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Discussion Starter #1 (Edited)
To whom it may concern, I need help to increase top speed for my Honda Monkey, I had tagegawa 181cc , power commander and air tune in my Monkey, my stock sprocket was 15t-34t, I can drive up to 62 mph, now I changed it to 16t and 32t, but my top speed 65 max, what is going on here :), thanks


Daniel
 

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Assuming your engine can reach the same rpm, it should have increased to ~70mph [62*(0.5/0.44)]. But, you have probably just run out of horsepower, and can't go any faster than that. Maybe lie down on the tank and peer over the bars (no windshield, of course), and you might get another 1 or 2.
 

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In pics of the Monkey, it looks like the speedometer is driven at the countershaft (front sprocket), not the front wheel. If that is so, the speedo will not read accurately after the gearing change. In fact I would expect actual speed to be 13% above indicated.

If the speedo is indeed driven at the front wheel, I don't know what the heck I'm talking about so you should ignore this post.
 

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Same as what Wintr is hinting at. You need more horsepower to go faster, and it gets much worsa around 90.
Wot revs were you doing before, wot are you doing now. Wot revs can you get in the lower gears. Can you get close to that in top gear. With out knowing these things, the question can not be answered. If the missing info is not provided, go back to the original. You need more horsepower.

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If anybody want's a somewhat technical explanation of the nature of Horsepower vs Air Resistance related to speed, you can get it here:

This is actually simplified, because the coefficient of drag has been shown to change with speed, but close enough to give you the idea.

Here's a calculator I've used:

Old school motorcycles, and naked bikes will have a Cd around 1.0. I'd put the Monkey in that class. You can estimate the bikes frontal area by your seated height x width of outside your hands on the bar x something like .75. A more accurate method is to use a long lens to take a picture of rider and bike, then superimpose this on graph paper or use a program to calculate area. Weight is combined weight of bike and rider which affects rolling resistance but not air resistance. Since the OP knows his top end velocity and rated horsepower, with a good estimate of his frontal area, he can back out the Cd of his machine.

Which comes down to saying just what WintrSol is saying:

Does anybody know where there is a nice chart or graph that shows the relative contribution of rolling resistance and air resistance at a range of speeds?

What is the expected horsepower of your modified Tagegawa 181 ?

As Eddie A. hints, you would want to use GPS to verify speed. With a 13% increase in gear ratio, and if the speedo comes off the sprocket, that 65 indicated vs the old 62 means you were going 73-1/2 mph. Did it FEEL that much faster?

Where I live I can calibrate my speedo by driving past a park or school where they have one of those signs that nags you to slow down by posting your speed as you go by.
 

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If you wanted a fast bike, the Monkey was not the way to go. You just need a bigger bike with a more powerful engine. The Monkey is like my little Honda PCX150 scooter. I love riding it around town and for quick errands, and I can get it up to just about 65 mph in stock condition, which is enough to safely ride on 55 mph roads. But if I want speed, or to go on the highway, I take out my Goldwing and can cruise comfortably if desired at triple digit speed. But even a small, but larger than the Monkey, motorcycle of 300cc or higher would be enough to get up to highway speeds, even if the buzziness of a little engine at high revs didn't tire you out. FWIW, I have found in my many years of riding that when you make the motorcycle work hard by keeping it high in the rev range, it made ME feel tired. Even my old Triumph America, with 853cc (if I recall correctly) seemed like it was straining when I was on the Interstate, especially two up, and it wore me out quickly. When I moved up to a Triumph Thunderbird, with a 1600cc engine, two up 80 mph riding was a breeze. But nothing compares with the smoothness and comfort of my Goldwing. Good luck with whatever you decide to do, but I think a trade-up to a bigger bike makes more sense than trying to squeeze out a bit more power from that tiny Monkey engine.
 

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Is the quest for more speed to ride highways or is it more just to see how much can be squeezed out of the little thing? I thought it was the latter but could be grossly wrong which I rarely am
🙄🙄🙄😀😀😀🤪🤪🤪
 

