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Old 21st July 2008, 09:42   #1
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Default Right air pressure after an upgrade

Guys,

With my limited searching ability I did not find any thread here which discusses this topic in detail. I saw threads where people have asked about the correct pressure to inflate their tyres after an upgrade. But the responses were more from experience than logical reasoning.

One suggestion I saw was to adjust the tyre pressure after looking at the wear, but then it is somewhat late since one has to drive till such a time with improperly inflated tyres.

Can somebody clarify why it is recommended to keep the pressure slightly lower than OE when upgrading? Hope some of the experts here can clarify the impact of tyre width, profile, rim size etc on choosing the correct air pressure after an upgrade.
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Old 21st July 2008, 12:34   #2
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Watashi,

Your best bet is to trust the pressure range suggested by the tire manufactuer for that specific tyre (and size). Depending on the result and the weight of your car - you could stray 1 or 2 psi this way or that.

cya
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Old 21st July 2008, 13:45   #3
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Watashi,
The way I understand this is that when you upsize - the contact patch is increased. This would allow you to reduce pressure by about 1-2 PSI as compared to OE tyre.

I can share my experience of my Indica TDI -
OE tyre is 165/65/R14 with a recommended tyre pressure of F-28 and R-24
I've upsized to 175/65/R14 and maintain tyre pressure of F-27 and R-23

I drove the car on upsized tyres with the original tyre pressure for about 2 months - but the ride was quite harsh and hence reduced pressure slightly. This seems to be working fine - no adverse wear issues.
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Old 21st July 2008, 14:30   #4
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Hi viper, I think you may be right.

These are my opinions.

1. Tyre width - If the contact surface is increased, the amount of load that can be supported also increases (weight = pressure X area). Hence a tyre at the same pressure behaves like a slightly overinflated tyre.
2. Tyre profile - When a lower profile tyre is used, the amount of flexing decreases. With the same pressure as OE this would result in a harsher ride.
3. Tyre size or diameter - Obviously the contact surface increases. Other than that I am not sure.
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Old 24th July 2008, 10:15   #5
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I had been looking for this answer since a long time. This is a useful bit of information. I have upgraded & upsized tyres running on different cars. But have been maintaining manufacturer reccomended tyre pressue all along.

Have not really had any problems such as excessive tyre wear or rough ride, but yes running 2 psi lower may help the ride. Will try it out.


Cheers
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