Topic: Rear wheel options

[cuz]

Just wondering what people think of the 16" rear wheel on the 750's.  What was the reason people started making this conversion? My project bike came with a 16" already installed and my parts bike has a stock rear wheel.  Both are K7's.  I'm getting ready to paint rims and hubs so looking for a bit of advice as to what size would look and/or perform better.  The restoration will be of the cafe style.

Thanks in advance for any input!

[70CB750]

Mine came with 16" wheel too, it was all about the lay back riding position I guess.

18" wheel, you want to be as close as possible to the original handling.

[Terry in Australia]

Back in the "Chopper Years" (the 1970's) someone discovered that you could lace a Honda hub to a Harley rim, and everyone and his dog fitted 16 inch wheels to their CB750's.

When I sold my Henry Abe mag wheels to a Japanese collector for a huge sum I needed to put some wheels back on my bike, so I fitted this 16 inch rear that I scored somewhere, and actually, with a new Bridgestone BT45 rear tyre and 40 tooth rear sprocket (17 front) it still does 60 MPH at just under 4000 RPM, and with the fat tyre, doesn't feel any different than it did with an 18 inch rear wheel.

I do have a wide 18 inch Borrani rim to match the front which I'll eventually lace to a hub and put on, but I kinda like the way it looks now? Cheers, Terry.

 

[Stev-o]

Mine came with 16" wheel too, it was all about the lay back riding position I guess.

18" wheel, you want to be as close as possible to the original handling.

K7's came with 17" rear wheel, that's what I would put on it. 

[70CB750]

Mine came with 16" wheel too, it was all about the lay back riding position I guess.

18" wheel, you want to be as close as possible to the original handling.

K7's came with 17" rear wheel, that's what I would put on it.

What he says, I was too lazy to check references, sorry 

[SOHC4 Cafe Racer Fan]

If you are building a chopper, or just want to use a fat wider tire, the 16 is a good choice.  Otherwise, you might want to source a 17.

[cuz]

Thanks for the replies everyone.  I just looked again and the wheel on the parts bike is a 17.  I wonnder if it was late model k7 and k8 bikes that had the 18" wheels.  I am certainly not building a chopper so maybe the stock 17 is the way to go.  It's interesting that both tires on the 16 and 17 are 130/90's.  Whoever put the 16 on didn't really try to go any wider or fatter.

[flybox1]

K7/8's came with 17"
I run a 120/90 on my 17"

[Stev-o]

K7/8's came with 17"
I run a 120/90 on my 17"

I ran a 130/90-17 on my K8.  I like the wider tires...

[flybox1]

K7/8's came with 17"
I run a 120/90 on my 17"

I ran a 130/90-17 on my K8.  I like the wider tires...

a wider tire?  that's not very 'old fashioned' 

[Stev-o]

K7/8's came with 17"
I run a 120/90 on my 17"

I ran a 130/90-17 on my K8.  I like the wider tires...

a wider tire?  that's not very 'old fashioned' 

not really. have seen plenty of 70's era muscle cars with "fat meats" on the back!

[oldhatt45]

flybox1

Don't know about old fashioned, but I ran a 130 Continental K112 on my 76 CB750 from the get go in 76. 

Charlie

[flybox1]

I was just playin' off of steve-o's 'old fashioned' comment in another thread.

[Stev-o]

I was just playin' off of steve-o's 'old fashioned' comment in another thread.

yeah, knew that!  foot in mouth.....

[oldhatt45]

OOOOpppppsss,

Guess I was not as observant as I should have been.
Maybe I can claim that my Oldtimers disease was acting up again.  LOL

Charlie

[flybox1]

OOOOpppppsss,

Guess I was not as observant as I should have been.
Maybe I can claim that my Oldtimers disease was acting up again.  LOL

Charlie

Its all good.  No one should expect you to know whats going on in all the threads   

[evanphi]

K7/8's came with 17"
I run a 120/90 on my 17"

I ran a 130/90-17 on my K8.  I like the wider tires...

This is what I have on mine now (17" rim). Same diameter as the stock rim/tire of the earlier bikes, but a little bit wider.

[Rookster]

I think it would be very difficult to tell the difference between a 16" rear wheel and tire from an 18" wheel and tire under normal riding conditions provided a decent tire is used (not the square section 16" tires).  In truth the 18"/19" combo wasn't ideal either.  The cr750 used 18" front and rear.  The later K bikes went to 17" rear wheels and almost by the end of the 70s the 18"/19" combo went away on performance motorcycles.  A wider rear wheel is more consistent with what we think of performance wheels and tires today.  An easy way to get a wider rear tire on a CB750 is to go with a 16" rear wheel.  I'm not arguing that it is any kind of performance upgrade because it isn't but it's probably not a performance downgrade either.

Update: I just measured the diameter of a rear 18" wheel with a 4.10x18 Dunlop K81 and it came out at 26".  I then measured the diameter of a 16" rear wheel with a MT90x16 Avon AM9 and it came out at 26".  Both wheels are mounted on motorcycles so these diameters aren't exact but they are very close to the same diameter.

Scott

[Terry in Australia]

Yeah mate, it largely depends on tyre sizes, when I replaced the 16 inch rear wheel on my CX500 Custom for an 18 inch CX500 Shadow wheel with a new 120/90-18 tyre there was a noticable size difference when compared side to side, and it reduced the RPM in 5th gear @ 100 KPH (60MPH) from 6000 with the 16 inch wheel to 5000 with the 18 inch wheel. If you look at the "Before and After" pics, below, you'll notice the difference.

I put a fat 140/90-16 BT45 on my 16 inch "Hog" wheel, but with the 48 tooth rear sprocket it was pulling close to 5000 RPM @ 100 KPH, so I had to install a smaller rear sprocket (40T) to reduce the RPM to just under 4000 RPM, as it was previously with the 120/90-18 tyre that was on my HA rear wheel. Cheers, Terry.