[adrock82]

Hey guys,
So I picked up this Sierra a couple of weeks ago and the guy had put 31" tyres on it but not touched the gears.
I'm just trying to figure out what that would have done to the current ratios, and what I would need to change to get it back to stock or better taking into consideration the bigger tyres.
I was out in it today and high range 1st is pretty much unusable on anything that goes up or down, and low 1st is barely cutting the mustard on anything that gets relatively steep.
Good for cruising on the highway though! Sitting on 110kp/h and only pulling about 3200rpm!

So two things I guess:
1. What is the calculation for an increase in tyre diameter against stock gears to figure out what its currently sitting at?
2. What would it take to get back to being "capable" offroad? (I'm not rock crawling or anything, mainly just bush tracks and beach to go camping, but at the moment its kinda useless).

Cheers,
Adam

[Blkfxx]

http://tireconvert.com/

[bumstein]

Either 4.9 reduction gears in the transfer (although can go lower but you'll raise your revs on 110kph even more). You'd likely be able to get away with 4.16 too if you sourced some.

Or a 1ltr transfer case. 4.9's will lower your low range more than 1lt gearing, will also be closer to stock gearing in high. But either will make an improvement and 1ltr cases can be found for not heaps of money.

[adrock82]

Thanks bumstein,
Someone told me about the 1.0 case but also said they are near impossible to find. haha

In terms of a set of 4.9 transfer gears, is there anywhere in Aus for these or does everyone get from the states? I see them on lowrangeoffroad or rocky-road.com but nothing is Aus seems to come up when searching.

[Gwagensteve]

Your tyres are circa 18% taller than factory.
6.5 transfer gears offer 17% reduction in high range.

That takes care for high range.

Some people find 6.5 too low for 31's off road. You definitely won't need to use 1st low much.
IMHO 1.0 transfer isn't low enough off road for 31's unless you only drive on the beach.
4.9's are probably ideal. road revs will be al little lower than standard but it should be reasonable. Offroad will be fine.

Lowrange offroad is the preferred source. Local sources aren't competitive because they still pay shipping and add their own margin.

[adrock82]

Gwagensteve wrote:

Some people find 6.5 too low for 31's off road. You definitely won't need to use 1st low much.

Quote:

That's what I was thinking... I won't be driving anything extreme so reckon 6.5 would be overkill.