Why is a square tire setup best?

Mandersm · 10-17-2014, 01:17 AM

Everyone says that a square wheel and tire setup gives the car best handling and balance.
But can anyone please explain why?

If I go 245-18" up front (widest I can have) and 265-18" in the rear, will the car be bad to drive or will I ruin the handling of the car?
As I understand I don`t need 265 tires on a 125i (128i), because there is less power than the 135i.

I want the car to be fun to drive, But I also want the car to look "beefy" with wide rear tires, like a Beemer should look

Can`t I have both if my first priority is handling???

(Winter plans for the car is a full suspensions upgrade, M3 parts, swaybar, subframe bushings, dampers, LSD etc...)

Pyrat 2 · 10-17-2014, 09:51 PM

Square setup will give approx equal contact patch front to back. When going around a curve the front and back will tend towards achieving maximum grip at the same time. Other factors such as alignment setting as well as front and rear sway bars also come into the picture but the contact patch is a big player in balanced handling. Recall that the 1 like most BMWs has a relatively even weight distribution so having a proportional contact patch is a good starting point.

Worra · 10-19-2014, 11:45 PM

^ Exactly what heeltoe said. This will also result in less inherent understeer.

128Convertibleguy · 10-20-2014, 01:37 PM

It's all very complicated, and depends on the specific car, the driver, and how the car is being used. BMW has sold the 1 both ways. There's no simple answer.

Many people with modded cars prefer a square setup. Doesn't mean it's a big deal for everyone, or even correct for them.

Olgeezer1 · 10-26-2014, 04:53 PM

As the owner of a car just like yours I like my square setup alot. 225/40/18 non-runflats on the stock(Canadian Sport Pkg.) #263 wheels. Stock 215/245 setup was not enough in the front and too much for this car in the rear. Lots of understeer and not enough power to bring the rear around. Now much more fun to drive. Less understeer, more neutral handling,better grip, faster at the autoX. I think the looks are great too. Too much tire is not going to give you a better handling car.

10-17-2014, 01:17 AM	#1
Mandersm Mandersm 38 Rep 35 Posts Drives: E92 M3 Join Date: Jun 2012 Location: Norway iTrader: (0)	Why is a square tire setup best? Everyone says that a square wheel and tire setup gives the car best handling and balance. But can anyone please explain why? If I go 245-18" up front (widest I can have) and 265-18" in the rear, will the car be bad to drive or will I ruin the handling of the car? As I understand I don`t need 265 tires on a 125i (128i), because there is less power than the 135i. I want the car to be fun to drive, But I also want the car to look "beefy" with wide rear tires, like a Beemer should look Can`t I have both if my first priority is handling??? (Winter plans for the car is a full suspensions upgrade, M3 parts, swaybar, subframe bushings, dampers, LSD etc...)
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10-17-2014, 09:51 PM	#2
Pyrat 2 Colonel 1418 Rep 2,560 Posts Drives: Rapidly from A to B Join Date: Jun 2005 Location: Chicago 'burbs or TN Smokies iTrader: (3) Garage List 2022 Porsche GT4 [9.64] 2018 Porsche GT3 [9.33] 2007 Z4 M Roadster [8.33] 2020 BMW X1 [0.00]	Square setup will give approx equal contact patch front to back. When going around a curve the front and back will tend towards achieving maximum grip at the same time. Other factors such as alignment setting as well as front and rear sway bars also come into the picture but the contact patch is a big player in balanced handling. Recall that the 1 like most BMWs has a relatively even weight distribution so having a proportional contact patch is a good starting point. __________________ '07 Z4MR '22 GT4 '18 GT3 '16 GT4, '16 M2, '14 X1, '13 135is, '06 330i, '03 323 Ci, '01 330i, '99 M3 (RIP), '96 318is, some non-BMWs
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10-19-2014, 11:45 PM	#3
Worra Captain 49 Rep 970 Posts Drives: 2013 135is/6, 1995 540i/6 Join Date: Jul 2013 Location: SF Bay iTrader: (0) Garage List 1995 BMW 540i [0.00] 2013 BMW 135is [0.00]	^ Exactly what heeltoe said. This will also result in less inherent understeer. __________________ 2013 Black Sapphire 135is (526/586) 1995 Jet Black 540i Past cars: 94 530i, 95 530iT, 09 328i, 90 325i
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10-20-2014, 01:37 PM	#4
128Convertibleguy Captain 60 Rep 704 Posts Drives: 2010 128 Covertible Join Date: Jan 2014 Location: Mountains iTrader: (0)	It's all very complicated, and depends on the specific car, the driver, and how the car is being used. BMW has sold the 1 both ways. There's no simple answer. Many people with modded cars prefer a square setup. Doesn't mean it's a big deal for everyone, or even correct for them.
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10-26-2014, 04:53 PM	#5
Olgeezer1 Lieutenant 183 Rep 505 Posts Drives: 2010 128i 6MT Sport Pkg. 18" Join Date: Jul 2013 Location: Ottawa, Canada iTrader: (0) Garage List 2010 E82 128i N52 [0.00]	As the owner of a car just like yours I like my square setup alot. 225/40/18 non-runflats on the stock(Canadian Sport Pkg.) #263 wheels. Stock 215/245 setup was not enough in the front and too much for this car in the rear. Lots of understeer and not enough power to bring the rear around. Now much more fun to drive. Less understeer, more neutral handling,better grip, faster at the autoX. I think the looks are great too. Too much tire is not going to give you a better handling car.
	Appreciate 0 Quote