Topic: 1977 cb750 17 inch rear wheel tire options

[547]

I bought a set of Dunlop k70 tires for my 1977 CB750K but the rear that I bought was for an 18 inch rim which is what I thought my bike had. Turns out one of the many alienating little differences my '77 has is a 17 inch rim. It also turns out that Dunlop does not make a 17 inch k70. At least I can't find it. I have already mounted the front tire so I can't return both and start over.
Does anyone have an idea of a comparable tire that will look good with my front k70?

Or can someone advise me on weather or not I can mount my 1977 brake panel and hardware as well the sprocket assembly including flange to a 1976 cb750 rim and hub and then put it on my bike with the stock spacer and axle? Also will a 4.00 - 18 size tire right for a 1976 rim?
here is the rim in question on ebay
http://www.ebay.com/itm/331174477776?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[Airborne 82nd]

I run a battle axe Bridgestone BT45 on my 78 rear 17". I don't know what it would look like with your front. What I don't understand is why or how you pick the tire you have. The size is stamped on the wheel plus on the old tire. I don't know if you will have to change spokes or not if you lace the 18 to your hub I think they may be short but someone here will it has been done but usually with a 16" for the big fat tire look.

[Stev-o]

Not sure what was stock on your bike...

17" rear was stock for the '77-78 750K's.  I had a Dunlop D404 130/90-17 on my K8.  The rim is wider than the earlier models too.

It's best to have matched tires.

[enwri]

I'm pretty sure the 18" wheel is the same hub as the 17" except for the angle of the beveled edge where the spoke heads lace through, the spokes lean in towards the centre a little harder on the 17" wheel, but that only matters if you're going to lace the 18" hub into a 17" rim. other than that, your 17" sprocket and cush drive hub is slightly wider to get the chain away from the tyre, and it's outside spacer is shorter to compensate, there is an internal stepped spacer as well that is longer to keep it from getting crushed into the rubber bits too hard, you should notice if it goes in too far. Also, it's either the axle length or the nut that was different, to get the split pin holes in the right place. I only noticed all this after finally respoking the 18" wheel that I had jammed into my swingarm for about ten years, into the 17" rim, ( I had used the outside spacers from the 18" with my sprocket hub and internal spacer. It fit, but I had to squeeze it in.)
If the top left hand shock absorber mount is visibly longer, 3/8" or so, than the right side , it's supposed to have the 17" wheel.

I've ended up with a matched set of Bridgestone Battlewing Tyres that my neighbour gave me after taking them off his Yamaha 1200 Tennere, I think they're semi off road tyres , but they were the right price, nothing. 110/80  19, and a 150/70  17, no clearance troubles with the 18" or 17" wheels.

[750K]

I've never tried it but from what I've read on here you should be able to run the pre77 rear wheel, as you've already said you will need your 77's axel, spacers, sprocket carrier, brake hub. Honestly the 18" of the earlier bikes looks a bit nicer as well so you win on both fronts, bigger rear wheel and matching tire. I can't comment on the rim width though, I'm sure someone will chime in about that.

[lucky]

Here is what I would do.

Buy a SET of Avon Road Rider 26 tires (available for your 17 inch rear wheel).
Then sell the ones you have to another CB750 owner that has a 18 inch rear wheel.
There is a Forum here for selling parts.

That way you do not have to get a different backing plate for the rear hub and make spacers or anything else. Also there is the sprocket alignment issue.

IT is easier to sell your new set of tires that do not fit, (as a set), than to change all of the parts of the rear wheel. Also the 17 inch and 18 inch end up having almost the exact same outside diameter when you are all finished anyway.

And that brings up one last problem you may not have even thought about.
The 1977-78 CB750's have a higher 4th and 5th gear.
So if the rear TIRE dimeters are bigger or smaller, then stock your gear ratios can be slightly different. I think if I remember there is a 3/4 inch difference in outside diameters.

I have already researched the 17 inch tires to death.
Outside dimeters of all brands etc.,.


Just get the Avons and sell the others ones. Easy solution.
The Dunlop K70's are a 40 year old design.
The Avons are a modern road tire.

Outside tire diameter formula:
http://www.rbracing-rsr.com/tirediamcalc.html

[flybox1]

I'll second the Avon AM26's.  I'm running a 120/90-17 rear

[Stev-o]

I'll second the Avon AM26's. 

I'll third em. I have a set but not on my K7.