RC30 forks

[93 VFR750 RC36]

Gents,

I'm looking for fork options for an RC30 special (former race frame) with a 750F engine.

Does anyone know the dimensions/specs of RC30 forks? I don't have any, hence this thread. I know they're 43mm right-side-up forks but that's all. I'm considering both RSU and USD forks.

The bike will be a mixed road and track bike. Race plastics but single endurance style headlight to allow day/night running.

The Options:

RSU -

F4/F4i or early F-Sport/600RR - if CBR600 forks are the right length then the whole front end, triples and all, might be a good setup. It would look pretty close and with decent valving/springs, performance should be as good, if not better than the original.

USD - Fairly wide open here from what I can see

RC45 - work well but too rich for my blood.

CBR600RR - Good option?

929/959, R1, ZX-6R, etc

Any thoughts or comments welcome.

[Veefer800Canuck]

How about CBR900RR forks?

[SEBSPEED]

Is there something extra special about the RC30 frame? If that's the only RC part you have, I'd be tempted to sell it and let it pay for a regular VFR frame and the forks...

[JZH]

I have one.

(RC30 fork leg, that is...)

How do you want it measured? Preload in, out, middle? I can't guarantee it's got stock internals, having never taken it apart.

RC30 forks have kinda unique quick-release axle-pinch bolts (mimicked by the early '90s CB1000F "Big One"), but require special axles, I think. They also have 25mm cartridges, rather than the usual Showa 20mm cartridges (again, off the top of me head). Bling factor would be up there, but practicality not so much...

Ciao,

[93 VFR750 RC36]

SEB,

Frame and swingarm. With the exception of a tank, forks and plastics, I've got most of what I need in bits. Engine, carbs, airbox, wiring loom etc.

I want a sports bike rather than a sports tourer. The RC36 and 36a frames are for a bigger bike and I've got one of those already.

This'll be an RC30 Special.

JZH,

Full unloaded length from cap top to axle centre please. Not including preload screw or the cap nut casting.

Thanks in advance.

Stew

[gll429]

check out http://durbahn.de/

[kgsmotorcycles]

Best right way round front end i ever used was the 45mm 98/99 CBR 900 forks.

They carry 2 finger good, silver 4 pot brakes similar to SP1. This blade ran 310 discs same as OEM RC30. Very good they were too!

I also used custom DBR(MSSKawasaki milling man) yokes and rear sets as they were cheap and avaliable.

My mate also uses the 98/99 forks on his race bike here on the isle of man and agrees with me they give race winning feedback through the clipons.... He came 3rd first time out on his modded vtr1000 honda. A very good result by any means... but thats another story..

My current upsidedown 929/954 forks have never felt as good, not yet anyway... Running gold brakes similar to the SP2...

A revalve and respring on my rear ohlins is needed(929/954 shock conversion), maybe front also on current build to bring things up to similar perfect feedback as the 98/99s forks did.

These brakes are 1 finger only, better, but the discs are 330s on the 929/954 setup so a touch more weight.

The tank from the RC30 is important as it is made of light weight ally ..££££

Its all about the final weight !

less is always more.... not my motto but one i use often..

The swingarm is also important as it looses plenty of weight in the hub compared to 750f, altho i would junk the brake for aftermarket for further less unsprung weight....

Then dont start me on oil cooler rad options.. as the 30 does not have one, but a water cooled option...

If you have an exhaust system that will fit and run on your RC30 frame with 750f engine then fine..... else make sure there is room for the oil filter - oil cooler option to fit behind the front down pipe if anything exhaust is fabbed up... saves a whole lot of head ache in the end....

Also avaliable, slipper clutches and lithium race batterys for the 748f engine.. all made in UK..

[93 VFR750 RC36]

I've been looking at the right side up CBR600RR forks. They're 45mm and carry the same brake sizes as the RC30. Probably similar to the CBR900 but slightly later.

I'm considering a composite tank, maybe fab one in carbon. I'm an aeronautical engineer by education and a homebuilder/fabricator by hobby so I thought this might be a cool option. I could do a custom airbox and ram air intake (similar to the Durbahn) that fit the bottom of the tank like a glove.

A slipper clutch is a must for me, we'll see where else I manage to go.

All good fun this planning.

[kgsmotorcycles]

If you can get a mold together for a vfr composite tank i would be very tempted, hopefully still with a good amount of fuel in the tank for the odd endurance race....

Its the only part i have not taken weight out of yet on my current vfr build..

Have no experience with the 600 forks, but have considered it cant be too much trouble... They can definitely perform...

I test a sigma slipper clutch on my 750vfr this weekend here... have an electric water pump also, but not plumbed in yet...

The lithium battery seems to keep a steady 14.2 volts even under load....so should run pump with ease.

My family are based in Wroughton, Wiltshire so not too far away from Oxford.... I moved to the Isle of man a few years ago to play bikes..

[JZH]

Update: found the RC30 fork, but forgot about the axle arrangement--need to clamp something of the appropriate diameter in there, but I don't know what diameter is supposed to fit! The RC30's quick-release clamps mean that the usual method of looking up the bearings or seals won't work (they are 28mm ID) so I'll have to see what other axles/rods I have that might work...

