Sprocket change suggestions

[dzl862]

I’m looking at the sprockets, now knowing that a larger front and a smaller rear increases top speed (see my last post to see me learn the hard way), and I want to make the gears as tall as possible, meaning increasing my top speed with disregard for torque lost. This would mean that I use the biggest front sprocket I can find and the smallest rear, which would be a 17F and a 34R on a 428 chain, or a 14F and a 30R on a 520. Which would ultimately increase my top speed, make the gears taller, and push my bike further?

[Megadan]

Originally Posted by dzl862

I’m looking at the sprockets, now knowing that a larger front and a smaller rear increases top speed (see my last post to see me learn the hard way), and I want to make the gears as tall as possible, meaning increasing my top speed with disregard for torque lost. This would mean that I use the biggest front sprocket I can find and the smallest rear, which would be a 17F and a 34R on a 428 chain, or a 14F and a 30R on a 520. Which would ultimately increase my top speed, make the gears taller, and push my bike further?

Yes, your thinking is correct. A larger front and/or smaller rear sprocket do indeed decrease the gear ratio numerically, also known as making the gearing "taller" which would decrease RPM for the same relative speed.

The 14 tooth 520 front sprocket is a bit too big to use on the CG engines, the 13 is the largest practical sprocket, but is more than sufficient to achieve any ratio you may need or desire.

That now being covered I would suggest not going too extreme. These little motors are torquey, but their output is limited and it is entirely possible to reach a point where the torque output at the tire is insufficient to push the bike along, and contrary to what you might think, a bike with shorter gearing (numerically higher) can actually end up having a higher top speed.

If you are a small light person living in fairly flat country at lower altitudes, you can likely get away with a 2.30 ratio on a bike with a 110/100-18 rear tire, or a 17 front 40 rear on a 428 chain, or 13 front 30 rear on a 520 chain.

Me, personally, the tallest ratio I would run on a 110/100-18 rear tire bike like the Hawk is around a 2.5X ratio, which would be a 17 front 43 rear on a 428, or 13 front 33 rear on a 520.

I still like the 2.70 ratio the most as the best balance for a mostly on-road use bike. In my opinion it strikes the best balance of speed/RPM and acceleration (and hill climbing ability) with the limited output of the CG250 engine.

You need to keep in mind that these bikes are not very aerodynamic and have limited horsepower. Trying to achieve more than 65-68mph top speed is not really that realistic. I have done it, as have others, sure, but even with the work I have done, the top speed increases are minimal thanks to the square laws (4 times the power to go twice as fast in simple terms). I kept my bike geared at a 2.70 ratio and instead use that extra power for better climbing and acceleration instead, and have been quite happy.

If you want to go any faster, get a different bike and save yourself the struggle. Even a more street oriented 250cc chinese bike like the Venom X22R is going to be able to go faster with the same amount of power.

[buzz]

listen to Dan

[krat]

Yes, horsepower and torque are forces in balance. We associate torque with acceleration, but your top speed is more a harnessing of the horses.

After you get to a specific speed depending on your torque your top end is determined by how many horses are pulling the gears.

You feel that fast climb to speed through the gears and then when you hit 5th you are making a slow assent to max speed. When it levels off and will not go any higher, or the rpm turn any faster, you have whipped all you can get out of those ponies.

The perfect gearing is where the top end is the fastest speed your horses can pull. After that your speed will actually decrease. Of course there is a weight restriction too! Jockeys are midgets for a reason.

You only have 15 of them to play with, and all the mods in the world are not going to increase that amount by much. You can spend a couple of thousand $$, or weeks of time, on mods that will never get you past 70, and you could have done that on any used $1500, 250 Honda Rebel.

[Megadan]

Originally Posted by krat

Yes, horsepower and torque are forces in balance. We associate torque with acceleration, but your top speed is more a harnessing of the horses.

After you get to a specific speed depending on your torque your top end is determined by how many horses are pulling the gears.

You feel that fast climb to speed through the gears and then when you hit 5th you are making a slow assent to max speed. When it levels off and will not go any higher, or the rpm turn any faster, you have whipped all you can get out of those ponies.

The perfect gearing is where the top end is the fastest speed your horses can pull. After that your speed will actually decrease. Of course there is a weight restriction too! Jockeys are midgets for a reason.

You only have 15 of them to play with, and all the mods in the world are not going to increase that amount by much. You can spend a couple of thousand $$, or weeks of time, on mods that will never get you past 70, and you could have done that on any used $1500, 250 Honda Rebel.

I don't even have a couple thousand in mods on my entire bike, and it's one.ofnthe most modded ones here. A ported head and cam with an exhaust, 300 to 400 tops, and a decent bump in power considering the starting point.

