4th Gear Ratio?

[Nick The Greek]

Whats the ratio of 4th gear? I'd like to accurately work out what BHP i'm getting at the fly....

[Adie]

Whats the ratio of 4th gear? I'd like to accurately work out what BHP i'm getting at the fly....

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What was the figure at the wheels?

[Nick The Greek]

Whats the ratio of 4th gear? I'd like to accurately work out what BHP i'm getting at the fly....

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What was the figure at the wheels?

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174 :D

[Mr Morse]

Flywheel BHP is irrellevant......

RWHP is the only number that matters

[Nick The Greek]

Flywheel BHP is irrellevant......

RWHP is the only number that matters

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I know, but I need to know the flywheel bhp...

So whats the ratio/conversion factor?

[Mr Morse]

Flywheel BHP is irrellevant......

RWHP is the only number that matters

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I know, but I need to know the flywheel bhp...

So whats the ratio/conversion factor?

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If I am correct, the IS200 in 5th gear has a 1:1 ratio.

[Nick The Greek]

Dynos were done in 4th :(

I need to know the conversion factor because i'm running a little competition on my website

and also because all of my car-numpty mates won't understand RWHP

[RoadRash]

Flywheel BHP is irrellevant......

RWHP is the only number that matters

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I know, but I need to know the flywheel bhp...

So whats the ratio/conversion factor?

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If I am correct, the IS200 in 5th gear has a 1:1 ratio.

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YEP! :winky:

[PhoneDrome]

1.15 without degree of efficiency ... :D LOOOL

[Nick The Greek]

so no-one knows the answer then? :(

whats the ratios of the gears, i've looked in the manual and searched on here but to no avail.

[RX-Men-8]

so no-one knows the answer then? :(

whats the ratios of the gears, i've looked in the manual and searched on here but to no avail.

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Search and you will find... It's on here :)

click me!

Must admit, searching on here with keywords like gear ratio diferential final drive etc. leads to nothing but a million posts. I knew to find it because of the one who posted it ;)

Cheers,

RX-Men-8

[Nick The Greek]

so no-one knows the answer then? :(

whats the ratios of the gears, i've looked in the manual and searched on here but to no avail.

←

Search and you will find... It's on here :)

click me!

Must admit, searching on here with keywords like gear ratio diferential final drive etc. leads to nothing but a million posts. I knew to find it because of the one who posted it ;)

Cheers,

RX-Men-8

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thanks!

[Nick The Greek]

4th Gear =1,223:1 (0,730:1)

So if I wanted to roughly work out what it is at the fly (ie, figure out how much transmission loss there is), then I simply multiply my RWHP by 1.223?

[Zee007]

So if I wanted to roughly work out what it is at the fly (ie, figure out how much transmission loss there is), then I simply multiply my RWHP by 1.223?

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Yes Nick...

[Nick The Greek]

cheers ears, I can now choose a winner for my competition :D

[RoadRash]

4th Gear =1,223:1 (0,730:1)

So if I wanted to roughly work out what it is at the fly (ie, figure out how much transmission loss there is), then I simply multiply my RWHP by 1.223?

←

No.... or do you think in 5th gear (1:1) you don't have any loss any more??

[RX-Men-8]

4th Gear =1,223:1 (0,730:1)

So if I wanted to roughly work out what it is at the fly (ie, figure out how much transmission loss there is), then I simply multiply my RWHP by 1.223?

←

No.... or do you think in 5th gear (1:1) you don't have any loss any more??

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Hi, the dyno actually measures force at the rear wheels, and the speed. In scientific units (Newton, metres per second) the force*speed equals power in Watt. Force can be related to the torque (wheel size + gearing into the equation) and speed to rpm in a similar way. Hence torque*rpm (in scientific units, Nm and rad/s) equals power in Watt.

The reason the measurement takes place in a certain gear is the 1:1 ratio in te gearbox, which assumes the least amount of drivetrain loss. For the IS200 this is 5th gear. Also, preferably a high gear is selected to have minimal wheel force to prevent slip, which makes the measurement inaccurate.

How do they estimate the drivetrain loss? Some do it like so: When making a dyno run the wheel power is measured. At the top rpm they depress the clutch and measure how quickly the drivetrain decelerates. The quicker it decelerates, the more drag it has and the more power it saps from the engine. This power (estimate!) is added to the wheel power to obtain the crank power.

Drive train losses aside, the gear in which the measurement takes place does not matter. In 4th the measured force will be higher, but the speed lower than in 5th, theoretically giving the same power.

So, like Roadrash already indicated, you cannot multiply the 4th gear power measurement to extrapolate it to 5th gear by the difference in ratio. It is merely a question of how much drag the gearbox has in 4th compared to 5th. This difference would be quite small, imho. The only way to find out is to redo a run in 5th gear.

Cheers,

RX-Men-8

[RoadRash]

4th Gear =1,223:1 (0,730:1)

So if I wanted to roughly work out what it is at the fly (ie, figure out how much transmission loss there is), then I simply multiply my RWHP by 1.223?

←

No.... or do you think in 5th gear (1:1) you don't have any loss any more??

←

Hi, the dyno actually measures force at the rear wheels, and the speed. In scientific units (Newton, metres per second) the force*speed equals power in Watt. Force can be related to the torque (wheel size + gearing into the equation) and speed to rpm in a similar way. Hence torque*rpm (in scientific units, Nm and rad/s) equals power in Watt.

The reason the measurement takes place in a certain gear is the 1:1 ratio in te gearbox, which assumes the least amount of drivetrain loss. For the IS200 this is 5th gear. Also, preferably a high gear is selected to have minimal wheel force to prevent slip, which makes the measurement inaccurate.

How do they estimate the drivetrain loss? Some do it like so: When making a dyno run the wheel power is measured. At the top rpm they depress the clutch and measure how quickly the drivetrain decelerates. The quicker it decelerates, the more drag it has and the more power it saps from the engine. This power (estimate!) is added to the wheel power to obtain the crank power.

Drive train losses aside, the gear in which the measurement takes place does not matter. In 4th the measured force will be higher, but the speed lower than in 5th, theoretically giving the same power.

So, like Roadrash already indicated, you cannot multiply the 4th gear power measurement to extrapolate it to 5th gear by the difference in ratio. It is merely a question of how much drag the gearbox has in 4th compared to 5th. This difference would be quite small, imho. The only way to find out is to redo a run in 5th gear.

Cheers,

RX-Men-8

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Amen! :)