I am considering replacing my 110 Tdi's 7.50 XZY tyres (tread width actually 6 inches!) with BFG A/T's in either 235-85 or 265-75x16 in order not to get stuck in soft sand and in the dunes quite so often as the big engine, big tyred Toyotas! I would have thought 265 would have been better but there seems to be a school of thought that wider tyres can sap engine power in deep sand. Does anyone have experiences of narrow and not so narrow tyres on 110 Tdi's?

You are usually better off sticking with 7.50 R16, as you can replace them (and their tubes) absolutely everywhere. As you get more exotic, your chances of finding what you need in the event of problems lessen dramatically.

Also, storing wider spare tyres can get interesting - ie the bonnet is often ruled out as an option.

Sam.

I'd concentrate on diameter rather than width. For a very small increase in turning circle (you have to adjust the lock-stops), you can fit 255/85-16's to a Defender.

It will raise your gear ratios a bit, and you will have to decide if this is a good or a bad thing.

When a tyre sinks into the sand a given depth, a larger diameter tyre provides less resistance (the "uphill" angle is more gentle). And big diameter tyres give deceptively good flotation when pressure is reduced (the length of the footprint is huge, even though the width may not be that impressive).

Another advantage is that other things being equal, you can run a bigger diameter tyre a bit softer without overheating the sidewalls as much, because there is more sidewall to absorb the flexing. (Having said that, there is more risk of the bead popping off, for the same reason).

While bigger tyres will add strain to your transmission (need more torque to turn them), this may be offset by the improved ground clearance, and the reduced susceptibility to potholes and corrugations.

If you go for wider OR larger diameter tyres than standard, you will probably need other rims. My choice would be steel Wolf rims as fitted to military vehicles. They are wider than normal, and have the correct offset. And for good measure, they are MUCH stronger than the standard LR rims.

I would fit tubes, but that's just me. If you fit tubes into a tubeless tyre on a tubeless rim, check your pressures often after filling the tyre from empty, as the initial pressure reading can include air trapped between the tube and the tyre, which will escape gradually around the outside of the valve-stem. Wiggling the valve stem around while filling can help this air escape. Be aware that your tube may not last very long, as there are ribs inside the tubeless tyre which can apparently chafe the tube. This has never happened to me, though, and I always use tubes.

All this advice is free, and probaby worth every penny! IMHO, DYOR, YMMV, etc.

Regards,

Michael...


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SandyM

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Ran 7.50 R16 for about 2 years on Defender. Changed to 265/75/16 BFG MTs for the 7 month trans africa trip. Much better all round tyre, far better than an AT. With defender fully loaded and with higher profile - higher suspension, higher tyres, roll cage, roof rack, roof tent, the large tyres sit far better. Wouldn't go back. However definite downsides as highlighted by Sam of lack of availability and difficulty in carrying spares - tyre to wide to go on bonnet, 265s won't fit on rear double rear wheel carrier which used to carry 7.50 R16s. Hence bit of a pain.

I have fitted Discovery 5 spoke steel rims to my 110 and use BF Goodrich LT235 85 R16 Trac edge tyres. I used this set up for a 10 month Trans sahara trip and found the following:

The Pros with this set up are:

Wider tyre width gives you increased stabilty and traction when driving on roads and tracks. Particularly good news when cornering with a large expedition payload.

The sheer sidewalls on the BFG tyres reduce the amount of damage by thorns and rocks. I had to fit some Michelins in Bamoko to replace spares and they had both incurred punctures in their sidewalls (thorns) within a week!

Cons:

The tryres were found to have too aggresive a tread for my liking in the dunes.

I beleive that when you are bogged down in the sand you it is harder on the clutch and engine to turn the wider tyre when tying to extract yourself. The engine would sometimes stall before turning the wheel.

Running tubes in tubeless tryes did lead to two blow outs. As suggested the ribs inside the tubeless tyre will eventually go through the inner tube.

