With a number of upgrades going with the increased weight of larger brakes (calipers and rotors) and wheel spacers, does it concern anyone about how harder it is to keep the rubber on the road with this extra weight momentum stressing the suspension?

If there is a discussion of this unsprung vs. sprung weight topic, please direct me to it.

Is there a discussion of wheel size/tire size to obtain the lowest possible weight while achieving performance with reliability?

 

It's kind of a give and take thing. Bigger brake calipers can reduce weight if made of a lighter material. Bigger rotors increase rotational inertia which could give more rolling resistance. Bigger wheels allow for shorter sidewalls for less deflection and roll and wider tread for more grip, but again create a larger mass moment of inertia (For a constant total wheel/tire weight) because the distance of equivalent mass concentration from the center of rotation is greater. If you get a wheel/tire combo that weighs less and has an equal or lower mass moment of inertia about the hub center than whatever set is currently on the car then you can have your cake and eat it too. Same goes for switching from steel to aluminum big brake calipers and lightweight rotors.

 

Nice write up. That is a thorough explanation that included the effects of rotational inertia that I had overlooked. Now the next step is to find real world applications by CL'ers. What wheel size/ tire combos have worked on the SC? How have you reduced weight of calipers? This is tricky for safety reasons.

 

I switched to LS400 aluminum calipers in the front.

 

But calipers are not rotational weight ,yet its stil unsprung. So you are reducing the unsprung weight, yet increasing rotional with bigger rotors ,plus bigger wheels so........ummm bigger wheels need a bigger brakes ..........I think i just popped a vessel in my brain

 

Do bigger wheels need bigger brakes if the outside diameter is unchanged? Great question. Aren't the rotors for LS and SC400 the same? Do any LS series come with aluminum calipers or are they after market?

Bartledoo - need more info on your calipers.

 

The LS rotors are slightly bigger, 12.4" versus 11.65". The 4 piston aluminum calipers came stock on the LS 95 and above.

 

You could still decrease the moment of inertia with the bbk if you get light enough brake rotors. Just how much lighter than stock they would have to be to overcome the radial change I'm not sure of. The manufacturer of each rotor would probably have inertia or radius of gyration calculations which could be used to decide that. Getting OE rotors with the supra TT or LS400 BBK will increase the inertia, of course.

Bigger wheels in most cases will be no lighter than stock and since the barrel and tire mass will be farther from center then yes, you will increase inertia. You could get a light enough wheel and tire package to combat that change though. Again you would need some advanced calculations to determine anything, and every wheel's weight distribution is different. I'd say 18's generally are the best choice for our cars performance wise. Anything more just seems to be for looks really and you certainly don't need any more brake clearance than 18's provide. You can't really say that bigger wheels need stronger brakes, though. It depends on other variables.

 

Lighter is always nicer, but you have to compensate for it. If you lighten up unsprung mass when the shock's compression valves are set for something much heavier, you can yield unwanted results.

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When you're talking about unsprung mass, you're just talking about the mass, period. The larger rotors won't affect the suspension's performance if it weighed the same as stock. The rotational inertia matters more from an acceleration standpoint, which is a separate entity. If suspension performance is your main concern (seems like it is), concentrate on lowering the mass. If you have a 20lbs 15" wheel and an 18lb 17" wheel, the 17" will be more favorable for your suspension.