Best combination of tyres/lockers/diff ratios?

Treads · 30th July 2008, 05:39 PM

Sorry about the wordy explanation, but I want to get this right the first time.

As I've mentioned in a couple of threads I'm looking for a set of M/T's to use for both our 96 Disco Tdi and our 96 Defender Tdi.
We run A/T's now for daily driving; however we also want a set of tyres for serious offroad work, and especially for the Cape trip next winter. We have a set of spare 16x7 disco steel rims ready and waiting.

Each vehicle has the following listed for standard fitment:

Discovery
235/75 R16
diameter = 29.87 in
= 75.89 cm
revs/mile= 675.01
revs/km = 419.43

Defender
7.50 R16
diameter = 31.64 in
= 80.36 cm
revs/mile= 657.30
revs/km = 408.42

We currently run:

245/75 R16 on Disco
diameter = 30.46 in
= 77.39 cm
revs/mile= 661.93
revs/km = 411.30
speedo difference = 1.977% slower

235/85 R16 on Defender
diameter = 31.72 in
= 80.56 cm
revs/mile= 655.70
revs/km = 407.43
speedo difference = 0.244% slower

I'm pricing a few different tyres in 265/75 R16 to suit both vehicles. Mickey Thompson MTZ's are currently the pick of the bunch, and while I'm waiting on prices from other dealers, I have one firm quote of $312 per tyre.

However, my concern is that while 265/75's will match the current tyres on the Defender almost perfectly, they will cause issues with the Disco:

265/75 R16
diameter = 31.65 in
= 80.39 cm
revs/mile= 637.23
revs/km = 395.95
speedo difference disco = 5.933% too slow
speedo difference deefer = 0%

Obviously getting 235/85's will also raise the same issues for the disco (keeping this size for the deefer has been mentioned to me before). Also I reckon the disco would look strange on narrow tyres

.

Since I've been promised a healthy tax return (here in about 2 weeks

), it's been decided that the Disco will get a 2" spring/shock lift & at least one ARB locker, but I'm not sure if I should change my diff centres to a ratio that will better suit the big tyres at the same time.

If I do change ratios will it adversely affect touring while the A/T's are on the rig? I'm a bit lost when it comes to gearbox/transfer/diff ratio sums

so I'm hoping someone might be able to help with experiences or knowledge on the subject.

**2_door** · 30th July 2008, 06:43 PM

265/75's wont go on a 7 inch rim, sorry

I reckon that because you have Tdi's, stick to a tyre size close to standard or when touring, it will really struggle up hills. If you go to bigger tyres, then change diff ratio's.

stay with a 245/75/16 (roughly 31 inch) on the disco and go 255/85/16 (33inch) on the deefer and you will have no probs with diff ratios.

as for diff locks, take your pick, they have no effect on final drives and tyres sizes.

good luck

ps. I didnt vote as the options didnt appeal to me

Treads · 30th July 2008, 06:50 PM

Originally Posted by shorty

265/75's wont go on a 7 inch rim, sorry

That's strange, all the tyres I've looked at (BFG, Goodyear, Kumho, Hankook, Toyo & MT's) say 7" is fine

For example:

Mickey Thompson MTZ LT265/75R16 - 10 Ply - 123Q Rating - 7-8" Rims

Originally Posted by shorty

ps. I didnt vote as the options didnt appeal to me

Isn't option 4 what you just recommended?

mcrover · 30th July 2008, 07:22 PM

Ok,
a. 235 85 16 BFG Muddies or equivelent
b. 2" spring lift with new shocks and a good steering dampner
c. Rear Airlocker and 4.11 gears

My mate Jamie has this set up other than he runs 265 75 16 Silverstone somethings on off set rims with LRA flares and it works very very well.

Ive got the same minus the locker and with 235 85 16s in Allterrains mainly so I didnt have to go the flares and offset rims and still have a turning circle that is reasonable and I find it is a huge improvement over the standard and goes most places within reason.

Next step for me, money permitting will be the rear locker and 4.11 gears.

Edit : You could get back to original gear with a deefa TC in the Disco on 235 85 16s as an option but I dont think it would be much cheaper than going for 4.11s

**Slunnie** · 30th July 2008, 07:26 PM

265/75-16 absolutely will fit 7" rims. Thats generally about the limits though some Mickey Thompson 285/75-16's may fit.

If you are looking to share 265/75-16 muds between the trucks for offroading, but want to run the 245/75-16 on the Disco for touring then I would be inclined to leave the diff ratios alone. The difference in gearing between the Defender and the Discovery is only the high range ratio, the low range is the same. If anything, then perhaps it may be worth finding some 30% low range gears for the Discovery while offroading - these make a big difference to drivability when things get gnarly.

**2_door** · 30th July 2008, 09:06 PM

Originally Posted by Treads

That's strange, all the tyres I've looked at (BFG, Goodyear, Kumho, Hankook, Toyo & MT's) say 7" is fine

For example:

Mickey Thompson MTZ LT265/75R16 - 10 Ply - 123Q Rating - 7-8" Rims

Isn't option 4 what you just recommended?

yes and yes....sorry

having a seniors moment

**DiscoDan** · 30th July 2008, 09:50 PM

I went option 4 as if you put 265/75/16 you would have to do some major trimming in the rear guards.

I run 245/75/16 on my disco and only two inch lift, no trimming at all, a friend has 235/85/16 and had to do a little trimming. 265/75/16 on a Rangie with 2 inch body and 3 inch springs and they touch but no trimming of metal.

I also found that the 245/75/16 corrected the speedo as it was reading fast, however the Odo is no out 10kms = 9.75kms

As pointed out low range stays the same, the best in the job. Diff locks make a huge difference but in saying that some people put them in before they are able to read and drive the terrain. Sounds strange but I have seen very capable cars ie twin locked Cruisers on the poo due to the driver not understanding where or how their car would perform over that part of a track.

If you decide to go the the larger tyres and change the diff ratio's throw in some lockers and watch the opposition weep

Good luck with which way you go

**Redback** · 31st July 2008, 07:07 AM

OK, this may through a spanner in the works but this is what i would do

2" lift, F & R lockers, leave the diff ratios, have the 245 or 265/75/16s for touring in the Disco, put 255/85/16 BFG MTs on the Defender they measure a tad over 33", when you want to play in the Disco (i'm assuming the wife doesn't want you to play in the Defender

) take the 255s off the Defender and put them on the Disco

I don't know if anyone else makes a 255/85/16 other than BFG, you may want to find out

jddisco200tdi · 31st July 2008, 10:18 AM

If it were my car I would leave the gearing alone and run 235/85R16 mud tyres on your extra set of rims.
I would tweak the injection pump on the disco to be able to push the tyres better in high range.
For a trip to the cape because of the road distance involved, I would use the AT tyres.
A rear locker is a good thing to have no matter what tyres you use.

Regards

John D - Defender 110 2.4

**Utemad** · 31st July 2008, 12:15 PM

What I would do is get 235/85 16 mud tyres as well as a spring lift.
These tyres would make good play tyres for the Disco and are standard for the Defender.
Leave the diff ratios alone so you can still use your smaller tyres for the road and easy trips.
Drive it like that and see how it goes before getting lockers.

This assumes both vehicles spend most of their time as commuters on the blacktop like you said.

I have 245/75 16 mud tyres for play and much prefer driving on the 225/75 16 all terrains for day to day stuff. This is a manual V8. Mostly due to road noise and handling than gearing.

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