New 20" rims now clutch feels different.
 

Hello guys thanks for looking. I recently upgrade my rims to CV3 Vossen 20x9F and 20x11R. My clutch is feeling a little different I have 18000 miles on my car.

Any advice

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You have those heavy a$$ rims on a car not known for its torque. Higher rotational mass is robbing your power. I would have just stuck with 19's. I don't see any logical reason to go larger than 19 on this vehicle. Wheels the size of a 19th century wagon don't have much of a place on modern cars, let alone a sports car. With the stockers being forged rays (sport), it only magnified the difference.

MotorDyne's Informative Dynograph Write-ups/Comparisons - Nissan Titan Forum

This thread shows the power-robbing effect of heavier rims. So yeah, I'm guessing what you are feeling is all from the increases weight as well as having the weight even farther away from the axle (higher rotational inertia)

20 inch cast wheels. keep in mind the typical rule of thumb is to multiply unsprung weight by four. that's equivalent spring weight you just added to the car. on top of the added power you need to actually turn those heavy wheels.

Larger rim, larger diameter tire. Changes the overall gear ratio. How much larger in diameter is the new tires from the stockers?

My tires are
THE FRONT RIMS ARE 9 INCHES WIDE X 20 INCHES, THE REAR ARE 11 INCHES WIDE X 20 INCHES------THE TIRES ARE NITTO 555 EXTREAM ZR -----FRONT TIRE SIZE ----255-30ZR-20----REAR TIRE SIZE ------285-30ZR-20

What was the stockers?

This is 100% correct. The larger the size the greater rotational mass you will encounter. Unless you have 500+ HP there is absolutely no need to go 20. 19 are pushing it also but this is the perfect size between performance and looks. 370 has huge tire cavity so you need to fill it. Genearlly speaking when regarding 350-370z platform.

17-18 (pure performance)
19 (balanced between look and performance)
20+ (purely for aesthetic purposes as you will experience a degrade in performance)

You're changing your final drive ratio.
Thats why it feels "different".
Z's were not made for 20's.
I'd like to get 17's.

3 Things change when you play with your wheels.
1. Mass change: You'll need more energy(power) to spin up and more heat will be generates to slow down your wheels.
2. Diameter+Mass change: Gyro effect will make it will feel a little more difficult to turn your wheels and car at speed.
3. Diameter change: Gear ratio is made longer with a larger wheel. And your speedometer is registering a slower speed then your actual.

Your noticing #3 most of all which is why you think there is an issue. Changing the clutch will not effect anything since your clutch is not slipping in the first place any more then it would have before. What is happening your asking your engine to do more then it had to do to accelerate before but your HP remains the same so it feel different (and is slower).