Introduction

[this entire article is still in the making - changes and additions are planned to be made soon]

One of the most common questions about improving vehicle's all-terrain performance and endurance is "what is the most effective modification to apply to my vehicle?". Well, using proper tyres, and using them properly, is arguably the most effective vehicle "mod" for all-terrain use.

Notice: "Most effective" can generally mean in the context of cost, performance, simplicity or endurance. Using proper tyres properly can be the most effective "mod" in all of those ways!

This document includes the following topics:

• 1. Choosing a proper tyre type for the desired usage;
• 2. Choosing a tyre size;
• 3. List of various tyre models with remarks;
• 4. Best practices on tyre usage (wheel rotation, wheel balancing, air pressures, rim and tyre repairs);
• 5. Special situations and combinations;

General remarks

First of all, some basic remarks about using tyres on four wheel drive vehicles:

• 1a. Inherent restriction of most four wheel drive transmission systems (Jimny's included) is that the vehicle has to use all four tyres of the same profile (size). Furthermore, all four tyres should be the same model and have a very similar tread depth (even small differences between rotational friction and wheel circumference among wheels can damage the transmission in the long term). This limits the combinations when choosing (buying) tyres.

• 1b. The stated restrictions also apply to the spare (5th) tyre, which must not be overlooked! Topic of spare tyre utilization has its own dedicated sub-chapter in the chapter of tyre rotation.

• 2. Frequent checking (and adjusting) of air pressures is much more important for all-terrain use than for ordinary on-road use, because pressures significantly affect traction as well as the risk of tyre damage.

• 3. Wheel (dis)balancing is a much more prominent issue for all-terrain use, especially for Jimnys as they are notorious for developing a "death wobble" issue. It is a genetic trait derived from their short wheelbase and solid (rigid) front axle suspension design.

• 4. For all-terrain use, higher profile tyres are always preferred against lower profile tyres (a "higher profile" means "taller" tyre). Reasons: higher profile tyres cushion the ride better on all-terrain both for the vehicle and for the passengers, they decrease the chance of rim damage, and they allow better air pressure management. Their only disadvantage is worse performance when the vehicle corners fast in a bend, but it is insensible anyway to do so in a high, narrow, wobbly, jumpy, twitchy vehicle. Therefore, putting oversized rims with thin tyres on a 4WD vehicle is like putting ballet shoes on a village farmer.

Choosing a proper tyre type for the desired usage

Introduction

Tyre designs for passenger and light truck vehicles can be (among other ways) designed and built for regular "on road" use (the vast majority of tyre models) or (to an certain extent) for all-terrain use.

The difference between those two design approaches is not just in the tread pattern (traction capability). Another equally important aspect is tyre's robustness (resistance to various types of trauma, which regularly occurs off the asphalt), which is generally given dedicated design attention (based on tyre's exploitation expectancy). For ordinary road tyres, robustness is barely considered on itself. Also, tyre's adaptability to different weather conditions is also sometimes given more design thought.

There is no official standard to differentiate various kinds of all-terrain tyre designs.

There are three "industry categories" of all terrain tyre designs, based on loose practical usage classifications (from "worse" to "best"):

• 1. HT - "Highway Terrain"
• 2. AT - "All Terrain"
• 3. MT - "Mud Terrain"

Tyre manufacturers usually use this classification to position their all-terrain tyre models in their marketing catalogue.

HT tyres generally have the best on-road performance and worst off-road performance of all three categories, while MT tyres generally have the opposite performance characteristics. AT tyres are generally in the middle - being good but not great for both.

Since these are loose classifications, there are "weaker" and "stronger" tyre models in each category, so each tyre model should be precisely evaluated on its own. For example, Dunlop Grandtrek AT20 could be classified either as a "mild AT tyre", or as an "extreme HT tyre" :). Another example is Uniroyal Laredo HD/T, which could be classified either as a "mild MT tyre" or as an "extreme AT tyre".

HT tyre class

Highway terrain tyres are generally meant to be used predominantly on road, with only slight & light off road excursions (possibly rougher gravel, some grasslands, etc.). Their overall tread design and depth is generally quite similar to ordinary road tyres. That means that they generally have equally proficient on-road performance and endurance even for sharp or very fast driving (and similar fuel economy), but almost equally bad all-terrain performance as ordinary road tyres. However, having the "terrain" part in their name, HT tyres should be slightly more robust than ordinary road tyres.

Conclusion - for (almost) always on-road driven all terrain vehicles, HT tyres can be an optimal choice if the vehicles are driven sharply or at high speeds. They are always recommended over ordinary on-road tyres for two reasons - they should be more robust and they at least formally "suit" the all-terrain image of the host vehicle. However, AT tyres are definitely a better choice if proper all terrain driving is even occasionally performed, and/or if the vehicle is not driven fast or sharply.

AT tyre class

All terrain tyres are generally meant to be used in mixed on-road and all terrain conditions (anywhere between 30% and 70% of time for either). They usually have significantly rougher (and a bit deeper) tread design compared to HT and ordinary road tyres. They are a performance compromise which is usually hard to achieve. They are generally good on-road except for sharp or very fast driving, and generally good off-road except for boggy and/or harsh conditions (deep mud, deep snow, sharp rocks, river crossings ...). They are usually significantly more robust than ordinary road tyres. They should slightly impact fuel economy. They can be a challenge to balance properly. Many AT tyres are "all season", which further adds to their "all terrain" value (for example, mountaineers can encounter ice and snow even in June and as early as September).

