It is not without a reason that a wheel is considered one of mankind’s most important inventions. It revolutionized practically everything. Therefore, it should come as no surprise that we start the series on off-road car modifications with this subject.
Frankly speaking: wheels is one of the fundamental aspects which must be thought over very carefully at the planning stage for any additional enhancements of one’s car. They are, after all, the ‘connector’ between the car and the surface we’re driving on. They determine:
comfort of driving (issues related to tyre’s rubber properties);
terrain possibilities (diameter of a new wheel will always be greater than diameter of a standard wheel which will result in greater clearance; and the greater the clearance the more we can do in the field);
To be more specific: thanks to the tyres which are big enough, we can easily go over obstacles which give no chance to a ‘standard’, non-modified vehicle.
In the text below, we will focus on the appropriate selection of rims, tyres and accessories associated with wheels of an off-road car. Once familiar with this material, you will have sufficient knowledge to plan the design of your car with awareness and in accordance with your needs and expectations.
Please remember though, that it is impossible to consider all of the situations and configurations. This is why, if something remains unclear, you will need additional explanations or advice which is suited to your particular needs. You can always simply call us or write to us. We will definitely find a solution for you :)
What do you think? Let’s start!
There is no point in denying it – selecting the right rim is very advanced. Due to the multitude of parameters, choosing it is problematic for both the beginners as well as those already experienced in 4x4 modifications. To be completely honest: there are few people in the field who are competent in it.
The definition of a rim is simple: an element of car chassis, a metal rim on which the car tyre is placed (or tyre and inner tube). Difficulties arise when we try to determine which rims will:
firstly: fit to our car;
secondly: suit our driving style and car’s designation;
thirdly: visually match the rest so that everyone’s jaws dropped at the sight of our car :).
Centre hole (or centring hole) enables precise centring of the rim on the car’s hub (hub is the ‘bolt’ which supports the whole wheel). Its diameter is expressed in millimetres.
We must know the centre hole’s size in order to know if the rim can get fitted onto the hub. In practice, the hole may be larger than the hub (the difference will be eliminated using a centring ring) but never the other way around.
The majority of car manufacturers have established standard hub sizes and the same applies to the rim’s centre hole. For example, for Jeep this is 71,6 mm.
Another criterion for the selection of rims is the bolt pattern which may be different for every car model. This parameter is presented in the form of, for example 5X127 where the first value represents the number of bolts and the second – distance between the bolts (calculated diagonally in millimetres) which is the diameter of the circle on which they are embedded.
The above example (5X127) means that the rim has 5 bolts and the distance between them is 127 mm.
WRANGLER (1987-2006) / LIBERTY
|WRANGLER JK (2007 - ...)||5x127|
Another issue is the rim’s width which on the one hand determines the car’s stability and confident driving and on the other hand is of course responsible for the visual aspect.
In this selection, one should primarily consider the ET parameter (offset) which determines the rim’s offset i.e. the distance between the rim’s centre of symmetry surface and the surface of the rim’s adherence to the hub. The rule is as follows: the lower the ET, the wider the rim’s width. And the other way around. The more positive the ET, the more hidden the rim is in the wheel arch.
An optimal ET is a specific issue for each particular rim in a given size (i.e. it is not something that is permanently attributed to a particular car model).
Selecting an optimal ET value is a specific issue for each particular vehicle model, therefore offset changes shall always be treated individually.
In fact, car manufacturers allow changing track width within the range of approximately 2%. This means that, for example when the track width is 160 cm, the allowed change is 3,2 cm (32 mm). This gives us the allowed ET offset of 16 mm on each side.
As a standard, this parameter is positive, in modified Jeeps often goes down to zero or negative values which makes it possible to move the tyres away from the hub. Thanks to this, the tyres do not collide with the swing arms.
At this point, it should also be considered whether installing wider tyres in the car will not result in legal issues. Currently, the regulations in Poland and other countries of Western Europe do not allow for the tyres to go beyond the car’s outline.
Of course, the enforcement of this law varies. Nevertheless, it is worth being on the safe side and as long as we wish to also use our modified car on public roads – we should install appropriate fender flares. This will allow us to install wide tyres with a negative ET with clear conscience. Let’s not forget that extensions also perform an aesthetic role.
Rim size is one of the first things which is clearly visible when we look at a particular car. During the modification process, clients usually go for 17-inch rims. This choice is mainly determined by practical aspects: this size has the widest range of choice for tyres and these tyres offer the best value for money.
