235/45/17 vs. 235/40/17

[markseven]

Hi Gary / All,

235/45/17 is the factory tire size for my '00 540iT Sport. I'm interested in the BF Goodrich KDW2 (KDW new tread), but the closest size available for my fitment is 235/40/17 or 245/40/17.

Two questions:

1) Is one of the two available KDW2 sizes better?

2) Should I go with another tire that is available in my car's factory size?

Thank You,
Mark

[doeboy]

Hi Gary / All,

235/45/17 is the factory tire size for my '00 540iT Sport. I'm interested in the BF Goodrich KDW2 (KDW new tread), but the closest size available for my fitment is 235/40/17 or 245/40/17.

Two questions:

1) Is one of the two available KDW2 sizes better?

2) Should I go with another tire that is available in my car's factory size?

Thank You,
Mark

You generally want to pick a size that minimizes the change in overall diameter of the tire. So I'd say 245/40/17 would be better. If you go 235/40, the wheels will be smaller than stock. But I haven't sat down and actually calculated it out (cuz I'm lazy :p ) so...

[Gary@Tirerack]

Correct, 235/40R17 is too short and not recommended. 255/40R17 would maintain the diameter, but is pretty wide for the front.

The other size to use all around on the E39 is 245/45R17, but there is no KDW2 there either. Are you sure on the KDW2? It has good ratings for wet and dry grip, but can get pretty loud as they wear. I'd consider the Bridgestone RE750 or Avon Tech M500 for something similar with less noise, or a step up with the Goodyear GSD3.

Tires
http://www.tirerack.com/a.jsp?a=BN4&url=/tires/index.jsp

[markseven]

You generally want to pick a size that minimizes the change in overall diameter of the tire. So I'd say 245/40/17 would be better. If you go 235/40, the wheels will be smaller than stock. But I haven't sat down and actually calculated it out (cuz I'm lazy :p ) so...
Thanks Doe :) is there a web site that I can do the tire calcs on?

-Mark

[markseven]

Correct, 235/40R17 is too short and not recommended. 255/40R17 would maintain the diameter, but is pretty wide for the front.

The other size to use all around on the E39 is 245/45R17, but there is no KDW2 there either. Are you sure on the KDW2? It has good ratings for wet and dry grip, but can get pretty loud as they wear. I'd consider the Bridgestone RE750 or Avon Tech M500 for something similar with less noise, or a step up with the Goodyear GSD3.

Tires
http://www.tirerack.com/a.jsp?a=BN4&url=/tires/index.jsp
Thanks Gary - I'll look into Bridgestones :) :thumbup:

-Mark

[doeboy]

Thanks Doe :) is there a web site that I can do the tire calcs on?

-Mark

I'm sure there is somewhere... but since I'm a nerd I use my mathletic skills and do it myself. :loco: :rofl:

[Gary@Tirerack]

Here is one I found :

http://www.miata.net/garage/tirecalc.html