Correct Tyre pressure after upsize

Gansan · 13th July 2009, 12:46

A general question about filling air. I know pressure should be checked when the tyres are cold. I get off the bike and place it on central stand while checking air. Far car too, I get down and check pressure on an empty car. But I notice sometimes four or five people sitting inside the car checking the pressure without getting out and driving away. Which is the correct method? Will not the additional weight of 5 people show a wrong reading?

mithun · 14th July 2009, 11:09

Quote:

Originally Posted by Gansan

A general question about filling air. I know pressure should be checked when the tyres are cold. I get off the bike and place it on central stand while checking air. Far car too, I get down and check pressure on an empty car. But I notice sometimes four or five people sitting inside the car checking the pressure without getting out and driving away. Which is the correct method? Will not the additional weight of 5 people show a wrong reading?

Always check the pressure without any people on board. If you're having people on board there might be a difference of 2-3 PSI.

sdmn · 21st July 2009, 13:23

Folks,

Can anyone point to a definitive source of information that explains whether tire pressure needs to be increased or decreased after an upsize? I understand that tire pressure is an optimized value - optimized for ride quality and tire wear / fuel mileage. However, assuming all other parameters to be the same, how must the tire pressure change with an increase in tire width?

I bought a Verna CRDI a year back, and upgraded from Bridgestone B250 185/65R14 86H stock to Bridgestone Turanza 195/60R14 86H right at the showroom before delivery. Hyundai recommends 32psi (all wheels / 2 front passengers) and 33psi (all wheels / full load). It also provides recommended pressures for alternative tire sizes, but unfortunately, not for this size. Ironically, this was the Hyundai dealership recommended upgrade!

I shot off a mail to Bridgestone immediately after purchase asking them the same question and they replied telling me to maintain the same pressure as what Hyundai recommended for the stock tires. I have been following their advice during the 1 year of ownership and have had no problems whatsoever. However, I am not convinced with the answer I got from Bridgestone India, since keeping everything else the same, when you do a tire upsize, there must be a corresponding change in the recommended tire pressure too. I realize that the difference is perhaps too small - but there has to be a difference and I want to understand that.

I found contradictory views on team bhp too about whether tire pressure must be increased or decreased when there is an increase in tire pressure. Other than the 'you decide based on your taste' logic, I am looking for a definitive, scientific answer.

Who can help?

watashi75 · 21st July 2009, 14:23

I have asked this question in this forum and I did not get any definitive answer. So I have formed my own opinions about correct tyre pressure after an upgrade. See here -

http://www.team-bhp.com/forum/techni...ml#post1139159

If you upgrade to wider tyres you need to reduce tyre pressure for better straightline grip.

If you upgrade to lower profile tyres you need to reduce tyre pressure for better ride quality.

If you upgrade to lighter alloys the load decreases so you need to reduce tyre pressure.

If you upgrade to better rubber you don't need to do anything.

In all cases it would be a safe bet to reduce tyre pressure after an upgrade.

sdmn · 24th July 2009, 22:56

Thanks watashi75. Your suggestions certainly will help.

I'm still looking for a definitive answer through.

saketa · 2nd March 2011, 19:11

Quote:

Originally Posted by watashi75

I have asked this question in this forum and I did not get any definitive answer. So I have formed my own opinions about correct tyre pressure after an upgrade.

So assuming you dont care as much for ride quality as much as you care about mileage ... Is it okay to over inflate low profile tires by about 1-2 PSI?

13th July 2009, 12:46	#16
Gansan Senior - BHPian Join Date: May 2009 Location: Chennai Posts: 4,535 Thanked: 5,561 Times	A general question about filling air. I know pressure should be checked when the tyres are cold. I get off the bike and place it on central stand while checking air. Far car too, I get down and check pressure on an empty car. But I notice sometimes four or five people sitting inside the car checking the pressure without getting out and driving away. Which is the correct method? Will not the additional weight of 5 people show a wrong reading?
	() Thanks

21st July 2009, 13:23	#18
sdmn BANNED Join Date: Jan 2009 Location: Bangalore Posts: 135 Thanked: 39 Times	Folks, Can anyone point to a definitive source of information that explains whether tire pressure needs to be increased or decreased after an upsize? I understand that tire pressure is an optimized value - optimized for ride quality and tire wear / fuel mileage. However, assuming all other parameters to be the same, how must the tire pressure change with an increase in tire width? I bought a Verna CRDI a year back, and upgraded from Bridgestone B250 185/65R14 86H stock to Bridgestone Turanza 195/60R14 86H right at the showroom before delivery. Hyundai recommends 32psi (all wheels / 2 front passengers) and 33psi (all wheels / full load). It also provides recommended pressures for alternative tire sizes, but unfortunately, not for this size. Ironically, this was the Hyundai dealership recommended upgrade! I shot off a mail to Bridgestone immediately after purchase asking them the same question and they replied telling me to maintain the same pressure as what Hyundai recommended for the stock tires. I have been following their advice during the 1 year of ownership and have had no problems whatsoever. However, I am not convinced with the answer I got from Bridgestone India, since keeping everything else the same, when you do a tire upsize, there must be a corresponding change in the recommended tire pressure too. I realize that the difference is perhaps too small - but there has to be a difference and I want to understand that. I found contradictory views on team bhp too about whether tire pressure must be increased or decreased when there is an increase in tire pressure. Other than the 'you decide based on your taste' logic, I am looking for a definitive, scientific answer. Who can help?
	() Thanks

21st July 2009, 14:23	#19
watashi75 BHPian Join Date: Jan 2008 Location: Hyderabad Posts: 518 Thanked: 12 Times	I have asked this question in this forum and I did not get any definitive answer. So I have formed my own opinions about correct tyre pressure after an upgrade. See here - http://www.team-bhp.com/forum/techni...ml#post1139159 If you upgrade to wider tyres you need to reduce tyre pressure for better straightline grip. If you upgrade to lower profile tyres you need to reduce tyre pressure for better ride quality. If you upgrade to lighter alloys the load decreases so you need to reduce tyre pressure. If you upgrade to better rubber you don't need to do anything. In all cases it would be a safe bet to reduce tyre pressure after an upgrade.
	() Thanks

24th July 2009, 22:56	#20
sdmn BANNED Join Date: Jan 2009 Location: Bangalore Posts: 135 Thanked: 39 Times	Thanks watashi75. Your suggestions certainly will help. I'm still looking for a definitive answer through.
	() Thanks