RE: Replace tyres at 3mm: research
Thursday 19th May 2005
Legal limit not safe says researchIndependent research undertaken by MIRA -- the Motoring Industry Research Association -- reveals that braking performance deteriorates in wet conditions when tyre tread depth drops below 3mm.
Replace tyres at 3mm: research
Tyres lose wet grip before becoming illegal
Legal limit not safe says research
Although the legal tread depth limit is 1.6mm, a threshold set by motoring experts some 13 years ago, industry-supported road safety group RoadSafe said there is now "compelling evidence" that motorists should check and change their tyres at 3mm. Road accidents where wet conditions are a contributory factor are on the increase, said the group.
It's only fair to point out, though, that members of Roadsafe stand to gain if motorists follow their advice.
The trend is already upwards according to Town and Country Assistance who said that road accidents where wet conditions are cited as a major cause have increased from 1 in 12 in 1998-99 to 1 in 4 in 2003-04.
“There has been a long-standing belief within the motoring industry that wet weather tyre performance deteriorates more rapidly as the tread depth wears away. A comprehensive test of different vehicles and tyre tread depths now scientifically confirms these claims,” says MIRA’s senior engineer, Simon Aldworth, who carried out the research into tyre wet grip performance at the organisation’s headquarters in Nuneaton.
MIRA’s research was carried out on four separate vehicles, a mid-range family hatchback, an MPV, executive saloon and a high performance saloon car, measuring stopping distances at 50 mph in conditions that represented moderately heavy rain (0.5mm to 1.5mm water depth). The research discovered that tyres with a 3mm tread had a 25 per cent better performance than those at 1.6mm.
In terms of stopping distance this represents an extra eight metres (25ft) in wet conditions. In one test, when a tyre with a tread depth of 8mm was compared to one with only 1.6mm, the stopping distance increased by 13 metres (42.25ft).
“No-one is suggesting that 1.6 mm tyre tread depth is not safe,” says Adrian Walsh. “However with 300,000 crashes every year and a climate which is now much more susceptible to heavy rain, particularly in the summer months, there is a need to take action now. If motorists replaced their tyres sooner stopping distances would improve, accidents would reduce and lives would be saved. With over 3,500 road deaths a year, what bigger incentive can there be to replace tyres more frequently?”
It’s also a view that several car manufacturers hold and they specify in their owner manuals that tyre performance and safety margins decrease once the tread depth reaches 3mm, owing to a reduction in grip and an increased rise of aquaplaning.
On the back of this research, RoadSafe is supporting an autumn campaign to educate motorists on tyre safety and encourage more frequent tyre replacement. RoSPA, which is also lending its support to the campaign, is advising motorists of a four point tyre health check to help increase driver safety:
Every two weeks check the pressure of your tyres when they are cold.
Check the tread depth of your tyres. Although the minimum legal UK tread depth is 1.6mm, RoSPA recommends that tyres should be replaced when the tread depth reaches 3mm. As the depth decreases stopping distance in wet weather will increase. This is more notable on cars with larger wheels and wider tyres.
Check tyres for damage. Look out for any cuts, cracks or bulges as these can lead to slow punctures and blowouts.
Finally, don’t forget to check the pressure and tread depth of your spare tyre.
Discussion
Normally you have to wonder who funded these types of studies, in this case were tyre manufacturers or distributors involved?
However in personal experience my own tyres were near the TWI and were pretty ridiculous in the wet. Roundabouts were either very slow manouvers or a great laugh when clear and empty.
Totally agree with other comments about pattern, dry weather etc.
Also remember Tiff Needell doing a test at MIRA with premium, budget and remoulds. I am sure the differences were at least 20%.
Encouraging people to change tyres more often might lead to more supercrap specials for Mums MPV's.
However in personal experience my own tyres were near the TWI and were pretty ridiculous in the wet. Roundabouts were either very slow manouvers or a great laugh when clear and empty.
Totally agree with other comments about pattern, dry weather etc.
