BUMP! A Bump and a HUMP for Bike-Porn value alone. Some lovely early period-correct rear disc-brake conversion bits going on right there. Nonsense caliper-hangers notwithstanding. Some truly worthwhile BUMP stuff to BUMP give a BUMP and a HUMP to.
(bump)
Am now officially declaring that I'm in love with those disc brakes! How big are they? They LOOK around 300mm-ish. Would that be correct? They look big even on the (ridiculously tall for a bike with racing pretensions) 19" front rims.
Is it true that the REAR Kimtab wheels came in 3.00x18", or is that just a mis-measured 2.50" true width? Surely they offered an 18" front though, hey? If not, I'd be keen to use the rear wheel up front, and an Aluminum rear specimen weld-widened for a matching rear wheel, say around 4.25x18" size. The hubs don't seem all that much different, so surely the rear wheel would require minimal modification for a front wheel, and could then take a 20mm front axle (Which IMHO is a mod we ALL should be exploring for the OEM Honda forks!) Maybe THEN you could talk my into a pair of these wheels?
I've always been curious about a Harley-spec (as in without cush-drive) 3.00x16" or 3.50x16" rear chopper sized KIMTAB wheel. Not so much for a chopper per say, but rather - for a BMW R100 or better still K100/K75 based '80s Superbike project, with 16" front and a rear Beemer Kimtab-clone "Snowflake" wheel weld-widened Kosman-Industries-style, out to 4.25x18"-5.00x18" - IMHO this could make for some truly awesome ... Cherry-It's of the GAWDS, '80s Endurance-Racer gorgeosity, but retro-fried to some early-mid to mid-late '70s aesthetic design sensibilities leaning toward the R80RT beauteous-hideousness end of the spectrum. Can you visualize it? Can I get an AMEN?
Okay, so I don't want to build the damn thing MYSELF - or at least not FOR myself.
(((I'd really like to SEE that bike built, though. The K100/K75 or S1000R version of which that is. I picture it as something like some bizarro race-shop prototype pre-production 1975-vintage K1, with all sorts of R80RT running gear and pre-production version of the R80RT/R90S/K1 slash pre-production Daytona Guzzi Australia "Doctor" style bodywork. Like a truly retro-fried early K100 prototype factory-team racer but built to late '80s tech specs. OR, a retro-fried R80RT homage S1000R for that matter. Any which way, it STARTS with the 3.00x16" & 4.50x18" Kimtab/Snowflake wheels on ANY sort of 1985+ era Beemer platform....)))
(((Hey - can you think of any OTHER use for a 16" chopper-spec Kimtab rim? I mean to say - A use for it which DOESN'T suck donkey balls? Harley Shovel-Head choppers would be out of the race by that definition alone. OR, if you chose they could simply LOSE the race in traditional fashion. Either way, that's NOT an appropriate use for a 16" Kimtab rim! The only alternative left would be to use 'em as a FRONT wheel on my K100RT/"K1RT" idea, OR perhaps to use THREE of the things, appropriately weld-widened, for a '70s era Beemer RACING SIDE-HACK OUTFIT project. As an updated counter-point to all of the countless '40s-'50s style Beemer-Boxer racing outfits with the Earles forks, drum hubs and grubbing up all of my precious Borrani 3.00x16" Record rims, that are so ubiquitous to the classic Hack-Racing scene....)))
*COUGH* Like I was saying, either way I don't plan on building such a bike, I'd just like to light the fire under the ass of some '70s/'80s Beemer Endurance-Racer fan to build it and take photos of it FOR me.
As such, for my OWN (immediate?) purposes, I'm not so much interested in the Kimtab rims or any OTHER cast-mag wheels for that matter. (Composites like wire-spoke and COMSTAR wheels are where it's at, IMHO.)
However I AM very much interested in those light-weight 1/8" thick period-correct rotors!
And that smaller Honda front caliper used as a rear brake, and it's a period-correct part? I'm VERY interested in that type of thing.
I've looked into the Hurst "Airheart" calipers, but much as I like their cast fins etc, they seem rather flimsy & small.
But if anybody's got a decent rear caliper of this type, for a compact lightweight rear disc brake - and/or the Kimtab original front discs? They're very very cool looking IMHO and no doubt a decent high-performance period-correct disc-brake. You could get the weight of a heavily cross-drilled version of the original CB750K0 disc yet still utilize the full surface of the working or pad-swept area.