In conclusion the wider tyre is excellent for most of your driving needs most of the time. Going forward I intend to try the BFG AT tyre (less aggressive) and perhaps better in the dunes and also the Michelin XS desert trye too see how much difference a pure desert tyre makes.

I know I keep saying this, but you must not fit tubes on tubeless rims.

It is dangerous and your insurance will no longer be valid. Technically you will be breaking the law as you will be driving without a valid insurance policy.

The reason it is dangerous is because the tube cannot function properly because its cross section is not a sphere. In fact you must not fit tubes inside very low ratio tyres (ie below 70%) because the sphere is too “squashed”. The 7.50 R16 has an aspect ration of 100 in case anybody is wondering.

But with today’s tyre technology you don’t need tubes anyway.

Sam is making an excellent point. If you trash one or more of your tyres in North Africa, the only size you will find locally is the 7.50 R16. Believe me, I’ve looked!

I suggest you either stick with what you’ve got or use the similar sized 235/85. Getting through soft sand is all about rolling circumference (not static circumference which is a different thing altogether), or width. The Michelin 7.50 R16 tyres have a rolling circumference of 2,450mm, compared to 2,443mm for their 235/85 tyres, so virtually no difference once you take tyre wear into consideration.

If you decide to change, then if you want really tough tyres to deal with the rocky areas I suggest you go for the BFGoodrich All-Terrain T/A LT235/85 R16. If you want a more flexible tyre to deal with soft sand go for the Michelin 4X4 - O/R 235/85 R16.

If you stick with your XZYs remember that they have a maximum speed rating of 75mph. This is the maximum speed that a perfect tyre with exactly the right pressure can sustain in a laboratory for 30 minutes. If you belt down the European motorways with an overweight 110 for hours at a stretch at 120kph you will almost certainly destroy one of your tyres before you even get to North Africa.

Given the above, I’m starting to have some doubts about the tyres I’ve been using on my Nissan Patrol.

I’ve been using, for a couple of years, Michelin 4X4 -AT 235/85 R16 (now they have changed to Synchrone designation I believe). After more than 100000kms I’ve never had a single puncture, nor in highway, road, rock or sand.

But if everyone is telling that if you trash one or more of your tyres in North Africa, the only size you will find locally is the 7.50 R16, then should it be worth to change to these tyres ?

Perhaps, it’s a dumb question, given my extremely good experience with the 235/85 R16. But to be on the safe side, is it really worth changing ?

Patrols come with standard 15 tyres. I’ve already changed it to 16 tyres. The 7.50 R16 is even a more height tyre. My Patrol has an high-roof, thus with the roof-rack it already tops above 2.10m height. By fitting higher tyres, and thus increasing even more the total car height, this will cause more instability, especially with an overloaded roof-rack. Won’t this tyre change increase to much the risk of roll-over ?

Thanks

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Terry,

those of us who use tybeless tyres with inner tubes do it for a good reason. 99.9% of us are smart enough not to hurt ourselves and would not fit an inner tube into a tyre that is not suitable for it, regardless of what the law might say. I have done 150k miles on BFG MT's fitted with inner tubes and never noticed that the tube's cross section was not a sphere. Besides, my insurers were as happy as I. So what's the problem?

José,

At the risk of stating the obvious, a 235/85 R16 tyre is equivalent to 7.50R16. It has almost the same diameter, just a bit wider. For all practical reasons it won't make any difference to the drivetrain.

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Roman (UK)
www.polandrover.com

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Roman (UK)

Terry,

Thank you for the legality issue re running tubes inside tubeless tyres, I for one did not know it was illegal.

However latterly for performance / safety reasons I did not run them with tubes after continued blow outs, which ironically was what I was trying to stop happening! I had been told a "war-story" about a Landrover traversing along a rough hillside track that had knocked its front downhill tyre off its rim causing a sudden destabilising deflation which caused the Landrover to roll with nasty consequences.

