I'm swapping from my stock 275/65/18 to 305/55/20

I'm going to use a figure of 2596 (this includes squish factor)

Can anyone double confirm this is the right calculation?
I used the formula from the gryphon manual. I also got some help at PHP. There's some very nice and helpful people over there! : )



Anyone out there make this tire swap and do the adjustment? Mind sharing what figure worked?

Thanks!

 

Why don't you just try and it and see how close you are? Then adjust as needed.

 

All you need to do is compare the Gryphon speed to a GPS and fine tune it.

 

5% squish: 2517
4% squish: 2544
3% squish: 2570

I would try 2570. As suggested, fine tune using this formula:

 

Actually, for anyone reading this, a 55-series tire "squishes" less than the more normal 75-65-series ones. This is because the wheel is mostly metal (as viewed from the side), and metal does not "squish". For a 55-60-series tire, I'd recommend a 2% squish factor, which, in the OP's case would give 2596.

But, as Shotgunz pointed out, any number is just a "starting point".

- Jack

 

Thanks for the help guys.

I was able to change the value but it won't accept it?
The stock value read 2356, the value I want to use is 2596.

I make the change hit enter then done, it then instructs me to turn off my key then back on so it can write the program. Once it says comPlete I go in and check it and it still reads 2356????

What am I doing wrong?

Thanks guys!

 

PLEASE, read the FAQ link I gave you in my PM. It explains this, and a few other things that are commonly misunderstood.

For anyone reading this, the link is on PHP's website, and I don't think it's a member's only thread, so here it is: http://forum.gopowerhungry.com/faqs-...ions-menu.html

- Jack

 

Thanks Jack.

Question?

When I go to my 87 performance tune scroll to load previous settings hit enter,it will then read the value I entered? (2596) or even though it reads 2356 it's still going by what I entered 2596?



Also, this won't reload the original stock canned tune will it?

It's just that something that says load previous settings on my custom tune I get to thinking it will load my original level 1 canned tune so I'm very cautious.
I apologize if I'm mistaken, I just don't want to delete my tune and then have to wait 6+ weeks.

Edit: I went to my level 2 canned tune so as not to mess with my custom tune and changed my tire value to the correct one hit enter and followed all the steps. Once completed I went back to my level 2 tune and again, origInal value was there 2356. I then hit load previous settings then went back to check my tire value thinking it would read the value I entered buy it still had the stock value 2356?

What in the heck am I missing here? So even though it reads 2356 does that means its still just using the value I entered and the 2356 is just a generic placeholder?
Totally think I'm overthinking this but I feel I'm so darn close!


What a PI the A

 

No, "Load Previous Settings" simply applies the "customized" values YOU used the last time you tuned your PCM to the current tune. It DOES NOT refer to the "canned tune" at all. And, until you actually enter some "custom setting" when you load a tune, there is NO "previous settings" file to load.

If you have entered a value for TS of 2596 and you later open the "Custom Options menu" and hit "Load Previous Settings", you'll find when you go to the Tire Size option, that you now have a value very close to 2596 and not the 2356 value. It will probably not be exactly 2596 though, because of the "rounding errors" I explain in the Q&A.

- Jack

 

Bingo!!! Worked like a charm!
You were right the value changed but only by 1. Showed 2597 instead of 2596.

Thank you again!!

 

Right! And if you leave that new 2597 value in and repeat the "Load Previous Settings" step the next time you change the tune, it will likely not change at all, because eventually the truncating/rounding error going to and from revs per mile "stabilizes" and stops changing.

- Jack