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Discussion Starter #1
Umm.....how important is a cush drive ie; squishy bits where you sprocket mounts to the rear wheel.

I've got a buddy who's running a CB750 front hub on the rear of his project bike with the sprocket bolted (via an aluminum adapter) directly to the hub. He's flogged the shit outta this thing and it seems to be holding up.

So really...what the need adn true purpose?
Anyone?
 

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Discussion Starter #2
.....anyone?



..............Bueller........Bueller..........?
 

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race bikes didint use to have cush drives. not sure how long itll be before it wears out. but it most likely will at some point.

jc
 

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I think the purpose of the cush drive was to smooth out the engine's power hit (shock load) to the rear wheel and absorb vibration. Engines are kind fo notchy, espically when you are on and off the throttle and that can be kind of hard on parts.

There are some KTM dirt bikes that still do not have a cush drive. For a street bike I don't think that is a good idea.
 

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forgot to mention, if there is nothing to absorb the shock load to the rear wheel - it gets sent back to the engine and will eventually lead to transmission failure. eventually.
 

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plenty of single and two cylinder bikes run no cush drive and the resultant wear and breakage in the driveline is just part of it

my relatively weak 45" twin had no cush and shredded primary chains and ripped sprockets from the flimsly brake hub with constant regularity

it has been tuned extensively and those frail parts just couldn't handle the magnitude of thrashing it got or the duration of the beating

stock, without any horsepower robbing driveline compensation, they work good and last a very long time

relatively speaking....the fewer cylinders you have...... the more necessary a cush drive, compensator sprocket, or spider/cush clutch hub becomes

an inline multi....... ahhh why worry about it

one of my favorite rants would be belt drives but hardly applicable to most UJM's

so what application are we talking?

have any specific or engaging questions?

I enjoy the subject and may or may not be able to give a layman's dissertation depending on what you actually want to know
 

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I'd say pretty important. If you were running on the dirt where grip was limited, probably no big deal to run w/o the cush. On the other hand, sticky tires with a lot of grip will not let the energy of the power stroke dissipate as easily and some of those loads will come back through the drive line. I would consider it a recipe for increased wear and to what advantage?
my .02 cheers, bcr
 

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Most Honda twins have TWO cush drives, one in the rear hub and one in the clutch. I'd say they certainly don't HURT to have them, and they certainly DO help the drive train live longer.

I wouldn't say "race bikes" don't have them, plenty of them do in one form or another.

Hack...I must have re-riveted the sprocket ring on my 45 a half dozen times. Never stayed tight for more than a couple of weeks it seems like. Maybe it was the copper rivets I was using, maybe it was poor technique. I remember when I put a belt drive primary on my shovelhead, it was an instant improvement.
JohnnyB
 

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my experience with belts has been the exact opposite

they sure seem have about zero "cush" or stretch

which is why companies like Jessel assure their SBC belt drives will hold cam timing to within 1/2 of a degree

and a Mercedes Benz V8 engine with an amazingly long pair of roller chains driving the cams does well to hold cam timing to within +/- 4 degreees

all the bikes I've put belt drives on, especially those in which the cush drive clutch hub is replaced with one without a cush, exhibited a very pronouced midrange roughness that did not exist prior

and some were harsh enough that the harmonic generated would break things that would otherwise last longer than the rest of the bike

including crank pinions, trans cases, crank bearings, frame tabs....... etc


since many HD's do not have them to begin with, many from the HD camp seem maybe even oblivious to this phenomena

when I belted my 45 it got a very soft power robbing cush on the rear wheel

but really chain final and primary drives do absorb much more shock than a non-gving belt ever thought about

however for a gear primary engine and a ham fisted non-smooth rider (which would be most of us humans) ..... no cush on many is merely a kiss of more rapidly approaching death for something mechanical

obviously since we all agree there are many many bikes, even the highest performance variants, have no cush at all

it is easy enough to speculate that many manufacturers use cush drives to keep us non-robotically perfect masses from tearing up their stuff

or using them as a "cushion" so that many driveline parts can be made of either lesser material, smaller, or lighter weight.... maybe give a bearing or casting a fair chance of making it thru the warranty period or longer...... lots of possibilities but I am quite certain that many inline or other UJM's I've ridden are certainly over-cushed

but most cush drive rear wheels are really very heavy

I guess many hipo bikes today make do with just a slipper clutch

so maybe these things can be pondered


not all very hard hitting HD vtwins had cush drives at all but many did indeed become fitted with a compensator sprocket on the engine's crank pinion as power levels increased

