Changing to non-OEM Wheels

[drafting]

I do not have much knowledge of the ramifications brought about by changing from OEM wheels. I am considering replacing the turbo wheels on my '04 TT (when it finally shows up) w/ Gemballa Competition 18s. The stock wheels are 8 x 18 (front) and 11 x 18 (rear). I may go to 8.5 x 18 (front) and 11.5" x 18 (rear).

What does the "et 33" or similar nomenclature typically addended to the Gemballa part number (eg. 11.5 et 33) mean? Is this the depth of the rim?

At what point do wheels require (if ever) spacers to properly fit on the car?

Will my stock tires, Michelins on the OEM wheels, fit the new wheels?

Are there any other issues presented by changing the wheels to a slightly different size like this (fender rub, suspension adjustment, etc.)?

TIA,

Jeff

[Loren]

What does the "et 33" or similar nomenclature typically addended to the Gemballa part number (eg. 11.5 et 33) mean? Is this the depth of the rim?

ET is the wheel offset in millimeters. Offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. If you want your new wheels to fit without any rubbing for sure -- then choosing wheels with the factory widths and offsets should work great.

At what point do wheels require (if ever) spacers to properly fit on the car?

Spacers are usually used to move the offset further out. This may or may not cause problems depending on your tire an wheels widths. Again, Porsche recommends accepted spacers for each of their cars.

Will my stock tires, Michelins on the OEM wheels, fit the new wheels?

In general if you go with a wider wheel then you can use a wider tire. You should again check with Porsche and folks like TireRack.com to verify that tires are available for your wheels widths.

Are there any other issues presented by changing the wheels to a slightly different size like this (fender rub, suspension adjustment, etc.)?

Perhaps. Again going with Porsche widths and offsets should be pretty safe.

For instance, your MY04 TT could use GT2 wheels and tires since the fender dynamics are the same. You could go with 8.5 x 18 et 40 front wheels and 12 x 18 et 45 rear wheels. With tires like: 235/40 ZR 18 front and 315/30 ZR 18 rear.

[drafting]

Loren ---

Thanks for the fast response. To summarize what I think you've said;

If I choose to go w/ the Gemballa 8.5 et 33 fronts and 11.5 et 33 rears, that should be okay based upon the GT2 setup which is even further outside the envelope required by these wheels (although I don't know what kind of offsets are stock for the TT, it is not more than the GT2).

Looking at the tirerack.com website, it does appear that my present OEM Michelin tires (225/40 front and 295/30 rear) will fit the slightly larger Gemballa rims, so I can simply have them swapped and balanced until they wear out , at which point I can push up the size a bit.

Again, thanks for the info!

Jeff

[Loren]

I would be a little concerned with the 33 mm offset since that will move the wheel/tire further in-board towards the suspension. I am not saying it won't work I'm saying you will need to look at it closely to make sure it will not hit suspension or brake compnents during the full suspension travel.

[drafting]

Thanks, understood. As I do not know what the stock offsets are, (from what you mentioned in your initial reply I take it that the TT wheels are less offset than the GT2, but that the GT2 wheel/tire combo is a larger package than the TT) I figured that if needed I could utilize one of the Porsche OEM spacer kits that you have recommended for use in other posts to make up any difference.

If you happen to have the stock offset numbers for my TT in your bag o' info and would be willing to share that, I'd certainly be an appreciative P-car owner!

Jeff

[Loren]

If you have the MY04 TT stock wheels (Technology or Monoblock Top) then the offset on the front is 50 mm and rear is 45 mm.

[drafting]

Loren ---

Thanks for the info; I have the OEM turbo twist wheels for '04(not sure if that's the correct nomenclature), and don't know what the "Monoblock Top" type wheels are that you mentioned.

If the stock offsets f/r are 50/45 mm respectively, it appears that I'd have to add several of the Porsche 5mm spacers or maybe one of the 17 mm spacers to make up the difference w/ the et 33 wheels. As well as the correct length bolts for whatever configuration I end up with.