Conclusion - for all-terrain vehicles which are used for everything - commuting, intercity travel, and various all terrain conditions, AT tyres are the solution. They should not present a jeopardy on the road, and they should be a trusted companion off the road, in the sense of traction and in the sense of reliability.

MT tyre class

Mud terrain tyres (also called "Maximum Traction") are generally meant to be used predominantly off road, with only slight easy-going on-road excursions. They usually have very deep and striking ("tractor looking") tread and sidewall appearance, and very high robustness capability through various reinforcements. They excel in boggy and/or harsh conditions (deep mud, deep snow, sharp rocks, tree roots, river crossings, etc.) and offer the best protection against punctures, cuts and chipping. However, they are generally noisy on the road, wear faster and present a real jeopardy if not driven slowly and carefully on a wet road and especially on packed snow or ice. Also, they usually significantly affect fuel economy. Due to their coarse construction, they can be very hard or impossible to balance properly.

Conclusion - for all-terrain vehicles which rarely touch the asphalt and are used on tough terrain, MT tyres should be the weapon of choice. However, they can be a jeopardy on regular road surfaces and they wear out faster and louder on road. Also, if not balanced entirely, they will cause issues on road.

Choosing tyre size

Factory size and approved sizes

The factory tyre size on all Jimnys is 205 / 70 / R15 (except possibly for some JDMs - Japanese domestic models).

According to some South African and Australian forums (example: this forum topic), their local Suzuki dealers' official policy is to allow +-3% variation in wheel diameter. Therefore, if your Jimny is under warranty (or you want to be mechanically moral), +-3% is your expansion border.

Reasons, benefits and issues

Why would you want to change your tyre size? Well, for all terrain vehicles, the usual strive is to increase ground clearance. Increasing wheel diameter by increasing tyre profile (the second number in tyre size marking) is the most effective way to achieve this. It lifts the entire vehicle (including the axles!), and is dead simple to do for mild increases.

There are additional advantages of increasing the tyre profile ("tyre height") - as mentioned in the General Remarks chapter.

Note: When a wheel diameter is changed by a certain amount, the vehicle's (and the axles') ground clearance will change by only half as much (by the amount of wheel's radius change) - basic school geometry explains why.

However, increasing the wheel circumference/radius incurs the following technical issues:

• 1. The vehicle will accelerate harder / slower and will move faster downhill on engine braking (in any gear);
• 2. Transmission will have a heavier duty to perform, leading to premature wear in the long term;
• 3. Fuel economy can be slightly decreased (because of harder acceleration);
• 4. Speedometer and tachometer measurement will change as much as the circumference has changed;
• 5. Larger tyres might not fit - they might rub on the bodywork when the wheels are turning or the suspension is compressed on uneven terrain;
• 6. The larger spare tyre might not fit in its spare position (contact with some vehicle body parts) and/or in its case/cover;

The extent / severity of these issues highly depends on how much the wheel radius has been increased. They should be negligible to slight at most, if you stay roughly within +-3% of the factory size.

Some of these technical issues can be (and usually have to be) remedied in case of significant tyre size increases:

• 1. Impact on vehicle's acceleration and engine braking can be remedied by altering the transmission gears ("regearing").
• 2. Regearing the transmission will also remedy the load on some parts of the transmission, but some parts, like the wheel bearings for example, will remain under heavier duty;
• 3. Tyres can be made to fit properly by two methods - firstly by lifting the vehicle's body or suspension and/or secondly (usually irreversibly) altering the bodywork (trimming the wheel arches, inner arch linings, etc.), the extent of which highly depends on tyre size;
• 4. In Jimny's case, the larger spare tyre can be made to fit to the tailgate by installing a spacer on the tyre holder, but the spare tyre vinyl cover or hard spare tyre case has to be custom-made (if badly needed);

Some of the mentioned remedies can be quite expensive to apply, and might also imply further modifications. For example, higher suspension lifts require modified radius arm bushes, brake hoses, propeller shafts, adding wheel spacers, buying a new loan at the bank ....

Note: using non-factory tyre size might be illegal or require some vehicle recertification, depending on country or region.

Tyre sizes for Jimny rims

The following table shows all possible sizes which fit on Jimny's stock steel and alloy rims:

TABLE NEEDED HERE

The availability of different tyre models in desired tyre size will vary significantly. Not all tyres are manufactured in every listed tyre size.

As it is evident from the table, even if you choose to stay within Suzuki's alleged 3% allowed wheel diameter increase, there are several tyre profiles which can be used to achieve the goal of higher ground clearance. It is preferred to achieve the goal by increasing sidewall height (second number in tyre profile) instead of altering tyre width. Maximum gain is achieved if both are increased at the same time.

Interesting sizes are 195 / 80 / R15, 205 / 75 / R15 and 215 / 75 / R15.

More to be written further down and in between! Come back later for more!