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Old 23rd January 2008, 04:32   #1
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Default Correct Tyre Pressure For Upsized Tyres

I am really surprised to have not found a thread discussing this on Team-BHP...

Well, i want to begin this thread to gain knowlege on the correct tyre pressures after upsizing your tyres.


Q1. Does upsizing your tyre (Rubbers or Rims) make a difference to the tyre pressure?


Q2. If Yes, How?


Q3. If Yes, then what should be the new tyre pressure?


[Example - 165/80 R14 upsized to 205/55 R15]
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Old 23rd January 2008, 08:49   #2
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Default

Whatever your size of tyres if is generally recommended to stick to manufacturer specified pressures.

Oh and there are plenty of threads that discuss this. For eg.
http://www.team-bhp.com/forum/tyre-a...-pressure.html

You need to know where to look.
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Old 2nd April 2018, 09:41   #3
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Default Air Pressure in tyres after upsize

Many of us upsize the tyres on our cars. Post the upsize, many people reduce the air pressure in the tyres. I use the same pressure as before. Which is correct ?

Pressure is (fairly) defined as perpendicular force exerted over a unit area. In case of air pressure in tyres, I will say that we could consider it something like total volume inside the tyre, vs total un-compressed volume of air filled in it. (Of course, the filled in air is now compressed) If this is (farily) correct, then, when we upsize a tyres, we should continue to maintain the same tyre.

From what I remember, for a car model, where the tyre sizes are different between two trim levels of the car, the recommended pressure is sometimes different. ( I have not compared this data across cars, hence dont have much information in this angle).


What say ? USe same pressure after upsize or change ? If change, then why ?
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Old 2nd April 2018, 10:21   #4
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Default Re: Air Pressure in tyres after upsize

Here's a pdf link that might help you.
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Old 2nd April 2018, 10:32   #5
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Default Re: Air Pressure in tyres after upsize

There are several threads on this specific subject on Team Bhp - the ones below are just two, there seem to be more:

http://www.team-bhp.com/forum/tyre-a...er-upsize.html

http://www.team-bhp.com/forum/tyre-a...zed-tyres.html

To put it simply, Michelin, manufacturer of arguably the best tyres in the world recommend sticking to the same tyre pressure after upsize and nobody probably knows tyres better than they do.

There are various schools of thought on this, most of which result in an analysis paralysis situation rather than actual benefits to users so it's best to stick to the guidance of someone who knows his onions.

Last edited by AMG Power : 2nd April 2018 at 10:42.
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Old 29th July 2020, 21:48   #6
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Default Re: Air Pressure in tyres after upsize

Quote:
Originally Posted by AMG Power View Post
To put it simply, Michelin, manufacturer of arguably the best tyres in the world recommend sticking to the same tyre pressure after upsize and nobody probably knows tyres better than they do.
Can you kindly guide me towards the link which says so?

I have upgraded the stock Bridgestones of my XL6, 185/65R15, to Michelin XM2 195/65R15, and am struggling to find the sweet spot wrt air pressure. Recommended pressure for stock size is 29PSI. I have tried 32 PSI and for single occupancy, the ride feels a bit too stiff.

Regards,
Shashi
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Old 30th July 2020, 06:26   #7
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Default Re: Air Pressure in tyres after upsize

Quote:
Originally Posted by Leoshashi View Post
Can you kindly guide me towards the link which says so?

I have upgraded the stock Bridgestones of my XL6, 185/65R15, to Michelin XM2 195/65R15, and am struggling to find the sweet spot wrt air pressure. Recommended pressure for stock size is 29PSI. I have tried 32 PSI and for single occupancy, the ride feels a bit too stiff.

Regards,
Shashi
That post was based on discussions I had with Michelin engineers. However I see that the link on their site adds something more :

https://www.michelin.in/auto/faq-cars

Apparently they are now asking you to contact them.

Correct Tyre Pressure For Upsized Tyres-1image.jpeg

However if you've upgraded from 185/65/15 to 195/65/15 the tyre pressure would be the same as recommended by the manufacturer for the OE size. It is only if there is substantial difference between the OE and the upsize (much larger wheels etc) would there be a need to change the tyre pressure.

In your case, it would be best to stick to 29 or 30psi. Let me know after you hear from them.
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Old 30th July 2020, 21:26   #8
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Default Re: Air Pressure in tyres after upsize

Quote:
Originally Posted by AMG Power View Post
In your case, it would be best to stick to 29 or 30psi. Let me know after you hear from them.
I contacted them today, and got a call from their technical team within an hour. They reconfirmed the load index and recommended pressure of stock size and asked me to stick to the recommended 29PSI or drop to 28 if it still felt uncomfortable.

I'm currently running on 30 at front and 29 at rear, and this feels much better for my needs.

Thanks again.

Regards,
Shashi
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Old 31st July 2020, 16:28   #9
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Default Re: Air Pressure in tyres after upsize

Quote:
Originally Posted by condor View Post
.... for a car model, where the tyre sizes are different between two trim levels of the car, the recommended pressure is sometimes different...
Quote:
Originally Posted by AMG Power View Post
.. However if you've upgraded from 185/65/15 to 195/65/15 the tyre pressure would be the same as recommended by the manufacturer for the OE size
This is what the manual of Fiat Palio says - which hopefully addresses the above -

Correct Tyre Pressure For Upsized Tyres-airpressure.jpg

1.2 and 1.6 petrol have two different tyre sizes, but tyre pressure is same.

Whereas, 1.2 petrol land 1.9 diesel have the same tyre size, but tyre pressure is different. So, I agree with -

Quote:
Originally Posted by vikram_d View Post
Whatever your size of tyres it is generally recommended to stick to manufacturer specified pressures
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