4.6 diff versus 4.3

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Originally Posted by dom14

2.8GU came with 4.6 diff(and some may be 4.3) 4.8 crown wheel and pinion is an after market Italian import, according to the internet. Yes, AFAIK, 2.8GU diff is H233B, which is a straight swap for GQs. I'm not sure the exact amount of lift on mine. I have take a guess and can say it's above 2". You get the engine braking by switching from higher to a lower gear than suitable for particular speed and revs go high as a result, while car slows down. I'm not sure what you meant by engine braking not happening until 2500/3000rpm.

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Sounds like he is saying the car runs on going down hill with the 35' rubber compared to the 31'

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Originally Posted by liftlid

Sounds like he is saying the car runs on going down hill with the 35' rubber compared to the 31'

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Pretty much this.. It's hard to explain, but take your car down a long steep hill and stop. put it in first and just let it roll down. You'll find you'll roll to a certain speed, and then generally the engine will start to hold the speed. In diesels, this is generally pretty low, in my rb30, this is generally 2500-3000rpm. This of course varies with how steep the hill is. Having 35's on as opposed to 31's means that the speed I am doing in this rev range is increased, and hence steep descent's on rough terrain can mean some brake/clutch work.

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Originally Posted by Throbbinhood

Pretty much this.. It's hard to explain, but take your car down a long steep hill and stop. put it in first and just let it roll down. You'll find you'll roll to a certain speed, and then generally the engine will start to hold the speed. In diesels, this is generally pretty low, in my rb30, this is generally 2500-3000rpm. This of course varies with how steep the hill is. Having 35's on as opposed to 31's means that the speed I am doing in this rev range is increased, and hence steep descent's on rough terrain can mean some brake/clutch work.

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Yeah, I think I understand what you are trying to explain. You get less of an engine brake with 35" than with 31" on a given gear and steep angle down a hill. I think the reason is 35" goes further on the ground per turn of the wheel than 31", making the engine braking slightly less effective.

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Originally Posted by liftlid

Sounds like he is saying the car runs on going down hill with the 35' rubber compared to the 31'

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Yeah, I'm experiencing the same thing in a different degree when I switched from 225/75 R16 to 235/85 R16 for highway driving. So, I do understand it now. :)

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Originally Posted by dom14

Yeah, I think I understand what you are trying to explain. You get less of an engine brake with 35" than with 31" on a given gear and steep angle down a hill. I think the reason is 35" goes further on the ground per turn of the wheel than 31", making the engine braking slightly less effective.

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Correct..

RB30, 1st Gear, Std Low Range @ 2500rpm

Diff Ratio	Tire Size	Speed (km/h)
4.375	31	12.63
4.375	35	14.26
4.625	31	11.95
4.625	35	13.49
4.880	31	11.32
4.880	35	12.79
5.130	31	10.77
5.130	35	12.16

RB30, 1st Gear, 43% Reduction Low Range @ 2500rpm

Diff Ratio	Tire Size	Speed (km/h)
4.375	31	8.92
4.375	35	10.07
4.625	31	8.44
4.625	35	9.53
4.880	31	8.00
4.880	35	9.03
5.130	31	7.61
5.130	35	8.59

Engine braking sucks in an rb30 anyway. Bolt the 35's on, and go from there ;)

35's mean you will notice decreased perfromance with your braking as well.

Larger tyres mean a greater pedal effort for the same amount of deceleration.

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Originally Posted by Throbbinhood

Engine braking sucks in an rb30 anyway. Bolt the 35's on, and go from there ;)

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It wasn't that bad with 225/75 R16(29 inch diameter), but of course 29" is way too small for a GQ. :)

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Originally Posted by the evil twin

35's mean you will notice decreased perfromance with your braking as well.

Larger tyres mean a greater pedal effort for the same amount of deceleration.

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Absolutely! I'm already experiencing that with by switching from 29" to 32" tyres.
I originally thought, 'cos larger diameter tyres get a slightly more grip from slight increase on tyre to road grip surface area, so better braking.
But, that's not the case.