This one will be easy for many of you, but I'm clueless. My son's car is a 1989 735i. They recommend size 225/60/15 but he found a great deal on used size 225/55/15. Will they work on his car ?
Thanks !

Yes they will work. However, the overall diamter will be 5% smaller than the OE size. I believe the recommended size difference is within 3%, plus or minus of the OE size. The only major effect would be your speedo will read a little faster, but it probably won't be that noticeable...in other words, speeding tickets will be the least of your worries...

Hope this helps...

For info, the tyre size is a mixture of metric (mm) and imperial (inch) vcalues and decomposes as follows:

225/60/15

225 mm wide
15 inches (wheel) diameter - the inner tyre radius.
60 - a percentage factor of the height of the tyre compared with the width of the tyre.

There are many interactive tyre size calculators on the web, eg:
http://www.miata.net/garage/tirecalc.html

As stated, changing from a 60 % to 50 % aspect tyre won't feel greatly different. You *may* notice a more communicative ride, feeling the road a little more but I doubt I could tell the difference.