new tune or just change tire revolutions per mile?

p185 · #1 04-20-2009, 10:43 PM

Hi,

I purchased an XCal3 last fall with VMP custom tunes. I have been very happy with them but everything on my truck was stock when I got them. If I upgrade my stock 32" tires to 33" tires do I need to get a full re tune from VMP to adjust shift points etc? Or is it sufficient for me to just change the revs per mile in my XCal? That would fix my speedometer but I don't know if that is all I need or if other things need to be changed too. I would appreciate any info on if I need to do more than just change revs per mile when I upgrade my tires.

Truck is a 2006 5.4L 4x4 Supercab with 3.55 gears.

Thanks!

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**Bluejay** · #2 04-20-2009, 11:11 PM

You just change the size of the tires with the tuner.

p185 · #3 04-20-2009, 11:16 PM

Quote:

Originally Posted by Bluejay

You just change the size of the tires with the tuner.

Thanks for the quick reply Bluejay. I understand that I change the revs per mile in the Xcal3 and I understand how to do that also.

Here is the question I am trying to get at: Is there anything else that you would change in a tune to make the truck run better and compensate for the larger tire size? For example...are shift points independent of tire size or are should they be tweaked to match the tire size I am using? I am just not familiar enough with the tunes to know if that matters or not.

Thanks again.

**Bluejay** · #4 04-21-2009, 12:01 AM

Quote:

Originally Posted by p185

Thanks for the quick reply Bluejay. I understand that I change the revs per mile in the Xcal3 and I understand how to do that also.

Here is the question I am trying to get at: Is there anything else that you would change in a tune to make the truck run better and compensate for the larger tire size? For example...are shift points independent of tire size or are should they be tweaked to match the tire size I am using? I am just not familiar enough with the tunes to know if that matters or not.

Thanks again.

Are you on the canned tune or a custom tune? Regrdless, when you change the tire size it automatically changes the shift point accordingly. The tire size is the only adjustment you need to make.

p185 · #5 04-21-2009, 12:11 AM

Quote:

Originally Posted by Bluejay

Are you on the canned tune or a custom tune? Regrdless, when you change the tire size it automatically changes the shift point accordingly. The tire size is the only adjustment you need to make.

I am on VMP custom tunes. I did not realize that changing tire size in the XCal3 would change the shift points. It will be a simple fix then when I get the new tires on! Thanks again for the reply!

p185 · #6 05-03-2009, 03:59 PM

So my understanding is that I don't need a whole new tune when increasing tire size? I just need to change the tire size in my tuner and be done with it? I wasn't sure if the tune would be written differently with the larger tires and things like shifting etc would be different also. I don't see how changing the tire size in my tuner affects the shift points? Thanks again for any useful info.

brianjwilson · #7 05-03-2009, 06:31 PM

Quote:

Originally Posted by p185

So my understanding is that I don't need a whole new tune when increasing tire size? I just need to change the tire size in my tuner and be done with it? I wasn't sure if the tune would be written differently with the larger tires and things like shifting etc would be different also. I don't see how changing the tire size in my tuner affects the shift points? Thanks again for any useful info.

All you need to do is change the tires size!
Shift points are based off of RPM, load, etc etc. Changing tire size only means that you get to that rpm, load, etc at a higher speed.
As long as you aren't going through setting WOT shifts by MPH, just change the tire size.

150Lariat2000 · #8 05-03-2009, 09:39 PM

I have my tunes from VMP and I love them. Only problem I have had since when I got them is my speed gauge is not correct. The first time my speed gauge was about three miles faster then I was going. I talked to Justin and he told me to change the revs. Now since I changed things, I my speed gauge is 3 miles slower now. Anyone know the correct setting. I am on stock 20s with 3.73 rear. Everything is factory except the exhaust and intake. I told him about when I ordered it.

**Bluejay** · #9 05-03-2009, 10:05 PM

Quote:

Originally Posted by 150Lariat2000

I have my tunes from VMP and I love them. Only problem I have had since when I got them is my speed gauge is not correct. The first time my speed gauge was about three miles faster then I was going. I talked to Justin and he told me to change the revs. Now since I changed things, I my speed gauge is 3 miles slower now. Anyone know the correct setting. I am on stock 20s with 3.73 rear. Everything is factory except the exhaust and intake. I told him about when I ordered it.

Just change it to half of the initial change you made.

Keep in mind, Ford speedos are about 2 mph fast at 65.

brianjwilson · #10 05-03-2009, 10:35 PM

Quote:

Originally Posted by 150Lariat2000

I have my tunes from VMP and I love them. Only problem I have had since when I got them is my speed gauge is not correct. The first time my speed gauge was about three miles faster then I was going. I talked to Justin and he told me to change the revs. Now since I changed things, I my speed gauge is 3 miles slower now. Anyone know the correct setting. I am on stock 20s with 3.73 rear. Everything is factory except the exhaust and intake. I told him about when I ordered it.

Yep, it's really more about trail and error. Change it back by half and check it again. It's no more complicated than that.

i.ride.suzuki · #11 05-04-2009, 03:49 AM

Quote:

Originally Posted by brianjwilson

All you need to do is change the tires size!
Shift points are based off of RPM, load, etc etc. Changing tire size only means that you get to that rpm, load, etc at a higher speed.
As long as you aren't going through setting WOT shifts by MPH, just change the tire size.

Normal shift points are based off pedal position and mph.

There is also max rpm shift points for each gear.

p185 · #12 10-10-2009, 12:24 AM

Quote:

Originally Posted by i.ride.suzuki

Normal shift points are based off pedal position and mph.

There is also max rpm shift points for each gear.

Can I adjust my normal shift points with my XCal3? I only see options to change the mph for WOT shifts. My truck irritates me because it will shift into OD as low 45 or 50 mph if I'm not getting on it hard. Is there a way I can increase the speed at which it shifts into OD? If I could put it at 55 or 60 I would be a lot happier. I see no reason to be in OD under 55 mph. If I move the setting to +7 on my WOT shift point what will that do? Will it only change the shift point by 7 mph at WOT? Or will it affect normal shifts too? I would appreciate if someone could point me in the correct direction on how to modify my normal shift point speeds.

Thanks!

Pat

Windsor · #13 10-10-2009, 06:49 AM

The only way you can make changes in the shift points is if the tuner provided options for doing it. If you don't have that ability, call the tuner and ask how much he'd charge to program a few transmission changes. I think most would consider that as part of your initial tune, if the wait is not too long after you bought the tune.

There is another parameter that controls shifts for tire and gear changes, beside the tire itself and gear settings and has to do with the speed sensor. I just don't think it will make that much difference for a 5% increase in tire size.

With regard to revs per mile data, that information is published on the tire manufacturer's website. But as already posted, you could split the difference from the last change and you should be close.