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A-Z of Gearing Problems Post & How to get it right after Changes


Hybrid_From_Hell

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Hi All,

I've been on LR4x4 now since 2005 when it started, and there is a subject matter that raises itself

over and over again, time and time again, come rain snow or sun - namely "Gearing".

As I have just spent some more considerable time tweaking mine and thus made changes I thought

maybe the time was right for an article to explain what happens to gearing, why, and how to fix

and what the options are to do it etc. This should give anyone interested enough knowledge to

not only make the changes with conviction and understanding, but also get exactly what your after

when the changes are done :) So, here goes ......

It goes like this - you buy your Std 90 / 110 / RR / Disco etc.... and love it. :)

You maybe get into off roading, and then find your Acme No-Hoper 205 x 16 ATs don't exactly "Cut It"

in the mud, what you need you decide are some Carlos Fandogo Mud Guzzler Mk7 Super F Mutnuts Gurglers

and in a much much bigger size,... and the lift kit, ...and winch bumper ,.... oh a big winch, ..erm..

and a highlift, ..maybe a cage, carry some spares, then a A Bar, some spots, some on the top of the

roll cage, and so it goes on......

So, ...do a mix of the above and you have :

Altered the gearing with the bigger tyres.the bigger the tyres the bigger the change in the

gearing (more later)...oh ...and you have added some weight, this also affects performance

.....your puzzled ?

OK think how your 4x4 behaves when you add a trailer and spares to sell maybe a sodbury, ? - it

'aint so lively now is it ?....Thats what weight does for you :rofl:

Ok, so lets look at gearing.

When your LR xxx left the factory the chaps there did some calculations.

These were around the gearing, and were based on a selection of things....

The engine

The wheel size

The Gearbox (Primary) Ratios

The Transfer Box ratios

The weight of the truck

The "Planned speeds"

Economy

Performance

Noise

Anticipated usage

A bit on these :

The engine

A V8 has a different power band and behaviour to say a 2.5 Naturally Gasping, so can take more

The wheel size

What the factory decided to fit can alter the characteristics, they took tyre size(s) into account

for the final outcome, that one reason there are so many Transfer box ratios out there :)

The Gearbox (Primary) Ratios

1st 2nd 3rd 4th 5th - different gearboxs have different ratios, and if you have different ratios

maybe you will need at the factory to tweak these to get your planned result - with different

TBox ratios ?. And also differing tyres sizes affect this too, getting a picture yet ?

On LT77s there are 2 differing ratios for the gearsets ! - make sure you know which yours is !

The Transfer Box ratios

More than you would think are out there, boxes go from near 1:1 ratio, to 1.667:1 ratio - a

VAST range this range was used often by the factory to get to the desired plan with mixing

with Primary boxes 1 2 3 4 5 gears etc and differing tyres sizes / model variants, its because

they did this that we have options to play with - more later

The weight of the truck

Think about your truck with and without loaded trailer - which goes better, actually to get it

to "Go" you have to use LOWER Gears this is key to this post "Under Geared" is a 4x4 that does

0-60 in 2 seconds, except the gearing is such it only gets to 42 mph in 5th :lol:

OVER Geared is the truck, with a selections of mismatched bits that is so over geared that in 5th

you'd be doing 200 mph in 5th at 2000 RPM :lol:

Extreme examples but easy to comprehend I hope.

The "Planned speeds"

The factory had targets, a committee sort of said, we want this to have a 0-60 of X, a top speed of Y,

and to cruise at ddd RPM and be doing say www MPH , bits were jiggled it was tested, did the above,

was built ... and left the factory all fresh and ready for the world....then it met you :lol:

