P38 Aftermarket Tyre Size Guide

I can confirm my 33's run out about 10% according to GPS but dont have TRUSPEED! another Gadget on my list;)

Hi, just want to add another size to the list.
I have just fitted m/t 235/85/16.
They are road stone, and also fitted to discovery 2 rims which I believe are narrower.
I did get some slight rubbing on front mud guards for the first couple of km, but pushed them back and no more rubbing. I have taken it off road and no scrubbing.
Standard suspension.

Edit:
After a couple of days I have decided to remove front mud guards as they continued to rub

Hey all

Have purchased a Nanocom Evolution recently (although I already own a Faultmate MSV-2), I thought I'd let you know that under "instruments", and in the "settings" tab, you can add a modifier number to offset larger diameter tyres. I had not looked far enough into it on my Faultmate, but did have a play with the Nanocom.

So for those of you with access to a Nanocom and who want to correct the speedo readout with a tyre size change, it can be done without needing to splice wires.

Cheers
Keithy

No way. How did I not notice that. I thought I went through every function on the Nanacom Evo to see what was there.

Have you changed the value and found it made a difference?

Your BECM is locked as per factory I assume?

Good to know (once mine is back on the road again).

I didn't change it on mine, did do it on a D2 and it took effect.

When I'm home next I'll do it to mine.

EDIT: So, go to P38 (whichever EMS yours has), then "instruments", then "settings" and it's right there as "Tyre Modifier" or something very similar (can't remember the exact words as I'm not at home at the moment).

EDIT 2: Once in "instruments", scroll all the way across to instrument setup, it's called "Tyre Coefficient".

Cheers
Keithy

Thanks Keith.

Mines a Motronic (Bosch). I'll be sure to change it once my BECM is talking to me :)

Did some digging about tyre sizes today. I even made a few phone calls to both engineers, and to the VSI department of the QLD Transport.

This virtually applies to all states, but for the purpose of this post, it's purely QLD related as I've not dug further into the fine print in other states.

If you've read the VSI doc in my original post in the lift thread you'll note that they mention combined heights for lifts and tyre combinations. The lift can be 50mm (with engineering you can go higher), but tyres are a firm 50mm diameter increase. No exceptions. The engineers told me the best I could do is submit at "Intent to modify" form with the QLD Transport and hope they feel good that day. They also said that rulers and calculators are both different in real life, so depending on the copper (or anyone else who wants your blood) you could fit a 32" or thereabouts tyre onto a P38 "legally" if you can convince them hard enough that it's a very close 50mm diameter increase.

I smiled and nodded.

Then I called the QLD Transport modification department (can't remember the exact name), and old mate was very firm on the 50mm rule. He said that 4wders call up every day saying they saw a million of 4wds the same as theirs with much larger tyres. He said in no uncertain words or tone that "it is not legal, nor engineerable, to run tyres that are more than 50mm larger in diameter than the largest tyre offered in that particular 4wd".

I'm not convinced that it's any less safe to run 3 1/2" larger diameter tyres (so that's 1 3/4" or roughly 40mm) ground clearance increase over stock, compared to a suspension lift that any old backyarder can make.

I will lift the fight to the 4wd Clubs Australia level and see if something can be done about it (even if it means we need to get them engineered).

Cheers
Keithy

I looked into this when they first changed the rules in Qld and it seemed to boil down to

lifting the roof height of the vehicle by

50mm via longer suspension
50mm via body lift on vehicles not fitted with airbags
25mm via larger tyres (so 50mm diameter)

BUT in total the roof height cannot be raised by more than 75mm by any combination of these modifications.

I presume that as a p38 can have a lift that doesn't effect the roof height on the road we could fit 10 inch spring lifts if they were available. .

I was given the impression by main roads that engineering beyond these limits was not an option in Qld.

Just my understanding, if I am wrong or things have changed I am happy to be corrected

That's it!

I wasn't trying to touch on lifts in this post, more so the tyre limits. Lifts from 75mm to 150mm are engineerable in QLD but not via >50mm tyre size.

Cheers
Keithy