Big Tyres. Gearing and Economy

[mrapocalypse]

I've got a DII V8. Needs new tyres, currently running 265/70/r16 Cooper STs. I already have noticably taller gearing, speedo error is at about 8% and I feel the slight loss of torque! It's hard to know with the V8 whether the ecomony is affected because i can't help driving it like it's stolen.....

I want to go up a size to 265/75/R16... small difference yes but noticable I'm sure! It will probably be MTRS.

THE QUESTION....
Do I need to drop the diff gearing or can I just get lower low range and keep the cruising speed of the taller diametre tyres. Are there really any benefits in having the taller gearing at the diffs. I mean does it take more fuel to turn those tyres anyway???

I think with lower geared Low range and standard diffs I'm going to suffer anyway right???

[walker]

If you change the Diff ratio to 4.11's than you will be overgeared as 4.11's are about right for 33's and it will rev too high when cruising on highways.

Another option is to put in a Defender transfer case which will improve your gearing but I can never remember if it improves it in high range or low range. If it is in high range then I reckon this would be your best option.

Whatever you do, if you decide to change gearing, it is going to cost you a fair bit.

There are a lot of people running 265/75's without changing the gearing at all.

[HSV Rangie]

all LT 230 t/cases have same L/range.

high ranges are different.

Michael.

[walker]

Ok, thanks.

And you will burn more fuel with 32" tyres. On the V8 I found a difference of at least 2litres/100km.
Really the Disco still has a pretty good low range even with 32's and I would try to lower the high range to get better fuel economy. I know you cna do a Transfer case swap for a few $$$.

[Loanrangie]

The difference between 265/75/16 and 265/70/16 is just over 13mm in tyre height.

[Mick G]

Depends how you want it to drive really. I have a manual TD5 D2 and when I changed to 265/75R16 muds there was a noticible difference in low range gearing......1st low range would move along way too fast for the sort of off road driving I do and intended to do. Normal road driving was just acceptable although very sluggish off the lights.
As my car is set up prodominantly for off road driving I decided to fit maxi drive 4.11 diff gears which was a massive improvement to the already good low range greaing. As walker says, the 4.11's maintain original gearing with a 33"tyre, but I find the gearing perfect for the 32" tyres as it give great low range crawlability and to be honest I don't notice any difference or over reving with highway drving over standard D2 tyres and gearing.
I did however fit a speedo correction unit for peace of mind - Truspeed - which allows you to run 2 sets of different diametre tyres and simply flick a switch on the unit - again depends if you want to accurately know how fast you are going - I do.
Anyway, depends how you drive it and what you intend to use the car for but I can highly recommend the 4.11's if you like low and slow stuff but as mentioned, they will set you backa few $.......plus you may as well consider lockers while the diffs are in pieces

[mrapocalypse]

Interesting. So even though you get taller gearing on the highwy you chew more fuel because the torque has suffered.

And all Tcases have the same low ratio it's just the high that's different!

I'll need to have a rethink. Can't afford Maxis!

Thanks guys.

ian

[Slunnie]

I found with my TD5 that when I changed to 33's with standard geears that the town economy became worse, but highway improved. Then when I changed the tyres to a mud pattern that the economy dropped off. So in my opinion it's more the tread pattern that normally comes with a bigger tyre that causes the uel economy problems, rather than the tyre size itself. I then changed to 4.11's and it didn't really improve economy, but it did reduce fluctuations in the economy.

[Micka]

I think the Defender LT230 is geared differently in both high and low range to a D2 disco.

Fender in 2003 was: 3.320/1.411:1 low/high
D2 in 2003 was: 3.269/1.211:1 low/high

The BIGGEST difference between the Defender and D2 though is in the gearbox.

Fender in 2003: 1st gear 3.692:1
D2 in 2003(ZF): 1st gear 2.480:1

Fender ends up with 43.4:1 crawl ratio
D2 ends up with 28.7:1 crawl ratio

Just buy a Fender

[Slunnie]

You're comparing an auto to manual gearbox though. What is the first gear ratio for the Disco manual?

[ashtrans]

I think the Defender LT230 is geared differently in both high and low range to a D2 disco.

Fender in 2003 was: 3.320/1.411:1 low/high
D2 in 2003 was: 3.269/1.211:1 low/high

The BIGGEST difference between the Defender and D2 though is in the gearbox.

Fender in 2003: 1st gear 3.692:1
D2 in 2003(ZF): 1st gear 2.480:1

Fender ends up with 43.4:1 crawl ratio
D2 ends up with 28.7:1 crawl ratio

Just buy a Fender

Hi,

as said earlier the low ratio in ALL STOCK LT230 boxes is the same 3.321, the difference in the 1st gear ratios comes from the fact you are comparing a manual to an auto,

the cheapest way to drop the high range from disco 1.222 to defender 1.410 (about 15% drop) is to just but a gear kit, you need :

FTC5089
IEH000120
FTC1741

we sell this kit for £ 200, carriage about £ 90 to you but you may be able to source locally,

[ashtrans]

You're comparing an auto to manual gearbox though. What is the first gear ratio for the Disco manual?

the diesel manual boxes are the same ratio in the disco and the defenders

[Reddo]

Does the gear kit drop the low range too???

Excuse my ignorance, but not sure where the kit fits

If not, then 4.11s seem better option and certainly fixed our Disco on road and gave great off-road improvement to the gearing.

[Loanrangie]

Does the gear kit drop the low range too???

Excuse my ignorance, but not sure where the kit fits

If not, then 4.11s seem better option and certainly fixed our Disco on road and gave great off-road improvement to the gearing.

The kit is basically replacing the high range gear set form a defender into a disco/ rangie lt230, low rangie is not effected. If you will be running larger tyres permanently then the 4.11's would be better overall if not more expensive.

[Aquarangie]

I run 255/85R16 BFG muddies and have notice it does roll alongh a bit more off-road, especially since I have an auto and stock 3.54 ratios.

Highway I find it isn't too bad really, it hates the hills and will kick back to 3rd gear more often thasn it did with the 31's on. Despite that, I am more than happy with the current set-up.

4.11's are on the cards, one day when I have a spare $1500 or so again

Trav

[Reddo]

Thanks, thought that might be the case.

So, would definetely recommend the 4.11s, worth saving up for ....and the lockers too whilst the diffs are out...and the upgraded axles.....argh...this stuff is costing way toooo much

I know its been said before, but diff swaps are also worth considering if u can get good Nissan ones cheap and have access to some engineering talent.

[mrapocalypse]

I'm just going to put the tyres on in about 20K, live with them for a while and see.

I've been underwhelmed by the Cooper ST's. they are noisy and haven't improved the beast off road much at all.

AND the step up to 265/70R16 has raised the gearing, the speedo is out by 8% (GPS Thanks v much)

I think the V8 auto can cope with a bit taller gearing and I can't imagine the MTR will make it that much noisier. Especially now it's got a straight through exhaust!