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Originally Posted by valcax
Its very interesting technical exposure, but I would like to know tyre pressures you wear.
Best regards.
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Hi,
Start out with the simple formula: Curb weight / 100 + 2 (+ 2 on heavy end), and then experiment to what suits your individual Driving Style, Regional Roads, mix of Expressway/Street Driving, and Typical Load. There is no Right or Wrong Pressure beyond applying this formula. What may be correct for one, may feel off to another. Don't Poll and go by what others say.
Significantly Higher Pressures in the Rear will tend to induce some Understeer (Understeer = Safety for the Average Driver), while higher Front Pressures will tend toward Oversteer.
One thing people don’t usually take into account is their Load Factor. If you keep your Fuel Tank topped up rather than allow it to drain, you’ll want more pressure. If you have more
Junk in the Trunk (both literally and metaphorically..
), likewise, you’ll want a few extra pounds. Same if you more often than not have a Passenger.
But, you never want to use the Manufacturers Tire Pressure Placard. Since 09.03, the NHTSA has mandated that Manufacturers must state the Manufacturer’s
Maximum Load Rating (Maximum number of Persons in Seating Positions and Cargo), the Original Tire Size (including Spare) and the Manufacturer’s recommended cold tire pressures per axle, nothing more, nothing less. Unfortunately, the new placards do not tell the Customer that the Manufacturer’s recommended cold tire pressures are intended for a
Fully Loaded Vehicle where weight bias is in the Trunk area.
Due to the Underinflation (among other) issues that apparently caused some Tire failures on Ford Explorers, it appears NHSTA now prefers Tires inflated for Full Load use, all the time. It appears they also think that more information on any Tire Pressure label is distracting and confusing for customers, and they actually paraphrase those feelings in the ruling itself – see:
http://dms.dot.gov/search/searchFormSimple.cfm and enter 13678 in the blank docket search field.
Remember that, while Higher relative Tire Pressures make the Car seem to come alive, consistent, long term use of anything more than 40 psi on even a Stiff Carcass Performance Tire increases the likelihood of accelerated Inner Tread Wear (results will vary). Interestingly, Tire Manufacturers did not petition against the Pressure Amendments because the Higher recommended Pressures are actually good for business.
The Accepted and Proven method in Autocrossing is that one try to determine and use the absolute Lowest Tire Pressure that is effective for events (using a pyrometer), depending upon Course Layout, Driving Experience, Ambient Temps, Concrete vs. Asphalt surface, etc. With the exception of pyrometer use, the above would serve well for Spirited Street (everyday) use as well.
It’s easy to go Up/Down with Pressures, no $$ are involved, so experiment and find a combination which
you like. Judge the Drivability, Noise and Ride Quality you’re comfortable with. You might even jot down a couple different combinations to adapt to different Driving and Load Conditions. Hope this helps…
Happy Motoring!... Jim’99