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 Zuma 125 Gear Ratio Upgrade 
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Post Zuma 125 Gear Ratio Upgrade
Zuma 125 Final Drive Gear Upgrade
By: Electrojake

Scooter owners are always looking for a tad more spunk; 155cc kits, CVT upgrades, even windshields with blue flames or those famous C3 mirrors. Anything to grab an extra MPH or two. In my quest for yet more of those elusive MPH’s I chose to upgrade my final drive ratio from 10.5:1 to a reasonable 8.5:1.

The stock ratio of a Zuma 125 is set at ten and a half turns of the clutch bell will give you one rotation of the rear tire. The gear mod I did means that now my engine only has to turn the clutch bell eight and a half times to get the rear tire to make one revelation. <got that?>

By changing two simple gears (about a one hour job) I was able to add 4 MPH to my top speed with no loss in acceleration. I was truly impressed with the improvement.

Rather than make you all suffer through another one of my Electro489 YouTube videos, I’ll just do the review right here.

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As you can see here, you have to pull the variator out to get to the gearbox. The gearbox cover is held on with the exact same size 8mm bolts that hold on the CVT cover. Oh yeah, remember to drain the gear oil before you pull the cover.

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Another shot of the gearcase with the gears removed. No special tools required, they simply slide right out.

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To keep things simple, do not pull apart these shaft parts once this cover is removed. It all slides back in very nicely as a single unit.

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Another shot of the gearcase cover. Nothing has to be done here.

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Here on the purple mat is a shot of the new gears before assembly. They looked a little rough to me, perhaps a lower quality than the stock Yamaha gears.

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This shot of the stock Zuma gears is very important!
The stock gear shown to the left in the above photo has to have its center shaft pressed out and then the new shaft (the one on the right side of the purple mat photo above) has to be pressed in.

Fortunately I have a 12 ton hydraulic press in my shop so it was no problem but, If you don’t have a press, it would be mighty difficult to do this simple gear change. You might be able to substitute a press with a nice hefty bench vise and a couple of deep well sockets though.

The gears are available in the following ratios:
13/38 or 2.92:1
14/36 or 2.57:1
15/36 or 2.40:1
17/36 or 2.12:1
Keep in mind that a stock Zuma is 11/44 or 4.00:1
The gears set I chose was 2.92:1. It represents the mildest upgrade available. It bought me an extra 4 MPH with no loss in acceleration! <Results may vary> An even higher ratio may have made my Zuma even faster but I was worried about getting behind the torque curve which might take the pep out of the bottom end. Another added benefit of this gear change is that now when I cruise along at 40 MPH my RPM’s are substantially lower and the bike runs noticeably more relaxed. I expect an increase in fuel economy too! Note that if I do slam open the throttle at a 40 MPH cruise, I still get a nice sharp blast of acceleration thanks to the CVT set-up I got from SamuraiScoot.com.

The gear set I used was distributed by http://www.liang-huei.com.tw but I strongly suggest you chat with Smelly at http://www.samuraiscoot.com before you take the plunge.

Special thanks to the tech staff at SamuraiScoot.com for dialing this in for me. With additional fine tuning of the CVT, I am expecting those gears to give me even more at the top end, perhaps 5, 6, 7 MPH or more? We’ll see.

Thanks Smelly!
-Ej-

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Fri Mar 20, 2009 6:59 pm
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Post Re: Zuma 125 Gear Ratio Upgrade
Very nice write-up!

Write-ups like these are clear and leave little room for error. Well done.

Thanks, EJ! :cheers:

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Sat Mar 21, 2009 9:14 am
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Post Re: Zuma 125 Gear Ratio Upgrade
:thumbs up:

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Sat Mar 21, 2009 9:40 am
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Post Re: Zuma 125 Gear Ratio Upgrade
I was actually thinking of doing this myself but was worried to lose a lot of my low end torque/acceleration.

I guess going with the 2.92 gears isn't all that bad?

What your top speed now?

myke

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Sun Mar 22, 2009 5:55 am
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Post Re: Zuma 125 Gear Ratio Upgrade
Awesome write up EJ :cheers:

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Sun Mar 22, 2009 8:02 am
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Post Re: Zuma 125 Gear Ratio Upgrade
I agree, awesome write up. I will be ordering this soon. Working on a suspension upgrade and then will move to gearing.


Sun Mar 22, 2009 8:27 am
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Post Re: Zuma 125 Gear Ratio Upgrade
Great information.

Might I suggest you post you weight if you don't mind.
If your a buck fifty and someone else is a deuce and a quarter -- results could be quite different.

i have decided to get a 125 so I am collecting all the best info I can. :q:

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Sun Mar 22, 2009 8:32 am
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Post Re: Zuma 125 Gear Ratio Upgrade
IBJanky wrote:
What's your top speed now?
myke

In the generic sense I’ll say 60 MPH.

Not being a mechanic, it has been my observation that. . .
These little 4 stroke engines seem to be plenty robust in the lower RPMs. It’s at the top that all the fine tuning and tinkering becomes a necessity. The torque curve drops off drastically and of course my seat-of-the-pants dyno testing is affected by mood, wind, and the cager in front of me. :D

The pleasant surprise was the added drivability that I gained in the middle cruising range. The entire bike feels more relaxed at the frequently traveled 40 to 50 MPH range. People say I’m nuts but is sure seems as if my 5 to 25 MPH launch has been greatly improved by the gear-up too!

