Tyre sizes - Including asbuilt Calculator

kfa1950 · Sun Apr 05, 2020 9:15 am

2017 XLT, Tyres 265 65 17. Speedo reading 6 kph fast.
Just checked original figures in BCM 726-12-01 0938. PCM 7EO-01-01 5C30.
That becomes BCM decimal 2360 & PCM decimal 23600. Tyre circumference is 2438mm
If re-calculating for standard tyre size to get better speedo and trip readings, what about BCM 0970 & PCM 5E60. The reason wanting to use 0970 in the BCM is close to maximum without generating DTC's. That would give me a value of BCM decimal 2416 & PCM decimal 24160. This is a lot closer to tyre circumference.
Has anybody made changes for standard tyre sizes?

Josh L · Sun Apr 05, 2020 12:12 pm

Yeah, nah.

Tried with the new calculator and mine still seems to have an issue.

I get two DTCs;
Code: P0825 - Gear Lever Push/Pull Switch Circuit (Shift Anticipate)
Code: P1635 - Tyre/Axle Out of Acceptable Range

Not sure if you remember Stewart, mine's almost the only manual Px2 that seems to be a turd when trying to change to allow for 33s.

Any light to possibly shine on it yet?

Tezza · Sun Apr 05, 2020 1:04 pm

Did you try a pcm relearn afterwards?

Josh L · Sun Apr 05, 2020 1:48 pm

Tezza wrote: ↑Sun Apr 05, 2020 1:04 pm Did you try a pcm relearn afterwards?

Yup.

Mine's been a weird anomaly the whole time when it's come to this.
Being it's a manual vehicle, I should've been able to do it a couple of years ago, but didnt work for some reason, even with a visit to Stewart's.

Sun Apr 05, 2020 8:05 pm

Tezza wrote: ↑Sat Apr 04, 2020 6:19 pm So I made the change in the PCM and wrote the line with success. I also successfully did a PCM relearn.

None of this made any difference though (that I can see)
The scangauge speed still flicks between spot on and 4% out every 10sec (approx) and the mild tcm tune still throws a fault code.

Might talk to Barry to see if he can look into the mild tcm cal. Should I mention anything specific, or just P code 1635?

Put the factory PCM tune in. See if the flicking stops, if it does then the flicking is probably due to something in the PCM tune.
While factory PCM tune in try both TCM tunes. Let me know the outcome. If it still throws P code on mild tune then the tyre limitation has not been removed on that TCM tune.

Sun Apr 05, 2020 8:12 pm

kfa1950 wrote: ↑Sun Apr 05, 2020 9:15 am 2017 XLT, Tyres 265 65 17. Speedo reading 6 kph fast.
Just checked original figures in BCM 726-12-01 0938. PCM 7EO-01-01 5C30.
That becomes BCM decimal 2360 & PCM decimal 23600. Tyre circumference is 2438mm
If re-calculating for standard tyre size to get better speedo and trip readings, what about BCM 0970 & PCM 5E60. The reason wanting to use 0970 in the BCM is close to maximum without generating DTC's. That would give me a value of BCM decimal 2416 & PCM decimal 24160. This is a lot closer to tyre circumference.
Has anybody made changes for standard tyre sizes?

Not sure why you would do this. Monitor the speed with ultragauge or scangauge and compare to GPS (forget about what the cluster says), they will nearly be identical. Soon as you move it closer to max you are removin the 4% factor that Ford put in for the cluster.

Mine will show around 5 over GPS speed and I have DTE within .03 on each refill. Yes you can refine a litte bit for a closer DTE but moving it 3% ish will just through your DE out 3%.

Sun Apr 05, 2020 8:15 pm

Josh L wrote: ↑Sun Apr 05, 2020 12:12 pm Yeah, nah.

Tried with the new calculator and mine still seems to have an issue.

I get two DTCs;
Code: P0825 - Gear Lever Push/Pull Switch Circuit (Shift Anticipate)
Code: P1635 - Tyre/Axle Out of Acceptable Range

Not sure if you remember Stewart, mine's almost the only manual Px2 that seems to be a turd when trying to change to allow for 33s.

Any light to possibly shine on it yet?

I think I do remember. Happy to look again if you want to run down Seaford area at some point, from memory you work in Bayswater.

Tezza · Sun Apr 05, 2020 8:41 pm

saeb wrote: ↑Sun Apr 05, 2020 8:05 pm
Tezza wrote: ↑Sat Apr 04, 2020 6:19 pm So I made the change in the PCM and wrote the line with success. I also successfully did a PCM relearn.

None of this made any difference though (that I can see)
The scangauge speed still flicks between spot on and 4% out every 10sec (approx) and the mild tcm tune still throws a fault code.

