Motorator Experts - How can I set the tire size with a Granatelli Fuego tuner

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How can I set the tire size with a Granatelli Fuego tuner

I have a Granatelli Motorsports Fuego hand-held tuner. I want to change the tire size on my Mustang since I put on 315/35-20 rear tires, however, it don't understand the code it wants. You can't just select a tire size in the Fuego.

Asked by: den1320

User type: Enthusiast

Asked on: January 09, 2009 16:11

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Answers

Motor8rMatt
User type: Enthusiast
Posted: about 1 year ago

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The Granatelli tuner uses a calculation based on Tire Revs per Mile. This is how it’s done.

On a 315/35-20 tire:
315 - tire width
35 - aspect ratio
20 - rim diameter

Calculate tire diameter.
Tire height = tire width x aspect ratio
Wheel Diameter = (2 x tire height) + (rim size x 25.4)

One rotation is equal to the wheel’s circumference, so…
One rotation = wheel diameter x 3.141592654
Tire height: 315x0.35 = 110.25
Wheel: (2 x 110.25)+(20 x 25.4)
Diameter: 220.5+508 = 728.5

Calculate the rotation or Revs per Mile
One rotation: 728.5x3.14159=2288.64832

Repeat the same calculation for the front tire and take the average of the two.

----- Here are the numbers for your Mustang -----
255/35-20

255 x 0.35 = 89.25
(2 x 89.25)+(20 x 25.4)=(178.5)+(508)=686.5 x 3.14159=2156.7015

315/35-20
315 x 0.35 = 110.25
(2 x 110.25)+(20 x 25.4)=(220.5)+(508)=728.5 x 3.14159=2288.6483

So 2288.6483+2156.7015/2 = 2222.6749 is the average. Just select the number closest to this in your Fuego.

Granatelli Motor Sports Hand-Held Fuego Tuner

References

http://www.granatellimotorsports.com/product_display.php?gid=4

TheRipper
User type: Enthusiast
Posted: about 1 year ago

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One other thing, it is more accurate to just measure the diameter of the tires and do the calcs from that. Since most tire calculation are for a give Round unloaded tire, the stock size calculations might be off a tick more then the acutall properly inflated tire on the car.

Motor8rMatt
User type: Enthusiast
Posted: about 1 year ago

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You're probably right, the most accurate way to determine Revs would probably be to measure the tire. However, the above formula is what I got from Granatelli for their tuner. So, I guess the question is, does the Fuego tuner go by a real accurate reading, or is the code in the tuning device based on the algorithm they gave me. Again, the goal here is to program the Fuego for the new tire size, not just determine the actual Revs per mile. I guess I don't know the real answer :-)

TheRipper
User type: Enthusiast
Posted: about 1 year ago

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Check your math, I calculated it and also looked up the a typical 315-35-20 Tire at the Tire Rack and it shows the value at 726 Revs/Mile. I think you may have an extra slice of 'Pi' tossed into the mix.

You can also get it from the calculators at the pages below

The Ripper

References

http://www.gtsparkplugs.com/GearCalc.html
http://www.gtsparkplugs.com/TireCalculator.html