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It seems for most people that whatever bike they buy they immediately seek to increase its power or top speed. Going to after market pipes (which I never found had the benefits that some seemed to claim, I think that after spending the big bucks and hearing the louder sound they convince themselves that the bikes are SO much better), then changing sprockets, and on and on. I think a more reasonable method is to buy low priced used bikes, trading up often until you reach the point where you have the power, weight and comfort that you seek. If its just speed, then looking at any cruiser is a futile effort for the most part. Even an older 600cc sport bike will have the acceleration and top speed that will far exceed most riders needs or use other than on the racetrack. And at some point, some start to feel that the size and weight of the bike that can comfortably transport them at high speed and little or no vibration is just too big to still give them the sensation of riding that they sought in the first place. But with a bit of trial and error, I think most people can find their niche in the motorcycle world, and change niches when so desired. Just be true to yourself. If inwardly what you really want is a cool looking cruiser that you can take to the local tavern and have admired by your drinking buddies, then don't waste time with sport bikes, or sport tourers or anything but a big V-twin and just live with the limitations of that style bike. Personally, I started with a cruiser, went to a standard, went back to a bigger cruiser, switched to a mega-scooter after double knee replacement, then back to even bigger cruisers and now loving my touring bike, a 2016 Goldwing with all the bells and whistles (I doubt I could ever go back to less than a fairing or really good windscreen, to built in cruise control and GPS navigation, or the ability to relatively quietly ride along at top highway speed in comfort, but that's just me and my age speaking).
 

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Discussion Starter #9
Assuming your engine can reach the same rpm, it should have increased to ~70mph [62*(0.5/0.44)]. But, you have probably just run out of horsepower, and can't go any faster than that. Maybe lie down on the tank and peer over the bars (no windshield, of course), and you might get another 1 or 2.
thank you for reply
 

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Some Google sleuthing shows that the Monkey's speedometer is driven off the countershaft. If you haven't installed a calibration device or manually corrected the 65 mph speed before you posted, that speed reading is wrong. The correct reading is as johnnyvee posted: Add 13%. So after the sprocket change, 65 mph indicated is actually 65 + 13% * 65 = 75 (just as johnnyvee said).

That's very good! Congrats. Not only did you raise top speed, but I'll bet you also improved acceleration significantly and will get up to that speed much quicker.

Were you expecting more? At the risk of spoiling the ending of johnnyvee's links, that's about as good as it gets with your mods. Increasing displacement by 45%--from 125 to 181cc--will in the best case increase power by 45%. It's not necessarily going to be that much, however, since intake and exhaust tracts may not support such a big cylinder.

How much more speed should you expect from a 45% power increase? The power required to maintain a certain speed increases with the cube of speed (to double top speed you need eight times as much power). A 45% power increase will raise top speed by the cube root of 1.45 or 1.13--coincidentally the same as your gearing increase. I'd say you got as much speed as you could expect from the 181 kit and got much better acceleration, too.

Also a note about measuring top speed: It's hard to do accurately and reliably. A barely noticeable grade or wind screws it up. Don't put too much faith in an indicated difference of a few mph unless you've been very careful about standardizing conditions.
 

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Discussion Starter #11
thank you for reply
In pics of the Monkey, it looks like the speedometer is driven at the countershaft (front sprocket), not the front wheel. If that is so, the speedo will not read accurately after the gearing change. In fact I would expect actual speed to be 13% above indicated.

If the speedo is indeed driven at the front wheel, I don't know what the heck I'm talking about so you should ignore this post.
I should say my stock bike can run 61mph max but take time to get there, so I upgrade to 181cc with what ever I have to add to make it run better , I even change my front sprocket 1 t up and back sprocket down 2t but my cell gps show only 65mph max might go up 5 more mph with down hill :)
 

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Just a note. If you raise the gear ratio, you will NOT improve acceleration. Sometimes you do not improve top speed. You only have so much horsepower to work worth. Next step is to reduce drag. However you are below the speed where air drag becomes a big problem. 70 mph with 181 cc 4 stroke motor is a lot.
Use a GPS to check your speed. Original stuff is not reliable. Having a reliable number for horsepower also helps.
They all run faster on Saturday nights.

UK
 

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Discussion Starter #13
Just a note. If you raise the gear ratio, you will NOT improve acceleration. Sometimes you do not improve top speed. You only have so much horsepower to work worth. Next step is to reduce drag. However you are below the speed where air drag becomes a big problem. 70 mph with 181 cc 4 stroke motor is a lot.
Use a GPS to check your speed. Original stuff is not reliable. Having a reliable number for horsepower also helps.
They all run faster on Saturday nights.

UK
Just a note. If you raise the gear ratio, you will NOT improve acceleration. Sometimes you do not improve top speed. You only have so much horsepower to work worth. Next step is to reduce drag. However you are below the speed where air drag becomes a big problem. 70 mph with 181 cc 4 stroke motor is a lot.
Use a GPS to check your speed. Original stuff is not reliable. Having a reliable number for horsepower also helps.
They all run faster on Saturday nights.

UK
got it, thank you very much
 
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