CBX Racing

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Re: CBX Racing

Postby EMS » Fri Apr 05, 2019 8:01 pm

Yes, it is "progressive". That's what "Pro-Link" stands for. The ratio between axle travel and shock compression is indeed 2.78:1 at full extension changing to 1.92;1 at full bump.

I am personally interested what number you have used or measured for the rake angle of the stock bike? The specification for that in common Honda literature is notoriously incorrect. It is NOT 27.5 degrees.
If you use 24 degrees and calculate with a change of 3.5 degrees, you are off quite a bit. This is another one of these "contentious" issues among CBXers, where one camp insists the rake and fork bridge offset is the same between Prolink and earlier bikes and the other camp says it is not.
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Re: CBX Racing

Postby Warwick Biggs » Fri Apr 05, 2019 8:55 pm

Thanks for that. I can now be a little more confident about what to expect as I experiment with raising the ride height.

My prolink rake angle came from Computrack metrology however, you have to allow for the fact that the bike was already modified and from memory at that time was on 18" Bol Dor rims fitted with Conti RaceAttacks, had a 640 Wilbers shock extended about 5mm and stiffer front springs. I'm trying to arrange another measuring session but it may not happen for another 6 months.

When trawling thru' the suspension part of the forum I noticed on one post that you mentioned using a "chassis program". Which one may I ask? I have been talking to GMD Computrack about providing a web based program to enable customers to bench test modifications to individual components. There are legal concerns preventing this at the moment that have to be worked thu'. I'm interested to know who else is providing chassis software.
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Re: CBX Racing

Postby Warwick Biggs » Sun Apr 07, 2019 10:19 pm

I should also add this EMS; I had the bike Computracked before having the head stock cut, pulled back to 24 degrees and then shut. I haven't had the opportunity to measure it since so that rake angle was a the measurement with the bike as described above. Just using basic tools when it was in the jig after being cut and shut, I can say it is now around 24 degrees.

Currently the forks are down 8 mms from stock and the ride height is up about 2mms at the shock to about 297 mm length and if my arithmetic is correct that should equate to a bit less than 8 mms. Once I get it back to the track I will start with these settings and ten drop the forks fully so that they are flush with the top triple clamp and then try bringing up the rear in 1mm increments. Hopefully, if it all works out OK I will have the same quick and stable steering I had when I had the head cut (I should clarify here that the 24 degree rake really improved things and enabled me to change line mid corner without compromising stability at speed) but I will have an additional 1" of ground clearance.

I've attached some pics of the Computrack measurements I have described above.....
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Re: CBX Racing

Postby Warwick Biggs » Sun Apr 07, 2019 10:21 pm

And here are a few more measurements from th same session....
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Re: CBX Racing

Postby Warwick Biggs » Sun Apr 07, 2019 11:28 pm

Perhaps I should summarise where we have come from and where I hope we are heading.

With the conversions to date the best compromise between handling, grip and ground clearance was achieved by the simple expedient of bolting is a set of wider 18" Bol Dor rims (those boomerangs that people seem to find so attractive). I still had a bad speed wobble that was solved when I changed from Avon and Dunlop tyres to Conti Race Attacks. They have a stronger sidewall and handled the weight of the CBX quite well. This was the best compromise overall. The move to even wider 17" rims in order to have a better tyre choice was not so simple and produced a bike with better grip but it was now so slow as to be unable to easily change line mid corner, useless for racing. The 24 degree de-rake was imperative to improve things, restoring and actually improving the steering. But in doing so and using that improved handling I hit the deck with the crank end caps and front exhaust headers, meaning ground clearance became a problem. Something that I'm now attempting to address.

Of course, you may say I should have stuck with my pretty 18" wheels and that would be a valid conclusion to draw. Hindsight is a wondrous thing.... Anyhow, there are other options still to be explored, apart from fiddling with the ride height. A more modern swingarm than the Prolink would allow a 5.5" rim and 190 rear tyre that would not only give improved grip at race pace but improved ground clearance at full lean, assuming that I still have any trail to spare. Another reason to re-measure the bike on the Computrack. I suppose this all sounds like a lot of arcane fiddling about to little benefit. It has been said.
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Re: CBX Racing

Postby Syscrush » Tue Apr 09, 2019 11:02 am

Thanks for sharing all of this info, Rick.

