Michelin PS4

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keenklee

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sinistral said:
I disagree.

Rear tyres may not be as 'hot' as the front tyres after driving around some time on a hot sunny day. Likely explanation is that the front brakes do most of the braking work, so heat dissipation at the front brakes are higher compared to the rear, so the front tyres tend to be slightly higher in temperature.

That is why the recommendation is to pump when the tyres are cold, where the tyres have the same temperature as the ambient temperature.
Click to expand...

IMHO.
I never mentioned that they are to be pumped at the same pressure.
My equal all around is with compensation.
Rear tyres will unlikely have the same temperature as the front.
Rear tyres will also unlikely to have the same temperature between them.
This is the same for front tyres.
In most instances, it is depend on the design of the engine system.

Equal all around also meant that, when the tyres reach operating temperature, the front tyres will be both of the same pressure and likewise for the rear.

The recommendation of cold tyre temperature still stands - it is easier.
I would also say that that if the tyres are pumped based on the cold tyre pressure, on a cold rainy day, the tyres will be slightly under-inflated especially the rear tyres.

In addition, cold tyre pressure to different drivers have different meanings. What's your take on cold tyre pressure during the hotter months of the year?
 
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sinistral

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keenklee said:
IMHO.
I never mentioned that they are to be pumped at the same pressure.
My equal all around is with compensation.
Rear tyres will unlikely have the same temperature as the front.
Rear tyres will also unlikely to have the same temperature between them.
This is the same for front tyres.
In most instances, it is depend on the design of the engine system.

Equal all around also meant that, when the tyres reach operating temperature, the front tyres will be both of the same pressure and likewise for the rear.

The recommendation of cold tyre temperature still stands - it is easier.
I would also say that that if the tyres are pumped based on the cold tyre pressure, on a cold rainy day, the tyres will be slightly under-inflated especially the rear tyres.

In addition, cold tyre pressure to different drivers have different meanings. What's your take on cold tyre pressure during the hotter months of the year?
Click to expand...

I have to caveat first that I am not an automotive engineer; my comments are based on my own observations in my cars.

The rise in tyre pressure appears to be linearly correlated to the rise in tyre temperature. A 10 degree Celsius rise in temperature typically increase the tyre pressure by 4 PSI (0.2bar). The tyre temperature will rise regardless of the weather, due to friction with the road surface.

I don't think there is a specific 'operating' temperature of the tyres, i.e. tyres still work in cold climate v.s. warm climate. I guess you are inferring 'optimum' temperature where the tyres may provide the best benefit (grip, fuel efficiency). This seems to be a range of between 2-8 PSI increase from cold tyre pressure. I derived 2-8 PSI from driving in different periods of the day. 2 PSI increase is at night, where the ambient temperature is low, and the rise in tyre temperature is mostly due to road surface friction. 8 PSI is when the road is extremely hot under a hot sunny day, where I observe my tyres temperature reaching 50 degrees Celsius. This refers to normal day-to-day driving, instead of racing tyres, as I understand racing slicks do have operating temperatures for optimum grip on the track.

The issue with pumping tyres while they are hot is that there is no reference point to tyre pressure vis-a-vis tyre temperature for the 'compensation'. For example, if you were to pump your tyres at a petrol station while your tyres are hot, you can only see what is the current type pressure, not the tyre temperature. You cannot provide an accurate 'compensation' because there is no information whether the tyres are hot @ 40 degrees Celsius, or hot @ 50 degrees Celsius. When the tyres' temperature drops to ambient temperature, your tyres may not be at the recommended cold tyre pressure.

I can't see how tyres can be slightly under-inflated if you pump a specific pressure (say, 32 PSI) at the cold tyre pressure. It is still 32 PSI regardless it is a cold rainy day or a hot sunny day.

To me, the difference of cold tyre pressure on cooler months of the year compared to hotter months of the year is not significant. The tyre pressure will rise regardless once you start driving, and it would be within the range of optimum temperature.

I also understand that front and rear tyres need not be of the tyre pressure, that's why I did not bring it up. B-segment cars (Swift, Jazz) that i have driven tends to have higher pressure for the front tyres. Recommended cold tyre pressure for my Swift was 36 PSI front, 32 PSI rear, while Jazz is 35 PSI front, 33 PSI rear. D-segment cars (Mazda 6, Merc C-Class) that I have driven have the same recommended cold tyre pressure for all four tyres.
 
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sinistral said:
I have to caveat first that I am not an automotive engineer; my comments are based on my own observations in my cars. Same.