Also remember Tiff Needell doing a test at MIRA with premium, budget and remoulds. I am sure the differences were at least 20%.
Encouraging people to change tyres more often might lead to more supercrap specials for Mums MPV's.
A lot of this is common sense wrapped in propaganda to sell tyres. We're going to need to replace those tyres sooner or later anyway, so I don't see it as revenue biased propaganda.
I never let my tyres get right down to the wear indicators as in our climate it is obvious that on a day like today you will have less grip when you might need it (outside lane of motorway, 70mph, puddle, brake hard ...).
I never let my tyres get right down to the wear indicators as in our climate it is obvious that on a day like today you will have less grip when you might need it (outside lane of motorway, 70mph, puddle, brake hard ...).
targarama said:That's the point. 1.6mm is a somewhat arbitrary figure - as is 3.0mm for that matter. However, more tread is going to clear more water.
A lot of this is common sense wrapped in propaganda to sell tyres. We're going to need to replace those tyres sooner or later anyway, so I don't see it as revenue biased propaganda.
I never let my tyres get right down to the wear indicators as in our climate it is obvious that on a day like today you will have less grip when you might need it (outside lane of motorway, 70mph, puddle, brake hard ...).
I wouldn't be sure about bald tyres giving better grip in the dry either. Racing slicks are designed to operate in these conditions, but road tyres aren't. Also, when bald they have gone through a tonne of heat cycles, and will not be up to scratch. It is easy to feel the dry performance of the S02's on my Honda going away towards the end of their life (but before the wear indicators).
I am normally fairly anti most of these reports, as has been said, you never really get a true picture. BUT tyres are the most important component fitted to any car (just ask Schumacher senior at the moment), and to suggest that there is no benefit in early changing is ludicrous.
Rob_the_Sparky said:
Bet this is a rather simplistic look at a large area...I'm sure some new cheap tyres will have poorer performance than a really good but worn wet weather tyre.
Yep, my 2 Pirelli P3000s have much better performance as the 2 Vikings (say what?). And they wear much faster . . . Two new P3000s this month . . .
Typically muddled thinking from a supposedly road-safety oriented pressure group.
Accidents happen more in the wet than they used to therefore we should have to change them more often. Not a word about addressing the real problem - improve driving standards so that people leave more of a gap in the wet. Teach people braking techniques and the details of how ABS works and how it can't help you if you don't give it a chance (by being too close, driving too fast or applying the brakes too late).
On a separate note, I'd be interested to know where the current 1.6mm limit came from. I wonder if there may be a clue in the report in that the testing was in water depths of up to 1.5mm. Does the 1.6 come about because "we test in depths of up to 1.5mm", do they test in depths of up to 1.5mm because any deeper than that is particularly rare in the UK, or what?
It wouldn't surprise me if the 3mm they refer to was picked because it's double 1.5mm either.
Accidents happen more in the wet than they used to therefore we should have to change them more often. Not a word about addressing the real problem - improve driving standards so that people leave more of a gap in the wet. Teach people braking techniques and the details of how ABS works and how it can't help you if you don't give it a chance (by being too close, driving too fast or applying the brakes too late).
On a separate note, I'd be interested to know where the current 1.6mm limit came from. I wonder if there may be a clue in the report in that the testing was in water depths of up to 1.5mm. Does the 1.6 come about because "we test in depths of up to 1.5mm", do they test in depths of up to 1.5mm because any deeper than that is particularly rare in the UK, or what?
It wouldn't surprise me if the 3mm they refer to was picked because it's double 1.5mm either.
V8 Archie said:
...Not a word about addressing the real problem - improve driving standards so that people leave more of a gap in the wet. Teach people braking techniques and the details of how ABS works and how it can't help you if you don't give it a chance (by being too close, driving too fast or applying the brakes too late)...
Could not have put this better myself.
V8 Archie said:
It wouldn't surprise me if the 3mm they refer to was picked because it's double 1.5mm either.
