Oil weight for track only car with a lot of cooling?

[Ultramaroon]

Originally Posted by RT-BRZ

At least that's how I've understood it.

Correct.

[GrandSport]

Originally Posted by RT-BRZ

It has always been my understanding that tighter clearances were the result of higher precision machining and manufacturing. It seems logical to me that the tighter clearances allowed for less drag by having the ability to use lower viscosity lubrication. When clearances were bigger, higher viscosity lubrication was needed to "fill the space" to reduce wear. All in the name of efficiency.

At least that's how I've understood it.

Taking tolerance/precision out- wouldn't you want a thicker layer of thicker oil there rather than a thin layer of thinner oil for durability though?

[RT-BRZ]

Originally Posted by GrandSport

Taking tolerance/precision out- wouldn't you want a thicker layer of thicker oil there rather than a thin layer of thinner oil for durability though?

Well, I think it's a story of tradeoffs. The lower viscosity oils are more "slippery" apparently which gives the appropriate amount of lubrication. A thicker oil may offer more "cushion" and may better maintain it's heat resistance but it may also increase parasitic drag and lower efficiency (mileage, power, etc.).

Honestly, I'm not the design engineer for these engines and I'm definitely not qualified to determine what's better. All I am is a caveman trying to understand the wheel.

[GrandSport]

Okay, I have what I bet is a really dumb question:

Higher number = thicker

IE: 40weight is thicker than 50 weight oil.

Okay, then why is the first number (cold temp/winter) number always lower than the hot number?

5W40 means the oil is thicker at temp than when it's cold?
I dont see how the hell that is possible, and I'm damn near certain it's not unless I'm losing my mind.

So why is it numbered like this?

[Ohio Enthusiast]

Originally Posted by GrandSport

Okay, I have what I bet is a really dumb question:

Higher number = thicker

IE: 40weight is thicker than 50 weight oil.

Higher number is thicker, so 50 is thicker than 40, not the other way around.
A 5W30 will behave like 5 in cold temps (W rating is at 0 degrees Fahrenheit) and like 30 in working temps.

[GrandSport]

Originally Posted by Ohio Enthusiast

Higher number is thicker, so 50 is thicker than 40, not the other way around.
A 5W30 will behave like 5 in cold temps (W rating is at 0 degrees Fahrenheit) and like 30 in working temps.

Yes, so why is it 5 when its cold and 30 when its warm?
Thicker = higher number
cold number is lower.

[villainous_frx]

LMGTFY:
https://www.valvolineglobal.com/en-k...g-oil-weights/
https://www.castrol.com/en_us/united...explained.html
https://knowhow.napaonline.com/under...s-bottle-mean/

[Ohio Enthusiast]

Originally Posted by GrandSport

Yes, so why is it 5 when its cold and 30 when its warm?
Thicker = higher number
cold number is lower.

Ah, I think I see your confusion. A single grade oil (and most substances, really), would get thicker the colder it is, and thinner the hotter it is. So a straight 30 weight oil would be very thick at 0 degrees and won't be able to provide protection to the engine.
A multigrade oil (like 5W30) is able to run thinner in cold temperatures while not being super thin in working temperature. So the W (Winter) number is low because the oil is pretty thin when cold, and the regular number is higher to offer protection at working temperatures and above.

[GrandSport]

Originally Posted by Ohio Enthusiast

Ah, I think I see your confusion. A single grade oil (and most substances, really), would get thicker the colder it is, and thinner the hotter it is. So a straight 30 weight oil would be very thick at 0 degrees and won't be able to provide protection to the engine.
A multigrade oil (like 5W30) is able to run thinner in cold temperatures while not being super thin in working temperature. So the W (Winter) number is low because the oil is pretty thin when cold, and the regular number is higher to offer protection at working temperatures and above.

So it thickens up as it gets hotter?
How is it only "5" at cold temps and "30" at 200 degrees!?

Also, this not only doesn't follow my common sense test, but it doesn't follow my data either. My oil pressures are definitely lower at 200 than startup.

I get a straight 30 weight would be much thicker in the cold, so they use multigrade, but shouldn't it be a higher number? Ie instead of being 100 in the cold, it's only 40.

