Going with a skinnier tire?
 

Pretty self explanatory

I bought a set of 18x8 altima SE-R wheels that currently have bridgestone potenzas on them. They are 225/40/18, however have very little tread left and I will need to buy new tires soon.

I was just curious, would going with a 215/40/18 be beneficial in any way?

Use this:

http://www.miata.net/garage/tirecalc.html

You'll shorten your gearing, so you will accelerate faster. You will also reduce fuel economy and your speedo and odo will have a slight error (the speedo will say you're going faster than you really are, and the odo will show more milage than you actually accrue). In your case, the tire sizes are pretty close so the error is small enough that it won't be noticeable.

215/40/18 might be difficult to squeeze on to a 8" wide tire (don't know, just guessing).

You will be reducing the meat between the rim and the road and it will make you more prone to denting the edges of the rims in pot holes and things like that.

Berz out.

Your tires would be stretched as hell. Do you want stretched tires? I think the only benefit of running narrower tires is the price.

Holy shit guys. The tires wont be stretched as hell. And your gearing and fuel mileage is gonna be effected probably as much as it would be by being 1 psi underinflated so relax. You wont dent the edge of your tire because the 225's over hang, the 5 mm a side difference isn't drastic enough to leave your lip bare. Performance wise, no benefit....atleast none that you'll notice. Yes you lose 10mm of contact patch but depending on the make and model of tire that figure can very. Not all tires with the same sizing are actually identical in their measurements.

Out of curiosity, what car are these going on?

They're going on an 08 Sentra SE-R

No.....and why would you want to?

I didnt say that I wanted to, I was just wondering if there were any benefits of going with a slimmer tire

don't forget to compare the load and speed ratings on both tires to see if they suit your needs... if the stock 225/40R18 has a higher load rating than the 215/40R18, double check if the load rating on the 215 is still capable of supporting similar vehicles...

wider is better. Looks meaner

:Orly:

Everything depends on application.

just so you know from experience, 215/35/18 is completely flush and square on a 8" wide wheel, and you can see any of the rim, let alone if you are using tires with rim protectors which will cover everything, usually 215/40/18 is not cheaper than 225/40/18 either, it's a specialty size for the honda civics, and preludes and is not too cheap. i think stick to 225/40/18

going wider gives you more tread contact so you'll probably have better control...and ya, no doubt a 215 would be fine on a 8" rim

the wider the tire, the more the tires tend to twitch. so it has it's toss ups.

on a 8" i'd go 225,

going for skinner tires, only exception I think of it's for snow tires, you are getting more tractions.
Otherwise I wouldn't think it's a good idea :)