Odd tyre size?

[AussieAub]

Hey guys,
After having a side wall ripped open to a rear tyre yesterday, by an exposed rock on a sand track, I had to swap with spare. The 4 tyres on the Disco were 245/70x16, but the spare is a 235/70x16. Obviously its on now as I had no other choice. But HangOver mentioned something about "diff wind up", something I'm not familiar with. Would this, what I consider a small difference in wheel circumference, give me any major issues?

We are due to go away down to Bridgetown for a few days (no 4WDing, just some site camping), in a few days time. Do you reckon its safe to leave this spare on, or should I be doing all I can to get replacements before hand? I would assume I need to replace both sides due to uneven wear?

Anyone NOR have a decent contact for tyres? VERY tight budget right now....!!:(

Any help/advice appreciated.

Cheers,

..:: KIEREN ::..
2000 Disco II Auto V8
Object Of Mass Consumption

[dullbird]

I would be replacing the tyre.....235.70 is the standard that a lot of disco's came out with not good of the person that changed to 245's and didn't change the spare.

its not good for the car to have such a variant in rolling diameter between the to wheels..
change it as soon as you can

[AussieAub]

Thanks for that mate.
Yeah, unfortunately the Disco came with the 4 bigger tyres and original spare when I bought it. Something I always knew about, and one of those "I'll get round to changing that one day" things.

Now its too late. Bugger! :(

Cheers,

..:: KIEREN ::..
2000 Disco II Auto V8
Object Of Mass Consumption

[dmdigital]

245/70R16 is the next size up but definitely not a common size. It will fit a D2 as easily as the 235/70 so no need for suspension lift etc. What DB said stands, I'd not drive it much until you get a 2 new tyres to mach the other 3 (or 5 new tyres that match).

[Lotz-A-Landies]

As an alternative fix for the short term you can use your rolling radius to adjust the air pressure in your car. A higher pressure in the 235 and lower pressure in the 245s adjusted to give you the same height from the hub to the road when hot.

The 235 should be on the rear and not the steer axle.

Diana

[dullbird]

245/70R16
is the next size up but definitely not a common size. It will fit a D2 as easily as the 235/70 so no need for suspension lift etc. What DB said stands, I'd not drive it much until you get a 2 new tyres to mach the other 3 (or 5 new tyres that match).

I was sure that some disco's got released in 245/70

the later D1's

I could be wrong on that of course

[dmdigital]

Not in Australia at least. The D2's did come with 235/70R16 and 255/60R18 which are near enough to the same diameter. Coopers and others now make a 255/70R16 which they will tell you is suitable for the Disco - I had these on my D2.

The difference in diameter between 235/70 and a 245/70 or 255/70 is 15mm or 28mm respectively. The overall diameters are: 29", 29.6" and 30.1".

[slug_burner]

get two replacements and relegate the 235x70 to ebay or a trailer and put the surviving 245X70 onto spare tyre duty.

I would try to get that 235x70 off the car soon without panic but I would not go on holidays with it on the axle.

[lambrover]

you won't get wind up unless the center diff lock is on, the differental action will allow for the differance in diameter just as when you go around a corner one wheel is going faster then the other, but if you could imagine the diffs would be doing double time and a half to allow for this and this puts heat and stress on the diffs not good. someone said letting the tyre pressure down on the other tyres could work but remember that lower tyre pressures at highway speed give bad handling and the tyre temperature increases and you can delaminate the tyres so go slow I would say no faster than 70k on the bituman.

[AussieAub]

Cheers all.
Decision made to get new tyres on the rear before any haul, long or short.

Now the decision. Do I get the same 245/70's and have a "difficult size" to get hold of in an emergency? Somebody here (and I won't mention names yet!) reckons I can get standard Deefer size tyres to fit, but can't remember what size off hand. These are a much more common size, and will defo fit with the +2" springs recently fitted, with no issues, and give me more clearance to the diffs.

Any one any rough ideas on cost differences, and of course - and I know irts been done to death elsewhere - but any recommended tyres?

Cheers,

..:: KIEREN ::..
2000 Disco II Auto V8
Object Of Mass Consumption

[dmdigital]

If it was me I'd look at 235's or 255's in 70's. If you want to go up in size then this is a good reference: Clifton: Disco2 Tyresizes (http://www.clifton.nl/tyresizes.html)

[Sprint]

with a 1.9% difference in circumference, i wouldnt be overly concerned with windup, but i would be replacing the blown tyre asap

[AussieAub]

Just thought I'd post an update and some pics.
Decided to go for a set of 235/85R16 Hankook RT-03's.

