TheLouvre101
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What’s the ideal tire size on a square setup? Can I have a 315 in the rear and a 285 in the front on 20x9’s?
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What’s the ideal tire size on a square setup?
At first glance, a 20x9 is going to be too skinny for either tire sizes referenced.Can I have a 315 in the rear and a 285 in the front on 20x9’s?

This is a great article written by Billy Johnson on selecting tire and wheel fitment for performance tires and performance driving.
https://motoiq.com/how-to-properly-select-and-size-tires-for-performance/
Nice catch.I thought square tire setup meant same size tires all the way around.
I missed that. 
i currently have a a 275/35/20 on all 4 and really it’s just daily driving. Car is on Stock suspensionWelcome to the forums.
At first glance, a 20x9 is going to be too skinny for either tire sizes referenced.
Can you give us some insight as to 1) what your objective is, 2) what you have on-hand now? Others can provide ideas as to tire type, size and possible suspension changes to support.
https://www.tyresizecalculator.com/charts/tire-width-for-a-wheel-rim-size-chart
https://www.1010tires.com/Tools/Tire-Size-Calculator
I always refer drivers to the sites above, to help determine rim and tire size.
There is an ideal tire width for each rim width.
Regarding tire diameter, it's a good idea to keep the replacement tire's diameter +/- 3% of the original. Straying too far from +/- 3% could lead to problems with shift points, ABS, speedos, etc. People can and do stray from +/-3, but I cannot speak to what anyones' limit would be for thier car.
A very common square setup on S550s is a 19x10 rim with a +35 offset; these are paired with a 285/35/19 tire. Take the old off. Bolt the new on. Done.
People do use 20" rims all the time; they look and work great. As the thread progresses, they can chime in and offer insights on their setups.
Again, welcome.![]()
ok, so why the question? So far you've not brought a new wrinkle to a discussion that's been had a dozen times already.i currently have a a 275/35/20 on all 4 and really it’s just daily driving. Car is on Stock suspension
The bottom line is for those tire sizes you need wider wheels. And 315 in the rear would be appropriate for a staggered setup (for example, 20x11 wheel in the rear).What’s the ideal tire size on a square setup? Can I have a 315 in the rear and a 285 in the front on 20x9’s?
Absolutely, a 30 profile is good, for example 285/30/20, and depending on what lowering springs you have, a 35 could work....What’s the ideal tire size on a square setup? Can I have a 315 in the rear and a 285 in the front on 20x9’s?