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Depends how much top speed you are willing to trade in order to get the fastest acceleration. Any given bike also depends on how much the power curve is falling away on the top end which is quite a bit on this bike unless you cut down the intake runner and fit a pod filter.
My bike redlined with stock gearing only 3 times (indicated 171/2kph) and that was a long 3-5km downhill, most other times 169kph took some effort. TX_Dj and SS got similar (102mph on USA speedos @10500)

Now it redlines with 13t front on the flat or slight downhill provided there is nil wind and the temps are warmer than 30 degrees.

Before it would be back to 152kph uphill or into wind.
Now it keeps accelerating everywhere.

The 6% gearing change is more than offset by having the power to do a higher average topspeed anywhere.

But I doubt you'll understand, looking at torque graphs may work on paper dont always work in practice.. you need to be above the torque curve.
 

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I ride too. And do a lot of testing out on the road. I never talk about downhill top speed. It is meaningless and not standardized for discussion. A CBR250R will do 200 mph at 0 rpm if you throw it off a cliff with the key in your pocket.
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Power is down 3hp from 8,700 to 10,000. The more you gear past 8,700 rpm, the slower your top speed will be
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You and TxDJ have a pipe. My engine is stock with the airbox lid off.
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My top speed is up to 96 mph, 155 kph at 8,500 rpm with my longer gearing. Up from the 92 that I used to get with the stock gearing. The speed that most of the fastest people get with a stock bike. That was with my tank bag in the way and my duffel bag on the rack on my way to work. I could get a couple more mph out of it if I made a better run.
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Longer gearing will get left behind on the drag strip but I will race any other combination of gearing with a stock engine for top speed and will beat them with an honest, flat road, two way no wind run with my 15/ 36 gearing.
 

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Discussion Starter · #105 ·
OMG, I totally got schooled on this thread! This was where I learned gearing multiplies torque - not horsepower! Embarrassing for me, but one of my all time favorite forum debates none the less. I understand this stuff way better now days, haha.
 

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As to your CVT comment. Standard transmissions are very efficient. Automatics including CVT are comparably inefficient. It's like taking a 10-15% horsepower reduction. This number may have improved recently since I haven't been into CVTs for a while. The controlling mechanisms, as with any automatic, aren't perfect either. They're also no fun so screw CVT's and other automatics.
I've been a big fan of the Honda Wave which has been the top selling model here in Thailand for many years. I bought a new 125cc with FI and a semi-automatic; you have to close the throttle and then shift without a clutch, so not much different from a clutch-operated bike when it comes to acceleration. I noticed that the Airblade 125 is faster off the line, mainly because it doesn't have the shift breaks - it just pulls without interruption and is gone! Now I ride a Yamaha Nouvo 135 with CVT and I'm very impressed. It out-accelerates the Airblade but of course not the PCX150 (which is an ugly-looking, small-wheeled scooter, IMO!).
No more Honda Waves for me!
Fuel consumption may be higher but who cares on small bikes like these.
Also in city traffic you just open the throttle at any speed, no need to select the right gear and match the revs to the clutch. Also no drive chain to oil and adjust, but a belt which needs to be replaced after about 20 -25K km, like a chain, depending on your style of riding.
Sorry about talking about CVT (not to be confused with a multi-gear automatic or a dual clutch transmission) but it may be worth looking into the latest models which feature them. Here in Thailand they are taking over the small-bike market.
And they convinced me, after riding clutched bikes for about thirty years!
 

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My bike redlined with stock gearing only 3 times (indicated 171/2kph) and that was a long 3-5km downhill, most other times 169kph took some effort. TX_Dj and SS got similar (102mph on USA speedos @10500)

Now it redlines with 13t front on the flat or slight downhill provided there is nil wind and the temps are warmer than 30 degrees.

Before it would be back to 152kph uphill or into wind.
Now it keeps accelerating everywhere.

The 6% gearing change is more than offset by having the power to do a higher average topspeed anywhere.

But I doubt you'll understand, looking at torque graphs may work on paper dont always work in practice.. you need to be above the torque curve.
170 km/h!

That's faster than some riders can go on their CBR500Rs!

Is there any "Australian outback voodoo" involved?

My VTR250 wouldn't go faster than 140 km/h.
 

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170 km/h!

That's faster than some riders can go on their CBR500Rs!

Is there any "Australian outback voodoo" involved?

My VTR250 wouldn't go faster than 140 km/h.
See where I said 'indicated'
Metric bikes have a 10% speedo error.
 

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I ride too. And do a lot of testing out on the road. I never talk about downhill top speed. It is meaningless and not standardized for discussion. A CBR250R will do 200 mph at 0 rpm if you throw it off a cliff with the key in your pocket.
.
Power is down 3hp from 8,700 to 10,000. The more you gear past 8,700 rpm, the slower your top speed will be
.
You and TxDJ have a pipe. My engine is stock with the airbox lid off.
.
My top speed is up to 96 mph, 155 kph at 8,500 rpm with my longer gearing. Up from the 92 that I used to get with the stock gearing. The speed that most of the fastest people get with a stock bike. That was with my tank bag in the way and my duffel bag on the rack on my way to work. I could get a couple more mph out of it if I made a better run.
.
Longer gearing will get left behind on the drag strip but I will race any other combination of gearing with a stock engine for top speed and will beat them with an honest, flat road, two way no wind run with my 15/ 36 gearing.
200mph in a free fall ! Ever heard of terminal velocity ?


Sent from Motorcycle.com Free App
 

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Some of my favorite threads from the glory days of CBR250.net when the traffic was high and there were engineers and scientists posting here to explain things.
I enjoyed that one. Ive heard this 'leverage' theory about gear diameters before.
I'm also of the opinion that there's no such thing as a free lunch and you cant generate power by changing sprocket diameters, but if you do gear it down then of course its gonna feel more grunty when blasting through the box.
 
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