Thread: oversize tyres for the disco

Originally Posted by kingyrules

is your Tran auto or manual?, I've got a similar tyre size same radius 225/75/16 with no probs not as wide but still, and still got the original gear box (mines manual don't know if that will make a diff), my advice get a second opinion, just don't tell em that its new box etc, just tell them about your tyre and lift upgrades, see what they say. either way you will find out whos honest.

in the above, Kingyrules was comparing his tyre size to Streaky's, from the previous post.

Originally Posted by streaky

I have 265/75-16's on my series I Disco combined with Dobinson 2' lifted springs.
I've replaced the front radius arms with 3 degree cranked ones and left the rear standard. I've trimed all four arches and fitted extensions to them.

Now here's here my contension sets in. The Transfer box and gear box started to makes nasty noises on the over-run at 70mph. The work shop who fitted the gearbox and transfer box are saying that the lift and slightly over size tyres are the reason for the premature wear in the gearbox.
Now I think they are talking out of their backside and just don't want to replace the faulty tranny.
Has anyone ever had issues with the gearbox and transfer case because of slighty oversozed tyres and a 2" lift?
We all know that UJ's and propshafts can be subject to vibrations and premature wear...but the tranny also??

I'd be surprised if any one has.

Sorry to be picky, but 225/75/16 is approximately 29.3" (call them 29s), and 265/75/16 is approximately 31.6" (call them 32s). They are very different tyre diameters. Please note, the 75 part of the tyre equation means that the sidewall is 75% the size of the section width (Widest part of the tyre,and not necessarily the width of the tread) - that is, 75% of the first number!

Tyres and tyre sizes, just gotta love them.

PS. I run 245/70/16 Goodyear ATR as daily driver tyres on both Discoveries, and I love them. I run Dunlop MT2 in 235/85/16 for play days on the D1 and the S2a (luckily the wheels are interchangeable); I have a 40mm lift courtesy of some OME coils, and I cut the rear guards on the D1. The Dunlops occasionally rub inside the rear guards on full compression, never worried about it. They also rub on full lock because I didn't adjust the steering stops, again not a major drama. I haven't broken anything in the driveline - yet

If someone is running 33s then you really need to look at either 4.11s or the t/c gearing. 33s are a 13% increase in circ. over stock so make a big difference.

Ok well what do you want to do here.

Body lift is pretty much for asthetic reasons only until your running over 33" tyres or running offset rims as nothing will foul the guards until then due to the tyres tucking up under the guards.

If you run offset rims or larger than 33" tyres you will crease panels when the tyre hits on articulation unless you extend the bump stops which on a LR is IMHO a ruining a good thing.....Articulation.

With 235 85 16's on mine I find that it is a little slower off the mark and loads up on hills and with a head wind more than with the old 225 75 16's ( I think they were) so a Deefa transfer case would be a good thing to even out the gearing again.

Increasing rolling diameter increases load, increasing load increases fuel usage and loads on driveline so yes it will cost more to run larger tyres unless you take ratios into account.

I have heard that when running 33/34/35" rubber that wheel bearings can be a issue but up to 32" isnt a real issue due to the bearings being designed for the loads that is exerted on them but if you start playing with offsets then it is increasing load again, Im not sure on the exact formula but it increases load on one bearing and not the other and can cause premature failure.

As far as hights go, pull the old sun visor down and check the roof hights and get the tape out to check suspention hight and your tyre placard tells you your standard tyre sizes.

Originally Posted by mcrover

Body lift is pretty much for asthetic reasons only until your running over 33" tyres or running offset rims as nothing will foul the guards until then due to the tyres tucking up under the guards.

.

Nothing to do with keeping the COG low, 33's Will foul the inner gaurds, without BL, or your suspension is to hard

Originally Posted by mcrover

I have heard that when running 33/34/35" rubber that wheel bearings can be a issue but up to 32" isnt a real issue due to the bearings being designed for the loads that is exerted on them but if you start playing with offsets then it is increasing load again, Im not sure on the exact formula but it increases load on one bearing and not the other and can cause premature failure.

Now thats some crazy shizzle, Rover wheel bearing are way oversize compared to most anyhow, never had a problem, or anyone else on 35's that I know of

With my RRC, 33's have def taken to 'grunt' out it, so I will be doing some 4:1 thinggy changes too.

Shorty, just get some 33's on the sucker, ill get my grinder out and we can start making the necessary hacking... err, modifications