Ok I'm hoping you guys can help me understand my new tuner a little bit better. I have a 2007 4x2 f150 cc lariat with exhaust, cai and 285/65/18's. I just purchased a Gryphon tuner but am just using the canned tunes until my custom ones come in.

So I was looking at another thread where someone was asking what axlethey had on their truck. I went to my truck and according to the door sticker I have the 3.55ls.

I was running the gryphon on level3 I had changed my tire size after doing the calculations provided in the book. I tried to set it at 2600mm but it kept turning it into 2604mm...This an issue or did I calculate wrong?

Secondly when I checked the gearing ratio it said 3.73??? So I returned it to stock, checked again and this time it said 3.55???? So suffice to say I am a little confused now as to which is right and what to do?

I retuned it back to level 3 and checked and it wanted to make it 3.73 again so I manually set it at 3.55???

Can you guys help me understand so I am comfortable that I am not going to destroy my truck by making these changes.

Thanks

 

Also when my custom tunes com will these variables be set already or will they be something I will set manually again?

 

It IS confusing, isn't it? The stock settings seem to be something Edge (the original manufacturer has put in to their canned tunes).

So, in your Level 3 tune, go on to the custom settings and reset your gears to 3.55 and press Enter to save.

Go ahead and set 2600mm in for the tire size (and yes, the device will "round it up to 2604, just an artifact of the way the thing is programmed). Actually though, I'd set the tire size to 2522 to account for the "squish" factor. (Your loaded tire radius is less than the unloaded radius). The programmer will probably move that figure to it's nearest acceptable number too.

Test drive it and keep playing with the tire circumference until your speedo is fairly accurate.

When Bill gets you your custom tunes, these settings will be the default settings and you won't have to play with them.

Hope I've helped with this explanation, and welcome to the band of happy Gryphon owners!

- Jack

 

got question: if the edge/gryphon's tire calculations are based on wheel circumference, then there should be no squish factor, right? u mean, the tire's circumference is the same no matter what shape is is in, right? just a little confused about that. if anyone has a definate answer, could you please chime in. thanks.

 

Sorry, the figures shown in the manual are based on an unloaded tire's circumference. What you'd get if you put a tape measure around it, off the truck, at full inflation.

However, when your truck "sits" on it, the distance to the ground from the axle is reduced by the amount the tire is "squished" due to the weight of the truck. This distance (the loaded radius of the tire) is the same all the way around as the tire is rolling. The loaded circumference "C" (or the distance the tire moves in a full revolution) can be calculated by the formula:
where "R" is the loaded radius (the distance from the axle to the ground in milimeters).

This is actually fairly hard to measure accurately, so a good starting point is the unloaded circumference minus 3% of it for "squish". In your case, 3% of 2600 is 78, so 2600 - 78 = 2522mm.

The 3% is actually a guess. In your case it could be less or more. If the speedo reads high with 2522, reduce it by 20 or so. If the speedo is slow, increase it by 20. See what happens. Continue playing with it until your speedo is correct.

- Jack

 

So the Gryphons speed is the correct speed with the correct axle entered?

The tire size is really the adjustment for the speedo then?

 

I'm not sure what you just said, but:

Each program in a tuner has a default gear ratio in it. Youshould always check that default and change it if your gears are different.

The squish factor is different for some tires, plus, the air pressure will affect the squish. It becomes a guessing game. I used a GPS to get the mph on my Gryphon exactly correct. With my current tires, it was a 5% reduction from the calculation.

Usually, the digital mph will be less that your trucks speedometer by 2 to 3 mph. Ford builds them that way. Is it to make your warranty run out sooner? Don't know, but just think about how many miles they cut off the warranty when every vehicle they sell is 2 mph fast.

 

I think, Jim, he was asking does only the tire size effect the speedo? The answer to that is no. You have to have the correct gear ratio AND tire size entered to make the speed read accurately.

In modern 150's, there's no mechanical linkage to the truck's speedo. It gets its information directly from the PCM, which can be programmed by the Gryphon to tell it almost anything. So, when you enter a gear ratio and tire size that makes the speed reading on the Gryphon 100% accurate, the truck's speedo will read about 2mph above that. If the Gryphon's speed reading was 5mph fast, the truck's speedo would be 7mph fast.

Anything you put into the Gryphon effects both the Gryphon's speed reading and the truck's speedo, since both are monitoring the truck's PCM.

- Jack

 

Ok, I have the right axle gear ratio, and using the calcs. from PHP, get that my tire size should be 2478. With that entered in, my Gryphon will read 35mph and the speedo on the truck reads 33mph, which is correct? Don't have a gps to double check.. and better yet, how do I get them to match readings? or is that even possible?

I am a bit slow today...

 

They won't match, but I'm surprised your Gryphon reads higher than the truck's speedometer. For everyone else that's posted on this, it's the other way around.

Could you take your truck out on the interstate and for a fairly level stretch, set the speed at say, 60mph on the edge and drive it through a few mile markers? For instance, if you're going exactly 60 mph, you should pass 1 mile in exactly 60 seconds. If you drove it 10 miles, it should take you 10 minutes.

If you set it at 75mph, you should travel 5 miles in exactly 4 minutes. You can use your results to "dial" it in. If the speed you set turns out to be slow, try increasing your tire size, say in steps of 10mm.

It would be good to do all this while gas is still cheap!

- Jack

 

i understand that the squish factor works, but arent the loaded and unloaded circumference the same? no matter how much you squish it, the string will still be the same length. now if the edge or the pcm used the circumference to figure out the radius, then used the radius to determine the speed, then the squish factor would make complete sense. just wanted to get to the truth.

 

No. Take some clay or playdoh and roll it into a pretty decent ball. Take a string, wrap it around and mark it. Now squish some of it so it flattens out a little, measure again. Not the same.

You're just not understanding basic geometry right now...

 

Arca, I'm not sure you are quite right, because, as the bottom of the tire "squishes", the rest of it "balloons" out. I suspect the tire's circumference actually does not change much.

Let's look at it differently. Inflate the tire to max pressure and drive it forward one revolution. Measure the distance the vehicle moves. At this pressure, "squish" is minimized.

Now let all the air out, so the tire is essentially sitting on the rim. Notice the part of the tire not in contact with the ground is still fairly "round" and has close to the original radius. But, the part in contact with the ground has a radius that is only slightly more than the radius of the wheel. "Squish" is at a maximum. Now drive it forward one revolution. Since the part of the wheel in contact with the ground has a smaller radius throughout this revolution, it is effectively like riding on a smaller tire (one the size of the rim). In one revolution it does not go nearly as far.

This is what squish is all about - the distance a wheel rolls is determined completely by the radius to the ground, not the unloaded radius of the tire. It also shows that underinflating a tire will increase the number of revolutions it makes in a mile. In fact, that's how some (not very good) low tire pressure sensors work. They measure the difference in rotational speed between tires on the same axle. If they aren't nearly the same, a low tire pressure condition is reported. I say this is not a good system because if both tires on the axle are underinflated, no problem is reported.

Does this make sense?

- Jack

 

This may help!

 

No, because it's wrong.

Thank you for a visual demonstration of what I've been trying to say the whole time, might help a couple people understand.