Tire Sizes For Stock 16" Wheels?

[2KGTS]

It's gonna be rubber time again for my GT-S. I'm using the 16" stock wheels. Options for 205-50x15s are very few. Going to 205-55-16 will give me more options but more rolling diameter and less footprint on the pavement (if I understand correctly). I'd like to have a tire that is wider in the wheel well. When I put on my 225-50-15s for autocross the tire actually fills the width of the wheel well out to the edge. I REALLY prefer that look. Anyone know what ranges of sizes will work on the stock 16x6.5 wheels? I'm not as interested in tire opinions - just size opinions!

Thanks!!!

[NoCones]

205/55 will increase rolling circumference but it shouldn't give you any change in contact patch size...changing weight or tire pressure would be the only way to do that. (and even if you go wider with 225, that won't change the size, just the shape)

225/45 is practically identical in circumference to 205/50, but I don't think that's a real popular size either.

205/55 isn't too far off...your speedo will be 3.3% too slow (of course, it's probably already reading a little high with oem tires). and your gearing will be slightly taller.

play with sizes here:
http://www.secret-secret.com/turbo/DIY/tirecalc/turbotire.html

[NSX_GTR_LM]

actually changing profile does change the contact patch a bit. You may want to go to tirerack.com and check out their link on plus sizing.

[NoCones]

been there...don't see anything about contact patch...you're gonna have to help me out a little more...

the aspect ratio change may introduce a change due to a change in the stiffness of the sidewall, but from 50 to 55 with constant width, I would think that's negligible.

Bryan

[erok]

A quick search on www.tirerack.com yeilded 10 different tires in 225/45/16. This would probably fit on the stock rim but it would look funny and possibly not handle any better. The sidewalls would look like this /_\ instrad of this |_|. It's virtyually the same diameter as the 205/50/16. Would work and look better on a 7-8" wide wheel though.

[NSX_GTR_LM]

sorry bou tthat dude. Here is the link. Your contact patch will change with profile.

http://www.tirerack.com/tires/tiretech/general/contact.htm

[NoCones]

That page doesn't contradict what I said at all. And it really doesn't support the claim that aspect ratio alone will affect contact patch. Their example shows a 315/35R17 tire and a 205/70R14...there's a little more change than just aspect ratio going on there.

Also note that that tirerack page doesn't really say that aspect ratio affect contact patch size--it says shape. That's what I was saying...even going to a wider tire doesn't necessarily give you a bigger patch, just shorter and wider--same area.

The only way aspect ratio alone is going to change the contact patch is if it changes the stiffness of the sidewall. I can't see the change from 205/50 to 205/55 being too significant there.

Bryan

[NSX_GTR_LM]

well, if you haven't done it, its hard to explain. You will get much better lateral support from a 50 series tire. The conact patch size will change, becaues it will be fatter. Your tread patch will change with a different aspect ratio, or else what would be the advantage to a 215/35 over a 215/45? Basically, you will handle better on the edge, but the 55 series will be more predictable at breaking away. You may also want to read this quote from tirerack, or calll them up if you have any other questions.

"The shape of a tire's contact patch or "footprint" greatly influences its performance and is dependent on its profile or "aspect ratio". Low profile tires (most performance tires) have a short and wide contact patch that is effective in converting the driver's input into very responsive handling, cornering stability and traction...especially on dry"

[NoCones]

ok, look at it this way:

Assume the car is sitting still. Look at a rear tire...for a ballpark figure, one rear tire has to support 500lbs of car. Let's say the sidewalls alone support 50lbs. That leaves 450lbs of car to be supported by air pressure. Put 30psi in the tire. You've got a contact patch of 15 sq. in. Nowhere did I mention aspect ratio to determine the size of the contact patch. You could get that 15 sq in in various shapes, depending on the width of the tire.

Yes, I assumed that the weight the sidewall can support is constant across aspect ratios...probably safe to assume for 205/50 vs. 205/55.

And, again...that tire rack page speaks to the SHAPE of the contact patch...never does it mention SIZE of the contact patch (except in discussing it relative to Shaq's shoes). And the reason that their example shows such dramatically different shapes really isn't due to aspect ratio, it's due to section width--315 vs. 205 certainly will change the shape. Even though their quote says "aspect ratio"...they really seem to be talking more about width.

Ever consider that the advantage of 215/35 over 215/45 might be a shorter/stiffer sidewall? They just might have the same size contact patch generating the same lateral grip capability, but the taller sidewall gives up sooner (and more gradually, as you said).

