I want to try the Dunlop Direzza Sport Z1 Star Spec tires on my R56 OEM 17" crown-spoke wheels. These tires come in 215/40/17 and 215/45/17 sizes. I think the 215/40/17 size would create too much wheel gap. I have the R56 JCW suspension that lowers the car by about 10mm relative to the stock suspension. Can I put the 215/45/17 tires on my 17" wheels without worrying about rubbing issues or anything else?

 

Not sure about rubbing issues, but remember if you go with a larger diameter tire, it can slow down acceleration by acting like you have higher gears on your car.

If you go with a small diameter tire, it can help acceleration by acting like you have lower gears on your car.

My main PC crashed, but there's a great gear ratio/tire diameter spreadsheet that I found via Google on a BMW board.

If I could find the link, I'd post it here.

With 205/45/17s going to a 215/45/17s were the equivalent of a 3.42 to 3.56 change, I think... so just a little more and the speeds would only "loose" 5mph in each gear... so not that significant for a daily driver.

 

Should be OK but it depends on the offset of those OEM wheels. My OEM GP wheels have a 52mm offset. I use 215/40-18 with a tire diameter of 24.77" which will be close to your 215/45-17 tire diameter of 24.62" I have the JCW suspension. I did not rub with stock wheels (52 offset). I added 15mm spacers (equivalent to 37mm offset) and I now have slight rubbing in the rear. You should be fine.

 

Thanks, I think the offset on my stock 17" wheels is 48 mm, someone please correct me if I am wrong.

Also, I forgot to mention that I want these tires primarily for track events (not racing, just high performance driving school type events on the track). I read good things about these tires, that's why I want to try them. Would the 215/45/17 size be a good match for the track?

 

If only for track use, I would go with 215/40-17 to reduce the overall tire diameter. If you are going to use for street and track then you might want 215/45-17 due to your appearance (tire gap) concern when driving on the street.
If you are going to have a track set of tires and a street set of tires, I suggest you purchase a lighter set of wheels to mount the track tires.

 

Thanks, I will see what I can do. I already have another set of 18" OZ Ultraleggera wheels which I am using for the street. I was thinking of using the stock 17" wheel set with good sticky tires just for the track. I realize the stock 17" wheels are a bit heavy and I may get another set of lighter wheels just for the track.

 

I used the 215 45 17 Dunlop Direzza star spec on 17" OEM rims on the track last year and it worked quite well. Could go lighter weight on the rims but I did not want to buy another set of rims.