Look fairly darn rugged, and big thumbs up and thanks to Beefy for supplying a spare in the same size, and giving me a hand refitting the spare wheel carrier to suit. Cheers again fella.

Thanks also to all who replied to this thread supplying really useful info, as always!

So here's some pics taken over the weekend just gone down in Bridgetown, WA....

Cheers,

..:: KIEREN ::..
2000 Disco II Auto V8
Object Of Mass Consumption

[JDNSW]

I cannot remember a reference, but I have seen results of an actual test of the change of effective rolling radius with tyre pressure. The result is that for radial tyres, there is no appreciable change in rolling radius for any realistic change in pressure.

The reason for this is obvious if you think about it. The distance travelled for one revolution of a wheel is equal to the length of tread laid down on the road during that revolution. For a radial tyre (even for a crossply pretty much) the belt prevents any stretching of the tread with changes in pressure, until the pressure gets so low that the belt buckles, carrying the load on the sidewalls and sliding the tread. This means that the same length of tread is laid down in one turn of the wheel, regardless of the pressure, even if the length of the contact footprint increases at low pressures. For it to be any different implies that either the tread and hence the belt has changed in length with pressure, or the tread is sliding on the ground.

So I conclude that changing the pressure to equalise the rolling radius for different size tyres simply will not work.

Anyone who wants to check this can do so - simply find a hard, level surface, put a chalk mark on a tyre, and on the road, move exactly one (or more) revolutions of the wheel, mark the road and measure the distance between the marks. Repeat for a different pressure. The distance will be the same within the accuracy of your work for any practical pressures.

John

[4wd4fun]

245 70 R 16 is a common size tyre and i have run this size on my rovers since 1994. On Performance Wheels 16 X 8.
The last model shape Holden Jackaroo had them and the previous model Nissan pathfinder also had this size from factory plus a few other jap models.
I currently run Pirrelli Scorpion AT, but have also tried Bridgestone AT, Goodyear wrangler , Toyo and Bf Goodrich Trail TA's.
I have found them to be a good compromise for general driving trail,sand and road without affecting performance and fuel.
My 95 Disco TDI 5 speed with 245 70 R16
http://img87.imageshack.us/img87/3730/fid1.jpg
My 85 RRC V8 5 speed with 245 70 R 16
http://img511.imageshack.us/img511/7994/range862new.jpg
The Blue disco D1 in Sinature is my 94 V8 auto same wheels and tyre size.:D
http://img87.imageshack.us/img87/1341/myweddingcar.jpg

[D3Jon]

Just thought I'd post an update and some pics.
Decided to go for a set of 235/85R16 Hankook RT-03's.

Look fairly darn rugged, and big thumbs up and thanks to Beefy for supplying a spare in the same size, and giving me a hand refitting the spare wheel carrier to suit. Cheers again fella.

Thanks also to all who replied to this thread supplying really useful info, as always!

So here's some pics taken over the weekend just gone down in Bridgetown, WA....

Cheers,

..:: KIEREN ::..
2000 Disco II Auto V8
Object Of Mass Consumption

So what's the legality of an 85mm overall vehicle lift? (35mm from Kieren's new tyres + the original 50mm suspension lift).

I can't seem to find anything definite for WA on here: Vehicle modifications (http://www.dpi.wa.gov.au/licensing/1412.asp)

Jon

[brianwood]

Hey Kieren,
Do you have any trouble with tyres fouling on the body?
Also, if its not too rude, can you tell me what the Hankooks were worth?
They look excellent, might be what I'm after..

[harlie]

So what's the legality of an 85mm overall vehicle lift? (35mm from Kieren's new tyres + the original 50mm suspension lift).

I can't seem to find anything definite for WA on here: Vehicle modifications (http://www.dpi.wa.gov.au/licensing/1412.asp)

Jon


I would think the lift is OK, but the 71mm increase in tyre rolling diameter is definitely not legal. 71mm that’s 9.6%, so the speedo is 9.6% out and (the main reason why it’s not legal) the brakes are now 9.6% less effective than designed.


The "New" rules that have been mentioned lately here are as follows;
Quote from the National Code of Practice for Light Vehicle Construction and Modification (NCOP)


OVERALL DIAMETER


The overall diameter of any tyre fitted to an off-road passenger vehicle or a commercial vehicle must not be more than 50mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model.


So these tyres are not legal under the NCOP. But wait there more…


"Please be aware that the NCOP only represents the technical requirements that must be met - administrative requirements are dealt with separately by each state and territory's administrative guidelines or business rules."


