It's been discussed a few times here and is obvious enough, so I thought I'd do a small experiment with my new A2 1.4 SE TDI, Open Sky. As a keen racing cyclist, the link between speed/energy input and tyre pressures is very clear - more pressure is more speed or less effort....but only up to an optimum value, where "hard-wheel" discomfort and the risk of punctures becomes disproportionately greater than the speed/effort gains.
I'd been running my A2 at 30 psi on all 4 tyres, and have increased this to the "full-load" maximum of 38 psi in 2psi increments with each new tank of diesel. What I find, in very broad terms, is that for every extra 2 psi, I'm getting back an extra 1-1.5 mpg - at 30 psi, I was getting around 56 mpg, at 38 psi I'm getting around 62 mpg. Obviously, it's very different to keep all the other variables constant - although I've tried fairly hard (only one passenger (ie the driver) in all tests etc - but as a rule of thumb, it seems like higher pressures have a definite effect. Quite whether there are any downsides of running on these higher pressuires, I have yet to discover....
I'd been running my A2 at 30 psi on all 4 tyres, and have increased this to the "full-load" maximum of 38 psi in 2psi increments with each new tank of diesel. What I find, in very broad terms, is that for every extra 2 psi, I'm getting back an extra 1-1.5 mpg - at 30 psi, I was getting around 56 mpg, at 38 psi I'm getting around 62 mpg. Obviously, it's very different to keep all the other variables constant - although I've tried fairly hard (only one passenger (ie the driver) in all tests etc - but as a rule of thumb, it seems like higher pressures have a definite effect. Quite whether there are any downsides of running on these higher pressuires, I have yet to discover....