Increased whp by having lighter wheels - Page 2 - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Dimman · 07-02-2012, 01:21 AM

Quote:

Originally Posted by Captain Snooze

Ahhhh....nope.
But I still don't understand why this should result in an increase in power.
F/m=a. Decreasing the mass (or inertia) increases the acceleration. Understood but you are not increasing the power. The engne output has not been changed.

As pointed out by others, that has never been said. The dyno measures engine torque that fights through the drivetrain's inertial and frictional losses. So reducing the mass of the wheels makes the path easier, in a manner of speaking. This is why there is a difference between the number a chassis dyno spits out and the number a factory tells us which comes from an engine dyno.

rice_classic · 07-02-2012, 01:25 AM

Mr. Snooze. Who is it exactly that is claiming that lighter wheels makes more power? I re-read the thread and people are talking about how a reduction in rotational mass changes the readings on a dyno. Nobody is claiming the engine itself is making more power.

Captain Snooze · 07-02-2012, 02:21 AM

When I see dyno graphs they usually display power and/or torque. The OP posted a dyno graph. It shows before and after. To me the implication was that if the "numbers" had changed the power had changed. If "a reduction in rotational mass changes the readings on a dyno" what readings are you referring to?

Captain Snooze · 07-02-2012, 02:24 AM

Quote:

Originally Posted by Dimman

This is why there is a difference between the number a chassis dyno spits out and the number a factory tells us which comes from an engine dyno.

Understood.

Dimman · 07-02-2012, 02:27 AM

Quote:

Originally Posted by Captain Snooze

When I see dyno graphs they usually display power and/or torque. To me the implication was that if the "numbers" had changed the power had changed. If "a reduction in rotational mass changes the readings on a dyno" what readings are you referring to?

Just to clarify.

These are chassis dyno figures. They calculate the net torque as measured at the vehicle's drive wheels. This is NOT a representation of power/torque at the flywheel.

speed3 · 07-02-2012, 02:29 AM

Quote:

Originally Posted by Captain Snooze

When I see dyno graphs they usually display power and/or torque. To me the implication was that if the "numbers" had changed the power had changed. If "a reduction in rotational mass changes the readings on a dyno" what readings are you referring to?

Take 2 cars

Car 1 stock
produces 200hp from the engine
produces 160 hp at the wheels

Car 2 stock except wheels
produces 200hp from the engine
produces 162 hp at the wheels

You aren't making any more power just increasing the efficiency of the drivetrain.

Captain Snooze · 07-02-2012, 02:55 AM

OK! I have just been reading about inertia type dynos. Sorry, it has been about 25 years since I have been in a dyno workshop. I was not familiar with such devices.

Jordo! · 07-02-2012, 02:56 AM

The difference is probably due to the air filter...

speed3 · 07-02-2012, 03:52 AM

Quote:

Originally Posted by Jordo!

The difference is probably due to the air filter...

Or random variation between runs.

Type[R]+ · 07-02-2012, 10:17 AM

Quote:

Originally Posted by speed3

Or random variation between runs.

Or lighter wheels.

DanVIIIVI · 07-02-2012, 10:06 PM

So what are the weights of the stock 17" wheels on the fr-s/86?

Mitch · 07-02-2012, 11:01 PM

Quote:

Originally Posted by DanVIIIVI

So what are the weights of the stock 17" wheels on the fr-s/86?

I think I've seen 20lbs for the tire and 21lbs for the wheel for a grand total of 41lbs.

DanVIIIVI · 07-03-2012, 01:46 AM

Yeah, I found another thread that outlines the weight of all components on the vehicles. The OEM 17" wheels come in at approx 21.4lbs = 9.706 kgs.

Should be very easy to shed some weight there.

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07-02-2012, 01:25 AM	#16
rice_classic Senior Member Join Date: Jun 2012 Drives: Nevermorange FRS Location: Seattle, WA Posts: 4,159 Thanks: 755 Thanked 4,200 Times in 1,803 Posts Mentioned: 77 Post(s) Tagged: 1 Thread(s)	Mr. Snooze. Who is it exactly that is claiming that lighter wheels makes more power? I re-read the thread and people are talking about how a reduction in rotational mass changes the readings on a dyno. Nobody is claiming the engine itself is making more power.

07-02-2012, 02:21 AM	#17
Captain Snooze Because compromise ® Join Date: Jan 2012 Drives: Red Herring Location: australia Posts: 7,685 Thanks: 3,967 Thanked 9,235 Times in 4,098 Posts Mentioned: 60 Post(s) Tagged: 0 Thread(s)	When I see dyno graphs they usually display power and/or torque. The OP posted a dyno graph. It shows before and after. To me the implication was that if the "numbers" had changed the power had changed. If "a reduction in rotational mass changes the readings on a dyno" what readings are you referring to?

07-02-2012, 02:55 AM	#21
Captain Snooze Because compromise ® Join Date: Jan 2012 Drives: Red Herring Location: australia Posts: 7,685 Thanks: 3,967 Thanked 9,235 Times in 4,098 Posts Mentioned: 60 Post(s) Tagged: 0 Thread(s)	OK! I have just been reading about inertia type dynos. Sorry, it has been about 25 years since I have been in a dyno workshop. I was not familiar with such devices.

07-02-2012, 02:56 AM	#22
Jordo! Enjoy it, destroy it. Join Date: Oct 2009 Drives: Datsun Racing Hen Location: Blank Generation Posts: 820 Thanks: 6 Thanked 61 Times in 48 Posts Mentioned: 1 Post(s) Tagged: 2 Thread(s)	The difference is probably due to the air filter...

07-02-2012, 10:06 PM	#25
DanVIIIVI Senior Member Join Date: Jul 2012 Drives: 86GTS 6M Location: Australia Posts: 194 Thanks: 51 Thanked 54 Times in 34 Posts Mentioned: 2 Post(s) Tagged: 0 Thread(s)	So what are the weights of the stock 17" wheels on the fr-s/86?

07-03-2012, 01:46 AM	#27
DanVIIIVI Senior Member Join Date: Jul 2012 Drives: 86GTS 6M Location: Australia Posts: 194 Thanks: 51 Thanked 54 Times in 34 Posts Mentioned: 2 Post(s) Tagged: 0 Thread(s)	Yeah, I found another thread that outlines the weight of all components on the vehicles. The OEM 17" wheels come in at approx 21.4lbs = 9.706 kgs. Should be very easy to shed some weight there.

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