Tire Confusion

[prufrock28]

I just purchased a 1979 CB750K and ordered new tires, as the ones on it are 15 years old. Online resources indicate that the OEM tire was a 3.25/19 front and 4.00/18 rear. My shop manual indicates a 3.50/19 front and 4.25/18 rear. I ordered Dunlop K70's in the only available size of 3.25/19 front and 4.00/18 rear. I received them today and they look SO SKINNY. Could this really be the OEM size? Anyone else running these?
Thanks!
-Doug

 

[brettp]

Pics?

 

[mrtwowheel]

One brand tire can be a lot different than another brand, even when marked the same size.

 

[Walt]

I'm not sure how the size for a 1981 custom translate but these are a 110/90 19 front and a 130/90 16 rear.
Yours may look wider once installed and inflated?

 

[Old_Crow]

On my '79 Anniversary edition I have the Comstar wheels instead of spokes. I'm running a 100/90-19 on the front and a 130/90 18 on the rear. No clearance issues, but the speedo reads a couple of mph slow.

 

[brettp]

On my '79 Anniversary edition I have the Comstar wheels instead of spokes. I'm running a 100/90-19 on the front and a 130/90 18 on the rear. No clearance issues, but the speedo reads a couple of mph slow.

I'm pretty sure Honda speedos read 5-10% higher on purpose. Even my 2007 VTX1800 does. You can get a more accurate reading by increasing tire circumstance.

 

[prufrock28]

Here's a pic of the tires. Left to right Dunlop K70 4.00x18 (for rear), Dunlop K70 3.25x19 (for front), Bridgestone Accolade 100/90x19 (presently front). Of course, when mounted and inflated, the Dunlops will gain a good deal more in width, but hard to imagine them not still looking too thin in the end. The present rear, a Bridgestone Accolade 130/80x18 also looks way wider than the Dunlop K70 could be after mounted and inflated. Metric conversion charts suggest that the width of both the front and back should only be 1/4" thinner. Hard to believe.

My goal is to keep the bike as close to original as possible. In 1979, most bikes shipped to the US came with Bridgestone Mag Opus tires, 3.50x19 front and 4.25x18 rear. I ordered a Dunlop K81 4.25x18 rear and Dunlop K70 3.50x19 front to compare with these and maybe I'll be able to mix and match for a final solution.

Any good suggestions for a bias ply, tube tire combo with an old school tread design?

Thanks to all for your responses!

-Doug

 

[Old_Crow]

You can't really judge the size of the tires until they're mounted. Even my slightly oversized tires looked small when they were banded like that for shipping.
As far as a supplier for stock looking tires, I have no idea. Even when I had my first 750 back in the 90's I ran oversized tires on it. I prefer the look of slightly more rubber.

 

[alex961]

If it helps, here's picture of my restored 1981 CB750, with OEM standard dimensons tires.

 

[prufrock28]

Wow! What a beauty! Helpful, Thx!

 

[prufrock28]

Thanks to all who responded. I'm mounting the 3.25/19 and 4.00/18 Dunlop K70s front and rear and will post a pic.