Green Wheel Dust Covers

Jgtcracer · August 28, 2022

My car has had green dust covers fitted since I first got it in April and had a sneaking suspicion that it meant something. Having had a google it seems that the tyres could be nitrogen filled. Anyone every done this and actually noticed it making a difference? I've tried it before to no effect so don't anticipate I will be getting it re-done in the future but as the car was previously owned by Lexus UK and maintained within their network I though it interesting to see it used.

Any ideas?

Marcus

NemesisUK · August 28, 2022

As normal air is 80% nitrogen anyway you'd need to be an F1 driver to appreciate any difference!

Filling tyres with nitrogen also limits one's refill opportunities plus the additional costs.

Pretty sure Lexus wouldn't bother using nitrogen so guess the previous owner did it, probably when renewing the tyres.

IMHO a total waste on a road car.

Linas.P · August 28, 2022

I suspect it has tyre sealant (Slime) inside rather than nitrogen. I had it in bicycle tyres and package comes with green cap. This is most likely because car comes without spare. It is still useless for sealing tyres, but somewhat better than milk which comes with the car, because it has glass fibre reinforcement in it, so it may actually seal small hole rather than running out, but if you have puncture 9 times out of 10 it won't work.

As for nitrogen - I had it in my tyres before and it does make a small difference, but certainly worth £3 it costs to fill. What is the difference? That is your tyre pressure remains the same all year long and both on the cold morning and after driving for long time at high speed. So you never need to worry that tyre pressure will be low on cold morning before the trip and generally it saves money as "free-air" is increasingly rare at service stations, some now charging £2 to refill. Whereas air - although 75% nitrogen, has 25% of other gases and some water. The water is what matters, because it expands when warm and contracts when cold, which is what makes the 3-5Psi difference between the seasons. Technically "dry-air" is 90% as good as nitrogen, but air is NEVER dry, especially not in crappy petrol station pumps.

So my logic is - you can spend £3 for lifetime of the tyres to make them maintenance free, or spend ~£8 a year for 2-3 years adjusting for seasonal temperature changes and for longer trips. It is tiny but positive difference and when fitting the premium tyres for £1000 it is well worth it to keep them in best possible shape.

I guess if car ever went on track that would as well be warranted as it is easier to keep consistent air pressures on the track when using nitrogen. But again I don't think your tyres have nitrogen, if they did it would be more logical for cap to be blue rather than green.

Jgtcracer · August 28, 2022

1 hour ago, NemesisUK said:

As normal air is 80% nitrogen anyway you'd need to be an F1 driver to appreciate any difference!

Filling tyres with nitrogen also limits one's refill opportunities plus the additional costs.

Pretty sure Lexus wouldn't bother using nitrogen so guess the previous owner did it, probably when renewing the tyres.

IMHO a total waste on a road car.

My car was owned by Lexus UK until I bought it so not sure if tires would have been done at a local main dealer rather than another company that may offer nitrogen as a service.

At the cheap price it is I would possibly use it when considered against the cost of a tyre but certainly don’t notice any performance increase. Stability through the year will no doubt be better however.

NemesisUK · August 28, 2022

8 minutes ago, Jgtcracer said:

Stability through the year will no doubt be better however.

Nitrogen obeys the same gas laws as normal air, so it will still change pressure as the ambient temperatures change.

Just check your pressures first thing in the morning before the sun warms them. I find around December as the average ambient temp drops the pressures drop and then in April/May time the temps rise and they need reducing again. Been like that since Adam was a boy..😉

LenT · August 28, 2022

1 hour ago, Jgtcracer said:

My car has had green dust covers fitted since I first got it in April and had a sneaking suspicion that it meant something. Having had a google it seems that the tyres could be nitrogen filled. Anyone every done this and actually noticed it making a difference? I've tried it before to no effect so don't anticipate I will be getting it re-done in the future but as the car was previously owned by Lexus UK and maintained within their network I though it interesting to see it used.

Any ideas?

Marcus

Frankly Marcus, as your car was around 4 years old when you got it, unless you deflated the tyres and did a gas analysis of the contents, then Lexus-owned or not, there’s no way of knowing what they now contain!

I suggest you just regard them as having nice green dust caps.

If you think Nitrogen is worth the extra and can find a source, then I would start with a clean fill - ideally combining it with a new set of tyres.

The main benefit, I suggest, is that with Nitrogen being a bigger molecule than Oxygen, it will leak out of the tyre slower than the oxygen component. Which would suggest that a Nitrogen-filled tyre would retain its set pressure for longer.

