[tdsports]

I just upgraded to a 305/55/20 tire and im trying to update my gryphon cs to have the correct size. The tires come out to be 33.4" tall but when I try and change the tire size it will only let me select 33" or 33.5", nothing in between. I know its not much but its still off 2 mph according to the GPS.
Any way to change the settings to let me get it more exact?

[shotgun]

Can't you enter the circumference, 2664 mm?

[tdsports]

No, there is no option other than in inches.

[shotgun]

Hmmm. I need to check my CTS on my way home.

If it will let you enter 1/10s for the circumference, try 104.9".

If it doesn't, then I think something is wrong with the unit. Come to think of it when I entered mine, it allowed me to enter 31.5" (diameter) for my stock 275/65R18, so there must be something screwy with the unit.

You might want to e-mail Edge and/or fill out a PHP trouble ticket.

[tdsports]

If you dont mind letting me know what yours says id appreciate it. If its different I will just fill out the form and see whats up.
Thanks

[JackandJanet]

Originally Posted by tdsports

I just upgraded to a 305/55/20 tire and im trying to update my gryphon cs to have the correct size. The tires come out to be 33.4" tall but when I try and change the tire size it will only let me select 33" or 33.5", nothing in between. I know its not much but its still off 2 mph according to the GPS.
Any way to change the settings to let me get it more exact?

Accounting for "squish" which on those low-profile tires should be minimal, I think your correct Tire Diameter is 32.54". So, I'd try 32.5" in the Custom Options Menu. You should be able to enter a value there to the nearest tenth of an inch though, so it should be possible to enter 32.4, 32.6, and so on.

Your goal is to get the Gryphon speed readout to match the GPS. Once that occurs, the dash speedo will read about 2 mph faster in the 70 mph range because Ford built it that way. Your odometer will be correct though. If the Gryphon reads FASTER than the GPS, your TS is too large. If slower than the GPS, increase the TS.

- Jack

[tdsports]

Ok, I had the Gryphon exactly right on my last set of tires which were smaller and come out to be a 32.2 but when I upgraded to a 305/55/20 it will not let me set the exact height to 33.4" which is what the size of the tire is according to Nitto. I have the tire size set at 33.5 now but it is still 2 mph slower according to the GPS. It will not allow me to increase tire size by a .1" only in increments of .5"

Im really wanting to know if this is the way the Gryphon is set up or should I be able to adjust it more precisely?

[Skip_1074]

I just installed my CTS and checked the stock size...It reads 30.9. I haven't messed with it because of my dilemma.

I went and looked at my calibration options real quick and, you are only allowed to use preset sizes on these units. I hope this helps.

[JackandJanet]

tdsports - Didn't I answer your questions in my last post?

I THINK, you are trying to set the Tire Size (TS) in the "Options Menu" (page 46 in the CS/CTS manual I have). That will probably NOT give you the granularity you need.

You need to adjust the TS in the "Custom Options Menu" (page 30 in my manual). You get to this menu by choosing "YES" to the question "Create a custom program?" when you are programming to a different power level.

In that menu, you will see an entry that probably reads: Tire Size - stock". Select it and you should be able to enter your tire size in tenths of an inch. For instance, I set mine to 31.1" which accounts perfectly for "squish".

Now, I'm guessing you have Nitto Trail Grappler M/T tires? And according to this chart: Nitto Tire: Tire Sizes and Specs - TRAILGRAPPLER, the inflated diameter is 33.39" (or 33.4 as you say), but: please notice the "Revs Per Mile figure of: 622. Here, they are telling you the "effective" diameter of the tire when it is "squished" due to the weight of the truck. 622 works out to a diameter of about 32.425" when you do the math. My initial "guesstimate" of 32.5" was off a bit it seems. You should try 32.4" in the Custom Options Menu.

You are free, of course to try 33.4", but I guarantee your Gryphon speedo will read faster than the GPS (probably about 2 mph faster at 70 mph), and your dash speedo will read about 2 mph faster than that.

- Jack

[JackandJanet]

Skip - Please follow the instructions I'm giving tdsports. You should be able to enter the size you desire that way. Give me a second, and I'll see if the value you are trying to enter seems reasonable.

Edit: OK, Skip. For some reason I can't locate a spec page for your tires that gives me the Revs per Mile. I calculated 660, using the squish percentage I find normally works for a 70-series tire, so your figure of 657 is probably correct. For 657 RPM, I get 30.72" so try 30.7 in the Custom Options Menu. Don't be afraid to check the speed (on the Gryphon) with your cell phone's GPS. I would think that device is probably pretty accurate if your speed is stable. By the way, 660 RPM works out to 30.6, so we're certainly in the ballpark.

- Jack