Picking up on your Michelin O/R tyre recommendation, looking at the pictures I have seen I would say that it looks pretty much like the BFG Trac Edge tyre. Whilst undoubtedly a good tyre the self cleaning open lugs still look too aggressive for dunes. Has anyone tried the Michelin XS on a 110 and with what rims?

ctc,

I've used Michelins XS, not on a 110 but on a Discovery with Wolf rims. Great tyre for sand dunes! It can be aired down almost flat to make up for the lack of LR engine power. The downside is rather vulnerable sidewalls. It must be used with inner tubes so watch out for the inner tube sliding on the rim with little pressure on the beadlock.

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Roman (UK)
www.polandrover.com

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Roman (UK)

Hold on there chaps. I didn’t say that you can’t put tubes into tubeless tyres. There is no problem with that. It’s tubes on tubeless rims that’s the problem.

Most rims these days are designed for tubeless tyres and these rims are a different shape to the old fashioned rims such as the Defender 5.5 rim, ie they are not “V” shaped. Tubeless rims do not allow the tube to function correctly.

You can run with tubes inside tubeless tyres until the cows come home, but you must fit them on the correct rims.

Thanks to everyone for your contributions. I have. All most interesting. It seems then, that I have a choice of going taller and/or wider in order to reduce total ground pressure. Going taller on a Land Rover (at least under desert conditions)is probably not a good idea (ok on Land Cruisers though, according to Chris Scott in Sahara Overland). So the other option is to go wider. The greater the width, the greater the difficulty in stowing spare tyres, and anyway, once a certain limit(width) is reached the benefits begin to tail off. A lot of people I have spoken to have told me that 235-85x16 is all you need - no more, at least on a 110. Maybe a bit more width is desirable for a heavier Land Cruiser. Having shed 140kg off the roof and stowed both spare tyre/rims behind the front seats instead of one hanging on the back door, and also cut down on other excessive gear, the car may perform better on the skinny 32 inch tall XZYs now it's lighter and with better weight distribution. If it's still not good enough, then I think a set of 235-85s would tip the balance enough to be acceptable. Of course Land Cruiser owners don't have to be quite so scientific in their approach, with their big engines and stronger transmissions!
Thanks again everyone.

Best wishes
Andrew .

Andrew,

I don't follow your argment about Land Rovers and not using taller tyres specifically in desert conditions.

If you are doing rock crawling or very heavy towing, then taller tyres will put more of a strain on the transmission. You will need to be in a lower gear to achieve the same effective torque as with a smaller tyre.

But in heavy sand, this will be offset by the bigger footprint AND (most significantly) the gentler effective gradient of the sand barrier.

The *percentage* of your tyre that sinks into the sand is what determines how hard the vehicle has to work to push its way through. A wide tyre won't sink so far because it has more surface area.*** Lowering the pressure of a tyre increases the surface area too. But a tall tyre not only has a bigger surface area, but also, any given depth represents a lesser proportion of the wheel's whole diameter.

So why does everyone concentrate on wide tyres instead of tall tyres? Because wide is easy. Most vehicles can't accommodate even slightly taller tyres without suspension modifications. Most vehicles are designed around good on-road manners. A Defender can take 33" tyres without suspension mods, and it *has* no on-road manners!

Having said all that, I do agree about the availability advantage of 7.50-16s. An advantage not to be disregarded, if somewhat self-perpetuating!

Regards,

Michael

*** The story about more sand piling up in front of a wide tyre is only true in some very specific circumstances. Yes, a wider tyre *does* have to dig its way through a wider front of sand, but the greater surface area of the tyre means that vehicle sinks in less, and therefore this heap of sand isn't as high. Of course, if, as rarely happens, there were a solid layer underneath the soft sand, then you would want narrow little tyres that cut through easily.

