Tyre temperature
Dec 29, 2016 17:15:56 GMT
Post by WDB on Dec 29, 2016 17:15:56 GMT
I'd wondered for a while about this one. A few years back, when the British public were first alerted to the existence of 'winter tyres', the message from the tyre companies was that, while 'summer tyres' (or, as we were used to calling them, 'tyres') were just fine for most of the year, their performance declined markedly at temperatures below 7°C. What I wondered was, temperature of what? Because the wheels on the bus go round and round, and that makes the tyres get warm.
Well, today's a mite chilly round here, bright but barely above freezing all day. And I'd just been out in the bus on a little errand, 20 minutes' driving each way, at up to dual carriageway speeds. Arriving home, the untreated road outside our house was icy enough to induce a tiny slither as I braked to a halt. So I popped inside for my infrared thermometer.
Road surface, where the sun had been: +2°C
Road surface, in shadow all day: -2°C
Rear tyres: +10°C
Front tyres: +12°C
It's a safe bet that the temperature of the roads I was on didn't exceed about 4°C except perhaps in a few patches that had had a lot of sun. And the car felt just fine - admittedly on treated roads - all the way there and back until that final slither on our frosty road. This, of course, was on Michelin Crossclimate 'winter tyres', supposedly exempt from the 7°C threshold. Would my 'summer tyred' chariot have felt noticeably different?
No conclusion here, just musing. Presumably what suffers in a 'summer tyre' at low temperatures is its ability to grip dry tarmac as its stickiness diminishes. But I've not noticed that on either car, whether with today's tyres or with the 'summer tyres' the E used to have. (Slipping on ice at low speed felt pretty much as I'd have expected too; no drama and no more than 60cm from start to finish.) Could that be because normal use raises any tyre's temperature to 10°C above ambient, so that in all but the harshest conditions it's actually well within its comfort zone?
Well, today's a mite chilly round here, bright but barely above freezing all day. And I'd just been out in the bus on a little errand, 20 minutes' driving each way, at up to dual carriageway speeds. Arriving home, the untreated road outside our house was icy enough to induce a tiny slither as I braked to a halt. So I popped inside for my infrared thermometer.
Road surface, where the sun had been: +2°C
Road surface, in shadow all day: -2°C
Rear tyres: +10°C
Front tyres: +12°C
It's a safe bet that the temperature of the roads I was on didn't exceed about 4°C except perhaps in a few patches that had had a lot of sun. And the car felt just fine - admittedly on treated roads - all the way there and back until that final slither on our frosty road. This, of course, was on Michelin Crossclimate 'winter tyres', supposedly exempt from the 7°C threshold. Would my 'summer tyred' chariot have felt noticeably different?
No conclusion here, just musing. Presumably what suffers in a 'summer tyre' at low temperatures is its ability to grip dry tarmac as its stickiness diminishes. But I've not noticed that on either car, whether with today's tyres or with the 'summer tyres' the E used to have. (Slipping on ice at low speed felt pretty much as I'd have expected too; no drama and no more than 60cm from start to finish.) Could that be because normal use raises any tyre's temperature to 10°C above ambient, so that in all but the harshest conditions it's actually well within its comfort zone?