"Roadspraff type" Hmm, Mways are dangerous in the wet. Speed limit is ludicrous 70 just now, half that figure and minus 10 is 30. Much better. Matches the tyre figure as well!
Fairly obvious statement when taken into isolation.
I'm getting sick and tired of all the responsibility lying on the driver's shoulders. Where is the condemnation of poorly designed roads? I'm talking about adverse cambers on bends (there's a particularly nasty one on the M40 which has a bump mid corner), lack of investment in improved road surfacing and drainage, and the general state of the roads (e.g. potholes) all of which are dangerous to drive on even more so in the wet. If the government/industry took the state of the roads as seriously as it takes tyre depths then there would be fewer accidents.
I'm getting sick and tired of all the responsibility lying on the driver's shoulders. Where is the condemnation of poorly designed roads? I'm talking about adverse cambers on bends (there's a particularly nasty one on the M40 which has a bump mid corner), lack of investment in improved road surfacing and drainage, and the general state of the roads (e.g. potholes) all of which are dangerous to drive on even more so in the wet. If the government/industry took the state of the roads as seriously as it takes tyre depths then there would be fewer accidents.
kojak71 said:
Fairly obvious statement when taken into isolation.
I'm getting sick and tired of all the responsibility lying on the driver's shoulders. Where is the condemnation of poorly designed roads? I'm talking about adverse cambers on bends (there's a particularly nasty one on the M40 which has a bump mid corner), lack of investment in improved road surfacing and drainage, and the general state of the roads (e.g. potholes) all of which are dangerous to drive on even more so in the wet. If the government/industry took the state of the roads as seriously as it takes tyre depths then there would be fewer accidents.
Well said: the condition of the roads is mediaeval! (I suspect many left wing councils deliberately leave tarmac to crumble, as part of their Marxist, anti(car)-ownership agendas, per se.)
Vagabonds.
I suppose this sort of repetitive and obvious (with a tiny amount of understanding and thought) can be justified on the basis there are thousands of new motorists or people becoming responsible for their own vehicles every year.
That said the Michelins (yes, I did say Michelins!) on the front of mine were at about 3mm when I got the car last September. Lower than expected usage means that they are now just coming on to the wear bars 5000 miles later. Not bad for 250bhp through the front wheels.
Very even wear and they have never lost grip though I suspect an excellent traction control and ESP system has helped on a couple of occasions when accelerating.
To be fair I don't recall having any particularly unpleasant conditions to drive through. Very wet, yes, but semi-flood no. I have experienced aquaplaning and loss of cornering grip with much more tread in other vehicles with other tyres. Sometimes older style Michelins.
Police vehicles tended to have tyres changed when half worn. However with some release agents and the extra heat from deep treads I would guess that initial grip is not so good (I recall a few tyres that seemed to take over 1000 miles so feel right) and wear rates higher. But then they do get a big discount!
2 new fronts (rears are fine) being fitted on Tuesday. Wonder what the effect will be?
Edit: Typo - finger and keyboard not working in unison.
>> Edited by LongQ on Saturday 21st May 16:58
That said the Michelins (yes, I did say Michelins!) on the front of mine were at about 3mm when I got the car last September. Lower than expected usage means that they are now just coming on to the wear bars 5000 miles later. Not bad for 250bhp through the front wheels.
Very even wear and they have never lost grip though I suspect an excellent traction control and ESP system has helped on a couple of occasions when accelerating.
To be fair I don't recall having any particularly unpleasant conditions to drive through. Very wet, yes, but semi-flood no. I have experienced aquaplaning and loss of cornering grip with much more tread in other vehicles with other tyres. Sometimes older style Michelins.
Police vehicles tended to have tyres changed when half worn. However with some release agents and the extra heat from deep treads I would guess that initial grip is not so good (I recall a few tyres that seemed to take over 1000 miles so feel right) and wear rates higher. But then they do get a big discount!
2 new fronts (rears are fine) being fitted on Tuesday. Wonder what the effect will be?
Edit: Typo - finger and keyboard not working in unison.
