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Desert Travels - Motorcycle Journeys in the Sahara and West Africa!

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  #16  
Old 26 Jan 2003
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Thanks all - real food for thought there.

I must admit, my experience of tyres in sand has been strange inasmuch as as well as using VSJs and XSs, I also have travelled dunes (Erg Chebbi) with XCLs - aggressive mud pattern - which did not sink! Moreover the Nissan that was with us (lighter, less heavily laden and bigger engine) *did* sink repeatedly on fatter tyres.

Bagnold et al and their experience in the 1930s and 1940s comment that fatter tyres are better and Id agree for the most part, but Roman's point makes interesting comparison. There must be a balance, therefore, for a given weight of vehicle, pressure of tyre and sand density, between fat flotation tyres and narrow resistance-lessening types....

Anyway, acid test, the Defender is going out this weekend to the dunes heavily laden with XZLs on all four paws, so lets see what happens. As a comparison we are taking a second identical CSW 110 on XSs!

Ill report back....

*edit*
Afterthought - Ive seen some of the huge 'serious desert' drilling and mining buggies used by Schlumberger etc out here and they definitely go for the 'fat tyre' route - so much so that one that drove out to sea (dont ask!) actually did *float*. They are the only machines that will drive into the worst parts of the saltmarsh of Qattara and stand a chance of getting out.

Bagnold's experiences from the 1930s started off with Model T Fords on thin thin one and two inch width tyres, so 'fat' is a relative term (Something to tell the girlfriend...!)

[This message has been edited by LandRoverNomad (edited 26 January 2003).]
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  #17  
Old 27 Jan 2003
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Just to add to the tyre question. Ive just got back from Tunsia with a 110. before heading down there, i was desperate to get hold of a set of XS (which incidentely look far wider than 'ordinary' 750s, but is it just optical?), anyway a set of 5 new Pirelli 750 Dakars came up at an incredibly low price - buy 1 get 4 free!

being a totally unknown tyre to me, i was a bit worried heading out into the desert, but once let down performed amazingly well and i went places that would have been a bit worried about with my previous tyres. that said i used to run on 235/85 trac edges, which were ok in the sand when deflated, but allways seemed to struggle to get going from standstill, presumably due to the more aggresive tread?!

anyway, i'd always thought that in sand the wider the better, but these narrow 750s seem to be challenging that view. interesting to see what develops! Rich M
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  #18  
Old 27 Jan 2003
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We went through the desert last year in the "heavy" 101 on XCL's. They were surprisingly good and we only got stuck once. They did sink a bit more than the locals on XS's but we also did not let the air out as much as we could have done. When we got back an "old desert hand" said that they used to reverse the XL's and XCL's in the desert and this helped prevent them digging in. Food for thought?
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  #19  
Old 2 Feb 2003
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Just got back from two days in the sands with the 110 on XZLs..... they *do* dig in more than wider patterns like VSJs or XSs. The 110 with us on wider pattern tyres (albeit with more horsepower too) dealt with the dunes, the Landy on XZLs dug in (both heavily laden 110 CSWs). I think even wide road pattern would be better at dune sand than XZLs.

However the XZLs were much better at dealing with harsh non-dune terrain. A Toyota that came along with us (on All Terrains) shredded a tyre on sharp rocks that the XZLs didnt even notice.

No surprises really, though next time out (next week probably) I will experiment more with mixing VSJs and XZLs at varying pressures.

One other thing.... that TDi 300 really is a stonking good engine!

LRN
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  #20  
Old 6 Feb 2003
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Hi LRN,

Were the XZLs the same nominal size as the Xss? Were they noticeably narrower, as Michelin apparently stated?

I can imaging them not being as effective, being narrower, AND having a less ideal tread pattern. I believe they are designed for just as low pressure, though - down as far as 0.6Bar. (?)

XZL's would still be my first choice for general expedition tyres, though.

And yes, isn't the 300TDi a stonking good engine?!

Regards,

Michael...
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  #21  
Old 7 Feb 2003
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Quote:
Originally posted by SandyM:
Hi LRN,

And yes, isn't the 300TDi a stonking good engine?!
???????[gulp] Better than a 4.2L 1HDT?

Rgds,
Roman (UK)
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  #22  
Old 8 Feb 2003
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Tdi would be better if it was 3 litres plus....

Has anyone tried newer versions of XZL, in sizes such as 8.25-16 or 255/100-16???

Andrew.
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  #23  
Old 8 Feb 2003
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Yeah, more power would be nice. But it's a simple, reliable, durable engine. And economical. And light, for a diesel.

255/100-16 is a 36-inch tyre, but fairly narrow. Anyone know what kind of lift/other mods would be needed to fit them to a Defender? I didn't know the XZL's came in that size...

