Xcal3 & "Z" tune - Cannot calibrate speedometer - huh?

[Mote]

With my speedometer at 60, 2 different GPS say I'm going 57.

I have:
* SCT Xcal3 and I've been using the "Z" tune - There were 2 versions, one for stock gears and one for 410's - I've been using the 410 one since I changed gears.
* 265/50 rear tires - Should be 709RPM.

I plug in the SCT select my tune, select adjust options, set the RPM to 710, load the tune and it still measures at 57mph. I changed it to 705 to compare and no difference. I tried both "saved options" and "default options".

I even loaded the non-410 tune, changed the RPM and gear ratio, and still 57. I have *not* tried my dusty "DR" tune(I never liked the shift schedule).

What am I doing wrong? Any ideas? Thanks

[ctrlraven]

I have the same exact issue. I even changed the gauge cluster thinking it was off and changed my RPM to 695 revs (255/55-18 size) and it still reads faster. GPS on my pioneer navi unit and several gps apps on my phone both read the same but show a slower speed than the gauge cluster. Even have my scan gauge unit plugged in and that reads slightly slower than the gauge cluster.

It very well could be something in the tune. Mine can read between 3-5 mph faster than I am actually going.

[martyo]

It is in the wheel rotation setting.

If you have Zack's tune, I would get in touch with him and ask him for a hand. It is a pretty simple fix and I am sure he will help you out.

[03mmmonroe]

With my speedometer at 60, 2 different GPS say I'm going 57.

I have:
* SCT Xcal3 and I've been using the "Z" tune - There were 2 versions, one for stock gears and one for 410's - I've been using the 410 one since I changed gears.
* 265/50 rear tires - Should be 709RPM.

I plug in the SCT select my tune, select adjust options, set the RPM to 710, load the tune and it still measures at 57mph. I changed it to 705 to compare and no difference. I tried both "saved options" and "default options".

I even loaded the non-410 tune, changed the RPM and gear ratio, and still 57. I have *not* tried my dusty "DR" tune(I never liked the shift schedule).

What am I doing wrong? Any ideas? Thanks

I have had the same concern and was able to adjust the Rev Per Mile and get it resolved. It may take a few miles or 10-15 min of driving for the setting to change. It is a learned setting. If you make the change drive your car and give the PCM time to change. I have done it so can you.

[ctrlraven]

I have had the same concern and was able to adjust the Rev Per Mile and get it resolved. It may take a few miles or 10-15 min of driving for the setting to change. It is a learned setting. If you make the change drive your car and give the PCM time to change. I have done it so can you.

What tire are you running and what RPM did you find that worked out?

[03mmmonroe]

What tire are you running and what RPM did you find that worked out?

I just used the RPM from discount tire web site for my tire size. If you are fast or slow change the number by 5 until you get it right on. You will find that you can get it correct at 60 mph and it will be with in .5 at 30 mph or 80 mph. Hope that helps.

I am running now 255/50R18 on all for wheel. Hope that helps. Just make sure to dirve the car and give the PCM time to update.

[Mote]

I *finally* got around to contacting SCT. Great service btw. He updated my tuner remotely (remote controlling my laptop). Good news: The Xcal3 is up to date.

I changed the revs/mile and no dice. So I changed to 600 which is waaaay off and the speedo was reading like 70 when the GPS said I was travelling 37. I then started over at 710 - I incremented until I was 1mph off at 60mph - I have the revs/mile set at 735 which is just whacky. It works, but...

[Zack]

The stock Marauder program has 723 revs/mile programmed in.
If you use any online revs/mile calculator, its says a 245/55/18 tire is 705 revs/mile.

723-705= 18
709+18= 727 (close to 735 right?)

Its wierd how that all works, but it never bothered me so I never fussed with it.
I always found that 04's did odd things compared to 03's....never figured it out either.

[justbob]

The 723 I believe comes from the front 740 minus the rear 705.

35 divided by 2 = 17.5

740-17.5=722.5

Or

705+17.5=722.5

And as like taxes, time cards, and/or the size of your member...

Round up! :wink:


Self proclaimed Builder Of Badassery.

Buy it, Break it, Build it BETTER.
"Since 2004"

[IwantmyMMnow!]

And as like taxes, time cards, and/or the size of your member...

Round up! :wink:


Self proclaimed Builder Of Badassery.

Buy it, Break it, Build it BETTER.
"Since 2004"

:rofl::laugh:

....

[Zack]

Interesting Bob. MPH is based off of the VSS, which is determined by the rear tires.

Interesting nonetheless....
Is that info you gave verifiable?

[L.Mark]

WOW, I'm trying to follow all this...:dunno::corner::wflag:

[justbob]

Interesting Bob. MPH is based off of the VSS, which is determined by the rear tires.

Interesting nonetheless....
Is that info you gave verifiable?


No, but I'm sure that I'm certifiable..

Just makes sense to me with staggered wheels.


Self proclaimed Builder Of Badassery.

Buy it, Break it, Build it BETTER.
"Since 2004"

[Green96]

I think you need to divide by pie....mmmm pie.

[ChiTownMaraud3r]

I always went off the rear tires with all the VSS talk. I did not believe the numbers posted as there were inconsistencies. Some said 705, tire rack says 724, some said 728..I actually measured the rears, radius (center of center-cap) to ground.

2*pi*r = circumference

1 mile = 63360 inches

Revs/mile = 63360/circumference

Obviously this is an approximation as the tire inflation, measurement precision and human accuracy will affect numbers. But I did the math, was closer to 740 I believe, punched into the tuner, and GPS verified to be almost spot on.

This higher number made sense as the revs/mile given are most likely that of the tire with no load. Once our 4200lb car sits on the tires, there is a sidewall flex which compresses it a bit. Even a half inch shorter will cause almost 30 revs/mile more about ~ 2mph difference at 60mph.