We have searched for the information, but we were not able to find how many car models British customers can choose from. We’d bet there are a few hundred to pick, but there is no way to tell that for sure. That said, you can imagine that being among any list there can be either very good or very bad. The Tesla Model S was in the regrettable side as one of the 15 least reliable cars in the UK, according to Carwow.
The video above starts by presenting how Carwow managed to create this list. Warrantywise helped by providing the frequency of warranty claims to calculate how likely it is for the car to present issues. In other words, how many claims happened in a given time period. Carwow mentioned the last ten years, so that was probably the period chosen in this calculation.
In that sense, a car that had 10,000 claims is more reliable than one that had 100,000 in the same period. We wonder how Carwow corrected the fact that there are probably fewer units of the Tesla in the UK than the Ford Galaxy, the 12th on the list. Perhaps with the frequency of warranty claims per car sold? The video does not clarify that.
That number was then multiplied by the average cost per claim to create the ranking. According to Carwow, the lower on the list the car is, the more it exposes its owner to issues. We did not understand the logic.
Gallery: Carwow says Tesla Model S is among the 15 least reliable cars in the UK
Classic frequency definition states it is the number of occurrences a repeating event has per unit of time – or one divided by that number. The larger the number that divides one, the lower the result is. That said, it makes sense to have the worst cars in lower positions on the list. But why multiply that by the average cost per claim?
If our reasoning above is correct, a car with a high average claim cost will benefit from a high frequency of issues: it will make it look smaller.
Imagine this example: car A has 10 claims, and car B has 100 complaints, which obviously means it has more defects. If you divide 1 by 10, you’ll get a frequency of 0.1 for car A. If you divide 1 by 100, car B will have a frequency of 0.01.
If both cars have the same average claim cost – £1,000, for example – car A will get 100 as a result and car B, 10. The lower one on the list really is the least reliable. But what if car B has an average claim cost of £10,000? Both cars would get 100 on the list. Yet, car A has less and cheaper claims. That would be a massive distortion.
Trusting the calculation without a good understanding of how it was made is an act of faith. Although both Carwow and Warrantywise are reputable firms, we would love to see a more extensive explanation. Not on the results, but the methods.
According to them, the Model S is the 15th on the list, with a £1,322 average claim cost and £4,402 for its most expensive warranty claim, related to its air suspension.
Consumer Reports has already stated the Model S is not a very reliable vehicle, but it also says the Model X is much worse than the Model S.