[arobwk]

Time for 3nd set of tyres for my 4WD Dacia Duster at 78.6k miles:  the 2nd set, with slightly more open treads, were not much better for my on-field (soft ground, often wet) needs in the end.  So I am going to bite the bullet and buy much gnarlier/proper off-road tyres this time (especially as my on-road mileage is reducing). 

Choices for gnarly tyres ("designed" for 80% off/20% road say) for a 16" hub are not overly common, so I'm having to search carefully. 

BUT to assist me in my selection, can anyone advise whether they have found much difference between wide or narrow "proper gnarly" off-road car tyres on their fields in soft/wet/muddy ground.

My standard tyre is a 215/65 (8.5" wide tyre), but 235/60 (9.25" wide) and thinner 205/70 (~8" wide) and 155/90 (~6" wide) would all do.  So, if it's a proper gnarly tyre is it better to go wide or narrow for soft ground use or doesn't it make much difference (from your experience) ??  (A Dacia Duster is not particularly heavy as 4WD cars go.)

[chrismahon]

The way I look at it is the gnarly tyres give more pressure on the contact surfaces allowing them to dig in. So narrow tyres will in theory dig in further. But you could reach a point when there are not enough contact points on soft ground and the surface just rips up, so you would then need the widest tyre. As conditions vary I think so will the tyres, so you are just aiming for a compromise and I'd go middle, so 215 or 205.

[Glencairn]

I made the change from highway terrain to all terrain tyres this year.

On the positives, going to my woodland is a lot more pleasant.

On the negatives, the tyres are much more heavily constructed, so I'm a little down on power, my fuel economy is down 10% and roadholding on wet A roads in the corners is a bit squiffy.

I generally feel its usually best to stick to a tyre size that came with that car as a factory option.

215/65/16 has a good range of offerings.

Like the yokohama GO15 Geolandar A/T, I'm aware people have spoken favourably about these tyres and they are not expensive at £65.20 from camskill and a similar price from demon tweeks.

[arobwk]

I am actually running the yoko' G015 ATs now: indeed they do/did get good reviews as all-terrain treads, BUT unfortunately they do not suit my fields. (Thanks for the suggestion though [member=171683]Glencairn[/member] - are you actually using these or something else ?)


In response to Scarlet.Dragon's points: my soil is very soft/loose (without much clay content); top-soil is thin in some field margins and extremely deep elsewhere (I have pulled tractor into the soil up to axles in in-attentive moments with a box blade without reaching sub-soil !).
No matter what 4WD mode I might be in or try, my soil seems to be able to foil Nissan's very clever electronically controlled 4WD system.  In very wet conditions, if one wheel breaks through the sward and momentum is lost, then the others will quickly follow more often than not and the car gets bogged down.  (Luckily the G015s seem to have better off-road traction in reverse and I've only towed the car out once with the tractor.)


I thank you all for your thoughts so far:  they've helped me think through this issue better (I hope) & I reckon I should avoid narrower tyres and maybe go wider (235/60 is only 0.4% greater in diameter than a 215/65 so won't affect speedo, torque etc by much at all) or stick with 215/65, but with a much more open tread on either.  I'm on the search. 
(I know my mpg will suffer - sorry world - but I'm not on high mileage and I don't heat my house so I must surely have a few "Browny points" to use up.)

[Glencairn]

I am actually running the yoko' G015 ATs now: indeed they do/did get good reviews as all-terrain treads, BUT unfortunately they do not suit my fields. (Thanks for the suggestion though [member=171683]Glencairn[/member] - are you actually using these or something else ?)

I'm running Bf Goodrich KO2's, mostly on rough forestry tracks though, have done very little on grass.

Having a quick search for mud terrains only really throws up insa turbo, which I can't help but think might be more of a compromise than your yokohama geolandars.

[arobwk]

Again, thanks for replies. (Another long post from me, but someone might benefit down the road - or up the hill or across the bog !?)

Back to the Yoko' Geolanders;  I found, some 33k miles ago, that they do different tread spacing with the one for passenger cars (smaller wheel sizes) being the least open tread.  (I wonder whether this is due to computerized scaling* according to wheel size !?)  I'm thinking the Insa Turbo for a R16 wheel is worth a look instead. 

Insa Turbo comes in at least 2 tread patterns - Dakar & Ranger - with Ranger being a copy of the Goodrich KO2 (which is less aggressive than the Dakar), but am wondering whether scaling (*as above) to a R16 wheel will end up with something like Event Tyres' alternative/copy of the KO2 tread pattern (reported as having quite soft rubber compound). I might go for the Insa Turbo Dakar version !

