[JamesMA]

My car came with standard M-Sport 18" all season wheels from the factory.

I had my dealer throw on M405 20" rims/parellis before delivery and I kept the 18" to put on for winter use.

I recall my dealer suggesting that the car needed to be coded to use the need wheel set.

Dors any one know if coding is necessary when changing wheel sizes some have to bring the car to the dealer to "sync" the wheels, or can I do it myself?

[justinnum1]

Originally Posted by JamesMA

My car came with standard M-Sport 18" all season wheels from the factory.

I had my dealer throw on M405 20" rims/parellis before delivery and I kept the 18" to put on for winter use.

I recall my dealer suggesting that the car needed to be coded to use the need wheel set.

Dors any one know if coding is necessary when changing wheel sizes some have to bring the car to the dealer to "sync" the wheels, or can I do it myself?

have the dealer do it.

[E36toF30]

Why would any coding be necessary when changing wheel sizes?

[justinnum1]

Originally Posted by E36toF30

Why would any coding be necessary when changing wheel sizes?

Speedometer... larger wheel needs to be calibrated

[Maz335i]

Originally Posted by E36toF30

Why would any coding be necessary when changing wheel sizes?

I never had anything done to my car. What will u do when u put winter tires on? Code it again?

Just leave it as it is.

[Rick4345]

Just because you have larger wheels shouldn't matter. If everything is done right, the total diameter should be the same. Hence, you don't need anything coded. He's more full of crap than a Christmas turkey.

[EnerJi]

Just be warned, assuming the diameter of your new tires is roughly equal to the difference between the 18" and 20" wheels (1/9 larger), then your speed (and the trip meter and odometer) will be approximately 90% of the true value. Your speed will show 65 when in actuality you're going about 72.

[auptown]

Wait - can coding adjust the speedometer? Mine reads high, I would love to make it accurate!


Andrew

[BMoutlaW]

Depends on tire size because if they dont match up perfectly it will effect your speedo. As the others have said

[ZMM_OMG]

The dealer might have been referring to re-setting the Tire Pressure Monitoring System so that your car doesn't throw an error code after the new wheelset is installed.

Dunno how to do this myself, but apparently it's in the owner's manual.

[ric124]

Originally Posted by ZMM_OMG

The dealer might have been referring to re-setting the Tire Pressure Monitoring System so that your car doesn't throw an error code after the new wheelset is installed.

Dunno how to do this myself, but apparently it's in the owner's manual.

I changed my wheels and I used a set of new TPMS. Once I drove off after wheel install iDrive prompts to reset TPMS when come to a complete stop. At my next stop light i run the reset and thats it.

figure out what is the correct size tyres to mount so that the diameter does not change and you should be fine.

you can use this site to help
http://www.rimsntires.com/specs.jsp

[lukeb817]

Originally Posted by EnerJi

Just be warned, assuming the diameter of your new tires is roughly equal to the difference between the 18" and 20" wheels (1/9 larger), then your speed (and the trip meter and odometer) will be approximately 90% of the true value. Your speed will show 65 when in actuality you're going about 72.

Outside diameter remains very close to the same when properly upsizing...larger wheel means lower profile tire. When going from the OEM 18s to the OEM 20s, the difference in outside diameter of tires is miniscule and the difference in speedo readout is practically nonexistent. Not sure if the speed is measured from the rotation of the front or rear tires, but see the attached file to see the speedo differences for front and rear. (That's not to say that some of the configurations that I have seen on here won't make a difference as I have seen several setups here where the outside diameter is smaller/larger by a more significant amount based on the tires sizes people are using)

To the OP, I'm pretty sure your dealer/service advisor is just referring to the TPMS reset, which as ric124 notes is very easily done yourself.

[E36toF30]

Originally Posted by Rick4345

Just because you have larger wheels shouldn't matter. If everything is done right, the total diameter should be the same. Hence, you don't need anything coded.

That's why I was confused. Maybe with 20" wheels it's best to go with higher diameter tires though, so they aren't super low profile. Although, as lukeb817 said they're probably just talking about the TPMS reset.

[JamesMA]

Thanks for the responses guys, I am going to measure the wheels/tires themselves and compare.