Topic: Gear ratio influence on RPM

[gunr]

Thanks to the Braintrusts my 77 CB750 clutch is AOK !     Thank You smart guys!
Now on to new Horizons!

I'm studying old posts and JT Sprockets site for new gearing and chains to address my RPM of 4000 @ 55MPH.
That increases to 5000 RPM @ 60ish MPH while running through second to fifth pretty quickly.
JT Sprockets imply a 2.72 ratio from a 15 tooth front with a 41 tooth rear and a 630 size chain although I haven't counted teeth yet.

I think a taller ratio would be more in my comfort zone, say 65 to 70 MPH at 4000 to 4300 RPM
A CB650 front sprocket in a 16 tooth 530 variety with a 39 tooth rear would net a 2.44 ratio.

A chain of 106 links of 530 size nets 66.25 inches whereas the old length was/is 66 inches.
Do you all think I'm in the right ballpark?

Also, measurements of rear sprockets list sizes as: 10 x 10 x 5 or 10.5 x 10.5 x 5.
What does the dimension explain?
Thanks!

[bryanj]

But thats the rev band its supposed to be in.
Honda had problems with a 16 tooth so personaly i think 15 is a no no

[newday777]

Your 77 750 came with 630 size chain and sprockets.
Are you staying with the 630 chain size or going to new sprockets and chain for the 530 size chain, as was used on the 76 and earlier 750s?
(You mentioned both sizes, 630 uses different sprocket thickness)

[newday777]

The 76 750K came with 17T front and 48T rear with a 530 chain. Back then, I put on 18T front (taller gearing) and IIRC....I might have put on a 45T rear(taller gearing) to lower my highway rpm’s but I had built my motor with more power. If you have a stock 736cc motor(), how much are you going to be riding it at highway speeds??

[TwoTired]

You aren’t going to make this high RPM Honda engine into a low RPM Harley engine.  It needs RPM to make HP and torque.  Let it rev, it is perfectly happy doing that, and you get the desirable throttle twist response it was born to have.

If it is too uncomfortable and fatiguing to ride at that sound level, get more effective mufflers.  Then you get a smooth ride and coast to coast riding pleasure. 

If you are in competition to have the loudest bike, maybe a Harley better suits you?

[denward17]

I can tell you what I am running on a '78 K8.

I converted to 530 chain / sprockets.

JT sprockets
18T front---I think this sprocket was listed under CB650.
48T rear
chain length is 104 links, did not have to take any out.

If I recall I'm around 4300RPM @ 60mph.

[gunr]

Well, it appears someone has already done a 530 chain conversion on my bike.

I don't want a loud low revving machine. Other than my 73 with the shorty pipes and velocity stacks my motorcycles are original equipment exhaust, airbox and jets .

77's came with 630 size chain and cogs of 15T front and 41T rear for a ratio of 2.73 and that's what I "assumed" was on it.
The chain feels like it has a stiff section and I wanted to replace it.

After further inspection a previous shade tree mechanic put a 17T front sprocket and a 45T rear sprocket for a ratio of 2.65  in a size 530 with a master link that original 630 chains didn't use.
I can see he used a front gear from an older series because of the hugh washer and spot welds on the bolts that affix it to the shaft.
 
The original front sprockets are not flat and have a shoulder on the outside and don' t need a hugh washer to take up the space.
My research of old post suggests using a gear from a CB650 because it also has that shoulder.

My intent was to use a 530 set because who needs a 630 chain size and weight for a stock displacement engine that won't exceed the rating of a size 530 set.

The rural roads I run most, at less than hi-way speeds, in fourth gear just needs a little more gearing but not as much as I get in 5th gear with low rpms.
At hi-way speeds of 65 -70ish in fifth gear it "feels" to me the rpms are a little fast.

[newday777]

Too fast compared to what??

[seanbarney41]

The problem with what you intend to do, is that you will lose most of the bikes ability to accelerate rapidly.  If you are ok with that, have at it.  In my opinion, acceleration is a major part of what is fun about motorcycles and a cb750 crippled with too tall gearing does not have enough. 

[gunr]

I took her out for a rip and wound up the rpms. 
I may switch out the front to an 18T with the shoulder for the CB650 because it will fit right and not need welded on.
I will replace the chain.

Thanks for the guidance.

[Tracksnblades1]

I took her out for a rip and wound up the rpms. 
I may switch out the front to an 18T with the shoulder for the CB650 because it will fit right and not need welded on.
I will replace the chain.

Thanks for the guidance.

I’ve used the 18/45 on a CB750F1 with a 130/90/17 rear tire since I was a young guy.for sustained 70+ mph interstate riding. At 55mph you will shift down to disappear. Ran 90+  all the way in to St.Louis on I70 in 7:30-8:30am traffic. Only once though, pouring coffe, fixing makeup,eye liner, doing hair,shaving , tying ties, reading the Wall Street j, falling asleep etc, then.  Couldnt imagine with texting nowadays.

Used a 17 Honda front sprocket with the same 45 on the back for week end terrorizing with buddies. You will be in one gear lower when drag racing a CB750K5 wearing a 130/90/16 and 16/48 combo. You will shift up at nearly the exact same time and he’ll be up near 500rpms at the shift.  The naked launch at the starting line wasn’t as bad as you might think. The 76F has a slightly different trans ratios…