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Post by Nelson on Sept 19, 2017 15:38:51 GMT
Mrs B and I were watching an old episode of Top Gear last night (plenty on Dave to choose from) and one question from Mrs B during one item has stumped me for an answer
Why do all new tyres have a tread depth of 8mm? she asked as she saw some knobbly off-road tyres on a bespoke vehicle and wondered why can't road tyres have a deeper tread and what would happen if they did?
Good question i thought...
What would the effects be on ride, handling, braking etc of having a new tyre with a tread depth of say 12mm or more or would there be little difference it's just a marketing ploy to get you to buy tyres more quickly.
Seems a daft question but one out on the road today I have failed to come up with a logical answer in my head
Helllllllllllllpppp
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Post by johnc on Sept 19, 2017 16:10:43 GMT
The deeper the tread, the more flexible the tread blocks become. I am sure it would be possible to have deeper treads on road tyres but there would be a drop off in performance in the dry and they may even overheat and wear out faster.
The last 20 years have seen an increase in width and emphasis on performance and I can only assume that someone has come up with 8mm as being the optimum depth to maximise performance and minimise overheating and wear. |
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Post by LandieMark on Sept 19, 2017 16:32:09 GMT
My BFG A/Ts on the Land Rover have a lot more than 8mm! 12mm according to a quick search.
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Post by Deleted on Sept 20, 2017 7:51:10 GMT
I think mine were 6mm from new, but I could be wrong.
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Post by alf on Sept 20, 2017 8:17:08 GMT
On-road tyres tend to have 8mm from new. I think part of the reason must be that tyre tests are conducted with new, just scrubbed-in tyres. More tread depth would make them perform worse in extremis on a track. There is a trade-off between how well it performs new, and how long it lasts, and for whatever reason 8mm seems the common trade-off.
I doubt tyre manufacturers particularly want them lasting longer either...
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Post by Roadsterstu on Sept 20, 2017 11:29:32 GMT
I'd agree with John, deeper tread blocks will result in more flex in the tyre. Then engineers would have a harder job maintining a consistency of feel and performance throught the life of the tyre as the tread depth reduces. No idea why 8mm specifically. I assume it's been determined through international regulations and type approval processes. Off road tyres are totally different, of course, as on road handling is secondary to off road performance. Good question from Mrs Nelson, though.
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Post by Blarno on Sept 20, 2017 15:24:01 GMT
Depends on the tyres. Our new Kumhos are 7mm at the absolute max when brand new, nearer to 6mm.
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Post by Martin on Sept 20, 2017 15:30:22 GMT
The Porsche rated P Zeros are 7mm, the Goodyears were 8mm.
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Post by PetrolEd on Sept 20, 2017 15:40:40 GMT
Martin, you may know, when are the PS4's available in N Rated spec?
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Post by Martin on Sept 20, 2017 20:44:04 GMT
I don't I'm afraid.
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Post by grampa on Sept 22, 2017 9:58:10 GMT
I'm sure I've read somewhere that they don't do it because the extra depth of tread would be very quick to wear - myth perpetuated by the tyre manufacturers because they don't want longer lasting types? - apart from a few tyre technicians, who could say? - the only thing that suggests it's true to me would be that one manufacturer could soon steal a marketing lead by introducing a road tyre with say 10mm depth.
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Post by Deleted on Sept 22, 2017 10:01:44 GMT
I guess you also wouldn't want a tyre's circumference to change too much during its lifetime - would have an effect on speedometer and odometer readings, I'd have thought.
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Post by bryan on Sept 22, 2017 14:23:01 GMT
I thought it was to do with wear ie first couple of mm wore through quickly then slowed as they got lower and aged - guess the 7-8mm is the happy balance?
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