glaggs

Cool a couple of Jimny's entered - should do OK 'cos its gonna be a nice tight course.

Why would you want to? All that salt water is just going to eat your truck!

Saw the same Landy at the Lincoln Steam Rally, a group of Landy enthusiasts were try to control their emotions as we walked past. It does look like its never seen mud - but hey Que Sera Sera n all that.

In that case the band better be playing..........

Hows everyone else's preparations going? We're ordering some more mud for the mud run as this seems to be in sort supply at the moment, water however is still available in large quantities. See you there.

Apparently only Landrovers are air sensitive and must be run on oe air - part no; O2CO2NO2-H2O and is only available at main dealers and must be fitted by a certified technician.

OK if this was true why not just run' solid tyres and leave out the air altogether. You could engineer them to deform to give the right contact patch on the road surface and even offer some help by deforming over bumps etc. Answer because they would over heat because the air pocket is an aid to keeping the tyre at the optimum temp. Adjusting the amount (mass/volume -delete as you wish) of air inside the tyre will influence the operating temp of the tyre. Temp. of the tyre is crucial to the tyres performance, ever heard about warming up the tyre?

Try hot air, there seems to be plenty of that freely available.

Depends on the Fish.

Sorry stand corrected on mixing up the terms volume and mass ref the air inthe tyre. Still maintain its the 'mass' of air that is the crucial factor in bearing the load. Tyre construction has an influence but only a samll one. The industry talks in terms of air volume not mass, sorry. Applying the calculation from the link I need 17psi per tyre based on a gestimation of vehicle weight, which sounds about right. Off to buy some chalk and see if we were close?

No you are confusing the internal area of the tyre with the amount of gas compressed into that space. If your theory was correct putting air into a tyre would be like putting water in a glass, By doubling the volume of air you will also increase the pressure. As I said earlier Iwasn't trying to start a debate, these are facts and I think simply explained in the link. I was hoping to maybe find a tyre technician on the forum who could add to the collective knowlage, not argue proven and tested science! Keeping it simple - Larger tyre = larger space in side it. To inflate it to the same pressure as the original tyre you will have to add more air ie a greater volume of air. But your truck will now handle like a person I'm not that keen on. Let air out and reduce the pressure to one equal to a figure as calculated in the article and your truck will handle OK again. Take it off road and let more air out so it'll grip on the mud etc. Air volume supports the vehicle FACT! - not air pressure.

I knew there was something out there that supports the facts as I understand them.... check this link out you non-believers! http://www.4x4mag.co.uk/novfeatures/novtyres.htm

Sorry but no. Volume of air could be measured as its introduced into the tyre. The more gas put in, the higher the pressure. Yes the internal volume of the tyre is constant but volume of air changes proportionally to the pressure. Its not easy to measure the volume so we measure the pressure. However it is important to understand that on a given vehicle, fitting bigger or smaller tyres, you can't assume that running the manufacturers recommended pressure will be OK. The air volume supports the vehicle, thats the fact, the way of checking correct volume is by measuring the pressure. I wasn't looking to debate this, just to find an easy calc link!

As pressure is dependant on volume or mass of air in the tyre and vice verca then yes. To control or adjust the temp at which a tyre runs then the pressure is adjusted. Your owners handbook will probably recommend increasing pressure(volume) for sustained high speed driving. The danger is - run a low profile tyre at manufacturers recommended pressure n you'll be in deep pooh! The pressure needs to be increased to conpensate fo the smaller tyre volume - the question is by how much and how to work it out. The same applies with larger tyres. Run em at manufacturers recommended pressure n the tyre will be over inflatted, at the extreme this could be dangerous because of reduced contact area and tyres running at below optimum operating temp.

OK, I'll throw another spanner in the works. The volume of air in the tyre controls the temperature at which the tyre runs. Rubber compounds are formulated to offer the best grip/wear rate compromise at a given temperature. Too little air (pressure) too low and the tyre will over hea, which causes excess wear, tyre cooking and delamination. Too much air (pressure too) high and the tyre will not reach design opperating temp and therefore not grip efficiently. I appreciate this is not a big issue with tyres designed mainly for off road use, but anyone reading this thread and sidding with the pressure is primary impotance side of the agument should be carful if messing with road/performance tyre pressures. ps. I worked for Dunlop for 7 years and sold tyres (motorcycle) for 10+yrs.

Is this why the air in old tyres smells like fish? ps. "Argh The moral of the story is: Just put 30psi in the darned thing and it won't be flat ".......................... and, you'll get stuck in the muddy bits.

