[diablo]

I recall reading on one of the threads on here that some i30 owners seem to use rather high pressures in their tyres. 40 psi if I recall - mainly from Australian posters. I don't think they use different sorts of pounds or inches down-under so it is rather more than the 32 recommended in my handbook.

I assume this is to save fuel, but doesn't it wear out the middle of the tyre somewhat? Are there no effects on handling and braking?

Just puzzled.

[eye30]

Yes I've been concerned at running at way above the recommended pressure.

Here in the UK if you are involved in an accident, the Poilce will check such things as tyre pressure.

If greater by + or - a specific tollerance then you could be at fault even if you are not at fault.


Here are 2 links to old postings:
https://www.i30ownersclub.com/forum/index.php/topic,2902.0.html

https://www.i30ownersclub.com/forum/index.php/topic,4793.0.html

[Myowni30]

I assume this is to save fuel, but doesn't it wear out the middle of the tyre somewhat? Are there no effects on handling and braking?

Just puzzled.

One of my mates is a tyre fitter (23 years experience).

Over inflated tyres are dangerous, especially in the wet. And at least 20% of all tyre replacements are because the centre on the tread has work away because of over inflation. Modern tyre construction does not stop this.

[Dazzler]

I recall reading on one of the threads on here that some i30 owners seem to use rather high pressures in their tyres. 40 psi if I recall - mainly from Australian posters. I don't think they use different sorts of pounds or inches down-under so it is rather more than the 32 recommended in my handbook.

I assume this is to save fuel, but doesn't it wear out the middle of the tyre somewhat? Are there no effects on handling and braking?

Just puzzled.

 

Long term member John (Lakes) is probably the biggest exponent of higher tyre pressures on here.. I believe he likes his inflated to around 40PSI and has no premature wear issues.   

Personally I prefer 34 all round or 36 front and 34 rear anything higher is overkill in my opinion and a bit to firm for me (although I respect John's right to run higher pressures)

I'm sure you wouldn't be at fault in an accident if they found say 36 in your tyres (but maybe OVER 40 might be a different matter) I guess it depends on the circumstances of the accident (e.g. if caused by a blow out)

I would like to hear our resident Tyre Expert's opinion (Doug AKA Surferdude)

[Surferdude]

I recall reading on one of the threads on here that some i30 owners seem to use rather high pressures in their tyres. 40 psi if I recall - mainly from Australian posters. I don't think they use different sorts of pounds or inches down-under so it is rather more than the 32 recommended in my handbook.

I assume this is to save fuel, but doesn't it wear out the middle of the tyre somewhat? Are there no effects on handling and braking?

Just puzzled.

 

Long term member John (Lakes) is probably the biggest exponent of higher tyre pressures on here.. I believe he likes his inflated to around 40PSI and has no premature wear issues.   

Personally I prefer 34 all round or 36 front and 34 rear anything higher is overkill in my opinion and a bit to firm for me (although I respect John's right to run higher pressures)

I'm sure you wouldn't be at fault in an accident if they found say 36 in your tyres (but maybe OVER 40 might be a different matter) I guess it depends on the circumstances of the accident (e.g. if caused by a blow out)

I would like to hear our resident Tyre Expert's opinion (Doug AKA Surferdude)

It's Trev, Dazzles, not Doug.
40 psi is OK.
There is a reference work called the Australian Tyre and Rim Association Manual with equivalent publications in Europe, USA and (I think) Japan. These are used by all signatories (including car manufacturers) with regard to fitment of tyre sizes to rim sizes, load and speed indices and pressure as it relates to load carrying capacity. Each tyre is given a maximum allowable pressure.
You need to remember it is the air in the tyre which carries the load (picture a tyre with no air in it and the weight of the car on it).
One of the things which happens these days is shoulder wear on the front tyres due to (a) power steering which at the initial application is more savage than a car without. and (b) roundabouts where, once you enter the roundabout pretty well all the weight on the left front (RF in Europe) is concentrated on the outside shoulder for the duration of the roundabout. Even simple things like turning right are done at more speed than turning left (reversed in Europe) so the LHF always cops more of a hiding.
Wheel alignment won't stop these things although it will reduce it. Slightly increased tyre pressure will though, as it stiffens up the sidewall a bit more, thereby reducing tread distortion. Lower profile tyres can also help, except that, if your alignment is out the wear is accentuated dramatically.
40 psi won't cause centre rib wear unless in a wide section tyre on a vehicle which spends a lot of its time on the highway - more consistent centrifugal force.
40 psi won't affect the footprint of the tyre enough to give problems in the wet either, although you wouldn't have to get much above this to start causing traction problems.
Personally I use 36 front and 34 rear (36 all round if travelling)
And the biggest danger to tyres is underinflation which allows heat build up. Most people set their pressures and then don't look at them again for weeks/ months so if they end up around 24 (and most do), then they are running dangerously underinflated and under load specs for much of that time. Siewall failures or tread separations can then occur months later.

