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Post by KSR Moto on Mar 21, 2019 5:43:40 GMT -5
I noticed that there are several stock gear ratios for 139qmb, some take 11 rotarions of the clutch bell for 1 rotation of the wheel, I even came across with engines that had 15:1(10" wheel), while long case engine often has 13:1
Are there any 9:1 gears that I can buy, I want to install them on 139qmb short case with 47mm BBK, and which ratio would you recommend
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Post by 90GTVert on Mar 22, 2019 7:10:15 GMT -5
The numbers that you are quoting are final drive ratios. Gear sets are usually sold for either primary or secondary gears. Both primary and secondary gears are in the gearbox and combine to make the final drive ratio. More info on that here : 49ccscoot.proboards.com/thread/3472/primary-secondary-final-drive-ratioSo if you are aiming for a specific final drive ratio, the best bet is to find out what primary and secondary ratios your scooter has. Then look for either a primary or secondary gear set that will put the final drive ratio where you want it, or close. Here are some calculations of secondary gear sets for the 139QMB and what the final drive ratio would be with them. For final drive ratio I am assuming stock primary ratio is 3.25:1 (52/16 primary gears). These are common, but I don't think all 139QMBs use these. You will need to know for sure what your gear ratios are to know what your final drive ratio is or will be. Secondary
Tooth Count
| Secondary
Ratio
| Final Drive Ratio w/
3.25:1 Primary Gears
| Brand Or Seller
| 52/14
| 3.714:1
| 12.071:1
| Naraku NK900.57
| 51/15
| 3.4:1
| 11.05:1
| Common Stock
| 50/16
| 3.125:1
| 10.156:1
| Top Racing
| 49/17
| 2.882:1
| 9.3665:1
| ScrappyDog, Top Racing, Scooters To Go
| 42/16
| 2.625:1
| 8.531:1
| Hoca
| 46/18
| 2.556:1
| 8.307:1
| Hoca
| 41/17
| 2.412:1
| 7.839:1
| Hoca
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Post by KSR Moto on Mar 22, 2019 13:13:49 GMT -5
Excellent explanation as always thank you!🙂
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larryhobman
Scoot Enthusiast
Posts: 117
Location: Delaware beaches
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Post by larryhobman on Mar 27, 2019 8:15:50 GMT -5
I would not run the 9:1 (49/17) with a 47mm. I did that and I was forever changing weight and springs to get the desired results. I feel it might be ok with a 50mm set up but the 47 is too light. I went back to a 11:1 ratio. I have 2 other scoots one has the 15:1 and the other has 13:1. The 15:1 has a lot of low end so it all depends on what you are trying to get out of it. Do you need high speed or low end power.
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Post by benji on Mar 27, 2019 9:04:34 GMT -5
11:1 is considered "perfect" for little scooters by some guys. Anything taller than that, and you're going to need some decent power I think.
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larryhobman
Scoot Enthusiast
Posts: 117
Location: Delaware beaches
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Post by larryhobman on Mar 27, 2019 9:18:41 GMT -5
I'm going to stick with the 11:1 I feel that it is best too. I have 3 scoots to play with trying different combinations.
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Post by idoseadoo on May 8, 2019 11:49:53 GMT -5
What top speed can I achieve with the stock 10" tires and a 11:1 ratio provided I run the engine around 8000rpm? What's a healthy RPM for a 70cc BBK? I hear going anywhere near 80cc or higher is real detrimental to the crank connecting rod bearings... I don't want to build this thing only to have it blow the crank...
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Post by jdaley1847 on Jun 16, 2019 18:28:17 GMT -5
What top speed can I achieve with the stock 10" tires and a 11:1 ratio provided I run the engine around 8000rpm? What's a healthy RPM for a 70cc BBK? I hear going anywhere near 80cc or higher is real detrimental to the crank connecting rod bearings... I don't want to build this thing only to have it blow the crank... 8000 to 8500 rpm is power band, with that lower ratio want to say 40 to maybe 45mph. |
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