Lets talk about ring & pinion gears

[tinker trek]

How many of you have changed your gears from stock.

I have a 96 Discovery with 245/75R/16 tires & stock 3.54 gears.
I think that is stock?....Anyway I live in Colorado and going up passes
in the mountains is a joke!

I'm running 2250 RPM's at 65 mph.(4 speed automatic transmission)
Most people I read about are changing to 4.11 gears?

I can't see how this is enough of a change? From what I can tell it would
seem that going to 4.75 gears would be better?

note: 4.11 & 4.75 are the gears available for the Discovery that I know of.

I'm going off this chart
http://therangerstation.com/tech_library/gearandtirechart.html

Please if you have changed out your stock gears I'd love to hear your opinions on this.

Thanks.

 

[Alaska Mike]

I think with 245s (essentially a 31" tire), you're likely to be overgeared with 4.75s. If you went with a larger tire, say 33", you could probably make use of that extra gearing. If you retain your current tire size, I'd run with the 4.11s.

On my project Rover, I'm actually going with 3.54s and a 31" tire initially. Since the plan is long-distance travel and I have a 4 speed manual transmission (no overdrive) and my final ratio is 1:1 to the axles, I expect that my RPMs will be on the low side. We'll see how it works.

I'd also make sure the engine is running properly and all tune-up related items are done.

 

[tinker trek]

I'd also make sure the engine is running properly and all tune-up related items are done.

She's purring like a kitten...other than the lovely ticking..
(not sure it's a lifter, may be a exhaust leak?)

126k miles on it, maintenance up to date since I've had it.
(I've only had it for 6 months)

Anyway going up steep grades & at altitude 8k feet and up just wipe it out
kills it when loaded down with camping gear.
When I bought it it still had stock 235/70/16 tires & wasn't much better then.

 

[proper4wd]

The ticking you are referring to is most likely a rocker shaft. They do that- nothing to be worried about.

at 126k your motor is starting to get tired, I would say the money invested in regearing would be better invested in freshening up and waking up the motor a little. A fresh valve job, get all the carbon out of it (you will be amazed what it looks like in there), and maybe a cam and some light head work. Start reading the web about Rover V8 upgrades. Theres a lot you can do.

That motor was rated at 188hp IIRC from the factory, even with 4.11 gears theres only so much you can do! In the meantime just downshift the tranny. Tightening up the kickdown cable helps a lot too! Fuel mileage goes way down though...

 

[DiscoveryXD]

I'm running 4.11's now, with 33's, and a new 4.6.

The gears do make a big difference when climbing hills, and the truck is definitly "zippier" going around town.

It's hard to say though cause you're at twice the elevation I am!

 

[TeriAnn]

<<QUOTED OUT OF SEQUENCE>>

Hint - Never think of a ratio by itself. Always think of it as part of a group of ratios that combine into an overall ratio.

note: 4.11 & 4.75 are the gears available for the Discovery that I know of.

NOTE: This information if for pre Disco II LRs only

3.54:1 = Standard pre Disco II coiler ratio
4.7:1 = standard Series ratio
4.75:1 = Aftermarket ratio that is much stronger than stock 4.7:1 gear set
4.1:1 = Aftermarket ratio designed for coilers.

4.7:1 R&P requires the use of a spacer plate when used in the coiler diffs, ARB & Detroit diffs.

Q: Are series & Coilers geared that differently?

A: Calculated at the axle, A Series with an overdrive is geared just a little lower than a 5 speed coiler. The Series has a lower ratio in the transfercase and a higher ratio at the R&P. A Coiler has a higher ratio in the transfercase and a lower ratio in the R&P.

An interesting difference between Series and coiler transfercases is that Series has a single high range ratio across all the versions and the low range ratio differs. Whereas coiler transfercases have a single low range ratio and the high range ratio differs amongst the models. An obvious way to set up a coiler gear set would be to pick the ring & pinion gear set for the low range first gear that you want then pick the version of LT230 for the high range top gear that works best in your terrain, altitude & desired speed.

LT230 high range ratios:

1.00:1 - early range Rover
1.22:1 - V8 Discovery
1.41:1 - models with 300 tdi & V8 D110
1.67:1 - Early Defenders (Ninety & One Ten) fitted with 2.5 LR diesel (pre-tdi)

I'm running 2250 RPM's at 65 mph.(4 speed automatic transmission)
Most people I read about are changing to 4.11 gears?

I can't see how this is enough of a change? From what I can tell it would
seem that going to 4.75 gears would be better?

Sounds like one of my rules to live by: If a little is good then more is better and too much is almost about right.

