the throttle pinned as soon as I tipped in to avoid a tank slapper on the way out.

Because of a concern for loss of ground clearance I had put 15psi in the front forks to lift the front end a half an inch. Roly thinks this stuffed up the geometry and possibly contributed to the problem. I think he might be right because the last time I ran any air pressure in the front forks was, guess where – at Phillip Island.
So I was generally 4-5 seconds a lap slower on slicks than on the 18” Conti’s when I was hoping for a 5 second improvement. However, the new wheels and brakes are only the first stage of the conversion. Next, I have to arrange to have my Prolink shock extended by 40mm and a set of 30mm clamps made up to achieve the optimum 24 degree rake and 120mm trail, 30 degree swingarm angle and increased ground clearance.

The longer than normal racer trail is to make the steering lighter on such a heavy machine. My arms are still aching from pushing the lump around a circuit where corner speed is critical and the lap record is held by a 125, in spite of a quickish straight. Lacking a local race track within Cooee of my home, development is delayed and difficult because I can’t test the small things as I go and have to combine multiple changes at each meeting; never a good idea. Now I have to pull it all apart again…

Can anyone add to Simon's comments about the correct shock length to ride height ratio for the Prolink? If my assumption of roughly 1:1 is incorrect then my proposed changes will be totally wrong and all my efforts will be for nought.

Some pics;







Rick.

[FalldownPhil]

You are out there doing it, congratulations !!
And a podium to boot
Best,
Phil

[steve murdoch icoa #5322]

Rick, regardless of your competition or class you are RACING a CBX on the track and you both finished in one piece.
Don't see a "worst part". haha.
Congratulations!

[cbxmel]

Rick,

James Fisher of the UK cbx club has been racing a modified 79 with some success for nearly two years. His father Alan raced sidecar outfits with some success several years ago. Still gives exhibition runs with a cbx powered outfit to this day.

good luck with your endeavours

Mel Uk #1876

[Warwick Biggs]

Thanks guys. Does anybody have a clue about the Prolink linkage ratio? I'm confronting a significant expense to measure and model the linkage motion before I can resolve the correct shock length and knowing the ratio would help enormously.

R.

[steve murdoch icoa #5322]

Rick, i don't suspect this is info you are looking for but in this article it says a ratio of 2.78:1 at full ext. and 1.92:1 bottomed.
http://www.cbxclub.com/davespage/cyc81-3.html

[Warwick Biggs]

Yes thanks Steve, I have seen that and to it I could add Trevor Manley's advice that he measured the movement of the linkage on the Beastess and that it was 'fairly linear'. He has also suggested that extending the rear shock by more than 7mm would be foolish as it would raise the swingarm angle and make the bike unrideable. He thinks its irremediable without cutting off and re-angling the head stock a la Maquardt.

Nigel Pitch's advice is to place transponders on the axle and shock and actually measure the motion throughout the range. That makes sense, I guess. Some conflicting advice to work through. Or maybe they will both end up being correct?!

Rick.

[NobleHops]

Rick,

Looking at your photos it seems that you could pick up a lot of clearance by working on your body position, getting lower and shifting your weight to the inside. When I started road racing I was mashing my feet against the engine and grinding bevels onto my boots. When I retired two years later the only time I touched hard parts was when I was crashing.

Put the bike back to its sweet setup and shift your focus to your body: strength, conditioning, and position.

/$.02

[Warwick Biggs]

Hi Nils,

Trevor Manley says the same thing with less subtlety but to be frank, I'm not comfortable enuf' with the handling yet to be moving around too much. It is too easy to let the rear chatter turn into a tank slapper. I raced a production Honda 400/4 against legions of RD400's with some success many years ago and I had to step off it a looong way because the exhaust scraped easily so I can ride that way but not on the CBX, yet. With all that weight in the rear it has to be kept under tight control, so smooth and firm is the best way to go for this little wood duck.

At the moment there is too much loose weight in the rear and the geometry is still all wrong for a racer. I'm only half way through the 17" conversion and its actually slower and much heavier on slicks than 18's. The next stage is getting the suspension pointing the right way. As Trev and Roly have reiterated, the Prolink steering head angle is too chopper-esque and needs to be de-raked by a quite significant 4 degrees and the wheelbase shortened by at least a couple of inches. This was confirmed by the Computrack. These are quite significant numbers. Nigel's description of the handling I could expect with it as it is now was "like a barge" and to that I would only add 'with a loose cargo slopping around on deck'.

