PDA

View Full Version : Tire pressure question


Russell
10-09-2004, 06:02 PM
With stock 15 inch wheels and new tires, would lower or higher tire pressure ride better? I always thought lower pressure would ride better. I am not so sure with newer tire design.

Just a question as I have been thinking too much today!
Jr ///M5
10-09-2004, 07:37 PM
Use the pressures that are on the label on the inside of the drivers door jamb. The fronts should be about 2 psi lower than the rear.

BMW is one vehicle that just a couple of pounds of pressure will indeed have an affect on the way the car handles.

Jr
Russell
10-09-2004, 08:08 PM
Seems wrong pressure if I reduce load such as driver only. Anyway, still would like to know if lower or higher pressure will ride better. Guess i will experiment. Thanks for your comments.



Use the pressures that are on the label on the inside of the drivers door jamb. The fronts should be about 2 psi lower than the rear.

BMW is one vehicle that just a couple of pounds of pressure will indeed have an affect on the way the car handles.

Jr
black_bird_blue
10-10-2004, 05:55 AM
Anyway, still would like to know if lower or higher pressure will ride better.

Lower pressure will lower the vertical spring rate of the tyre and give less sensation of the "texture" of the road. Some may interpret that as a better "ride". However, the wheel moves more on the tyre and gives more "shake" after small bumps. Some may interpret that as worse "ride".

Lower pressure also reduces the so-called "cornering stiffness" of the tyre and results in more steering delay at the front of the car and longer turn-in delay at the rear of the car. Some may interpret that as worse "handling".

Finally, lower pressure increases the temperature of the tyre and results in higher friction levels (provided they aren't cooking). Some may interpret that as better "grip".

My recommendation would be to experiment on the fronts first if you are going down and the rears first if you are going up since this will preserve stability.

I recently reconstructed a fatal accident where it had been done the wrong way round (albeit by quite a large amount). Be careful during your experimentation and be careful experimenting with high speed stability.

During your experiments, be sure to do "A-B-A" testing (where you go back to the original pressures). It helps stop you imagining the answer you wanted. And be sure to evaluate the results on a consistent piece of road at consistent speeds.

Be sure to post your conclusions!


Damian