Z1 Sprocket change question

I have a '73 Z1-900 that was running a 42T rear sprocket on a 16" rear wheel and stock hub. I'm swapping to a '80 KZ750G 16" rear wheel and it mocks up perfectly, but the sprocket on that wheel is a 38T and obviously much smaller in diameter than the 42T that was on my Z1. If I buy a 42T rear sprocket for the '80 KZ750G wheel (the sprocket on the Z1 hub has a larger bolt pattern), will it be the same size as the 42T Z1 sprocket? Sorry if this is a stupid question, as this is my first time altering gearing.

if chain series is same diameter of sprocket should be same i would think

Buckeye73z1 wrote:

I have a '73 Z1-900 that was running a 42T rear sprocket on a 16" rear wheel and stock hub. I'm swapping to a '80 KZ750G 16" rear wheel and it mocks up perfectly, but the sprocket on that wheel is a 38T and obviously much smaller in diameter than the 42T that was on my Z1. If I buy a 42T rear sprocket for the '80 KZ750G wheel (the sprocket on the Z1 hub has a larger bolt pattern), will it be the same size as the 42T Z1 sprocket? Sorry if this is a stupid question, as this is my first time altering gearing.

whoa dude, the 73 had a 35 tooth as a stock sprocket (for 18 inch wheel), a 42 ???? I did the same change (to a 80 750) and actually went down a couple to a 33, just order for the 750, what tire u running, that would make a difference, the tire I'm running actually made the outer circumfrence about the same on the 16 ( by way of a higher profile)as the 18, that would be something you would want to know, that being said it probably would be enough of a difference to matter significantly, besides the sprockets arent that expensive, as wirenut said the chain is the same so it should be the same as far as sprocket size

Run the numbers through this website: www.gearingcommander.com

Buckeye73z1 wrote:

I have a '73 Z1-900 that was running a 42T rear sprocket on a 16" rear wheel and stock hub. I'm swapping to a '80 KZ750G 16" rear wheel and it mocks up perfectly, but the sprocket on that wheel is a 38T and obviously much smaller in diameter than the 42T that was on my Z1. If I buy a 42T rear sprocket for the '80 KZ750G wheel (the sprocket on the Z1 hub has a larger bolt pattern), will it be the same size as the 42T Z1 sprocket? Sorry if this is a stupid question, as this is my first time altering gearing.

Stock Z1 has 35T rear (and 15T front).
42T is oversize. Even 38T is oversize.
Oversize rear produces lower top gearing (i.e., relatively higher rpm at any given road speed).

Stock Z1 has 18" rear wheel.
Rear tire on 16" wheel with about same overall diameter as rear tire on 18" wheel won't by itself make a significant difference in overall gearing, especially if the distance from rear axle to road surface is equivalent. My Z1 with 18" rear wheel and KZ900-B1 LTD with 16" rear wheel have approximately equal rear tire heights (and rear axle heights).

Would first test ride with the 38T rear, and then decide whether lower top gearing is desired, because the 38T is still producing lower top gearing than the stock 35T.

The 1976 KZ900 standard model kept 35T rear in the USA and Italy, and changed on UK models to 33T rear (slightly taller overall gearing which sometimes produces less buzz at highway speed).

Good Fortune!

and if u get a new sprocket, u will need to get a new front sprocket AND a new chain, dont mix old and new

I haven't looked at the tooth count on the front sprocket yet, but the 42T rear, front sprocket, and chain that were on the bike when I got it have maybe 200 miles on them, if that. The rear is lowered 2"-3" on struts with a 130/90/16 tire. I rode the bike (was my buddy's previously) with the 42T (and a 150/80/16 on the old 4" wide 16" rim)and it screamed. Revs weren't completely out of control at highway speed and he had the bike up to an (indicated) 130mph and he said the bike had more in it. I know 130mph may not be 100% accurate due to natural margin of error in a motorcycle speedo and regearing, but my point is it has PLENTY up top and is no slouch off the line. According to the gearing commander, with the set up that was on the bike, the front sprocket must be at least an 18T to get 130mph with a 42T on the rear and the 150/80/16 tire on the back. I'll check when I get home this evening to confirm the front sprocket size.

well the rear tire size will explain some of the extra teeth, I had a 130/80/18 which would be a little larger, not to much though, I'm betting the front spocket is not a stock number of teeth

check the pitch of the chain. pin center to pin center - 530 = 5/8", 630 = 3/4".

MFolks wrote:

Run the numbers through this website: www.gearingcommander.com

This is AWESOME! Thank you!

Jeff.Saunders wrote:

check the pitch of the chain. pin center to pin center - 530 = 5/8", 630 = 3/4".

ah yes a possible chain conversion, didnt think of that one

Jeff.Saunders wrote:

check the pitch of the chain. pin center to pin center - 530 = 5/8", 630 = 3/4".

Excellent. Thanks, Jeff. I need a 903z account (like 401k) that would automatically deduct a set amount from each paycheck and wire it to Z1E. I wonder if the IRS would allow me to make pre-tax deductions for "bike support". LOL, it's almost like one of my children :laugh: BTW your service is top-notch and I got my last order in 1.5 days after it was placed. AWESOME!