Even though 17-inch rims may not look that spectacular or evoke the ‘wow’ effect, in most cases they turn out to be the correct choice in terms of the modified car’s driving capabilities.
Whilst the selection of larger models (18, 19 inch) is associated with less choice and tyre availability, they frequently prove essential in case of higher lifts. It is mainly due to the mechanical and practical aspects as well as the fact that with a big enough lift, smaller tyres simply look ridiculous and disproportionate.
Sometimes, there are 20-inch rims (and even bigger) though they are mainly used in ‘boulevard’ applications – using such a rim in car dedicated to off-road driving has almost no logical justification. The visual aspect is another issue :)
In our shop, the parameters which determine the rim’s width and size are specified as the first ones in the product name. For example, ‘8X17’, where the first value determines width and the second – the rim’s diameter. Both values are expressed in inches.
An aluminium rim is an element of the car which affects not only the aesthetic aspects of the vehicle (let’s be honest though, it is damn important in this respect) but also determines safety and comfort of driving. It also affects the rate of the suspension system’s wear and tear and participates in the cooling process of the brake system (by using a material which emits heat better and thanks to its specific design – we mean the rim’s design - which ensures air circulation around drums and discs).
In practice, aluminium rims are installed in newer car models. The price range: from PLN 1000 up to PLN 3000 per item. The most expensive models are beadlock type rims which are designed for hard terrain where it is necessary to drive with tyre pressure which is low enough (e.g. below half a bar) to create a risk of the tyre slipping from the rim. A mechanical beadlock (external) is a ring which is mounted to the rim and always keeps the tyre in the same place in relation to the rim. It also secures the internal rant against stones.
Steel rims constitute more of a budget option, especially for older car models. Their main advantage is the price: PLN 300-700 per item. Disadvantages (apart from the lack of most disadvantages of aluminium rims) include the tendency to rust
However, there is nothing that stands in the way of installing a steel rim in the car which is exclusively for intensive usage in conditions which are at least hard, without the need to stress about what the car looks like after such driving :D
Due to limited usefulness, unreliability and questionable aesthetics, we don’t recommend purchasing these rims for cars intended for ‘normal’ driving.
The tyre used in the car (an element which is much more complicated than it is commonly believed) stipulates the consensus between an attempt to obtain the best possible properties which, unfortunately are mutually exclusive.
Example: it is desirable for the tyre’s rubber to have the largest possible point of contact surface with the road surface. The easiest way of achieving this is through reducing the hardness of the rubber mix used for its production. However, a tyre which is too soft will rub off quicker, limiting its product life. And this is one of the reasons why selecting the right tyre for our rim is not the easiest decision.
In case of tyres for off-road vehicles, we have two main categories:
AT - All-Terrain, in other words: a universal tyre. It is not outstanding in terms of its capabilities but it works in all conditions. It is a typical example of a compromise between various extremes.
This tyre is a sensible choice in case of cars which are used both in off-road conditions and on the asphalt.
MT - Mud-Terrain, in accordance with the traditional division, this is a dedicated tyre for off-road driving. It is characterized by a much thicker tread, it also has a special system for cleaning tread from mud. However, when on asphalt, it is loud and causes disruptive micro vibrations. This problem disappears in newer, more expensive models (see the model installed in our demo car) with which you can travel at highway speeds over really long distances.
We hope you’re already used to the fact that there is nothing simple about off-road driving – the issue of tyre size is another example of how simple matters can get complicated. Especially when we have to use metric and imperial measurements at the same time…
Tyres are generally described using the following three parameters:
- external diameter (how big is the whole wheel?)
- tread width (can the wheel be fitted inside the wheel arch? is it suitable to be fitted on our rim?)
- hole diameter (does the tyre fit into our rim?).
Therefore, a marking of 37X12,5R17 means that:
tyre’s external diameter (calculated diagonally!) is 37 inches;
tyre’s tread width is 12,5 inches (it must be equal to rim’s width);
tyre’s hole diameter is 17 inches (must be the size of rim’s width).
We use the imperial system (inches) in the product name. The metric system can be found in the product description, however, please be particularly cautious here.
This is because from the metric marking we cannot read the tyre’s external diameter but the number which characterizes the tyre’s profile height (the relationship between side height and tyre’s cross-section width). Let’s also not forget that only the profile height and the tyre’s width are quoted in millimetres; the marking of the rim’s hole remains in inches.