I agree that a gas at a given pressure will occupie a given volume of space ie the inside of the tyre. By putting more gas into the given space it is compressed and thus presure increases, this allows a larger volume of gas than the tyres actual internal volume, again increasing pressure. http://answers.google.com/answers/main?cmd...w&id=232922 http://answers.google.com/answers/threadview?id=233041 These links does help expain the science.

Surely unless it's gone dead flat, the volume of a tyre is reasonably constant? Mind you, I only have the two Science GCSE's The internal volume of the tyre is constant, but as air is a gas it can therefore be compressed, this is why as you add more air the pressure increases. You are forcing more air volume into a fixed(for sake of argument) area. If the volume of air a tyre could hold was constant you wouldn't have to add air, there would be enough in there when it was fitted and you'd never have worry about punctures!. Max pressure is limited by the tyres strength of construction not by its internal volume. And sorry I didn't do GCSE's I did good old fashioned O levels. If your not convinced by the theory pleaes check the links. I agree that tyre manufacturers finalise recommended pressures by testing, after applying an educated guess.

OK I know the suck it and see method of calculating pressure but was looking for a more 'scientific' method of working out pressure for road use when fitting over size tyres. Yes pressure is important for a given size of tyre carrying a given load. Pressures are quoted because they are the easy way to check if a tyre has the right volume of air. Check your Discovery (or what ever ) manual and different tyre sizes are shown with different recommended pressures. Add weight and the book recomends adding more air volume to support the weight, but again the easy way to check this is by checking pressure. On racing tyres the temp of the tyrte can be tuned by adjusting the volume of air doing the work. More volume = higher pressure = trye runs cooler but looses grip. Less volume = lower pressure = hotter tyre and more grip. This is simplifying things a bit but the theory is soun. I was looking for a quick calc matrix which might help with tyre size/pressure calcs? Boy racers fitting bigger rims and ultra low profile tyres have to run higher pressure to maintain the volume of air in the tyre and thus keep tyre performance at its optimum. The reverse must apply for bigger tyres to be run safely on the road? http://answers.google.com/answers/threadview?id=233041 This link may help, but its back to GCSE physics time!

The theory with tyres is, it is the volume of air that is critical not the pressure. Therefore if you fit larger tyres inflated with the same volume of air the resulting pressure will be lower. Couldn't find any sites that could give a conversion matrix so had to resort to some basic GCSE physics. According to my calculations the Jimny with 31x10.5 -15 tyres fitted should now be running 13.6psi ! Currently they have 20 psi in, and the oe fittment 205/70-15s recommended pressure was 24 psi. With 20 psi in they hardly deform at all at the bottom, so perhaps the calculation is right! Anyone got any links for easy calc. sites?

OK just a couple of points. It seems to me reading this thread that some people are mixing up "expert" and "enthusiast" and fogetting that neither description imply that one must a top points scoring competitor. Secondly I wasn't trying to sayt this thread or this forum are one make bias, as my clumsy english seems to have been interprited. I was likening some of the biggoted coments to those that I have encounted at Landrover shows, on Landrover forums and from Landrover owners. Generaly I like this forum because of the diversity of vehicle that I know the members drive and their ingenuity and imagination when trying to create the ultimate off roader.

Until reading this thread, or more accurately some of the comments in this thread I had been quite happy with the banter on here, but I hate it when it gets personnal. Costructive critism is great and the guys at TOR will agree I'm sure, but to start getting personnal ain't cricket, or off roading!

My interest in off roading came from picking up a copy of TOR. I enjoyed the read and got the bug. Since then I've bought and read all the other Landrover biased 4x4 mags. usually because they have an article which aroused my interest. On the whole I still find TOR gives a better balance of read for those who like to use their trucks as God intended. I also know Steve through meeting when he photo'd my truck for the mag and subsequently at many of the events he has attended. I find him friendly, open minded and a true 4x4 enthusiast. I would like to have him as a friend, perhaps now I'm being biased. A mag like TOR which is so specialised to the point that it struggles for circulation will consequently struggle for advertising revinue. Anyone who knows anything about the world of magazine production knows this is where the money is made, not the money they get from off the shelf sales. It would be a shame if TOR disappeared from our newsagents, but alas with the biggotted, ill informed bleatings that I've read from some people on here I can see that the Landrover best sod the rest biggotry I find at Landrover shows, in mags and on various forums will win the day and those who don't want to follow the flock will have no where to get our fix. TOR don't always get it right, who does, but they feature vehicles and products because of what they are, not for the badge on the bonnet. Rant over - sorry - see you in the mud somewhere soon!

Had a great weekend marshalling and got some good piccies. Judging by this one you guys enjoyed your selves too!