And no, I’m not writing it. I’m as confused as the next guy. So, can someone far smarter than I explain the pros/cons of the various offsets, why 15 is supposed to be the best when OEM is 33 and which offset wheels should have which spacers, because none of it makes any sense to me and I’m sure I’m not the only idiot who can’t figure it out.
The offset, spacers, track etc explanation
SpeedSmith
#2
IMO, there is no right answer or specific combination of offset that can be applied to all Spec E30’s. That said, +15 offset wheels can allow you to get closer to the max track width (66" & 3/16") without the need for wheel spacers. Though some folks prefer to run a +25 offset allowing them to use spacers for additional tuning. For instance, it may be beneficial to have a little less track width in the rear to help the car rotate. What we’ve found recently is not all Spec E30’s track measure the same (variation is year (crash damage, etc). As a result some folks with +15 wheels can still make use of additional thin spacers.
For me, the allure of ET15 wheels was a quick and easy way to increase the track width, remain hub-centric, and still be within the track width rules. However, recent measurements confirm that I can go a little wider yet. This opens up some options for tuning with very thin spacers (under 5mm) while still allowing me to stay hub-centric. Note: many folks have gotten DQ’d for approaching +10 offset. Your best course of action is to try a few different sizes of spacers and measure your track width using Longacre Toe plates (PN# LAR-79500). Keep safety in mind and make sure your studs are long enough to accommodate your spacers. Hope this helps.
Ranger
#3
Pros and Cons. Pro: Additional track reduces lateral weight transfer. This means more net traction because as you transfer weight from inside tire to outside tire in a turn, you loose net traction. That is to say the inside tire loses more traction due to “unweighting” then the outside tire gains due to “additional weighting”.
Con. Spacers reduce relative spring and shock rates. This has both lateral and longitudinal implications. Suspension is a bit of a black art and I don’t pretend to understand the interplay of all the variables very well. High spring and shock rates reduce weight xfer, reduce the time needed for weight xfer and help keep the wheels on the track. On the downside high spring and shock rates make the car more easily upset if the tire hits larger surface imperfections.
There’s a good book on suspension by Puhn. It’s call something like “How to make a car handle”. I’d have to go back and reread some chapters in the book to try to write any better explanation.
ddavidv
#4
Makes sense to me so far. Good work fellas. I dislike the idea of spacers for multiple reasons: another piece of the puzzle to deal with when changing wheels (particularly if your different wheel sets are different offsets, like mine), expense (good ones aren’t cheap), etc. So even the common 25 offset wheels are an improvement over stock. Is the difference between a 25 (or 20 Konig) and the mythical 15 coming from Phil’s really worth worrying about for someone with not-top-3 talent?