[Dazzler]

It's Trev, Dazzles, not Doug.

Sorry Trev (don't know where i "dug" that up from..)  ..

I want to add one extra point to what Trev said.

A high proportion of accidents are rear-ending someone. Suddenly realising the car in front has stopped and is now much closer than it was a few moments earlier... you jump on the brake and confront that sinking feeling as the gap shortens in apparent slow motion while you utter one of your favourite expletives.

Whether you stop or not in time will depend a lot on the shape of the front tyres during the emergency stop.  If the extra load on the tyre causes the tread to become concave (effectively underinflated) they won't stop you. 

This simple fact influences my decision to run the fronts with 38psi in the 16" rims.

[Surferdude]

Good point Pip.
I think though, that the give in the sidewalls would mostly over-ride the tendency to lighten the load on the centre rib, thus widening the footprint and actually giving you more grip.
However, at that point the ABS would be kicking in and shaking the crap out of the car and lengthening your stopping distance anyway.
Horrible feeling in the pit of your stomach isn't it. 

Incidentally, did some testing on gravel and tarmac once. The quickest way to stop is to pull on the handbrake and get the car sideways - wider, shorter footprint always works better than a narrower, longer one. 

Discalimer: Not advocating this in a road situation but it helps to be aware of what your tyres are capable of.

Good point Pip.
I think though, that the give in the sidewalls would mostly over-ride the tendency to lighten the load on the centre rib, thus widening the footprint and actually giving you more grip.

Not sure I agree with that.  The tread bearing on the road (footprint) is directly influenced by the tyre pressure and the load. Hard decelleration transfers weight to the front wheels, significantly increasing the load which must alter the footprint, even if the tyre is designed to resist it. If the pressure chosen is towards the higher end of normal it might slightly compromise day-to-day driving but will I believe help the day you meet your inevitable stopping emergency.

Admittedly many years ago, I was able to test this on a closed track with my own car. Actually a company car which as we all know can withstand greater mistreatment than ones own car for an unknown reason.

Results were spectacular WRT to stopping distances when tyre pressure was increased from manufacturers recommendation to what some thought were ridiculously hard.

[diablo]

I'm a little confused by the replies here. I'd have thought that a tyre inflated to 'normal' pressure would have the maximum road contact area in emergency braking. Maybe widthways the over-inflated one would have the edge, but the length of tread would be greater for normal, surely ?

I'm also a little puzzled by the fact that the recommended tyre pressures are the same for diesels as for for my light petrol engine. The extra weight of the diesel engine is 220 pounds - all over the front wheels - like a fairly porky bloke sat on the bonnet.    

Then again, why wouldn't Hyundai recommend higher pressures if it gave them better MPG figures and was safe?


I'm thinking maybe 34 rear and 33 front at the moment.

[Surferdude]

Good point Pip.
I think though, that the give in the sidewalls would mostly over-ride the tendency to lighten the load on the centre rib, thus widening the footprint and actually giving you more grip.

Not sure I agree with that.  The tread bearing on the road (footprint) is directly influenced by the tyre pressure and the load. Hard decelleration transfers weight to the front wheels, significantly increasing the load which must alter the footprint, even if the tyre is designed to resist it. If the pressure chosen is towards the higher end of normal it might slightly compromise day-to-day driving but will I believe help the day you meet your inevitable stopping emergency.

Admittedly many years ago, I was able to test this on a closed track with my own car. Actually a company car which as we all know can withstand greater mistreatment than ones own car for an unknown reason.