I don't know anything about slush box ratios or if Rover put a different ratio LT230 behind a slush box than behind a gearbox. So any numbers I provide will be for a five speed gearbox & V8 Disco LT230 unless stated otherwise.

Another thing to note is that on a five speed gearbox, fourth gear is 1:1 and fifth gear is an overdrive gear. I assume that for a four speed slush box, third gear is as close to 1:1 as it gets and 4th is an overdrive ratio. Most everyone I know shifts out of overdrive while driving up hill. The overdrive is for levelish highway driving fuel economy. You do drive up hills in third high range don't you?

A Discovery I with gearbox and V8 has a combined overall ratio of 0.8906:1 measured at the transfercase output shaft.

In fifth (overdrive) gear high range that gives:

With 3.54 R&P, 3.15:1 overall measured at the axle
With 4.1:1, 3.65:1 at the axle
With 4.75 (aftermarket), 4.23:1 at the axle

With 31 inch dia tyres, this calculates out to:

3.54 - 2221 RPM @ 65 MPH
4.1 - 2573 RPM
4.75 - 2980 RPM Overdrive highway economy cruise ratios

In fourth gear (1:1) you have a overall ratio at the prop shaft of 1.21:1. So with 31 inch dia tyres you have:

3.54 - 3018 RPM @ 65 MPH
4.1 - 3495 RPM
4.75 - 4049 RPM 1:1 non overdrive high gear ratios

Please note that overdrive gear & a 4.75:1 R&P will give you very close to the ratio of fourth gear (non overdrive top gear) with the stock 3.54 R&P. So a 4.74:1 R&P basically shifts all you gear ratios down one. You can achieve the almost identical ratio just by shifting into fourth gear.

Like I mentioned previously I don't know anything about slush boxes but I suspect that the slush third gear ratio is closer to that of a 4th gear on a gearbox, and that slushbox fourth has a similar ratio to a gearbox's overdrive 5th gear.

In conclusion going from a 3.54 R&P to a 4.75:1 is the basically same as down shifting one gear. Great if you need a lower low range first but pretty useless in high range.

Going from 3.54:1 to 4.1:1 is basically the same as down shifting half a gear ratio. I suspect it was developed for people putting 35 inch dia tyres on their Defenders but it could be useful if you are constantly finding top gear too high and the next lowest gear too low for your driving. Such as taller tyres and high altitude.

Try driving the mountains in third gear & see if it works for you. If the revs are too high maybe a 4.1 R&P would be best for you. If stock third gear works for you, save your money for a pretty black out bonnet decal or something.

 

[tinker trek]

The ticking you are referring to is most likely a rocker shaft. They do that- nothing to be worried about.

at 126k your motor is starting to get tired, I would say the money invested in regearing would be better invested in freshening up and waking up the motor a little. A fresh valve job, get all the carbon out of it (you will be amazed what it looks like in there), and maybe a cam and some light head work. Start reading the web about Rover V8 upgrades. Theres a lot you can do.

That motor was rated at 188hp IIRC from the factory, even with 4.11 gears theres only so much you can do! In the meantime just downshift the tranny. Tightening up the kickdown cable helps a lot too! Fuel mileage goes way down though...

These pionts are well received...

I'm marreid & it may be easier to "sneak" these gears in now....The engine work can always be a "must do" later...LOL

Thanks for the replies so far!

 

[tinker trek]

Going from 3.54:1 to 4.1:1 is basically the same as down shifting half a gear ratio. I suspect it was developed for people putting 35 inch dia tyres on their Defenders but it could be useful if you are constantly finding top gear too high and the next lowest gear too low for your driving. Such as taller tyres and high altitude.

Try driving the mountains in third gear & see if it works for you. If the revs are too high maybe a 4.1 R&P would be best for you. If stock third gear works for you, save your money for a pretty black out bonnet decal or something.

Before I put the 245 tires on, this is what I was running into 4th was way to high and third was running my rpm's up to high.

I need to take it up to the mountains & play with it fully loaded again
maybe I can get a better feel for what gearing to choose?
I'm willing to give up open highway performance (mpg) for better performance
on inclines at altitude.

 

[UnfrozenCaveman]

Greetings...

152k mile '94 Disco here....automatic and 235/85's.

It was barely acceptiboe here at under 1,000' altitude with the 3.54's.

With the 4.10's it's just "okay", though a little busy at highway speeds.

Now, just for the sake of confusion.....have you considered changing the Hi-range transfer case gear rather than swapping diff gears?

Seems that the change from 1.22 to 1.4 might be just about right if you're only going to put 245/75's on it????


KAA

 

[tinker trek]

Greetings...

152k mile '94 Disco here....automatic and 235/85's.

