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Best Tyre for Best Grip
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Mr Tyre
Mud Obsessed


Joined: 17 Jun 2002
Odometer: 4880
Location: Darlington Co Durham



PostPosted: Wed Feb 10, 2016 2:07 pm    Post subject: Reply with quote

Tyre pressures are as important if not more off road as they on.The less ground pressure you put on the ground the better the traction, and less ground damage you will do, (to a certain extent).Let me give you an example or two.A Suzuki SJ or Vit running 195/80R15 tyres,if you AXLE load isn't more than say 600 to 650kgs then you can go as low as 12 psi on tracks or similar, if you were in sand/mud AND carrying around 800kgs you can still run 12 psi due to ground you are on.Another example is that at around 1400kgs axle load on tracks where you normally run around 30 psi, for sand/mud you are looking at around 23 psi.
Whether you don't see so many of the 38-40+ tyres in 10.5 or less is down to either lack of availability or just sheer cost i have no idea, i know people running 40 inch diameter BFG on the road on LR 90/110's whether that is something to do maybe how cheap RRS wheels are to buy secondhand i have know idea for that either.
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Xpajun
Mud Obsessed


Joined: 22 Sep 2008
Odometer: 3233



1988 Mitsubishi Shogun

PostPosted: Wed Feb 10, 2016 7:16 pm    Post subject: Reply with quote

RichMayo wrote:
Thanks Xpajun. That's really helped my understanding of what's going on.

Next question...

A lot of trucks I see seem to be running large diameter tyres at least as wide as 12.5". By the time you've worked up to a 40" tyre you could be running as wide as 13.5" - or more? I'm thinking the challenge style trucks, often space frame - I figure they'd weigh even less so need even more help cutting down.

Are they compensating by running lower pressures? Or otherwise? Or are the other benefits of bigger tyres just too great?

So how come there isn't a 40" (or similar) tyre available that runs on a very large rim, which is say 10.5" or less? If there is - why don't we see more of them in the uk in this kinda wood environments where cutting down helps (does seem pretty common over here). Could those 33x9.5's you were talking about out perform a 40x13.5 in terms of traction (assume similar patterns)? I'd be really interested to see.

Sorry for hi-jacking thread (I seem to do this a lot recently :S) but I think we're still on topic.


In challenge you are looking at clearance, a 40" tyre gives 5.5" more clearance under the diff compared to a standard tyre, also with challenge you are less worried about traction because you have a winch so width doesn't matter so much - Americans have 44" readily available and they will run them at low pressure - under 10psi - the tire tread will wrap around a rock and provide traction that way. Americans also have 54" tires and 28" rims - at over $2000 a piece - (although I've only seen 36"tires to fit those rims).

We had some 42" swampers advertised on here some time back but they were for a 17.5" rim.

Tyres and rims are available here but it is very much horses for courses:
Trials you need a narrow tyre so you go fro a max of maybe 235/85/16 (33x9.5x16) Insa Special Track
Challenge a tall tyre for clearance and worry less about the width
Comp Safari I'm guessing at maybe the special track again but in a wider size maybe the 265
Euro trials really wide paddle wheels Laughing

It would be nice to see a tall narrow tyre on a large diameter rim but, I wonder about wheel strength and astronomical cost - possibly $3-5000 per corner?

so lets look at portals Laughing Laughing Laughing

Which would be worse - a simexed track or a portaled one Twisted Evil Twisted Evil
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Big Dunc
Just got MTs


Joined: 09 Aug 2010
Odometer: 134




PostPosted: Thu Feb 11, 2016 8:52 am    Post subject: Reply with quote

The other thing about pressure, is allowing the tyre to move. On the road I have around 35 PSI and the tyre is rock hard.

The trials regulations state a minimum pressure of 21 PSI, so everyone is just above that. At that pressure, the tyre is a lot more flexible and this movement allows allows caked mud to clear from the tread blocks.

