[Akhilash95]

In real life conditions, if we run two identical motorcycles, both at same same rpm but one in 2nd gear and other in 5th gear, why is it that the former is less fuel efficient?

[girimajiananth]

Originally Posted by Akhilash95

In real life conditions, if we run two identical motorcycles, both at same same rpm but one in 2nd gear and other in 5th gear, why is it that the former is less fuel efficient?

I am not sure if I understood your question .Assume there is a bike 1 and bike 2, will you be running bike 1 at 1.5K rpm in 2nd gear and bike 2 @ 1.5K rpm in 5th gear ? Is that what you are trying to ask ? If so , bike 2 will start lugging , knocking and eventually stall. I believe that the thumb rule is right gear at the right RPM.Lower gear higher rpm will give more power and hence consumes more fuel.

[ArizonaJim]

Originally Posted by Akhilash95

In real life conditions, if we run two identical motorcycles, both at same same rpm but one in 2nd gear and other in 5th gear, why is it that the former is less fuel efficient?

By the phrase "both at the same rpm" I will assume we are speaking of the engine speed.

Perhaps the easiest way to understand the situation is to assume the engine is using the same throttle setting (although in the real world this would be unlikely).
With the same throttle setting, each time the cylinder is charged with air/fuel, both motorcycles will be burning the same amount of fuel per engine crankshaft revolution.

In second gear, the engine will need to turn many more rotations per Km traveled than it would in fifth gear, resulting in a great increase in the amount of fuel/air being burned to cover the same distance.

Using my 500cc Royal Enfield as an example, the crankshaft must rotate 9.673 times in second gear to rotate the rear wheel once.
In fifth gear, the crankshaft must rotate 4.805 times to rotate the rear wheel once. Therefore, the engine will burn about twice as much fuel in second gear to travel 1 Km than it would burn if it was in fifth gear.

[ArizonaJim]

My apologies but I didn't get back to my previous post fast enough to add this:

In a more real world setting the engine has an easier time of rotating the rear wheel if the transmission is in second gear. This is because of the higher number of turns the engine needs to make.
To keep the engine at a certain speed (doing the same amount of work) in second gear the throttle would not have to be opened as far as it would to do the same amount of work if the transmission were in fifth gear.
In other words, each charge of air/fuel needed would be somewhat less in second gear.

To a degree, this makes the difference in the amount of fuel used to cover 1 Km in second gear less than the above ratio numbers would seem to indicate however the difference in throttle settings will not offset the effects of the different gear ratios.

[basuroy]

Originally Posted by Akhilash95

In real life conditions, if we run two identical motorcycles, both at same same rpm but one in 2nd gear and other in 5th gear, why is it that the former is less fuel efficient?

An automobile returns the best fuel efficiency at the rpm where it generated maximum torque . The rpm range between max torque and max horse power is known as power band and the range where one should stick to for optimum fuel efficiency in any given gear .

But said automobile at a lower gear will attain a lower speed than at a higher gear with the engine rpm being same in both gear while consuming similar amount of fuel over a give time period - as such the distance covered will not be same due to the difference in speed hence higher gear returns better efficiency because it covers more ground at a fixed engine rpm while consuming a theoretically same amount of fuel .

[rathsubhajeet]

Originally Posted by Akhilash95

In real life conditions, if we run two identical motorcycles, both at same same rpm but one in 2nd gear and other in 5th gear, why is it that the former is less fuel efficient?

The situation is that you are selecting an engine rpm and giving acc input on your bike to maintain that.

Let us go through some basics first.

At any given rpm there is a max torque an engine can produce and a corresponding torque 'T' available at the wheels. For any given vehicle speed the vehicle experiences road resistance and other Loads 'L'. 'f' is the fuel consumed per engine rev and 'D' is the distance traveled per engine rev.

Best FE is obtained when D/f ratio is highest.

If we keep the gear same and increase the engine rpm, T-L will decrease. Hence, more fuel will be required to sustain that speed. So f will increase and after a while when T-L is 0, f will be constant. D will increase linearly. For most cases D/f ratio increases to an extent and then has a sharp drop. For a typical 150 cc bike that comes between 5k to 7k rpm.

