Primary drive reduction ratios

[paulbaker1954]

Been playing with some numbers but now confused.

The tech spec I have shows the primary reduction ratio as 2.0 for the 500 Four but 3.063 for the 550.

I thought they would be the same so I am a little confused

Can any 4 gurus shed any light on this?

[AndyH]

According to the Honda Shop Manual, those figures are correct.

[Bryanj]

550 has a different clutch to the 500 so hence the difference

[paulbaker1954]

Thanks Bryan
Now that’s interesting as I have been playing with the gear commander site www.gearcommander.com

If you load their data for HONDA CB500 all the gear ratios are right except the primary reduction

Change the primary reduction to 2 and the calcs show a speed of 196.5 at 9000

What the hell am I doing wrong

[K2-K6]

Are there two components to primary on that engine?

Does it drive crank to layshaft plus layshaft to clutch?

The 750 drives direct to clutch shaft from crank,  and then again from gearbox to sprocket output.

The two combined in both bikes equals the primary reduction but the gearboxes spin at different speeds as far as I can see.

Proviso of counting chain and sprockets as secondary reduction.

[Bryanj]

500/550 has primary chain reduction then gear reduction to clutch basket

[paulbaker1954]

Sorry all I am still really confused

I am trying to calculate speed vs rpm for different wheel/ sprocket combinations and really confused

Is there a difference in the primary chain reduction between the 500 and 550 then.

Since both bikes have same gear ratios and very close final drive ratios (17/34 and 17/37) but hugely different primary reductions (2 for the 500 and 3.063 for the 550) I am missing something here in my calculations I can only assume therefore there is a difference in the primary chain reduction between the bikes but I have no data on what the primary chain reduction is in my tech specs

[Bryanj]

I think primary chain is same but primary gear and basket gear vary

[paulbaker1954]

Sorry all but I think I am not explaining my problem clearly!!!

I am trying to calculate road speed vs rpm for the 500 four and somewhere I am missing something

I have Avon 400/18 rear tyre which has a circumference of 82.9 inches and there are 63360 inches in a mile, so 1 rev of rear wheel is 0.0013 miles

For the 500, spec is a 2.0 primary reduction and 5th gear is a 0.9 reduction and final drive is a 2 reduction assuming stock 17 and 34 teeth as per spec. This in 5th gives an overall reduction of 2x0.9x2 which equals 3.6 so 1000 rpm equates to 60,000 revolutions per hour or 60000/3.6 =16,667 rear wheel turns which is 16667x0.0013=21.67 miles

So this means 21.67 miles per hour for every 1000 rpm which gives 21.67 x 5=108 mph at 5000 rpm which is clearly nonsense as I know it’s more like 12 mph per 1000 rpm

I am missing something obvious I know but dont know what

[Trigger]

I think primary chain is same but primary gear and basket gear vary

Chain is the same on the 500, 550 and 400. Just different gearboxes, clutch, sprockets and chain length .

[SteveD CB500K0]

As Bryan says, surely there’s a reduction to the clutch basket?
As you say, there’s something missing. I rode my original for months with no speedo and always estimated speed at 12mph/1000


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[paulbaker1954]

Can anyone confirm the number of teeth on clutch basket and primary shaft?

[K2-K6]

I understand what you mean Paul, just not so familiar with the exact layout.

Primary reduction is usually given as crank to first ( in this case chain to the first shaft it's driving) then there is the reduction of that shaft driving the clutch through a gear set,  so the clutch shaft speed into the gearbox has arrived via two reduction methods.
 It looks like just the first stage is quoted,  the others on here should be able to tell you how many teeth are on the crank and the other end of the chain. If that's a times two reduction, then you've got to then add the clutch gear set reduction to it.

I'm more familiar with the 750 which drives, crank straight to clutch in one chain run and no gears. Then,  when leaving the box has a paired gear set to drive the output sprocket. How they quote these two units on both engines I don't know,  but they are both altering the total output to final chain, and obviously not incorporated in the 5 gear ratios.

If that makes sense.

Nigel.

[K2-K6]

Those figures for the 550. Give clutch reduction of 2.625  so there must be the other component on the primary chain to make total of 3.063.

If you work the 500  figures and assume 2 more teeth on the clutch,  then that's going to be 2.826  on the clutch alone,  so you still need the number of teeth for both primary chain sprockets to add to both of these illustrations to give total primary reduction.

May have found another error in Honda manual,  the one that states primary reduction of 2.0 it just can't be that figure.

[paulbaker1954]

The primary shaft gear, the very large one the primary chain runs on is the same for the 500 and 550, they share the same part number, the smaller one which sits inside the clutch casing is different, the 500 has a 23T gear and the 550 has a 24T gear. The 550 clutch basket has 63T but the 500 isn't shown in the parts book.

The 500 clutch basket has 64 teeth (just counted them on a spare I have) so what I am now missing is the number of teeth on the crank and the primary shaft where the primary chain runs.Anyone have these figures?