mundo123

Have a set of 20" staggered Sport Edition 2's off a 991 narrow body that I'd like to put on my '09 997 c2 narrow body.
Offset on the new rims are Front 51mm and Rear 70mm.
Porsche dealer says original rims on 997 were Front 57mm and Rear 60mm and therefor other rims will NOT fit per Porsche specs.
Understand Porsche has strict specifications...but will the new rims fit, perhaps with 5mm or 7mm spacers if even needed?
Really appreciate it!

nwGTS

If the wheels are the same width then a 10mm rear spacer solves your problem. The extra 6mm in front will not make a difference from what I understand.

PVKPorsche

51 is actually a preference so they are pushed out more to the edge but definitely a spacer in rear and I would go more than 10, likely go 15 to 20 so they are equally pushed.

nwGTS

Yeah, if you want them equally pushed get a 15mm rear spacer and a 20mm spacer if you want the rears pushed a bit more.

semicycler

The critical piece of information is missing. What are the widths of both sets front & rear? The calculations for spacers change if there is a width difference between the 20" set and the 19" set. The offsets are only half of the equation.

mundo123

I went back and read my initial question to the group and realized I had left out the width of the new rims. 8.5x20 for front. 11x20 for rear. And....the car initially had 18" rims.

mwolfe

I hope my own confusion does not muddy the waters, but I would be careful with the more positive offset in the front. If I remember this right (big IF), the more positive offset will push the wheel in more. I would be surprised if the fronts have enough clearance to fit over the calipers with that 6 mm more positive offset.

Am I right? Am I getting this wrong? This may be fixable with a spacer up front--at least 6 mm to push the wheel out to the OEM specs. 10 mm may be perfect for a better look. Rear would likely be fine but a spacer would push it out better for looks (if you want that) like others have done (15 mm spacer will line the OEM wheel up better with the fender)

mundo123

What I'm beginning to understand by all the posts is that with the right spacers, these rims will fit.
I hope I am not coming to the wrong conclusion.
Assuming not, the million dollar question is will the dealer do this work? I get the impression from them that spacers are verboten because they change the original specs.

Mumbles

You will have to change the sensors from the 20's to your original 19" wheels

semicycler

OK, here are the numbers for the two sets:
Current: F 18x8.0 ET57, R 18x10.5 ET60 (taken from 997.2 owners manual)
New: F 20x8.5 ET51, R 20x11.0 ET70

You have width differences in both the front and back so the offset comparison is little more complicated. Fortunately there are online calculators that make it easy. Here's one that compares just widths & offsets: http://www.1010tires.com/Tools/Wheel-Offset-Calculator

For the fronts you are going from 8.0 ET57 to 8.5 ET51. The inner edge position will not move. The outer edge pushes out 12mm. The 12mm is a combination of 6mm differnece on the offset, plus half the width difference (1/2"=12mm, split on both sides so 6mm to the outside). The effect is like adding a 12mm spacer to your current setup. It's been done before and should fit fine, just a more aggressive look. So no spacers needed in the front but the wheel will push out 12mm more than your current setup.

For the rears you are going from 10.5 ET60 to 11.0 ET70. The inner position moves in by 16mm, outer moves in by 4mm. You definitely need spacers here. To get the same inner clearance you need 16mm minimum. The outer then pushes out 12mm (16mm spacers minus the 4mm you lost = 12mm). Notice how they both then move out 12mm? So yes these fit but only if you add a 16mm spacer.

Bottom line compared to your current setup: fronts fit without spacers pushed out 12mm, rears need a 16mm spacer minimum for inner clearance and will push out 12mm more. Should look great!

semicycler

If you can change a tire your can add spacers, it's really simple. Otherwise I'd take it to a Porsche independent shop in your area. They can confirm the calculations above, source the spacers, install, program the TPMS changes, perform ongoing maintenance, etc. all at prices much cheaper than a dealer.

mundo123

Semicycler.
You rock!
Thanks for the detailed thought process.
This helps so much. Going to walk the dealer through this logic and see if they are 'willing' to install (have to have tires mounted as well).
One factor, albeit nominal, is tires. I can go with a 305/25's on the rear, but could, if clearance is really a concern, go with 295/25's.
Thoughts?
Cheers!

semicycler

My 19" rear setup sticks out another 3mm calculated compared to your new 20"+16mm spacer. I have plenty of room and no rubbing. I wouldn't worry about changing tire sizes to play with clearance. Play with spacer size to adjust clearance.

For example, 16mm is the calculated value. That size might be difficult to find. Go with 15mm then since they are easy to find. Yes the inside edge will be 1mm closer than your 18" setup but that's way too small to make a difference. The outer edge will be 11mm further out than your 18" setup and still 4mm less than my 19" setup. That's plenty of room. No need to adjust tire size here to adjust clearances.

Or go the other way with 20mm readily available spacers. The inner edge pushes out 4mm compared to your current setup. The outer edge pushes out 19mm compared to your current setup. That's only 1mm more than what I have now. The 1mm difference is still way too small to make a difference in the clearances I have. There's still plenty of room.

semicycler

And for piece of mind, go to your car and measure how much space you have between the rubber tire and the inner edge of the fender. Now subtract 1/2" (12mm). That's how much clearance you will have with the new setup.

mundo123

Think I'm going with:
Front-245/35/20 on the 8.5x20
Rear-295/30/20 on the 11x20

That should be a good fit. We'll see.