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View Full Version : Sprocket diameter



buildstoys
09-08-2006, 06:11 PM
What sprocket size/diameter are people using?

Just trying to mock-up my bearing carrier.

I should be clear on the sprocket side, but have to redo my header solely because of the brake rotor hitting.

Also, I remeber someone on a Yahoo group helping me calculate my Honda 250 sprocket ratio. What ratio should I be using for my 2003 Honda VTR1000 engine in dirt/mud with, say 25" tires?


Kasey

Gene
09-08-2006, 08:12 PM
My car was originally chain driven and had a 14 countershaft and a 64 sprocket. It had 31 inch tires and was geared too high. A 13/70 would have been much better, 13/80 better yet.

Other's will offer different opinions. Based on my experience with my 'Busa engine, 6.5:1 is a good target. My current setup should give 6.94:1 and I expect that to be very good.

I should be able to release the clutch in first without having to give much or any throttle and it will just pull away. First gear will top out in the high 20's or low 30 mph range. Sixth gear should give me 120. I want to spend my time in 2nd, 3rd and 4th - not 1st as was the case when I had sprockets.

Gene

buildstoys
09-08-2006, 08:29 PM
How are you arriving at that ratio though, or how should I arrive at a ratio for my setup (without buying 15 different size sprockets)?

Also, what is the diameter of your rear sprocket?


Kasey

Bugpac
09-08-2006, 08:37 PM
there is a few guys on here that can run it on a gear chart for you, rowyco being one of them, if you ask he may help you out... 8)

Gene
09-08-2006, 10:04 PM
When I talked about sprockets I was simply dividing larger by smaller for a ratio. It is simplistic and does not account for tire diameter.

What I know about my orignial setup is sea-of-the-pants. It would go 50 + in 1st and I think that is ridiculously hard on the engine and tranny. I used 3rd but could easily attain 100 mph at higher RPM. I made it to 6th but it was nuts.

On the first page of my build I posted a spreadsheet on final drive ratio that took into account tranny gearing and tire size and allowed you to plug in various differential ratios.

You can use that too. Just determine your sprocket ratio and plug in the numbers. Excel will do the rest for you. Of course you will need your tranny ratios but those are generally available.

I can help you if you don't have excel. Just tell me your tranny ratios and tire diameter. I'll make several spreadsheets to depict speed in gear at RPM to give an idea of where you are with speed. If you know torque curve then you can figure out where your engine begins to breathe or expire.
Gene

K-fab
09-09-2006, 06:00 AM
you can figure out where your engine begins to breathe or expire.
GeneOver the years, mine engines seem to expire when they:
1) Sieze
2) Drop a valve
3) Run out of fuel
4) Run out of coolant
5) Loose oil pressure

How'd you figure these aspects out with Excel? :shock: :?
Idiots, er, enquiring minds wanna know! :roll:

buildstoys
09-09-2006, 06:06 AM
I have a gear calc program (screenshots below) that I can use.

I just didn't know how you arrived at your determined sizes, ie did you just think you should only go 30mph in first and that would give you the right amount of torque, etc....

I don't care what my top speed is, just obviously want smooth usable power in middle gears. Since I don't want to spend money on trying out 10 different sprocket sizes, I thought I'd ask if there was a "target" ratio to shoot for.

Gene
09-09-2006, 09:23 AM
I was really talking about knowing the engine torque curve, then selecting a final drive ratio that complemented torque curve overlap between gears at speeds that seem reasonable for driving pleasure.

My engine starts to breathe at about 3500 to 4000 RPM and begins to expire at 9000 or 9500. for me, breathing is where the torque curve begins or where the engine comes on the pipe and expiration is when the torque curve begins to flatten.

I want to stay in the torque curve. I look at my Excel results to see how gear selection at speed will maintain torque curve targets. I consider how fast I think is reasonable for a particular gear and when I shift to optimally stay on the pipe.

Inference does it - not Excel.

Gene

yoshi
09-09-2006, 11:03 AM
I have a gear calc program (screenshots below) that I can use.

I just didn't know how you arrived at your determined sizes, ie did you just think you should only go 30mph in first and that would give you the right amount of torque, etc....

I don't care what my top speed is, just obviously want smooth usable power in middle gears. Since I don't want to spend money on trying out 10 different sprocket sizes, I thought I'd ask if there was a "target" ratio to shoot for.I kept clicking the "buggy pictures" folder on the top right of your screen but it wouldn't open up?

rowycoracing
09-09-2006, 11:59 AM
One idea to consider is to shoot for being in the middle of the gear box and the middle of the power band at about 45 - 50 mph or so. If you are not planning to use a jack shaft that will likely give you a pretty huge rear sprocket, but you can then either go with a jack shaft or adjust the sprocket down within reason. I would predict that you are going to end up somewhere around 6 or 6.5:1.

buildstoys
09-09-2006, 03:20 PM
Tim and Gene, thanks for the info.

I don't want to use a jackshaft and have the manual for the engine, so I'll see what I can come up with.

Yoshi, not sure why your mouse isn't clicking so I did it for you :D



Kasey