What gear Ratio to use for a 35inch tyre

I have a 300dti 90 Defender and I put on 35inch tyres. As you can understand I lack of power especially in hill climbing. I want to change the differential ratio in order to come back to the original ratios but this time with the 35inch tyre. What ratio I should use???

You could always change your transfer box, you should probably have a 1.4 version, but you could fit a 1.6 option (think they are fitted to some 110/130s?

If you look on the ashcroft website, they have a gear ratio thingy where you put in details like tyre size, gearbox, diffs etc and it tells you how far out your ratios are. Have a play on that and change options round to work out the best for you.

Ashcroft Transmissions - Ratio Calculator

Can I use the Crown Wheel & Pinion of a series Land Rover (Ratio 4.7:1) on defender differential? The goal is to increase the ratio on my defender. What do you suggest?

Check yer engine - it should cope fine with the standard ratios! Summat else is wrong which you won't sort by changing the ratios. It should be at optimum efficiency on 33+ wheels in the UK (the air's lovely and cold!)

valent1n0s said:

Can I use the Crown Wheel & Pinion of a series Land Rover (Ratio 4.7:1) on defender differential? The goal is to increase the ratio on my defender. What do you suggest?

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you can use 4.7 crown wheel and pinion but you have to use 4.7 dif carrier as well or spacer plate in between otherwise crown wheel wont reach pinion

4.7 from 3.5 is at teast 30%, reduction more than tyres would make other way 4.1 crown wheel pinion would be better

Measure the actual tyre size aswell because many 35 inch tyres come up small. A good 300 should be fine with a 1.4:1 tranny box. Before you go swapping stuff consider that 4.7 ratio diffs are weaker the crown wheels are more prone to breaking than 3.5's.

I have 37 inch tyres on 4.7:1 diffs. 1.00:1 Transfer box. The ratios are now sweet. its taken some yime but I'm happy now it will sit at 70-75mph without revving its tits off but still drivable and low range is useable once again.

The axles: Rear is a Salisbury almost bullet proof ish being a hypoid diff and a huge 4 pin centre and gears its far stronger than a rover item. Front is a std 10 spline late (circlip cross pin) series diff. I do have a 4 pin centre however I am running the early 90 CV's and want the strongest setup at a reasonable cost so as soon as I can afford a set of ashcroft front shafts I will have a pretty strong 4 pin centres front and rear. Will also transfer my detroit locker from my old Salisbury 3.5 diff time permitting.

as jai said check actual tyre size
on the left is my 35" simex and on the right is the silverstone extreme 35" it actually measured nearly 33"
the 200 tdi and the 300tdi both had no problems with this size tyre

a fender aint the quickest thing in the world to start with