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My reluctance to use taller tyres on a Land Rover (under desert conditions, specifically crossing the Erg's) is due solely to the relative weakness of the LR transmission system as a whole, and the half shafts, and diffs in particular. The 110's components are designed around each other and introducing extra stress due to a non standard part (a taller tyre), could, when trying to ascend large dunes for example, cause failure of a diff or half shaft. Not recommended when you are 4 days from the nearest town. I understand that Land Cruiser transmissions are over engineered instead of just adequate, and can cope with bigger tyres, to a point, no problem.

I hear what you are saying about the footprint being bigger offsetting the increased strain on the transmission, but the wheels still have to be forced to turn in soft sand and on steep ascents with heavy loads - I would still be worrying that something on the 110 would go pop at just the wrong moment.

Having said all this, is 33 inches the biggest tyre you can us without mods? It's only 1 inch more than standard - would it make much difference?

Regards,


Andrew.

Hi Andrew,

Last question first: A 7.50-16 tyre has a 31" nominal diameter, so 33" is indeed less than 7% bigger. (Standard tyres on a Ninety can be as small as 29", which makes 33" a 14% increase, though!).

However, even 7% does make a noticeable difference in a variety of ways. Incidentally, changing from a 29" (235/70-16) tyre to a 31.7" (235/85-16) tyre on my Discovery hugely improved its performance in sand, though the tyre width stayed the same. I did, however, have to take a hacksaw to the rear wheel-arches!

I don't want to rekindle a whole debate over the pros and cons of TLCs vs Land Rovers, or how strong the transmissions are. But where Series Land Rovers were notorious for breaking shafts, this has not been an issue for any of the coil sprung vehicles, starting with the Range Rover in 1970.

The Rover type diffs *can* be broken, but seldom in the kind of conditions we encounter in the desert. Typical failures are the result of shock-loading, such as in slippery mud, or rock crawling, when a spinning tyre suddenly catches on a rock etc.

The diffs also tend to fail when water, especially muddy water, has entered through the hub seals, the axle breathers, or the pinion seal, and the gears get worn. The damage to the teeth, and the resulting increased backlash make the diff very prone to breakage.

This "flood damage" applies to the Salisbury diffs too, which are based on a Dana unit, and are otherwise almost bullet-proof. The snag with the Salisbury is that it is more difficult to field-repair or replace, and that te "pumpkin" hangs lower, reducing ground clearance.

The components of a Rover diff most likely to break under shock loads are the planetary gears. Replacing the diff centre with the relatively rare 4-pinion version used in the rear of V8 Ninetys will make it almost as strong as a Salisbury. So will using an ARB locking diff centre (though when it is locked, it will also be more vulnerable to mistreatment). I guess other locking/lsd centres might also uprate (or downrate) the diff's strength, but I have no personal experience of them.

The weak point in the transmission systems of modern Defenders is unquestionably the main gearbox - the LT77 as used in 200Tdis is dire, and the newer R380 isn't much better. The transfer boxes seldom fail, though the centre diff can break if mistreated (used on tarmac etc.), and it will often do some collateral damage to the xfer box!

Tall vs wide tyres is always an interesting debate. There are lots of downsides to tall tyres: they might require body/suspension mods; they add to unsprung weight; they can adversely affect braking; they have bigger and therefore more vulnerable sidewalls; they are expensive; they may be harder to find; they often don't fit in the standard spare tyre positions; they raise overall gear ratios; they might increase the turning radius; the transmission has to work harder to make them turn; the speedometer has to be recalibrated; they look funny, etc.

Nonetheless I stand by my judgement that they are much better in thick sand. Other things being equal there is no *torque* penalty for using tall tyres in soft sand (in fact just the opposite), because of the beneficial offset of a reduced sand barrier. Furthermore, the *power* requirements with tall tyres are actually lower in thick sand, other things being equal. Torque causes breakage, power causes wear, so tall tyres have a significant advantage, imho.

I'd be interested to compare notes with others who have gone for bigger diameter tyre in desert conditions, especially if you have tried different sizes under similar conditions.

Regards,

Michael...



[This message has been edited by SandyM (edited 13 October 2002).]

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