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Tyre sizes - Including asbuilt Calculator

Twinpiston77
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Hi All,

So after reading all this info, it only relates to PX2, so PX1 and BT50 cant make this change and there is no way to update any tyre information to try and level out the speedo?
Thanks
Corey
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saeb
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Twinpiston77 wrote: Mon Aug 27, 2018 9:03 pm Hi All,

So after reading all this info, it only relates to PX2, so PX1 and BT50 cant make this change and there is no way to update any tyre information to try and level out the speedo?
Thanks
Corey
PX1 can be changed with the 3 preset sizes although every hi rider or 4x4 PX1 I have checked has already been set at the highest.

See PX1 programming here viewtopic.php?f=12&t=1213
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Twinpiston77
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Thanks Stewart, is there something I am missing as I see a question about the presets but is that because they have looked at there own system? Also what are the presets?

Is there anybody around Brisbane that can have a look at mine, preference is Ipswich area.

Cheers
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saeb
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Twinpiston77 wrote: Tue Aug 28, 2018 8:17 pm Thanks Stewart, is there something I am missing as I see a question about the presets but is that because they have looked at there own system? Also what are the presets?

Is there anybody around Brisbane that can have a look at mine, preference is Ipswich area.

Cheers
PM me your VIN and I will tell you what you currently have. No point chasing something you already have.
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Twinpiston77
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saeb wrote: Tue Aug 28, 2018 5:55 pm
Twinpiston77 wrote: Mon Aug 27, 2018 9:03 pm Hi All,

So after reading all this info, it only relates to PX2, so PX1 and BT50 cant make this change and there is no way to update any tyre information to try and level out the speedo?
Thanks
Corey
PX1 can be changed with the 3 preset sizes although every hi rider or 4x4 PX1 I have checked has already been set at the highest.

See PX1 programming here viewtopic.php?f=12&t=1213
Hi Stewart,

Just wondering, I know you couldnt get the value to change for the fuel tank, but is it possible to find the root default values for the tyres sizes and change them in the database at all, maybe start with the 265/65/17 equivalent and throw 2 sizes in larger than that, that you know work in the PX2 for instance?

Cheers

Corey
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saeb
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Unfortunately, the PX1 does not work this way, it is an entirely different beast.

There are default values in the firmware which we cannot change. You can select one of the 3 default values and that is all, anything out of that is invalid.

It is best not to change asbuilt manually in a PX1 and the IPC backs up the BCM and no location in a PX1 or PX2 are the same. Class it as Holden vs Ford.

I do have a PX1 cluster being sent to me. I going to strip it down and see what chips it is running to see if a manual firmware edit it plausible for tyres and or dte. I do not have high hopes but it is something.
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Twinpiston77
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Ok thanks, ill check back.
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saeb wrote:So it appears that the IPC pulls the odometer value from the PCM.

Changing just the BCM will not affect the odometer then (speed and odometer 2 different things ), the change that will help keep the odometer correct needs to be made in line 7E0-01-01 of the PCM where tyre size is.

Ideally PCM and BCM should be changed.
Hey just like to get a bit more detail in what to change in PCM for adjusting the odo. I gather BCM and 0977 for auto to change the speedo? I'm running 285/70 R17 Mickey Thompson ATZ.

Is there any other new info or updates to consider changing?

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Shane_2 wrote: Wed Sep 19, 2018 3:43 pm
saeb wrote:So it appears that the IPC pulls the odometer value from the PCM.

Changing just the BCM will not affect the odometer then (speed and odometer 2 different things ), the change that will help keep the odometer correct needs to be made in line 7E0-01-01 of the PCM where tyre size is.

Ideally PCM and BCM should be changed.
Hey just like to get a bit more detail in what to change in PCM for adjusting the odo. I gather BCM and 0977 for auto to change the speedo? I'm running 285/70 R17 Mickey Thompson ATZ.

Is there any other new info or updates to consider changing?

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Yes that is correct 0977 is the highest you can go for the auto. It will be better than what it was.
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saeb wrote:
Shane_2 wrote: Wed Sep 19, 2018 3:43 pm
saeb wrote:So it appears that the IPC pulls the odometer value from the PCM.

Changing just the BCM will not affect the odometer then (speed and odometer 2 different things ), the change that will help keep the odometer correct needs to be made in line 7E0-01-01 of the PCM where tyre size is.

