Pontiac Solstice Forum banner

Wheel Size

  • 19"

    Votes: 3 12.5%
  • 18"

    Votes: 17 70.8%
  • 17"

    Votes: 3 12.5%
  • 16"

    Votes: 1 4.2%

  • Total voters
    24
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Discussion Starter #1
With many voicing their opinon in favor of large wheels with minimal tires and little fender well gap, I wonder if there are others who would prefer slightly smaller wheels with more tire and a bit of suspension clearance for urban driving. I have no plans to ever race this car and hope to use it as a daily driver. Slowing for RR tracks and pothole dodging gets old.

I hope Pontiac offers an option. Those that are obsessed with the biggest wheel they can wedge under a fender are never going to be happy with what ever Pontiac comes up with, and are likely to replace the stock wheels anyway. Many will be totaly happy with the 18"ers on the prototype. Some may want something smaller with more tire for bit better ride quality. I also hope for a styling option. Maybe between light contemporary spokes and a more retro style with holes. I not sure what I want yet, I just would like the option. Any thoughts?
 

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This is a two seat roadster not an Escalade. 20" chromies would look stupid on this car. The appearance of wheel gap does not get better with bigger wheels. It gets better with a lower suspension. The reason everyone thinks bigger wheels looks better is because most cars that go bigger also go lower. In some cases much lower.
 

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I think 18s will look good on this size car.

I put 19s on the vette and lowered it to get rid of the wheel well gap. If I can swing a Solstice to put beside the vette I'll probably put on 18s and lower it. I doubt that I will stick with the factory wheels. I like my cars to be unique.
 

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Hey Troy, you got some pics of your Vette and wheels? BTW, I believe 19's are fine with a Vette because it has the power to move them. I do think the Solstice will look good with 18's as most cars do, but don't think the 170hp base Ecotec will turn them without a huge acceleration penalty. A base Ecotec should come with 17's stock that way if I want to wring her out N/A or autoX I can stick with lightweight 17's and not look stupid. LOL
 

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This isn't a great shot but it gives you an idea. I'll keep looking for a better one. The gap on the front is lower now. There was a frozen bolt that I hadn't freed up before that pic was taken.
 

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Ah, sweet ride man. Yeah, I was going to say there is something wrong in the front unless the C5's require a "different" type of set up for auto X. LOL
I can't tell what type of rims those are in that pic. Looks like ADR M-sports maybe....

I was just looking at a '98 C5 for the same price as I paid for my Tib 18 months ago. Oh well, it was the right car for me at the time. If I could go back in time though.....
 

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Discussion Starter #9
Does anyone know off hand the lug spacing for the Solstice? Just want to check out what wheels are available for it now. :D
 

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Can almost promise the base car will not come with 18s & even 17s are unlikely. Don't forget the "base" '84 Fiero came with 185x80x13s (no, the "80" is not a mistake - look it up), midstream cars got 14s and only the GTs received 15x7s (15x6 on front of 88).

I would expect the tires (as just about everything else except the driven end) to follow the Chevvy Cobalt. Those specs are:
P195/60R-15 Touring
P205/55R-16 Touring
P205/50R-17 Performance
P215/45R-18 Supercharged

Base automatic Solstice will probably get 16s, and maybe manual trans the 17s (General is now charging extra for M/T (see GTO) so hope we get a few extras thrown in).

Those who have seen my maunderings before may remember that I said that a 245 was a silly size for a non-race tire, a 2800 lb 50/50 Solstice would not be able to load sufficiently for peak cornering though looks great standing still.

Hope they do not use the Cobalt wheels though (hope the Cobalt SS does not use the wheels shown on the Chevvy web site ) as they appear to be four-bolt. Last four bolt wheels I saw used by GM was on the old RWD H-bodies and used to break one at every autocross. 5 on 100 would make a lot more sense. 5 on 115 for 17s or 18s expected to take high side loadings would make even more sense.

Must admit that an updated "Snowflake" would keep the Pontiac image though have seem some very strange wheels out of the wide track people lately. Just please, no spinners...
 

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Discussion Starter #11
I was kinda hoping for gold spinners with white walls cuz they make ya go faster and look so kool. :lol
 

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I won't be autocrossing either, so prefer minimal wheel gap - that is one of my biggest pet peeves with some of GMs cars - something that BMW and Infiniti generally do a great job of. Thus, I voted for the 18s. I think 19s might be a bit much for this car...

BTW, is this really off-topic? Seems pretty on topic to me :)
 

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padgett said:
Can almost promise the base car will not come with 18s & even 17s are unlikely. ...

Base automatic Solstice will probably get 16s, and maybe manual trans the 17s (General is now charging extra for M/T (see GTO) so hope we get a few extras thrown in)...

Those who have seen my maunderings before may remember that I said that a 245 was a silly size for a non-race tire, a 2800 lb 50/50 Solstice would not be able to load sufficiently for peak cornering though looks great standing still.
...

Sorry Padgett, gotta big time disagree with you. I'll bet you a lunch that 18" are standard. They showed P245/45R18 tires at the Detroit Autoshow, and stated over and over that this is the car you can buy for "around" $20,000. I asked about wheels and tires and they said: "This is the production car, that's the size wheels that will be on it.."

Granted, that is just the showperson, but there's article after article out there emphasizing the 18's as a feature. It will have 18 inch P245 wheels and tires standard - they would be crazy not to after all this harping on it.