As to car/wheel control;  I can quite accept that I might not be doing everything right, but, believe me, I have researched best advice for driving in off-road slippery conditions and tried every variation of 4WD settings (auto, fixed and with or without traction control) in 1st, 2nd or 3rd for any retries when I have failed to make way.  (I should add that this is mainly an up-hill issue, BUT by no means always - bogging down sometimes happens on the flat.)  I shall, however, keep Scarlet.Dragon's wise words in mind when a wheel next snatches.
As to forward v reverse gear:  Duster 4WD reverse gear is much higher ratio (too high IMO) than its 1st gear, but lower than 2nd, yet car has only failed once to pull itself out of a mess in reverse!  I'm still of a mind that my Geolanders' tread works better in reverse when off-road on soft ground !!??]

Autosocks:  never heard of, but thanks for pointer S.D and I've checked out.  Very interesting, but I need to renew my tyres anyway so I'm going to see how new "80 off/20 road" tyres fare first before trying Autosocks as an extra (@ some £70 a pair). 
(Autosocks company advise their socks can help with wet grass, but not at all if there is any mud. I'll deffo get the new tyres 1st !  I can always try out Autosocks later.)

Finally;  my wee tractor has never once been stranded in soft ground (apart from silly circumstances already described) even when towing-out my stuck car in very saturated ground;  so, again, further thought suggests I should go as wide and as aggressive as possible, but taking into account that road use is/will still be the greater car use".   

 

A very useful/thoughtful exchange from my point of view:  again ta and I'll report idc which new tyres I went for.



 

[Rupert the bear]

Ok so from what you're describing your ground will be reacting similar to sand or deep snow. 

The reason you're bogging down is too much speed on the throttle and they will work better in reverse due to lower gearing. 

]You need lower pressure on the tyres to spread the load and wider tyres will do better than narrower in these conditions (similar to sand surfing on the dunes). 

You need to keep your revs low (so use a higher gear than you should; ie start in second not first and keep the revs just above stalling point). 

I'm not convinced that gnarly tyres are your best option here... they are more likely to scuff the surface (which if your sward isn't deep rooted will just get you through to the sand to dig in quicker).  You may find you're better on 'wide slicks' in these conditions.... although they wouldn't be road legal... It may be worth trying something like auto-socks on your road tyres to see if they help to stop the tyres digging through the surface and enable them to travel over the top before you look at changing the tyres.

This x 1000 , Ive no problem dropping tyre pressures to 10 psi , the tyres will still stay on the rim if you dont go mad ! 've pulled trailers through muddy, boggy parks with my Isuzu D-Max , not a light vehicle. And when on the hard surface I have a cordless tyre inflator https://www.argos.co.uk/product/8814401?clickSR=slp:term:tyre%20inflator:2:23:1  that  re-inflates them.

[arobwk]

As an update for anyone who might still be the least bit interested:  I checked out tyre speed-ratings advice, regs & insurance implications.  It seems to me that mounting treads with a lower speed-rating than the official top speed of one's vehicle might, just might, have insurance implications if Ins' Company wants to be difficult.

So, unfortunately, I will not be going for the Insa Turbo Dakar after-all (Speed rating Q = 98/99 mph).  Instead I will go for Insa Turbo Ranger spec' - less aggressive tread (spec'd as 50off/50on) with speed-rating "S" (112 mph).  This is based on the BF Goodrich KO design. (If I mentioned KO2-copy before, that was a mistake - the older KO version was much respected also!).   

AND, I find I have a local tyre fitter who will supply and fit Insa Rangers for some £86 a wheel.  Brill - result !!

[  Insa tyres are re-moulds, but that doesn't worry me - air-travelers are (oh umm, that should be "were") frequently making contact with terra firma on re-moulds ! 
Insa is a well-known company based in Spain (thankfully not in France so I don't need to boycott them!) and re-moulds are just that little bit more environmentally friendly - in theory.  (I haven't done the eco' research yet re tyre recycling.)

Am looking forward to the "up-grade" from my Geolanders even if the Insa Rangers are also just categorized as 50off/50on !  ]

[arobwk]

Scrub some of the preceding (no pun intended):  Mr Numpty will not be "up-grading" his car tyres immediately after all !!!
As much as Mr Numpty would like to improve traction ont' fields with different tyres, he has just applied his own tread-depth gauge to his car's tyres.
He finds that, contrary to his last two MOT records, his car tyres have relevant tread-depths substantially above 3mm (leaving aside the legal min' of 1.6mm)
One tyre is worn down, in places, to the "indicator" 3mm lug, but, even so, Mr Numpty's gauge says the tread at the 3mm indicator lug actually measures 4mm !!)
What!!??
Mr Numpty has now vowed not to be such a lazy/trusting numpty in future and will also put up with his existing tyres for a while yet, in the interest of his bank balance and the planet.
 

[Glencairn]

I believe its not uncommon for unscrupulous garages including main dealers to under read tyre tread depths. They must get away with recommending replacements otherwise I doubt they would do it.

A tread depth gauge is a useful addition.

Along with a trolley jack, axle stands, 12v inflator, torque wrench...   

Lidl's do the 'ultimate speed' line up occasionally, some of the stuff is the same as the other brand stuff in Halfords but cheaper.