Legal requirements for tyre load ratings in the UK
Can someone point me to the exact legal text on how to determine the load rating requirements for tyres for a specific vehicle, in order for the tyres to be deemed legally roadworthy?
e.g. should it be the maximum axle weight as defined by the manufacturer divided by 2 to get the minimum load that a single tyre must support on that axle.
Or should it be the "revenue weight" as defined by the UK governments database for each vehicle divided by 4?
The background for this question: I am currently in a disagreement with a local garage. I brought in my Renault Zoe ZE50 (2022) for an MOT - and over the phone also gave the go ahead to let them install new tyres, as the old ones were getting there in terms of tread depth - but also already endured some puncture and slash damage. I requested a specific brand and model - but trusted that the garage would choose the correct size and load rating for my road wheels and car. So unfortunately I did not have a preceding quote where I could double check the properties of the tyres myself.
However, as it turned out later, they only installed tyres with a load rating of 87. And by all accounts that I can find, the Zoe ZE50 needs a load rating of 91. It previously had 91 on them (that's why I also assumed that the garage would choose the same load rating for the new ones) and Renault's documentation also only ever mentions tyres (and air pressure) with a load rating of 91.
The garage however only installed 87 as they divided the "revenue weight" from the UK gov database by 4. But if you look at the car's maximum axle weights according to its VIN plate - the front has 1187 Kg, while the back has 1042 Kg. Meaning the front needs at least a tyre rating of 90 (i.e. 91). The air pressure that Renault documents also only relates to the 91s - with 38 psi in the front and 33 psi in the back (since the back axle has 145 kg less maximum axle weight).
Even the MOT inspection manual, section 5.3.2 states
> Make sure the tyre load rating is suitable for the axle weight.
though this leaves some room for interpretation on whether they actually mean maximum axle weight I suppose.
In any case, the garage is being very stubborn and not accommodating at all, only reciting that the tyres fulfil the legal requirements and thus do not want to fix it. They asked me to produce written documentation by Renault and my Insurance that would state otherwise.
So I am in the process of gathering evidence (also asked around in other garages, but haven't heard back from them or Renault) - one of which is the legal clarification. In theory this should be clear-cut from my point of view - i.e. the law should stipulate in detail the requirements for a tyre to be deemed "legally road worthy", but other than the MOT inspection manual reference (wich the garage ignored to comment on) I haven't found anything so far. I even contacted my insurance and they could only tell me, that the tyres need to be "legally road worthy" (well, of course) - but also could not really tell how they would define that in the end.