Jeff

[Loren]

I don't think multiple spacers are safe. If you are going to use spacers use the correct width and longer bolts. To be safe check with some company like Wheel Enhancement. They have done almost every wheel possible and I have found their advice to be sound. Talk to John Brown if possible.

[drafting]

Loren ---

I did call John Brown @ Wheel Enhancement, he was very courteous and helpful. I had actually misunderstood what you had said about offset, and now do get that the offset (in mm) is the distance from the centerline of the wheel to the outside face of the wheel. So, if I go to a wheel w/ a 33 mm offset (from an OEM wheel w/ a 50 mm offset), that will actually result in the outer rim of the wheel being further away from the centerline of the car (closer to the fender lip). No spacers required, and according to John there is no risk of the tire rubbing on the fender.

Thanks for all of the guidance.

Jeff

[Jack(LA)]

Jeff:

I went with the Gemballa Comps using 8.5"et46 front and 11"et40 for the rear. If you then add the Porsche 5mm spacer kit (spacers and bolts/locks), you'll come pretty close to GT2 specs. Using the stock tires on these wheels with spacers will result in the front wheels being "pushed out" (towards the fender lip) about 15mm more than stock (about 1mm less than the front GT2 setup) and the rear will be about 10mm more than stock(and 2 mm less than the GT2 rear setup). You will have no clearance issues with this setup, even with a lowered Turbo. Here's a photo showing the "offset" of the Gemballa's ("speced" as stated above) with 5mm spacers and Pirelli tires.....

And just for additional viewing , here's a side view of the car with the wheels....

Edited November 6, 2003 by Jack(LA)

[Jack(LA)]

Loren --- So, if I go to a wheel w/ a 33 mm offset (from an OEM wheel w/ a 50 mm offset), that will actually result in the outer rim of the wheel being further away from the centerline of the car (closer to the fender lip).  No spacers required, and according to John there is no risk of the tire rubbing on the fender. 

Jeff

First, let me say that I respect John at WE very much -- he's very knowledgeable when it comes to Porsche wheel fitments. However, you must also take into account that the Gemballa front wheel is .5" wider than your stock wheel. As a result, going with the 8.5" wide et33 wheel (over your stock 8" wide et50 wheel) will result in your front wheel being "pushed out" closer to the front fender lip by approximately 23.3 mm (not 17mm) more than stock. That will be more aggressive than the GT2 setup. While this aggressive an offset MIGHT work without rubbing (which would cause me some concern if you plan on lowering the car), from an aesthetic point of view, your front wheel/tire assembly will stick out beyond the fender well. Only you know if you'll like that kind of a "look".

[drafting]

Jack ---

Thanks for the pics and info. I've gone ahead and purchased the et 33 offset Comp 18s (eBay) and now am awaiting my car to see what I've got regarding the fitup of the wheels. I'm not planning on messing w/ the suspension anytime soon. If I get in any significant track time then that plan may change if I discover that I'd like a stiffer, lowered ride. As one of my every day drivers here in oh-so-flat Florida, the TT will not see the limits pushed (mine, or its own :rolleyes: ) very frequently.

I'll post here once things have been worked out. The car is in port awaiting offload and trucking to my dealer. I'm crossing my fingers that I'll be driving it again w/in two weeks.

Jeff

[SpawnyWhippet]

The tyres on my 996 TT are at the end of their lives. I'm not too keen on the current 'Champion RG5 Monolite' wheel styling and I got a quote of over $4000 to replace the tyres. I am therefore thinking of changing my wheels to these $4000 997 ebay wheels:

2006 Porsche 997 Carrera Classic

19 X 11 ET 67 X 2 WHEELS

19 X 8 ET 57 X 2 WHEELS

TYRES CONTINENTIAL - 295 / 30 ZR19, 235 / 35 ZR19

I don't know the offset of the current wheels or how to measure the offset, but would these wheels bolt straight on without spacers? Are spacers difficult to come by if required?

I suppose if all else fails, I can take the tyres from the new wheels, mount them on my old wheels and sell the 997 wheels again for $3k, leaving me with a full set of tyres for $1k.