[Ohio Enthusiast]

Originally Posted by GrandSport

How is it only "5" at cold temps and "30" at 200 degrees!?

The magic of viscosity index improvers. I won't claim to understand the chemistry of how they work, but they allow oil to be in the correct viscosity at 0 degrees as well as at 212 degrees.

To make it easier to think about, consider the W and regular weights to be on different scales that are un-related. Choose the W weight based on the coldest you expect the car to need a cold start, and the regular weight based on how hot you expect the engine to operate at.

[gen3v8]

A 215 35 r18 tyre is not wider than it is round. It`s a different measuring system.

[terboboost]

This is a great question, that I will answer with numbers pulled out of my a$$ for a simple explanation.

The oil weight is not a viscosity rating. The viscosity rating is measured in, for example, pascal-second (Pa·s). So lets lay out how to different motor weights change viscosity over temperature.

5 weight- 50 Pa·s @ 0*c ------------5 Pa·s @ 100*c
40 weight- 200 Pa·s @ 0*c------------50 Pa·s @ 100*c

With these totally BS numbers, we see that if we make a 5W-40, this oil will have the same viscosity at 0*c as it does at 100*c, 50 Pa·s. In reality, you aren't going to hold the viscosity the same over the full temperature range, so you do end up with a thinner oil as it heats up, maybe something like....

5 weight- 50 Pa·s @ 0*c ------------5 Pa·s @ 100*c
40 weight- 200 Pa·s @ 0*c------------20 Pa·s @ 100*c

So at operating temp it has a viscosity rating of 20 Pa·s like a 40 weight oil, and while it's still thicker at cold temperatures with a 50 Pa·s viscosity rating, it's much thinner then a 40 weight oil would be.

[GrandSport]

Originally Posted by terboboost

This is a great question, that I will answer with numbers pulled out of my a$$ for a simple explanation.

The oil weight is not a viscosity rating. The viscosity rating is measured in, for example, pascal-second (Pa·s). So lets lay out how to different motor weights change viscosity over temperature.

5 weight- 50 Pa·s @ 0*c ------------5 Pa·s @ 100*c
40 weight- 200 Pa·s @ 0*c------------50 Pa·s @ 100*c

With these totally BS numbers, we see that if we make a 5W-40, this oil will have the same viscosity at 0*c as it does at 100*c, 50 Pa·s. In reality, you aren't going to hold the viscosity the same over the full temperature range, so you do end up with a thinner oil as it heats up, maybe something like....

5 weight- 50 Pa·s @ 0*c ------------5 Pa·s @ 100*c
40 weight- 200 Pa·s @ 0*c------------20 Pa·s @ 100*c

So at operating temp it has a viscosity rating of 20 Pa·s like a 40 weight oil, and while it's still thicker at cold temperatures with a 50 Pa·s viscosity rating, it's much thinner then a 40 weight oil would be.

Ah, I see.
Is there some rule that something for cars can't be measured in a rational way?
We need to produce figures for viscosity at room temperature and operating temperature.
Definitely do NOT just state viscosity at those two temperatures. The first number okay, but the second number, make it how much viscosity an oil would have at room temp, based on how much it thinned out at operating temp.


How should we handle tires? Well, we will make the width in mm because metric is the standard of the world.
So the wheel size in metric too?
No.
Will we measure the overall height in metric?
No.
Imperial?
Also, no.
What? How will people know the over diameter
They won't. We will measure it making it sidewall
Oh, so like 245mm/100mm/17?
Heavens no. We will make it expressed as the percentage of the overall width.
For the overall diameter?
No just the sidewall
Okay, so the number will be the amount the sidewall adds as ratio of the width.
...half the sidewall adds.


Forced induction
Should we measure how much air is going in?
No, that can change too much based on conditions.
Should we measure it, at STP?
No, we will measure airflow by how much restriction the air intake system has
But that doesn't tell us anything for how much air, power, fuel etc its getting.
Precisely.


Okay, let's just measure the power output of this car and move on.
Take the transmission off first.

[CSG Mike]

Originally Posted by GrandSport

Ah, I see.
Is there some rule that something for cars can't be measured in a rational way?

Because that's just way too complex for the average consumer.

The average consumer also shops brake pads by mu and mot, typically, followed by price. Brake pads are so much more complex than that.