Gear Ratios/Engine Resistance
- Thread starter bobkyle2
- Start date
5th will allow the engine to turn over easier.... Ever tried to push the bike in 1st gear compared to 5th...5th will give more resistance.Ever try taking off in 5th gear from a stand still?
This is why when you drive a manual transmission automobile... You put it in 1st.. Not 5th....If you put it in 5th... A normal person could push the vehicle and it would turn the engine over... Put if you put it in 1st... It the gear ratio/to compression ratio is much lower...
Think of it as switching your front sprocket with your rear sprocket.. And then trying to ride it with the engine propelling it...
Math time.
Lets say for shits, this KTM 65
FINAL DRIVE ratios (engine:wheel)
1st ( 11.25 :1) 11 engine revolutions per one wheel rev
6th ( 4.26:1 ) 4 engine revolutions per one wheel rev
A 2T, single cylinder motorcycle has one compression stroke per revolution. (~200psi)
So while turning the rear wheel in first gear you will encounter 11 compression strokes.
Turning the rear wheel in 6th gear you will encounter 4 compression strokes.
SO, 1st gear would give you more "resistance per inch"
BUT, in my experience, neither gear will help breaking a bolt loose as there is no "solid" resistance to actually break it loose. I use the rear brake HARD with a larger cheater bar.
Good luck!
Lets say for shits, this KTM 65
FINAL DRIVE ratios (engine:wheel)
1st ( 11.25 :1) 11 engine revolutions per one wheel rev
6th ( 4.26:1 ) 4 engine revolutions per one wheel rev
A 2T, single cylinder motorcycle has one compression stroke per revolution. (~200psi)
So while turning the rear wheel in first gear you will encounter 11 compression strokes.
Turning the rear wheel in 6th gear you will encounter 4 compression strokes.
SO, 1st gear would give you more "resistance per inch"
BUT, in my experience, neither gear will help breaking a bolt loose as there is no "solid" resistance to actually break it loose. I use the rear brake HARD with a larger cheater bar.
Good luck!
James
Staff member
After discussing this with Big Dan, trying to rotate the countershaft with an impact and bump starting a bike are to different things (ratios).
From the PM...
Hang on, doesn't bump starting technically have the reverse effect? Power/force from the engine vs the rear wheel.
The debate is if the engine/countershaft has greater resistance in either 1st or 5th gear if you're starting from a standstill (under the engine's power/hitting a nut on the countershaft with an impact).
Let's say that the bike's 1st gear has a 12:1 ratio and 5th a 4:1. Put the bike in 5th gear (4:1 ratio) and try to take off with the engine's power, it'll stall as the force required is to great (from a standstill). However if you push the bike wouldn't the ratio technically be 1:4 as the power's coming from the rear wheel and not the engine(every rotation of the rear wheel rotates the engine 4 times)?
In 5th gear:
Engine - 4:1 - High resistance
Bump starting - 1:4 - Low resistance
Bump starting in 1st would have a 1:12 ratio, one revolution of the rear wheel would rotate the engine 12 times. Would it not take more energy/force/resistance to rotate the engine 12 times vs 4, by spinning the rear wheel just once (bump starting)?
In 1st gear:
Engine - 12:1 - Low resistance
Bump starting - 1:12 - High resistance
James
Staff member
Exactly, however if you were to start the engine you could drive off in 1st, but not 5th.
The reason that it works better to "park" in 1st is because your ratio is now in reverse. Using the same gear ratios as above, 5th gear would rotate the engine 4 times per every tire rotation, if you were to push the truck. And 1st gear would rotate the engine 12 times per every tire rotation, hence the reason to put it in 1st gear.