I also have a set of '03-'04 CBR600RR forks, which I'll measure for you while I'm at it.

Ciao,

[kgsmotorcycles]

Best right way round front end i ever used was the 45mm 98/99 CBR 900 forks.

They carry 2 finger good, silver 4 pot brakes similar to SP1. This blade ran 310 discs same as OEM RC30. Very good they were too!

I also used custom DBR(MSSKawasaki milling man) yokes and rear sets as they were cheap and avaliable.

My mate also uses the 98/99 forks on his race bike here on the isle of man and agrees with me they give race winning feedback through the clipons.... He came 3rd first time out on his modded vtr1000 honda. A very good result by any means... but thats another story..

My current upsidedown 929/954 forks have never felt as good, not yet anyway... Running gold brakes similar to the SP2...

A revalve and respring on my rear ohlins is needed(929/954 shock conversion), maybe front also on current build to bring things up to similar perfect feedback as the 98/99s forks did.

These brakes are 1 finger only, better, but the discs are 330s on the 929/954 setup so a touch more weight.

edit... To correct with new facts.. hopefully am correct this time.

After chatting to a mate of mine who did the similar conversion to his race bike, he tells me the billet yokes i used were more likely for the earlier blade as he tried fitting the cbr 98/99 forks with their matching year's yokes and they required further spacing to fit to his wheel, a vtr/blackbird 3 spoke.... same as mine, which did not need extra spacers... Only difference was the yokes which i am not 100% sure about their original fit... well until now anyway....

So, the earlier blade yokes(my billet ones) with any of the blade 45mm forks should be a bolt up pretty much

The 98/99 yokes must be wider....but improved brakes and larger 310mm discs.

If any others have done the same with yokes would be good to find out if they are wider....

[slo1]

98/99 forks, brakes, and rotors(?), with early yokes. That lets you use any of these wheels, vfr750/nc30/f3/S-hawk, etc.

cbr600rr 03-04 rwu forks are great, but a bit short. I have them on an nc30.

[JZH]

Interestingly, the RC30 fork doesn't seem to have an external preload adjuster, so I just measured it as is: 734mm from axle center to top of fork tube (the end cap adds about 1.5mm)

I also measured my 03-04 CBR600RR forks (with preload all the way out): 720mm from axle center to top of fork tube (the end cap adds 2mm)

And for good measure (sorry), I measured my 98-99 CBR900RRW-X forks (with preload all the way out): 730mm from axle center to top of fork tube (the end cap adds about 1.5mm)

Ciao,

[YoshiHNS]

Aluminum tanks are big $$$, but I'm not convinced that it is a good investment at the start. I picked up the entire plastic airbox assembly, and that thing felt like it was lead. Durbahn has the RC30 fiberglass/CF airbox, but that's still up there.

If you do make a CF tank, don't you also need to have a few layers of Kevlar in there? Can't remember if it was on the outside to keep the tank from cracking open as easy as CF, or on the inside because the gas would eat away at something in the CF.

[93 VFR750 RC36]

Thanks for the measurements, very useful. Anyone know what the offset on the RC30 yokes is?

As for the tank, I'd probably use a combination of carbon and kevlar. I have some experience with composite aircraft fuel tanks so I'll just stick with the same technology to start with.

[kgsmotorcycles]

Agreed with the carbon Kevlar mix... either sheets of carbon Kevlar mixed already or single sheets of carbon then Kevlar laminated.

Same idea i have been building high spec boats with for some years now... not the fishers.. but proper $$$$$$ yachts.

F1 cars use a softer type Kevlar inner that flexes on impact, but wont split not the same as but similar to your bullet proof vests and then a carbon outer. But thats all different development and money again..

It is the resin that will hold the fuel!

The outer or first application to your mold will be a gel coat to provide a tidy finish of your choice.. clear coat if you like to see the matting.

ATLAC 4010 or 382 or 590(high temp stuff) is the heavy duty resin used to coat the inside of massive industrial water or oil tanks among other industrial applications i have personally coated as a laminator working for a company called Sui Generis in the UK.. The matting laminates simply provide strength and structure for the resin...

There are other resins that will do the job, but Atlac is hardcore stuff...

[V4 Rosso]

Interestingly, the RC30 fork doesn't seem to have an external preload adjuster, so I just measured it as is:

No problem as changing preload barely changes the fork length. The top out spring is rather stiff compared to the fork spring.

[JZH]

Thanks for the measurements, very useful. Anyone know what the offset on the RC30 yokes is?

You're welcome.

It's either 39.5mm or 40mm, depending on who you ask...

Ciao,

[93 VFR750 RC36]

JZH,

I've just found data that suggests the RC30 offset is 37mm. Sound right?

Stew

[JZH]

Dunno. HRC did make different yokes with different offsets, so the correct answer is probably not so clear as with other bikes. I don't have any RC30 yokes to measure, so I have to go on other people's claims, but I think 40mm (or 39.5) is probably correct for a stock bike.

Ciao,