Hi All

My tyre pressue warning came on last night so I originally went round to put 29PSI in them as stated on the fuel cap. When I was putting them to 29, 3 tyres were about 32 and 1 was 25. It didnt feel right and the MPG dropped. I have since put them all to 32 PSI but for some reason the MPG is still lower than what it was.

Any ideas?

I have 07 VRS with 18's They are Pirelli Pzero Rosso 225/40 ZR18

I've some doubts about the recommended pressure on the fuel cap for my car too. The tyres look just short of flat when at their Skoda recommended pressure (2.0 bar (29psi) at the front 2.1 (30 psi) at the back for up to 3 passengers and light cargo IIRC). They look correctly inflated when I take the tyre to the max pressure printed on the tyre minus 10% (36 psi in my case). This according to some reading I found before is often used as a starting point for finding the optimum pressure to run a tyre.

As it stands there seems to be no change I can find in grip for braking and cornering, but I think (But am not sure) that the back end feels very slightly more fidgety than before, so I'll drop the pressure a couple of PSI today and seeing how that goes. What I was surprised by is that the fuel economy hasn't changed noticeably either as far as I can tell (Bits of town driving, a couple of 60 mile A road efficiency runs (57mpg one way and 52 return, usually 54mpg is about expected, but I did have 5 people and their luggage for that run) and a few hard backroad runs (Still end up over 50mpg thanks to traffic and urban speed limits) are all returning about the same mpg as before).

What I'm worried about with the recommended pressures is that the tyre flexes a lot while rolling, so it will build heat on long journeys, making it more likely to fail. If the pressure is too low or high, the only definite feedback you get if the handling and traction aren't noticeably changed is uneven tyre wear, but this won't show for a long time.

I'm guessing its best to stick to the manfr recommended figures, since they will have tested the tyres (probably in association with the tyre manufacturer) much more extensively than the average owner can. I think just looking at the tyres is not a good way to judge pressure - modern tyres nearly always look half-inflated to me!

Hi All

My tyre pressue warning came on last night so I originally went round to put 29PSI in them as stated on the fuel cap. When I was putting them to 29, 3 tyres were about 32 and 1 was 25. It didnt feel right and the MPG dropped. I have since put them all to 32 PSI but for some reason the MPG is still lower than what it was.

Any ideas?

I have 07 VRS with 18's They are Pirelli Pzero Rosso 225/40 ZR18

Here we go again! Do a search. There are as many opinions on here as there are tyre pressure combinations!

Most VRS owners are using 34psi. 29 is too low.

2.35 to 2.44 bars all round seems to be a favourite

The pressures on the fuel flap are the minimum recomended pressures. This minimum pressure is a compromise between ride comfort, fuel efficiency, handling, etc.

You will also see on the sidewall of the tyre a manufacturers maximum recomended pressure (usually about 44psi IIRC).

The optimum pressure for your car & driving style lies somewhere between these two figures.

As tyres are slightly porous & lose pressure gradually, unless you wish to check your pressure weekly, I'd recomend the base pressure + 10% (31psi) as a starting point.

Personally, I run 36F/34R.

Golf has the same chassis & similar size tyres/rims to the Octavia but the minimum recomended pressure is much higher (35F/35R) and the R32 is higher again (41F/41R).

IMO, the tyre pressures relate to the demographic the cars are aimed at - and they think Skodas are driven by old fogies with bad backs.

To be honest , I never noticed different MPGs with different tire pressures......at the mo I am having the tires inflated to 37 psi to check just this but this does not work because it is way to uncomfortable....

Some years ago I used to work for a company that did subcontract development work for tyre companies. In determining recommended pressures the main criteria was to ensure even tread contact with the road across the full width of the tyre. This maximises grip and ensures an even wear pattern.

The manufacturers recommended inflation pressure is not a minimum, it is an optimum, with a couple of psi tolerance either side to allow for gauge error. Basically you would tend to run the lowest safe pressure to maximise tyre grip over a longer period of time.Too high a pressure will deform the tyre and give less grip, but under certain circumstances you need the pressure to keep the tyre in shape due to high speed, high load, driving and to avoid the tyre overheating.