>> Edited by LongQ on Saturday 21st May 16:58
Rob_the_Sparky said:
Bet this is a rather simplistic look at a large area...I'm sure some new cheap tyres will have poorer performance than a really good but worn wet weather tyre.
Would be interesting to see the data rather than the news splash
Rob
>> Edited by Rob_the_Sparky on Thursday 19th May 12:49
I just replaced some 13 year old Dunlops which were still legal with perhaps 3 mm of tread. They had previously been on my wife's car (a mk3 cavalier) and I had moved them to my car (same fitting - a mk2 cavalier). They were replaced by some new Yokos and are now being used on my allotment to grow potatoes in. The wet weather perforance was scarey, but I think it had alot to do with AGING, rather than tread depth.
V8 Archie said:
Typically muddled thinking from a supposedly road-safety oriented pressure group.
Accidents happen more in the wet than they used to therefore we should have to change them more often. Not a word about addressing the real problem - improve driving standards so that people leave more of a gap in the wet. Teach people braking techniques and the details of how ABS works and how it can't help you if you don't give it a chance (by being too close, driving too fast or applying the brakes too late).
On a separate note, I'd be interested to know where the current 1.6mm limit came from. I wonder if there may be a clue in the report in that the testing was in water depths of up to 1.5mm. Does the 1.6 come about because "we test in depths of up to 1.5mm", do they test in depths of up to 1.5mm because any deeper than that is particularly rare in the UK, or what?
It wouldn't surprise me if the 3mm they refer to was picked because it's double 1.5mm either.
I think 1.6mm is 1 sixteenth of an inch, give or take. Originally a pragmatically chosen number. Same in the USA, which is still using imperial measures.
Rob_the_Sparky said:
Bet this is a rather simplistic look at a large area...I'm sure some new cheap tyres will have poorer performance than a really good but worn wet weather tyre.
Would be interesting to see the data rather than the news splash
Rob
>> Edited by Rob_the_Sparky on Thursday 19th May 12:49
The best information I have found for comparative tyre performance is the annual tyre test in Autocar magazine every autumn. Second best test report is Which Magazine that includes data on wear rates.
My son did a fascinating research project on tyres. This found that the wider the tyre the worse the wet-grip; this is annually confirmed by Autocar tests. Yes, there are significant differences in performance between makes of tyre that is most noticeable in the wet; it depends on compound and tread.
The tread is primarily to comply with the law and disipate water so that the rubber stays in contact with the tarmac. Directional treads are not much advantage when tyre new but usually has a significant advantage as tread drops to 4mm. Below 2.5mm the directional tread has insufficient passageway for water so performance begins to drop rapidly.
Hit a puddle with a 4mm directional tread at 70mph and you will feel the pull on the steering. Repeat with same puddle at 2mm and tyre struggles, at 1mm you WILL aquaplane (water-ski not touching road) on a wide tyre.
Once the rubber is touching the road it depends on rubber compound assuming carcus is holding tyre flat on road. Traditional rule of thumb is better wet grip gives shorter life. To counteract short life longer life is achieved by adding silicon to compound.
Unfortunately silicon has a problem is that it makes wet grip below 7°C but especially in snow and ice really awful. Those big chunky looking tread performance tyres make BMW's look stupid on snow; RWDrive becomes irrelevant compared to compound choice.
Bridgstone Potenza SO2's were brilliant in wet on my Impreza, but the early replacement SO3's had new tread with much less rubber on road from new tread pattern and were dangerously useless below 7°C (my opinion). They were OK only for Autobahn in a straight line in wet above 10°C, when worn not even good for that. Bridgestone refused permission for Autocar to test SO3s in wet or dry, I had a set and I now understand why as SO2 wet performance sacrificed for longer life.
>> Edited by harrap on Tuesday 24th May 01:19
OK, what about dry grip. Much less difference between tyres (as measured by test lap times) and at really high cornering speeds carcass design becomes important, eg radials better that crossply. Again, highlighted in Autocar test reports, it also mentions if a tyre gives confidence or not.
