Tier1Terrier

I’m in the early exploration stage of upgrading my wheels. My 991.2 C2S with RAS currently sits on 20” RS Spyder Design wheels. Also worth noting that the car is lowered about 1” on Eibach springs. These are the oem wheel specifications:

Front: 8.5 x 20 ET 49 / Rear 11.5 x 20 ET 76

I’m considering the following two options and would like some expert opinions:

1) Stick with exact same wheel specs except decrease the offset by 5mm all around so as not to requires spacers or extended lug bolts yet still maintain the appearance of my current OEM wheels with 5 mm spacers.

New specs would be: Front 8.5 x 20 ET 44 / Rear 11.5 x 20 ET 71

2) Increase wheel widths to 9”/ 12”. Since I would be increasing the width by 13 mm all around, I would INCREASE the offsets from OEM by 8mm all around. I am unsure if this would cause unexpected wheel/tire clearance challenges or adverse driving dynamics / decreased vehicle performance or alignment issues. In theory it seems that increasing the area of the tire contact patch would be a good thing, but I wouldn’t want to do so if the disadvantages outweigh the benefits.

New specs would be:

Front 9 x 20 ET 57 / Rear 12 x 20 ET 84

Am I thinking this through correctly? Is there something that I’m not taking into account with these calculations? Am I better off just sticking with the OEM specs except with decreased offset vs wider wheels?

Got Bearings?

I have the same wheels and they sit pretty flush to to the fender... and not sure how much more offset you can add but that's going to depend on your tire sizes and the clearance on the inside of the fenders. I see what you are trying to do -- split the difference between the inside outside of the wheels. I would see/measure how much clearance you have on the inside between the wheel/tire and suspension components. You might be able to tuck it inside without pushing the wheels outward. I am by no means an expert of wheel sizing for P Cars but I understand how offset changes affect fitment. I have no comment on how the car will handle--- good or bad --- since I have no experience.

Use this wheel calc--- it gives you a good visual on what the wheels & tires will do with various offsets and tire sizes - https://www.willtheyfit.com/

Corsa Forged

th3blue

one option that you have is to buy a few cheap wheel spacers in combos that you can stack to test a front and back wheel with the new offset.

stout

9s for front good (this from experience, and on the advice of an engineer who "should know" )

11.5s for rear just fine on an NB car with 305s (this, also, from experience)

Just my two cents

stout

Also keep in mind that all 305s save Michelins look stretched on 12s…actually, all save Michelins already look a little stretched on 11.5s.

This, also from experience…and I wish it wasn't so since I like all-seasons for my application for a good chunk of the year.

Tier1Terrier

@Got Bearings? Thank you! Could you post some pics of your wheels that show this flushness?

@stout Thank you! I realize that 11.5 is fine as that is the OEM spec. I'm just wondering what if going to a 12" width using proper offsets causes any adverse fitting/performance/alignment/clearance issues. If not, then I would think that having a larger contact patch will yield better performance.

Got Bearings?

To clarify... I have the same 20" RS Spyder Design wheels as you. I could take pics of the flushness but it would be better if you walked into your garage.

Tier1Terrier

Sorry, I misunderstood. you. I thought you meant that you have 20x12 & 20x9. I see what you meant now. Thanks!!!

Tay101

Good idea, but your offsets are way off.

There are a few of us on here who have done 20x9 and 20x12 on a 991.2 narrow body including myself.

The correct offsets are 20x9 ET40 and 20x12 ET76

See post #40 on for reference: https://rennlist.com/forums/991/1191...-wheels-3.html

IRunalot

You have seen my car in person and here are my specs. I could have gone to 12inch rears but I can fit 315 on 11.5s.

20 x 9 et44 – out 11mm compared to stock
20 x 11.5 et72 – out 4mm compared to stock

Tier1Terrier

@Tay101 Thank you! Those pictures are very helpful and your car looks great. I was worried that 12" in the rears might cause them to stick out too much, yet yours don't appear that way at all. Does your car have RAS? Have you encountered any problems whatsoever with the 12" wheels? Better yet, can you report any performance improvement or even a slight perception of improvement? When I say improvement, I'm thinking tire grip, lap times, etc.

@IRunalot That's right!!! In fact, I just pulled up a couple of photos I took of your car to look again. And i do recall they great. I'll have to take another closeup look next time.

Pappagray

Do both.

I went to a 9 and 12". I also went from 245/305 to 255/315 and couldn't be happier, My wheels are 20x9 +40 adn 20x12 +72 lowered on HR and DSC(doesn't matter). My car has TONS of clearance still, I even added some small HR spacers, just don't remember the size. Wanna say 5 or 7mm. Yes do I do track it on this setup, just open lapping, but I'm decently quick in comparison

Tay101

Yes my car does have RAS.

I have had zero problems with this setup. I am running the stock Pirellis and will switch to 255/35/20 and 315/30/20 once the Pirellis are done.

I can't say there is any performance improvement as again I am on the stock Pireliis and this is what I drive on the street, but it definitely looks better. I am all about fitting the widest wheels and tires possible and without spacers. This is my street setup, so I don't run it on the track.

I recently got a set of 19" Apex wheels for the track.

mhconley

I'm in the wrong place. I didn't see the .2 in the thread title.

I'm looking to put 12's on the back of a .1.

Martin