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I was truly amazed at how much the wheel and tire combination on my Q60 RS400 AWD weighs. It measures an even 60 lbs., which seems to be significantly heavier than the wheels on my G35 which I traded in for the Q60. I thought the tire was filled with concrete. Does anyone know if other run-flat tire/wheel combinations are this heavy?
 

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Yeah runflat tires are heavy by nature because the tires need to driven around 50 miles or so in the event of a flat. The wheels themselves might not be too bad but weight isn't always a concern for the OEMs unless it's a car that is meant to have crazy performance, etc where forged and light is expected for the wheels.

Otherwise, it's driven by cost. Most end consumers don't care about the weight of their wheels or tires. The ones that do will never be satisfied with something OEM and go aftermarket anyhow so it doesn't make sense to
 

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You can drop to a 22 pound wheel and a 25 pound Michelin Pilot and youre at 47lbs.

Thats 13 pounds of rotational mass off the car per corner. Thats 52lbs altogether.

The car will make 15-20 more WHP just off that. The increase in acceleration would be very noticeable.
 

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You can drop to a 22 pound wheel and a 25 pound Michelin Pilot and youre at 47lbs.

Thats 13 pounds of rotational mass off the car per corner. Thats 52lbs altogether.

The car will make 15-20 more WHP just off that. The increase in acceleration would be very noticeable.
Speaking of decreasing unsprung mass, changing over to 2-piece Akebono rotors front and rear on the Red Sport will net you a decrease of 30 pounds overall (10 pounds/front rotor; 5 pounds/rear rotor):

https://www.z1motorsports.com/brakes/z1-motorsports/z1-piece-akebono-front-rotors-p-7025.html

https://www.z1motorsports.com/brakes/z1-motorsports/z1-piece-akebono-rear-rotors-p-10990.html

 

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Speaking of decreasing unsprung mass, changing over to 2-piece Akebono rotors front and rear on the Red Sport will net you a decrease of 30 pounds overall (10 pounds/front rotor; 5 pounds/rear rotor):

https://www.z1motorsports.com/brakes/z1-motorsports/z1-piece-akebono-front-rotors-p-7025.html

https://www.z1motorsports.com/brakes/z1-motorsports/z1-piece-akebono-rear-rotors-p-10990.html

The wheels, tires, and rotor combo would make an insane difference in turning crispness and response. It would feel like an all new car.
 

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Speaking of decreasing unsprung mass, changing over to 2-piece Akebono rotors front and rear on the Red Sport will net you a decrease of 30 pounds overall (10 pounds/front rotor; 5 pounds/rear rotor):

https://www.z1motorsports.com/brakes/z1-motorsports/z1-piece-akebono-front-rotors-p-7025.html

https://www.z1motorsports.com/brakes/z1-motorsports/z1-piece-akebono-rear-rotors-p-10990.html
Any experience with the improvement to stopping distances? Is it better or is it just added lightness we're talking about here? It definitely seems like a cost effective solution if one has to switch their rotors out due to wear :)
 

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There are some Q50 guys with 18" wheels on RS. Needs to be some specific offset to clear the brakes from what I recall. The OEM 19" wheels are very heavy.
 

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Lowering rotational mass is definitely a big thing, I would love to see someone record time differences on the Q60 !!
From an acceleration standpoint, you want the smallest diameter and the lightest wheel & tire combination. A larger diameter wheel locates the rim, which has the most % of mass of the wheel, farther away from the center, which for the same amount of torque applied, will result in slower acceleration.

I found a simple explanation, with example of children and the merry-go-round:

As we might expect, the larger the torque is, the larger the angular acceleration is. For example, the harder a child pushes on a merry-go-round, the faster it accelerates. Furthermore, the more massive a merry-go-round, the slower it accelerates for the same torque. The basic relationship between moment of inertia and angular acceleration is that the larger the moment of inertia, the smaller is the angular acceleration. But there is an additional twist. The moment of inertia depends not only on the mass of an object, but also on its distribution of mass relative to the axis around which it rotates. For example, it will be much easier to accelerate a merry-go-round full of children if they stand close to its axis than if they all stand at the outer edge. The mass is the same in both cases; but the moment of inertia is much larger when the children are at the edge.

The reduced mass of the brake rotors help achieve quicker acceleration of the wheel assembly, and contribute to less unsprung mass for the suspension, which helps control the wheel's motion (more responsive).

As for braking performance, just as it is easier to accelerate a lighter mass, the opposite is true, too.
 
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