15fx43.5

Is there a way to change tire size with this tuner? I got custom tunes from 5* returned vehicle to stock like i read you have to do and can not find an option for changing tire size.. any help?

Franchi Motorsports

iTrader: (9)

Usually with custom tunes they will have the tire size calibrated ( assuming you provided them that info when you ordered your custom tune ) but far as adjusting tire size under the preloaded tunes, it's under user adjustable options, tire rev per mile.

15fx43.5

I calculated 275/55r20 at 632 revs per mile so I adjusted to 630 revs per mile. Tuner only does increments of 5

15fx43.5

Every website I look at has something different some are 632 some are 651

BoozeDaily

iTrader: (2)

Under my SCT tuner, the iTSX, there are user adjustable options once you select the tune. Options like rear axle ratio, tire revolution per mile, etc. These can be adjusted prior to loading the tune.

Unfortunately with the 2015s, you can select the tire revolution per mile but the PCM won't take the change due to the speedometer being calibrated through the BCM. The only way to correct your speedometer for tire size thus far is through the dealership or by purchasing a Hypertec Speedometer Calibrator (which works pretty well).

Once SCT figures it out and sends an update (which I was told back in July they were working on it) the tuners will be able to adjust this.

For the record, I use http://tire-size-conversion.com/tire-size-comparison/ for my estimated revolutions per mile.

15fx43.5

I did see where the tuner let me change revs per mile before loading my custom 5*. But you're saying it won't change anything?

BoozeDaily

iTrader: (2)

Yes sir, that is what I'm saying. As of July which was the last time I emailed 5* about it, there hadn't been an update from SCT for the tuners to change the the tire RPM through the vehicles BCM.

Unless there has been an update, which I am not sure of, then no. You can plug in the numbers and have the tune go through, but test your speedometer against a GPS and it will still be off. By how much depends on how much you changed your tire size.

I didn't know how long it would take for SCT to update and mine was off about 10% so I bought the Hypertec. Took a little bit of adjusting but all in all about 30 minutes of testing/loading to get it accurate. Once they release an update to the tuner I can plug the Hypertec back in and return to stock which will unmarry it from the truck and allow me to sell it.

b_wop

Can you use the hypertec to load your tire size then tune with sct

BoozeDaily

iTrader: (2)

Yes. You plug in the Hypertec to the OBDII port and after a few short prompts you set your tire size in inches. It goes in .25" increments. The program will load and let you know when complete. Go test it on the road with a GPS to ensure your speedo is correct. For example, I went from stock tires to 34" tires. Loaded 34 and my actual speed was about 5 MPH slower than the speedo readout at 60MPH. I ended up setting it to 32.75" to get it accurate and it's still about 0.5-1MPH off. I can live with that.

Once you set the size and all is good you can exit programming and unplug the Hypertec from the OBDII port and plug in your tuner. The only time you'd need the Hypertec again is if you change tire size.

Be advised, once the Hypertec sets a tire size it is married to that vehicle until you change it back to stock.