I can give a long list of hard hitting singles and twins that had no cush/compensation anywhere

another amusing thing about conventional belt drive thinking is that very robust belts designed for a certain tooth count pair of pulleys on very fixed distances

are adjustable over a reasonably wide range

they really aren't and combine that with the fact they really do not absorb any shock loads at all, but actually transmit them even more effectively to the next metal part....... as well as exhibiting almost zero tolerance for very slight misalignment

well that they work at all is a credit to our modern engineering and machining abilities

The 45 drum being a very thin stamped steel item...... well it will hold the sprocket in place with the proper steel rivets and proper punches used to peen them

but the assembly will not hold up to double factory intended torque loads

I ruined two sprockets and three drums in less than 4 years

the trick on them is to weld them in place but I hate star hub wheels and that useless brake anyhow



with certainty

for me to snap a diamond 35-2 primary chain or break the drum/sprocket on mine... the diamond 530 final chain has been a real soldier and is very under stressed

merely required a passenger, top gear, WOT roll on from 10-15mph, and before it reached 90mph

something would break and every time

you could feel it in your feet, hands, and butt

think I got it cured now so we'll see which cases start exploding with that weak link eliminated

be nice if it hangs together but I have started being nicer to it
 

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I think this has been alluded to in almost all of the replies so far. The answer will depend on what engine you are using, what the intended use will be and how much maintenance you are willing to give it. I have considered using a front on the rear of a CB350 racebike. I think it will work.
Ken
 

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My shovel was a 1976 FXE with lots of changes (see pic), I installed a Primo Belt, the one with wide spaced, very deep teeth...forget what they called it (8mm ?). This was in about 1985. Engine was almost all stock, on this bike you could feel the difference when the clutch engaged, considerably smoother....of course maybe I had been running the primary chain too tight or something. Don't think I ever got the belt aligned properly, there was always dust in the primary case...never saw any appreciable wear on the belt though. I also remember some problem I kept having with the clutch hub nut, I think I eventually installed something called a "super nut"....that still leaked too.
I put an early tank on it, changed to spoke wheels, put on an FLH front end cut down 2", aftermarket fork clamps, low bars blah blah.
JohnnyB

 

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many of the bultaco factory roadracers (aka "tss" models) had no cush in the rear hub. those conical hubs are now virtually non existant due to cracks/failures. some early street models had the same hubs. many are cracked (without the owner knowing) and ready to fail. later street models (metralla 250s) had very robust (heavy) hubs with cush drives. weight weenies give me a hard time about the heavy hub on my roadracer but i don't like the idea of trashing my rare transmission for the sake of a pound or two.
hack-man....never thought of belts as being more brutal to the mechanicals than chains.
-parks
 

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Parks,
I agree with everything you said. I wouldn't risk any part of a rare racebike either. However, I would risk a CB350 engine and trans, I have several spares. I think one of the points you made is that running without a cush drive requires frequent inspection and service.
Of course, the point isn't to run without a cush drive just because. I have a CBR600F2 front wheel that is a good width to run on the rear and without the width in the hub I can get it to fit better by using just some proper spacers. It is not a front burner project for me but is still worth considering.

Ken
 

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Here's what I know about belts...

One of Jesel's big selling points for their belt drives is that it doesn't transmit harmonics to the valvetrain like a chain or a geardrive will. Belts are super stiff in the roundy round way(hope I'm not too technical). I have seen many circle track motors with the snout broke off the front of the crank from running the dry sump belt too tight. The rule of thumb for a dry sump belt is being able to easily twist it a 1/4 turn which seems super loose.

I'd wonder how well the bearings will hold up in a front hub. Most of my stuff has two sprocket side bearings.
 

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Gotta be some strange dynamics I don't understand, but like Hack says, a belt has got to be hella stiff longitudenally (sp)...seems like it would self destruct pretty quick if it wasn't.

