07 GT Tire Size

[Bill]

Hello and thanks for keeping up the good work. My car is an 07 Mustang GT and I have Predator 7145. When I bought the car, I ordered it with 20" rims on it allready, and the speedo was set at the dealer.

Question is, when I install a tune, 93 octane, or any other tune, will it keep my speedo correct or will it be off?

Thanks for everything!

Bill
Portland, TN

[mikel]

Yes, the speedo will still be correct once you install the tune.

Thanks

[Bill]

Thank you for the quick reply Mike. Once again you guys rock!

[Bill]

Okay I am confused.. I just got my C & L Street that also came with the U7145. I have everything installed, went to oem, and selected the C & L Street kit. I then installed it and it had the 91 Octance C & L tune. Install went smoothly. Now You had said that it shouldn't change my speedo, but when I get up to speed, and check it by local Police Department (small town) and with my GPS unit it is off. How much off, when i run 60mph it is around 55, when i am doing 20 it is 18.7 roughly. The car had the tires upgraded at the dealer and they had set the speedo when i picked up the car. Any thoughts on what i can do with this.

Also Second question, When i did the 93 octane install it sounded Beefer, but when I installed the C & L tune it is a lot milder. Do they not have a 93 octane with c&L?

Thanks again

Bill
Portland, TN

[mikel]

Have you ever checked the speedo with the stock tune?
It may be off there as well, and such will still be off usiong the Predator.
If you can determine how much it is off, you could try to dial it in using the gear ratio parameter.

Also, you can turn the 91 C&L tune into a 93 tune by adding 2* to the global timing parameter.

Thanks

[Bill]

when I install the backup back into it, the speedo is back on track. It is only off if i install a tune. So if I just install the 93 tune it is off, if i install the 91 c & L it is off. No matter what i do it is off, now if I install the backup, it is correct again.

Once again you are awsome Mike you do not waste time, and is some of the best Customer Support one could ask for.

Bill
Portland, TN

[beauwulf]

I found a problem with my OEM tune (Western Motorsports) which caused the same thing, might be related. When I loaded the tune my speedo was reading high by about 10%. I reloaded the stock tune and the speedo was correct again.

It turns out that the axle ratio was incorrect in my OEM tune (no idea if this applies to other OEMs or the predator tunes though). '07 V6 and GT automatics have a 3.31:1 ratio but GT manuals have a 3.55: ratio. I edited the axle ratio in my OEM tune and reloaded it and the speedometer now reads correctly.

...one thought, I'm pretty sure I selected the OEM tune first, then set the transmission type to manual, but does it make a difference what order that is done in?...

Steve

[Bill]

Thanks for the thoughts Beauwulf. I will check it out, not sure what i will be looking for, but I belive it was allready set for 3.55 If not that would be great, now what about the rims being 20"? Is there anything i need to do for that?

Thanks

Bill
Portland, TN

[beauwulf]

There is a parameter for tire size somewhere in the custom tune section, it's in revolutions per mile, I believe, so you have to find the circumference of the tire in inches and divide the number of inches in a mile (numbers are in the manual).
But you should compare the tire diameter to stock first, it might not have changed. Many times larger rims are combined with a lower profile tire which has the same overall diameter as stock - that's the easiest way to upsize the rims since the dealer doesn't have to reprogram anything.

Steve

[Bill]

It looks like everything setup. My speedo is now on the money, it changed my axle ratio to 3.26 now i have it set at 3.54 and it is good upto around 140 =D. Now if I can only get the sound back.. Any idea on why when i have just the 93octane tune in it sound throater and when i put the 91 c & L and do a gobal advance 2* it doesn't sound any different than when it was all default? I currently have Roush Exhaust System (Off-Road) Cat back.

Thanks

Bill
Portland, TN

[beauwulf]

Glad you got that sorted out
I'm still curious if the axle ratio is set wrong in the tunes or if maybe selecting the transmission type before or after selecting which tune to load might have something to do with it. The ratios are different for GT manual vs. automatic, but V6's have the same for both.
I can't help much on the sound question, other than guessing it might have something to do with a different A/F map for the intake tune. My car has MAC cat backs and I can't hear much of anything over their rumble but it sure pulls harder with the intake and tune.