Results were spectacular WRT to stopping distances when tyre pressure was increased from manufacturers recommendation to what some thought were ridiculously hard.

Now I'm confused. It looks to me as though you and I are saying the same thing. Higher pressures are good.

Good point Pip.
I think though, that the give in the sidewalls would mostly over-ride the tendency to lighten the load on the centre rib, thus widening the footprint and actually giving you more grip.

Not sure I agree with that.  The tread bearing on the road (footprint) is directly influenced by the tyre pressure and the load. Hard decelleration transfers weight to the front wheels, significantly increasing the load which must alter the footprint, even if the tyre is designed to resist it. If the pressure chosen is towards the higher end of normal it might slightly compromise day-to-day driving but will I believe help the day you meet your inevitable stopping emergency.

Admittedly many years ago, I was able to test this on a closed track with my own car. Actually a company car which as we all know can withstand greater mistreatment than ones own car for an unknown reason.

Results were spectacular WRT to stopping distances when tyre pressure was increased from manufacturers recommendation to what some thought were ridiculously hard.

Now I'm confused. It looks to me as though you and I are saying the same thing. Higher pressures are good.

Well I have to confess I don't know what you meant now about getting more grip. I really thought we were disagreeing... so yeah, higher is better.

10% under max rated seems to give a safe margin. It's dark now and I can't remember what max is for my tyres... but 40psi IIRC fits the 10% rule. I found 40psi just a little too hard for comfort so settled on 38psi.

[Surferdude]

^^^ all cool, pip.

[eye30]

After reading all the above can anyone them please explain why manufacturers provide max pressure which appears to be below what is mentioned above.

I tried an experiment once and set pressure at recommended.  Ran for miles and miles and retook pressure.  It had risen, I think +4 or 6, which it would appear is normal due to the air inside the tyre heating up.

Now if I had set at say +8 then the increase would have not been +8 but probably +12 or even more.

Now you are not telling me that if, in this example, the pressure would be + 20 the car would handle correctly.

In my view this increased pressure, well in excess of manufacturers recommended, would contribute to poor handling and may contribute to an accident.

[Surferdude]

^^^
In effect, the higher your cold pressure, the less build up from heat (less sidewall flex).
So by increasing your cold pressure you reduce the build up.
Tyre manufacturers allow for this in the design of the tyre

Vehicle manufacturers will advise the lowest pressure which will carry the load of the car (taking into account things like weight transfer under braking etc) in order to provide the best possible ride. Their only concern is that you feel comfortable in your new car. Tyre manufacturers will recommend a slightly higher pressure because they want you to be happy with the way your tyres handle and how well they wear.

If you get a puncture which manifests itself as a slow leak,as the pressure drops the heat builds up, which I why you can often not know anything is wrong until the tyre blows out because the heat has literally melted the cords in the sidewall of the tyre.

[Dazzler]

Great Summation Trev... 

[Myowni30]

After reading all the above can anyone them please explain why manufacturers provide max pressure which appears to be below what is mentioned above.

I tried an experiment once and set pressure at recommended.  Ran for miles and miles and retook pressure.  It had risen, I think +4 or 6, which it would appear is normal due to the air inside the tyre heating up.

Now if I had set at say +8 then the increase would have not been +8 but probably +12 or even more.

Now you are not telling me that if, in this example, the pressure would be + 20 the car would handle correctly.

In my view this increased pressure, well in excess of manufacturers recommended, would contribute to poor handling and may contribute to an accident.

Spot on.

Over inflated tyres are dangerous - full stop.

They have less contact with the road, wet braking will be seriously affected. As will general road holding due to the smaller contact patch on the road.

[Surferdude]

After reading all the above can anyone them please explain why manufacturers provide max pressure which appears to be below what is mentioned above.

I tried an experiment once and set pressure at recommended.  Ran for miles and miles and retook pressure.  It had risen, I think +4 or 6, which it would appear is normal due to the air inside the tyre heating up.

Now if I had set at say +8 then the increase would have not been +8 but probably +12 or even more.

Now you are not telling me that if, in this example, the pressure would be + 20 the car would handle correctly.

In my view this increased pressure, well in excess of manufacturers recommended, would contribute to poor handling and may contribute to an accident.

Spot on.

Over inflated tyres are dangerous - full stop.

