Cobb Accessport Tire Settings.

[isis]

Hi there. Wondering why the tire setting measurement in the accessport for 2017 is 33.2”? I thought the tires were around 34.5 new so 33.2 would be bald or so right?

 

[K1llD4shN1n3]

I’m actually not sure on this. I tried setting it for my brand new Duratracs and the speed was off so I worked my way down until it was back inline [emoji2369]

Would love to hear from Cobb on this.


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[Gaptor]

I had contacted Cobb and they simply stated they matched what ford put in there. When you change sizes you’ll have to fiddle with it until you find the correct calibration. I put general atx’s 35x12.5’s and I think I put it at 33.9 to read correctly

 

[JLozano]

i Have always wondered the same, curious to see what the response will be.

 

[Chrishiznit33]

I had contacted Cobb and they simply stated they matched what ford put in there. When you change sizes you’ll have to fiddle with it until you find the correct calibration. I put general atx’s 35x12.5’s and I think I put it at 33.9 to read correctly

How’d you mess with it and know exactly what speed your going ?

 

[Gaptor]

How’d you mess with it and know exactly what speed your going ?

GPS app on my phone little by little. Pain all the way around

 

[TwizzleStix]

Ok, here’s how it works. The unloaded tire diameter is calculated to be 34.36”. HOWEVER, when the tire is supporting the weight of the truck it is compressed such that the effective (rolling) diameter is about 32.9”. The effective diameter can be changed by increasing/decreasing air pressure and/or the weight the tire supports. The way to accurately determine the effective diameter is with the truck loaded and tire pressure set as normal. Then measure the distance from the ground directly in line with the tire vertical center line to the horizontal center of the wheel hub and multiply the value by 2. Set this value into the tire diameter and the speedo should be right on actual.

 

[Chrishiznit33]

Is cobb the only way to do this ? Or can any tuner set tire size ?