I just got my 05 3500 and it came with a hypertech tuner. The tuner asked me my wheel size and I know my tires are 305's but the tuner is looking for wheel sizes like 25.5 26.0 26.5 and so on. So at the risk of sounding like a total noob can someone please tell me what a 305 tire size is and how to convert the numbers? Also my transmission when it shifts seems to slow down during the shift instead of surge ahead like my ford did, is this the way an Allison is supposed to shift or is there something up? Thanks.
Isaac

To convert from metric to english, we will need the whole tire size instead of just the first 3 numbers. Example: 305/xx/rxx. The engine may be defueling between shifts to keep from hurting the Allison, but you may want to look into changing the spin on filter for the tranny as well.
:welcome: to the Place!

ok cool , they are 305/70/18
Why would it be defueling? Is it a normal thing or are you saying the trans might have an issue.

Calculated Tire Size: 34.8" x 12"

It is normal, if it is defueling. You should ask that question in the Allison OEM section and they should be able to help you out better. I know you can have some harsh to delayed shifts if the spin on filter isn't changed regularly. I have not driven a Ford to compare to know what you are referring to, so I cannot really help there.

Thanks!

sounds like a defueled shift. reduces power/torque during the shift to avoid breaking stuff.
also the trans needs to learn the shifts for the amount of power you make it put out. if you don't drive it hard all the time and when you do it shifts funky that is why. the allison is an adaptive trans constantly changing the shift timing and feel. (speed of the apply/release of clutches, and pressure of the apply). all to save itself and give you the best ride possible. if you drive normal and once and awhile jump on it the shifts wont be that nice. it takes a while to learn it at the higher rpm and throttle position.