I would definitely say that it's worth listening to Roly, but ultimately you should make your own decisions based on the approach that makes the most sense to you. Someone telling you that this change will result in that problem only means so much when we're talking about 2 different bikes, and 2 different riders. I would always take my own data & results plus the analytical approach like you're doing over pronouncements from a guru.

Another factor to consider in terms of getting the cornering clearance that you want is that the static ride height is only half of the picture - maybe it would be a good idea to increase the spring rate front & rear so that the suspension compresses less - which would give you more clearance in high-speed turns. Obviously this would have other implications (including possibly giving up some traction), but something to weigh as you work out your holistic plan for further improvement.
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Re: CBX Racing

Postby Warwick Biggs » Tue Apr 09, 2019 8:29 pm

I've kind of tried that by mistake Phil. At one stage I over filled the forks and achieved hydraulic lock - effectively a rigid front end altho' funnily enuf' I didn't realise it until I unloaded the bike at home. You may think that in itself is very telling but when you are constantly changing things it is possible to overlook the obvious. That is a bit more than you are suggesting, I know but it certainly gave me a better understanding of the surface irregularities of the track as well as the effects of taking stiffer springing to the extreme.

Trevor Manley's words still resonate ... "You've just got to try harder!" referring to changing my old fashioned, 'blend with the bike' riding style. Standing the bike up in the corners by moving your body weight off the bike to the inside of the corner or "hanging off" in rider parlance. I think I'm slowly making progress on that front altho' its a very physically demanding thing, clambering all over the bike, corner after corner. Especially when you are trying to thread the needle. You really do have to achieve a higher level of physical fitness as well as aggressively disrupt your natural rhythm. Not helped by my 6'1" 90kg 67 year old, creaky frame.

But its' a truism that you don't go faster by standing still. Development is both the process and the goal.
R.
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Re: CBX Racing

Postby Warwick Biggs » Sat Apr 13, 2019 7:02 am

Here are some more pics so you can see our latest changes. Firstly, the new Delkevic 6 into 1. I assembled it on the bike, starting with the headers and working around with a rubber mallet while keeping all the fixtures loose, then tightening up working from the back to the front. I don't know if this is the best method but everything fitted together, even the muffler fitted the period correct Raasq rear sets.
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Re: CBX Racing

Postby Warwick Biggs » Sat Apr 13, 2019 7:05 am

IMG_5870.JPG
Very shiny and well tucked in.
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Re: CBX Racing

Postby Warwick Biggs » Sat Apr 13, 2019 7:07 am

You can still access the oil filter and extended sump and it does not foul the centre stand (altho' I have obviously removed mine).
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Re: CBX Racing

Postby Warwick Biggs » Sat Apr 13, 2019 7:09 am

There is hardly anything to the short stubby muffler and it is well tucked in.
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Re: CBX Racing

Postby Warwick Biggs » Sat Apr 13, 2019 7:11 am

You can see the extended Wilbers is a very tight fit in the Prolink swing arm.
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Re: CBX Racing

Postby Warwick Biggs » Sat Apr 13, 2019 7:24 am

This pic shows the 520 chain conversion. Originally when I acquired the bike it had a massive 630 chain fitted. Why? A 530 is correct and a good 520 works just as well and saps less power. I use rivet joiners and then a dab of silicone for safety sake. I have had to repair cases in the past when a link lets go so I don't take chances. What you cannot see is the 20 tooth countershaft sprocket that required some mods to the cases to fit. You can see that I have done away with the gear lever linkage by the simple expedient of reversing the lever. This little mod makes for a much more positive feeling shift and together with undercut gears, reduces the chance of missed shifts. You can also see the extension to the LH swingarm so that the chain is covered where a foot could be pulled into the rear sprocket when you fall off (it happens!). This safety mod is required under our rules. Without it there would be a lot of one footed racers hobbling around.
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Re: CBX Racing

Postby Warwick Biggs » Sat Apr 13, 2019 7:26 am

The centre connectors on each side are secured to the headers with springs. You have to apply some muscle to fit them.
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Re: CBX Racing

Postby Warwick Biggs » Sat Apr 13, 2019 7:28 am

The Venhill quck action throttle took me 2 days to fit. I'm in discussion with Venhill about a few things and I will let you know the outcome in due course.
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