Dholda Honda CB1100R with Conti Road Attack 2 CR , winner of the 4 hours of Spa endurance classics.
http://www.dholda-classics.be/bikes.php
I find some VERY VERY interesting innovations within this thread. For one thing, I've GOTTA check out "HOWELL"'s build thread, more than anything 'cause of that light-weight compact REAR drum hub, as per the Fontana 250mm 4LS up front. I've always been curious about this type of thing - "how low can you go", in terms of swapping out the OEM drum hub for something lighter but set up with good shoes, maybe some 2LS actuation, etc.
But more on track with what I'm doing right NOW, as relates to my "CB900K0 Bol Bomber" project, I find it very interesting to see what team DHOLDA are running for rotors up front.
One of their yellow bikes is on Wikipedia IIRC, using the 296mm dished CB1100RB-only (now in re-production form via Metalgear in Australia, and cheaper than their regular SOHC rotors at that!) on what could only be (to MY mind anyhow) the one-year-only, one-model-only, Canadian-only, POLICE-only, dual-disc wire-spoke FIVE-bolt front hub - from the CB750P7 or thereabouts. FULL-ON 24-carat Unobtainium right there.
However, what we see HERE are some RCB's -
(((Honda gave 'em full bikes from what I gather, but DHOLDA did their own tuning & set up their own suspension etc? Interesting that the WORKS bikes still beat 'em anyhow, ennit? I suppose the DHOLDA & JAPAUTO & "Honda Britain" teams also did well in their own right - Far more fascinating that in this era there were still a few SOHC 999cc engines running against the new DOHC engines, and both of 'em in alternative chassis. This is what I love about Endurance racing, is the whole mix-&-match approach not to mention the independent teams etc.)))
But yeah - THESE bikes might be running light-weight PVM Magnesium rims & all of this other fancy chassis tech & running gear. But look at what they're running for ROTORS - up front at least - the vented 296mm GOLDWING rotors, not just CB1100R versions but those are distinctly GL1200 center carriers in some of 'em.
Here I had been humming and ha-ing over whether to KEEP mine, from the Comstar rims over to the new wire-spoke conversion. Gonna be a pain in the ass, and the Metalgear-AU catalogue specs would indicate that it's impossible - and yet I've SEEN pics, GOT pics, of the vented outer rotors stuck onto the six-bolt SOHC era GL1000 etc center carriers. If these babies won't work, perhaps it's the somewhat more rare REAR vented rotors from certain GL1100 models, which should swap over to the six-bolt carriers. Which is to say it'd be even MORE of a pain in the butt trying to dig up a good pair of those guys -
But apparently it's worth it? I mean, these DHOLDA racers would've been a lot easier to set up with the six-bolt rotors given those SOHC-era skinny version PVM rims - So you'd think some cross-drilled early SOHC CB750K rotors, themselves also 296mm, would be the go-to set-up. Even if they're using later era five-bolt PVM rims or had converted the earlier version as such, there's a five-bolt CB750A Hondamatic 276mm rotor, just like all of the other SOHC-era 296mm discs, for the CR750 dual-disc look. And these thick vented things are definitely heavier than the earlier SOHC 296mm rotors, and no doubt more of that mass is outboard where it counts even worse. And you can't SKIM any of that weight off, 'cause the two outer sandwich layers are already pretty darn thin, and I've even found a worn-out rotor which seemed to get a regular WARP" where the thinner wearing surfaces had seemed to bend in between the gaps - just that wee lil' bit, there was simply a "washboard" characteristic to the worn down outer faces. If you were to cross-drill 'em it's either gonna have to go through the inner section which keeps the outer halves together, or avoiding that & hitting just the "skins" it's not only gonna have limited effect (holes of a diameter approximately that of the materials thickness are only going to keep surface area more or less the same, so you'd be talking about a whole buncha holes less than 3mm diameter) and you'd probably negate the whole air-vane effect by shortening those inner channels - Seems redundant to cross-drill the things. If anything, search for the lightest version of center carriers and I'm guessing that's just what DHOLDA did in choosing the '84+ vintage discs.
Now, the dished CB1100RB-ONLY discs are the lightest of all period-correct 296mm types, so you'd think they'd use 'em but then again they're very rare & ergo $$$ parts after all - Still, they've gotta still be available enough to use 'em for annual competition only? Maybe they would if they could. And on that note now that they ARE available again, it'll be curious to see whether DHOLDA makes the switch in 2016 ... or in any subsequent pics, as these ones are dated back to 2012 - Gotta dig around for newer pics....