Economy

Often was part of design processes, note that massively under geared and massively over geared BOTH will

be worse on fuel than std factory truck, Over geared cos you have to boot it non stop, under geared

cos its revving its nadggers off at 40 mph :D

Performance

You can almost prob answer this, over geared is flat as a Fa*t, under geared is screaming and making

you growl it won't "Go" faster, both are wrong, and both need fixing

Noise

Part of the planning, and here you can work out that a nice quiet refined purr at cruising could

easy = a dead as a dead thing in terms of 0-60 times, whereas a real strip burning lower geared truck

would equally make for a noisy screamy motorway wagon :(

Anticipated usage

RR = luxury, calm big powerful engine and kin heavy, different to say what might be viewed as a

Farmers laden 90, hence why they played about with the options, and thank gawd they did, or we

would be royally scr*wed" :lol:

Ok, so far so good ? :)

So, you have you 4x4, you love it, but you just wnat more, and the modding starts, on goes the cage,

the winch and winch bumper, some 35inch mud f***ers, a lift kit for the tyres, and more.

This makes the thing better in the mud, but golly gosh, its not anywhere as lively as it used to be :blink:

sort of 'feels dead', have to 'boot' it, 5th maybe is even now unusable, the slightest incline makes it

struggle, and whilst you love the new off road abilities the power is just not what is was, or what you

want, load it up with more weight and a long motorway trip sees gearbox changes like a Wimbledon player,

never used to be like this.....and if only ......

Well, it can, you have screwed the gearing and it weighs a load more, the above drivel is needed so

readers understand the exact reasons why things are now as they are, and then the routes to

solve become clearer :)

There are a number of routes you can take

Change to think back to standard :rofl: - Ok we will dismiss that :D

Change the 'transfer box' ratio.

Yep, a really good and maybe cheap option, but ALL LT230 boxes have the same LOW ratio amongst

all the options this means that changing the TBox will only alter its road manners,

off road will stay the same.

Ok an example,

You go from say a 1.2:1 Tbox to a 1.6:1, wow on the road it superb etc, but off road there will

be NO difference, consider off road driving, if you are going down a REALLY steep drop, its "1st low,

feet off everything" etc - Prob is if you have huge tyres now - and its over geared, the difference

will be the factory truck would be '1st low' but as you have screwed it then it might feel more like

'3rd low' :lol: - not good.

BUT - if you are a mainly ON road driver, then TBox may be the (cheaper) way to go, you just need to know

what to go shopping for, more later

BUT, if you do on and off road, then this 'aint gonna fix it, you need more, as you need to

change low and high ratios.

To do this you need to chnage Crown Wheels and Pinions at both ends.

The majority of modern LR4x4s have 3.54 ratios, Series had 4.7s, and early ones 4.88s, but there

are a range of after market ratios - 3.8:1,3.9:1 (rover Car) 4.1:1, 4.11:1, 4.75:1 etc, all having

the ability to change both High AND low box drive speeds :)

The other thing is you can change BOTH CWPs AND TBox Ratios, if need be, to get to what you want.

But. And a $1,000,000 Question - what IS what you want ? . You maybe know your not happy, but knowing

what you have is wrong is miles away from knowing what you need, for this you need to look at a

few things

My suggestion (and the route I took) is to 1st ask

  • WTF did my truck ACTUALLY do when it left the factory - at say 2500 RPM in top

and

  • WTF is it actaully doing now ???

which gives you the difference and maybe highlights the issue :D

Que my truck as an example, today saw a change of both CWPs, (more later), but to help

explain and give you the reader answers to you problem, lets use mine in a high speed learning curve

(no pun intended)

My Truck was a genuine V8 90

This meant that from the factory it had a

LT85, and a LT230 TBox, and 205 x 16 tyres

I have a spreadsheet built to do these calculations, it basically works out

rpm in upward steps, in all gearsand a RPM you can ask it to calculate speed - ie what speed

would I be doing at 2500 RPM in 5th (More later), and shows both HIGH and LOW Boxes speeds

So, with this program I Ran some calculations on a std V8 90 factory fresh, these are in a picture below :

Standard Factory gearing - 3.54 Diffs, LT85 Primary Box, 1.193 T Box 205 Tyres :

post-22-125949171141_thumb.jpg

So, I buy it and love it, as you'll see at 2500 RPM in 5th it does 64MPH :)

at 3000 it does in 5th 77 MPH, and you can see the low box and high box gears and RPMs and speeds

So, Mr Muppet ('Moi' :P:lol: ) goes and modificiddles it, out comes the 3.5 Carbed 120 BHP V8,

in goes a 250+ BHP JED 4.5 race engine :), and some bigger tyres too :blink: and on me 1st test

drive I was stunned Erm, and not in a good way, it was like a dead dog on a lead, but,

with near 100% BHP more why ?

