315 Feet

The car had to go to the tyre and brake people this week. I had noticed the feel of the brake pedal was changing slightly from smooth to a bit jerky when releasing pressure. This didn’t really concern me but the fact that the rear discs were looking rusty and there was only a thin band of clean metal had me worried.

The car went in to ATS Euromaster at 08:30 and I’d had the call by about 09:30. New pads and discs at the rear (I’d expected that), two new tyres as the fronts were worn to just about legal. I hadn’t really expected that but then I don’t hang around and a little sliding when it’s damp is good fun (no kids in the car and only where it’s safe and there’s space). I had mentioned that there was a slow puncture on the nearside rear tyre and it’s just aswell.

When I went to pick up the car it was still on the jacks so the guys could show me the problem that was causing the slow puncture. The inside of the tyre where the join normally occurs and is “welded” nicely was just a split. It had gone down to steel and would eventually have caused some serious issues. They believe it was a manufacturing fault and the tyre has been sent back to Pirelli and I hope I get a refund and I ended up paying for 3 tyres.

An interesting little fact that I hadn’t considered was that the new tyres went on the rear of the car and the worn tyres were swapped to the front. This is to try and ensure that when the car is on the limit it will understeer rather than oversteer. Understeer is much safer that oversteer and so by keeping the grip at the rear of the car (especially an estate where the rear is quite light) the car is safer to drive. Nice.

315 feet is the stopping distance of a car travelling at 70mph. This is the number given in the Highway Code. Most cars will stop much shorter than that. Should you ever be lost for a stopping distance then the formula s=v+(v^2)/20 works to give you the Highway Code numbers. The thinking and reaction time is the same number of feet as miles per hour and then the actual breaking distance is proportional to the speed squared. It’s all down to kinetic energy! See the Wolfram|Alpha stopping distance calculation here.

Stopping Distance Formula