Hypermiling your sprockets - Page 2 - Honda CBR250R Forum : Honda CBR 250 Forums
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post #11 of 39 Old 07-20-2015, 08:17 AM
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Originally Posted by Inst View Post
So the question I'm asking, instead, is that if I use the clutch instead to decrease engine load and thus push up the RPMs, would I be able to recover some of the acceleration ability I would lose by increasing the torque output? Or would the fact that the power transmission is being interrupted by the clutch destroy any regained acceleration ability?
Still not sure what you mean by "using the clutch". It's there to change gears and interrupt engine power to the wheel, which is not what you want to do if you want acceleration. Slipping the clutch is simply wasting energy that isn't going to forward motion. See previous post:
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Originally Posted by cbrlocal View Post
While it may increase RPM's, you're decreasing the amount of those RPM's that are being transferred to forward motion, thereby reducing your power and wearing out your clutch at the same time. Not a good move.
Gearing is also not going to increase your torque output. The engine will output the same regardless as to the gears attached to it. The powerband will be shifted to different speeds however. Regardless, the factory gearing is near perfect for this bike.

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post #12 of 39 Old 07-20-2015, 08:42 AM
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MPG is what you make it. My commute is 130 miles round trip, I fill up at the same station every day at the same time, and ride the same route. I've only done 2400 miles as I have only had the bike (I think a month now?), but first 5 tanks were all 70 +/- 2. 1st weekend I added the 2B slip on and started riding more aggressively, 5 tanks wildly different with a low of 64 and high of 72. Tossed in the JBpro with stock map 3% CL and +1 on the high RPM. Speeds increased as I started 'wringing it's neck' and MPG for 6 tanks was low 59 and high of 66.

Pattern, mods cost fuel. Braap costs fuel. Best MPGs are with a self imposed limit of 65mph and full tuck. 70 - 74mph and spirited riding turns in mid 60s with the mods and I'm okay with that, but likely will drop the JBpro and resell it.

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post #13 of 39 Old 07-20-2015, 10:10 AM
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There is more variation in fuel price from week to week or servo to servo than you could ever save by driving Miss Daisy style of riding or gearing changes.




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post #14 of 39 Old 07-20-2015, 01:03 PM Thread Starter
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@cbrlocal:

I think you're being imprecise when you say interrupt engine power; it's also there to modulate engine power. You can ride 5th gear at sustained 10 mph, provided that you stick the clutch deep into the friction zone, but from what you've told me it's counterproductive.

I was just asking whether or not you could get the effects of sprocket changes / gear ratio mods to some extent by using the clutch to force RPM into higher torque territories. You told me no, because the clutch in the friction zone eats up any increased torque, and I accept that.

@Aufitt:

Ironically, if you drive cager vehicles, educated hypermiling is often more fun than naive granny-driving, because granny-drivers want to drive 1000-1500 RPM, while hypermilers want to do half peak torque, which is often between 2000-2500 RPM. The RPM control does reduce your acceleration compared to driving at peak torque for max acceleration, but you get a good combination of fuel economy and performance. Amusingly, when I introduced Mom to using half peak torque to increase fuel economy, I ended up having to remark "you're an old lady, why can't you drive like one?" because she was driving so aggressively.

With a motorcycle, unfortunately, most bikes are ridden above half peak torque, so while acceleration is more brisk and more fun, fuel efficiency is lower. Practically applying RPM control to motorcycles seems to be more a matter of aggressive upshifts, i.e, the CBR250 hits peak BSFC at 3700 RPM, so the two challenges there are to upshift as soon as the engine can support it (BSFC maps usually suggest that more throttle / higher gearing increases fuel efficiency faster than moving towards half peak torque), and to stay around 3700 RPM once you hit an optimal engine gearing.
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post #15 of 39 Old 07-20-2015, 04:13 PM
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Originally Posted by Inst View Post
@cbrlocal:I think you're being imprecise when you say interrupt engine power; it's also there to modulate engine power. You can ride 5th gear at sustained 10 mph, provided that you stick the clutch deep into the friction zone, but from what you've told me it's counterproductive.

I was just asking whether or not you could get the effects of sprocket changes / gear ratio mods to some extent by using the clutch to force RPM into higher torque territories. You told me no, because the clutch in the friction zone eats up any increased torque, and I accept that.
Semantics. There's nothing imprecise about that; the clutch is meant to transfer engine power to the transaxle. The engine is making the same power whether the clutch is engaged or not, or anywhere in between. The difference is how much of that power goes into the drivetrain, and how much goes out like a fart in the wind. Modulating the clutch is only for motorcycle control such as sharp turns where the bike would be jerky if the clutch was fully engaged and the bike was only controlled by the throttle. Riding the clutch to get to whatever sweet zone in RPM's you're trying to achieve consistently will only result in less power to the wheels, higher fuel consumption, and a very short life expectancy for the clutch.
As for your RPM calculations, if you try to accelerate a CBR250 at 3700 RPM with 75% throttle in 6th gear, you're going to hear a lot of knocking and complaining.....soon you'll find pieces of your rod bearings in the oil filter too. Don't do it just to save $0.10 at the pump. Engine rebuilds are pricey. Shift before 5k RPM in slow easy acceleration and don't roll on the throttle too wide unless you've got RPM's to pull it. That will save you the most at the pump with this little bike. It's a totally different beast to try to hypermile than a car. Just ask Sendler.

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post #16 of 39 Old 07-20-2015, 07:27 PM
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It's more fun to wring it all the way out and get it movin. Inst has already said he'll be traveling at 80 on the highways, fuel economy is pants at that speed. Or buy a nice safe Honda Insight and hypermile that.

-Eric
Current stable: '72 GT750, '74 GT750x2, '75 GT750, '82 MB-5, '85 CMX250CD, '12 CBR250R, '14 Spyder RT-S
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post #17 of 39 Old 07-20-2015, 09:31 PM
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'stay around 3700 RPM'

The mind boggles at why these Eco people don't ride bicycles or take the bus.
If they are so poor that they cant afford to fuel up a cheap 250,
imagine the tyres, sprockets, brake pads and oil.
Or the state of the engine.


Buy a Harley if you want to do 3700rpm.



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post #18 of 39 Old 07-20-2015, 09:49 PM
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Quote:
Originally Posted by Inst View Post
...

According to what I've read, ICE engines are most efficient when they are performing at half peak torque, but most motorcycles are designed so that at cruising speeds their RPMs are way above that figure, supposedly so that they can support a second rider.

Theoretically, you can mod your bike so that the gear ratios would support half peak torque at highway speeds (and this would be a change of more than 75%!), but at the same time, I was told that this would likely lug the engines.
You want half peak torque?
Choose every rpm, that suits you, and close the throttle.
Torque is a result of the throttle position and the max. torque, you could get, at full throttle at this chosen rpm.
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post #19 of 39 Old 07-20-2015, 11:30 PM
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Inst, is this your first bike?
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post #20 of 39 Old 07-21-2015, 12:50 AM
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Quote:
Originally Posted by Aufitt View Post
The mind boggles at why these Eco people don't ride bicycles or take the bus.
If they are so poor that they cant afford to fuel up a cheap 250,
imagine the tyres, sprockets, brake pads and oil.
Let alone saftey gear. Or a comprehensive training course.
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Take care & ride safe.

2012 Honda CBR 250RAb, Sold.
2013 CBR 600RR, Sold.
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