The rise in tyre pressure appears to be linearly correlated to the rise in tyre temperature. A 10 degree Celsius rise in temperature typically increase the tyre pressure by 4 PSI (0.2bar). The tyre temperature will rise regardless of the weather, due to friction with the road surface. 1) Correct. However, the pressure can be different because the 4 tyre temperature can be different.

I don't think there is a specific 'operating' temperature of the tyres, i.e. tyres still work in cold climate v.s. warm climate. I guess you are inferring 'optimum' temperature where the tyres may provide the best benefit (grip, fuel efficiency). This seems to be a range of between 2-8 PSI increase from cold tyre pressure. I derived 2-8 PSI from driving in different periods of the day. 2 PSI increase is at night, where the ambient temperature is low, and the rise in tyre temperature is mostly due to road surface friction. 8 PSI is when the road is extremely hot under a hot sunny day, where I observe my tyres temperature reaching 50 degrees Celsius. This refers to normal day-to-day driving, instead of racing tyres, as I understand racing slicks do have operating temperatures for optimum grip on the track. 2) That is why the question on cold tyre temperature. Cold tyre temperature is in relation to the ambient temperature at the time of use. In your scenario, there will be many cold tyre temperature. So effectively, when the day is hot, there will be over-inflation if the cold tyre temperature is in the early morning. This is looking at the details but if not looking, anything also can. The challenge is finding the balance.

The issue with pumping tyres while they are hot is that there is no reference point to tyre pressure vis-a-vis tyre temperature for the 'compensation'. For example, if you were to pump your tyres at a petrol station while your tyres are hot, you can only see what is the current type pressure, not the tyre temperature. You cannot provide an accurate 'compensation' because there is no information whether the tyres are hot @ 40 degrees Celsius, or hot @ 50 degrees Celsius. When the tyres' temperature drops to ambient temperature, your tyres may not be at the recommended cold tyre pressure. 3) The tyre temperature will affect the pressure. If the tyres are pumped the same pressure at cold, the pressure at hot could be different because the tyre temperature could be different. So when it reaches back to the cold temperature, it will be different. So the question now is, which is better, e.g. front tyre, one side higher pressure then the other ? The compensation is based on one cold tyre pressure and not multiple. There is no solution to multiple cold tyre pressure except to average.

I can't see how tyres can be slightly under-inflated if you pump a specific pressure (say, 32 PSI) at the cold tyre pressure. It is still 32 PSI regardless it is a cold rainy day or a hot sunny day. 4) As mentioned by you in 1), it applies to drop in temperature as well. In moderate to heavy rain conditions, the rear tyre pressure will drop if the cold tyre pressure is higher.

To me, the difference of cold tyre pressure on cooler months of the year compared to hotter months of the year is not significant. The tyre pressure will rise regardless once you start driving, and it would be within the range of optimum temperature. 5) If it is not significant to you, then there is no difference. As you have stated in 1), there is a difference.

I also understand that front and rear tyres need not be of the tyre pressure, that's why I did not bring it up. B-segment cars (Swift, Jazz) that i have driven tends to have higher pressure for the front tyres. Recommended cold tyre pressure for my Swift was 36 PSI front, 32 PSI rear, while Jazz is 35 PSI front, 33 PSI rear. D-segment cars (Mazda 6, Merc C-Class) that I have driven have the same recommended cold tyre pressure for all four tyres. 6) AFIAK, tyre pressure is dependent on load. Usually the front will be of higher pressure because of the weight of the engine. The vehicle placard will have information. I did a search for Mazda 6 placard, front is 32psi up to 4 person/38psi full load and rear 32psi up to 4 person/45psi full load.
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IMHO.
 
sinistral

sinistral

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keenklee said:
IMHO.
Click to expand...
The main point is to pump tyres when cold (defined as not operating the vehicle for some time, say, 6 hours or more) is that all four tyres will be at the same temperature as ambient temperature, thereby given a reference point where all variables are known.

2) Pumping 32 PSI at 24 degrees Celsius (chilling SG day) v.s. pumping 32 PSI at 30 degrees Celsius (average SG midday) is just marginal of difference (6 degree is about 2 PSI), once you start driving, the tyre pressure will still rise between 2-8 PSI for that day. What is your definition for underinflation and overinflation, in terms of tyre pressure?

3) The problem of pumping tyres when hot is that there is an unknown variable, which is the tyre temperature. As you have stated, the front tyres and rear tyres may have different temperature when hot. I am not sure how you intend to compensate (if I get your definition right) the difference without knowing the tyre temperature such that when the tyres are cold, it will be at the recommended cold tyre pressure. The laymen only knows about tyre pressure. The air pump at the petrol station only provides tyre pressure readings. I myself have tried to pump my tyres at the petrol station while it's hot on different days, adding an additional 4 PSI on top of the current pressure, thinking that the tyre pressure will drop to recommended tyre pressure at cold. Let's just say that did not work out correctly.

