My vote is 18".

 

20's for looks. If you are going FI, then 20 is your only choice. You won't even notice the extra weight of the 20's. I barely notice them with my measly mods.

 

I'd say it's really about the same risk you would have with an 18" wheel. Not unless you're gonna drive like a jackass or hit a nasty pothole.

Just so you know, I didn't see anyone mention it, you're going to have a slightly less comfortable ride with 20's. Less rubber between you and the road means less to soften the ride. 20's also can be harder to keep balanced.

One more thing, consider your tire sizes you want. Many 20" tires are directional, which means they can't be rotated from side to side. (unless you dismount them and remount them correctly) Also, some people have larger size tires on the rear...which means no rotating from front to back. I am unable to rotate my wheels...makes keeping them balanced much more important. Just fyi...

Personally, I think 20" wheels look great and with the right tire, they fill out the wheelwell quite nicely!

 

Just like the guys above me said, its all about preference. Ive had both, 20s and 18s. FWIW,i get 100x more compliments with the 18s. That might be because i had foose nitrous wheels (sooooo common) but idk. The 20s do look great, but so do the 18s if done right. JMO.

 

I gotta vote for 20's I just put them on mine and it just finishes the look so well. Also some 20's look big and some look small, it's just the style of the wheel, to me blingy 20's looks to much but more subdued 20's (I think mine are) look great!

 

The very first time I drove my car it had a set of 20s the dealership had installed on it. The ride was quite harsh; I swear if I had run over a dime in the road I could have told you if it was heads up or down. I had them swap the 20s out for 18s as a condition of sale and couldn't be happier... handling is excellent and the ride is nice.

 

Bigger wheels = more weight = less power to the pavement. I ditched my stock 18" fanblades for a set of 17" stockers and dropped a tenth in the quarter consistently...

but 20"s look damn good.

 

I vote 20 and depends on what kind you getif they are going to be heavier or not. Nice set of 20's pawns 18 IMO

way I look at it is whats a extra 30 lbs or so, think when you take a passenger in your car thats a extra 200lbs or so . do you complain you have a passenger all the time cause your car is so slow? doubt it, if so tell anybody they cant ride with you cause you got 20's lol

everybody is always saying oh it slows you down so much, who cares its street driving if your serious about the track and your et's you have diff wheels and rims for the track.

I shot a GT500 the other day with custom 3 piece forged 22's on it and it looked awsome and I couldnt even tell that they were 22 I had to ask, it made the stance look sweet.

 

a 20 will sometimes reduce performance compared to an 18" wheel but something like Steeda's Ultralite 20's actually improve it.

I would hands down go with HRE wheels in 20" sizes for any lightly modified mustang if you want it to look good and they don't weigh much.

That's not just something that I recommend but straight from the mouth of the guys that work at the shop which does Pimp My Ride on TV when I had their Mustang Enthusiast on the phone for some exterior advice.

 

I love the look and the traction that i get with my 18x10 in back and the 18x9 upfront match the look great. I think, from what i have seen the 20's will give a lot harsher ride, and i think they look too big, but i have never got the whole 20/22/24/whatever that people put on the SUVs/what not.

just my 2 cents.