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Old 07-30-2017, 08:18 PM   #21 (permalink)
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Quote:
Originally Posted by Jez77 View Post
I'd personally never sacrifice grip to save a little bit of fuel especially in the rainy season (although in theory higher pressure is less likely to hydroplane ).

I wonder if the tables get turned on rougher roads?
I know with mtb bike tyres lower pressure means lower resistance on dirt trails within reason.
Once you get away from the citys the roads get pretty rough in OZ
The problem with saying "high inflation pressure" is there is nothing to compare against. Is 40psi high? What about 50? 60? 120? I run my tires around 45 in summer and drop them down to about 36 in winter. Never have a problem with wet roads.

It was mentioned before, but higher than stock pressure is often used in competition to make the tire more rigid and predictable. While you may get slightly SLIGHTLY less ultimate grip, it is much more predictable and enjoyable to drive as the car will more quickly respond to steering input.

Have i ever noticed less ultimate grip? No
Do i still drive with higher than placard tire pressure? Yes

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Old 07-30-2017, 11:55 PM   #22 (permalink)
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The reason some people think overinflated tyre have more grip is the same reason people think low profile tyres have more grip. They are more responsive.
In real world conditions where the roads aren't perfectly flat and have loose gravel a properly inflated tyre will give more ultimate grip because they will conform to the road.
Easy to test if you can find a deserted roundabout and see how fast you can go until the tyres start to let go.
My old van use to have 2 inflation pressures on the placard for heavy 60psi and light loads 45psi. It was very tricky to drive in the wet with 60psi but completely different car at 45psi.

Competition tyres are sometimes designed to run higher pressures so they stay attached to the bead under high cornering loads. They make up for the loss of grip with soft compounds. I had Tarmac rally tyres on an old Datsun for a while, you don't know what grip is until you've tried them
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Old 07-31-2017, 02:01 AM   #23 (permalink)
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I had extremely low profile Dunlop Denovo run flat tyres on a car, many years ago. They were very soft, gave phenomenal grip, and were worn out by 10000 miles. Of course, the extra grip made you want to use it, which didn't help with the wear!
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Old 07-31-2017, 04:14 AM   #24 (permalink)
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As for cornering grip, I can attest that raising the tire pressure does increase grip.
I have a specific corner when leaving the highway which I could take at 52 km/h max in the first months of ownership of my car.
Preserving momentum Wayne Gerdes style
When I raised the pressure to 40 PSI (from 28-ish) I could take same corner at 57 km/h.
I assume high pressure prevents sidewall deformation under lateral force so its contact patch stays in shape.

As for braking distance, IDK. It may or may not be affected. There is no lateral deformation then, so I think there is no gain in high pressure there.
But I'd accept a slightly reduced grip in a straight line if I get better handling for evasive moves in return.
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Old 07-31-2017, 05:57 AM   #25 (permalink)
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At the rate I plod around, grip in any axis means little except on ice and snow.
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Old 07-31-2017, 06:14 AM   #26 (permalink)
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Ditto. Although I always think you only discover you have a lack of grip when you need it the most!
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Old 07-31-2017, 06:41 AM   #27 (permalink)
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Even temperatures = even wear (~65PSI):

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Old 07-31-2017, 08:49 AM   #28 (permalink)
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What was that pic taken with?
The heat signature doesn't seem to line up with the tyre and to my untrained eye it looks as if the tyre groves are getting cooler from left to right.
That could be caused by bad wheel alignment and/or over inflation.
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Old 07-31-2017, 10:47 AM   #29 (permalink)
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The thermal image is overlayed over an outline image taken by the optical camera (about 1/2" apart), hence the ghosting at certain angles, the outline image is just there to help give definition to the image otherwise they all just look like blobs. The shot wasn't taken parallel to the tyre which I think is why the grooves look cooler on the inside edge, the tread is within 1*. The image on the opposite side shows the opposite so would tend to confirm that. In future I'll try to remember to keep the camera perpendicular.

I think the grooves might be hot because of the brakes transferring heat to the tyres, the rears don't show the same pattern at all.

Here's a (rear this time) tyre shot square on:



Yes, you could argue that the centre looks hotter than the edges, but again that represents only about a 1*C delta, and personally my tyres tend to die from feathered edges rather than worn centres.

If I'm going to put a bit of load in the back (or tow a trailer), I really don't want to have to drag out the foot pump as well, so I prefer to be prepared for a bit of load.
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Old 07-31-2017, 05:07 PM   #30 (permalink)
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Contacted Dunlop/Goodyear today and this was their advice.

Operating air pressure is determined by the vehicle manufacturer.

If you're using the same size tire that came as original equipment on your vehicle, the proper air pressure is indicated on the door
placard or owners manual of your vehicle.

The air pressure indicated on the sidewall of each tire is the inflation pressure required to carry the maximum allowable load for
that tire. Vehicle manufacturers have invested considerable time and testing to establish an air pressure that will provide a smooth
comfortable ride in addition to an even treadwear pattern.

Our recommendation would be to stick with the air pressure established by your vehicle manufacturer.

Thank you for your inquiry through our web site.

Vanassa F
Consumer Relations

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