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Old 07-16-2018, 07:24 AM   #31
sniper1rfa
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Originally Posted by stangmx13 View Post
drive force is higher in lower gears with the same power output.
In theory, this isn't true. If the power output is the same between both gears, drive force will be the same.

That said, power output of an engine is load dependent, and engines will make more power with more load, even if the RPM and throttle position are the same.


So there are many cases where you actually will make more power, and thus accelerate faster, in a higher gear. This would be much more pronounced in lower gears than higher gears, so short shifting a bit is often going to be fastest in gears 1-4. Smoother power application in higher gears is a sweet bonus.

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Old 07-16-2018, 02:05 PM   #32
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Originally Posted by sniper1rfa View Post
In theory, this isn't true. If the power output is the same between both gears, drive force will be the same.

That said, power output of an engine is load dependent, and engines will make more power with more load, even if the RPM and throttle position are the same.

So there are many cases where you actually will make more power, and thus accelerate faster, in a higher gear. This would be much more pronounced in lower gears than higher gears, so short shifting a bit is often going to be fastest in gears 1-4. Smoother power application in higher gears is a sweet bonus.
u have it backwards. in theory, what I said is true. in practice, there are more things going on. u cant get from Watts to Newtons through a drivetrain and tire without including the gear ratio and its torque multiplication. if torque is multiplied, so is drive force.

making more power != accelerate faster when u are comparing diff gear ratios. thats just wrong.
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Old 07-16-2018, 02:09 PM   #33
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Power is not modified by gears. Power into a gearbox is always the same as power out of the gearbox.

Gearboxes trade torque for rpm at constant power (minus frictional losses).

The graph shows more peak power (and more torque) in higher gears.

Power is the only thing that matters for acceleration.

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Old 07-16-2018, 02:25 PM   #34
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Power is not modified by gears. Power into a gearbox is always the same as power out of the gearbox.
I didnt say that.

Quote:
Power is the only thing that matters for acceleration.
nope.

u rly should try to calculate drive force yourself.
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Old 07-16-2018, 08:03 PM   #35
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I know this is pointless internet shit as well as totally off topic, but I'm really bored.

I've labelled the above graph with optimal shift points based on that dyno run (which is not entirely real life, but illustrates the point). Note how early you need to shift in order to produce the most power.




The 1-2 shift happens before you even reach peak power in 1st, because it's more beneficial to short-shift into second practically as soon as possible. All the other shifts happen far earlier than expected, and only shortly after peak power in a particular gear.



As for your 'drive force' thing. Horsepower = (Torque*RPM)/5252. You have a couple gear options for each wheel RPM - you want the one with the most power. Since the wheel RPM is the same (you're going the same speed), the gear option with the most power will also have the most torque (at the wheel, where it matters).

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Old 07-17-2018, 07:15 AM   #36
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As for your 'drive force' thing. Horsepower = (Torque*RPM)/5252. You have a couple gear options for each wheel RPM - you want the one with the most power. Since the wheel RPM is the same (you're going the same speed), the gear option with the most power will also have the most torque (at the wheel, where it matters).
You are so close to understanding what drive force is. So since we want the most torque at the rear wheel for the highest drive force... and since a gearbox multiplies torque, that says what about comparing drive force btw two gears? Assume power&torque are the same since we don’t know the output for this theoretical bike.

Ya u are off topic. The only point of mine u decided to argue about was a theoretical drive force comparison. Uve now picked a weird vehicle to make a point about shift points. Yes, I know that the steeper power falls off after max, the more likely you’ll have to shift before redline. My race R6 gets shifted at 15.5k even though it’ll spin to 16.5k. Each shift differs by a little because the gearbox matters, but it’s only 200rpm max and I can’t set my shift light different for each gear.
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Old 07-17-2018, 07:47 AM   #37
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You can test this, since you don't believe me. Take your bike, get it dyno'd in every gear and overlay the dyno plots for each gear as above (either power or wheel torque vs wheel speed, it doesn't matter - they're the same thing).

Then do two drags - one shifting at your normal 15.5krpm, and one shifting at the speeds indicated by the crossover of each dyno plot (which will have you shifting earlier than normal).

I bet you're leaving speed on the table, and by being in a higher gear for longer you're also dealing with more difficult throttle response than you need to. The folks you originally responded to are probably correct - a higher gear not only feels faster a lot of the time, it almost certainly *is* faster. The guy who said 'ignore speedo and tach when shifting' is easily the most correct response, because you should be shifting based on feel if you haven't done the above test with your particular setup.

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Old 07-17-2018, 08:04 AM   #38
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where did i say i didnt believe u

dealing with more difficult throttle response at 15.5k? wth are u talking about? its a race bike!! im only at 15.5k at WOT and then i pop the shift. and now you are advocating the butt dyno? OMG, stop

lets also acknowledge that the example plot u found is for a side-by-side that has 5 gears and only does 75mph. when talking about things where load, gearbox, and power matter a ton, u really picked a vehicle that differs dramatically from my bike and the OPs. u think the rpm drop from 2nd to 3rd is anywhere comparable btw that 4wheeler and my R6... unlikely. yes, the concepts still apply, but the amounts will vary considerably because of all the differences.
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