But man, anyone that's ever seen that "chuga chuga" thing that primary or drive chains do for instance with the rear wheel off the ground and an engine trying to start...never seen a belt do that. Gotta be something to do with the huge mass difference between a belt and a chain. Although...you'd think the extra mass of a chain would dampen power pulses. My guess is it's hugely different dynamic between a chain and a sprocket tooth than a belt tooth to belt sprocket.
JohnnyB
 

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Discussion Starter #16
Sounds like for anything that'll see any significant use, a cush-drive of some sort is a good idea.
It was just something I've been pondering for one of my project bikes. Doesn't sound like something I want to mess with..
 

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NECRO-BUMP-(HUMP)!

(hump-hump-hump)

Just lost a very long-winded post on this, but I'm hoping anybody else might chime in, in the MEAN-time, vis-a-vis "THE FRONT HUB TRICK", and bolt-up cush-drives. 'Cause it would really help me over the long term NEXT level-shit for my "CB900K0 Bol Bomber"

I've got several sets of rims, as I've stated before. But the principal difference in my rear wheels boils down to the two Akront 4.25x18" rims I have on hand, one drilled for the SOHC CB750F1 rear disc hub, and one with a HARLEY drilling pattern, for "the front hub trick" - so that I can shave un-sprung weight and use an even smaller rotor that what I'm sticking on the SOHC disc hub - 276mm with CBR1000F rear caliper, OR VF1000R 220mm (?) - getting conflicting #'s on VF1000R rear disc, from 286mm down to 210mm. But I do like that under-slung caliper!

AND this thread is relevant to the "KZ440LOL" which I'm building for my Ex-Daughter, where I've got all the NOS belt-drive stuff I'm ever gonna want, but I still wanna utilize the box-section swing-arm from KZ454LTD and it's rear wheel's ... combination pulley slash cush-drive. REALLY cool looking parts for a KZ400/KZ440, IMHO -

So yeah, while MY bike is gonna use 6-bolt front hubs from GL1000, I've found some great pics to share with you:

A CB1100F "Front Hub Trick" using DOHC CB750Kzabc wire front hub (yo-yo shape ala XS Yamaha etc) with a Ducati cush-drive, also five-bolt. Oddly, this still uses the full 296mm standard rear disc! Not my pics, but this is the exact parts I specified in a proposed design on the cb1100f 'F-orums some 7-8 years ago. "Great Minds Think Alike" aka parallel evolution, aka the ZEITGEIST thing! I passed over purchase of this wheel on eBay last year, due to the 5.75x18" Akront rim (READ: 200-spec tire???), then a month later scored an Akront 4.25x18" drilled for Harley. Would've been brilliant - but then a month later, I scored another 4.25x18" Akront this time drilled for the SOHC CB750F1 rear disc hub. However, I DO plan to use both - if and when I get it together to use the smaller/lighter rear hub, I plan to use the other one on a "Weld-Up Hub" as in the photo below of the CB900C rear hub (AKA GL1100/GL1200 rear hub - see where I'm going anyone????) which "6pkrunner" built & showed on the CB750C.com 'C-ustommunity/'C-ustommutiny - BRILLIANT method, applicable to ANY motorcycle when you wrap your head around it! I intend to use this "spare" hub on either a replica of the Swiss DLF "DONQUE" Endurance Racer '75 GL1000 which ran in the '76 Bol D'Or, qualified in the IOMTT - awesome 'Wing, a similar version known as "Wing Thing" mind-blowing stuff.... OR, on the Sabre/Magna based replica of the CZ Type 860, which I've been rapping about for some time now .... I suppose I've got RIMS enough to build ALL THREE at this point ... for my next 8 projects no doubt, and each just as weird but rims as awesome as I've just described.....


OH yeah, the pictures! AND - here's also, for your consideration and RIM-JOB centric, "I like big hubs and I cannot lie, when a bike rolls by with an itty-bitty cush...." BIKE-PORN enjoyment? HERE too, is a prototype COMSTAR, from the original '76 RCB Endurance Racer (1st version, with 750cc "480A" engine etc) from FACEBOOK of all places! "Caillou Bedier Racing" - if you're a fan of DOHC-four Honda, or if you even still THINK that the CR750 was the most awesome Honda 750, YOU NEED TO CHECK 'EM OUT!
 