Therefore, a tyre which is marked in an imperial system as 37X12,5R17 (we can find it in the product name) will look as follows in the metric system: 320x80R17 (we can find it in the product description).
We realize that tyre markings are neither simple nor intuitive – there is nothing we can do about it.
Please remember that should you have any problems with understanding these complexities or difficulties with selecting these parameters for your car, we are always at your service!
As it is often the case, also in the case of car modification, it is not recommended to apply extreme measures. An inadequately considered assembly decision, for example a decision to install wheels which are too large for your car, will quickly come back to haunt you.
We cannot forget that wheels (including rims and tyres, their type, size and everything else you’ve read about here) must work together with other parts of your car.
Therefore, we should be 100% certain that chassis bridges will withstand the weight of the new wheels and will adjust to their style of operation. At this point, it is worth mentioning that except for Jeep Wrangler Rubicon all cars will require bridge replacement into models intended for off-road driving, created for extreme overloads and even in case of this particular model bridge modification might become necessary in some cases.
We also have to make sure that wheels do not touch wheel arches during extended axle articulation. This may damage them and pull them out completely (both wheel arches and tyres). You will read about selecting suspension elements in a separate article which will soon appear on our blog.
At the modification planning stage – and at the very beginning of this process – you should also consider another mundane element, namely… the height of your garage. Many people completely forget about it even though new wheels mean that the car will be much higher! Many times we have heard of situations when the client leaves the shop in his freshly modified Jeep only to discover in dismay that he is unable to drive it into his own garage…
Various levels of pressure shall be maintained during highway driving and during off-road driving. If your car is intended for both types of conditions, you have to remember to simply deflate air from your tyres when entering off-road terrain. In such situations, you can be assisted by deflators which are small clamps which make it easier to evenly deflate pressure in all wheels.
Once you’re done with off-road driving, tyre pressure shall be returned to the initial levels upon return on the asphalt road. This can be done using an electric compressor which is directly connected to the car’s battery.
We have already mentioned that in off-road driving, the worse the better? :)
This rule, however, is only applicable when we are adequately prepared for the worst. For example, when your wheel gets damaged trying to drive over an obstacle. In such a scenario, we typically have two options: we can try fixing it using an appropriate repair set or, if the option no. one fails – use a spare tyre.
The repair set consists of a container with a sealant and a compressor. How does it work? Once a tyre has been punctured, we connect the compressor to the wheel’s valve through which we distribute the sealant inside the tyre. Compressors can usually be connected to the car’s lighter socket.
Eventually, the liquid fills up the puncture and you can drive to the nearest tyre repair service.
The repair set is great and we have no doubt that it may save your ass in certain situations but let’s be honest, we cannot repair a serious damage this way. And you know what it is like, when something goes wrong, it often goes really wrong. If that occurs, there is only one way out which is a spare tyre.
However, in our case, a spare tyre does not mean a small and light tyre which is attached to the car straight from the garage. In our case, we’re talking about a damn heavy piece of rubber (as heavy as 60-70 kg) which cannot be supported by a standard rear hatch of any car and attempts to hang it there will most likely cause bending of your boot hinges. This problem may be solved by installing appropriate clamping or placing the spare tyre on the roof rack.
At this point, it is worth remembering about one more little detail: following your car’s modification (raising it), an ordinary jack becomes useless. First of all, long-arm lifting sets greatly increase suspension travel. So: even if by some miracle you manage to raise the car, the wheel will stay on the ground anyway.
In such a situation, we are assisted by a hi-lift type device which is characterized by a very wide range of travel. As a matter of fact, it is worth investing in hi-lift not only because of its usefulness in tyre replacement. It will also be very useful in saving the car from various troubles which await on every off-road drive (such as mud which is damn deep and boggy).
We realize that selecting rims and tyres (as well as other topics related to car modifications) are not easy subjects. The number of factors which have to be considered may overawe and be scary. Don’t worry about it.
We know that the knowledge which is essential to reliably modify your car will not come to you in 5 minutes. It requires constant learning, testing, trying and experimenting. We’ve already been through this. You don’t have to. It is sufficient to use our experience.
The aim of the above article was to make you familiar with the subject of choosing the right wheels for your car with the consideration of what you really need and we hope that it has fulfilled its task. Please let us know in the comments section if you’ve found out something useful – it is important for us in writing subsequent handbooks!
However, for your own good we advise against purchases without prior consultation with our experts. We are serious. If you’re no 100% convinced that you know well what you want – call us or write to us. Describe your car and your situation. By doing so you can avoid many stressful situations:)