Gearing

If we levae everything else the same and add into the calculator the fact the tyres are no not 205s

but 34.10.50x16s (or in new money) 280 x 85 x 16 ...the figures now looked like this :

post-22-125949174024_thumb.jpg

Ooops !

2500 RPM in 5th it did 64MPH - now it trying to do 82MPH !

and at 3000 it did in 5th 77 MPH - now erm - 98!, and at 4000 a

stunning 130 MPH :rofl: not going to happen. This is classic Overgearing

Actually 4th gear at 2500 now does 65 mph, close to the st 64 in 5th, BUT

and its a big but and I missed this 1st time round, 1 is not too bad, 2nd worse

3rd worse still, 4th oh gawd its leggy, and 5th useless, overgearing affects

the entire driving feeling in every gear, worse the higher the gear

So, lets say we wnat to fix this, we need now say 64/65 MPH in 5th HIGH ONLY

Lets play with transfer boxes, I have a 1.19, so what about a jump to say 1.4 ?

post-22-125949191774_thumb.jpg

BINGO !!! - 65 MPH again, everything back to normal, and job done :blink: in high range

look at low range still the same, if you an ON roader stop now, and Off Roader you need to

fix your Low as well :(

If that didn't work then theres a range of them from various LT320s :

1.003, 1.119, 1.22, 1.41, 1.667 a vast range !

So, pop TBox back to what you have now 1.19:1, and lets play with CWPs :D

We have 3.54, I could go 3.8, or 4.1, and indded when I 1st did this some while ago I did

go this route with 2x Ashcroft 4.11:1 CWPs, and pegged too for added strength, as I found

I "Blew" a large number of 3.54s (but more why later) and here would be the calcs I did at

that time, my tyres LT85, Std T Box which I had down as 1.22 and now 4.11:1s

To pics now

1st is what I thought I had - I THOUGHT I had a 1.22:1 Tbox, actually I didn't I had

a rare V8 90 special ( :( ) 1.119:1 Tbox, not much diffetrence you might think, but there was

and it cost me dear - more later - the point is you MUST be sure what you have when doing

the calcas, as the pics now will show :(

So, what I thought I had :

post-22-125949239745_thumb.jpg

Thats looked pretty good to me, 67 MPH at 2500, but a number of mistakes I made here, 64 vs 67

seemed good, almost spot on, but it is still technically over geared, ok not by much but second,

the truck weighed a F load more, 3rd the rolling Mass of the tyres is more

(think of a towing - you'd wnat LOWER Gearing than std if you did it every day, here was

me HIGHER than std :(

But so It was, Dave did me what I asked for 2 x 4.11:1s pegged and fitted and BOY what a transformation.

But

250 BHP, I always felt it should have been quicker, and recently I have learnt a LOT about ratios

and gearing so I paid the old spreadsheet calculator another visit.......

I then found I had done my calculations on thinking I had a 1.22 Tbox, didn't know the V8 90 had a

different one so the 1.119 Tbox my tyres and 4.11 actually said this :

post-22-125949259638_thumb.jpg

And that said the magical 67 MPH which was what I went for wasn't - it was 73 :(:rofl:

such is the minor tweak in gearing via 1.19 vs 1.22 T Boxes, and that was me prioblem.