Might talk to Barry to see if he can look into the mild tcm cal. Should I mention anything specific, or just P code 1635?
Put the factory PCM tune in. See if the flicking stops, if it does then the flicking is probably due to something in the PCM tune.
While factory PCM tune in try both TCM tunes. Let me know the outcome. If it still throws P code on mild tune then the tyre limitation has not been removed on that TCM tune.

When I tried the mild tcm tune, the flicking on the scangauge stopped and was bang on where it should be. It’s just that it had the engine light and fault code P1635, otherwise I was happy with everything else. The max tcm tune doesn’t have the P1635 fault code, but has the flicking.

I will try both tcm tunes with the stock pcm tune and report back with my findings.

Tezza · Mon Apr 06, 2020 2:40 pm

Ok, I have tried with the factory PCM tune in and returned the same result.
Tried it with both the mild and max tcm tunes.

What I find interesting is even though the mild tune throws an engine light fault code, when I take it for a drive, everything is perfect, including the scangauge speed readings.

Will talk to BPT to see if there is something they can modify in their mild tcm tune.

MghtyMazda · Fri Jul 10, 2020 3:27 pm

me too wrote: ↑Fri Apr 05, 2019 2:35 pm
saeb wrote: ↑Sat Jul 08, 2017 7:31 pm New tyres so best I sort it.

Maximum size in hex in the BCM the Ranger will take before throwing PCM and TCM codes is 0977.

Standard XLT 265/65 R17 circumference is approx 2438mm

MT ATZ P3 at 265/70 R17 circumferance is approx 2519mm

What a massive difference.

Hex in BCM 726-12-01 xxxx-XXXX-xx was 0936 and I have changed to the maximum 0977.

0936 = 2438 265/65 R17 Factory Tyre
0977 = 2505 265/69 R17 - Non existent but closest we will get
0987 = 2520 265/70 R17 - Fault codes

So I have gained back 67mm and only fell 15mm short.

265/65 R17 410 Revolutions per kilometre
265/69 R17 399 Revolutions per kilometre
265/70 R17 396 Revolutions per kilometre

All in all I will probably pull back 2 of the 3 kph lost by putting lager tyres on and my DTE will be very close to what it should be. Also it will get even more accurate as the tyres wear down.

So if you have 265/70 or even 285's then max it out to 0977 as it will still be an improvement to your DTE and ODO. Imagine over 100k running larger tyres and no changes your car would actually be lying about how many kilometres it has travelled.

Good luck all.
Hi Saeb,
I am trying to adjust the tiresize in my 2015 BT50 but unfortunately I can not find the entry 726-12-01 under BCM.
The values I see are between 726-01-xx to 726-02-xx.
Does that mean I cant change it at all or do I need to get deeper in the guts of the software?
Cheers
Mike

Hi,
New to the forum but have been searching for some time. Been searching for more info regarding Mike's post above. I have a 2011 BT50 3.2L and like Mike, don't have the 726-12-01. BCMii doesn't list 726-12-01.
I've looked in the BCMii Central config and see Tyre size and Tyre circumference but the selections are far from 285/70/17 and the 2610mm circumference needed.

The 285/70/17 tyres have brought the speedo up to GPS (+/- 1-2km/hr) but the odometer is out. I have an UltraGuage that reads the speed accurately but I'd like the odometer to be accurate for actual distance travelled. Currently the odometer is short 0.6kms after travelling 8kms GPS which will add up to a considerable shortfall over large distances. Is there any further info that could be shed on this for the early BT50's?

Thank you in advance.

Sat Jul 11, 2020 7:08 pm

Only option on PX1 and BT50 is the pre selection. You cannot change any more than this and changing as-built will end in tears.

The location you talk of is not applicable to your vehicle.

MghtyMazda · Mon Jul 13, 2020 10:33 am

saeb wrote: ↑Sat Jul 11, 2020 7:08 pm Only option on PX1 and BT50 is the pre selection. You cannot change any more than this and changing as-built will end in tears.

The location you talk of is not applicable to your vehicle.

Thanks for the info, saeb.

simonj13 · Mon Aug 17, 2020 12:37 pm

Hi Tezza,
Any chance you sorted out the fault code?
I recently installed the same size tyres as you, got the updated TCM tunes from BPT loaded in and when I tried to change to asbuilt BCM file to "09DC" to reflect the correct tyre size it came up with the same error code P1635.

Sat Aug 22, 2020 10:01 pm

Most have said the same with BPT TCM tune and nothing I can do about it. Most seem happy because they have never corrected the as-built afterwards which makes no sense to me as it means nothing is corrected. Anyway I'm staying out of this one.

simonj13 · Sun Aug 23, 2020 9:17 pm

Following up from my previous post. I contacted Barry regarding the DTC and he advised that their TCM tune does allow for larger tyres but perhaps not the actual diameter. His suggestion was to try a smaller number so instead of using a diameter of 2524 (285/70R17 tyre) I ended up with 2504 being the maximum before it gave me the DTC. Perhaps that's something other people could try as it gets you much closer to the odometer being accurate than changing nothing.

