i have a 2010 ram 1500 with a superchips that i am very very happy with all except one issue no matter how much i mess with the tires size i am always off about 4 mph it says i am going 4 mph faster than i really am does anyone have the same problem or any tips i am running a 33x12.50x20 on a 20x10 fuel wheel should i set it for 35 or 32 HEEEEELP !!!! haha

 

It sounds like you're about a 1/2 off...have you tried to bump it up a 1/2? You shouldn't go by what the tire manufactor says without accurately measuring the tire yourself. They can be off from a half to an inch so measure it yourself and try using that measurement. Sishemi has a pictured diaphram on how to measure the correct height in sc released that is pretty accurate. Either that just wait for Scott@superchips to jump on this. But if you are showing 4 mph faster, then your height is set too low...1/2-1"

 

sweeet thanx for the advice ill have to go on toyos website and get the exact outter diameter but id def love to hear what the superchips rep has to say im a technician so i like dealing with the source haha

 

4 mph off at what speed? one easy way to compensate is as follows;

figure out the percentage you're off, for instance if you are going 60 and the speedo says 64, then you are 4/60 off = 6.67%. Now bump up the value of the tire size you are using by the same amount. If you are using 33 then make it 33 x 1.067 = 35.21

 

Until you get more help, measure it with a ruler or a yardstick from the ground up to the top of your tire. That would be a good place to start., good luck!

 

Forget all the math... If you look at your tire size while in "stock" tune with the programmer you'll see that it records the tire height as 31.5". This is because of the weight of the vehicle on the tires. When you program your tune if you didn't change tire size (it sounds like you didn't) don't change the tire size setting. If, for example, you install 35's, just bump the tire size 2" to 33.5" (you're going from 33's to 35's for 2" increase in tire size).

 

That's what I tell my banker...forget all the math, I know I had more money than that in my account, lol!

 

Setting the tire size at 32" on my stock 33s was pretty accurate with the GPS. Hope this helps.

 

on my stock 20" size tires, I set it as 32, even though the default was as noted 31.5. Driven through a few construction sites and they all have these speed monitors that show your speed and it seems exactly right on at this setting.

 

When you say default, do you mean superchips default according to your vin? Because my SC default is 30.5 and that's exactly what my old tires measured before I put these 31.5's on. I can tell the difference taking off too, even with that small increase in height.