So message make SURE you know what you have - go to

www.ashcroft-transmissions.co.uk , go to Transfer Boxes click on the pic at the base, go to tech Q,

and see a HUGER List that will give you either ref number to 4x4 of 4x4 to ratio you have, to find

your number get under you truck, rub the lowest point to the left of the Hand brake on the LHS digits

are stamped in, except on mine it was blank and I assumed wrong, early Tboxs and V8 ones are on the

LHS up near the F gearbox mounting - so do check !! - cost me dearly and thats just 1.19 vs 1.22 :(

Ok then, I now KNEW I had a 1.19, 280 tyres and a LT85, and it felt still a tad lardy, with the new

ashcroft 4.1s and pegged too,nothing had broken :D even with trying :P, so it was good news but not

great, the spreadsheet told it all, gearing was higher than factroy really, and I needed to tweak it.

Today I tweaked it, heres the Printout :)

post-22-12594927403_thumb.jpg

Now, I was looking for remember 64 uish Mph, on this its now 56 which look much lower, but now compare

at 3000 mph and remeber the effect of it gets worse as it goes up the rpm gear ranges ?

3000 RPNM Std 77 MPH, now with 4.75 and tyres its 67, go up more to 4000 and std is 103 and now would

be 89 MPH it would NEVER have done 103, that factory compromise, so lower gearing and a 250 BHP Motor

makes it go like a !Quite Quick Thing" :)

Hang on

103MPH ?...in a LR with simex, the areodynamics of a Bunglaow, and the handling of a p*ssed Pig on roll

skates carrying a climbing frame ?...not going to happen, well, not without full use of both lanes of a

dual carridgeway the use of the LHS Hedge, a nice paramedic with an abmulance and a policeman to maybe

also have a word as you come round in hospital :lol:

And thats my point, therory and practical use, I'll have me engine at 500+ RPM more at a sensible

cruising speed, I'll live with that, it might help conpensate for the add ons / weight etc (not me you

understand :P ), and hence why you should - you NEED to look behind the figures and think about the

end result...

The message, look at the speed your going to actually cruise at, tonight coming home I was running

around 2500 RPM shown via Megasquirt, and it fely beatuifull, boot it (in 5th) and you now KNOW thaere is

something under that bonnet, from 4.11 to 4.75 again minor tweak the difference is amazing, so think

long and hard before you commit.

Now I mentioned "strength" of gearing.

The 4.75 fitted today have been calculated to be 50% stonger than a std 3.54 - why I hear you ask ?

Well, one is the combo of the number of gear teeth and the pinion vs the crownwheel, the ratio

sort of dictates the sizes, so I took some pics to show, when / if you jump ratio, look at the CWP

you looking at how "Chunky" are the teeth, how big, Bigger teeth = stronger, heres the pic evidence :lol:

4.75 vs Land Rovers 'Offerings' :lol:

post-22-125949285498_thumb.jpg post-22-125949283786_thumb.jpg

post-22-125949282168_thumb.jpg post-22-125949288886_thumb.jpg

post-22-125949287294_thumb.jpg

As you can clearly see the thickness is MASSIVE. Pegging diffs does add even more strength,

but its tricky to do at the best of times, on these fat 4.75s its something next to impossible

as there is so little room to get in there. Aamazingly these have been modified and still retain the

pegging which meant modifying the insides of the casings to get cleances for the peg system...

and before you say "What a clever B*gger" ...diff building is beyond me (unless I wnat howling diffs :lol: )

...so huge respect to Steve at KAM Diffs who built these 'icckle bootifull' babys for me :) .

The result is I am chuffed as a chuffed thing, my error on Tbox for what seems a small amount cost me v dear

it was a whole load better with 4.1s vs 3.54s, hugely better , but not as good as it is now with 4.75 vs 4.1s

and the right Tbiox tyres added in and the clacs run, do you homework, think about the figures, look

BEHIND the numbers (103 in a 90 @ 4000 RPM when it (mine) will rev to 6250 ? - yes I'll take a tad lower

gearing thankyou sir :D:lol:)

Anyway, long long long post...... but hope it helps other understand Over and Under gearing and how to correct

the problems so many of us have when we add bigger tyres and a load of extra weigh :)

Nige

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I did ;)

Now, I was looking for remember 64 uish Mph, on this its now 56 which look much lower, but now compare at 3000 mph and remeber the effect of it gets worse as it goes up the rpm gear ranges ?

