If you run a car – a small, medium or even large one – then choosing replacement alloy wheels and tyres is pretty straightforward. However, if you own a T4 or a T5, then things are a little trickier. It’s not a problem, far from it, but you do need to be a bit more careful when it comes to choosing your alloy wheels and rubber.
Most obviously, Vans are heavier – in some cases, a lot heavier – than cars, and a set of wheels that work on a Mk7 Golf aren’t necessarily going to work on a T5. The key is to choose wheels designed to cope with the load you are about to place upon them.
The buzzword here is ‘load rated’. We spoke to UK replacement and OEM wheel manufacturer, Automotive Wheels, to find out what this means.
From a regulatory perspective, it means almost nothing, certainly in the UK for alloy wheels. Tyres are slightly different, but we’ll come to those in a minute Essentially, there is no current regulation in the UK concerning the suitability of a replacement alloy wheel, or its use. This means that there is no way of telling – easily – whether a particular wheel has been manufactured, tested and certified as safe for use on a vehicle that can weigh anything up to three tonnes. Crazy, but true.
There are standards in Europe though. Chances are you’ll have heard of TüV approval. The TüV is a German national standards body, which is responsible for testing and certifying car parts with a ‘National Type Approval’ or ‘ABE’. Every OEM (Original Equipment Manufacturer) or replacement alloy wheel must be tested and ‘TüV approved’ before it can be sold on the German market.
There is also a pan-European initiative, known as ECE124, which sets out the same standards for testing across Europe and was developed to regulate the production of pattern wheels to ensure they are to equivalent standards as OE wheels. Wheels granted European approval under this regulation must be of the same specification – diameter, width and offset – as the original wheels.
Amongst these many standards, there are three main strength tests that wheels need to pass to meet both the TüV and ECE124 standards before they can be sold in Europe. One is a bending test, where force is applied replicating vertical and lateral loads to simulate cornering. Another is a rolling fatigue test, which simulates the weight of the vehicle as the wheel turns. Finally, there is an impact test to simulate the wheel and tyre hitting something in the road. All tests are carried out with appropriate sized tyres fitted, relevant to the vehicle they are being tested for.
There are several factors that affect the strength of the wheel. Design is one and, using Finite Element Analysis (FEA), this can be simulated on computer before a wheel is even made. Another is the manufacturing process. Most wheels are cast by gravity or low pressure, where molten material is either poured or forced at low pressure into a mould and then allowed to cool and set. Stronger wheels can be produced by forging, where material is forced into a billet under high pressure and then machine finished. However, this pushes the cost up hugely, so much so that one forged wheel can cost the same as a set of cast ones.
The heat treatment processes a wheel undergoes after manufacture also affect its strength, with T4 increasing overall strength and T6 increasing hardness of the wheel. Both change the molecular structure of the material the wheel is made from to give the desired result.
When it comes to determining the actual load capacity for a wheel, this follows on from engineering data from the manufacturer, generally available in the brochures. According to Automotive Wheels, the published maximum rear axle weight for a T5 is 1,720kg, so the necessary weight capacity of a single wheel is 860kg. In practice, you should add a little extra to allow for the maximum permissible nose weight on the towbar if you plan to tow, which might add another 100kg in total, so an extra 50kg for each wheel.
Additionally, there are published guidelines on the relationship between the width of the wheel rim and the size of tyres that are appropriate for it. For example, an 8 x 18-inch rim should only be fitted with tyres with tread width from 215mm to 245mm, with 225mm or 235mm the ideal. According to the ETRTO (European Tyre and Rim Technical Organisation) standard, the wheel and tyre combination must be within 2.5% of the factory, or OE, rolling diameter.
When it comes to tyres, things are a little less complicated. If you follow the rules… The maximum weight capacity of a tyre is part of the designation and is marked clearly on the sidewall. It is a number next to the speed rating, which is a letter. For example:
235/45 x 18 105 H
235 is the width of the tyre tread in mm, which means this tyre is suited to an 8 x 18-inch rim
45 is the profile of the tyre expressed as a percentage of the width. It determines the sidewall height, in this case approximately 106mm
18 is the diameter of the rim it fits
105 is the tyre load rating, indicating it will sustain a maximum load of 925kg
H is the speed rating of the tyre, meaning it will sustain a maximum speed of 130mph / 210kmh
Keeping it personal
I recently had first-hand experience of the potential problems highlighted in this feature. Driving my new (to me) T5 Caravelle on 20-inch Range Rover rims home, there was a massive ‘bang’ and the inevitable flat tyre. I had to drive off the motorway to change it, so scrapped a tyre. My go-to guys came round the next morning with two replacement tyres and discovered both front wheels were cracked, and hence also scrap. Turns out they were cheap copies with no certification, no traceability and definitely no recourse. On closer inspection, the rears were completely different and appeared to be genuine parts. So, a lucky escape, and a lesson learned. Please take this as a warning.