Whether that would translate into a real-life motoring benefit is debatable.

Linas.P · August 28, 2022

37 minutes ago, NemesisUK said:

Nitrogen obeys the same gas laws as normal air, so it will still change pressure as the ambient temperatures change.

Just check your pressures first thing in the morning before the sun warms them. I find around December as the average ambient temp drops the pressures drop and then in April/May time the temps rise and they need reducing again. Been like that since Adam was a boy..😉

There are a lot of misconceptions in above statement. As I said before nitrogen vs. air makes minor difference, so I am nit-picking at best, but what you stating above is just incorrect.

First thing is water in air and it is an issue which nitrogen filled tyres don't get, as I have already said "dry air" would be 90% as good, but you can't generally get it, whereas you could get dry nitrogen. Key difference is not air vs. nitrogen, it is the content of water in your tyres. Because tyres are under pressure water boils and thus increase in volume significantly at relative low temperature (even below +40C), so running on air there will be huge difference between cold and warm tyre temperature, whereas there will be little to no difference when using nitrogen. The difference is small, but nitrogen is just better.

Secondly, tyre pressures are measured when driving and tyre is warm, not the first thing in the morning (that cannot be more wrong). Because it does not matter what tyre pressure you have on stationary car, what is important is that tyre pressure is optimal when you driving (the stated pressure are warm pressures, not cold pressures). And here many people have misconception that tyre temperature is the same as air temperature. No it is not - when you start driving tyres will warm-up to at least +20C and in hot summer day a lot more. So really nitrogen just needs to be stable between +20C and maybe +60C, which it is. So on nitrogen you are getting consistently stable pressure when driving and that is the only thing that matters.

As a bonus, because it is more stable, you get same pressures right when you start driving on cold morning and they don't change much when tyres are warm. As well you don't get uneven pressure if say you took two hard right hand corner and now your right hand front tyre is warmer. There are literally no downsides to nitrogen in the tyres, including the cost. I guess the only thing is that you need to find the place which offers it and dedicate a trip there to refill. ATS does nitrogen filling and generally because I use them for alignment and tyre fitting is the same trip anyway.

23 minutes ago, LenT said:

The main benefit, I suggest, is that with Nitrogen being a bigger molecule than Oxygen, it will leak out of the tyre slower than the oxygen component. Which would suggest that a Nitrogen-filled tyre would retain its set pressure for longer.

Whether that would translate into a real-life motoring benefit is debatable.

Properly fitted tyres don't leak anyway (at least I have not noticed it within say 6 months), so this is just another nice to have, but not real benefit. The problem with air in the tyres is not that it leaks out, but that you have to increase and decrease the pressure at least 4-6 times a year and you have to contently monitor it. That is not an issue with nitrogen - pressures just stays same all the time.

As well, as I have already said I don't think green caps indicates nitrogen.

LenT · August 28, 2022

1 hour ago, Linas.P said:

Secondly, tyre pressures are measured when driving and tyre is warm, not the first thing in the morning (that cannot be more wrong).

You’re something of a lone voice in this respect, Linus.

In the tire pressure section of the Lexus manual, it makes a point of stating that it’s the ‘Recommended cold tire pressure’. In fact I’ve never seen any recommendation to the contrary. Now you could make an argument for there being a variation in ambient cold temperature from day to day - and even country to country. But at least setting a cold tyre base temperature gives a consistent start point, whereas trying to standardise the conditions to arrive at a warm tyre point would involve too many variables.

In practice, of course, most people drive to a petrol station and top up their warm tyres there!

1 hour ago, Linas.P said:

Properly fitted tyres don't leak anyway (at least I have not noticed it within say 6 months), so this is just another nice to have, but not real benefit

Although I suggested it might be the main benefit of nitrogen, that’s only relative! Tyres are not impermeable to gas molecules, but more so to N2 than O2. But I think you’re right to say that the presence of water molecules will have a much greater effect anyway.

As for the green dust caps, I think that I have indeed seen claims that they are supposed to indicate a nitrogen fill - but unless I had personally done it, or witnessed it being done, I certainly wouldn’t rely on it. It’s just as likely to be the whim of someone who fancies green dust caps!

NemesisUK · August 28, 2022

1 hour ago, Linas.P said:

Secondly, tyre pressures are measured when driving and tyre is warm, not the first thing in the morning (that cannot be more wrong).

Manufacturers always recommend pressure in cold tyres as this value is calculated to give the correct hot running pressures without danger of over heating due to flex etc. If adjusted when the tyre is hot it will be significantly under-inflated.