Seriously though, excellent article there Nige. Something everyone should at least look into. Is that spreadsheet available somewhere? I'm sure I've seen one somewhere in the past huh.gif

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You should have checked the tech archive Nige, there is a very similar calculator linked in there, and it also lists the 1.192 ratio LT230 for factory V8 90's.

Good informative post though, and glad you got the gearing you wanted in the end.

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I shoved the 4.1s from Dave at Ashcrofts in there a 'goodly number' of years ago, prob before the

article you mention was written :(, the 4.1s did transform it from the 3.54s, big time,

but the 4.75s have almost done the same again :)

2 extra things now for me to investigate - 1st the fuel consumption, will

be interesting to see (what) changes it may have made, and 2nd to maybe do

sopme remapping of the ECU Fuel Table to see if Megasquirt wants to tweak fuelling

map now the gearing has changed significantly :)

I'll report back in time on these 2 things !

Nige

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Good call on posting this - has been something I have had to consider many a time in the past. Nothing to do with me, but I recently stumbled upon this Land rover gearing calculator on the web that I have found really useful - thanks to Daniel Collins, who put it together as it seems acurate, and takes gearbox, transfer and tyre size into account:

http://www.solemnwarning.net/transmission/?

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Nice article there Nige,

Would changing from say 3.54:1 to 4.1:1 ratio make the halfshafts (assume standard) more or less likely to snap?

I assume they would effectively see more torque and therfore be more likely to fail but I would like to have this confirmed.

Pete.

Yes

4.1s from whover are stronger than OEM 3.54s, so with these fitted even less likely diffs will fail, and more

looking at Half shafts, partly as it won't now be the diffs as the likley candidate and also as you say

you have increased the torgue loads by dropping the gearing. But easily sorted if you don't have early 10 spline diffs.

Nige

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Nige, good write up.

One point regarding diff strength vs ratios. Generally speaking a lower ratio (ie higher number) will be weaker. Yes, a larger tooth will be stronger but, because they're bigger, the load is spread over fewer teeth. Therefore, what you need to look at is the total size of the contact patch and this goes down as ratio is lowered on pretty much all diffs. There are exceptions (like the Ford 9") but, generally, any increase in strength in lowering the gearing ratio will be as a result of using higher quality materials.

BTW, how do you find the gearing now while cruising?

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  • 3 weeks later...

Weeeeeeeeeeeeell

For the Megasquirt Crew :lol:

After using for work and back, re datalogging over the period, and remapping the VE to suit the changed gearing

its has both improved again in terms of tractorbility (not in a deep fat fryer sort of way :P ), and having driven to

and from work, which are all B roads and worse, and "Enjoying" the V8 I have seen a significant improvment in the fuel

consumption.

The last tank full was measured very very carefully and the mileage both known and calculated via satelite, Internet Route Calculators

and sat nav etc etc,

I have done the numbers tonight and although poor, all things considered its not bad at all takinmg into the account the above "Stylee".

Fuel consumtion worked out at 17.3 MPG, before it was 13.8, just shows what gearing changes can do :)

Thought it may be of interest, the VE map is just subtle changes, but changes none the less

:)

Nige

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Excellent write-up Nige.

As im one of many with a "bitsa" truck,and since i've not had the chance to drive mine on the public highway yet,im interested as to how my gearing is in terms of on-road use.

Ive a 3.9i, ZF 4-speed auto, BW t/box, Series 4.7 diffs and 265/75r16 tyres sat in a S3 109" pick-up with no other add-ons.

