Tuning For Smaller Wheels

[RacerJJ]

I am going to be putting smaller wheels on my truck soon (16 inch) and the overall diameter should be a bit shorter. What do I need to change in the tune?

[Krambo]

Assuming you have HPTuners--which I believe you do, you will need to find out exactly what your overall tire height is first. Go to --> Waller Racing Tire Height Calculator and just plug in your numbers. Once you have that number (assuming you have HPT), adjust the overall height (that you just calculated) in your tune under Speedo > Speedometer. Keep your gear ratio the same, click on the "auto scale transmission tables" and make sure the "YES" is checked. Click on the commit button and all the tranny parameters will automatically adjust. Reflash this new tune.

 

Now, I did go back over my fueling however it was pretty darn close so if your Ve table and MAF table were close to begin with, it shouldn't change that much. Do a run and make sure it shifts where you expect it to and the converter behaves like it should. You may wish to manually alter the tranny settings however it is easier to start with the auto scaling feature. Good luck!

Edited April 16, 2009 by Krambo (see edit history)

[RacerJJ]

Thanks! Is it ok to not change anything if I'm not concerned with the speedo being correct?

 

Also, yes I do have HP Tuners and I run in OL/SD all the time. What changes occur in the trans parameters?

[chpspecial]

If you don't change anything you could run into a funny shifting truck. part throtle shifts will be off as well as full thorttle. you could possibly bump into the rev limiter due to the smaller wheels as well as abs codes and so forth

[BigCountry]

So, I'm plannig on running a set of 28" tall tires front and rear at the track... You're saying I'm going to need to tune for this? I thought that it would still shift at the same comanded rpm as before, just that the speed at that rpm would not be correct. OK, slap me now if I'm a dunce

[brobradh77]

I run a 17" wheel and a 28" tire just on the back at the track..I dont change anything and dont nootice any problems.

[SSThunder]

If you don't change anything you could run into a funny shifting truck. part throtle shifts will be off as well as full thorttle. you could possibly bump into the rev limiter due to the smaller wheels as well as abs codes and so forth

 

 

This happened to me at the track. For some reason the wrong tire diameter was in my tune and I would hit the rev limiter on the 1-2 shift. it would take forever to shift and probably wasn't good for the truck. Lucky for me I only ran 2 times before noticing the problem in my tune. That's what I get for messing around with my tune...doh

[RacerJJ]

So, the final verdict is that my new overall diameter will be 1.5 inches smaller than now. The question is do I (or should I, really) need to adjust the tune for this doing the auto scaling thing? I was thinking about adjusting my shift points anyway and a major goal of mine is to pull harder through the finish line a the track. What will happen if I do nothing to the tune in this case?