Some tyres really don´t respond to tyre pressure variations, basically, because of their stiff design, you might not even notice the tyre being totally underinflated, other tyres will show instantly they don´t like underinflation.

As a crude experiment you can draw a thick wax crayon line across the tyre and watch how it wears off. It should wear off evenly, not the centre nor the edges first.

It is only mainly just me driving with nothing in the boot, What would you suggest to me? And for the person that says search the forums. Type in "Tyre Pressure" in the top right, It brings back just 4 results.

Some years ago I used to work for a company that did subcontract development work for tyre companies. In determining recommended pressures the main criteria was to ensure even tread contact with the road across the full width of the tyre. This maximises grip and ensures an even wear pattern.

So how do you explain that an Octavia runs significantly different pressures to a Golf with the same size tyre & rim package?

Why is it that when you do an advanced driving course, the instructors get you to inflate your tyres up to 38psi?

While I agree that lower pressure will give higher ultimate grip, this will be at a trade off for edge wear if you are utilising that higher grip.

Ideal tyre pressures come down to where you drive, how you drive & the overall condition of the vehicle. As the dampers soften & the springs sag, you have to run higher pressures to compensate. Live in an area with lots of roundabouts (Canberra springs to mind) and you need higher pressures.

I don't think I drive like a hoon but if I didn't run at least 34psi in the Octy the tyres would have been bald on the edges at 20,000km.

Maybe it's not the case in the UK but down here the manufacturers admit that they recomend the lowest tyre pressures possible to improve the ride.

So how do you explain that an Octavia runs significantly different pressures to a Golf with the same size tyre & rim package?

My mother-in-law's Jetta (Golf with a boot) uses almost exactly the same pressures as my Octavia. It's a similar sized car, with similar sized wheels, driven in a similar way.

It is only mainly just me driving with nothing in the boot, What would you suggest to me? And for the person that says search the forums. Type in "Tyre Pressure" in the top right, It brings back just 4 results.

34Front

32 or 30 rear.

The higher pressure in the front will help turn-in a bit. The lower pressure in the rear will promote a bit of roll oversteer. For high speed corners probably not a good idea but for trundling about town it helps a bit.

I didn't notice a difference in comfort at all changing the tyre pressures - and I thought that would be the biggest change. Tyres are 205/55 R16 Firenzas. I'm guessing lower profile tyres are so harsh to begin with that they need to drop pressure for any kind of ride comfort...

May I remind Briscodians that in the UK there is a law governing tyre pressures (with stiff penalties) and I'm not sure how insurance companies will react in the event of an accident which was exacerbated by incorrect tyre pressures. I just play it safe (an old fogy with a bad back) and stick to the manufacturers recommended pressures which I measure with the tyres cold.

Just my opinion on this topic.

Can't say I've ever heard of there being a law (Or stiff penalties) on the subject. I've never heard of anyone being prosecuted for anything other than having tyres that are too worn. If anything I'd expect anyone used to looking at cars to conclude my tyres were underinflated if they looked at my car with the tyres at the recommended pressure.

I'm now a great fan of the handbook/fuel flap/elsawin quoted values.

I used to have the stock Bridgestone Turenza ER300 tyres (205/55R16), and ran them at over the book values (I think 32F/35R), on the grounds that they looked a bit flat, and to improve the handling.

However, I when I sold these the tyres had 6mm tread on the shoulders and 4.5mm in the middle after 17,000 miles, suggesting over-inflation. I go with the Skoda values now.

Personally I think it is about what your own compromises are. My view is that the recommended pressures are slightly soft, I seem to get better handling by putting them ovver by a couple of psi (but then this could be because my pressure gauge is slightly out of course, but I don't think by that much even so). In icy conditions I might put them back on the soft side to get the max rubber on the surface, and therefore a bit more grip.

