4WD Diff ratios?

[Rhod]

Another take on the 4Wd ttyre size debate....
I took the Bongo to a new garage for it's MOT this week (failed on a worn wishbone joint, but not the testers fault!). The owner runs a 4WD Bongo himself & has kept the standard 195/215, whereas mine has recently changed to 215s all round in the interests of interchangeability. Anyway, in the course of discussion he mentioned that he'd heard that the front & rear diffs have different ratios to take account of the slight difference in the standard tyre circumference & that running the same tyre size all round might actually cause more wind-up problems. I hadn't heard this theory before & wondered if anyone knows what the diff ratios actualy are?

[brorabongo]

I thought that although you may be using difference sizes front and back, at the end of the day you still have the same rolling radius? different side wall ratios?

I've been 215's all round for over two years now and get near 30,000 miles to my tyres, and have never had any problems. Before when on original sizes, ( 195 front, 215 rear) I was only getting 10,000 miles IF LUCKY out of my fronts. So I know what I'm sticking with......for now anyway.

[teenmal]

Another take on the 4Wd ttyre size debate....
I took the Bongo to a new garage for it's MOT this week (failed on a worn wishbone joint, but not the testers fault!). The owner runs a 4WD Bongo himself & has kept the standard 195/215, whereas mine has recently changed to 215s all round in the interests of interchangeability. Anyway, in the course of discussion he mentioned that he'd heard that the front & rear diffs have different ratios to take account of the slight difference in the standard tyre circumference & that running the same tyre size all round might actually cause more wind-up problems. I hadn't heard this theory before & wondered if anyone knows what the diff ratios actualy are?

Hi Rhod,

Don't know the actual ratios,...the part numbers for the crown wheel and pinion and planetary gears are the same for front and rear diffs.It would appear that the diff ratios are the same.

PS did he mention anything about the transfer box?


Cheers Mal..

[dandywarhol]

The different ratios are what the Freelander uses Rhod - to give the same effect as the different tyre sizes on the Bongo.

The different shaft speeds allow the 4WD system to be "Full Time" by allowing the silicon gel to drive both shafts. Unfortunately the system is designed to eventually fail and it's life can be prolonged by fitting the same sized tyres all round but then technically the system isn't then "Full time" - but so what?

[Rhod]

Dandy - thanks. That's what I though the Bongo spec was, but couldn't find the diff ratios to check. Just curious really since the Bongo handles at least as well on the 215s all round & I plan on keeping that configuration.