Best Diff Ratio

[d2dave]

My D2 is fitted with 265/75/16 tyres. A few years ago I cam across a pair of unused Ashcroft diffs fitted with air lockers and pegged.

The ratio was 4.11, which I thought might be a bit low, but the price was good so I purchased them.

Recently when driving at 110 kph the pinion nut cam undone, damaging crown wheel and pinion, so I need to replace them.

So I am seeking the opinions out there for the following.

Using Ashcroft's calculator this is what I get with different ratios.

With standard tyres (29 inches) and standard 3:54 diff, at 100 kph rpm would be 2172

With my 265 tyres (31.6 inches) and if I use Ashcroft's 3:7575 ratio rpm would be 2111, which is 61 rpm slower than standard.

When I had the 4:11 ratio I did not take enough notice as to what was the RPM, but using the calculator it would have been 2314

With the 4:11's it did feel like it was revving a bit hard especially at 110/115 Kph.

So what do I do? 3.54 which will reduce RPM from standard by 61 or stick with 4.11 and raise rpm by 142?

Would the extra 142 RPM increase fuel consumption by much, Would the minus 61 RPM be detrimental.

I have in the shed one of Td5 inside's hybrid turbo and fuel remap in my computer, plus a boost box, so there will be plenty of power.

So which diff? 3:75 or 4:11

[Vern]

How are your tyres? Due for an upgrade yet? [emoji846]

[SPROVER]

I'm running 255 85 16 mud tyres with my 4.11 gears. On a recent trip to qld sitting at 110 kmh my revs were about 2500 rpm. I have a remap by shack who is on the forum and it ran really well. I'm running a vgt turbo as well.

[SPROVER]

Also I had the pinion nut come loose as well after a trip to toolangi. I was getting a vibration through the drive line which I couldn't trace. Then I was doing a check to try and find it and found this. [emoji1751]
Tightened it up and it's been good since.
Touch wood! https://uploads.tapatalk-cdn.com/20210725/22d890ab16193557b99d4540b1c4ad70.jpghttps://uploads.tapatalk-cdn.com/20210725/cd4b2c37ebfa79a653b465f2307f9590.jpg

[d2dave]

How are your tyres? Due for an upgrade yet? [emoji846]

Why do you ask?

[Vern]

Why do you ask?Fit your 4.11 diffs and taller tyres, ie 255/85 or something

[d2dave]

I'm running 255 85 16 mud tyres with my 4.11 gears. On a recent trip to qld sitting at 110 kmh my revs were about 2500 rpm. I have a remap by shack who is on the forum and it ran really well. I'm running a vgt turbo as well.


Your tyres are 33 inches, so 4:11 is a no brainer. How do you fit these on a D2. I thought 31.6 was the limit and that is with a 2 inch lift.

As for the diff. I removed it and there was damage to the gears. Feathered the the edges of the gears to remove burrs and reassembled.

This was because I needed vehicle at the time on the road. From a reliability perspective it would probably be ok, but it now has a period whine.

[d2dave]

Fit your 4.11 diffs and taller tyres, ie 255/85 or something

Love your thinking, but I thought my tyres were the biggest you can get under a D2 with a 2 inch lift.

I have even read reports of others having minor rubbing issues with 31.6 inch tyres

[SPROVER]

Your tyres are 33 inches, so 4:11 is a no brainer. How do you fit these on a D2. I thought 31.6 was the limit and that is with a 2 inch lift.

As for the diff. I removed it and there was damage to the gears. Feathered the the edges of the gears to remove burrs and reassembled.

This was because I needed vehicle at the time on the road. From a reliability perspective it would probably be ok, but it now has a period whine.They fit mine with a 2 inch lift. The only rubbing I get is on the lra sliders. I'll be trimming a bit off the end when I get a chance. Also I have sls so I can raise the rear end up a bit as well. [emoji16]https://uploads.tapatalk-cdn.com/20210725/f2f39351edf3a748353925858212d422.jpghttps://uploads.tapatalk-cdn.com/20210725/acf51f538d1249290abf3fb9aff0c3a1.jpg

[Slunnie]

Love your thinking, but I thought my tyres were the biggest you can get under a D2 with a 2 inch lift.

I have even read reports of others having minor rubbing issues with 31.6 inch tyres

If your suspension works properly, then they are. Actually, even with a high articulation and long travel setup with full uptravel you can still have 265/75 rub on the rear doors.

All of the testing we have done with 2" lifts will have anything bigger than 265/75-16 rubbing inside the guards. 285/75-16 and 255/85-16 both rub everywhere. If they're not rubbing then I can assure you the suspension isn't getting full uptravel.

2" and 265/75-16 is right on the money.

[Slunnie]

They fit mine with a 2 inch lift. The only rubbing I get is on the lra sliders. I'll be trimming a bit off the end when I get a chance. Also I have sls so I can raise the rear end up a bit as well. [emoji16]https://uploads.tapatalk-cdn.com/20210725/f2f39351edf3a748353925858212d422.jpghttps://uploads.tapatalk-cdn.com/20210725/acf51f538d1249290abf3fb9aff0c3a1.jpg
Thats a good looking Disco!!

[Kaaaiju]

I run 33s on 4.12 and it revs under 2500 and is geared niced, your lucky to get Ashcroft diffs, locked and pegged as it cost me $6000 landed for both of my diffs last year but it's a killer setup

[RRT]

Went through this agony in choosing diff ratios myself, six tabs of ashcroft ratio calculator open and a whole lot of soul searching so to speak.

Came from the point of view of my D1 300 TDi when this went to 32's and the impact off road on the low range gearing. Where previously could toodle around the VHC in 2nd with the 29's and barely used 1st, the 32's had me constantly changing gear to modulate speed downhill in particular. So in going and changing diff gears in the D2 I wanted or hoped for something that approached the D1 on 29's in low range, cognizant of the fact the auto has different characteristics off road.

So at 10kph in Low Range 1st,

300 TD1 standard 3127 rpm
300 Tdi with 32's 2834
TD5 Standard 2100
TD5 4.37 32's 2350
TD5 4.75 32's 2554


On road at 100kph, well lets face it the 300 TD1 struggled on 32's so does not warrant comparison for this exercise!
TD5 Standard 2249
TD5 4.37 32's 2516 2285 (1.1 TF)
TD5 4.75 32's 2735 2484 (1.1 TF)


What does this show, only that compromises must be made between the off and on road when choosing diffs ratios. Have chosen the 4.37 as my compromise due to the distances travelled to get anywhere to go 4WDing but if I was to do this with no limit to budget would look at the 1.1 ratio in the Transfer box which would give standard cruising gearing or the compromise I am willing to accept with a better low ratio...

[d2dave]

I run 33s on 4.12 and it revs under 2500 and is geared niced, your lucky to get Ashcroft diffs, locked and pegged as it cost me $6000 landed for both of my diffs last year but it's a killer setup

I did well then. Mine cost $3000 and included a brand new ARB compressor.

[Kaaaiju]

I did well then. Mine cost $3000 and included a brand new ARB compressor.

Yeah very good find, i will run 35s now with it