Everyone knows tyre performance changes with wear, with the biggest change in tyre performance coming from all season and winter tyres in snowy and icy conditions.
The drop in performance can be so vast after 4mm that certain countries where "three peak mountain and snowflake" tyres are a legal requirement for winter driving, they can lose their legality after 4mm, meaning you only get to use half of your tyres tread.
Should this be the case? Michelin have been making alot of noise recently regarding the negative impact of having to scrap a tyre with half its tread life remaining, and their arguments are compelling. Not only are you costing the customer more, but you're also causing a much higher negative environmental impact by doubling natural resourse usage and doubling waste.
Europe's leading tyre testers at the German publication Auto Bild have decided to find out exactly who's right. On test are six of the best all season tyres, a set of summer tyres and a set of winter tyres. Each set of tyres was tested at new, 4mm remaining tread depth, and 2mm remaining tread depth.
First, the negative. To reduce the tyres tread depth Auto Bild milled the tyres down to just above the target tread depth, then ran the tyres on the road for 1,000km to re-bed them in. This isn't the ideal way of wearing the tyres, in the real world the longer duration of use and more extreme environment has an effect of the chemical composition of the rubber, but it's realistically the only way of doing it for this type of test, as wearing hundreds of tyres on the road is a very long and expensive process.
As for the results? It's certainly worth heading over to Auto Bild for the full picture as there's way too much data for us to summarise efficiently, so instead we'll concentrate on the popular Michelin CrossClimate, Goodyear Vector 4Season Gen-2, winter and summer tyres in the test.
During snow braking, the Goodyear all season tyre started the best, stopping the car in 27.6 meters, with the winter tyre and Michelin CrossClimate close behind. At 4mm the order was the same, but the gaps between the tyres closer, and by 2mm the Goodyear end as the worst of the three tyres, with the Michelin just beating the full winter tyre to being the best in the snow.
Snow handling saw a similar trend, but this time with the winter starting just ahead of the Goodyear. By 4mm the Michelin had taken the lead, which it further improved on at 2mm, proving to be the most consistent tyre on test. The summer tyre performed badly in both snow braking, and failed the snow handling test at 4 and 2mm tread depth.
The wet and the dry tests bring the summer tyre back into contention. Wet braking sees the order of tyre consistent, whatever the tread depth, with the Michelin proving best at all three levels of wear. The summer started ahead of the Goodyear all season, but the performance dropped off more at 2mm wear which means it finished tied, and the winter started the worst on test, and showed the largest drop in performance by 2mm.
Wet handling again showed the Michelin to be consistently the best tyre, and again the winter had the largest drop in performance as the milimeters decreased.
Dry braking proved to be an interesting test. While the winter tyre started extremely far behind the summer tyre and Michelin CrossClimate, at 4mm it was performing the best, and by 2mm it had once again dropped behind the Michelin, but remained ahead of the summer tyre.
The trend was broadly similar during dry handling, only with the winter tyre finishing the best. Sadly we do not know what winter tyre was used, or what temperature the wet and dry tests were conducted at, but it does highlight that once the "dry sipe disadvantage" of a winter tyre has worn away, the softer, more elastic compound of the winer tyre does have some benefits.
As this was primarily an all season tyre test, the testers at Auto Bild only considered the all season tyres in the final result, which are noted below. We recommend visiting the Auto Bild website to see the full data from all six all season tyres on test.
Exemplary all-rounder with balanced performance and the least performance degradation throughout the treadlife. One of the highest priced tyres, but the mileage balances with the price as the best wearing tyre on test. Highly recommended.
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Strong all-rounder with best performance on wet and snowy roads at new and 4 mm. Average dry grip to start with, but improves as the tyre wears. Low rolling resistance, and a good price to wear ratio. Recommended.
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Only good in the snow when new, after 4mm the performance drops. Too expensive for the mileage provided, and high rolling resistance. Conditionally recommended.
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4th: Hankook Kinergy 4S
Like the Pirelli, the Hankook is only safe when new, with the snow and wet performance dropping with tyre wear. The dry performance increases as the tread wears. Poor wear. Conditionally recommended.
5th: Vredestein Quatrac 5
Balanced performance when new, but by 4mm the performance has dropped significantly. Conditionally recommended.
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6th: Nokian WeatherProof
One of the strongest performances when new, but weakest when worn. Poor mileage. Conditionally recommended.