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[Yoddha]

Hey guys,

A mate of mine at a performance shop said that he used to rock 305 rear wheels on his E92 M3. I was wanting to ask you lot how that difference from the OEM competition package specs would affect speed off the line or fuel consumption and what not.

Cheers

[4corners]

The wheels don't support the tire sidewall properly on a 305 and you'll lose 'feel' and directness

[Yoddha]

Originally Posted by 4corners

The wheels don't support the tire sidewall properly on a 305 and you'll lose 'feel' and directness

I'm getting aftermarket HRE's though, so I'm not using stock wheels.

[ben@tirerack]

Speed off the line:

Probably helpful all else being equal. Though you may have to run slightly lower air pressure than stock if you really want to see a noticeable benefit. Keep in mind that the size of the contact patch will be about the same size for any given air pressure and vehicle weight.

Pounds of weight on rear axle divided by pounds per square inch of pressure = square inches of contact patch. (Like any simple formula applied to the complexities of real life this will break down somewhat in extreme cases such as 0 tire pressure).

Fuel economy:
Wider tires almost always make a car thirstier. Whether or not the difference in fuel mileage is noticeable probably depends on the individual case and how scientific your monitoring of the gas mileage is.

Keep in mind that different sizes often have slightly different revolutions per mile. This will slightly change speedometer/odometer. Changes in the speedometer/odometer readings will impact any calculation of economy based on the car's own reporting.

[Yoddha]

Originally Posted by ben@tirerack

Speed off the line:

Probably helpful all else being equal. Though you may have to run slightly lower air pressure than stock if you really want to see a noticeable benefit. Keep in mind that the size of the contact patch will be about the same size for any given air pressure and vehicle weight.

Pounds of weight on rear axle divided by pounds per square inch of pressure = square inches of contact patch. (Like any simple formula applied to the complexities of real life this will break down somewhat in extreme cases such as 0 tire pressure).

Fuel economy:
Wider tires almost always make a car thirstier. Whether or not the difference in fuel mileage is noticeable probably depends on the individual case and how scientific your monitoring of the gas mileage is.

Keep in mind that different sizes often have slightly different revolutions per mile. This will slightly change speedometer/odometer. Changes in the speedometer/odometer readings will impact any calculation of economy based on the car's own reporting.

Thank you for a great explanation mate, that helped me decide cheers