It was barely acceptiboe here at under 1,000' altitude with the 3.54's.

With the 4.10's it's just "okay", though a little busy at highway speeds.

Now, just for the sake of confusion.....have you considered changing the Hi-range transfer case gear rather than swapping diff gears?

Seems that the change from 1.22 to 1.4 might be just about right if you're only going to put 245/75's on it????


KAA

monkeyboy, Do you happen to know off hand what your rpm's are at 65mph?
Aren't 235/85's & 245/75's about the same dia.

If you were to do it over would you have gone with 4.75 gears?

 

[Yorker]

it is pretty simple to figure out the RPMs at any given speed

The ZF4HP22 Transmission's ratios are:
4th: .728:1
3rd: 1.000:1
2nd: 1.480:1
1st 2.480:1
Reverse 2.086:1

High Range ratio on the LT-230 is 1.222:1


If you want to simplify things in high range you can simply multiply the ring and pinion ratio by 1.22 in order to get a figure that would work for comparison to other vehicles(which generally always have 1:1 high range ratio)



Thus if you were to compare to a Jeep or Other vehicle your R+P ratio is effectively a 4.31 right now, switchig to 4.1R+P is like another vehicle with 5.00, 4.7 R+P is the same as 5.76 R+Ps.

Before you consider changing the Rings and pinions I'd make sure your kick down cable is correctly adjusted, and that your engine is properly tuned.

--------------------------

Using the #s for your truck right now I get
with 3.54's: 2215 rpm @ 65mph (in OD)
with 4.11's: 2571 rpm
with 4.7's: 2940 rpm

Try using this calculator to figure your gearing options:
http://www.4lo.com/calc/gearratio.htm

 

[michaelgroves]

In conclusion going from a 3.54 R&P to a 4.75:1 is the basically same as down shifting one gear. Great if you need a lower low range first but pretty useless in high range.

Going from 3.54:1 to 4.1:1 is basically the same as down shifting half a gear ratio. I suspect it was developed for people putting 35 inch dia tyres on their Defenders but it could be useful if you are constantly finding top gear too high and the next lowest gear too low for your driving. Such as taller tyres and high altitude.

Although it's true that changing a diff ratio (or a tyre diameter) is arithmetically much the same as just travelling in a lower (or higher) gear, you also should remember that it effectively might make your gears too far apart (or too close together).

It depends why you're making the change. If it is, as TeriAnn referred to, a compensation for bigger tyres, then of course well-chosen a lower diff ratio will put every gear back to where it should be. But if it's to compensate for lack of power, or heavy loads, (or the other way, to prevent over-revving), then you run the risk of making the vehicle much less driveable. (Gearing can compensate for torque problems, but not power problems).

As an example, if you felt your truck was revving too high in top gear when you travel at your most comfortable cruising speed, you might decide to go for bigger diameter tyres, or higher ratio diffs. This is all very well, but the higher overall ratio will apply in all your gears. If you've raised the ratios by, say, 25%, what you might find is this (based loosely on Discovery gearbox ratios):

With the old gearing @ 2500 rpm:
1st: 29 km/h
2nd: 50 km/h
3rd: 77 km/h
4th: 107 km/h
5th: 140 km/h

With the new gearing @2500 rpm
1st: 36 km/h
2nd: 63 km/h
3rd: 96 km/h
4th: 134 km/h
5th: 174 km/h

The problem is that your gears are now all spaced further apart from each other. 5th gear is more ideal than it used to be at around 140 km/h, because the engine is revving a lot more slowly, but you probably won't have the power (or the road handling) to use the extra 34 theoretical km/h from the engine. So what you have now is effectively a 4-speed gearbox instead of a 5-speed 'box, with bigger absolute differences in road speed between each gear. Each gear change takes the engine much further from its ideal 2500 rpm, than it used to.

 

[proper4wd]

I do also want to point out that you should not be afraid of revving this motor too high in 3rd gear. The rev limiter kicks in at around 5200, but with minor tweaks to the bottom end these engines are regularly run to 7000 (at least the 4.0 variety). They are short stroke, small displacement V8s with a cross bolted bottom end, dont be afraid to touch 4500rpm! In my experience, the ones that get run harder like that don't have as many problems. Its the grandma-driven ones that have stuck valves, blown gaskets, etc. Strange but true.

 

[TeriAnn]

The ZFHP22 Transmission's ratios are:
4th: .728:1
3rd: 1.000:1
2nd:1.480:1
1st1.480:1
Reverse 2.086:1

Are the ratios for first and second gears correct? Also what years & models LR & RR used this box?


Thanks

 

[michaels]

my RPM's are 2,000 with 255/85/16s and a 4.6 at 65 MPH