Has anyone went from factory 18's to factory 20's?
06-21-2014, 12:24 PM
#1
Senior Member
Thread Starter
Has anyone went from factory 18's to factory 20's?
I am wanting to swap out the 18's on my XLT for factory FX4 20's. Will this require a speedo recalibration? I am assuming that the tires are actually the same height and the 20's are just a lower profile. Anyone have experience to help me out?
Thanks.
Thanks.
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deanfx (06-21-2014)
06-21-2014, 01:24 PM
#4
Senior Member
deanfx - I am wanting to swap out the 18's on my XLT for factory FX4 20's. Will this require a speedo recalibration?
I am assuming that the tires are actually the same height and the 20's are just a lower profile.
This has the same diameter (or close to it) as the stock 18" tire size - 265/60 (4x2) / 275/65 (4x4)
Ergo, no PCM flash necessary to adjust the RPM (Revolutions Per Mile).
Anyone have experience to help me out?
.
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deanfx (06-21-2014)
06-21-2014, 01:52 PM
#5
Senior Member
I think the 20s are a lot heavier, so even if the rolling diameter isn't increased you may notice a reduction in handling, acceleration, and braking due to the increase in unsprung weight. I thought about putting FX 20s on my STX but I decided not to because of the increase in weight.
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STX196 (06-21-2014)
06-21-2014, 01:53 PM
#6
Blown Member
If you are talking about a 2wd with 265/60/18 tires going to 275/55/20 tires then yes you will need the speedo recalibrated. The 20s are almost 2" taller.
I've done this so I know. You can go to tirerack.com and look up the spec on these 2 tire sizes to see what I am talking about. Under the tire specs it will also give you the "revolutions per mile of each tire".
I downloaded a free GPS app for my phone to measure speed with the original tires to compare to the speedo at 45mph and 70mph. I used this data to see the difference after the larger tires and to make sure the speedo was correct once it was changed with a tuner.
From the factory mine was about 1mph slower than the speedo reading at 45 and somewhere between a 1.5-2mph slower than the speedo at 70.
The 20s were 2.5mph faster than the speedo at 70. It was a little over 4mph difference at 70 (speedo) between the 18's and 20s.
Bottom line with the 18s at 70 you are really going 68.5mph and with the 20s uncorrected at 70 you are really going 72.5mph.
Uncorrected it will throw your odometer off and gas mileage calculator off.
I've done this so I know. You can go to tirerack.com and look up the spec on these 2 tire sizes to see what I am talking about. Under the tire specs it will also give you the "revolutions per mile of each tire".
I downloaded a free GPS app for my phone to measure speed with the original tires to compare to the speedo at 45mph and 70mph. I used this data to see the difference after the larger tires and to make sure the speedo was correct once it was changed with a tuner.
From the factory mine was about 1mph slower than the speedo reading at 45 and somewhere between a 1.5-2mph slower than the speedo at 70.
The 20s were 2.5mph faster than the speedo at 70. It was a little over 4mph difference at 70 (speedo) between the 18's and 20s.
Bottom line with the 18s at 70 you are really going 68.5mph and with the 20s uncorrected at 70 you are really going 72.5mph.
Uncorrected it will throw your odometer off and gas mileage calculator off.
Last edited by LTNBOLT; 06-21-2014 at 02:01 PM.
06-21-2014, 04:03 PM
#7
Senior Member
Thread Starter
I should have clarified, my truck is 4x4. So it looks like I will be fine. I'm too concerned with unsprung weight. Thanks for everyone's input.