However, I also think that day to day, ice aside, that there can be problems with very ad pot holes if the tyres are soft (or on the recommended setting) - you are more likely to suffer some rim damage, particularly on low profile tyres on a vRS etc. I'd much rather have more air in the rubber to add to the cushoning to prevent this - or a repeat of the time a learner driver forced me onto a curb at around 30mph that also led to rim damage as the tyre wasn't hard enough to stop it...

Can't say I've ever heard of there being a law (Or stiff penalties) on the subject. I've never heard of anyone being prosecuted for anything other than having tyres that are too worn. If anything I'd expect anyone used to looking at cars to conclude my tyres were underinflated if they looked at my car with the tyres at the recommended pressure.

From askthe.police.uk website

"be inflated as to be fit for the purpose for use to which vehicle is being put (your manual will have the recommended inflation for your vehicle);"

That reads to me that if your pressures are way off, the manual pressure will be used as the benchmark. I'm sure one of the resident Black Rats will know more.

And insurance co would have a reason for wriggling out of a claim if you skidded in the wet with overinflated tyres

May I remind Briscodians that in the UK there is a law governing tyre pressures (with stiff penalties) and I'm not sure how insurance companies will react in the event of an accident which was exacerbated by incorrect tyre pressures. I just play it safe (an old fogy with a bad back) and stick to the manufacturers recommended pressures which I measure with the tyres cold.

Just my opinion on this topic.

Would you have a link or reference please? I'm not from the UK & would be interested in reading it. TIA

edit: disregard - found quote

I thought NSW was a Nanny State with our multitudes of rules & regulations (and nobody to actually enforce them unless it can be done via remote camera).

From askthe.police.uk website

"be inflated as to be fit for the purpose for use to which vehicle is being put (your manual will have the recommended inflation for your vehicle);"

That reads to me that if your pressures are way off, the manual pressure will be used as the benchmark.

Fair enough, but what do you mean by "way off"? having worked in the retail tyre industry (many moons back), I've probably seen a greater share of idiots & stupid things done with tyres than most people.

A few examples:

• Taxi drivers & (what they call now) hyper-milers wanting to run 185x14 at 60psi because it gave better fuel economy & compensated for their 200,000km old dampers.
  
• Motorists who, whenever it rained, deflated their tyres to 20psi "to help the tyres mold to the road" but didn't bother to adjust their driving speed to suit.
  
• Motorists who never checked there tyre pressure - ever.
  

The key words in the Police quote are "fit for purpose" and "recomended". Neither of them are a mandate & both imply subjective reasoning as to what presssure should be run.

Personally, I think it's criminal to run less than the recomended pressures. Because our tyres only ever lose (cold) pressure, running at the minimum recomended means you have to check the pressures weekly - if your happy to do that, then fair enough. For most of my customers, who would come for a service every 5,000km/6 months & never look at the tyres, I'd add 15% over the recomended so that they had less chance of becoming under-inflated. These days, with 15,000km/12month service schedules, helping the customer like that is a lot harder.

Anyway, opinions are like arseholes - everyone has one & everyone is different. I'll stick by my opinion that the lower pressure shown on the fuel flap is a minimum recomended pressure and the pressure on the tyre is the maximum and the answer lies somewhere in between depending on:

• road surface & conditions
  
• driving style
  
• brand, construction & dimensions of tyre & rims
  
• desired handling characteristics
  
• average ambient & road temperatures
  

and a good starting point is either the recomended pressures for a loaded vehicle doing high speeds or the minimum recomended plus 10%.

For my 80 year old father - he'd probably get away with the minimum recomended. For me, running 36F/34R - I still get edge wear from cornering. Maybe I just bought the wrong car?

edit: And I have & would take take the above to court. On 2 occasions I have been asked by insurance companies to make a deposition on my opinion of the condition of tyres on vehicles involved in accidents.

I stick with 31 psi at front and 32 psi at rear.Mainly only max of 2 people in car.