Winter Wheels - 17 inch vs. 18 inch

I am in the middle of a search for a set of winter wheels for my 2002 C4 Cabriolet. It seems that my two basic options are 17 inch wheels in 7 inch and 9 inch widths versus 18 in wheels in 8 inch and 10 inch widths. Will there be a significant difference between the same tire in these sizes? Certainly, it seems that matched sets are easier to find in the 17 inch sizes. I've got a lot of questions about offsets too. There are a lot of 17 inch front wheels with 55mm offsets, although the manual recommends 50mm offsets. Do they even make 5mm spacers? Seems awfully narrow for a spacer. Does that difference make any difference? These fronts usually are matched with rear wheels with the correct width and offset. I think these sets come off of Boxters but some also say they come off of 996's. Thanks for your guidance. David

Call tire rack for their opinion. I think 17s would be the way to go and cheaper too.

Sorry, you're not allowed to discuss winter until after Sept. 1st.

Bet winter-related things get a whole lot more expensive around then too! :-)

Diligently watch Ebay. I got a whole setup of stock 17 rims with winter tires for $600. There is still significant tread left, even after one season. I think you want 17's for the sole reason that roads quality declines dramatically in times after September 1 . So any major pot holes, or other nasty surprises that might taco your 18's, would not impact the 17's as much. Also, 17's are cheaper to replace. I guess it would also matter where you are located and how often your car is such weather.

I have been watching eBay. I do see some good deals on wheels. But it seems that the offsets are usually off by 5mm either in the front or rear. What are the offsets of your wheels? Do you have a C2 or a C4? It has been implied that the C4 is pickier about the wheels front-to-rear. Here in the DC area, there are only a handful of days with really bad weather. And maybe a couple of weeks worth of days with any significant snow lying around. David --

I use M3- Winter sports mounted on Millie Spiders "18 - nothing but perfection in the snow. !

What size tires and what offset are the wheels? Thanks, David

I got my Mille Miglias from Tirerack with 17s--I would check with them first concerning the offset etc. I drive a C4S, so it's different. The smaller diameter gets better traction and allows a greater selection of tires. I ended ujp with Blizzak LM25s because the Dunlops were sold out, and it was a great choice.

Late 996s (2002+) offsets are (IIRC): 17: x7 (et50) x9 (et55) 18: x8 (et50-52) x10 (et65) Earlier 996s had different offsets. i believe they ran 55mm in front. If I were you, I'd stick as close to the '02+ factory offset as possible. Also, I wouldn't trust the random bozo you get on the phone from TireRack as the expert. What they know is binary: it fits or it doesn't. Fits means it doesn't rub. Oh, and yes you'd be better of with 17s in the winter, though I ran 18s without a problem. Finally, Porsche makes 5mm spacers with new bolts/locks if you're interested.

I have a set of 17 inch wheels mounted with Dunlop snow tires (205s and 255s) which I ran on my 01 996 C4. As the 996 is now a dedicated track car they are redundant. If you are interested email me at [email removed] and I will respond with greater detail and pictures. The wheels aren't perfect but they are certainly straight and the tires have 80% tread. they are also located in Boston so the shipping should not be too bad to DC.

Yes, you are right about the factory offsets for the 02+ years. That is what they state in my manual and what I've seen posted elsewhere. Furthermore,that's what I have on my car! (Doh! Didn't think to check that already, did we? :-) I was going to try to avoid spacers if possible, but it's good to know that Porsche makes that option available. It seems that I read somewhere that Porsche authorizes the fitment of 11" wheels on the rear with 63mm offset. Although the wheels that come on the widebodies from the factory have a 45mm offset, so they definitely can't be used. David

These are the offsets and sizes of Laurence's wheels mentioned above: rear = 9 x 17 ET47 with 255/40/17 Bridgestone WT-05 winter radials front = 7 1/2 x 17 ET52 with 205/50/17 Bridgestone WT-05 winter radials Compared to a set of wheels with these sizes: rear = 9 x 17 ET55 front = 7 x 17 ET55 Which set (or either or neither) would be appropriate for a 2002 C4? I have seen various sources of "approved" wheel sizes and one even listed both 50 mm and 55 mm for the front offset in 7 in widths on 17 inch wheels. Just don't know what the source of that table was. I found it on Renntech.org. This same table also "approves" of 5mm spacers on both the front and rear axles with 55mm offset wheels in the stock 17 inch sizes. It's tough buying second hand wheels! Thanks for your thoughts. David

IMHO I'd stay as close to the stock 55mm front offset as possible, to preserve steering geometry and feel. Deviating from stock offset in the rear is going to less obviously affect the way the car drives, though I still would recommed staying w/OEM offset.

Unfortunately, stock front offset is supposed to be 50mm. At least that is the most commonly quoted number I see and the number that is mentioned in my manual. But as I said, there are some other sources of information that make it sound like 55mm offsets are acceptable as well for the fronts. Did anyone buy their car from the factory with 17" wheels and get 7 inch wide rims with 55mm offsets from the get go? My impression is that a lot of these 55mm offset front wheels are coming off of Boxters. David

Plus or minus 5mm is not going to make a difference. It's 5/25.4 of 1 inch.... or .2"... The different tire sizes between a 7" and 8" rim make a bigger difference.... And by the way, a 50mm offset sticks out more than a 55mm offset, so adding a 5mm spacer to a 50mm is thinking in the wrong direction (it would make it a 45mm offset).

Yes, that is my understanding. I mention the ability to use a 5mm spacer to suggest that any wheel of that width wth offsets of 45-55 should be OK. In the same chart, it also states that 17mm spacers can be used on the rear along with a 9x17 55mm offset wheel (but you can't use snow chains!) suggesting that any offset between 38mm and 55mm is acceptable for the rears. That seems like an awfully wide range to me. David

I believe the 55mm wheels are from the early 996s (pre '02). They should fit your car, they'll just be inset a bit. If it's just for winter, it's not a big deal. If you care about having perfect front suspension/steering geometry, get 5mm spacers (from Porsche) or 7mm from H&R.

Back to the 17 Vs 18s for winter topic... I'm sort of leaning myself towards 17s as they are cheaper, will grip better in snow being narrower and with a slighty larger profile will allow you to go tru a touchless carwash to remove the salt....am I missing anything ? Any reasons to go for the 18s beside better look ?

I live in Michigan where the snow is plentiful. I've had 18's for the past two winters and they're great. I struggled with the 17" vs. 18" dilema for a while. I decided on 18's because if there was ever a problem the wheels and tires could be changed out in an emergency. You'll have tons of fun driving in the winter whichever way you go. Happy driving!