The recommendation to check when cold is a recommended throughout the motoring world

https://www.rac.co.uk/drive/advice/how-to/checking-tyre-pressure/#:~:text=You should always check your,may give inaccurate pressure readings.

https://www.theaa.com/driving-advice/safety/tyre-pressures

https://www.bridgestonetire.com/learn/maintenance/how-to-check-tire-pressure/

https://www.michelin.co.uk/auto/advice/tyre-pressure/check-tyre-pressure

https://www.halfords.com/tyres/advice/video-tyre-pressure.html

Las Palmas · August 28, 2022

1 hour ago, Linas.P said:

There are a lot of misconceptions in above statement. As I said before nitrogen vs. air makes minor difference, so I am nit-picking at best, but what you stating above is just incorrect.

First thing is water in air and it is an issue which nitrogen filled tyres don't get, as I have already said "dry air" would be 90% as good, but you can't generally get it, whereas you could get dry nitrogen. Key difference is not air vs. nitrogen, it is the content of water in your tyres. Because tyres are under pressure water boils and thus increase in volume significantly at relative low temperature (even below +40C), so running on air there will be huge difference between cold and warm tyre temperature, whereas there will be little to no difference when using nitrogen. The difference is small, but nitrogen is just better.

Secondly, tyre pressures are measured when driving and tyre is warm, not the first thing in the morning (that cannot be more wrong). Because it does not matter what tyre pressure you have on stationary car, what is important is that tyre pressure is optimal when you driving (the stated pressure are warm pressures, not cold pressures). And here many people have misconception that tyre temperature is the same as air temperature. No it is not - when you start driving tyres will warm-up to at least +20C and in hot summer day a lot more. So really nitrogen just needs to be stable between +20C and maybe +60C, which it is. So on nitrogen you are getting consistently stable pressure when driving and that is the only thing that matters.

As a bonus, because it is more stable, you get same pressures right when you start driving on cold morning and they don't change much when tyres are warm. As well you don't get uneven pressure if say you took two hard right hand corner and now your right hand front tyre is warmer. There are literally no downsides to nitrogen in the tyres, including the cost. I guess the only thing is that you need to find the place which offers it and dedicate a trip there to refill. ATS does nitrogen filling and generally because I use them for alignment and tyre fitting is the same trip anyway.

Properly fitted tyres don't leak anyway (at least I have not noticed it within say 6 months), so this is just another nice to have, but not real benefit. The problem with air in the tyres is not that it leaks out, but that you have to increase and decrease the pressure at least 4-6 times a year and you have to contently monitor it. That is not an issue with nitrogen - pressures just stays same all the time.

As well, as I have already said I don't think green caps indicates nitrogen.

You forgot something my friend. I learned when I was a not very big boy (yes, that is long time ago) that Adam was created a man not a boy.

By the way if you want dry air it just could be (if not completely dry then almost) possible to get filling the tyres when op here in the mountains above the clouds.

Linas.P · August 28, 2022

Ok fine, I was wrong about measuring the tyre pressures.

Still nitrogen fill makes this moot point as difference between cold and warm tyres will be so small it no longer matters. Again that is just one of nitrogen benefits, because one no longer needs to deal with variable of of water expanding.

At least when I filled the tyres with nitrogen there was no mention of green caps, but I know Nissan used blue caps to indicate nitrogen on R35 which came nitrogen filled from factory, as well all the branding for nitrogen is usually blue. And I know for a fact Slime comes with green caps in the box.

Rob RCF · August 28, 2022

1 hour ago, Linas.P said:

Because tyres are under pressure water boils and thus increase in volume significantly at relative low temperature (even below +40C)

Just not true. In a vacuum water will boil even at room temp. Under pressure the boiling point of water increases.

I think I get what you're trying to say, that air with high humidity will expand more as it heats up than air with low humidity. But water boiling has nothing to do with it.

LenT · August 28, 2022

2 hours ago, Linas.P said:

tyres

2 hours ago, Linas.P said:

Key difference is not air vs. nitrogen, it is the content of water in your tyres. Because tyres are under pressure water boils and thus increase in volume significantly at relative low temperature (even below +40C), so running on air there will be huge difference between cold and warm tyre temperature, whereas there will be little to no difference when using nitrogen. The difference is small, but nitrogen is just better.

Sorry, Linus, but I think I may have noticed another nit to pick!