Smelly, who is not overly fond of the gear-up on these already under powered Zumas’ seems to feel that my pleasant increase in performance is indicative of an improperly tuned CVT. I am currently farting around with sliders, weights, contras, over sized belts, etc…

The trick is to stay on top of that torque curve when approaching the notoriously weak W.O.T. quadrant. I can’t help but wonder what would have happened if I went even higher with 2.57 gears.

So yeah, top speed results would be as follows. . .
Down hill in a tuck: 70
Flat ground, no wind: 63
On the highway with typical wind, traffic, etc,: 57
But keep in mind that if you’re cruising along at 60 MPH, it’s soft. The slightest hill or head wind is going to push you back down into the 50’s.

155cc can only go so far. You’re gonna hit the proverbial wall at about 58 MPH GPS speed. Anything above that is fun but not reliable due to how soft it is up there in the torque curve. Also, the gear swap is easy to un-do if you don’t like it.

So tell me I.B., are wrenching on those BIG bikes this much fun too?
Regards, :cheers:
-Ej-

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Sun Mar 22, 2009 8:48 am
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Post Re: Zuma 125 Gear Ratio Upgrade
ZumaScoot5 wrote:
Great information.
Might I suggest you post you weight if you don't mind.
If your a buck fifty and someone else is a deuce and a quarter -- results could be quite different.
I have decided to get a 125 so I am collecting all the best info I can. :q:

My riding weight, helmet, gloves, etc…
is 200 pounds.
I’m 6’3” tall so I’m a bit of a wind target. It’s kind of difficult for someone my size to “get small” behind a fairing or windshield.

You pose a good question though.
I would imagine that a smaller person would certainly get better performance results than I do.

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Mon Mar 23, 2009 2:05 pm
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Post Re: Zuma 125 Gear Ratio Upgrade
Nice post, is your Zuma stock besides the RRGS variator? If you have a 155cc kit obviously that changes everything. Do you have a tach? It would be interesting to compare your cruising (55-60mph) RPMs vs. the peak hp RPM.


Tue Mar 24, 2009 10:38 pm
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Post Re: Zuma 125 Gear Ratio Upgrade
dandydan wrote:
Nice post, is your Zuma stock besides the RRGS variator? If you have a 155cc kit obviously that changes everything. Do you have a tach?

As for the tachometer. . .
The short answer is “no”.
Yeah, I should stop worrying about the obnoxious price and the fact that I can’t seem to come up with a “slick” way to mount one. I have Tiny-Tach’s on two of my other bikes but damn they’re ugly. Couldn’t bear to hang one on my pristine Zuma.

Current excuses for no tach on my Zuma 155:
1.) A Tiny-Tach looks like crap.
2.) A Yamaha tach is $250 and too bulky.
3.) A sweet looking Dakota Digital tach costs about $425 with a mount. (My Zuma addiction goes well beyond the stimulus package). :q:

As for my scoot. . .
I have the 155cc up-grade kit,
The high cam,
K&S ECU mod,
And the version-2 Razer exhaust.
I am also running the complete CVT upgrade kit as sold by SamuraiScoot.com, (variator, clutch, bell).

Regards,
-Ej-

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Wed Mar 25, 2009 6:21 pm
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Post Re: Zuma 125 Gear Ratio Upgrade
Good to know about the 155cc kit and the cam. I wonder if a stock Z125 would have enough power to pull this taller gear ratio.

Regarding the tach, why don't you use one of your tiny tachs temporarily just to observe it's behavior? I have a tiny tach but I also have a Yamaha tach/hour meter that is very similar to the tiny tach. I got the Yamaha tach for about $45 and it's better than the tiny tach because there's just one wire instead of two and because it's way easier to get an accurate signal.


Wed Mar 25, 2009 10:26 pm
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Post Re: Zuma 125 Gear Ratio Upgrade
dandydan wrote:
It would be interesting to compare your cruising (55-60mph) RPMs vs. the peak hp RPM.

The positive effects of the engine relaxing at cruising speeds is obvious. No sign of lugging either. My final ratio change was a 19% increase. Just enough to take the edge off, but not enough to bog her down. <check that math, eh?>

I do agree with you though. . .
It would have been clever to create an MPH to RPM chart to show the difference of before & after the gear change.

By the way. . .
Do “YOU” have a tach on your Zuma 125?
Since your Zuma is stock, it would be nice to get a base-line RPM reading at 40 MPH so I could compare it with mine. (Once I finally get a tach).
And by the way, anybody know what the recommended red-line RPM is for these Zuma 125 engines? :confused:

Geez this got complicated :doh:

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Thu Mar 26, 2009 5:49 pm
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Post Re: Zuma 125 Gear Ratio Upgrade
I have a Yamaha tach that just wraps about the spark plug wire. I get my Z125 in 2 days and depending on the weather (I live in Whistler, BC, Canada) I'll hook up the tach and get that info.

The HP peak is at 8500rpm I believe and I think the redline is supposed to be around 9400 RPM. The torque peak is around 7000 RPM I think, so somewhere between 7 - 8.5K RPM would be where you'd want to be cruising at. Probably not too close to 7K or you'd fall off the power as soon as you start to slow down up a hill.


Thu Mar 26, 2009 7:40 pm
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Post Re: Zuma 125 Gear Ratio Upgrade
Thanks!
That’s great tech information.
Good luck with your New Zuma too.
You’re going to love the thing.
The older they get, the faster they go.
After about 1500 miles mine seemed to grow wings.

Regards, :cheers:
-Ej-

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Fri Mar 27, 2009 4:31 am
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