Somebody should ask Metalgear just WHEN they introduced their reproductions - I knew of their 276mm dished rotors for several years now, in fact I was ignorant of the full 296mm spec of those '81 homologated racers until a few months ago - I had assumed they were simply 276mm discs like all of the CB750F/CB900F CB750F2-SOHC etc. But you've gotta wonder - did they bring out reproduction rotors for a series of 1050 bikes? Or were more DOHC-4 enthusiasts & Goldwing nuts etc, requesting their 276mm versions be up-sized? Either way, it's simply awesome that they're offering the things! As for the 11mm thick VENTED discs though, nobody's making a replacement for THAT version, and it's complicated enough I wonder whether they ever will....
One would think, I mean - If I had MY druthers, which is undoubtedly feasible for a big well known well connected team like DHOLDA, it would be feasible to replace the outer rotors with some cross-drilled Cast Iron, or any other improved materials. Is it "ISR" that offers the superior stainless rotors with the better coefficient of friction?
So what's the deal here? Are they doing this for some DOHC-era authenticity? They're from 1981 model Goldwing & CB1100R, more to the point those solid center carriers are GL1200 ergo 1984-1987 period-correct. So if that's why they're doing it, they're a tad bit off the mark. I could see how some GL1200 carriers & solid outer discs from SOHC etc could make for some decent replicas of '76+ RCB rotors. Once I realized I was gonna have to mix-&-match the carriers, this was an idea which occurred to me, for some replica '76 RCB COMSTAR rims, with Akront "NERVI" rims on 18"/18" spokes, & CB900F front hub with possibly a disc-converted CB250N/CB400T rear drum or a lump of billet etc etc. Much as I love the fat alloy wire-spoke rims I'm building now I'm just as interested in a "re-invent the wheel" COMSTAR project. Even if it's Boomerang rims using that rear drum out of an XBR500 for the disc conversion etc - or two front rims what-have-you. So too, I've been obsessed with finding that CB750P7 Canadian-spec POLICE hub, and whip up a whole SCHWACK of different 5-bolt rotors for 'em, to be able to use the same rotors on either wire-spoke OR Comstar wheels.... Sure would simplify things that way, if one were to run say, a set of dry-track tires on the wire wheels and wet rubber on the Comstars. To hell with all of the aftermarket stuff, I'm talking about using Akront "NERVI" rims, where my wire-spoke 4.25x18" Akront weighs the same as the 2.50x18" hollow-shouldered version D.I.D. rim from a disassembled CB900F rear wheel - This would make a HUGE difference over the OEM version, and then figure out a way to either replace a smaller hub or use a bolt-up cush-drive on a front hub, etc etc. I'm hopeful that a pair of Comstar rims build this way would blow away all of these PVM Magnesium wheels. Diggin' the idea of the "TECHNOMAGNESIO" rims, where the Akront "NERVI" rim is bolted/riveted to a five-spoke core of cast/forged Magnesium. MARVIC did the same thing, albeit with three fat spokes inboard of both "Nervi" and regular old flat-deck Akront rims. But there's nothing more COOL on a Honda than an actual pair of Comstar rims. All the more cool if they can be rendered a little more "performance-oriented"....
WHATEVER. The point being, this seems to be a "GREEN LIGHT" on using them CBX pro-link / GL1100A Aspencade / GL1200 / CB1100R '82-'83 composite vented heavy-assed thick rotors.
On the one hand, it seems like early SOHC 296mm rotors in good useful condition are in scant supply, but then again if you SKIM the things, you restore the surfaces AND shed excess weight. I would think the economics of good SOHC rotors for a serious race team would be less about availability & more about the labour & tooling in setting 'em up right.
Whereas, THESE guys are still relatively cheap. Despite the prices of identical parts taken off '82-'83 CB1100R versus those from '81+ GOLDWING, & even CBX pro-link - where CBX may be "enjoying" increased values these days I'm under the impression that the early twin-shock models far outshine the later pro-link versions. But yeah, Goldwings are still the cheapest source of these rotors.
I dunno - I can see the better value for MY bike, as opposed to skimmed & cross-drilled rotors which probably STILL can't attain the level of surface area which the vented discs have. But for a top shelf team?
There's gotta be something to it! My GUESS would be that the added mass is actually of value here, for it's HEAT SINK properties. Which when paired to the massive surface area of this design, has got to allow for some very heavy brake usage, without penalty of fading at any point. The mass being enough to keep it cool during the slower corners - then once you hit the straights and gain some speed you're gonna dissipate that built-up heat and hopefully get 'em down to ambient temp or closer to it.
Would be nice if one could somehow dress these things up to look correct for a SOHC-4, maybe just a thin skin over the vanes in the "midriff" area? Possibly even just some silver paint on 'em, with blacked-out center carriers or swap 'em onto SOHC-era 6-bolt carriers of course, they might just stand in for bone stock CB750K/CR750 rotors.