Hopefully, we will eventually get there. If not I can always go back to the 18's. At the moment it is too unsafe to go into a bend with a bunch of bikes in a braking duel because once I tip in I cannot change my line by much and its a physically big bike too. I can go late and wide but you always run the risk that if you're on the outside and somebody comes off, they take you out as well and its not any old track bike to fix up with cheap parts from the wreckers. So generally unless I have heaps of room and I'm confident of where the other guy is going then I bide my time and do my passing coming out of the corners or on the straights using the big six's grunt.

You might also have noted that the Tingate clip ons I use are quite wide and have a more touring rise. This is so that I have the leverage to push it in and haul it up with more ease. I haven't weighed it but I'm guessing its around 280kgs wet and remember that I'm 65 and not the guy I was once upon a time. The whole seating arrangement is still production bike too and up the straight I have to really haul myself forward. In the process I've missed a few clutchless up shifts because its difficult to hang on, push forward and back off the gas to take the load off the transmission all at the same time. I've considered a smaller, lighter fibreglass tank and race seat with bum stop but I like the proddy bike look. Its not a race replica. Its the real deal and still more production bike than racer so to my mind there are some aesthetic integrity issues that mitigate against the committed racer crouch.

If we can get the handling issues sorted then we will see what we can do. If you look at the pic of Trevor at the Island supers on the Beastess on the CBXWorld site you can see what is possible with a highly developed racer. We are still a long way from there, Nils. Sigar, sigar as the Greeks say - slowly, slowly.

R.

[Warwick Biggs]

For anybody interested in purchasing a CBX historic racer they should look here:-

https://www.gumtree.com.au/s-view-detai ... =manage_ad

I'm in no hurry to sell but at age 65 I am prepared if the right buyer were to emerge. In the meantime it gives a good summary of the current stage of development with some new pics. In particular, I like the German CSG Moto head sliders that have enabled me to remove the crash bars. To my mind the bars being square in shape never suited the aesthetics of the unframed engine. Now it looks much cleaner. And you can see my trailer with its RC166 decals.

I am still waiting for the right surgeon to put their hand up to decapitate the bike and re-weld the head stock for a 24/90 front end. Not a job for beginners or amateurs.

Rick.

[steve murdoch icoa #5322]

Rick, it has to be a tough decision to list your bike after all the blood, sweat, tears and emotion you have put into it.
Because i have enjoyed following your track exploits it pains me to say....glws.

[Syscrush]

In particular, I like the German CSG Moto head sliders that have enabled me to remove the crash bars. To my mind the bars being square in shape never suited the aesthetics of the unframed engine. Now it looks much cleaner.

I am 100% with you on that. I understand why people put crash bars on their CBX's, but I'll never like the look. Those seem like a very cool solution, I might wanna get a set. Thanks for the pointer.

I am still waiting for the right surgeon to put their hand up to decapitate the bike and re-weld the head stock for a 24/90 front end. Not a job for beginners or amateurs.

Surely some of your fellow local racers would be able to refer you to someone. Is there an online forum for your regional racing association where you could ask?

[Warwick Biggs]

Thanks for the sentiment Steve but I'm not expecting very much interest. Our Period 5 grids are shrinking because the replicas are so much faster and the genuine article is becoming too valuable to risk on the track. That just improves my chances for more podiums!

I've given the bike to a guy called Laurie Alderton who was captain of the Australian ISDE team during a successful era back in the day. In fact he has just come back from Bergamo in Italy where he again raced his favourite Maico. Not bad for an octagenarian. See, there is a m/c life after 80!

Anyhow, Laurie fixes frames so I'm waiting to hear what he makes of the job. It currently has a rake of 27.7 degrees so I've simply asked him to reduce it by 3.7 degrees.

I would like to have it ready for the PCRA 1 Hour historic endurance race at the end of August. Le Mans start and 2 riders mandatory. Last year I entered it with Mark Lithgow, a 1980 NZ superbike champion, as co rider. Unfortunately Mark fell off his bike on oil in one of the support races and pulled a hernia. The medics put the kybosh on any further racing for him so it was a fizzer and we had to withdraw.

This year his old crew chief has built him an early Gixxer special and if its ready in time we'll race that in the very popular Pre Modern class. If not it'll be the CBX, if the frame is sorted in time.

Syscrush, the contact for the engine sliders is Veronica of Wild Hair in Phoenix. Just google Wild Hair motorcycle accessories. She has them made in Germany. When I last spoke with her she told me it was 125 degrees in Arizona.