Mon Aug 24, 2020 8:00 pm

Bit of a pain.

I have done 2651 on my own trans file without issues.

billborric · Fri Sep 11, 2020 1:04 pm

Hi, just fitted 285/70x17 tyres to my PXII. I have altered the BCM to read 977, done a relearn and no difference. In fact I have done it twice just in case something went wrong the first time.
Is there anything else I need to do to get speedo roughly 4kph less than actual and to get odometer about right (it is currently just below 7% out).

Fri Sep 11, 2020 2:37 pm

I have never seen one not at least recognise and move things back at a minimum of 4% with a 0977 change, after doing 100s and 100s of them.

If you want it correct then contact me and visit me in Seaford where I will write my custom transmission file to the vehicle. No it's not free.

This give give you the option to change back to factory specs and go well beyond the 0977 figure.

Mon Sep 28, 2020 4:53 pm

Code: P0825 - Gear Lever Push/Pull Switch Circuit (Shift Anticipate) - Need to test further
Code: P1635 - Tyre/Axle Out of Acceptable Range - Fixed

If anyone wants to attend Seaford I may have a work around for this now, unfortunately I can only do a partial test on the bench so cannot confirm 100% as I am working with an auto PCM. It will mean me writing a modified PCM calibration then you having to go for a drive for however long it usually takes to show the engine check light. Ideally you would make BCM change first to ge an idea on how long it would normally take to appear.

PX2 or 3, I'm not fazed.

Kittitorn · Wed Sep 30, 2020 1:20 pm

0977 is not 2505mm. It's 2423mm.

Wed Sep 30, 2020 6:28 pm

Last time I looked 2505 - 3.3% = 2422.335

Forscan do not take the Ford calculation into account even though I gave them the data about 4 years ago. Feel free to contact them.

spin addict · Tue Oct 20, 2020 3:46 pm

So I feel like I have done a fair bit of research through this topic and others but I haven't quite found a clear answer. I have a new (unmodified) 20.75 raptor and have successfully managed to change a number of codes using forscan (full version).
Where I seem to be having an issue is with correcting my speedo. originally the BCM as built read 726-12-01 = xxxx-09f7-xxxx. I used the calculator on the first post and the value calculated to write is 09DC. So I write the code, relearn the TCM, clear the DTC, no further DTC's test drive the car, speedo is still out by a few km/h. so then I try a bigger Tyre size of 0A31 (305/70r17), so i go through the process again. what I was expecting to happen by going bigger was seeing the speedo show faster than my GPS but this didnt seem to happen, it still seemed to remain the same as the 09f7 code. i had imagined that i would be able to correct the speedo even though this may have put the Odometer and DTE calcs out.

any clues as to what is going on?

Tue Oct 20, 2020 11:21 pm

Speedo is meant to be out by approx 4 kph. That is factory. Lower the number not increase to move the Speedo up.

What size tyre do you actually have. 33 ish at a guess which is stock. What is the reason for the change?

spin addict · Thu Oct 22, 2020 8:47 pm

saeb wrote: ↑Tue Oct 20, 2020 11:21 pm Speedo is meant to be out by approx 4 kph. That is factory. Lower the number not increase to move the Speedo up.

What size tyre do you actually have. 33 ish at a guess which is stock. What is the reason for the change?

Hey Stew,

thanks for getting back to me and thank you for the effort you have put into making this forum a great success.

So, Main reason for the change was (initially) to correct the speed error vs actual as I was seeing an error of >6kmh vs GPS. I then headed to forscan, to see what the Tyre size was set to and to my surprise the original configuration of the vehicle had a wheel size of xxxx-09f7-xxxx. If I'm not mistaken this equates to the following (as per the forum calculator).

True Circumference mm: 2638
Ford Corrected Circumference mm: 2551

Using the forum calculator for the original spec tyre that I have, 285/70r17, this equate to the following below.

True Circumference mm: 2610
Ford Corrected Circumference mm: 2524

I have no idea why the tyre size value isn't correct to begin with, but after making the changes my Scangauge speed now matches the GPS speed but as you pointed out the speedo module irritatingly deducts 4 km/h of the actual.

Sat Oct 24, 2020 12:59 pm

It is common for the PX3 to be set to 6kph under for whatever reason.

4 kph is for numerous reason, vehicle manufacturers are liable if the speedo shows above what actual is, tyre circumference changes with pressure and tyre wear.

Basically ADR states "The speedo must always read 'safe', meaning the vehicle must not travel faster than the speed indicated by the speedo." Last thing a vehicle manufacturer needs is another law suite on their hands.