Also, do XZLs come in 255/85-16? At 33", that's roughly the same diameter as the 8.25-16, I'd guess, but a bit wider. I am running 255/85-16 BFG MTs, but I'd prefer XZLs in something 33"x16 if they are available.
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  #24  
Old 10 Feb 2003
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Michael,

My information is that the 8.26-16 XZL has a 34 inch diameter. I don't think they do a 255/85 size, but you could ring Michelins technical department who are very thorough, and who can also advise on BFG tyres.

Apparently there is a new size to compete with the 235 BFG A/T's but I have not checked it or any other new sizes out.

Regards,
Amdrew.

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  #25  
Old 10 Feb 2003
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Be wary of using too exotic tyre/wheel combinations. When you start having punctures, your chances of being able to replace like-with-like become slimmer (to non-existent) as you get further from the Toyota/Land Rover etc. factory fitted standard.

Sam.
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  #26  
Old 11 Feb 2003
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Quote:
Originally posted by Sam Rutherford:
Be wary of using too exotic tyre/wheel combinations. When you start having punctures, your chances of being able to replace like-with-like become slimmer (to non-existent) as you get further from the Toyota/Land Rover etc. factory fitted standard.

Sam.
Quite true, Sam. Of course, if things go wrong, the best size tyre to have is a 31" diameter, since this is the size of most 7.50-16s - as has often been pointed out.

However, you can run a 7.50-16 (or better, a pair of them) in conjunction with slightly bigger (or smaller) tyres for many thousands of kilometres if necessary without doing any damage to the vehicle. (I expect the handling would be, umm, mischievous, so not at high speeds).

I'd guess a 33" tyre could be run reasonably happily alonside a 31", if push came to shove. (I calculate that at around 70kph, the diff spiders would each take around 4 seconds to complete one full revolution. That low speed certainly won't present a problem for the diff - but isn't it sad that I did that calculation???).

Regards,

Michael...


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  #27  
Old 14 Feb 2003
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Hi all,

Anyone got experience of Michelin XZL O/R 235-85/16 in desert?

Andrew.
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  #28  
Old 14 Feb 2003
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Running larger XZLs can be done with sufficient lift on a Defender. See www.safarigard.com in California. Greg has run 35 to 36 inch XZLs on his D90. I don't know about Land Cruisers.

Graham
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  #29  
Old 14 Feb 2003
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One small anecdote re different tyre sizes and effect on Diffs etc.

I run a Defender on BFG 235/85's. On route I had to buy a Michelin tyre (same dimensions) with a different tread type. Whilst running this new tyre I noticed that the transfer lever (for high and low ratio and locking the central diff) would ease out of its normal (unlocked)position.

When I repaired the punctured tyre and refitted it the transfer lever behaved normally. Whilst the tranfer lever did not move to such an extent that the centre diff became locked (which could have had serious consequences - wind up etc)it does show how even a small difference in tyre size can upset the vehicle's equilibrium.

After this experience and given any choice in the matter, I would only run different tread types let alone different tyre sizes in pairs and would prefer all tyres were exactly the same.

Having different tread / wheel sizes is a serious pain when you start collecting the inevitable punctures and have to start playing "musical tyres" in the heat of the day. You also have to carry more spares tyres and sods law says you'll blow the same tyre type twice.
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  #30  
Old 15 Feb 2003
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Quote:
Originally posted by ctc:
*snip*
Whilst the tranfer lever did not move to such an extent that the centre diff became locked (which could have had serious consequences - wind up etc)it does show how even a small difference in tyre size can upset the vehicle's equilibrium.


I am not sure what you mean by this. What would make it lock? Of course I agree about the damage if the diff does get inadvertently locked. It would be a bad problem with identical tyres, but a worse problem with odd-size tyres.


After this experience and given any choice in the matter, I would only run different tread types let alone different tyre sizes in pairs and would prefer all tyres were exactly the same.

Having different tread / wheel sizes is a serious pain when you start collecting the inevitable punctures and have to start playing "musical tyres" in the heat of the day. You also have to carry more spares tyres and sods law says you'll blow the same tyre type twice.
Yup, I'd only use unmatched tyres (and have done so) if I was already in a bit of a pickle.

I am interested in your anecdote about odd tread patterns causing the effects you described. I can only ascribe it to some sort of vibration effect, because the centre diff should comfortably cope with minor variation in tyre diameter - indeed, up to several percentage points variation. Any theories to explain it, given that the tyres were almost identical size?

Michael...


[This message has been edited by SandyM (edited 15 February 2003).]

[This message has been edited by SandyM (edited 15 February 2003).]
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