[Deckard_Cain]

Originally Posted by krat

Yes, horsepower and torque are forces in balance. We associate torque with acceleration, but your top speed is more a harnessing of the horses.

After you get to a specific speed depending on your torque your top end is determined by how many horses are pulling the gears.

You feel that fast climb to speed through the gears and then when you hit 5th you are making a slow assent to max speed. When it levels off and will not go any higher, or the rpm turn any faster, you have whipped all you can get out of those ponies.

The perfect gearing is where the top end is the fastest speed your horses can pull. After that your speed will actually decrease. Of course there is a weight restriction too! Jockeys are midgets for a reason.

You only have 15 of them to play with, and all the mods in the world are not going to increase that amount by much. You can spend a couple of thousand $$, or weeks of time, on mods that will never get you past 70, and you could have done that on any used $1500, 250 Honda Rebel.

Originally Posted by Megadan

I don't even have a couple thousand in mods on my entire bike, and it's one.ofnthe most modded ones here. A ported head and cam with an exhaust, 300 to 400 tops, and a decent bump in power considering the starting point.

Same... Full exhaust, upgraded carburetor, ported head, camshaft, timing advance, pretty much every upgrade/mod that doesn't replace half of the engine with something else- and I'm all in for just under $400.

I can hit 74mph GPS confirmed. Don't ever need nor want to.. probably can wind it out more for higher speed, but no point. I should be able to hit 80 at 8000 ish rpm. But again, no desire or need.

So I can say that your point about thousands spent for never past 70 is factually incorrect.

[drstansbury@yahoo.]

I probably have more mods than most and dont really have much in everything. I have a cam, roller followers, ported head, cg300 cylinder, exhaust, 4* advance key, nibbi carb, nibbi coil, upgraded chain and sprockets, shinko 244 tires (although not really a mod), 3d printed chain slider, tt250 seat, aftermarket dash, and levers. Heres roughly what I paid for everything
Cam, followers, keyway, ported head (including cost of extra head and all gaskets) $400
cg300 cylinder $165 (is only about $105 right now)
digital dash $100
levers and hand guards $70
tires and tubes $160
exhaust $80
nibbi carb, jets, intake and air filter $120
nibbi coil $20
tt250 seat $89
sprockets and chain $50
3d printed slider was free provided by a friend

[krat]

How about if you guys work in some shop time at $100 an hour and re-work those totals?

You heavy mods guys know how to work on bikes and do it as a hobby, not necessarily because you put a bike together out of a box and it will not run.

Even at that you are getting a 20%+- horsepower increase that equals 3-4hp added to the original 15! It's not even an increase up to what a box stock used 1990s era Honda, Kawasaki or Yamaha 250 produces.

Most of the people that come here do so in desperation, because they can find no one anywhere, at any price, to work on their bikes and they know absolutely nothing about motorcycle mechanics.

They don't know what a CAT is, or where it is. The inside of a carb is equal to a heart transplant, valve lash was what their granny had surgery for and half their electrical problems can be cured by turning on the kill switch. And you guys are talking about advance keys, porting heads and big bore kits.

For the average guy that comes here with a problem, the only way their China bikes will ever see 70mph is in the back of a pickup!

My 50cc derestricted moped was faster than my TBR7 when it came out of the box. I had a top speed of 45mph. Valves adjusted, a new re-jetted carb ( I have no idea how many times that carb has been apart or how many hours I have spent getting it right), cone filter, high performance exhaust and I have it up to 60, flat out, down hill with the wind behind me.

I will not spend any more money, or time, on the TBR7 trying to get it past 60mph. If I could sell it I would.

My $900, 150cc scooter will do 70 on the same piece of road.

[XLsior]

As far as I am concerned anything under 250cc is not a highway speed class of bike. To prone to buffeting and wind sheer.

for pootliing around on back roads and building riding confidence the value for money is undeniable.

The CG engines were not designed for performance but simplicity, reliability and lack of maintenance.

However what the China bikes and their respective engines provide is a cheap platform to learn on and not feel to concerned about making mistakes with such a low entry fee.

For tinkerers. fettlers and modders with minimal funds its a reasonable choice.

For those who don't like spinning spanners china bikes might be best avoided.

The parts are so stupid cheap. QC issues aside. A cheap dremel and a few carbide bits will port a head and header and derestricted exhaust and get the +3hp with ease...that's just regaining the performance loss from a mass produced product. Chasing performance past this is more of a hobby prospect.

17-42 seems the preferred top speed on flat geographical.

I live in steep country so opted with 16-45. I also want to be able to 1st gear idle crawl/technical.

[Deckard_Cain]

Originally Posted by krat

How about if you guys work in some shop time at $100 an hour and re-work those totals?

You heavy mods guys know how to work on bikes and do it as a hobby, not necessarily because you put a bike together out of a box and it will not run.

