Question for those that understand and know
Im having a new TX box built currently with the std Defender 1.4 ratio as it was suggested that a Disco 1.2 ratio would overgear my 110 too much due to the tyre size (285/75/16) which isnt changing)
So would a 1.3 be a happy middle? Not a "slow" as a 1.4 but not overgearing it too much with the 1.2.
Any insights?
I can't give you an exact answer, but I can impart some experience and views on it.
First up, looks like you have a Td5? What sort of power are you pushing?
Do you tow much?
What is your driving style? i.e. do you like acceleration or are you more of a plodder?
What types of roads/speeds do you drive at a lot?
Overall the 1.4:1 works pretty well at most things. Your bigger tyres will already have lowered your cruising rpm for a given speed too.
A 1.2 will generally blunt performance, less peppy. But should in theory allow lower cruising rpm.
Some issues you may encounter.
1st gear will feel taller when pulling away. You'll notice this at junctions and round abouts and you will feel like you need more revs and more clutch slip to get away quickly. If you tow, you may find this even more of an issue.
5th gear, the taller transfer ratio means 5th is a lot higher. A Tdi vehicle on large tyres will struggle to maintain speed on hilly roads and will often have to downshift to 4th, where with the 1.4 box you wouldn't. With a Td5 this should be less of an issue, but it will depend how heavy the vehicle is, a caged 110 weighs a lot more than a pick up 90 for instance. And what state of tune you have and if mapped, what sort of map, as some can produce high EGT's under load.
You'll also find the 1.2 transfer box and tyres the size you have, that 5th gear really only is useful at 50mph+, and 4th will be nearer to 40mph. Meaning if you do a lot of 30mph roads, you'll be in 3rd gear a lot more often.
The taller 5th gear in the R380 will likely be too tall with the 1.2, so is for the 1.4 transfer box only. It'll give you similar mph/1000rpm in 5th as the 1.2 box with a stock 5th gear. A friend has this in his overland Defender 90. By and large it works well on motorways. Although when he was Tdi powered it did impact towing and he ended up in 4th gear a lot with the caravan behind him. He now has a heavily tuned Td5 engine and it pulls it a lot better.
When out laning, we often trundle about at 50'ish mph on the roads. He ends up using 4th a lot, a bit like with the 1.2, you probably need 50mph+ to really make use of 5th. But when he went down to Morroco it was very good for cruising at near 80mph on the French motorways.
So maybe the 1.3 is the sweet spot, apart from knowing Ashcroft is offering these, I don't know anyone with them.
There are over drives you could consider also, not cheap, but another option. For a peppy country lane setup I wonder if a 1.6 with an over drive would be the way to go. The Td5 revs quite well. This is certainly what I'd want for a V8 setup. But then I'm less fussed about high speed running in a Land Rover and will normally be content to sit at 65mph.
I do say this all as somewhat of a hypocrite. As I have a 1.2 box on a Lt-77 vehicle currently shod on 285/75R16 tyres...... and it goes a lot better than I think it should. So well that I have no intentions of changing the gearing at all on it. It does suffer the points I mentioned above, i.e. 3rd gear for 30mph and 1st it taller pulling away. But overall I like how it goes.
