OffSet Confusion
 

So when doing some test fitment on my rally Car my crew chief noticed something.

going from my factory Subaru 13" steelies (X5 wide) to my 94 turbo legacy alloys (15X6) the front offset barely changes, which then gives you all your extra width towards the inside of the car (ie my track width is the same)

The legacy rims are i think a 52 offset

RS Factory OFFSet +53 16x7 ???

So at full steering lock i used to have about a full inch of clearance to the inner wheel well. but now i have about a 1/4 inch.

am i missing out on available track width that won't be damaging to my wheel bearings ? :?: I know i've seen a lot of other use the same Legacy rims on their RS's for rally cross (in person) and i've seen pics of people using them on imprezas for full stage... I think the Team Dynamics that people run use the same offset.

could i safely use rims that would widen my track width a bit (or spacers)? I know i can't go much wider with spacers with out having to worry about lug strength / thread issues...

(The wheels do clear the brakes no problem though) :D and i'm out of time and budget for my next rally to make any changes.. but i'm just curious at this point.

Don't run spacers on stock studs period - it's a bad idea on a street car, bad idea on a GC/GM with early bearings, etc, let alone on a car that sees the abuse a rally car does. 3mm MIGHT give you almost enough engagement, but it's totally dependent on seat thickness, etc.

Also, if the offset doesn't change, you get an even split between front and back faces - offset is the hub mounting flange relative to dead center on the wheel, not either edge. If you go to an inch wider wheel, you add a half-inch to the inside, 2 inch wider wheel, an inch to the inside. The offset may change significantly between your steelies and your alloys, which is why the wheel moves around relative to the hub mounting flange. - by definition, a change in the front-rear (or inside/outside, if that's easier to visualize) balance of a wheel means the offset is different.

You might be able to run a wider wheel, or a lower offset wheel, like a 16x7.5 or 16x8, but with a fixed tire width like a 205, the increased wheel width will just stiffen your sidewall, which may or may not be an optimal change. Keep in mind a significantly wider wheel, and more importantly a lower offset wheel (moving the leverage point farther out) will have increased bearing wear especially in off-road conditions due to increased load, and you mess up your steering geometry - that may be a huge deal, or may not be something that bugs you, but it does change how the car turns in and returns to center, and again puts more load on all of the front end components.

aah, good to know I have noticed that i have never seen wheel spacers on a rally car (though i haven't been looking for them)

Oh i got you. I can't be certain that the offset changed but it appears to have gone from a 40 ish on the 5" wide rim to a 50 on the 6" wide rim. The rim got a full inch wider, but about 3/4 of that is sitting more inward now.

My new rally tires are a 185/65/15 on Stock 92-94 Turbo legacy rims 15X6 (50 offset?)

My old rally tiers were 165/65/13 on stock 93 impreza steel rims 13X5 (40 offset ? ) I can't seem to find the offset listed in the factory service manual.

Guess i'll try and check around the service area what other teams are running (i think the team dynamics put the size and offset on the face of the rim)

good to know. I'll just use the stock Legacy turbo rims with out any spacers and check up what others are doing.. just seemed odd to me that the RS lost a bunch of inner wheel well clearance compared to the 93 .

Alex, play around here: http://www.rimsntires.com/specs.jsp

Offset, rim width, etc. becomes super obvious when you can see it in a picture and manipulate the numbers.

A 1 inch change in width is just over 12mm on each side to the inside of the rim lip at the bead.

Are the new rally rims steel or alloy? Alloys often have a rim lip that is twice as thick or more than a steel wheel, so add a few extra mm for that change if it is one and you are right around that 3/4" you are seeing.

Also, different manufacturers may have 7" rims that are plus or minus up to 1/4" different from each other at the bead. I think it is really X inches +- 1/8" which is why the Solo rules allow for up to 1/4" different than stock.

The new rally rim is a Stock Subaru Turbo Legacy 92-94 . Alloy 15X6jj
the old was a stock subaru impreza 93 Steel 13X5

Wow Scott, now that's a great online tool!

I believe this is what i changed from and to : Old 13x5 ET 45 New 15x6 ET 52
My backspace changed by 19 mm (0.7'') deeper. But as written above, I'm using what (I believe to be) how subaru would have setup an impreza Circa 93-01 with 15" rims

Hey Cory what size are your rims on your RS ? how much inner wheel well clearance do you have at full lock? :)

thanks

also anyone have an RS and the stock rims still? (just so i could peek at how subaru set it up) :) thanks

Using the tool linked to by scott, it looks like a 40 offset is going to bring the rim in too close to the brakes?

I like the look of these : http://cgi.ebay.com/ebaymotors/ws/eB...m=280618755448 Price seems pretty decent $330 for 4 new alloys, .. hmmf

Weight and strength an issue with those? They look like a good deal.

Well they will be primarily for paved commuter driving, maybe some autoX , and track days. though double checking my bank account and its telling me 'WAIT' :( lol

Offset has little to do with brake caliper clearance- that's all in the design of the wheel. I had a set of wheels with a 35 offset that cleared stoptechs, and a set with 45 that won't clear 4 pots.

17x8 ET48. I've got plenty of clearance on my 245 width tires, but that's because I "massaged" the inner fender with a big fucking hammer.