Even at that you are getting a 20%+- horsepower increase that equals 3-4hp added to the original 15! It's not even an increase up to what a box stock used 1990s era Honda, Kawasaki or Yamaha 250 produces.

Most of the people that come here do so in desperation, because they can find no one anywhere, at any price, to work on their bikes and they know absolutely nothing about motorcycle mechanics.

They don't know what a CAT is, or where it is. The inside of a carb is equal to a heart transplant, valve lash was what their granny had surgery for and half their electrical problems can be cured by turning on the kill switch. And you guys are talking about advance keys, porting heads and big bore kits.

For the average guy that comes here with a problem, the only way their China bikes will ever see 70mph is in the back of a pickup!

My 50cc derestricted moped was faster than my TBR7 when it came out of the box. I had a top speed of 45mph. Valves adjusted, a new re-jetted carb ( I have no idea how many times that carb has been apart or how many hours I have spent getting it right), cone filter, high performance exhaust and I have it up to 60, flat out, down hill with the wind behind me.

I will not spend any more money, or time, on the TBR7 trying to get it past 60mph. If I could sell it I would.

My $900, 150cc scooter will do 70 on the same piece of road.

Your points are all valid. But your shop time/labor analogy can also be applied to say, preparing food and cooking a meal. There are people that don't know how to work an oven.

And those that don't know how to work a lawnmower?

The point is, if you don't know how to do something, either you learn or you're going to pay someone who does know. Applies to everything.

So when someone who cooks at home says their grocery bill for them and their spouse is only $80/week... to someone who can't cook, how about you toss in some chef prepared kitchen time and re-work that total?

These bike platforms were never meant to go past 60mph anyhow... but anyone who knows enough to ask about it, either bought the wrong bike and should sell it and buy something else, learn what it takes to get it going faster, or just deal with it. But if they're even asking, 50% chance they can do the work necessary to get it there.

Without spending thousands. Besides that, all the upgrades and mods needed can be installed in roughly 4 hours if it was all sitting in front of you. So at $100/hr shop time, you're only adding $400 to the total cost. You'd still be in less than $1k.

But at $2500 invested into a new Hawk/Tbr7/Brozz/Whatever, better spent on a used- anything else. Hell, a first gen Ninja 250 will do 105 on stock gears and a MINT example can be had for $2000. Never mind a newer Ninja 300...

[Megadan]

Originally Posted by krat

My 50cc derestricted moped was faster than my TBR7 when it came out of the box. I had a top speed of 45mph. Valves adjusted, a new re-jetted carb ( I have no idea how many times that carb has been apart or how many hours I have spent getting it right), cone filter, high performance exhaust and I have it up to 60, flat out, down hill with the wind behind me.

I will not spend any more money, or time, on the TBR7 trying to get it past 60mph. If I could sell it I would.

My $900, 150cc scooter will do 70 on the same piece of road.

So, this explains your negative nancy attitude. You bought a bike with unrealistic expecations and are now bitter about it.

Fact is, dual sports are not and will never be as fast as a road bike even with the same engine. Large diameter wheel and tire combinations, even if they weighed the same as your scooters wheels and tires, have a MUCH higher moment of inertia thanks to the mass being a whole lot further away from the rotational axis.

The total frontal area of a dual sport motorcycle is much larger than that scooter too. The bike is much taller and wider. Then add in the high front fender, guards, plastic scoops, etc. all designed to direct airflow, protect parts of the bike, and so forth catch a hell of a lot of air which makes for a horrific coefficient of drag. Your scooter meanwhile has a low mounted, shielded, front fender and body plastics making for a smoother and more directed airflow around the bike and rider.

Hell, I could keep going, but the point is, even with the same engine as say a street bike, a dual sport bike will always be slower than a street bike or scooter. That's the nature of the beast.

Nobody here with any real reputation or intelligence has ever sold these bikes as a true 70mph bike. I often and quite regularly tell people this, as do most others. The issue is, people will listen to that one person speaking out of their rear end before the 10 people who tell them "Nah, not really" because they hear what they want to hear. These bikes are realistically 65mph top speed machines with their single lobe cam 2 valve 229cc engines. They have no real top end.

I appreciate your realism, but you are also taking it a little too far the other direction and being a bit salty. Not meant to be an insult, just an observation, so don't take it negatively.

Lastly, if anybody is buying these bikes and doesn't have the basic mechanical aptitude to do these types of mods, they honestly shouldn't be buying these bikes to begin with. This is a concept I have always kind of emphasized with any Chinese motorcycle because the lack of support at a local level is often zero and you have to rely on yourself. If you buy one of these bikes without being able to do basic mechanical work, which does include removing the head and cylinder, you are just setting yourself up for a headache in the long run.