Bryan

[NSX_GTR_LM]

either way, you are still going to get much better performance out of a lower profile tire, its simple to see. You may want to consult tirerack about the actual size of a contact patch, but the size is not nearly as important as the shape. The contact shape also does change with the aspect ratio. A 35 series tire will hold longer than a 45 series tire under track conditions if they are of the same compound etc. If you dont get it, call them and consult with them.

[NoCones]

Well, the original question wasn't about performance. And I haven't doubted your contention that lower profile yields better performance (although that's not universally true...there's certainly a point where your sidewall gets too short and too stiff...won't deal with inconsistencies in the driving surface well).

Can you describe for me how you think the 205/50 patch will differ from the 205/55?

Bryan
P.S. thanks for the repeated suggestion that I call tirerack, but I don't think I'm confused on this.

[NSX_GTR_LM]

Te lower the profile, the wider the patch. Thats why (like it said in the article,) snow tires are a higher profiel. They give a longer tread patch. Sort of like this, a 205/70 would resemble more of a lengthwise elipse, whereas a 205/40 would resemble a widthwise elipse. I also understand what you mean about imperfections in the road, which is why a 40 series is as low as I will go.

[NoCones]

I just don't see how that can happen. The width of two 205 contact patches can't vary much...the tires are the same width after all.

The only way I can see the width of the patch varying would be if you said that the taller sidewall would flex more--essentially yielding more width by having some sidewall laying on the road.

Bryan

[NSX_GTR_LM]

well, believe what you want man, but I am telling you, the contact patch is going to vary in shape with the profile. You may want to create a new post and ask the question, but I am pretty sure thats how its gonna work. Take some extreme examples for instance. A 205/70 patch is gonna be different than a 205/40 patch. I suggest you make a new thread and get input from other people as well.

[NoCones]

actually here's a page that I think would support what you're saying:

http://www.toyo.co.uk/files/TTT_08.pdf

Assuming a higher aspect ratio gives a smaller crown radius (sounds like a good assumption)...the contact patch will change as you describe.

Bryan

[NSX_GTR_LM]

Thats pretty much about what I am sayin, thats a nice find BTW

[erok]

Why do Nascar and Formula 1 teams use such high profile tires then? On another note, it's hard to see how the contact patch will change if the width and overall diameter remains constant.

[autxr]

Dems be the rules.

Nascar uses the tires they use because they have to, same with F1 (my theory, I don't know the rules).

F1 does use 13" wheels, that kind of restricts how low a profile tire you can run. If it were a 335/10-13 the car wouldn't be able to have all the body work.

Not sure why NASCrap insists on sticking with old technology...Probalby partly because Goodyear makes the tires, and Goodyear doesn't want to change them.

Scott

[NoCones]

maybe a few reasons:

1. you don't get to run whatever tire you want...you run what the rules say you can run
2. while some of those tires may seem to have a tall sidewall, the aspect ratio may still be pretty low...a 335/40 tire has a taller sidewall than a 235/50
3. as was said above, there's definitely a limit to the benefits of a shorter/stiffer sidewall...at some point you don't get enough flex to handle imperfections in the road--at 150-200 mph, little bumps are not insignificant.

back to the contact patch: you're right, if you keep the same width (diameter shouldn't matter), you're not going to see much change in shape...only if you get dramatically different tires like a 205/70 snow tire vs. a 205/40 summer tire...they would have very different crown radii, and would have the effect like that toyo page describes.

If you're talking 205/50 vs 205/55 like the original question, any diff in contact patch would be negligible

Bryan

[erok]

I don't see any connection between aspect ratio and contact patch. The crown radius effects are a factor of design, not size. Clearly there is a CORRELATION in the real world between a longer narrower contact patch and high aspect ratio in tires, but from a purely technical standpoint the aspect ratio alone has nothing to do with it.

[NSX_GTR_LM]

Originally posted by erok
Why do Nascar and Formula 1 teams use such high profile tires then? On another note, it's hard to see how the contact patch will change if the width and overall diameter remains constant.


This is true, and if you run a 205/50 16, it has the same diameter as a 205/40 18, but the patch on the 18 will be more of a sideways elipse than the one on the 50 series. Comparing a 205/70 and a 205/40 are not of the same diameter.

sorry bout the typo

[NoCones]

I hope you meant 205/40R18.

I think it's possible that aspect ratio alone has some effect on contact patch shape/size...whether due to sidewall stiffness changes or crown radius changes. However, I think the effect is pretty negligible--especially within the range of tires we would typically look at. Certainly width is going to affect the shape more than aspect ratio.

And, I still believe that the only way you're going to significantly change size is with weight or air pressure.

Bryan