Off-Roading Concepts: Tyres

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Concepts
Tyres

A set of sticky tyres is probably the most cost-effective performance mod you can make to your 4x4. Tread patterns offer varying degrees of performance in different terrains, larger tyres increase clearance, broader tyres may or may not offer better floatation, etc. Here is the concept of the "whole 4x4". You want your tyres to work with everything else. How much articulation, ride quality or safety do you sacrifice when you change tread pattern or fit really huge tyres? I've recounted some of my own experiences below, hoping it will make your decision easier. I've also included links to a tyre glossary, as well as a page describing what you'll see on metric, floatation and numeric tyre sidewalls.

I drive a Jeep Wrangler TJ which takes me to work every day, but also does a fair amount of weekend off-roading, and about 6 trails a year. For starters, the Jeep came with Goodyear Wrangler GS-A's as standard issue. I found out soon enough though, that they were slightly less than adequate for the off-roading I get in to. The pic at right is a Goodyear Wrangler GS-A after stripping off my wheel while climbing a rock wall that offered fair challenge, but can be crawled up without wheelspin. Also, traction with the Goodyears was shocking, although through my ignorance I didn't know.

So after that escapade I started reading up on tyres. I found out about tread designs. There are five basic tread patterns, with a few sub-classes. They are generally biased towards excellent performance in one area, but a careful choice will give you a tyre that is excellent in your particular environment, and generally ok when you stray from it.

	Highway Terrain
	This is an ordinary passenger car tyre and works well on tar. Potentially useful in sand and certain types of rock because of its non-aggressive tread, they are often seen on Freelanders, RAVs, Honda CR-V's, and the like. Beyond this, they are essentially useless on the trail. There is no real advantage to having them unless you do very little or no off-roading.
	All Terrain
	AT's are designed to perform well in a variety of off-road conditions. It is a fairly recent innovation that has closed the highway/trail gap. The closed tread design performs well on rock and sand, and is usually quiet on the highway. They are generally decent in rain, snow and ice. As you'd guess, they tend to load up in mud but some of the AT designs are suprisingly proficient in the goo.
	Mud Terrain
	Mud tyres come in a variety of styles, from the old bias-ply mudders that give new meaning to the term road noise, to modern radial designs that are suprisingly quiet and docile on tar. Apart from their obvious attributes in mud, they are generally oustanding in rocks and good in deep snow. The flexible radial MT's can also be very good in sand, but are at their worst in rain and especially on ice.
	Snow Terrain
	A good snow tyre is not an open-lugged design like a mud tyre. It is moderately open for self-cleaning, but close enough to compress the snow inside the tread and use its cohesion to supply traction. Snow tyres also use sipes and kerfs. A sub-class are tyres that are rated M&S (Mud and Snow), which have some potential as a pseudo AT, but dedicated ST's wear quickly on dry roads.
	Sand Terrain
	Sand tyres are designed to compress sand, rather than cut through it. Sand driving often requires a reduction in pressure to improve floatation, and as sand driving is often coupled with driving over rocky terrain, sand tyres tend to have flexible and robust sidewalls. These tyres wear fast on tar, and are slightly noisier that their HT counterparts, although less so than AT's and MT's.

Through reading and surfing the 'net I found out about load and speed ratings. Every book I found belaboured the difference between cross-ply and radial tyres. I believe that this is becoming a bit of a dated debate (cross-ply is out of date, and rarely used).

The 2" lift I'd fitted to the Jeep is significant as this allows me to fit larger than standard tyres to increase both under-axle clearance and the Jeep's breakover angle. Also, I have this inexplicable fixation with mud and water. Thus my reading was starting to send me more and more into the direction of Mudders. I then started thinking about tyre size . I'd read that with a 2" lift I could safely go with 31x11.50's. Being in South Africa these numbers meant thing to me, and I then figured out that these were floatation tyre sizings. I also learnt that a change in tyre size would change my overall gear ratio from 3.07:1 to 2.7:1, meaning an indicated 10.4km/h increase in my speedometer reading at 100km/h.

My concern now was three-fold: one, afternoon thundershowers on the highveldt are numerous in summer, and MT's don't do that well on wet tar. Two, I love snow-skiing, so my tyres had to get me to Tiffendell and back safely. I have a sister who's a PRO for the Higlands Water Project, so Lesotho ice was also a concern. Everyone I knew, and all the books I'd read were extolling the bad manners MTs have on ice. Lastly, as I drive down to Mozambique and the northern parts of KwaZulu Natal at least four times a year, their performance (or rather, lack of) on sand was at issue.

Then I discovered siping. Sipes are slits or cuts in the tread blocks that allow the blocks to move and grip. Siping usually enhances the wet and icy performance of the tyre, and are sometimes added by the manufacturer but more often than not added by off-roaders themselves.

By reading through predominantly American newsgroups I discovered Super Swampers, apparently a good and popular tyre over there. I was specifically interested in the Radial TSL's. Unfortunately I couldn't find a local distributer, and with my awesome bank balance I was forced into remebering the Jeep parts shopper's credo - "the mostest for the leastest". Exit importing expensive US tyres and enter the BF Goodrich Radial Mud-Terrain T/A.

The BFG MTs are obviously good in mud. They have an incredibly strong and flexible sidewall (3 plies), and are thus very suited to lower tyre pressures and rock crawling. Sand driving cost me a little more fuel than normal. While they tend to push quite a lot of sand before them, I was unable to bog the TJ in 2 wheel drive without a very heavy foot.

Environmentally they're good - the traction provided by the MTs has all but elimitated wheel-spin, keeping the trail intact. Lastly, siping on the two center lugs vastly improved hard braking in wet weather, although I have yet to try them out on ice. They're definitely noisier than HTs and ATs, although the Jeep's open top and loud music drowns that out.