Though I'm sure they'd be superfluous in all but the most demanding applications, hey? Maybe, 100HP+ big-bore monsters, for heavy track use? I'm sure a dual-disc set-up with the regular early 296mm or possibly even 276mm rotors would likely be more than enough for bone-stock motors and street-bikes. But say, upwards of 900cc's and ridden as a get-away for bank robberies or some such - for THIS I'd suggest trying it on a SOHC-4.
For myself, well. For the time being I'm gonna try & satisfy myself with something like a CR750 look-alike front end on my "CB900K0 Bol Bomber" - however, recent images of the '67 MV Agusta 4C6 have me worried just how close to the CB450K0 Black Bomber a DOHC-4 even COULD look, so I'm all the more hard-pressed to come up with a DRUM front end for the bike, being the "Faux-Leading-Shoe" GL1500 thing, ideally with 310mm rear discs from GL1500SE but 296mm OEM rotors from GL1500 front end will have to do. With that, MAYBE just MAYBE this bike will look somehow "correct".
And with that big fake front drum, one might THINK I'd consider an internal disc wire-spoke converted CBX550F fake drum. But I'm thinking instead, I'd like to run an actual DRUM rear hub. And for the 985cc DOHC-4 I'm thinking this for once would be a good application for the OEM 750 drum. I'm whipping up a light-weight DOHC 750 for my kid to ride, when she outgrows the "KZ440LOL" with it's little Suzuki 4LS etc. And I'd really like to run a bigger 4LS on it, with the 4LS-only converted 39mm CB900F fork from the KZ - but will very likely stick with the dual-disc 39mm fork on it, with the 296mm rotors etc. However for IT'S rear drum, I've been thinking for some time now just which of the smaller drums would be appropriate.
(This is why I'm so fascinated with HOWELL's pics!)
So I've got a 3.50x18" "Super-Akront" super light-weight RIM for the thing, which sadly can't be set up tubeless 'cause these older rims don't have the bead retention ridges. Ah but they're GORGEOUS though. But yeah, it's a pre-drilled rim, set up for a KZ rear drum. I've always figured I'd just swap a Honda drum straight across. but NOW I'm giving serious thought to whether it'll fit the early KZ400 40-spoke rear drum. It's a massive weight savings, yet it's a full 180mm drum.
(I'd somehow gotten it into my head that the SOHC & DOHC rear drums were 190mm???)
I had a KZ650CSR drum and an early KZ400 drum side-by-side, and it's a HUGE weight savings. Narrower for sure. The main difference between the drum linings themselves would seem to be the thickness of the lining, and a little bit of width as well. So yeah, this is a drum which you could over-whelm with HEAT FADE a lot quicker than a CB750K or other KZ drums for that matter. But I'm hopeful that I can whip up some good air vents for it. Maybe even find a sprocket type replacement for the belt-drive outer pulley on the light-weight rear sprocket carrier slash pulley center carrier - from the KZ454LTD liquid-cooled model. Some custom stuff that. Truth be told, I've also got some NOS belt-drive bits for KZ400 and I'd really like to see whether this could be converted over to work on the DOHC Honda. Would be nice either way. But the main point of wanting to use that KZ454LTD rear carrier is to get more air blowing through the drum - I wanna set it up as a "FAN" of some sort, to suck air in vents & scoops on the right side and out the left side via the center of the sprocket/pulley. Well, I'm thinking of setting up an alternative rear wheel and/or pulley for the KZ440LOL, the key factor being that the KZ454LTD carrier should fit the smaller 36-spoke drum, and doesn't have the outer diameter suitable for the 40-spoke hub. But it would be a nice test case to be able to run the same drum brake on both bikes and to play around with the ventilation thereof. There's an earlier version of this drum, from the Kawasaki S1 or S2, too-smoke triples & I believe it was even used on the H1 500cc too-smoke triple - anyway it looks just like the KZ400 drum but it's got four huge triangular holes in the central wall, where the later KZ version has a casting in much the same shape, as though the holes were simply not milled out. But yeah, this should indicate the possibility of cutting some holes to vent the drum from right-to-left.
Of course, if and when I ever get around to sticking a FULL-sized drum on the back end of my 900, I'm keen to try some new mods with that one as well. Being that it's so much heavier built, it should be able to take some lightening holes. And I realize this is probably the most "death defying" modification I want to try out, but I want to CROSS-DRILL - the friggin' DRUM lining itself. An old trick of automotive hot-rodders, it's surely far more suitable for say, a Harley "Juice-Drum" or Norton Commando etc - 'cause they're one-piece solid cast "BELLS" of Iron, whereas all of these Japanese hubs are what are called "AL-FIN" which is to say a machined ring heated & inserted to the mould where the Aluminum is cast all 'round it. Very different effects were you to drill the one vs the other. But yeah, I wanna try it, just a little bit at least. Maybe only a half-dozen holes or less, and small ones at that. The REST of the hub however, the Aluminum portion, I'm gonna ventilate the living heck out of that thing. I only wish to heck I could do the same with the '75-'76 CB750F1 rear DISC hub that I've got on hand for the 1st rear wheel I'm building for this bike. Got an identical 4.25x18" Akront rim to lace to a FRONT hub, with bolt-up cush etc. But somehow I don't think that's gonna LOOK right with the big front hub I'm eventually sticking onto this bike. Besides I expect the best weight savings I'll be able to achieve with this alternative rear disc hub, it's only gonna be on par with the drum anyhow. And I'd bet that on a dollars-to-donuts comparison between OEM drum & OEM disc rear brakes, the drum's probably got the better one-shot PANIC stop force. Sure it might fade with heavy repeated use, but truth be told with MY riding style at least, the rear brake doesn't even get used that much.