I think you are correct in stating that it’s the water content in the tyre that’s probably more significant. However, liquids convert to a gaseous phase at lower temperatures as the pressure above the liquid is reduced.

Which is why it can be such a pain to boil an egg on Everest!

ColinBarber · August 28, 2022

Continental sum it up well:

https://www.continental-tires.com/car/tire-knowledge/tire-care-maintenance/tire-pressure/nitrogen-in-tires

Nitrogen in highly specialized tire service applications

Thanks to these inert properties, tires inflated with nitrogen are beneficial for highly specialized service applications in demanding environments, such as aviation, mining, or construction.

Dry nitrogen mitigates tire pressure variations, so nitrogen-filled tires are also used in professional race car driving, where even the smallest changes in pressure can impact ultra-high-performance vehicle handling at extreme speeds.

So, now we come to the big question: is nitrogen right for your tires? The fact of the matter is that inflating tires with nitrogen is not necessary for typical everyday use on a passenger car. It might even be considered a frivolous waste of money.

To be clear, inflating tires with nitrogen is not harmful. Moreover, the PSI stays steady in the long term. (Tires filled with regular air lose pressure through permeation a little more quickly.)

But for the most part, nitrogen makes absolutely no difference when it comes to a loss of pressure caused by tire punctures, tire bead leaks, valve leaks, or other mechanical leaks. There’s no discernible benefit over air-filled tires, and that includes performance factors such as rolling resistance, fuel economy, and tire aging.

Linas.P · August 28, 2022

.

Jgtcracer · August 28, 2022

I almost wish I hadn’t asked, though the thread has been somewhat entertaining!

With the car having been previously owned by Lexus I wasn’t sure as to the rationale they would have used when inflating with nitrogen or whether it was indeed them that did it!

Thanks for the input from all involved, think I will just go with my gut as and when I change tyres, if the garage I use even does it!

Marcus

LenT · August 29, 2022

7 hours ago, Jgtcracer said:

… think I will just go with my gut as and when I change tyres, if the garage I use even does it!

I think that’s the way to go, Marcus. Choosing a new set of tyres is the most important decision. If they come with an N2 fill - like they claim at Costco - then there’s very little in the way of downsides.

( Coincidentally, Costco Is currently offering up to £100 off a set of Michelins ).

Having said that, I’ve had a couple of new sets from Costco and there have been occasions when at least one tyre has had to be refilled with ordinary compressed air and I can’t say that I noticed any difference.

Mind you, I didn’t get any new, fancy coloured dust caps either. Makes you wonder? 🤔

PRT68 · August 29, 2022

My mountain bike has Slime anti puncture fluid in the inner tube. And they're fitted with green dust caps.....

mr2lad · August 29, 2022

Just put helium in your tyres for a laugh 😂 also will lift car up and less wear on your tyres 🤦🏼‍♂️…… just mind the string and weight when you park up so it doesnt float away….. sorry not helpful but made me smile just coz im childish 😆

hockeyedwards · August 29, 2022

This took a turn in a direction I did not forsee, love it when we get all science-y (albeit warped). Great read guys 😛

Jgtcracer · August 29, 2022

2 hours ago, hockeyedwards said:

This took a turn in a direction I did not forsee, love it when we get all science-y (albeit warped). Great read guys 😛

As an engineer I love the science and tend to understand it well, makes the car more relatable to me if I understand the ‘why and how’.

hockeyedwards · August 29, 2022

24 minutes ago, Jgtcracer said:

As an engineer I love the science and tend to understand it well, makes the car more relatable to me if I understand the ‘why and how’.

I love all the nerdy stuff and completely agree to understanding the wizardry behind what we drive each day. But equally, find it down right hilarious that a question about green dust caps could spark such a thread 🤣

Plasticrat30 · August 29, 2022

There's more......🙂

It's all about the vapour pressure of water which increases considerably with temperature.

A tyre inflated with damp air on a rainy day will put on more pressure than the same tyre inflated with dry air as its temperature rises in use.

So as the dry air tyre warms up with use the air expands, the damp air tyre will expand more and so put on more pressure.

Nitrogen is used as it is dry before it is compressed and bottled. The difference between dry nitrogen and dry medical air would be marginal.

Rob RCF · August 30, 2022

15 hours ago, hockeyedwards said:

I love all the nerdy stuff and completely agree to understanding the wizardry behind what we drive each day. But equally, find it down right hilarious that a question about green dust caps could spark such a thread 🤣

Ha, the real question is, what happened to the original metal F-Sport caps? Those aren't cheap!