4 and 5) While there is a difference, it is not significant. Interestingly, it does seem that the tyre pressure may drop while driving in heavy rain conditions, but my experience and TPMS readings suggested that there is no change or marginal increase in tyre temperatures on all four tyres driving in the wet.

6) There are other factors as well but let's keep the discussion to the points above.
 
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keenklee

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sinistral said:
The main point is to pump tyres when cold (defined as not operating the vehicle for some time, say, 6 hours or more) is that all four tyres will be at the same temperature as ambient temperature, thereby given a reference point where all variables are known.
0) Ambient temperature change. Very simple experiment. Let the vehicle park under shade in the open for your stipulated time of 6 hours. Pump to defined pressure. Move the vehicle a short distance to a place where the left side of the vehicle faces the afternoon sun. Compare the right tyres and left tyres for pressure difference.


2) Pumping 32 PSI at 24 degrees Celsius (chilling SG day) v.s. pumping 32 PSI at 30 degrees Celsius (average SG midday) is just marginal of difference (6 degree is about 2 PSI), once you start driving, the tyre pressure will still rise between 2-8 PSI for that day. What is your definition for underinflation and overinflation, in terms of tyre pressure?
1) 3- 4 degrees Celsius is a lot of difference for me. That equates to 5 kPA. My rear tyre pressure do not usually change more than 20 kPA. 5kPA is 25%. The difference is also whether my rear tyre will squeal when goes over painted surfaces while turning. I had mentioned before, 20-30 kPA difference equates to 6% decrease in contact area size.

If one follows the placard and pump at the specified pressure, when the ambient temperature change, automatically the tyre will either be over inflated or under inflated ? Since it is a marginal difference to you, the question is pointless.

3) The problem of pumping tyres when hot is that there is an unknown variable, which is the tyre temperature. As you have stated, the front tyres and rear tyres may have different temperature when hot. I am not sure how you intend to compensate (if I get your definition right) the difference without knowing the tyre temperature such that when the tyres are cold, it will be at the recommended cold tyre pressure. The laymen only knows about tyre pressure. The air pump at the petrol station only provides tyre pressure readings. I myself have tried to pump my tyres at the petrol station while it's hot on different days, adding an additional 4 PSI on top of the current pressure, thinking that the tyre pressure will drop to recommended tyre pressure at cold. Let's just say that did not work out correctly.
2) I am different from you because I have no unknown as I measure the tyre temperature and compensate based on the same rules you presented. Re your 4 PSI methodology which i recall that i read somewhere else, you are assuming that the temperature difference is more than 20 degrees Celsius on a very hot day. You have to also take into consideration of the engine size and if it is turbo-charged as well as single or twin exhaust. These are the parameters that affect the tyres temperature. The 4 PSI rule of thumb likely to be from US and may not necessary applies unless driving a high capacity engine car. Anyway, it dates as far back as 2008 based on internet search.

A layman can just pump based on cold and live with the marginal difference. To be effective to getting the tyres to their "optimal pressure", fix the cold tyre temperature and pump the stated pressure. After driving a usual route, with the same cold tyre temperature, pump at maybe +30 kPA. When connecting the nozzle, take note of the initial pressure. That is the pressure you want. If it is the same route always, that is the default pressure - it won't change much.

4 and 5) While there is a difference, it is not significant. Interestingly, it does seem that the tyre pressure may drop while driving in heavy rain conditions, but my experience and TPMS readings suggested that there is no change or marginal increase in tyre temperatures on all four tyres driving in the wet. My pressure will least likely to drop because my reference temperature is 25 degrees celcius at times. On the hotter months, I will move to maybe 27 or 28. Under normal driving condition, my TPMS show rear tyre pressure at 21 when hot. On days of moderate and heavy rain, it will show 20. Had I not compensate my cold tyre temperature, it may show 19. The tolerance of the TPMS is taken into consideration i.e. > 19.5 will show 20 and also that the air inside the tyre has become mostly nitrogen.

6) There are other factors as well but let's keep the discussion to the points above.
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IMHO.
 
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keenklee

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myviowner said:
????
Click to expand...
IMHO.
Don't worry about it if you're ok with the slight difference in pressure.
For the front, It is not that noticeable when you go over hump.
For the rear, the difference is more, but usually won't feel anything unless fish tail.
 
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