I often wonder about whether it is worth inflating back to 35 PSI just for the drive home, then the drive to when I am next off roading? To be honest, it doesnt seem to make much difference on road.
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Xpajun
Mud Obsessed


Joined: 22 Sep 2008
Odometer: 3233



1988 Mitsubishi Shogun

PostPosted: Thu Feb 11, 2016 10:25 am    Post subject: Reply with quote

Is that a local regulation? - never had that enforced we tended to run anything from 17psi down
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Big Dunc
Just got MTs


Joined: 09 Aug 2010
Odometer: 134




PostPosted: Thu Feb 11, 2016 10:59 am    Post subject: Reply with quote

No idea whether it is logical, but tyre pressures are checked by the scrutineer so it is enforced.
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RichardD
Marshall


Joined: 13 Mar 2003
Odometer: 22856
Location: State of Confusion



PostPosted: Thu Feb 11, 2016 12:22 pm    Post subject: Reply with quote

Xpajun wrote:


so lets look at portals Laughing Laughing Laughing

Which would be worse - a simexed track or a portaled one Twisted Evil Twisted Evil


Portal axled vehicles don't need to dig to victory - they have the ground clearance to simple trickle over everything unless driven by a leaden footed moron.

Bear in mind that many larger simex style tyres are remould on van tyre carcasses and don't have the side wall flexibility at any pressure. My fedimas have nowhere near the side flex as the creepy crawlers.

__________________________________
Poking the Grim Reaper with a stick then running away. The devil made me do it but God said it was okay with him.
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Mr Tyre
Mud Obsessed


Joined: 17 Jun 2002
Odometer: 4880
Location: Darlington Co Durham



PostPosted: Thu Feb 11, 2016 2:11 pm    Post subject: Reply with quote

Big Dunc wrote:
The other thing about pressure, is allowing the tyre to move. On the road I have around 35 PSI and the tyre is rock hard.

The trials regulations state a minimum pressure of 21 PSI, so everyone is just above that. At that pressure, the tyre is a lot more flexible and this movement allows allows caked mud to clear from the tread blocks.

I often wonder about whether it is worth inflating back to 35 PSI just for the drive home, then the drive to when I am next off roading? To be honest, it doesnt seem to make much difference on road.


If you are 5 feet from the place then no i wouldn't inflate other than i would inflate them.You don't need 35 psi in them, something 28 -30 psi should suffice not unless you carry a ton of weight in the back
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Big Dunc
Just got MTs


Joined: 09 Aug 2010
Odometer: 134




PostPosted: Thu Feb 11, 2016 3:21 pm    Post subject: Reply with quote

To be honest, I have been wondering whether to find a compromise pressure, say around 25 PSI that is OK on both the road and the mud.

Dont normally carry much in the back of any weight (although I am hoping to have a new set of wheels / tyres in it tomorrow) and dont normally drive on the road, other than to/from off road events.
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Mr Tyre
Mud Obsessed


Joined: 17 Jun 2002
Odometer: 4880
Location: Darlington Co Durham



PostPosted: Thu Feb 11, 2016 3:27 pm    Post subject: Reply with quote

Big Dunc wrote:
To be honest, I have been wondering whether to find a compromise pressure, say around 25 PSI that is OK on both the road and the mud.

Dont normally carry much in the back of any weight (although I am hoping to have a new set of wheels / tyres in it tomorrow) and dont normally drive on the road, other than to/from off road events.


25 psi is a good place to start, getting tyre pressures right is sometimes down to what you are happy with.
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Big Dunc
Just got MTs


Joined: 09 Aug 2010
Odometer: 134




PostPosted: Thu Feb 11, 2016 3:40 pm    Post subject: Reply with quote

I am just getting a bit fed up of lowering the pressure in the morning, then increasing it again at the first garage I pass on the way home.

OK, its only once a month or so, but....

