Best Diff Ratio

**d2dave** · 25th July 2021, 06:07 PM

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** · 25th July 2021, 06:12 PM

How are your tyres? Due for an upgrade yet?

**SPROVER** · 25th July 2021, 06:23 PM

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** · 25th July 2021, 06:29 PM

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.

Tightened it up and it's been good since.
Touch wood!

**d2dave** · 25th July 2021, 06:35 PM

Originally Posted by Vern

How are your tyres? Due for an upgrade yet?

Why do you ask?

**Vern** · 25th July 2021, 06:44 PM

Originally Posted by d2dave

Why do you ask?

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

**d2dave** · 25th July 2021, 06:45 PM

Originally Posted by 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.

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** · 25th July 2021, 06:51 PM

Originally Posted by Vern

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** · 25th July 2021, 07:09 PM

Originally Posted by d2dave

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.

**Slunnie** · 25th July 2021, 07:34 PM

Originally Posted by d2dave

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.

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