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15" vs. 16" Wheels/Tires

4580 Views 8 Replies 5 Participants Last post by  saabreur, 
dan-the-kid
So, I need new tires for my SPG, and figured I'd upgrade to Super/Aero wheels while I was at it.

But..
I just picked up some sweet snows on 15" steelies for a good price. Now I'm thinking I want to do something a bit different with the wheel set up then what I had been thinking before.

Let me know what you guys think of this.

Put the snows on the SPG wheels, and paint the steelies matte black. I think it would look wicked awesome on eddy gray. The only question I have is, should I really be looking for 16" wheels? Or is it more of a bling thing with bigger wheels.

For tires, I'd probably get the General Exclaim UHP 205/55/R15. Right now I have 205/60/r15 and they dont rub at all, but I'd like a bit smaller of a side wall.

Really what I'm asking is, are 16's really worth it? or should I just stick with the wheels I got(less money to spend, I have no job :() And its different.
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justineffingp
dan-the-kid said:
So, I need new tires for my SPG, and figured I'd upgrade to Super/Aero wheels while I was at it.

But..
I just picked up some sweet snows on 15" steelies for a good price. Now I'm thinking I want to do something a bit different with the wheel set up then what I had been thinking before.

Let me know what you guys think of this.

Put the snows on the SPG wheels, and paint the steelies matte black. I think it would look wicked awesome on eddy gray. The only question I have is, should I really be looking for 16" wheels? Or is it more of a bling thing with bigger wheels.

For tires, I'd probably get the General Exclaim UHP 205/55/R15. Right now I have 205/60/r15 and they dont rub at all, but I'd like a bit smaller of a side wall.

Really what I'm asking is, are 16's really worth it? or should I just stick with the wheels I got(less money to spend, I have no job :() And its different.
Click to expand...
Dude, i don't dig the steelies idea. The whole time they were on my spg i hated it. I run 17's now and i think theyre just right. They have 205 45 17 hankooks on them and i'm pretty satisfied with them (should've gotten sdrives because the hankooks appear to be wearing quickly, but i drive hard so that could be it too). I guess to make a long story short I would definately find some 16's if not bigger for that thing :D

my 2 cents

-Justin
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DelaViggen
I'm with Justin, the steelies aren't the way I'd shoe an SPG. But let's get to the tech question on 15" vs. 16" wheels/tires. While a move "up" does include an appearance thing, there are some technical/performance advantages to be had by increasing size.

Your 15" steelies are only 5.5" wide, which limits the width of tires you can/should install on them. 16" Aero/Super Aero wheels are wider, 6.5" or 7" I believe. They'll readily accept wider tires, which means lower profile tires, which should improve handling and grip.

You may find a visit to this website helpful: http://www.miata.net/garage/tirecalc.html
It's a tire size calculator where you can enter "stock" tire values and find the closest match when moving up in diameter. This can be important when figuring how accurate/or inaccurate your SpeedO will be after you change wheel/tire sizes.

Here are two examples using your SPG: OEM tires for SPG are 195/60x15. To go to 55 series, you need 215/55x15 in order to keep wheel revs/mile (and speedometer) as accurate as possible (0.4% slow). If you move to 16" wheels/tires, the optimum size is 205/50x16, resulting in revs/mile being 0.6% fast. In both cases SpeedO is "off" by less than 1 MPH.
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justineffingp
4
To really do my part in discouraging you from steelie's here's a quick comparison.

My spg this winter on steel wheels...


and stock spg wheels


vs. My spg this summer on 17" bbs replicas




-Justin
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Green9kAERO


15s with 205/50s = Less unsprung weight,
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dan-the-kid
I love the look of the steelies painted matte black.

I may still find some aeros for normal tires, and just paint my steelies for the snows.

I just wanted to save myself some monies.
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saabreur
Green9kAERO has the right thought:
15s with 205/50s = Less unsprung weight
Click to expand...
There's at least on sports car that uses small dia wheels (13 inch?) for racing, and a more "normal" dia for dress-up (15 inch?)

Unsprung weight is a major consideration for handling, as well as saving money. The wheels are less expensive, and so are the tires ;) Wheels with a lower angular moment of inertia accelerate more quickly, too.

This is also something to think about when considering a 9000 calliper front brake upgrade, which adds about 14 lbs (I'm not certain about this number) to the unsprung weight each side, making springs and shocks work harder. Ceramic pads on the other hand add next to no weight, and give great improvements in brake performance.

I agree that the larger contact patch is better, but you need to realistically assess the mechanical needs of the driving you do, want to do, and can afford to do, too. As long as you're clear about your reasons, you'll enjoy your choices! :)
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justineffingp
Who's to say you don't get a 16 or 17 that is lighter than the 15 inch wheels you would be running? Also, the acceleration is a factor of the tires' size. If you run a tire equivelant to that which would be on the 15's wouldn't that be the same?
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saabreur
Good point, justineffingp; and we're talking about a couple of different effects....

Yes, smaller overall diameter wheels have a gearing advantage I think, that increases acceleration. Likely less weight and rotational inertia, too. Also probably stiffer sidewalls, which improves handling. Same overall diameter = no gearing advantage.

The other effect is due to inertia; it just takes more effort/energy to increase the rotating speed of a heavier wheel than a lighter wheel (that's why lighter mags are popular). The weight and mass location of the rubber on the rim also affects the energy needed; as the rim diameter increases and the profile decreases, the weight of the rubber moves further away from the centre of the wheel and needs more energy to accelerate it. Whether there is a significant change if the overall diameter is kept the same, and the rim weighs less, would need to be calculated.

I think that's the physics theory; I haven't done any calculations to determine whether these effects are minuscule or not. And with the loads of power that many here have, I'm not going to bother! ;)

And that's completely leaving aside any considerations of unsprung weight, which is a really worthwhile weight loss program to undertake, if you can! So, reduce your unsprung weight, reduce your angular inertia, and you'll have really hot wheels! ;)

Picking rims is a very personal self expression, and one man or woman's poisson is another's poison! ;) ;) I say run what you like as long as they fits...
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