Clutch Inertia

BGTV8 · 05-01-2014, 10:26 PM

I'm researching clutches for my up-coming Z34 build and stumbled across the attached article in F1 Magazine (written out of an interview with Pat Symonds).

Read the bit about rotational inertia varying as the square of the overall gear ratio to give an equivalent mass to be accelerated ...

This implies a light clutch is vastly better for the engines ability to accelerate the car in the lower gears than a heavier one.

Can the mechanical engineers and/or physics graduates here amplify this for me !!!

I was concerned at overall clamping pressure as a key variable but diameter and overall mass would seem to be another significant variable as well.

I was originally thinking about a 184mm 2-plate clutch but now am re-thinking.

Since our class cannot run Forced Induction, max torque won't be much more than 400 ft/lb at absolute best ..... but I was surprised at the quote ...

2011 Nismo#91 · 05-02-2014, 10:03 AM

Lighter rotating parts will allow your cars acceleration and deceleration to occur quicker.
In simple terms
Anything with mass (weight) rotating has stored rotating energy. (think of it as a mechanical battery)
Increasing rotational speed puts more energy into that battery.
Decreasing rotational speed required energy to be removed from the battery.

1slow370 · 05-02-2014, 12:18 PM

the flywheel in an f1 car is just a heatsink for the clutch though, application is very different. for a race car the lighter the better, If you actually drive it starting the car from a dead stop with a 7.5" 10lb clutch and flywheel is a mother bitch

ChipsWithDips · 05-02-2014, 07:30 PM

Yep the effects of rotational inertia (clutch and flywheel and pulleys and all that really) are more significant in lower gears. I've posted about this before in relation to dyno readings in different gears: Dyno pull in 4th any equation to tell how much it would've made in the correct gear?

Keep in mind that rotational inertia isn't just about the mass of the object, but also how far along the radius that mass is distributed. Twin and multi-plate clutches are typically able to be made in a smaller diameter than a single plate for the same or more clamping force.

Take a look at the thin solid disk example here: List of moments of inertia - Wikipedia, the free encyclopedia

The equation given for its moment of inertia is this:

So the inertia is directly proportional to the mass, but also directly proportional to the square of the radius. This means that reducing the radius will have more effect than reducing the mass by the same factor.

Less inertia in your clutch is equivalent to a slightly lighter flywheel for the parts of the clutch that rotate with the flywheel(pressure plate and diaphragm spring).

And for the friction disks that are connected to your transmission input shaft, less inertia on them will mean less load on your synchros during fast shifts.

BGTV8 · 05-03-2014, 05:36 AM

Quote:

Originally Posted by ChipsWithDips

Yep the effects of rotational inertia (clutch and flywheel and pulleys and all that really) are more significant in lower gears. I've posted about this before in relation to dyno readings in different gears: Dyno pull in 4th any equation to tell how much it would've made in the correct gear?

Keep in mind that rotational inertia isn't just about the mass of the object, but also how far along the radius that mass is distributed. Twin and multi-plate clutches are typically able to be made in a smaller diameter than a single plate for the same or more clamping force.

Take a look at the thin solid disk example here: List of moments of inertia - Wikipedia, the free encyclopedia

The equation given for its moment of inertia is this:

So the inertia is directly proportional to the mass, but also directly proportional to the square of the radius. This means that reducing the radius will have more effect than reducing the mass by the same factor.

Less inertia in your clutch is equivalent to a slightly lighter flywheel for the parts of the clutch that rotate with the flywheel(pressure plate and diaphragm spring).

And for the friction disks that are connected to your transmission input shaft, less inertia on them will mean less load on your synchros during fast shifts.

Light-bulb moment ... thanks for the post ....

Dreamin'Z · 05-03-2014, 07:24 AM

Hell of a thread fellas, I learned something new today. Keep it up!!!!

05-02-2014, 12:18 PM	#3 (permalink)
1slow370 A True Z Fanatic Join Date: Aug 2009 Location: In the D Posts: 3,732 Drives: v8 74 260z ;) Rep Power: 7251	the flywheel in an f1 car is just a heatsink for the clutch though, application is very different. for a race car the lighter the better, If you actually drive it starting the car from a dead stop with a 7.5" 10lb clutch and flywheel is a mother bitch __________________ ANSWER PRICE LIST Answers - - - - - - - - - - - - - - - - $0.75 Answers (requiring thought) - - - - $1.25 Answers (correct) - - - - - - - - - - $12.50

05-02-2014, 07:30 PM	#4 (permalink)
ChipsWithDips Enthusiast Member Join Date: Mar 2011 Location: Austin, TX Posts: 279 Drives: '11 Gunmetal 370Z MT Rep Power: 14	Yep the effects of rotational inertia (clutch and flywheel and pulleys and all that really) are more significant in lower gears. I've posted about this before in relation to dyno readings in different gears: Dyno pull in 4th any equation to tell how much it would've made in the correct gear? Keep in mind that rotational inertia isn't just about the mass of the object, but also how far along the radius that mass is distributed. Twin and multi-plate clutches are typically able to be made in a smaller diameter than a single plate for the same or more clamping force. Take a look at the thin solid disk example here: List of moments of inertia - Wikipedia, the free encyclopedia The equation given for its moment of inertia is this: So the inertia is directly proportional to the mass, but also directly proportional to the square of the radius. This means that reducing the radius will have more effect than reducing the mass by the same factor. Less inertia in your clutch is equivalent to a slightly lighter flywheel for the parts of the clutch that rotate with the flywheel(pressure plate and diaphragm spring). And for the friction disks that are connected to your transmission input shaft, less inertia on them will mean less load on your synchros during fast shifts. BGTV8 and gomer_110 like this. __________________ PPE Headers SS/Coated/Wrapped \| Ebay y-pipe \| Custom 3" single exhaust w/ Magnaflows \| UpRev \| Racingbrake 2pc Rotors \| 40th calipers \| Eibach sways \| SPL endlinks, diff mounts \| RJM pedal \| Stillen Intakes, UDP, Flywheel \| M370 Manifold \| Z1 engine mounts, CSC-EK, Clutch \| Forgestar F14 18x10 \| Conti DWs \| Quaife diff/4.08 gears \| Nismo diff cover Last edited by ChipsWithDips; 05-02-2014 at 07:45 PM.

05-03-2014, 07:24 AM	#6 (permalink)
Dreamin'Z Base Member Join Date: Jan 2009 Location: Fort Walton Beach, FL Age: 40 Posts: 147 Drives: 14 370Z PW 6spd Rep Power: 16	Hell of a thread fellas, I learned something new today. Keep it up!!!! __________________ Pearl 6MT Base with Sport Package

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05-02-2014, 10:03 AM	#2 (permalink)
2011 Nismo#91 A True Z Fanatic Join Date: Mar 2011 Location: NJ Posts: 2,400 Drives: slowly Rep Power: 40569	Lighter rotating parts will allow your cars acceleration and deceleration to occur quicker. In simple terms Anything with mass (weight) rotating has stored rotating energy. (think of it as a mechanical battery) Increasing rotational speed puts more energy into that battery. Decreasing rotational speed required energy to be removed from the battery.