Running 205/55R16 instead of 225/50R17 - s'aight?

[ragingfish]

Ok, here's my deal.My G6 coupe came with the 17" cast-aluminum ChromeTech wheels (running a 225/50/17 tire). The dilemma: OEM tires are crappy-nentals. Same BS tires you find on some Vibes. As most of us know, their wet traction leaves a lot to be desired. Obviously, snow use is not an option.Having SERIOUSLY depleted the fundage on the new car purchase, I am looking for ANY way to get ahold of some decent snow tires for this coming season. My trip to work is 25 miles each way, and I don't want a single one of those miles to be travelled on an unsafe tire. My ideal situation would be a green diamond tires mounted on a set of steel or otherwise non-attractive wheels. Green Diamond doesn't make a tire in 225/50R17. But I already have a set of 205/55R16's from the Vibe that have less then 8000 miles on them. They're practically new.While poking around the Pontiac site one night, I stumbled across something that gave me hope. The G6 4-cylinder and G6 V6 (bottom two models) come with 16x7 steel wheels, wrapped in 215/60R16 tires, standard. They also have available 16" cast aluminum painted wheels as an option. The G6 COUPE only comes with 17" wheels. But there's also now G6 V6 coupe -- only a GT and GTP.My question is this.I contacted Green Diamond, and they assured me the 205/55R16 tires I had last season with the Vibe can be safely mounted and used on a 16x7 wheel (instead of the 16x6.5 they're on now). I asked my service advisor if he felt there would be any issues using the G6 and G6 V6 16" wheel on the coupe. He said not to do it, it would confuse the computers and possibly cause some of the systems not to work properly (i.e. brakes). I checked using that handy-dandy tire size calculator, it says that the car would be running about 3.8% slower with the snows -- i.e. when the speedo says 60 i'd really be doing 58 mph.My question for people who know their stuff is this: Is there REALLY problems that could come from running a 16x7 wheel on the coupe? Because I was of the understanding the sedan/coupe were identical underneath, in which case I can't fathom there being any reason why the sedan could run 16's and the coupe couldn't.Thanks in advance!

[Mavrik]

I wouldn't do it. its a 3.8% difference in size, resulting in about a 57.7mph when your gauge says your going 60. Its going to throw a lot of stuff off... You want to get a size no different in % then 1.0% and I don't recommend that either. A P215/60R16 is 5.3% different in size also...Think Base Vibe P205/55R16... sure everything on the body is the same as a GT, but the GT is set up with a P215/50R17... a different size tire.It may be expenseive but I suggest trying to find some winter HANKOK tires in a 17" size and put them on.

[ragingfish]

A lot of base owners who had 16" wheels upgrade to 17's though...What's different about that then just going backwards?Just curious...I REALLY am strapped for cash and if there's any way i can reuse these tires i want to...And if I can't reuse them, would it be safe then to use 215/60R16's as would normally come on the base G6 models?

[Mavrik]

You have to remember people going from 16 to 17" on their Vibes have for the most part been keeping their tire diameter the same. For example I have stock P205/55R16 tires for my Vibe. But my summer tires are P214/45R17 which is under 1% difference in tire size/diameter. So very little is effected. However you want to put a completely different diameter size tire on your car. The car is not programmed for that much of a difference. It will throw off your speedo reading, your fuel, your odometer, it "may" effect your braking and ABS as its programmed for a certain size on the car. Handling will also become a factor, the vehicle's ride height will also be effected. All this is important to consider when changing your tire size. I would not even recommend using the tire that comes on the other G6 models... for simple reasons as I would not recommend someone with a Base Vibe on 16s to run 17" Vibe GT wheels. The tire is visually a different sized tire. The best size on a 16 that I would recommend is a P225/55R16 as it is only a .4% difference in size.