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Hmmm - correction, that CB1100F bolt-up rear hub, seems to be using something different in the middle. Now - one possibility is that I haven't yet SEE the '76 Canadian-spec POLICE bike front hub, which was a CB750P using CB750F2 front end, drum rear hub, and wire-spoke rims. As per the Police force requests. I don't know of this model appearing in any other markets, but it DID exist: a 40-spoke FIVE-bolt front hub!

OR - and this concerns me. I've had a GL1000 front hub get partially melted in a house-fire. And what this showed me was that within the hollowed out center of the hub, only the bolt-holes themselves have any "MEAT" around 'em. Which is to say, drilling an alternate rotor-bolt pattern in these hubs leaves you with a thinner wall and less material for the bolts to grab or threads to lock into, etc.

I have assumed - no, maybe I DO have a pic - that the POLICE type 5-bolt hub, was externally similar to the DOHC CB750Kzabc ('79=Z, '80=A, etc) SINGLE-disc hub, or for that matter this here '78 CB750K8 dual-disc hub - they're solid cored but with a "Yo-Yo" shape, skinny center with taller flanges, and bumps where the bolts go in. Six bolts in the '78, five in the '79-'82 version.

So yeah - the drum style/motif "cooling fins" of an earlier SOHC-era hub MIGHT indicate some inherent weakness In that particular wheel as pictured. Then again, maybe the "Yo-Yo" shape is even worse? Tough to say.

But put it this way - if I had my DRUTHERS, and could build the ideal rear hub then have an NOS un-drilled rim made to suit that hub, it would follow the "WELD-UP" model same as the 6pkrunner wheel. Just think of it - whether using the core of this here SOHC CB750F1 rear hub OR the core of a CBR rear wheel, maybe even the core of a VFR single-sided-swingarm rear wheel with a single-sided twin-leading-shoe FRONT hub on it, the outer ring of spoke-flanges with cooling fins doesn't need to come from the enormous 190mm CB750K rear drum. They could come from a much SMALLER drum say, 140mm or 160mm - you'd still get that beautiful look of a pre-'75 rear disc CONVERSION, plug type with the Hurst Airheart caliper etc (aftermarket look was far better aesthetically, albeit much heavier!) you'd ALSO get the compact rotor and lighter un-sprung weight, rolling inertia, etc. Best of ALL worlds! Can you picture it?

Well - I suppose a lot of folks with smaller bikes must wonder - why not use RD250 rear wire-spoke disc hub, or Yamaha TDR250 etc?

Truth be told, IF I were working on a bike small enough, light enough, low powered enough to DO that? I'd want a DRUM rear hub on it anyhow. I'm speaking here of wire-spoked conversion where a disc-brake is required. I'd love to use a drum on my 985cc DOHC-4, heck I'd love to use a drum on anything else for that matter. A "retro-fried" CBR954RR café, or what have you. No, I'm not talking about dressing up a CB400F to LOOK like a SOHC CB750F1, I'm not even talking about the SOHC CB750F1 that I'd stick a drum on it anyhow just to shave weight and a CB550 drum at that, simplify the rear-sets etc - same deal with a DOHC era CB750F maybe even a bone-stock CB900F for that matter, might be about the limits - Now that's where I'd wanna use the full-sized SOHC 750 rear drum. No, I'm picturing here a wire-spoke 140HP CB1123F, GL1200 based replica of the DLF-1000 ie DLF-1200 maybe even DLF-1500!!! (aka the Valkyrie that Honda SHOULD'VE built!) or a 1200cc+ Katana, KZ1100, maybe even ZRX12 or GSX1300 etc. So there's a certain weight trade-off that you're gonna have to accept, even just for a modern engineering of the thing alone. Of course, being that we're shying away from modern tech due to the fugly aesthetic sensibilities of modern motorcyclists (slash science fiction fans or vidiot game addicts) I guess it's a GOOD thing, that so many of these vintage machines were so over-built - to the point that they've survived all of these years, if not the harsh environs of actual running machinery then at least the swamps and bayous they've been parked in all this time. The trick though, is in finding "legit" vintage stuff, which gives some competitive advantage over the other legit classic machinery. Within the "Superbike" milieu, which is to say - shy of going full-on too-smoke TZ750, or at least stretching the race past the point where the too-smoke machines have blown up - ENDURANCE racing, or Iron-Butt rallies if you prefer - Where big heavy engines are de rigueur, yet where any other competitive advantage one might glean from the chassis, rims suspension ergonomics perhaps a fairing etc - THIS is the domain wherein one might pretend that a Honda was a highly competitive machine, post ... perhaps 1973 or thereabouts.