Now if we compare different gears, T will be less for 5th and more for 2nd gear. Hence, with upshifts T-L decreases, again increasing f. D increases from 2nd to 5th. So if you keep on increasing gears at a particular engine rpm both D and f increases. Now typically a combination of low rpm lower gear and high rpm high gear gives better FE.

So say you are driving a bike at 5k engine rpm. If you change gears from 2nd to 5th, it'll give better FE. The reverse will be true for 2k engine rpm.

[giri1.8]

Saw this on Hero's facebook page, don't get the "over reverse" part

Edit: Hope its not a typo! might be over revving if that is the case.

[a4anurag]

Originally Posted by giri1.8

Saw this on Hero's facebook page, don't get the "over reverse" part

Edit: Hope its not a typo! might be over revving if that is the case.

It is a Typo!

It does mean Over Revving! Look at the below line in the picture which gives the answer - 'It may damage your bikes engine'

[rangakishen]

Over reverse is definitely the wrong phrasing.

But I think they meant over revving while downshifting while braking from high speeds. (Aggressive engine braking)

Revving the engine usually (throttle) at any speeds will not do any damage to it as long as it is a well maintained machine.

[emperorofindia]

What's a sprocket and how will it help me get a better acceleration for my Suzuki Gixxer?

[Ricci]

Originally Posted by emperorofindia

What's a sprocket and how will it help me get a better acceleration for my Suzuki Gixxer?

A sprocket is one of the 2 gear wheels of the final drive (chain). For better acceleration, usually people gear it down (use a higher ratio) by either smaller front (driving) sprocket, or bigger rear (driven) sprocket. If your stock set up is 14 tooth front, 42 tooth rear, someone might replace the rear 42T with a 44T sprocket for quicker acceleration ( usually at the expense of top speed ). Alternatively, the front 14T sprocket could be replaced with a 13T one - assuming in either case, the centre hole (for the countershaft or rear axle rod) and the mounting holes are of compatible size and placement.

[gauravanekar]

Adding some recent technologies (words:Wikipedia):

A quickshifter is a device that allows clutchless gearshift on a manual transmission, and is commonly used on motorcycles. It increases safety and comfort of the vehicle since it eliminates the need of adjusting the clutch or throttle before and after gearshift.[1] Since they eliminate the need of adjusting clutch and throttle during gearshift, they are quicker(usually shift in less than 50 millisecond) and also used as performance enhancement on motorcycles.

A dual-clutch transmission (DCT) is an automated automotive transmission, closely related to a manual transmission. It uses two separate clutches for odd and even gear sets. It can fundamentally be described as two separate manual transmissions with their respective clutches contained within one housing, and working as one unit. Although usually operated in a fully automatic mode, many also have the ability to allow the driver to manually shift gears in semi-automatic mode, albeit still using the transmission's electrohydraulics. Eg: Honda DCT system

A slipper clutch (also known as a back-torque limiter) is a specialised clutch with an integrated freewheel mechanism, developed for performance-oriented motorcycles to mitigate the effects of engine braking when riders decelerate.

The main purpose of a slipper clutch is to prevent over engine rev and rear wheel hop (or clatter) especially under hard braking in a vehicle

[gauravanekar]

Cornering ABS is an ABS system which accounts for acceleration/deceleration forces, lean angle of the motorcycle apart from the wheelspeed to determine the application of braking forces required for each wheel. This helps in perfecting ABS function during cornering. While cornering the motorcycle, the effective circumference of the wheel changes(differently for front & rearwheels), grip level changes, this intelligent system should be able to cope up with all these variables.

Crossplane crankshaft is a type of crankshaft used by few motorcycles by Yamaha. Generally in inline 4 cyl engine crankshafts are forged at 180deg angles(flatplane crankshaft) between cranks whereas in crossplane crankshaft the angle between cranks is 90deg. Supposedly this helps in greatly reducing the inertial torque, subsequently the weight of the flywheel will be reduced significantly. There are other advantages too, which are mentioned here: https://www.yamahapart.com/crossplanecrankshaft

variable Valve timing is a ystem similar to the famous Vtech/IVtech of the Honda cars wherein the Valve actuation timing is altered according the rpm. At higher rpm it is benificial to have big overlap between inlet and exhaust valve opening duration wheres at lower rpms its is beneficial to have least valve timing overlap. Usually in engine which doesnot have variable valve timing a best compromise is designed and set.