As far as peak cornering, I respectfully think your statement is oversimplification. There's plenty of data that shows a 245 wide tire is or can be a very appropriate size for great cornering. The new honda s2000 rear tire is exactly a 245 wide tire. Z4 is running with a 225/255 split (at curb a little heavier than Solstice). The extension of your statement is that heavier loaded tires corner better - this is obviously not the case. If it was, than the corvette would still be running around on 185 tires (max load for the width, right?)

[TIRE LESSON FOR THOSE WHO CAN'T SLEEP:]

Peak cornering is highly dependent on distribution of footprint pressure, and the wider the tire the lower the footprint pressure.

Also, the lower the load on the tire, the lower the footprint pressure.

Both of these will generally increase peak lateral traction.

What does tend to happen is the "edge" or peak lateral force gets "peakier", meaning that if the tire doens't have enough sidewall give to allow deflection and redistribution of normal force through the tirepatch, the car gets less controllable at the peak lateral traction. This is all carefully balanced (hopefully) when the tire is "tuned" by the guys who develop ride and handling.

Also playing into the equation, probably as big if not bigger a factor, is the tread compound used (assuming you have a decent hi-perf tread pattern). A good all 'round compound will have a different mix of characteristics, grippier compounds tend to generate heat which (on road racing applications) increased pressure, which increases footprint pressure (if you started at optimal pressure) which leads to cornering fade as the race goes on.... you get the picture.

This isn't as much a factor on autox (heat generation), and one easy way to get around non-optimal tire grip is to work with a tire pressure and camber setting that generates the right amount of grip. Problem is you only get four runs to tune this in, so it helps if you've figured out a decent setting to start with...

[/TIRE LESSON FOR THOSE WHO CAN'T SLEEP:]

You can have too much tire, sometimes, but at 2800 lbs or even 2900 lbs (curb) I don't think the Solsice is in danger of being there.

Max lat will tell some of the picture, but haven't seen anywhere that information on the solstice exists (at least not yet).

18's are a little big (and heavy) for this car, but looks sell cars, so what can you do?

-solsticeman
 

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Well yes and no. If you plot lateral vs downforce for a given tire you get a skewed bell curve. Exceed the max and you fall off a cliff (slide) but the backside is just as important. At the top you have a plateau of max lateral for downforce but beyond the plateau lateral drops off faster than downforce.

If lateral acceleration is important, you want to size the tire/rim/pressure to the expected loading. This is especially important when using street tires that do not have the choice of compounds that racing tires do. Racing tires are also constructed for extreme use, something a DOT approved tire is (usually) not. (I have seen some DOT approved from Kumho and others that have interesting characteristics if you do not mind a 10,000 mile useful life).

Footprint is very important, it determines whether you can reach the max sideforce capability available. This is why I like a rim that is wider than the tread, it reduces the distortion while cornering and you need less of a kludge (increased static camber) to compensate.

Everthing combines to determine what your performance on an autocross circuit is going to be (and some closely approximate racing conditions, have been well over the ton several times, in fact speeds exceeding what is possible with a B/P Corvette at Waterford Hills).

Never said that a Corvette would be faster with 185s (well maybe with studs in ice racing) just that the tire size needs to be matched to the car and that a 245 street tire is too big for something the size/weight of a Solstice to load properly. A 215 would be a better match with an 8.5" rim.

You mentioned cars with different sized front and rear tires. Yes you can go larger on the rear of a RWD car, it is not as critical as the front, is not as involved in the "turn in" at the start of a curve, and can produce both driving and lateral forces. With an exceptionally powerful car like the Corvette it can also help match tire life. Also looks good.

Personally I prefer to use the same sized tires front and rear. Put new ones on the back and rotate them to the front when run in enough to really grip. Of course I also prefer slight oversteer in an Autocross car.

Keep in mind that the above is specific for maximum performance with street tires, my daily drivers have 225x60s on 7" rims which works very well.

As to the last bit I have no doubt that 18s will be available on some Solstice versions, just doubt that they will be on the base model.

BTW does anyone have rotational inertia figures for 18s vs say 16s ?
 

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I know we're probably a thou miles apart, but I betcha a dinner the base will have 18's.

Or a $30 Amazon gift card... to be resolved next year?

As for 245 street tire too big... again depends on how well the 'street' tire is tuned. We'll have to see.
 

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Discussion Starter #19
As with everything in engineering, there must be compromise based on application. Remember the car also has to go in a straight line too. Big fat wide tires and rims add weight and drag. There is a happy medium and it seems to lie with what ever the individual wants to get out of his or her car.

This is why I like a rim that is wider than the tread, it reduces the distortion while cornering and you need less of a kludge (increased static camber) to compensate.
Padgett- I guess you dont live in a city and have to parrallel park very often! :lol
 

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Said daily drivers have 225x60s on 7" rims :smile but thought the discussion was about maximum performance. I have always used a different set of tires/rims for autocrossing than for street since Baldinis are best on a dry track (mfrs usually provide shaved tires for serious competitors) and I like Michelin X-Ones (now replaced by something else but I forget what) for Florida's frequent "liquid sunshine". Entirely different functions.

Keep in mind that we are talking about the last few tenths of a second here, if you have a car that can take the class by a couple of seconds, the difference between 215s and 245s is not going to make much difference. However when talking state, divisional, or national championships it takes a lot of little things and attention to every detail to make up an "unfair advantage". This is one of them.

For a really nut theory, try this: I believe that on a stock Solstice, 215x45x16s would be faster both in the 1/4 mile and on an autocross circuit than with 245x45x18s on all four.
 
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