I dont expect the truck to perform like a standard Series(hence the engine change :D ) but from a rough guess i would have said the overall high-range to be something close to a 90 2.5TD........am i anywhere close?

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Thanks for the read Nige. Went through similar process with mine to see what to do, despite not changing the tyre size from standard. We changed the transfer box gearing as we only use low box in emergencies. I could still do with going lower as we rarely get into fifth on events and certainly never top out!

However I have taken into account that we always carry two spare diffs so the investment in a CWP set gets quite pricey when you have to double it!

... But you missed out on what those of us with a BW TBox should do (apart from putting in an LT230, not going to happen). Is it possibly to change the on-road gearing in these?

On the BW front - Tomcat Motorsport do a conversion to a lower ratio a new gear and chain. We have it in the racer. I don't think it is as quiet as standard, but is otherwise excellent!

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Good call on posting this - has been something I have had to consider many a time in the past. Nothing to do with me, but I recently stumbled upon this Land rover gearing calculator on the web that I have found really useful - thanks to Daniel Collins, who put it together as it seems acurate, and takes gearbox, transfer and tyre size into account:

http://www.solemnwar.../transmission/?

can someone advise me on what gearbox and transfer box i have? 99/00 td5 90 truck cab? i know its a r380 and a lt230 but what suffix?

also what are my diff ratios? 2005 110 4 pin 110 axles?

i have transfered this set up into my 110, want to know what size tyres to buy, gonna give the new BFG KM2's a go,to get me a better top end/cruising speed.

the td5 will be getting mapped and a hybrid turbo as they are poor off boost. want to get a larger tyre for ground clearance without over gearing.

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can someone advise me on what gearbox and transfer box i have? 99/00 td5 90 truck cab? i know its a r380 and a lt230 but what suffix?

also what are my diff ratios? 2005 110 4 pin 110 axles?

i have transfered this set up into my 110, want to know what size tyres to buy, gonna give the new BFG KM2's a go,to get me a better top end/cruising speed.

the td5 will be getting mapped and a hybrid turbo as they are poor off boost. want to get a larger tyre for ground clearance without over gearing.

Diffs, assuming factory spec, will be 3.54:1.

Defender transfer boxes are all currently 1.4:1 AFAIK

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thanks.

tyre sizes in inches anywhere?

Tyre sizes vary a little depending on manufacturer and tread type - as a guide I have recently measured a few -

cooper discoverer STT 235/85/16 are 31.5 inches - probably quite similar to the KM2 in size?

cooper discoverer STT 215/85/16 are 30.5 inches

205's are about 28.5

hope that helps

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The next common size up is 255/85R16 (just over 33inches) or a 285/75R16 (just under 33inches). The 255 section width is only available from a few manufacturers - luckily for you BFG Mud Terrains are one of them.

However a lot of people will go straight from a 235/85 to a 34 or 35 inch tyre, as this is what most other people are running around on, particularly for competitive off-roading and otherwise you just get hung up in all of their ruts. You'll need a ~2inch lift and probably want to consider lower (numerically higher) diff ratios once you start getting above 32inch diameter tyres; as the opening thread stated all T-cases have the same low ratio gears so you're starting to get a bit overgeared for hill descents otherwise.

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The next common size up is 255/85R16 (just over 33inches) or a 285/75R16 (just under 33inches). The 255 section width is only available from a few manufacturers - luckily for you BFG Mud Terrains are one of them.

However a lot of people will go straight from a 235/85 to a 34 or 35 inch tyre, as this is what most other people are running around on, particularly for competitive off-roading and otherwise you just get hung up in all of their ruts. You'll need a ~2inch lift and probably want to consider lower (numerically higher) diff ratios once you start getting above 32inch diameter tyres; as the opening thread stated all T-cases have the same low ratio gears so you're starting to get a bit overgeared for hill descents otherwise.

thats ok then. used the gearing calc on 33" tyres.So she'll be slightly under geared for towing and being loaded up.

this is a road biased 110 with miles in mind!

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  • 2 weeks later...

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