They have less contact with the road, wet braking will be seriously affected. As will general road holding due to the smaller contact patch on the road.

Don't think anyone will disagree with you on this.
However, what is the definition of over-inflated?
As per my posts above, 40 psi isn't and will, if anything, have a beneficial effect on handling (which must include turning and accelerating as well as braking)
I think the critical point is that at 40 psi, you get a lot less pressure build up than at 34.
Which is the opposite of what is reported here.

After reading all the above can anyone them please explain why manufacturers provide max pressure which appears to be below what is mentioned above.

I tried an experiment once and set pressure at recommended.  Ran for miles and miles and retook pressure.  It had risen, I think +4 or 6, which it would appear is normal due to the air inside the tyre heating up.

Now if I had set at say +8 then the increase would have not been +8 but probably +12 or even more.

Now you are not telling me that if, in this example, the pressure would be + 20 the car would handle correctly.

In my view this increased pressure, well in excess of manufacturers recommended, would contribute to poor handling and may contribute to an accident.

[simon@mgr]

I run 39 front 36 rear in my diesel with no handling problems.

To accurately assess the performance of a tyre you need to measure the temperature across the width of the tyre.
If the temp in the middle is the same as the side then it is correctly inflated.
If it lower then it is underinflated, higher, overinflated.

If your alignment is correct, tread depth during the life the tyre should be the same right across the tread. Deep centre tread indicates underinflation.

Contrary to what has been said so far, low pressure in the wet is dangerous because it holds water in the centre of the tread and the contact area is reduced. This is why wider tyres become skittish in the wet.

[Surferdude]

Contrary to what has been said so far, low pressure in the wet is dangerous because it holds water in the centre of the tread and the contact area is reduced. This is why wider tyres become skittish in the wet.

True.
You'll notice how the WRC cars run narrow tyres in the snow. Helps with penetration.
And the same applies in mud. You  need good trea but not a lot of tread width.
Somewhat similar in water, up to a point. But there's no doubt wider tyres have a greater tendency to aquaplane: it's one of the reasons directional tyres are so effective.
I'll see if I can find a couple of "glass plate" pics

[Shambles]

Hi all. This topic is temporarily in the new Tips & Advice board, to help surferdude prepare his thesis on "all things tyre"

Go Doug!

[2i30s]

I'm running nitrogen in my tyres [38 psi all round] and in a year those pressures haven't changed. 

[eye30]

I'm running nitrogen in my tyres [38 psi all round] and in a year those pressures haven't changed. 

Never heard of using this in UK

[Surferdude]

Now I'm not a chemist/ scientist but it works something like this.
Nitrogen has larger molecules than normal air mix, so you lose less through the tyre (even tubeless tyres aren't totally airtight), so as 2i30 says, you don't need to check your pressures as regularly.
Nitrogen also runs cooler so there is less wear in the tread. I think that also means you run a slightly higher cold pressure to compensate for the lack of heat/ pressure build up on the road.
the practice was and probably still is widely followed in northern Australia by trucks, especially road trains where the tread wear gains are substantial.

Down sides are that you get lazy about checking your pressures and a slow leak can go unnoticed for long enough to destroy a tyre.
If you need to top up your pressures you have to go where there is Nitrogen (Bob Jane or Jax).
If you get a puncture you have to go where there is nitrogen.
It costs, generally a minimum of $5 per tyre at the time of purchase.
The NRMA ran some tests a few years ago when the practice became commonplace (?) in cars and concluded that the benefits were minimal, provided you checked your air filled tyre pressures regularly, as you should anyway.
I'm a bit ambivalent about the whole thing but  then I keep a close eye on my tyres anyway.

Oh! And many years ago, Hans Tholstrup ran a CIG sponsored GT Falcon at Bathurst using nitrogen in the tyres.

[agentr31]

im pretty sure normal atmoshperic air is around 75% nitrogen give or take a few % 

[Surferdude]

im pretty sure normal atmoshperic air is around 75% nitrogen give or take a few %  

Yep. But it's the pure nitrogen which 2i30s is talking about. It's the oxygen in the normal air mix which seeps out of a tyre, causing pressure loss over time.

I see what you mean regarding my post above. I was probably not as clear as I could have been but I was making a comparison with the normal compressed air mix we put in our tyres, versus the nitrogen from a bottle which you pay for.