So yeah - there are some limits, or requirements if you will.

PREREQUISITES:

20mm axle (preferably up FRONT, too)

Cush-drive - and not a rinky-dink token one either!

disc-brake - ideally

WIRE-SPOKED - 'cause the mag wheels won't allow the same flexibility and adaptability in SIZE to allow better rubber, cast/mag wheels are heavier in the periphery, & are just plain FUGLY - the tube-less advantage was lost years ago & many of 'em weren't tubeless in the first place - it's MY contention that wire-spoke rims could be the very best most competitive period-correct or period-correct-ISH wheels for these bikes.

SO - what does this leave in terms of hubs?

- KZ750B/KZ1000A conical-composite alloy with steel right flange, GLUED ON WITH EPOXY! Full-sized cush yet it's the lightest of all period Superbike rear disc hubs. Yet this epoxy thing is worrying. Plus it's hard to find an NOS pre-drilled rim to suit it, you're limited to UN-DRILLED rims, or NEW rims (blech) with perhaps some suitable rims from British ($$$) conical "Comical" DRUM hubs in 40-spoke - fantastic selection in 36-spoke 2.50x18" Akront from late '70s-'80s Euro MX-ers, but WE'RE looking for 3.50x18" maybe 3.00x18" minimum, right?. Best advantage of KZ rear hubs are the plethora of taller "top-hat" cush-drives, to allow for a wider off-set chain-line with alternative engines/frames etc.

- KZ1000LTD 40-spoke KZ1000CSR 48-spoke - could be the heaviest! Both come with an alloy rim but it's 3.00x16" and heavy thick D.I.D. at that. 48-spoke
version has such small intervals between spoke holes, it's gotta be prone to cracking. Especially around the valve hole - So they made it really THICK. As in HEAVY. However, in a decent sized rim, 48-spokes might translate to a very strong wheel, to run on a big powerful bike and sleep peacefully about it. Cross-drilled rotors available from later VULCAN series.

- GS1000 - HEAVY, but might feasibly suit smaller lighter rotors, such as Honda 6-bolt 276mm front off GL1000/CB550 etc. Could lace to typical "drum-drilled" rims interchangeably with the others.

- CB750F1 '75-'76 - HEAVY with big heavy 296mm rear disc (I'm sticking dual 296mm up FRONT, hope to use 276mm max diameter in REAR brake - Honda got it BACKWARDS!) '78 or '77-'78 SOHC and later DOHC 'K and 'C type sprocket-carriers add 10mm off-set, available dished sprockets give additional 10-20mm off-set, plus Cognito-Moto sprocket spacers @ 3/8", you could power a side-car wheel or trike at this point....

What else?

Some later Cruiser stuff? Even heavier, even more spokes than 48 on 'CSR??? No Thanks. Most of 'em are shaft, chain drive are typically drum. Just look at the Cruiser hubs Honda used on the 2015 CB1100 wire-spoke version, to see what I'm talking about. Looks like a Yam XS650 Heritage Special wheel-set, only worse. I'm sure they're stiff, but can't this be accomplished with less spokes? And at what weight penalty?

Possible cush-drive carrier customization of SHAFT-DRIVE hubs? Such as GL1000 & various Yamaha models. Is it worth it? Does it shave weight? I sincerely doubt it.

