Most efficent RPMs for high gas mileage riding? - Honda CBR250R Forum : Honda CBR 250 Forums
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post #1 of 21 Old 10-23-2019, 09:26 AM Thread Starter
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Question Most efficent RPMs for high gas mileage riding?

Hey guys,

I'm actually doing a lot of commuting through town, mostly at very low speeds, and I'm not sure what the best RPM might be in terms of saving gas.

I think my most common speeds are between 30 kph (approx. 20 mph) and 60 kph (approx. 36 mph). In a modern car it's easy because most of the time you choose the highest gear to cruise fuel efficient, the head unit will tell you anyway what gear to choose.

But how is it with the single cylinder four-stroke CBR250RA engine? I don't think it's efficent, to let's say for example, ride in sixt gear while cruising only 50 kph (approx. 30 mph). So what do you think might be the best? Second, third, fourth or even fifth gear?

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post #2 of 21 Old 10-23-2019, 12:43 PM
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Highest gear without bogging excessively.

For just cruising on level ground at those speed 6th may indeed be too much - but give it a try. Obviously if you need to accelerate you have to click down a couple, but chugging along on flat ground at 1500 RPMs (or whatever) should be doable.

Given a chance, open it up occasionally. Engines don't like extended running at low RPMs for the most part, and will build-up deposits in the combustion chamber. That can lead to detonation. Bogging (high load/low RPMs) can cause detonation as well. Detonation will cause engine damage eventually.

Running a strong fuel system cleaner once per season is a good idea.
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post #3 of 21 Old 10-23-2019, 01:21 PM
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When I had my CBR I used to change up between 5000 and 7500rpm depending on how much of a hurry I was in and change back down if I was going to drop below 4000. That got me a regular 85mpg (UK measures) which is about 10 better than the average on Fuelly. I never deliberately rode for maximum economy, just did what felt comfortable at the time.
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post #4 of 21 Old 10-23-2019, 02:24 PM
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There are a couple members here - Sendler and Greenaero - that get huge mileage numbers from their CBRs.

Maybe they will chime-in with what works for them.

Sendler's is basically stock I believe, but Greenaero's has extensive aero bodywork.
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post #5 of 21 Old 10-24-2019, 05:42 AM Thread Starter
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Quote:
Originally Posted by jkv357 View Post
Highest gear without bogging excessively.
At first, that's what I thought as well, but I was a bit under the impression that I had a lower fuel consumption when I was not always riding a lot at the highest gears.

When I'm thinking about the infamous Honda Innova (scooter) which is one of the lowest fule consumpting wo-wheeled vehicle, it's only 125cc and they generally ride at a higher rpm, l like most scooters and they are generally good in fuel consumption.


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When I had my CBR I used to change up between 5000 and 7500rpm depending on how much of a hurry I was in and change back down if I was going to drop below 4000. That got me a regular 85mpg (UK measures) which is about 10 better than the average on Fuelly. I never deliberately rode for maximum economy, just did what felt comfortable at the time.

What kind of streets where you driving? Did you went through a lot of town traffic with much stop and go traffic and tons of traffic lights or more like country roads and highways?

Gearing up between 5000 and 7500rpm is far away from riding in the highest gear with low rpms, so your statement kind of contradicts to the first reply of this thread.

Your fuel consumption was pretty low, 85mpg would be something like 2,8/100km. There is a german gas milege tracking website where are CBR250 riders logging their fueling, the average fuel consumption is 3,5l/100km which is 67mpg

So maybe the coefficient of performance isn't at a very low rpm?

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post #6 of 21 Old 10-24-2019, 06:58 AM
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What kind of streets where you driving? Did you went through a lot of town traffic with much stop and go traffic and tons of traffic lights or more like country roads and highways?
Usually an even mix of town, country roads and multi-lane. The best economy I ever got was 94mpg (UK) over a tankfull exploring the far north of Scotland at 40-50mph on deserted small roads.
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post #7 of 21 Old 10-24-2019, 11:00 AM
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Quote:
Originally Posted by Baumstamm View Post
When I'm thinking about the infamous Honda Innova (scooter) which is one of the lowest fule consumpting wo-wheeled vehicle, it's only 125cc and they generally ride at a higher rpm, l like most scooters and they are generally good in fuel consumption.
You can get high MPG with a small engine running at it's most efficient RPM, but there's usually not much additional power available - just enough to hold a moderate speed.

For larger engines that doesn't work as well, and you usually go for the lower RPMs and smallest throttle openings that you can get without excessive bogging and the need to open the throttle significantly.
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post #8 of 21 Old 10-24-2019, 02:53 PM
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My NX 250 (water-cooled, carburated, DOHC single) provided good fuel mileage and adequate acceleration when run at 1/2 to 5/8ths red-line rpms. That bike was redlined and 8K so I typically rode it at 4000 to 4500 rpm in the speed range that you have discussed.

For top speed I ran it right up to 8K in 5th before shifting into 6th gear. The bike topped out at 90 mph, but it took a long while to get there. If I could not pass using 5th gear, I did not attempt passing.

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post #9 of 21 Old 10-24-2019, 03:43 PM
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My NX 250 (water-cooled, carburated, DOHC single) provided good fuel mileage and adequate acceleration when run at 1/2 to 5/8ths red-line rpms. That bike was redlined and 8K so I typically rode it at 4000 to 4500 rpm in the speed range that you have discussed.

For top speed I ran it right up to 8K in 5th before shifting into 6th gear. The bike topped out at 90 mph, but it took a long while to get there. If I could not pass using 5th gear, I did not attempt passing.
That's probably pretty close to the torque peak for that engine, which usually translates to very efficient running.

What MPG did you get cruising at that RPM?
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post #10 of 21 Old 10-25-2019, 10:28 AM
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Just as a comparison, Ninja 250 owners regularly get mileage in the 50 MPG range for average riding.

My '06 SV650n, at almost 3 times the displacement, will do the same.

Mileage doing high RPMs with a small engine and low RPMs with a bigger engine ends up about the same in some instances. The bigger engine will max out quicker.

When you are talking really big numbers the small engine will win, especially if aided by aero improvements.
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