Lighter wheels / Wider tires / Lowering

[srkerd]

I know lighter wheels helps consumption and lowering will improve aerodynamics and wider tires will make it worse. But I am trying to gauge the effect of these.
I am planning to go from 20" PUP wheels to a 19" forged , so that should make the wheels significantly lighter and lower the car. However I am wondering what happens to the gain if I go from 8.5" wheels to 9.5" for the rear. Does anybody know how much of an effect each would have. Should expect to come out even?

Obviously I am not looking for an exact answer but wanted to know in general which has more of an effect. I guess offset of the wheels also would factor into this equation (since the 9.5" would sit wider)

 

[Needsdecaf]

**TOTAL WAG ALERT**

Depending on your driving, I would theorize (total guess here but based on logic, hear me out) that you'll be net negative. Lighter wheels will help unsprung weight, which increase efficiency when accelerating and decelerating, but doesn't do much while you're rolling at steady state speed.

Aerodynamics wise, you probably won't see much lowering effect at all from the 19's, as your overall diameter of your wheel and tire should remain relatively unchanged. You will increase your sidewall height while you decrease your wheel size. If you don't keep the same overall diameter, your wheels will have more revolutions per mile and your speedometer will be off. But even if you dropped 1/2", you'll pick up some aero benefit, but the overall car is still fixed. i.e. the total frontal area, the overall shape and coefficient of drag are due to the car, not he height of the car relative to the road. Wider tires will hurt aero too, as they will widen your overall frontal area you're presenting to the wind.

And of course, wider tires will have more rolling resistance.

As for quantifying this? I have no idea. I'm an engineer, but not a mechanical one or an aerodynamacist. So how much net negative you'll be I don't know. Or I don't know for sure if you'll actually be negative. But my guess is that you are.

 

[MountainPass]

What tires will you be using?

 

[srkerd]

MP, I am going to look into a all season setup for the tires.
I am not going to track or auto cross the car at all, I am doing this just for looks, more utility and comfort. The reason for going wider wheels at the rear is more for the offset ( I don't like to use spacers if I don't have to)
I miss the comfort and the look of the smart air suspension from my Model S.

Needsdecaf, I am not even sure why I care about efficiency as much, but I guess when I spend the money for new tires, wheels, suspension, It would be nice to have a more efficient car too

 

[FlyNavy01]

I have 19x9.5" wheels (275/35/19 PS4S tires) on my car in the rear and the total average efficiency I've seen is very similar to the 20x8.5" stock setup, and I think slightly less around town due to the weight savings. Although to be fair I only drove ~150 miles on the stock wheels.

I'm currently running staggered with 19x8.5" (245/40/19) up front to help reduce the aero penalty and my lifetime efficiency is 284 Wh/mi over 5,200 miles. I've been seriously thinking about getting a pair of 9.5" wheels for the front as well so I could run a square 275 width tire setup for more balanced handling at track and the ability to do tire rotations, but I'm sure it would come with a large range penalty.

 

[srkerd]

FlyNavy01, thanks for the info, interestingly enough you have the exact setup I want to get. VFF103 on 19” on a white P3D+ And more interestingly my consumption on stock 20” for the last 4300miles is also exactly 284Wh/mi.
Any chance seeing more picture of your car some where?

 

[FlyNavy01]

FlyNavy01, thanks for the info, interestingly enough you have the exact setup I want to get. VFF103 on 19” on a white P3D+ And more interestingly my consumption on stock 20” for the last 4300miles is also exactly 284Wh/mi.
Any chance seeing more picture of your car some where?

Will post some later tonight.

 

[FlyNavy01]

Sorry wasn't at my computer earlier. Here are some photos of my car, but I can DM more if you want to see anything specific.

The only annoying thing was the wheels come with a narrow 60mm center bore from the factory, so I talked Vorsteiner into boring them out for me to 64.1mm when I ordered so they would fit the car. If you go that route I would also recommend getting the machining to account for the special hub on the Performance brakes, otherwise you'll have to run 3mm spacers like I currently am. Otherwise I love them.

 

[Johnabis]

Sorry wasn't at my computer earlier. Here are some photos of my car, but I can DM more if you want to see anything specific.

Can you confirm whether or not your 0 to 60 and 1/4 mile times improved ? your current wheels are both lighter and wider then stock. for the spring I am debating about going staggered or squared. I made the stock 20's my snow wheels with snow tires.

 

[FlyNavy01]

@Johnabis
I'm getting what seems to be roughly the same numbers as stock. The 0-60mph may have improved by ~0.05-0.1sec if I average all of them versus before, but that's a small enough change that other factors play a bigger role. The car isn't limited by grip so going wider will not help (at least for drag racing) but going lighter will, very marginally.

I went with staggered for the middle ground compromise between aesthetics, performance, and efficiency. If I were to do it again I'd probably go square 265/35/19.