As the title states. Would focus mk2 Rs alloys fit on a mk3 ecoboost?

Yes they are the same pcd and bolt pattern as far as I'm aware.

Yep, they'll physically fit as above.

But you'll need to keep the mk2 wheel nuts with them unless it's a very early mk3.  The later global nuts from mid 2012 onwards can't be used witg mk2 alloys.

Also, depending on how late your mk3 is, you may need to have tyre pressure sensors added to the RS alloys.

And if your car only came with small alloys (17s or under) you should use a steering rack stop to avoid rubbing at full lock.

Original MK2.5 RS wheels have an offset of 60 mm. This is needed because of the RevoKnuckle suspension of the MK2.5 RS.

MK2.5 RS wheels can be used on a MK3/MK3.5 but spacers are required to compensate for the high offset of the wheels. Without spacers the wheels will rub. 

If its any help ive just fitted brand new Mk3 Rs wheels on my Mk3 Zetec S they are 19x8 with an offset of 50mm and they sit just inside the arch with tons of clearance on the inner arches and no rack stops (I was advised by ford to fit rack stops but they are miles away even on full lock)

10 hours ago, wayne stevens said:

If its any help ive just fitted brand new Mk3 Rs wheels on my Mk3 Zetec S they are 19x8 with an offset of 50mm and they sit just inside the arch with tons of clearance on the inner arches and no rack stops (I was advised by ford to fit rack stops but they are miles away even on full lock)

Any photos?

ill get it washed and the pics done over the next few days and post them.

tar

wayne

here are some pics

and some under front arch....eg no scrubbing without rack stops 

its shod with new continental 235 35 19

hope they help

wayne