I am sure that the special tracks will be a huge improvement over my last tyres, but I expect if my driving were to improve, that would make a much bigger difference than a few PSI here or there.
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Mr Tyre
Mud Obsessed


Joined: 17 Jun 2002
Odometer: 4880
Location: Darlington Co Durham



PostPosted: Thu Feb 11, 2016 4:13 pm    Post subject: Reply with quote

When tyres are soft or low on air they run very hot running them at a lower pressure means they get hotter quicker which could lead to the tyre de-laminating (breaking up) on the inside.
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Big Dunc
Just got MTs


Joined: 09 Aug 2010
Odometer: 134




PostPosted: Thu Feb 11, 2016 5:33 pm    Post subject: Reply with quote

Yes, but I am think I will be safe at 25 PSI, unless you tell me otherwise.
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Xpajun
Mud Obsessed


Joined: 22 Sep 2008
Odometer: 3233



1988 Mitsubishi Shogun

PostPosted: Thu Feb 11, 2016 6:15 pm    Post subject: Reply with quote

Big Dunc wrote:
No idea whether it is logical, but tyre pressures are checked by the scrutineer so it is enforced.


Not sure if your logical was a typo but I said local - what club are you trialing with?


And now for a bit of fun...

If I put a set of high load with a high maximum pressure on a lightweight Suzuki which would mean the maximum pressure in the tyres should be 20psi the scrutineers would disqualify me or make me over inflate my tyres? Twisted Evil Twisted Evil
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Xpajun
Mud Obsessed


Joined: 22 Sep 2008
Odometer: 3233



1988 Mitsubishi Shogun

PostPosted: Thu Feb 11, 2016 6:23 pm    Post subject: Reply with quote

RichardD wrote:
Xpajun wrote:


so lets look at portals Laughing Laughing Laughing

Which would be worse - a simexed track or a portaled one Twisted Evil Twisted Evil


Portal axled vehicles don't need to dig to victory - they have the ground clearance to simple trickle over everything unless driven by a leaden footed moron.

I understand there are a lot of leaden footed morons with portal axles around
RichardD wrote:

Bear in mind that many larger simex style tyres are remould on van tyre carcasses and don't have the side wall flexibility at any pressure. My fedimas have nowhere near the side flex as the creepy crawlers.


There is a school of thought that biased or biased belted tyres are far better than radial tyres for off-road because of the stiffer walls keeping the tyre shape under low pressure with the low pressure allowing the tread to wrap itsef around hard objects rather than spinning on them - radials/soft walled tyres are useless off-road but excellent on tarmac (same school)
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Xpajun
Mud Obsessed


Joined: 22 Sep 2008
Odometer: 3233



1988 Mitsubishi Shogun

PostPosted: Thu Feb 11, 2016 6:30 pm    Post subject: Reply with quote

Mr Tyre wrote:
When tyres are soft or low on air they run very hot running them at a lower pressure means they get hotter quicker which could lead to the tyre de-laminating (breaking up) on the inside.


Radial tyres are more likely to do this but mainly on tarmac not so much off-road, biased or cross-ply tyres are less likely to break up because they are stronger
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Big Dunc
Just got MTs


Joined: 09 Aug 2010
Odometer: 134




PostPosted: Fri Feb 12, 2016 12:15 pm    Post subject: Reply with quote

Xpajun wrote:
Big Dunc wrote:
No idea whether it is logical, but tyre pressures are checked by the scrutineer so it is enforced.


Not sure if your logical was a typo but I said local - what club are you trialing with?


And now for a bit of fun...

If I put a set of high load with a high maximum pressure on a lightweight Suzuki which would mean the maximum pressure in the tyres should be 20psi the scrutineers would disqualify me or make me over inflate my tyres? Twisted Evil Twisted Evil


Sorry, I mis-read local for logical.

S.R.O.C.
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Big Dunc
Just got MTs


Joined: 09 Aug 2010
Odometer: 134




PostPosted: Sat Feb 27, 2016 7:38 pm    Post subject: Reply with quote

All fitted now, but I am away on business and it is SORNed from Tue as I wont get a chance to use it for the next few months
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