That alone has got to be a key advantage of the Kimtab upgrade. Dunno whether it off-sets the Cast/Mag wheel factor which is to say, taking a bunch of mass off of the hub and moving it out to the wheel's periphery where it'll do ten times the damage to the bike's handling. I'm sure a lighter over-all wheel weight has gotta be better for suspension compliance, but the greater outer rim wall thickness of the cast/mag wheels will NEVER match the performance of a good light-weight brand/profile of the rolled extruded hoop-bent butt-welded COMPOSITE rim, such as a wire-spoke or "NERVI" type Akront rim bolted up to a rebuilt COMSTAR wheel - with a decent hub upgrade an "improved Comstar" wheel, (ie "front hub trick" type of deal or the smaller drum type rear wheels from CB400T/XBR500 with the hub converted to disc-brake or better still swapped out to a billet lump or disc type hub core cut out of a more modern 5/6-spoke cast/mag wheel) wheels such as this will ALWAYS display better characteristics than the cast/mag wheels. And if the wire-spokes seem too CUSHY well that's 'cause back in the day they were built that way intentionally, so as to supplement the lousy period suspension. Sure, they might have been an improvement upon the OEM inner-tube type chromed-steel rimmed wheels with over-built drums full of thick walled AL-FIN cast-in liners etc - But then again just about ANYTHING is an improvement upon that design! A re-interpreted WIRE wheel, with heavier gauge spokes and a light-weight compact rear disc hub or idealized lightened/ventilated drum, and light-weight period-correct extra-wide optimum-profile rims with bead-retention ridges and aquarium-silicone sealed spoke holes??? Will make these old cast/mag wheels look like the old western prairie frontier COVERED WAGON wheels which you know at heart they really are! THIS is my intention with the wire-spokes on my DOHC-4 projects, and down the road with some optimized Comstar wheels for some RCB replica type of #$%*.
ANYWAY yeah - Like I was saying before I so rudely interrupted myself: it's the BRAKE stuff from Kimtab which I'm primarily interested in here.
-Sigh.
POST-SCRIPT:
WTF would I want the Kimtab rotors FOR? One might well ask?
I've got some odd stuff going on with the back end of the "CB900K0 Bol Bomber" in that the Marzocchi Strada-II shocks can't sit right due to the piggy-back impinging on the DOHC-era OEM rear caliper - with the shocks flipped around to the front, the piggy-back canisters are VERY close to the swing-arm and you can see that they've "kissed" at some point in the past, when everything was at full extension.
And it's an original CAL-FAB alloy swinger, so I'm not all that keen to weld another bung on the underside for an under-slung caliper. I'd be open to a full-floating caliper, especially if I can get an alternative hanger for the VF1000R caliper, to up-size from it's 210mm vented rotor. I'm also not very comfortable with the huge heavy assed 296mm rear disc, so I'm down-sizing to 276mm max, preferably 260mm or better....
I've got two specimens of the 4.25x18" Akront rim, one drilled for the enormous heavy assed boat-anchor of a rear disc hub from CB750F1 -
(((The center core of which, sans cush-drive sprocket or rotor, weighs the same as the center section of the GT750J 4LS drum - which always gets such a bad rap as an over-weight brake!)))
And a 2nd which is drilled for the HARLEY rear hub, which will be laced to a Honda FRONT hub, plus a cush that I'm cutting out of a fire-damaged KZ750B conical disc hub.
(((A very light-weight hub in it's own right, but flimsy with it's epoxy affixed chromed-steel spoke flange on the disc side - good potential though, if an alloy flange were welded up OR if the original flange were solder-brazed to the core....)))
(((And yeah I already know which one of these two 4.25x18" rims that I WANT to use but I've already got the hub etc for the worse version, and the better one would involve some $$$ machine-shop services on top of more parts hunting & bearing swaps, custom spacers extra-long rotor bolts etc. It would be nice to use the light-weight compact albeit complicated version, and then use the "BIG hub" version on a weld-up SHAFT-DRIVE rear hub, like "6pkrunner" used on his wire-spoke CB900C chopper, for a GL1200-based DLF-1000 replica, or V65 based "CZ860K0 Sand-Cast" homage to the CZ Type 860 - more likely a Gold Wing I suppose, if only 'cause they're 50x as common on the ground around here....)))