Plug-type disc conversions of SOHC CB750 rear drums are still available from CYCLE-EXCHANGE - for the life of me, I don't understand why they don't do it with smaller drums instead! And rather than a heavy solid lump to interfere with the drum lining, why not do an exchange basis and mill out the Iron liner? Then somehow cap off the face of the drum or leave it open for that matter, and attach the disc to the bearing cup area? This has gotta be heavy as shit!

And my favourite - bolt-up flange plates, usually steel, on a Comstar rear hub? I myself proposed this method on the www.CB1100F.net 'F-orum as far back as late 2003 or 2004 (ie, when I was a NOOB) - But there's a problem with it. Stripped down, sans BOLTS, the Comstar rear hub is only a couple of grams shy of the SOHC wire hub! WTF!!! Might well be the HEAVIEST HUB POSSIBLE - It WAS useful on a shaft-drive, made popular on the CX series (though now obsolete thanks to the Weld-Up Method!) but should be avoided at all costs in any chain-drive applications. It's probably as heavy if not heavier than the plug type insert drum-to-disc conversions from '68-'74 etc.

WHICH, I suppose, counts as another method. Though it might just pre-date all the others. With the possible exception of a Harley "Star-Hub" substitution OR the related "Front-Hub-Trick" - Just sayin', if this list were in chronological order - these three would be at the top. Though of course, the "RICKMAN" Eddie What's-His-Pickle, conical Magnesium disc hubs were also made as a REAR wheel. And of course there were British front disc hubs & other aftermarket types. The "Quick Change" hubs from the likes of BARNES, as well as FONTANA broke into the disc-brake market with rear hubs for race-bikes. Of course in this context I am speaking more of the DIY stuff and UNOBTAINIUM of all sorts have no place in these "deliberations"....

So yeah, everything out there that meets these pre-requisites is HEAVY AS SHIT. Proverbial boat-anchor material. Stick 'em on a coffee table use 'em as an ash-tray slash candy-dish. (Though never both at once!) I prefer 100mm front CUB/Passport front drums for this. Or as a "Cow-Bell" on a drum kit.

Ergo - preferred method? DRUM!!! (Notwithstanding their usefulness for baking "BUNDT" cakes - be sure & remove all asbestos residue ... or give the cake to someone you hate....) DRUMS - work really well in the wet, and a slightly smaller one ie CB500/CB550, shaves a TON of weight! Plus they look cool. Do you think the CB750F1 rear disc is lighter than the 'K type drum? Weigh up the ENTIRE brake system! Caliper, hydraulics, ROTOR and all!

OR - one could do either "the front hub trick" (ideally, with a really trick front hub?) or even better still, a WELD-UP HUB!!!

Hey - it needn't be perfect, the spokes will true the wheel! So it needn't be as fussy as the KOSMAN INDUSTRIES WELD-UP CAST/MAG RIMS - at $500ea USD, back before they shut down.

I'm thinking, some brave and enterprising young 'F-eller should set up a service - on exchange basis, once established. And buyers should expect prices significantly Southward of $500ea ha-ha.

"DISH" could be set by the weld-up job, ergo spokes would be stock. With a standard size of flange for a given class of hub "core" - say, CBR/VFR/GSX-R/ZX etc, the diameter would remain fixed. Ergo, the spokes could be standardized and mass produced - rims could be drilled in batch-production fashion -

"Economy Of Scale" - if you don't know what I mean, price out a pair of custom HARLEY, wire-spoke, tube-less sealed, ready-to-fit wheels. Then price out a project like mine, with the same sized rims! Argh. ECONOMY OF SCALE!!!

AND you keep the stock brakes, chain-line, etc. Well, on a DOHC Honda, you can fit 170/55 with the stock front sprocket - and 180/55 spec tires, with nothing more than an off-the-shelf sprocket from the CBX six cylinder "pro-link" models. Or RC30, FZR - several OEM front sprockets that fit with "FREE" off-set! Maybe on a KZ or GS, you'll pay through the nose? Even so - this mod is about wire rims more so than fatter tires! Though IMHO, it's nice to have both!

Check this out: 2.50x18" removed from CB900F rear wheel, and Akront 4.25x18" wire-spoke. SAME WEIGHT!

And another, for the COMSTAR lovers - Akront "NERVI" rims, almost that very same ultra-light weight as regular Akront!
 

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