Thursday, Jan 27, 2011 at 08:57
I'd agree 100% with Swaggie, though the actual pressures you use depend on a lot of factors, especially type of tyres and loading. With fat tyres I use 30-35 psi (when the tyres are cold) on bitumen for our Troopy, and I'd drop to about 22-25 as Swaggie suggests in the sort of conditions in your movie, maybe down to about 18 if necessary. I usually think in terms of % of bitumen pressure - I go down at least 25% on rough gravel, 50% for very loose or sandy. As
well as more comfort for vehicle and occupants, the aim is to increase traction through increased footprint - half pressure will roughly double footprint.
Last resort for me is about 10-12 psi. Below that there is real risk of the vehicle actually walking out of its own front tyres. At such low pressure you must drive slowly and steer very gently.
The 4 psi rule - basicly, run your tyres at a pressure where they flex enough to warm up so that the pressure rises by about 4psi. It's a very rough guide, since there are so many variables - hot bitumen, sun shining on tyres, etc , but useful to get a feel for what's about right.
It's important to drop your speed when running at reduced pressures. Certainly never attempt highway speed without highway pressure!
Agree completely with your comment about the accuracy of gauges. Recommend don't use an ultra cheap one, but use the same one consistently as your reference. Every gauge is different, but consistency is more important than absolute accuracy.
Cheers
John | J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein
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