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Discussion Starter · #1 ·
I bought a staggered set of rims and tires this weekend and it just occurred to me that i may need a tune, which will suck. I have 18x9 with 255/45 up front and 18x10 275/40 in the back. Anyone know if i need to blow another paycheck this month haha. Thanks.
 

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Edens5 said:
I bought a staggered set of rims and tires this weekend and it just occurred to me that i may need a tune, which will suck. I have 18x9 with 255/45 up front and 18x10 275/40 in the back. Anyone know if i need to blow another paycheck this month haha. Thanks.
Long term the answer is yes. You would need a tune if the overall diameter of the tires change. The tune would adjust your speedometer. If you have a gps or something that uses gps to gauge your speed can work until then
 

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Discussion Starter · #3 ·
Which tune would u recommend. N how does that work? I buy it, they mail it to me n i plug it in?
 

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You don't need a tune for new tires. Your speedo might be off a bit, but I think that can be fixed by Ford or maybe a tire shop without voiding your warranty.
 

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I switched to wider tires as well and got it retuned. Not sure by how much the speedo was actually off, but still feels the same.
 

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Discussion Starter · #10 ·
Wen u guys say re tuned, do u mean u got like a bama kit or took it to a performance shop
 

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do the math, see if the overall tire height is different, if so why did you buy the wrong size tires?

take a tire number

245/45/17

the first number is MM wide (how wide in MM the tire is and ever 25.4mm = 1 inch)

the second number is a percent 45% of 245 = sidewall height (in MM)

the last number is rim width the tire fits



so if you have a 245/45/17 tire and you want to run a 275 wide tire you want a 275/40/17 so the sidewall height of the tire is about the same (245 * .45 is about 275 * .40)

if you go from 17 to an 18in rim then you need a shorter sidewall to make up for the extra rim. For one inch gain in rim size you need to drop the sidewall .5 inches~
 

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Discussion Starter · #13 ·
American muscle didnt really give me a choice, i jus click checkout and they do the rest haha
 

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Its not really a tune that you need. You need to recalibrate your speedo if its off. The dealership can do this for you. If you buy a tuner from american muscle or such, I believe the tuner is equipped with the recalibration feature for your speedo. Hope that helps
 

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What were your factory Wheels? I'm assuming the standard 19s.. If so you had 245/45-19s.. Which is only .25 mm (.0098in) taller than your 275/40s... That being said you do not need to change your speedo or tune or anything bc that isn't enough to effect anything.. There can be twice that much difference just between different brands or styles of tires that are the same size..

---------- Post added at 05:41 PM ---------- Previous post was at 05:31 PM ----------

Forgot that you switched wheels sizes.. So basically w your 18s your tires are almost exactly 1" shorter than your previous set.. Which can make a difference.. Can affect your speedo and mileage accuracy..
 

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Discussion Starter · #16 ·
Well nbd. Ill have my buddy do all that wen i take it in next. As long as its not going to hurt my car, i doubt the 20 miles i drive it a week is going to have an impact lol.
 

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The difference won't be TOO much. Gears are what REALLY throw off the car. Otherwise you'll be ok unless a few MPH is strict where you live.
 
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