Clutch diameter differences

[Spetz]

Hi everyone,



I noticed there are a few different flywheel/clutch diameter options for a car I am considering of converting to manual from auto.



What effect does this have to how the clutch feels or operates?

I assume that a larger flywheel/clutch combo means more bite without added weight on the pedal?

 

[demarpaint]

I had the option of using either a 10" or 11" clutch in my E-150 when I replaced it years ago. The flywheel is the same and is drilled and tapped to accept either size. I went with the 11". More mass, more surface area to grip, longer lasting. Having said that, it is a van used for work and always loaded up. In a sports car where a person might track the car and do spirited driving they might opt for the smaller lighter clutch, the engine will rev faster, however the clutch won't last as long. Which could be a moot point. You have to decide what you want. I would imagine there would also be a small hit in fuel economy with the larger clutch, it's heavier. With a hydraulic clutch there wasn't any noticeable difference in the pedal effort, at leas that I could remember.

 

[Linctex]

Originally Posted by Spetz
without added weight on the pedal?


Clutch surface area will not change pedal feel - - that will be in the design/type of the pressure plate.

 

[DrDanger]

Getting the lightest/smallest flywheel available is the most mechanically/fuel efficient option
https://www.youtube.com/watch?v=7K4W4hA6aV4

 

[Whimsey]

Originally Posted by demarpaint
I had the option of using either a 10" or 11" clutch in my E-150 when I replaced it years ago. The flywheel is the same and is drilled and tapped to accept either size. I went with the 11". More mass, more surface area to grip, longer lasting. Having said that, it is a van used for work and always loaded up. In a sports car where a person might track the car and do spirited driving they might opt for the smaller lighter clutch, the engine will rev faster, however the clutch won't last as long. Which could be a moot point. You have to decide what you want. I would imagine there would also be a small hit in fuel economy with the larger clutch, it's heavier. With a hydraulic clutch there wasn't any noticeable difference in the pedal effort, at leas that I could remember.


I had a 1989 F-150 with the 4.9 L6, it came with the 10" clutch disc. Trying to not ram a stupid teenage girl who decided to cut in front of me from the left lane to the right lane that I was in I ended up blowing the clutch slave cylinder. Ford upon replacing the clutch assembly put in a 11" clutch disc. The clutch action was much nicer than with the original 10" clutch disc. But that was a heavier truck not a sports or small car.

Whimsey

 

[supton]

I'd think, all factors equal, that an 11" might grab faster than 10", more surface area to grab. That said, nothing is ever equal--the 11" could have less coefficient of friction, or other ways to lessen its "grab".

Eons ago I put in a much stronger clutch into a car, and was rewarded with... a much easier pedal. ? Shocked me, but it was shockingly easier to drive, despite like 2x the torque rating.

 

[demarpaint]

Originally Posted by Whimsey
Originally Posted by demarpaint
I had the option of using either a 10" or 11" clutch in my E-150 when I replaced it years ago. The flywheel is the same and is drilled and tapped to accept either size. I went with the 11". More mass, more surface area to grip, longer lasting. Having said that, it is a van used for work and always loaded up. In a sports car where a person might track the car and do spirited driving they might opt for the smaller lighter clutch, the engine will rev faster, however the clutch won't last as long. Which could be a moot point. You have to decide what you want. I would imagine there would also be a small hit in fuel economy with the larger clutch, it's heavier. With a hydraulic clutch there wasn't any noticeable difference in the pedal effort, at leas that I could remember.


I had a 1989 F-150 with the 4.9 L6, it came with the 10" clutch disc. Trying to not ram a stupid teenage girl who decided to cut in front of me from the left lane to the right lane that I was in I ended up blowing the clutch slave cylinder. Ford upon replacing the clutch assembly put in a 11" clutch disc. The clutch action was much nicer than with the original 10" clutch disc. But that was a heavier truck not a sports or small car.

Whimsey

That sucks!

The 11" clutch was for HD applications and/or towing. For me it was a no brainer. 11" flywheel already machined for it, why not? The only thing needed for the conversion was bolts, the 11" used a slightly heavier bolt. Everything else was the same aside from the disk and pressure plate.

As I said I didn't feel or notice anything out of the ordinary. If it were mechanical linkage, I would imagine there would have been a noticeable difference. Keep in mind a new clutch vs. an old one is going to feel different. In this case pedal effort was pretty close, but it has been a lot of years since I did the conversion.

 

[JLTD]

More torque with heavier flywheel - ok not engine torque exactly but with more rotating mass there is more momentum.

 

[marc1]

We need to be clear on a few points. The examples above and my own personal example I will give you below are cases where the flywheel is the exact same one, it is simply dual drilled. My 70 GTO (RAIV) came with a 10.4" clutch from the factory but the flywheel was drilled to accept the larger 11" clutch. I upgraded to the 11" clutch pretty quickly in my time with that car and never looked back. The 11" gave much longer life and the slight rotational inertia increase was no issue for the synchos to speed match the rotating clutch disc during shifting. Nor was there any perceptible laziness to rev with the slightly larger (ergo heavier) clutch pressure plate and disc. Synchros are much more sensitive to the weight change than the engine. This is hopefully not an issue with your transmission either but be aware. You will never notice any change in "pedal feel" going to the larger disc, those are mutually exclusive and are purely a function of the pressure plate involved. A 2800# PP with a 10.4" disc will feel the same as a 2800# PP with an 11" disc. What can happen is the PP for the 11" has a different rating which makes you think it was the diameter change but in reality it isn't.

The value / ease of going to a larger diameter disc is a little bit different if you have to change the flywheel due to the flywheel being specific for diameter A or diameter B. If they are not the same flywheel these are potential issues: starter motor is different, rotational inertia is noticeable during acceleration, engine balance.

If your swap is simply a dual drilled flywheel, then yes put the largest diameter PP and clutch in. If it isn't then proceed with caution and look at the potential issues I indicated above.