[MR_TJ]

Can anyone advise me the approriate size rotor for 2005 e90 320i ( front & Rear)

[Stuart@BMRAutowerkes]

Original size is 300mm front, 336mm rear

Fronts can accept 292-300mm and rear 300-336mm as replacements

*don't blame me if wrong though!

[sbce90]

rear rotor is bigger?

[MR_TJ]

Originally Posted by bmroxm5

Original size is 300mm front, 336mm rear

Fronts can accept 292-300mm and rear 300-336mm as replacements

*don't blame me if wrong though!

Do u meant any size of rotor within the range is acceptable for the oem caliper?

[Stuart@BMRAutowerkes]

Originally Posted by ctjoon

Do u meant any size of rotor within the range is acceptable for the oem caliper?

Yep it's a 'range'... some replacement discs are as small as 292mm which is OK as long as the center hole is 75mm

Originally Posted by SBC

rear rotor is bigger?

BMW made the rear bigger to help with the heat dissipation due to the DSC system using the 'e-diff'... essentially, the 4bangers have the same brakes as the 6pots (bar twin turbo models) and you know how the dsc system brakes the wheels individually, these days under heavy acceleration the rears end up working more than the fronts.
Plus less fresh cool air compared to the fronts to cool the rear brakes hence further need for bigger rotors to dissipate heat.

[sbce90]

This is interesting. So why smaller caliper then? Why not have massive brakes all around? (Adjusting bias accordingly too)

[E92325i]

Originally Posted by bmroxm5

Yep it's a 'range'... some replacement discs are as small as 292mm which is OK as long as the center hole is 75mm



BMW made the rear bigger to help with the heat dissipation due to the DSC system using the 'e-diff'... essentially, the 4bangers have the same brakes as the 6pots (bar twin turbo models) and you know how the dsc system brakes the wheels individually, these days under heavy acceleration the rears end up working more than the fronts.
Plus less fresh cool air compared to the fronts to cool the rear brakes hence further need for bigger rotors to dissipate heat.

Not sure on the rears being a larger size...

I recently changed all four rotors on my 325i (E92) and the front disc size was 312mm and the rears were 300mm. From a visual inspection on the car, the front rotors are bigger than the rears as well

I've have no idea about the brakes on the 4 cylinder models though.

[MR_TJ]

I'm sure it's bigger frm the rear for E90. As long its within the range then it will be much choice for replacement. Thanks bmroxm

[Stuart@BMRAutowerkes]

SBC - It doesn't need a bigger caliper because there is enough braking pressure being applied... for some reason BMW thought that 4cylinders will have more wheelspin, therefore more braking will be applied to each wheel, therefore heating up the disc much quicker. As a result bigger disc = better heat dissipation.
Also bigger brakes all around would be more expensive.. and on the 'entry level' () e90s they are obviously looking to keep costs down.

Ye it's confusing... there are some common parts between NA 6cylinder models and the 4cylinder models but I can't quote anything caus


E92325i - were those brake rotor sizes the new replacements and were they OEM parts? brake rotors can vary in diameter by an inch or so and not cause too much drama..

Ctjoon - are you looking to replace brake rotors? I can suggest some for you if you like in either the OEM category or 'upgraded' rotors

[John_01]

Here's what I found on RealOEM website.

2005 320i, Front = 292mm, Rear = 296mm
2008 320i, Front = 300mm, Rear = 300mm
2009 *325i*, Front = 312mm, Rear = 300mm

[MR_TJ]

My seller is offering me 300 x 24 front and 300 x 20 rear. What do u guys think? The rear is obviously thinner?

[E92325i]

Originally Posted by bmroxm5

E92325i - were those brake rotor sizes the new replacements and were they OEM parts? brake rotors can vary in diameter by an inch or so and not cause too much drama..

All brake parts were OEM and exact same size as the ones taken off the vehicle (from the factory). Interesting that you can use different sized discs, I never knew that!

[Stuart@BMRAutowerkes]

Originally Posted by John_01

Here's what I found on RealOEM website.

2005 320i, Front = 292mm, Rear = 296mm
2008 320i, Front = 300mm, Rear = 300mm
2009 *325i*, Front = 312mm, Rear = 300mm

Hmm slightly different to what I had found above. Might vary slightly in different markets I guess?

Originally Posted by ctjoon

My seller is offering me 300 x 24 front and 300 x 20 rear. What do u guys think? The rear is obviously thinner?

Sounds about right! If they don't fit, just send them back to your supplier saying it's the wrong size!

Originally Posted by E92325i

All brake parts were OEM and exact same size as the ones taken off the vehicle (from the factory). Interesting that you can use different sized discs, I never knew that!

To a certain degree it should be ok... not sure if you'd have much luck fitting 380mm brembo discs on though lol