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I have an SCT Tuner with Brenspeed tunes and I have 1 major complaint! When I'm running 70-80 mph the speedometer is 4 mph higher than I'm actually going. I spoke to the techs at Brenspeed and they say I can make the adjustment in the SCT. I have no idea how to do that, does anyone here know?

I just dont like the idea of adding mileage to the car that it doesnt actually have.
 

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I have an SCT Tuner with Brenspeed tunes and I have 1 major complaint! When I'm running 70-80 mph the speedometer is 4 mph higher than I'm actually going. I spoke to the techs at Brenspeed and they say I can make the adjustment in the SCT. I have no idea how to do that, does anyone here know?

I just dont like the idea of adding mileage to the car that it doesnt actually have.

Wow. I would call them back and ask them to walk you through it if you're at all concerned. I've played around with mine and cant see any option for adjusting the speedo. Only tire size and gear size. Do you have new gears or tires? With the stock tune is the speedo right?

When I had my gears put on, my speedo was a nice amount off when you started driving fast. I hated it so I know how you feel.
 

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If you adjust the tire Revolutions Per Mile, it should bring the speedometer into line. Tire RPMs are based on the tire's circumference, depending on its effective diameter as it rolls down the road.

Since the SCT tuner only allows adjustment in five-RPM increments, you may get as close as possible - or useful - by reading the RPM figures from your tire size as displayed in the specifications accessible on Tire Rack dot com.

If you happen to be running a Ford Racing Performance Products intake with the Pro-Cal hand-held tuner, it allows corrections in one-RPM increments. I spent a couple gallons of premium running up and down the freeway (adjusting the wheel RPM between laps) to get the speedometer to match GPS MPH, and now it is accurate to less than half a needle-width.
 

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Choosing the right 5 RPM with the SCT gets it within less than a needle width. Changing air pressure and tire wear affect it as much.
 
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