Truck came with 245/70/17. I'm now running 35x12.50x17.

Obviously the speedometer is off, it's roughly 10 km per hour or 6 mph slower than your actually moving.

But does the tachometer get thrown off? I wouldn't think it would..what about the odometer?

And lastly is my overhead display all wrong now? I used to use the mpg, dte features on the computer but if the truck is moving faster than it thinks it is wont it think I'm using way more fuel for such a Low speed?

 

this is a neat tool.

http://www.1010tires.com/tiresizecal...cde-gen-by-svr

inputed your tire sizes. And you have a 14% change. This will affect your speedometer, and Odometer by 13%. So when your tach says 52mph your traveling at 60 mph. In a way its kindof good to have that offset. As long as you know your 13% off on your speed. So when you goto sell your truck, its showing less miles on it then there actually is.

But if your a purist. then everything is off. Just use that link i gave you, and input your old tire size and the new ones, it will show you all you need to know..

Dont forget to report if theres any large drops in mpg ( after you facter in new tire size)

 

The tach shows engine rpm. They are what they are. Your speedometer and odometer are now slower/lower than stock. With 285/70x17s, those read 4.3% low on my truck.

 

Yep. Basically your speedo, odometer and overhead computer are all off.

 

I had to recalibrate mine with a tuner. I bought the truck with 20" rims, but someone put them on after the fact, the truck didn't come with them.

I was able to verify my speedo when driving on the highway and my speedo read 110kph, but my gps told me I was doing around 130kph.

 

The size of the rims aren't going to make a difference if the overall wheel size is the same. The only thing that matters in this regard is overall wheel/tire diameter.

 

Biggest difference is your effective gearing ratio is now also 14-15% lower than before. so 3.1 or 3.4ish depending on original gearing. (3.55 or 3.9)

 

In my case the wheels are bigger. I'm not sure of exact size but I went with 33" and my speedo seems to be on track now.