QuestionBarry, I'm very sorry to ask such a long question. These are the details that I couldn't really figure out after reading as much as I could over the past couple of days on this website and many others. It looks like this is the best place to ask all of these.
I'm purchasing 4 new tires for my '03 civic ex. Currently it's got the recommended P185/65r15 86H mounted on the stock rims. I think the rims are 15x6... well they're definitely 15" diameter, but the best I can tell they are 6" wide. I'm very unhappy with the current tires, especially in snow and rain. I would like to widen the tires because I've been told that it will increase traction and also because much higher quality tires aren't really available in the 185/65r15 size. First of all, is it true that wider tires offer more traction? I would think in some cases it would be worse, such as snow. The coefficient of friction would be less due to the weight being spread out more and that would make the design of the grooves less effective. I'm interested in your thoughts there. Also, would a 215 really offer much more traction over a 205 (also 205 over a 185) given all other variables are kept constant?
Three tires I found that offer increased handling in all conditions have these available sizes: 205/60r15 91H, 5.5-7.5 rim width, 6" measured width, and 8.1" sect. width; 205/55r15 87V, 5.5-7.5, 6.5 measured,and 8.4 sect;
215/60r15 94H, 6-7.5, 6.5 measured, and 8.6 sect.
These three are all less than 3 percent change in diameter from the placard and the 205/60 matches less than 1 percent. All loads are better than recommended and speed rating is same or better. I added the measured width because it affects the sectional width and that is my real concern here.
My worry is that a 6" wide rim really won't be enough for the 215 or the 205 even though they all advertise for a 6" rim width. It seems like the sectional width would bubble out significantly over the rim, but I don't know if that's true. Wouldn't the sectional width of the 215 on 6" wide rims be somewhere around 8.4"? Is that too extreme? I'm worried about a compromised sidewall.
So if you say that these sizes are no problem, my follow up question would be: What is the difference in having the same make tire larger in diameter vs. smaller in diameter than stock size? I don't really understand how much it would affect things like gas mileage, torque, and speed. Thank you so much.
AnswerRyan,
Here's my comments:
".... I think the rims are 15x6... well they're definitely 15" diameter, but the best I can tell they are 6" wide...."
My book says they are 5.5" wide - which is going to severely restrict what options you have.
".....First of all, is it true that wider tires offer more traction?...."
Wider tires do improve dry traction, and wet traction if you discount the contribution of hydroplaning, but wider tires have less hydroplaning resistance.
Snow traction is a bit more difficult, because normally, you want the tire to penetrate to the road surface, and tha menas a narrower tire is better, but if you can't peneration the snow, then more surface area is better, and that means a wider tire is better.
I should mention that "all other things being equal" - which they never are. Tread compound has an enormous influence on traction.
".....My worry is that a 6" wide rim really won't be enough for the 215 or the 205 even though they all advertise for a 6" rim width...."
Well, the 215 is definitely out for a 5.5" rim.
It sounds like you are concerned about the rim width adversely affecting grip - and that is so. But you really don't have a lot of options here. If you don't change rims, changing tire sizes isn't that much of a change. In fact, there is more difference between different tires than there will be between the same tire in a different size.
"......What is the difference in having the same make tire larger in diameter vs. smaller in diameter than stock size?..."
The bigger question here is really: Does it fit under the fenderwell? And I don't know the answer to that, because the fenderwell has to be measured to be sure. There are folks that do those measurements, but they don't share the data. Tire Rack and Discount Tire both do those measurements and I suggest you contact them about possible interference problems.