[Lakes]

I have ( last time i checked ) 40psi all round, but i had been on a 1,000k plus trip with four full size adults in the car plus luggage.
i,m a driver, so what i leant, i learnt the hard way on aussie roads. plus a late & good friend of mine was like Trev here, and had worked with Tyres,M/Cycle Car,s, Trucks Bus's, tyres all his life ( till cancer got him @ 57 ) he also worked with tyre tech's that came out from Japan, they would give him tyres to give out to hi mileage opperators then come out and inspect them, my friend would also do inspections & keep data for the factory techs. he was the one that gave me ear bashings on how important it is to keep tyres inflated with high enough pressures. he said Car manufactures always under state tyre pressure, BUT it's the tyre manufacturer that design the tyre NOT the car manufacturer.
having said that i put 36 front 34 rear at start then Thumper started saying 40psi was giving him better economy. so i started useing 40psi front 38psi rear as the motor & drive at the front of car has more weight to support. in Hot aussie weather i would feel the temp of my tyres after driving, as hot tyres tend to wear more, if you can keep them cool enough they seem to last longer. well after 45,000k mine look to be wearing ok, not wearing out in center. so must be ok. but in GB the road temps would be much cooler. if any of you GB boys want to fly over and walk bare foot across an aussie tar sealed road on day when the air temp is around 40c you would understand what i mean
cheers Lakes

[Shambles]

... if any of you GB boys want to fly over and walk bare foot across an aussie tar sealed road on day when the air temp is around 40c ...

I'll pass, thanks

[Surferdude]

I have ( last time i checked ) 40psi all round, but i had been on a 1,000k plus trip with four full size adults in the car plus luggage.
i,m a driver, so what i leant, i learnt the hard way on aussie roads. plus a late & good friend of mine was like Trev here, and had worked with Tyres,M/Cycle Car,s, Trucks Bus's, tyres all his life ( till cancer got him @ 57 ) he also worked with tyre tech's that came out from Japan, they would give him tyres to give out to hi mileage opperators then come out and inspect them, my friend would also do inspections & keep data for the factory techs. he was the one that gave me ear bashings on how important it is to keep tyres inflated with high enough pressures. he said Car manufactures always under state tyre pressure, BUT it's the tyre manufacturer that design the tyre NOT the car manufacturer.This is a good post Lakes. I just want to clarify this point. This is true up to a point. There are many instances where with new models, the vehicle manufacturer dictates what he wants from an OE tyre and in order to retain or win the business, the tyre manufacturer must agree to it. Toyota are big on it, dictating what sizes they want on their new models. Ford in Australia did it with he Territory. In general, GMH want a tyre to perform one way ( steering reponse) for their Commodore range whilst Ford will want the same sized tyre to do something totally different (comfort) for their Falcon.  To be fair about it though, the vehicle engineers often spend many days working with tyre engineers to "tune" their suspension to the tyres and vice versa. But in a small market like Australia this can result in a tyre out there in the replacement market which is eminently suitable to one make/ model of car whilst proving only average on others.
having said that i put 36 front 34 rear at start then Thumper started saying 40psi was giving him better economy. so i started useing 40psi front 38psi rear as the motor & drive at the front of car has more weight to support. in Hot aussie weather i would feel the temp of my tyres after driving, as hot tyres tend to wear more, if you can keep them cool enough they seem to last longer. well after 45,000k mine look to be wearing ok, not wearing out in center. so must be ok. but in GB the road temps would be much cooler. if any of you GB boys want to fly over and walk bare foot across an aussie tar sealed road on day when the air temp is around 40c you would understand what i mean
cheers Lakes

[Surferdude]

im pretty sure normal atmoshperic air is around 75% nitrogen give or take a few % 

This has got me thinking. I see a conundrum and don't have the answer.
If the compressed air we pump into our tyres is 78% Nitrogen and most of the rest is Oxygen and Nitrogen supposedly has larger molecules which don't work their way out of the tyre through the rubber, how is it that if you leave your spare in the boot for a year or two, it will pretty well go dead flat?
Given that 2i30s has no loss of pure nitrogen in 12 months.
Calling all physicists/ chemists out there.
Help.