Ideally PCM and BCM should be changed.
Hey just like to get a bit more detail in what to change in PCM for adjusting the odo. I gather BCM and 0977 for auto to change the speedo? I'm running 285/70 R17 Mickey Thompson ATZ.

Is there any other new info or updates to consider changing?

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Yes that is correct 0977 is the highest you can go for the auto. It will be better than what it was.
Yes I have already completed that part of it and I am smack on the money gps 100kmh speedo 100kmh that's all good.

I want to know what I need to change in PCM to get the odo to be correct too.

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Do you have access to the PCM asbuilt?
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saeb wrote:Do you have access to the PCM asbuilt?
It does seem to show it in my forscan yes.

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7E0-01-01 xxxx-6298-xxxx for 285/70R 17
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saeb wrote:7E0-01-01 xxxx-6298-xxxx for 285/70R 17
Awesome cheers, I'll give it a go tomorrow. Hopefully it is as close as the speedo is

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saeb wrote:7E0-01-01 xxxx-6298-xxxx for 285/70R 17
Awesome cheers for that. I will give it a go tomorrow. Hopefully it is as close as my speedo.

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Hi Stewart, what’s the algorithm to calculate this field? I have 285/65/18.
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I have already calculated it for your tyre size.
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saeb wrote: Fri Sep 21, 2018 8:44 pm I have already calculated it for your tyre size.
Well, I cannot find it. Do you mind posting it again.
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It's a pain to calculate. If you want it I will post it when I have some minutes. If you want the hex for your tyre size then let me know your tyre size as it's quicker for me to calculate than write it all out at the minute.
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It’s 285/65/18
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rusty-pie wrote: Sun Sep 30, 2018 7:40 pm It’s 285/65/18
6234
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In relation to tyre sizes, we have found that there are tolerances in the PCM and TCM and both of these modules will need to be flashed before larger sizes that what we currently use can be used. At this point, it will need a fair amount of time spent on it and is not a near future option.
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HI Stewart,

So just trying to understand the impact of a bigger Tyre size on the odometer, speedo and DTE calculation. I run 265/70/R17 and have noticed:

My speedo is 100% accurate. I think this is right because the speedo is usually calibrated to read 3 or 4km/hr lower than actual, and the increased Tyre size corrects this.

I assume my odometer would be reading less km than actually travelled? What would it be roughly?

My DTE is not accurate. I have a 140L tank and changed the tank size, but a DTE reading of 0 (and I have gone past it by 20km or so in the past), results in a maximum 120L fill. So DTE is reading lower than it should.

Would all that be right?

If I "correct" the Tyre size with Forscan, Should all this be "fixed"? I'd rather the speedo was accurate, but hey can't have your cake and eat it too right?
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Hi Tezza,

I'll chime in if that's OK - Stewart can correct me if I get anything wrong... LOL

All of the internal calculations for speed, distance, DTE are performed on actual numbers, based on standard tyre size, so all of these are normally quite accurate on a standard vehicle. The speedo however has a 'correction' factor applied to it in the firmware (so it can't be changed) such that the speedo displays somewhat 'faster' than your actual speed. This to comply with the ADRs.

In your case, with bigger tyres, the speedo might read correctly, but all the other calculations will be out by 4 or 5 percent. The distance covered will show less than actual. If you correct this with Forscan, then all your calculations will once again be correct (or a least a lot closer), but your speedo will once again read high. If you display your speed using a Scangauge or Ultragauge, it will read 4 or 5% lower than the speedo dial, so the computer knows the actual speed and uses that for its calculations.

Re the tank issue, if you've changed it to a 140 litre in Forscan and the DTE is not accurate, I would assume that the float was not adjusted (bent) correctly when it was installed, although I'm not quite sure what impact (if any) your larger tyres would have on the calculations.

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I agree with you totally Gerry :)

Where is the gauge when you do a refill with 120litres, right at the bottom? Did you install it or ARB? If ARB then the float will be bent to their specs which is about right, 120 refill on empty.

I bent mine 2mm over spec and 0 DTE leaves 136 litre refill.

Although the fuel level doesn't realy seem to have a bearing on DTE it does seem to once the gauge level gets close to the bottom.

I think you will find most people dealer fit tanks are about the same as yours.

Also I do not believe your tyre size is a factor. Keep in mind vehicle dynamics, ABS, ESC, etc all rely on reading a correct tyre size and leaving it 4% out may or may not affect the safety features of your vehicle.

No corrections Gerry, I'm agreeing.
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