Hello Everyone! I just recently purchased my new Supercrew and am brand new to this forum. I have to say that it's an awesome community and I'm really glad I found this resource.

I've been reading lots of posts here recently that have helped me decide what to go with regarding my upcoming level and tire purchase. I've got a 2010 Lariat with 20 inch rims that I want to keep since I like their looks. On the other hand, I don't like the low profile look of the Pirelli Scorpions at all.

I am getting a 2 inch Ready Lift kit put in on Friday just to level out the truck. I considered getting 305/55R20 tires to fill in the space a little better, but I think the best choice for me will be 275/60R20 since they are the same height as the 305's and just 1 inch narrower, but about $100 cheaper per tire! I really like the aggressive look and the tread pattern of the Cooper Zeon LTZ tires, so I'm ordering a set tomorrow.

My question is this...Will the new diameter of my tires at 33 inches change the accuracy of my speedometer? They're only an inch taller but it seems to me that the difference would trick the vehicle into giving a wrong reading of speed and miles.

Thanks to everyone here for making this forum such an awesome resource for us all. I look forward to contributing all I can in the future.

 

Yes it will, not by much but it will. My last truck i had 33's and my speedo was like 2mph slower at 25mph and 4 at around 55mph and so on. You can get a programmer to reset the tire size or the dealer can even do it.

 

Hey, RUFFN-IT, thanks for the info! I'll be calling the dealership today to see if they can recalibrate my truck once I get those tires on. I'll post my findings as they happen. Thanks again!

 

Good possibility that they will not be able to reprogram to the larger tires. Usually their computer is set up to only allow them changes to OE sizes.

 

I installed 33" tires, and my speedometer reads 95.9% of actual now, compared to GPS. On my 348.1 mile (by GPS) trip to Chicago this week my odometer read 333.8 miles. Instead of using speedo to determine error, I use a long trip and compare GPS to odometer.

IowaAndy

 

you can go to www.discounttire.com and use their calculator to calculate the difference. If the dealer can't recalibrate, then you can buy a tuner or a similar devise to do so.

 

I would go with the narrower tires.

The change shouldn't be too bad but I know someone who got out of a speeding ticket by getting his tire size corrected at a dealership. If your nearest dealership can't fix it then you should probably get a tuner to correct it.

This is the best way to calibrate your speedometer.

 

Thing is - with a totally correct odometer, the speedo will be reading about 2 mph high. This is by design.

 

If you don't recalibrate, you'll get a few extra miles before your warranty runs out.

 

I know right?!? Except I just rolled 68k on my '09 so Ford laughs when I ask for any warranty consideration.

On a side note, it sucks when an interior part that is 12 months old fails, has been used maybe 15-25 times (rear seat belts) and I have to argue because the truck was at 50k miles at the time. I literally had to show the service manager my pristine rear seats (I work in sales, so the only real rear seat time is when I have customers with me). It took a while, but I finally got warranty coverage!

I always use the arguement that although it has miles on it, it's only xx months old, and shouldn't have plastic panels cracking, or seat belts failing, or leather delamination on the seats... Sometimes it works, sometimes it doesn't!

IowaAndy

 

I have 20x9's with 305/55/20 (33") Toyo MTs on a 2 level and like said speedo is off.

My edge with the tires programmed properly have my speedo off by about 2-3 MPH from 25-50 MPH and for my truck to cruise at 70 MPH on the freeway the needle on the dash reads around 76-77MPH which is accurate having tested against a random person driving their Honda accord on the freeway with their digital MPH display lol

 

Some have had some serious issues with TRaction Control and RSC on the 2009-10 when not recalibrating the computer after leveling and or increasing tire size. Some have experienced RSC kicking in going around corners, etc. The computer reads tire speed and pitch of the truck to detect rollover or skid... So recalibrating is needed for more than just correcting the speedo/odo on these new tration controlled rigs. Search leveling kit issues on here.