What this means is that ALL vehicles in the country must meet this as a minimum, and the State authority cannot introduce a rule that is outside these rules. It also means that the state can have their own laws that are tighter than these. I know that QLD, NSW and VIC are all currently specifying max of 15mm.


The NCOP also talks about speedo accuracy, and that when larger tyres are fitted the speedo MUST still comply with ADR18 (instrumentation). This ADR is full of mathematical equations but the simplest point (which is now failed) is:
5.3. The speed indicated shall not be less than the true speed of the vehicle
This is why most new cars display a higher speed than what you're actually travelling.


No mater what WAs state law is this doesn’t meet the new national laws…. So in the event of a good prang - I think you'll be on your own

[shad]

ive just put 235/85r16 on my defender it had coopers of the same size on it when i bought it i now have bridgestone lt 694 are these legal:confused:

[BigJon]

ive just put 235/85r16 on my defender it had coopers of the same size on it when i bought it i now have bridgestone lt 694 are these legal:confused:

That is the standard size for a Defender, so no worries there, provided you meet the load rating requirements.

[victa125]

So that makes my 265/75/16 on rrc ordinary. Wonder if fitting deefer brake upgrade would at least adress the braking issue. Should then get mod for deffer tyre size. Now 265/75/16 to 235/85/16 have to check my math before being sure.

[DiscoStew]

... and big thumbs up and thanks to Beefy for supplying a spare in the same size, and giving me a hand refitting the spare wheel carrier to suit.

Was the "refitting the spare wheel carrier" required because the new tyre would catch on the rear bumper. I am having that problem with my new mud tyres and I though I read somewhere an easy way to solve the problem but I cannot find it again.

I am currently thinking I will need to weld something on to lift it.

[AussieAub]

Was the "refitting the spare wheel carrier" required because the new tyre would catch on the rear bumper.

Hi Paul,
Yes mate. But all we did was turn the wheel mount upside down.
The carrier is tapered slightly, so turning it upside down raises the level of the bolts, but also shifts the centre more towards middle of the rear door. We didn't bother drilling the two additional middle holes, just used the four "corner" bolts, made sure they were tight, and all seems good so far. So a slightly easier job than what it states below.

Copied this from Clifton Scientific Text Services, the Netherlands (http://www.clifton.nl/index.html'tyresizes.html)
(I did the first option and the wiper arm JUST clears the bracket)

"Adjusting the spare wheel carrier is absolutely necessary for this size. Possible adjustments, all actually reported as really carried out by a DSII owner, include

* Inverting the carrier, which will raise the wheel by 3 to 4 cm (approx 1.5 inches). Downside is that it will also shift the wheel more to the left, and thus put more leverage on the door hinges plus obscure a larger part of your rear view. For this option you will have to remove the interior trim of the door, undo the six carrier bolts, re-use the four upper/lower fixing holes, and with the metal fixer as a template drill two new middle holes in the door, and re-attach the carrier. Also this option will need adjusting the rear wiper arm to allow full travel: undo bolt/screw, pull out, readjust on the spline, reattach. An afternoon of home-mechanic work, but it will give you a stable spare wheel carrier, allowing for all practical tyre sizes, up to and including 33-inch tyres.

* A reasonable alternative adjustment is drilling mounting holes lower down (20 mm, or 3/4 inch) in the carrier, which needs removal of the interior trim, flattening the pressed rib on the bottom of the mount, and some accurate drilling, and has a very stable result. Obviously, for this the interior trim has to be removed first, and put back on afterwards. A raise of approx. 2 cm (0.75 inch) seems achievable with this alternative, allowing for all tyres up to 32 inch as listed above.

* A next alternative is to wing it: just put on the larger wheel on the carrier and slam the door. You can help the bumper down a bit by loosening the two bolts which hold the bumper on the frame, and then slam the door and re-tighten the bolts. Effectively the bumper will be pushed down a bit. If you can live with the rubbing this is an easy way out, but only applicable for the tyre sizes between 30.5 and 31.5 inches.

* Lastly, you can put the wheel way higher up on the stock spare wheel carrier, using merely two bolts instead of the default three. The attached wheel will slightly tilt forward towards the rear window. Downside of this option is that the spare wheel will be attached to merely two bolts, both on the same off-centre (bottom) side of the wheel, causing leverage, with questionable stability. Obviously, you can make any tyre size fit."

Hope it helps.

Cheers,

..:: KIEREN ::..
2000 Disco II Auto V8
Object Of Mass Consumption

[DiscoStew]

Thanks for that.

I inverted the carrier and now all is good :D