2011 F350 CCLB with 20" and 3:31 rear

[sredmyer]

I recently traded my 08 King Ranch on a 2011 King Ranch. The 2011 had 3:31 gears and 18" wheels. My 08 had 20" wheels in fact the wheels I had on my 08 actually came off a 2011 King Ranch. When I traded trucks I had the dealer swap out the wheels so I had 20s on the 2011.

Problem was that Ford does not think the 20" tires should be paired with the 3:31 rear-end. This meant when the dealer tried to set the tire\wheel size and actual ratio in the computer it set the check engine light. However after driving it (with the light on) for a few days the code and resulting light just went away. So all is good right???

No so much. It seems now that the odometer (and therefore the speedometer and MPG reading) is off by 10%. So if the truck says I have traveled 70 miles, I would have actually traveled 77 miles.

So how do I fix this? I really don’t want to go back to 18" wheels...first because I don’t have any but more importantly I really like the look of the 20" wheels and think the 18" wheels are just ugly.

Anybody got any ideas on how to correct this?

Thanks,
Steve

[drunk on diesel]

enjoy having a 110k mile warranty?

[sredmyer]

Originally Posted by drunk on diesel

enjoy having a 110k mile warranty?

Yeah that reality hasn't escaped me

However, if I end up getting a bunch of speeding tickets it might not be worth it. Plus I really just want it right so I don't have to explain to everyone why my truck appears to be getting such horrible fuel economy.

Steve

[Summitman]

Do a search, its been talked about many times. Your dealer can easily fix it.

[bltp203]

Change the gear setting in the computer to 3.55 and see what that does.

[sredmyer]

Originally Posted by bltp203

Change the gear setting in the computer to 3.55 and see what that does.

While that will in fact work at least the PCM will allow those settings. However, since my actual axle ratio is 3:31 (not 3:55) whatever the odometer might read simply cannot be correct. Further, if the measurement of miles traveled is incorrect, the MPH (speedometer) and MPG (lieometer) will necessarily also be wrong.

Steve

[Painted Horse]

Go to a different tire size that is not as tall. ie LT305/55r20 is pretty much the same overall diameter as the 275/70r18 So you Speed-ometer will be correct but you will give up 600lbs per tire in payload.

[sredmyer]

What I don't understand, is that the trucks computer is set with the tire size and axle ratio that are actually on the truck...so why are the distance traveled readings wrong?

[Painted Horse]

It's probably not set for the actual size or your reading would be accurate. All speed-o-meters are off some. Just lookat the difference in new vs worn out tires. The Michelin LT 275/65r20 have 17/32 of tread when new, When you are running on worn out tires of 2/32 you have lost over 1/2" of tread which equals 1" of tire diameter. That converts a 20" tire from 34.4" tall to a 33.4"

[sredmyer]

Originally Posted by Painted Horse

It's probably not set for the actual size or your reading would be accurate. All speed-o-meters are off some. Just lookat the difference in new vs worn out tires. The Michelin LT 275/65r20 have 17/32 of tread when new, When you are running on worn out tires of 2/32 you have lost over 1/2" of tread which equals 1" of tire diameter. That converts a 20" tire from 34.4" tall to a 33.4"

Well the dealer tells me it is set to what is on the truck but I will ask them to check again when I take it in for service in the next few days.

Thanks,
Steve