Thread: 19" Maxxis AT Tyres

Originally Posted by Grentarc

Race Track pressures are basically the opposite of off road tracks - on a race track you want higher pressures so tyres don't heat up too much, you get sharper turn in with higher pressures and also less side to side sidewall movement around corners. On road you don't want/need any of those benefits of higher pressures.

You seen some of the pressures the guys in V8 supercars use when starting out? A lot lower than you'd expect at a mandated minimum of 17psi (which they indroduced a while ago on safety grounds as they where being run lower) - but then again they do that so the tyres heat up quickly and get to correct running pressures sooner and they also run a hell of a lot hotter than road tyres

Originally Posted by Grentarc

Race Track pressures are basically the opposite of off road tracks - on a race track you want higher pressures so tyres don't heat up too much, you get sharper turn in with higher pressures and also less side to side sidewall movement around corners. On road you don't want/need any of those benefits of higher pressures.

Some do want the higher pressures to maximise fuel economy,on road.

I also find AT/LT rated tyre pressures need to be higher than same size,vehicle,etc as P rated,as they seem to run hotter.That is on road,particularly at high speeds.

Originally Posted by shanegtr

You seen some of the pressures the guys in V8 supercars use when starting out? A lot lower than you'd expect at a mandated minimum of 17psi (which they indroduced a while ago on safety grounds as they where being run lower) - but then again they do that so the tyres heat up quickly and get to correct running pressures sooner and they also run a hell of a lot hotter than road tyres

They also run tyres that are constructed differently to road tyres.

I note most of the chat on this thread relates to tyre pressures for 19" tyre/wheels.


As my D4 has 18" BFG Ko2 LT tyres and is always loaded to a certain extent ( bulbar, winch, drawers with tools, recovery gear, axe, air comp etc ) with road day to day driving , any views on suitable tyre pressures for both on sealed roads and gibber type roads ? Currently run 40 psi back and front for around town - which seems to give me reasonable handling and fuel economy. And as for ride comfort, it seems much the same as the original Wrangler 19" tyres

OK given this seems to have turned to pressures some of our experiences after 4 months on the road fully loaded, towing an Ultimate camper. D697s on GOE rims on the car and Cooper AT3 on the camper

On the road(bitumen) and fully loaded. That is the car weighed around the same as with 7 people on board and we had the 3JC on the roof full most of the time plus a second spare, space case with tools and bits and pieces, 10l of petrol for the generator. I mean fully loaded.

Fronts 46 and Rears 52 with trailer matching fronts

Once we left the bitumen and this meant everything from the Finke Track, Kimberley, GRR, Mitchell Falls, Cape Leveque etc.

Fronts 28 and rears 32 and trailer matching fronts

Back in Adelaide and for around town and general travel duties, 32F and 34R

The wear pattern on the tyres was consistent across 22,000km and when we checked in with our Bridgestone tyre engineer his only comment was the wear pattern indicated we were heavily loaded. Won't bore you with how we get to that but my appreciation of that pattern and its explanation helped me appreciate even more how much development goes into manufacturing a tyre

Hope that all helps but clearly from this discussion and many others on this forum, we all drive differently and have vastly differing expectation and approaches to how we manage the four round black sticky things that keep us off the ground

Rob

Thanks for the feedback/information Rob - very interesting. I'm quite surprised how low you could run the pressures on dirt road with such a load on. Maybe I should give my 18' KO2's tyres ( LT ) more credit for their strength and not so reluctant to low pressure on them.

Originally Posted by Garfield

Thanks for the feedback/information Rob - very interesting. I'm quite surprised how low you could run the pressures on dirt road with such a load on. Maybe I should give my 18' KO2's tyres ( LT ) more credit for their strength and not so reluctant to low pressure on them.

One of the things we have learnt from around 20 years of off-road exploration and remote area touring is exactly what you just said. Folk are really reticent to lower tyre pressures to where, IMHO, they realistically should be. The end result for some/many is vehicle damage amongst other things. I reckon we have done over 20 crossings of the Simpson Desert to start with. Combined with the amount of testing we have done for a range of 4WD suppliers/manufacturers our data base is pretty large. On our tours we normally have around 8-10 cars and we collect data on tyres, pressures, vehicle weights and performance on all of them over an average 14-21 day tour. So once again we know rather than guess on performance in varying conditions.

All I can suggest is to give it a go. Collect your data including vehicle weight on specific occasions, it becomes intuitive after a while as you really get to know your car. Without the data it remains guesswork.

Pick a track you regularly use and make the changes record them and see how it goes.

I have to say most folk don't get as close to tyre manufacturers as we have the privilege of doing. This gives us a pretty solid appreciation of how each tyre is manufactured and I can assure you it is a complex process with a great deal of modelling and testing being done before the gear we use even comes to us and others for field testing.

An LT tyre for example is made strong across the tread face and sidewalls. That by design alone brings additional weight. The associated trade-off is normally around a 2% increase in fuel consumption. Not all LT tyres are made the same way. Some are made smarter to retain strength and balance that off against a significant increase in weight. As always there is no such thing, yet, as a puncture proof tyre. I can assure you they are around but there are significant penalties and from a commercial/retail perspective a long way from production.

So don't get me started on tyres

Just have a crack at going lower off-road and collect start point data, make sure you have a decent TPMS to help with that and use your calibrated seat of the pants and see how it goes. But please remember that lowering tyre pressures comes with an associated reduction in speed. On the GRR we rarely got above 90 kph. But that is about the same speed we always sit on when travelling the Oodnadatta track and others around Central Oz amongst other places including the Cape

I will be most interested to hear how you go

Regards

Rob

Excellent advice Rob... you share the same thought process.