Are the staggered tires (21") actually taller than the 19"s?

[ArbitrageMan]

My car has 21" twin turbines in staggered config. 245/35-21 front, 265/35-21 rear. According to my math (I'll show my work below,) the rear tire is 0.5 inches taller than the front. This surprises me because I would have assumed the total height of the tires to be the same all the way around, with the rears simply being a little wider.

Now for the real problem. I'm planning to get a set of 19" wheels and tires for winter. The 19" tires will be the same height all the way around. If i'm putting a smaller total height tire on the rear from what the car came with, won't that cause issues with...something (distribution of power, stance of the car, front to rear alignment?)

Math:
1. Total height of 19" - 245/45-19=
a. .45*245 = 110.25mm <- height of sidewall in mm
b. 110.25 / 10 / ~2.45 = 4.3 inches <- this is the height of the sidewall in inches
c. 4.3 + 4.3 + 19 = 27.7 inches <- two sidewalls plus wheel size = total height of tire

2. Total height of rear 21" - 265/35-21=
a. .35*265 = 92.75mm
b. 92.75 / 10 / ~2.45 = 3.7 inches <- height of sidewall
c. 3.7 + 3.7 + 21 = 28.3 inches

28.3 - 27.7 = ~0.5 inches: This shows that the rear 21" is 0.5 inches taller than the 19"????

3. The fronts of the 21" (245/35-21) are 27.8 inches, using the same math, which is ~the same as the 19".

 

[PaulusdB]

Your observations are right. The height of the car doesn't depend on the diameter of the wheels, however. It depends on the height of the axle from the pavement, so the radius of the wheel (half the diameter).

• Alignment is no issue anyhow.
• Height of the vehicle in the rear is different though; you could have Tesla adjust the ride height. I never bothered about those few millimeters.
• If you can get them, mount 255/45-19 tyres in the back (or even 265). No more front-rear rotation possible, but does lessen the height difference.

 

[ArbitrageMan]

The height of the car doesn't depend on the diameter of the wheels, however. It depends on the height of the axle from the pavement, so the radius of the wheel (half the diameter).

Ahhh, this is helpful! Its radius versus diameter.

So the radius of the 19 would be 4.3 + (19 * .5) = 13.84 inches
Radius of 21 in rear would be 3.7 + (21 * .5) = 14.15 inches

So that's only 0.3 inches difference, or 80mm, which is small - an average tire probably wears this amount over its life.

Thanks!

 

[Dithermaster]

I have a set of 21" and a set of 19". Tesla insisted they need to recalibrate the suspension when they are swapped, and it's not a DIY thing. So I've alway brought the car to them, which is a day trip for me. Has anyone figured out how to DIY this? If I were going to swap them myself, and just leave one suspension calibration year-round, which should it be?

 

[PaulusdB]

DIY ride height adjustment can only be done with after market kit like this: Adjustable Air Ride

Instructions are simple: http://www.adjustableairride.com/PDF/Tesla_S.pdf Although I would put the car into Jack Mode while working on the links.

But better yet, I wouldn’t (and in fact don’t) bother with these small adjustments and just go with the same settings (for stock size 21” staggered wheels) yearround.