Author Topic: Sorting '79 CB750k9 Tires  (Read 140 times)

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Offline TequilaSqueela

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Sorting '79 CB750k9 Tires
« on: November 06, 2019, 03:58:19 pm »
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.
« Last Edit: November 06, 2019, 04:07:53 pm by TequilaSqueela »

Offline Stev-o

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Re: Sorting '79 CB750k9 Tires
« Reply #1 on: November 06, 2019, 05:19:36 pm »


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...
'74 "Big Bang" Honda 750K [836].....'71 Honda 750K project.....'76 Honda 550F.....K3 Park Racer.....K5 Fiddy Dolla Special!......CB500 Fiddy Dolla Special too!!............plus plus plus.........

Offline TequilaSqueela

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Re: Sorting '79 CB750k9 Tires
« Reply #2 on: November 06, 2019, 06:16:31 pm »
Thank you very much. Where do you typically order from?

Offline Kelly E

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Re: Sorting '79 CB750k9 Tires
« Reply #3 on: November 06, 2019, 06:23:53 pm »
Why won't the shops mount tires? We put Avon AM26 Roadriders on all the old bikes we do.
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1974 Honda CB550 K0
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Offline simon#42

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Re: Sorting '79 CB750k9 Tires
« Reply #4 on: November 07, 2019, 10:22:35 am »
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

Offline Bankerdanny

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Re: Sorting '79 CB750k9 Tires
« Reply #5 on: November 07, 2019, 01:53:01 pm »
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.
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki 80 (K11 probably, it's been 30 years), '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Stev-o

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'74 "Big Bang" Honda 750K [836].....'71 Honda 750K project.....'76 Honda 550F.....K3 Park Racer.....K5 Fiddy Dolla Special!......CB500 Fiddy Dolla Special too!!............plus plus plus.........

Offline Don R

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Re: Sorting '79 CB750k9 Tires
« Reply #7 on: November 07, 2019, 08:39:31 pm »
 Just FYI, I have heard there are 1979 single cam 750's especially in countries other than USA.
If the things you own end up owning you, it's better to be owned by some cool things.

Offline Stev-o

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Re: Sorting '79 CB750k9 Tires
« Reply #8 on: November 08, 2019, 06:16:30 am »
'74 "Big Bang" Honda 750K [836].....'71 Honda 750K project.....'76 Honda 550F.....K3 Park Racer.....K5 Fiddy Dolla Special!......CB500 Fiddy Dolla Special too!!............plus plus plus.........

 

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