Tread depth and dry weather performance are related. We only get 7.5 or 8mm of tread on a new tyre for a reason. If tread is higher, say 12 mm, all Yorkshireman would be rubbing there hands together with glee (I am married to a Yorkshirelass so I know what "Tight fisted money savers" means)
Ever bought a set of new tyres and put them on the back wheels of FWD car. If car is not an understeering pig; then you may notice that some cars seem tail happy and very responsive to turn in. Those worn front are griping and turning in, the rears are "squirming" on their tread. You try gripping a road on stilts, that is what is happening. The tread blocks begin to bend above 6mm of tread. Get 12mm tread like a 4x4 tyre and they loose stopping and cornering performance. Porsche in the dry stops in 140ft (40m), Land Rover (or any 4x4) on new 12mm tread tyres takes 250ft (75m) to stop from same speed - remember Top Gear demo? Oh yes local authorities can help a lot by using good tarmac, properly maintained
Still don't believe me. There are firms that grind down new tyres to 4.5mm tread to stop tread squirm when owner goes racing on a standard tyre. The guy with the good tyres wins the race; good driver on 8mm has no chance in dry. Good rigid carcuses can sometimes perform with 5.5mm tread. These tyre carcasses give optimum dry grip but not as comfortable and quiet on road - see Which tests.
Me, I put new tyres on front to clean road and older tyres on back of FWD, I buy 4 tyres at once for 4WD Impreza. However some safety authorities point out that if cornering sharply in wet, rear tyre then cut corner into deep water or even front tyre's bow wave. This can make worn back tyre aquaplane before fronts leading to emergency spin off especially if you hit brakes simultaneously. My opinion is its new tyres front to cope with wet, worn on rear of FWD for grip.
I always look at results of Autocar / Which tests and look for good around wet performance for road use. I don't want fantastic dry performance that suddenly becomes useless in typical Bank Holiday wet weather.
I have a spare set of wheels that has winter tyres but for Nov. to April on my Impreza, but that's is another silicon story.
Tread depth and dry weather performance are related. We only get 7.5 or 8mm of tread on a new tyre for a reason. If tread is higher, say 12 mm, all Yorkshireman would be rubbing there hands together with glee (I am married to a Yorkshirelass so I know what "Tight fisted money savers" means)
Ever bought a set of new tyres and put them on the back wheels of FWD car. If car is not an understeering pig; then you may notice that some cars seem tail happy and very responsive to turn in. Those worn front are griping and turning in, the rears are "squirming" on their tread. You try gripping a road on stilts, that is what is happening. The tread blocks begin to bend above 6mm of tread. Get 12mm tread like a 4x4 tyre and they loose stopping and cornering performance. Porsche in the dry stops in 140ft (40m), Land Rover (or any 4x4) on new 12mm tread tyres takes 250ft (75m) to stop from same speed - remember Top Gear demo? Oh yes local authorities can help a lot by using good tarmac, properly maintained
Still don't believe me. There are firms that grind down new tyres to 4.5mm tread to stop tread squirm when owner goes racing on a standard tyre. The guy with the good tyres wins the race; good driver on 8mm has no chance in dry. Good rigid carcuses can sometimes perform with 5.5mm tread. These tyre carcasses give optimum dry grip but not as comfortable and quiet on road - see Which tests.
Me, I put new tyres on front to clean road and older tyres on back of FWD, I buy 4 tyres at once for 4WD Impreza. However some safety authorities point out that if cornering sharply in wet, rear tyre then cut corner into deep water or even front tyre's bow wave. This can make worn back tyre aquaplane before fronts leading to emergency spin off especially if you hit brakes simultaneously. My opinion is its new tyres front to cope with wet, worn on rear of FWD for grip.
I always look at results of Autocar / Which tests and look for good around wet performance for road use. I don't want fantastic dry performance that suddenly becomes useless in typical Bank Holiday wet weather.
I have a spare set of wheels that has winter tyres but for Nov. to April on my Impreza, but that's is another silicon story.
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