Topic: Sorting '79 CB750k9 Tires

[TequilaSqueela]

I never knew tires could be so complicated.

I have tires from 1982 currently mounted to my K9. The tires read 3.5-19 front and 4.25-18 rear.

Every shop in town has said they won't put tires on this bike. I look online and find information for k1-k8, but no k9. Bike sizing on JP, Bike Bandit, Revzilla, and Amazon are all over the place.

The FAQ tire section lists inch conversion should put me at 100/90 front and 120/80 in the rear, but that they don't actually line up correctly due to modern tire design not being square profile leaving me confused on if I am supposed to size up or not.

What I know:
The BT45s are the way to go with Avon Speedmasters and K81s as a close second. Tires manufactured for inches today are actually smaller tires with rubber added and wear faster. I can run tubeless tires, but I must add rim tape. I should drop a speed rating when doing so.

So, with that in mind I would figure I could order a set of K81s:
3.5 front (oops, dont make them)
4.25 rear (they make them, but I heard to not mix these tires with other tire types, so that's out)

Okay, Battleaxes then:
100/90x19 (available, cool, but stupid expensive)
120/80x18 (doesn't exist, but there is 120/90x18?)

Okay, then...Avon Speedmasters:
3.5x19 front (sweet)
only 4.0x18 rear (ugh)

Am I overthinking this? Every thread on this forum I have found with bikes of similar model (always 81, never 79) folks say the tire sizes don't match and the bike handles like a bear. I can't find a good recommendation with actual tire sizes.

I really wanted a shop to just take care of this for me, but that doesn't seem to be an option here. So, I apologize if my knowledge level isn't quite where y'all would want it to avoid hand holding, but I am doing my best. I apologize. I just want to hit the road with some spirited riding and not looking to cafe or mess with the bike any. That being said, though, should I just get modern wheels for modern sizes and call it a day?

Thanks.

[Stev-o]

Am I overthinking this?

Yes!   I have Bt45's and Avon Roadriders and both are great tires.

Just order 100/90-19 & 120/90-18 and you'll be good.

I order online and bring to a buddy who has a tire machine, give him some beer money and everybody is happy!   

Call around, someone will mount those tires for you.  BTW - get new tubes too...

[TequilaSqueela]

Thank you very much. Where do you typically order from?

[Kelly E]

Why won't the shops mount tires? We put Avon AM26 Roadriders on all the old bikes we do.

[simon#42]

not a great fan of the roadriders tried them a couple of times but both times took them back off . the bt45s have always been a good tyre and are very good in the wet .
the best tyres i have found in those sizes are continental classic attacks , brilliant in the dry and pretty good in the wet , expensive though

[Bankerdanny]

The '79 would not be a K9 since they switched over to a whole new engine at that point. But designation aside, I would base my tire choice on rim width. Pre-77 SOHC4 750's have 1.85" wide front wheels and 2.15" wide rear. My 750F had an old 4.5" rear and it was stuffed onto the rim. I have a 3.00 wide Lester on the back of it today and run a 120/80-18.

I get the appeal of the wider tire from a looks perspective, but on these bikes you will get better handling with something closer to stock size.

[Stev-o]

Thank you very much. Where do you typically order from?

Various online websites....

https://www.google.com/search?newwindow=1&safe=off&rlz=1C1SQJL_enUS786US786&sxsrf=ACYBGNQeodUN2n9fnw0KDTwjkUltp39DyA%3A1573164668952&ei=fJbEXbTeOYLcsAXQyK5I&q=100%2F90-19+bt-45&oq=100%2F90-19+bt-45&gs_l=psy-ab.12...39996.46176..47808...0.0..0.166.665.3j3......0....1..gws-wiz.......38j0i8i30j0i22i30j33i160._PYGcBQtaC0&ved=0ahUKEwi0jJCKj9nlAhUCLqwKHVCkCwkQ4dUDCAs

[Don R]

 Just FYI, I have heard there are 1979 single cam 750's especially in countries other than USA.

[Stev-o]

Interesting article here about the '79...

https://www.cycleworld.com/sport-rider/sr-archive-1979-honda-cb750f/