Tyre pressures

[CRC]

I'm confused .... it's not unusual, I know, but this makes little sense to me.

 

The recommended tyre pressures for my V6 are in the region of 38psi and I like to try and keep them there at least in the front tyres where all the weight is and the car rides better on the 17" 45 profile tyres.

 

Problem is that both front tyres will rapidly lose their pressure and in about than a week come down to 28-30 psi, and they seem to do it at the same rate ..... both front tyres always read about the same (using the same pressure gauge all the time.)

 

But then they stay there .... for weeks and weeks, almost as if they feel that 28-30 is the correct pressure and they just regulate down to that figure.

 

If they were leaking, I would expect them to carry on going down, and I also wouldn't expect them to leak at the same rate.

 

What could be causing it ?

[Gaz]

Bit of an odd one.

 

I don't have any problem with my tyres maintaining pressure, so there's something going on.  If you've not got punctures or leaky valves, might it be the tyres not sealing against the rim?

 

What about swapping them around, front to rear - that is if the back ones aren't doing the same. 

 

Gaz

[Alan16ac]

I have the same problem with my 2 front tyres too.

It's a 1.9 130 though.

When I bought it, it had Accelera Alpha crappy tyres on. These both deflated at the same slow rate. I'd inflate to 35 PSI. Give it 2 weeks and they'd be about 17-19 psi.

They had like 7mm if tread so didn't want to bin them, but the deflating coupled with no grip in the wet and then one being smashed by a raised grid I ended up buying 2 Goodyear Eagle Assymetric 2s or whatever they're called.

And the slow deflation is still happening! Confused!

[Flurry]

Hi all, I had a very similar problem with my superb earlier in the year. All four tires would slowly lose pressure, though at slightly different rates. The back left was the worst, losing about 10psi a week. I had the tires replaced in late spring as they were approaching the legal minimum tread and mentioned to the mechanic that they'd been slowly leaking and was there anything they could do about it. He said he'd have a look and after removing the tires from the wheels he brought me over to the car and showed me how uneven the inside lip of the wheel rim was. He recommended sanding the lip to create a better seal, and whilst I was slightly sceptical I decided to go for it. It cost me about £20 and now months later I've only had to put 1 or 2 psi in the tires since having them changed, approaching 8,000 miles ago. It may not be the case for everyone, but could be worth investigating!

[CRC]

Glad it's not just me ..... why the fronts should deflate more than the rear escapes me.

 

I've had cars in the past that hadn't sealed properly on the rims, and as you rightly say, sanding the rims down does improve matters, and sometimes you can get away with whacking the tyre close to wherever the fairy liquid bubbles are showing .... if it's a serious leak that is.

 

I've also heard of porous wheels that llow air to escape slowly, but my front wheels used to be my back wheels and they didn't have the problem when they were my back wheels .... if you see what I mean.

 

Suppose it's possible that as the front tyres are doing almost all the work ..... delivering power, delivering braking effect, turning againsthe direction of motion when steering in a corner that their temperatures will rise a fair bit more than the rear tyres, and as increased temperaure would result in increased air pressure, maybe that's enough to make the most of any slight weep and cause them to lose pressure more than the rears?

 

Is it possible to buy better valves? I know that my lad's push bike tyres held their pressure a lot longer when I (inadvertently) bought the presta valve tubes instead of the more normal car type valve (schrader?). The presta valve has a mechanism that mechanically pulls the valve rubber against the valve seat and locks it there, instead of relying on air pressure to hold it there.

[Flurry]

I do know the little screw lock ring thing on presta valves, but I've not come across them on cars. I suppose it could be that the valves are leaking, though as you say a quick test with water around the area of the valve should help to identify if it is that. Indeed, the font wheels take a lot more stress than the back wheels, added to which a large percentage of the weight is over the front wheels in the form of the engine. That would of course be slightly less true if you regularly have passengers in the back of your car.

 

I'm affraid that's reached the limit of my knowledge on the matter!

[devilman9050]

Mine do this too!!