No matter WHAT the two rims wind up being used for, it's very likely that the BIG rear hub will go onto this DOHC-4 build first and foremost, even if it's only as an interim place-holder wheel while awaiting funds and services to finish the IDEAL rear wheel - But what a pain in the butt to re-do the whole BRAKE system over again a 2nd time. And what an even WORSE pain in the "back-side", to use the already heavy CB750F1 rear disc hub WITH the enormous heavy-weight 296mm OEM rear rotor!
As such, it would be very very nice to be able to set up the BRAKE in identical fashion for EITHER of these two versions of the rear wheel.
So in this light, (not to mention the shock impingement issue AND weight savings) it would make a lot of sense for the FAT HUB version with the '75-'76 CB750F1 rear disc hub, to use an OEM CB750F1 rear disc cut down to 260mm/276mm. Possibly a center-carrier rivet-to-bolt swap, using a GL1000/CB550 front disc?
Or even better still: the early non-slotted dished one-piece rear disc from '78 CBX or '79 CB750FZ etc, but itself cut down to 260mm-276mm if not for weight shaving just to make it all work. The dished rotor is already very very lightweight, around 50% or less that of the 9-rivet composite disc. And the center "boss" hole plus one bolt already lines up perfect, as does the off-set. So really not much point in cross-drilling the damn thing, unless it's for the air-cooling factor alone, and at a sacrifice of it's already minimal heat-sink value no less. With that really low mass, the 276mm version really only sacrifices mechanical leverage over the 296mm version. Far smarter to try & shave that extra bit of weight from the HUB. But if it allows fitment of the "final version" rear CALIPER, and to flip around the rear shocks? Then it's WELL worth the trouble & expense.
As for the "final version" rear wheel using the "Front Hub Trick" hub, this could use a simple spacer with a front disc from either GL1000/CB550 in 276mm OR the 260mm 6-rivet disc from CB350F/CB400F modded for the 6-bolt pattern. Or possibly even a new bolt pattern drilled into the DOHC dished 276mm disc from CB900F itself, or CB1100F/GL1100/GL1200 276mm with the spiral-pattern center carrier, FT500 Ascot rear disc, etc etc.
However, from mocking things up, I don't feel it's a quick-fix to swap to a 276mm rear caliper from CBX750F, FT500, CBR1000F Hurricane etc. 'Cause the 2nd piston would still impinge upon the piggy-back shock, only 10mm lower down.
THIS is what's got me looking at stuff like the above pictured smaller SOHC-era front caliper on a DIY/Aftermarket (Same diff, in terms of fit & finish! Ha-ha.) alloy plate caliper hanger. 'Cause IMHO the later era CBR/VFR rear calipers have too much of a modern aesthetic to 'em, turning my whole "Retro-Fried" wheel swap into something more of a Super-Moto style wheel swap. For the hassle & expense, they'd damn well better look a #$%* sight better than Super-Moto #$%*e! Ha-ha. With the "Front Hub Trick" rear wheel I'll have to be especially careful to avoid these associations. That final version wheel is all the more important to seek out the SOHC-era or even '60s Aftermarket rotor and caliper - But I've an eye toward Honda OEM rather than the HARLEY type discs of typical "INVADER" rim rear disc conversions, plug-type insert drum-to-disc rear brake conversions, etc. Those look like ASS on a Honda, IMHO.
However, the KIMTAB rotors have something of the aesthetics from an early GRAND PRIX appearance/occurance version of disc brakes, IMHO - No doubt due to spending so many long hours ogling bike-porn of the old "Cycle" magazine BSA Rocket-III "70HP Beezer project" which had the full complement of KIMTAB wheels and brakes. Call it "the $415 option" if you will. Ha-ha. I mean, there were all sorts of tiny lil' rotors on early period Grand Prix disc brakes, as small as 230mm dual-discs on the likes of say, a typical Rob North Triumph. Not that bad for a REAR brake I suppose. But yeah these Kimtab discs could make a good set-up for an early CB450K0 based racer, or dual-disc/triple-disc conversion of the Sand-Cast for that matter. 'Cause they LOOK like they're around 300mm. Correct?
