# Gear Ratio Calculator

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J

#### jpilot

##### Guest
I wrote a little gear ratio calculator that some might find handy. The program can be downloaded from http://jimsitton.net/ratiocalc/ Just right click on the file gearratio.exe and select "save link as" and put it somewhere you can find it again. Once it's saved, double click on the gearratio.exe file and it will run.

The program allows for up to three ratios in series. If you have fewer just leave the unused ratios set to 1:1.

The program will also calculate speed based on engine RPM, drive ratio,and wheel diameter. Be sure to measure the outside diameter of your wheel for accurate results.

If you have any questions post them in this thread.

Have fun!

Thanks. That looks like it will be handy.

I was just playing with your calculator and using numbers for the Grubee 4-stroke set up I get a top speed of 28.9 mph for the 56t final drive sprocket @ 8000rpm. But yet members here have been reporting top speeds 10mph higher with the same set up. Why would the math and the actual mph differ so much? The Grubee Site indicates that their gear box provides a 4.20:1 reduction and then you have an 11t to a 56t final drive. Don't take these questions as a complaint. I've been punching in the numbers for various belt drive pulleys I've been considering for my current project and your program has been very helpful to compare various set ups.

ocscully

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I'm glad you found the program useful.

I can't explain the difference between calculated and actual speeds. I'm pretty sure my math is correct. Have the people that reported the higher speeds actually used a tachometer to measure engine revs or are they guessing?

i think peeps feel like they're going faster, so they report faster speeds...

i know i did...my analogue speedo said 40, i was clocked at 30, but it felt like 50

btw-thank you for a great contribution

Claimed MPH vs Calculator

http://www.motoredbikes.com/showthread.php?t=7224&page=11 At this link two members are claiming 40mph or better. likemyspoiler says 44mph and HoughMade is reporting 40+. perhaps they can offer how these readings were determined? I have no reason to doubt them, I just find it interesting that the math says something different is all, and am curious as to why?

ocscully

Excellent Calculator

Thanks!!!!--------->

the old Spitfire engine site had one....but not this cool!!

I didn't find any mention of engine RPM in the thread you referenced. Where did you get the 8000 RPM number? likemyspoiler said in the thread that his speed was verified by GPS but, again, nobody mentioned a value for engine revs at the stated speeds.

The numbers don't lie. If you enter accurate data for ratios and wheel size in my little program, you can adjust the value for RPM until you get the stated speed. That will be very close to the revs the engine was turning at the given speed. That, of course, assumes no slippage in the drive train.

I have to agree with Augi's post....sometimes I think these little bikes feel faster than they actually are....I have a bike outfitted with a digital tach and speedo and with stock gearing I really don't wanna go 30 MPH for fear of throwing a rod due to excessive rpm's....It feels like she may even blow at 27 MPH....I think it was pushing 5900 RPM but I'll have to double check cause memory isn't as good as it used to be!....YOu are right...if the formulas are correct hard to beat calculations.
Andrew

RPM's?

I didn't find any mention of engine RPM in the thread you referenced. Where did you get the 8000 RPM number? likemyspoiler said in the thread that his speed was verified by GPS but, again, nobody mentioned a value for engine revs at the stated speeds.

The numbers don't lie. If you enter accurate data for ratios and wheel size in my little program, you can adjust the value for RPM until you get the stated speed. That will be very close to the revs the engine was turning at the given speed. That, of course, assumes no slippage in the drive train.

I pulled the 8000 rpm from the power curve tables provided by Honda USA . They provide a power curve and torque chart as part of their specs on the GXH 50, 8000 rpm is at the high end of their recommended range for operating this engine. HoughMade has mentioned in other posts that he has disconnected the governer on his motor so perhaps you are right and the RPM's may be higher.

I'd like to again say that your calculator is really great. I've used it several times to day to compare various drive trains I've been considering. Thanks for a great tool.

ocscully

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