 

Last time I had it serviced the garage said there was a slight buckle on the front passenger side, so I just put it down to that as that one loses air faster than the driverside front. Although the rear passenger side loses air fairly quickly to!

[vprasanna]

I have also faced this same dilemma, always the front tyres look like they are punctured whenever I park in an uneven surface (very common here in Bangalore)

The recommended tyre pressure for V6 2.1 TDI is 38 PSI. I have recently replaced both my front tyres with Yokohama V550 AVS DB Tubeless P 205/55R 16 94 V.( at 17000 kms of previous tyre)

The tyre shop guy recommended 40 PSI for front and 38 for rear with Nitrogen filling. I prefer to stick to manufacturers rating, but I left it for couple of days to understand how the car behaves. The tightness in the steering reduced with higher pressure.

After a week when I checked the air pressure in a gas station, I have set the air pressure at 38 PSI for front and rear. Now the steering is bit tight. ( the tyre pressure has not dropped from 40 PSI when i checked the pressure, so i deflated a bit to bring it down to 38)

I am not facing the tyre pressure dropping within a week to 28 with the new tyres. But it used to be a problem in front tyres with old continentals..

The yokohoma DB tyres are amazing ( I have used them in my civic extensively, hence I have decided to go for it eventhought they are expensive than the stock continentals that Skoda India deliver with).

If any one need a picture of yokohama tyre, i can upoad them in the next two days time. I am traveling and not able to take pictures...

[rotodiesel]

Two observations.

 

Alloy wheels are often porous, give poor sealing to the carcass beads and sometimes to the valve stem. I had my alloy wheels changed to steel as a condition of delivery. No problems whatever with these and they are kerb tolerant.

 

The Superb handles (a bit) better with raised pressures. I run my 1.9 PD at 36 psi all round as a good compromise. Tyre wear is even across the tyre section. Raised pressures also reduce rolling resistance and hence fuel consumption.

 

Use the best quality tyres only to maintain reasonable wet grip.

 

rotodiesel

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[Codswalloper]

I recently changed to 17" Alloys from 16" steels.

Tyre pressures 40 all round seem to be holding OK.

2 things I have noticed, noise has increased considerably almost like as if a wheel bearing is gone.

also fuel economy seems to have reduced by a whopping 4 to 5mpg. Car is 2002 2.5V TDI manual.

Tyres size now is 225/45/17

Previous tyre size 205/55/16.

 

If this noise and poorer fuel economy continue I think I will change back.

If this normal with bigger wheel?

[rotodiesel]

I can't imagine why anyone would put one of these land crabs on lower aspect ratio tyres.

 

You would have to check with the tyre manufacturer as to the differing rolling resistances, but when I was in the tyre testing (not trade) business, any aspect ratio below about 60 was deemed unworkable in terms of ride, damage resistance and rolling resistance.

 

There is more fashion than theory applied to tyres in the UK. 205 - 55 x 16 tyres are also a lot cheaper as well as being, in my view, better.

 

rotodiesel.

Edited 17 October, 2013 by rotodiesel

[trundlenut]

I recently changed to 17" Alloys from 16" steels.

Tyre pressures 40 all round seem to be holding OK.

2 things I have noticed, noise has increased considerably almost like as if a wheel bearing is gone.

also fuel economy seems to have reduced by a whopping 4 to 5mpg. Car is 2002 2.5V TDI manual.

Tyres size now is 225/45/17

Previous tyre size 205/55/16.

If this noise and poorer fuel economy continue I think I will change back.

If this normal with bigger wheel?

You now have more rubber in contact with the ground and less of a side wall to absorb noise and vibration so neither issue is a surprise.

As for the OP my car came with Accelerate Alphas fitted and I have had zero issues with tyre pressures.

Sent from my Nexus 4 using Tapatalk

[rotodiesel]

Low aspect ratio tyres tend to give higher hysteresis losses as there is less rubber in the sidewall to flex under the same load. Feel how hot the tyres run after a long dry run. Good tyres run cool, bad tyres run hot (and blow out).

 

rotodiesel.