You've gotta wonder about the possibilities though. Of a really well set up rear drum hub, one that's either too small to lock up the rear wheel entirely, or set up in a dual TRAILING shoe linkage so as to obviate any self-energizing effects of the leading shoe - To use the rear wheel for controlled rear-wheel SLIDES, the way several famous former dirt-track riders brought to road racing. I dunno if I'd wanna ride like that on the street ALL of the time, but it sounds pretty exciting all the same. Pretty safe bet you'd wipe out in these parts. What with all of the sand & gravel spread on the roads during winter. (It sucks, but I wouldn't trade our endless stretches of remote unsupervised back-roads for anything!) Yeah I guess when it boils down to it, I'd want a certain brake set-up for street and a certain brake set-up for the track.
Doesn't only go for the rear brakes either. Here I've been looking at these FRONT rotors, these big thick vented 296mm discs sitting on my CB900F - one of the first upgrades I did upon purchasing this already tricked-out bike, and I've been trying to figure out how to KEEP 'em with the wire spokes, rather than just pop in the usual SOHC discs, I've been hunting for a five-bolt hub to utilize what I've got AND the SOHC discs in five-bolt form from CB750A Hondamatic (on Comstar-equipped versions only) plus the new production CB1100RB dished rotors - the best of ALL worlds, if one could pull it off. Might just be worth welding & re-drilling the Metalgear CB1100RB dished-discs (or ordering custom drilling if possible) plus swapped carriers in these babies, and some ordinary SOHC rotors - might just be less trouble & expense than the Canadian Police front hub anyhow. Certainly less trouble & expense & EMBARRASSMENT of running a Hardlyableson hub up there. Sure, they're five-bolt. But all of the other dimensions needing modded, adds up to a considerable expense as well. A pity, 'cause any problems with the rotors and they'll need to be done over again. But yeah - gonna swap the center carriers, & can't yet afford the Metalgear rotors anyhow.
But yeah - my POINT being, I was thinking of keeping the vented rotors on hand, being that my main purpose in upgrading & detailing the paltry 39mm front end anyhow, was for this planned DOHC 750 light-weight single-seater for Her Nibs to ride, and the whole point of the thing being that it be a light-weight bike of course the CB1100RB discs make the most sense, that or some heavily drilled SOHC rotors.
And then I got to thinking about taking these bikes across the Rockies to Vancouver Island, and how much as I'D love to whip through the Crowsnest Pass with all of it's twists & turns. However, the KID well she's a great rider but probably ... BAH - what am I saying? SHE'D be in great form to thread that needle. It's ME who's gonna have to do a re-think & cross the Great Divide via the Coquihalla highway straight up & straight back down again. Which is to say - coasting on those brakes the entire way down to sea level. Might as well turn the damn engine off, if it weren't for the fact of engine braking. Sure would be nice if you could engine-brake with the engine turned off somehow, but it's the fuel which keeps the damn thing cool, and a carbureted bike would suck fuel anyhow. So yeah - you're left with just the brakes the whole way down.
So for THAT purpose, I can see really heavy-duty rotors such as these having a purpose on the street.
Honestly though, I try & wrap my head around folks using 'em for a REAR brake now THAT one's hard to understand. I mean, unless you're constantly dragging the brake to fight the torque of the GL1100 shaft-drive? It's bewildering. Even on the biggest most powerful 1123cc CB1100F's & CB1100R's, or GL1100's & GL1200's - VF1000's & VF1100's for that matter, the OEM 296mm rear brake was already massive over-kill. So I toy with the idea of sticking one on the bike just for the triple-disc MOTIF if you wanna call it that, but it makes no sense at all. So I try & wrap my head around a 210mm version from VF1000R instead, but it doesn't seem like it'll fit this '75-'76 CB750F1 rear disc hub. Would be awesome with a disc carrier, even better on that FRONT hub wheel.....
Well, whatever - I just wanted to say, some VERY interesting pics in this thread. Completely different approaches for stopping a track-bike. But each of 'em helpful for my current projects plus the next ones over horizon.
Hella cool.
-Sigh.
