5/8 offset sprocket measure question

Im a lttle unclear in how to measure for an offset sprocket?

Where do you normally measure the delta from? For example on the 5/8 sprocket where does that 5/8s increase start from?

In my pic measured from the the outside of the exhisting front 630 sprocket and the. lazer is sitting on the the r1 wheel hub touching against the inside of the rear sprocket. Thinking back I probably should take the front measurement from the inside of the front sprocket.

#Fixed bad pictures.

Someone else may chime in to correct me (Leon) but where you are measuring from for an offset sprocket with the chain staying the same size is of little consequence. Inside face to inside face, outside face to out side face, center line to center line....these should all give you identical measurements. But because you are stepping down (I presume) from a 630 to a 530 chain/sprocket combo, you will need to reference center line to center line only, as this will remove the change in width of the sprockets from your measurement. For example, if you set up a line laser behind your bike and centered on the rear sprocket, it should paint a line straight along the chain run and onto your cases. Measure from the outside face of the stock sprocket to the laser line, then add 1/2 the sprocket thickness to your measurement and voila! You have your offset.

porchev914 wrote: Someone else may chime in to correct me (Leon) but where you are measuring from for an offset sprocket with the chain staying the same size is of little consequence. Inside face to inside face, outside face to out side face, center line to center line....these should all give you identical measurements. But because you are stepping down (I presume) from a 630 to a 530 chain/sprocket combo, you will need to reference center line to center line only, as this will remove the change in width of the sprockets from your measurement. For example, if you set up a line laser behind your bike and centered on the rear sprocket, it should paint a line straight along the chain run and onto your cases. Measure from the outside face of the stock sprocket to the laser line, then add 1/2 the sprocket thickness to your measurement and voila! You have your offset.

Thanks man but this may sound stupid but depending where and how I center the laser Im getting a notable variance in readings, enough that I cant be sure either way. I cant get my laser level and high enough for an accurate reading. The distance of the laser to the sprocket seems to generate different readings as well. Perhaps I need to break out the string but its clumsy to measure with strait edge in that area.

As far as measuring outside or inside from the front sprocket, since I am going from 630 to 530 I'm thinking you would measure from the inside then and add half the new (530) sprocket thickness because the 630 is thicker; if you add half the 530 to the outside 630 thickness you probly run a 1 mm or so too far.

If the wheel is centered id install the rear sprocket and stock front sprocket on the bike.
Then id lay a straightedge across face of rear sprocket and run it up to the countershaft sprocket and measure the gap,that should be your offset needed

What size rim are you using.
A 5.5" is the widest you can use without off setting the wheel.
The inside face of a 5/8th's offset is 101mm from the true centerline of the chassis regardless of chain pitch.
Machine your rear sprocket carrier so the mounting face is 101mm from the wheel center and you should be good to go.

IMO this process is over complicated by most of us although it is expensinve and needs to be as close as possible close is as good as your gonna get IMO.

when measuring mine i put the sprocket i was gonne use (have altered) where it goes took a measurement moved it out to the spot it was straight remeasured and it was 1/2 difference so I had Leon build me a 1/2 inch offset sprocket my chain lined up well and seems to be wearing well (no visible wear) adding 1mm to it in retrospect helped give me 190 tire clearance and still been within acceptable tolerances


I measured and measured anmeasured several different ways and fretted over it for a couple weeks before deciding it was 1/2 inch if I would have went 13mm it would have been just as well maybe a little better but like I said wearing grest as is measure three different ways take the common number LOL

Here's what I did. Clamped a straight piece of aluminum angle to the inner face of the rear sprocket, making sure to contact as much of the sprocket face as I could. Then measured the offset from the inner face of the front stock sprocket. Can't change where the sprocket meets the transmission so figured that was a good base. Came up with something larger then 5/8. Machined the cush drive hub to make the offset 5/8. Then made a spacer that was 5/8 minus the thickness of the 630 sprocket. Clamped it all together, back to the straight edge, and laid the chain on to verify alignment before making the offset sprocket. (Offset the wheel a few mm cause I have a 6" wheel, but don't tell anyone :sick: ).

Doesn't matter what sprockets you're using as long as you measure from the mount surfaces. If you're using different sprockets than you intend to use you'll need to account for that.

I have a 6 inch wheel with the 190 the rear tire I plan on getting a straight edge meter stick to complete the installation. I like the idea of combining the ruler with the clamp idea because it seems simple.

I also like the idea messing with the 101mm so look at that option this weekend if it comes down to it it will depend on how the ruler worked out first. It looks much closer to the frame than the tire that's for sure.

Thanks for the help everybody. I will let you the outcome in the next few days.

zed1015 wrote: What size rim are you using.
A 5.5" is the widest you can use without off setting the wheel.
The inside face of a 5/8th's offset is 101mm from the true centerline of the chassis regardless of chain pitch.
Machine your rear sprocket carrier so the mounting face is 101mm from the wheel center and you should be good to go.

I tried the meter stick but it was slightly flimsy so I dont trust it 100% it was showing 13/16s measuring from the back/inner front sprocket. Laser was around 3/4-15/16

So tired Zed's technique and from center of wheel to the back/inner rear sprocket I am 117mm!! Way over 101. Then I measured how much room I have between the wides point of the tire to the back/inner rear sprocket I am 20mm, so lets say 18 with expansion. A 530 chain is 25mm so 12.5 half. I don't think I can machine the carrier to 101mm otherwise I will be likely rubbing against the tire..

P.S. I can get 520 rear sprocket for the r1 no problem. That would save me 3mm on the front and 1.5 on the rear (IIRC) but the 520 offset kz's fronts seem non-existent.

Use a piece of aluminum or steel for your straightedge

wireman wrote: Use a piece of aluminum or steel for your straightedge

The light bulb just turned on for me. This is super simple. You don't need strait edges, rulers, lasers to determine the front sprocket offset. I feel like doc from back to the future and just hit my head on the toilet and invented the flux capacitor! :lol: :lol:

You guys tell me if I'm wrong in this theory.

Stealing part of zeds technique, to find the offset needed all you have to do is this;

1. Measure from the center of the rear tire to back/inside rear sprocket. My case 117mm

Now Zed says 101mm is the true centerline of the chassis using the 5/8 offset sprocket.

5/8's is 16mm.

2. Minus 16mm from 101mm that's 85mm (stock).

3. Use your measurement from step one and minus it by 85mm. Using mine; 117mm - 85mm = 32mm.

4. Answer I need a 32mm offset front sprocket which equals 1 and 1/4 front sprocket. FAK! :pinch:

So in my case what I can do is machine 5mm of the rear hub and that will give me a 27mm/ 1 1/16th front, subtract the conversion to 530 then that's 1" offset. Where is the crying emoticon? Cause 1" will hit the frame for sure..

I think the only thing I can do is get a custom 520 5/8 offset front sprocket made and take off 8mm then of the hub and find a skinny non o-ring yet high strength chain and accept the slight miss in 100% alignment.

Who's on first? :lol:

Good Fortune!