Larger tires...speedo?
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New User
Joined: Jun 2017
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Larger tires...speedo?
I currently have the stock 20in wheel and tire combo but just ordered new 20in wheels and 35in tires....will my speedometer be off? If so how do i correct? Newbie here dont hate me!!
Logistics Pro
Joined: Aug 2006
Posts: 4,477
Likes: 4,069
From: Raceland, La.
The difference is the tire height not the wheels . If you had 34" stock tires your speedometer may be only off 1 mph or so. Check with a GPS if possible. Can be corrected with a programmer.
Laughing Gas
Joined: Feb 2017
Posts: 996
Likes: 193
From: AZ
Not sure if you searched this forum but when you do you'll find answers to this and other questions.
https://www.ford-trucks.com/forums/1...bration-2.html
Laughing Gas
Joined: Jan 2007
Posts: 810
Likes: 34
From: Sarasota, FL
use this link and it will tell you exactly the difference. It's next to nothing.
https://tiresize.com/comparison/
https://tiresize.com/comparison/
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Laughing Gas
Joined: Feb 2017
Posts: 996
Likes: 193
From: AZ
THANKS! In all the reading I've done here I didn't realize I could use Forscan for 35" tires. I think I'm going with them instead of 37's.
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Logistics Pro
Joined: Apr 2017
Posts: 3,674
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From: SoCal
Watch Discount Tires website, they randomly have blow outs on 35's. I got my General Grabbers for $850 shipped to my door.
4wd Low
Joined: Sep 2015
Posts: 11
Likes: 1
any advice on how to use forscan to accomplish the adjustment? i have 35s but I can't figure out what value to put into the forscan app. the spreadsheet doesn't really have instructions for calibrating the speedo. I had 275x70R18s, and now have 35x12.5R20s
Tuned
Joined: Apr 2009
Posts: 252
Likes: 2
From: AL
Follow the spreadsheet and change the value to xxxx 0A94 xxxx. That’s what I used for 295/65-20 (about 35.5” tires) and my speedometer is dead on with GPS.
4wd Low
Joined: Sep 2015
Posts: 11
Likes: 1
perfect, i'll give that a shot! thanks! no issues with a check engine light? i've heard some codes for this will throw a code.
Logistics Pro
Joined: Apr 2017
Posts: 3,674
Likes: 51
From: SoCal
I used the 285 value listed on the sheet for my 35x12R18s and it's dead on. FYI.
4wd Low
Joined: Sep 2015
Posts: 11
Likes: 1
So, just to be clear, all you changed was the last two digits of the middle set of numbers to 4C? Sorry trying to make sure I understand all this so I don't muck it up.
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