Tech: Everything about Tyres

Ask questions or share info that applies across makes or models, things of general off-road interest.
pseacraft
Rank: Senior
Location: Missing my Navigator...
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Joined: Fri Jan 01, 2010 10:56 pm

Tue Nov 02, 2010 9:36 am

Yeah, and the bugger is that depending on which website you can even find a few charts for the same setup that are different. Of course when in doubt you can always ask the manufacturer. I had a devil of a time finding 4.56 anywhere so i went to Superior and asked them... They were surprisingly quick to respond to my questions about availability and even asked what my off roading goals were and then they added their professional opine to the mix. So here I am with 4.88 and happy as a peach on a tree in hot-lanta.
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pseacraft
PR
Rank: Expert
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Joined: Wed Apr 07, 2010 9:22 pm

Tue Nov 02, 2010 10:59 am

Still on the topic of tyres, for the record, the tyre pressure most commonly used offroad in UAE is around 15 psi. Lighter cars, and all cars in tough sand conditions, can go lower but under 10psi is pretty extreme and an invitation for the tyre to pop out. I like 12-13psi in tough conditions.

The tyre has two main parts: the tread and the sidewall.

The tread is the part that comes in contact with the ground:
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And the sidewall is the vertical part, where the markings are:
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For driving on sand, I prefer tyres with a soft sidewall that allows the shoulder to fold down nicely after deflating; I like ridges or protection on the shoulder between sidewall and tread (so when deflated you don't have thin rubber touching the ground); and I prefer a non-aggressive tread because I don't drive a powerful modified car. If you have the power to spin wheels, then more aggressive treads can give you more traction.

And an interesting fact, a narrow and tall tire when deflated is much better in the sand than a wide tyre! (less rolling resistance and a wider footprint area)
PR
Rank: Expert
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Joined: Wed Apr 07, 2010 9:22 pm

Tue Nov 02, 2010 12:08 pm

How to know how old your tyres are:

The date of manufacture is stamped into the sidewall, but it's a little tricky as it's not the normal day-month-year... it is a 4-digit code; the first two digits are the week and the second two digits are the year... so 4402 means the tyre was made in the 44th week of the year 2002, so around the beginning of November 2002.

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PR
Rank: Expert
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Joined: Wed Apr 07, 2010 9:22 pm

Tue Nov 02, 2010 12:25 pm

Importance of the tyre shoulder... when choosing a tyre make sure the shoulder is reinforced and imagine what it will look like when deflated and one inch of sidewall is rolling along the ground.

The only punctures I've suffered off-road have been at the shoulder.

See in the photo how the shoulder takes the rock:
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and see how a quad tyre, which is designed for pure off-road at low pressures, has great shoulder support:
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and how this tyre has zero reinforcement, and when deflated to 15psi, the bare sidewall will be running on the ground:
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PR
Rank: Expert
Posts: 582
Joined: Wed Apr 07, 2010 9:22 pm

Wed Nov 03, 2010 12:07 pm

Rims:

As light and strong as possible, but the key point is the backspacing and width.

Backspacing is how far away from the wheel hub does the rim sit - this is important because the closer the rim is, the easier it will rub the fender, especially in the front when turning.

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Offset also refers to backspacing, so don't worry about it.

A set of rims with the perfect backspacing eliminates the need for spacers; or, a set of rims with bad backspacing can still be used with the right spacer. (A spacer sits between wheel hub and rim, making the wheel stickout by an inch or two).

The second issue is the width of the rim. Most rims are 8-9" wide, and this is important because the lip of the rim traps the rubber tyre, making an air-tight chamber and keeping the tyre on the bead (or the tyre pops out).

Going to a wider rim, usually 10", can have a dramatic effect on making your tyres nice and rounded and good for sand - they look like quad tyres 8) but you need to make sure the tyre is designed to fit or it will pop out often when run at low pressures - or you will need to use beadlocks, which are shown in the photo below (technically not road legal):

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