i've made a few other threads and also searched about wheels but couldnt find this info.

i've been told that i should get some 18's when i get new rims. i have a 2003 gt thats dropped 1.5 inches. the tires on my stock 17x8's are 245/45/17, and the overall diameter is like 25.7inches (the tire itself) - 811rotations per mile

i looked at 275/40/17 and that was 25.7 as well

i then looked at 275/35/18 which was 25.9

lastly i checked 285/35/18 which was 25.9 - 805 rotations per mile

my findings show that:
18in rims=25.9 inch diam. tires
17in rims=25.7 inch diam. tires
-the 18 inch rims spin 6 rotations less per mile - how do you fix the odometer reading?

this being said, 18 inch rims fill in no more space in your fenderwells? everyone made it sound like that, and even some pictures i looked at seem like that too. to me, .2 inches is negligible, so im assuming that youre getting a bigger diameter rim but a lower profile tire? other than maybe for look, is an 18 inch rim going to fill out my fender well gaps? (the numbers show no, but maybe im wrong on something?)

if 17's and 18's have the same overall diameter with the tires on them, whats the point?


the whole reason im asking is because i need to get new rims soon, and wanna make the best decision. i was wary of getting 18's because i thought they would come way closer to rubbing my fenders and being cut. but it seems like theyre no taller/closer to the fenders than the stock rims i have now

detailed answers appreciated, i know its a long post, but its not something i wanna mess up

 

Wow... your looking into this way to much! Whenever you modify the wheel/tire combo from stock size you change you OD reading.... I think you can fix this with a tuner... dont know... i have never known anyone who has bothered! more wheel looks better than more tire, this is why 18's look better than 17's. you have no issues what so ever with the 18's as far as fitment, rubbing, etc. JUST DO IT!

 

yeah i know im goin a little too into it lol, only thing is after its all said and done its gunna cost me about $1400, and thats if i dont have to have the back fenders rolled. and if i got the 18's and the fenders werent rolled and i cut my tires on the fenders i'd be really annoyed, that and i kinda wanted to keep my speedo legit - this can be accomplished if i stayed 17's im sure a shop can change my comp to 18's for like 20 dollars though

 

Man your car must be really dropped low. I droped my car and I run 18x9's in the fron and 18x10's in the rear and haven't had any issues.

 

its dropped 1.5 all around with the bottom isos out in the front so its not that much of a drop, i dont have the 18's yet thats what im tryin to figure out.

 

Ok. I have a 2 inch drop all the way around. Ok, first i have 18X9 in the front, 275/35/18 and in the rear 18X10 315/30/18. No tire rub. Also for you MPH tach im only off by 3 MPH. It is not a big deal. When i drive past the radars on the street and says the MPH it says that im going 45 when my tach says 48. Before my rims it says i was going 45 and my tach said 45. If it is such a big deal use a tuner. Get 18's you wont regret it but if you get 17 then you will!

 

I have mine dropped 2" all around and I am looking at 18s. I bloted a set of my buddies 18x9 FR500s on my car and they fit just perfect. No math involved just drove around the street with them on.

 

I agree with GT and Soldier. I just changed from the stock 17x8 w/245 / 40's all around to 18x9's in the front w/255/40's and 18x10.5's w/305/35's in the back. Absolutely no issues. I'm not sure of the drop but it's 25 1/4" from the ground to the bottom of the fender. Hope that helps.

 

First off, you will never even know the difference of a 1/4" in tire size. Think about when you burn your tires and the tires are near balding! Think about it, your talking abut 1% difference. This equates to 1mph per every 100mph. Hardly noticeable. Another thing. Why would you think 18's would rub? Your talking about getting the same exact height tires! You are just getting a lower profile tire to accomodate the larger wheel so it retains the same height. I had 18x10's on my car with 285/35/18's and friggin hated them. The ride was way too rough. I sold them and put on a set of 17's. Much better!!! Sure 18's look a little better, but most people cannot even tell the difference. My car bounced like crazy with the 18's. I know have 17's with 275/40/17 up front on a 9" wheel and 315/35/17's on a 10.5" wheel out back and let me just tell you, it looks way meaner and the tires are sooooo much cheaper. You won't feel as bad when you do burnouts. They go from pinching your wallet and feeling sorry when you have 18's to OMG this is so much fun when you have 17's becuz they are nearly $150 a tire cheaper and you get a much wider tire as well plus a smoother ride! Go 17's with your lowered det-up. Unless you like a super stiff bouncin ride, then get 18's. I got package deal off ebay. AFS wheels. I had my car on the dyno and the wheels were super sraight and smooth when my tuner was runnin the car. Don't buy anything brand name OE Wheels from Ebay. I had them for my 18's and they wouldn't balance properly ad the clear coat was peelin.

 

All tires are going to be different heights even by the same manufacturer. Like BFG's for example, the KDW's are goin to be diff than their G-Force line up. I'm talking about fractions as stated above. Here's some help for tires that are the exact same size in HEIGHT! 245/45/17, 275/40/17, 305/35/17, 245/40/18, 275/35/18, 305/30/18 These are the most common sizes for the mustang. These are all the same size in height within a few revolutions per mile. Hope this helps. Ohh, my car is lowered 1.5" front and 1" back and I have 315/35/17's no tire rub on my 97gt. 315/35/17's are slightly taller than the tires sizes listed above, but it's so very small. 1/8" diff. 275/40%=110cm(height) 315/35%=110.25mm(height) I'll spell it out. 275 is the width. Take 275 and divide it by the aspect ratio which is 40. 40 is the height of the profile. 40 is a percentage of the width, so that would mean that the profile of the tire is 40% of 275. Take 275 and multiply that by .40 (.40 is 40%). This equals 110. Now 275 is metric MM. So, 110 is 110mm. This makes the width of the tire 275mm and the height 40% of the height which is 110mm or 4.33" and the 275 width would be roughly 10.83" wide. If you use this math for all tire sizes you will acurately be able to tell the same size tires. For those of you that don't under stand. Start out with say a 245/45/17 tire. For every 3 sizes in width you go up, you must drop down one profile ratio. so 245-275 (skipping 255,265) and dropping down from 35series profile to a 40 series profile keeps the height exactly the same and allows you to get a wider footprint.