final drive

[Beef03]

Im sick of going 110 sitting at 2.5k so was thinking of swapping the diff for one with a lower ratio. I dont know much about transmissions and diffs so I got a couple questions.

If i swap the rear diff, I assume i gotta do the same for the front diff too for when its in 4wd, is that right or am i way off?

If anyones done a swap in the past, what ratio do u recommend to cruise comfortably but still have enough torque to get going?

Ive got a 04 zd30.

Thanks in advance

 

[Old.Tony]

What kind of revs do you want the engine to be doing at that speed? We might be able to calculate the ratio required.

And yes, you must change both diffs. Or all 4 tyres (larger tyres will achieve the same result).

Note that in either scenario, your speedo will become inaccurate. You'll need to use a GPS device to provide speed information.

 

[Rumpig]

Yeah both diffs need doing. Going up in tyre size is easier and cheaper.
Tacho usually over reads by 10% when compared to ecutalk so probably not doing 2500 rpm anyway.

 

[Beef03]

What kind of revs do you want the engine to be doing at that speed? We might be able to calculate the ratio required.

And yes, you must change both diffs. Or all 4 tyres (larger tyres will achieve the same result).

Note that in either scenario, your speedo will become inaccurate. You'll need to use a GPS device to provide speed information.

Ideally it’d be around 2k at 100 or a little above. Right now 2k gets me around 80 in 5th.
Ive got 31s on atm but can’t go much bigger without getting a body or suspension lift.
And yeah i’ve got a gps speedo so no need to worry about factory one.

 

[Old.Tony]

265/75R16 tyres? You'd need a diff ratio of 3.73:1 (FS5R30A gearbox, 265/75R16 tyres) to do 100km/h at 2,000rpm. This assumes a 5th gear ratio of 0.811:1 (per that gearbox if it's standard). There is a diff with a 3.692:1 ratio in some of the YD25s that would give you a cruise speed of 101.2km/h.

It's substantially different to yours. You'll notice that the car will be harder to move off at the start - with a higher overall ratio, 1st gear will be taller and require more clutch feathering to take off (D40 owners are familiar with this). You'll also notice the car will struggle on the hills earlier than it used to.

It's a change that I wouldn't make to my own car.

 

[Horatius]

Im sick of going 110 sitting at 2.5k s

Thanks in advance

110kph at 2500rpm? Would be happy with that lol, never seen a standard zd30 nav rev so low, more like 2900 rpm at that speed. That's the same as my old V8 holden used to do back in the day (somewhere around 2500 rpm at 100 kph).

I think whatever you do will be trying to make a silk purse out of a pigs ear and means you got the wrong car to begin with. Make these things rev lower for the freeway and they're going to be a lot more gutless. It's not as though they're over endowed with power to begin with.

The SR5 Hilux with auto trans will drop back to about 1800 rpm on the freeway at 110 kph. They have an excellent auto transmission though and are probably the best touring/tradie dual cab of the lot IMO (a different story if you're really going "off road" though where the unbreakable claim falls way short lol).

That would be a better way IMO, get something that's designed to rev lower, otherwise you might be disappointed. I could be wrong though (often am) and we each have different ideas of what we want a ute for and all that.

 

[tweak'e]

the zd30 is a bit of a slug off the line in stock form. so i would not change ratio's unless you modify the engine a bit.
my old 2.8 hilux does 3200rpm @ 100kmh so zd30 is kinda low rpm for me.