I suppose ONE possibly quick-fix might be to use some type of extension blocks in the shock clevises, something like the old "Lowering block" chopper/bobber things - stupid idea, ennit? Perhaps they could be reversed though? Probably the one truly safe way to do this would be to have extended lugs welded onto the swing-arm itself, perhaps with all of the other mods such as the Freddie Spencer Replica AHM Superbike style under-brace, etc etc. Only at THAT point, one might as well go to an under-slung mounting anyhow! So it might be tempting to jack up the shocks an inch or two, it might be tempting to add another 5-10lbs to the swing-arm which would be better expended on welding the frame itself around the swinger PIVOTS anyhow - There's just no compelling argument for modding the swinger, IMHO. So yeah, some type of bolt-up shock extensions, which I had thought was gonna have to be added to the TOP end of some extensively modded rebuilt Marzocchi shocks - If I had my druthers, I'd really rather have the CB1100R OEM shocks, or if they've gotta be the Marzocchi piggy-back item then let 'em be the Strada-ONE with the fins all over the piggy-backs, with the larger rods from Strada-II and extensive mods to the dampener shim stacks, etc etc.
But for the time being, the one mod which makes the most SENSE is to shrink down the rear rotor and go to a light-weight single-puck caliper - ideally in a period-correct style to match the riveted composite style discs.
Though I'm equally keen on some 296mm dished 5-bolt rotors from CB1100RB,(in replica form from Metalgear Australia, ideal for CB750F2 Comstar brake upgrades!) or for that matter FT500 Ascot if one were on a tighter budget. I've got my eye on some dual 296mm CB1100RB rotors alright, for a featherweight 750 DOHC build which I'm collecting parts for. However, in the interests of shaving the maximum wheel weight, I'm planning a rear DRUM with that wheel-set. (2.5x18 & 3.5x18 alloy wire-spokes, 39mm fork, some sort of dust-bin fairing to go with this odd-ball fairing bracket, etc - just needs an engine rebuild and some tires at this point!)
Come to think of it, I'd really like to stuff a drum onto this 900 build, it's just that the hub would look very out of place with the 4.25x18" rim - the 3.50x18" is ideally matched, aesthetically speaking. But every pic I've seen of the 'K drum laced into the huge wide flat LATER-era Akront rear rims, they just look STOOPID, look like the rim's just wrong for the whole damn bike. I dunno whether anybody else would agree with this assessment, but it's just the way I see it.
So HOPEFULLY the disc-brake version of these wheels don't look just AS stoopid as the drum types which I've seen. If so, I'll have to cap it off at 3.50x18" on the rear wheel, and go to the COMSTAR wheels for anything wider. For all intents and purposes, I'm sure the "skinny" wheel bike would probably be faster anyhow. It's really only about the Sport-Touring RADIAL tires, it's not some kind of "Fat Wheel Fetish" over here. Truth be told, either one of these rims could meet somewhere in the middle with a 150/70-16 tire. But what I'll be hunting for would be the skinniest specimen of 160/70ZR18 which are the most retro-fried & skinny size of tire which the modern tire types are offered in. And I've decided long long ago that the 180/55ZR17 stuff just look like CRAP on the DOHC-4, it just throws off the entire proportion & profile of the bike. I'm sure the FAT 18" wheels will likely do the same damn thing. I've seen 'em in wire-spoke, beautifully proportioned and with this same Cal-Fab swing-arm, on CBXtacy's wire-spoke twin-shock CBX - GORGEOUS. And I'm sure they'd pull off the same effect, as a retro-fried/IMPROVED version of the wire-spoke 2010-2016+ CB1100 wheels. For the DOHC-4 I guess it's up in the air.
It's comforting to think though, that if so many SOHC-4 836 racers are getting away with a CB500/CB550 rear drum, that the OEM CB750K/CB650 rear drum will likely be MORE than adequate for my 985cc DOHC-4 - One could well imagine the 200mm Magnesium 2LS drum from CR750 would be perfectly alright for a CB1100F/CB1100R or even beyond that, for the wire-spoke converted Interceptor-spec VF1100C Magna / VF1100S Sabre based homage to the CZ Type 860, which I daydream about CONSTANTLY. I really like the idea of a 200mm rear drum, skimmed out to 203mm with 8" British 2LS plate & shoes etc. Gotta wonder how much less a drum like that would weigh, even in Aluminum, than the OEM CB750K/CB650 rear drum.....
Well first and foremost, I'm gonna take a CRACK at the smaller more light-weight rear DISC brake!
And the KIMTAB discs seem like a really tricked-out way of doing that. Especially bolted up to a "Front Hub Trick" rear wheel, cut down to 260mm-276mm, and ideally with the smaller Honda FRONT caliper slung off a compact DIY style period-correct hanger.....
-Sigh.
