Tire Size

[Jackpine]

Originally Posted by Longshot270

Try programming to the tow tune without making any custom changes. Then the next time you program, after you select "yes" for the custom options menu, go directly to "load previous settings" and see what value is in the tire size. I dont think it puts a placeholder value when you do that...at least it doesn't seem like it on mine.

Sorry, that won't work. He's got a "previous settings" file now and when he reloads it, he's going to get the 2646mm value.

So, by bypassing the Custom Options choice, you actually got a pretty accurate value, the one that's held in the PCM's VID area. However, there's no way for you to find out what that is! Seems weird, but that's just the way things are.

Here's what I'd do then. The Gear Ratio Calculator in Pegasus gives the 2560mm value assuming a 7% rubber squish (deformation due to weight on the tire). That's about the same as a 3% overall reduction in the unloaded circumference of 2646mm. I think 2560mm is a good starting point and is the value I'd put in for TS when you reload the Level 2 tune. Make sure the Gear Ratio is correct too. Now, when you let the Gryphon program your PCM with those values, they will be the ones saved in your "previous settings file".

Whenever you change your tune in the future, you can select Custom Options and then "Reload Previous Settings" as the FIRST step! This will replace the placeholder values with your saved TS and GR values.

If you discover the speed is still slow, increase the TS a bit. If the Gryphon is registering fast, you'll need to reduce the TS a bit. To give you an idea how much, a 1mph error at 70mph would call for about a 37mm change.

- Jack

[agood1]

How did you guys get so smart? I'm sure glad I found this forum.

I guess my next step is to figure out what my rear gear ratio is.

[Longshot270]

That should be listed in the door jamb where the latch is.

[Jackpine]

What Longshot is pointing you to is the "VIN sticker". You'll see a code under the word "Axle". Mine is B6, which is a 3.73 Limited Slip differential. These are the OEM codes:

19 = 3.55 open
H9 = 3.55 LSD
26 = 3.73 open
B6 = 3.73 LSD
27 = 3.31 open
18 = 3.08 open
25 = 4.10 open
B5 = 4.10 LSD

Aftermarket axles can have different ratios.

Some of us, like me, got "smart" by haunting these forums and then reading everything I could find on the new vehicle designs. When I got my truck, I decided it was running on "magic" since there was no distributor, plug wires or throttle cable! It's terrible when you find out everything you learned about vehicles back in the 60s is all meaningless!

- Jack

[Paw Paw]

JackandJanet, I know what you mean about everything that you learned about in the automotive world from the 60's is meaningless.
Heck , I cut my teeth on a 51 model ford FLATHEAD V8 . I still love the sound of the old FLATTIES.
PAW PAW

[Longshot270]

Originally Posted by JackandJanet

Some of us, like me, got "smart" by haunting these forums and then reading everything I could find on the new vehicle designs. When I got my truck, I decided it was running on "magic" since there was no distributor, plug wires or throttle cable! It's terrible when you find out everything you learned about vehicles back in the 60s is all meaningless!

Dont worry Jack, we are in the same boat. A year ago I didn't know what a PCM was and look at me now.

[BigSur]

I wanted to use this thread to clarify TS for myself. I have 285-65 R18's. The manual calculation puts at about 2522 (w/ 3% squish). I tested it today by pacing w/ my wife in her car. Speed seemed to be fairly accurate but a little fast at times. However, Over an approximate 4.8 mile ride (according to the Camry), my odometer was .1 mile low. SO, I need to increase TS, correct. I'm thinking 2575????

[shotgun]

Originally Posted by BigSur

I wanted to use this thread to clarify TS for myself. I have 285-65 R18's. The manual calculation puts at about 2522 (w/ 3% squish). I tested it today by pacing w/ my wife in her car. Speed seemed to be fairly accurate but a little fast at times. However, Over an approximate 4.8 mile ride (according to the Camry), my odometer was .1 mile low. SO, I need to increase TS, correct. I'm thinking 2575????

You got it!



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[Jackpine]

Originally Posted by BigSur

I wanted to use this thread to clarify TS for myself. I have 285-65 R18's. The manual calculation puts at about 2522 (w/ 3% squish). I tested it today by pacing w/ my wife in her car. Speed seemed to be fairly accurate but a little fast at times. However, Over an approximate 4.8 mile ride (according to the Camry), my odometer was .1 mile low. SO, I need to increase TS, correct. I'm thinking 2575????

You would increase TS if your truck's odometer reads lower than actual. However, if the Gryphon speed PID is reading high, then you should REDUCE your TS! As has been said before, the dash speedo will read a bit fast (about 2mph) when the odometer and Gryphon are accurate.

The Camry's odometer can be off too. Everything is fairly approximate. I personally like to use interstate mileage markers (the longer the run, the better) or a GPS. I have a Garmin hiking GPS that shows current speed as well as distance.

Your 2575 figure is correct, however, for a 0.1 mile error in 4.8 miles (About 2%). And, your initial figure of 2522 is what I would have started at too. Personally, I suspect it is VERY close to the right number, Camry or no Camry!

- Jack