On 05/07/2024 at 18:42, DerekU said:

 So Skoda's advice that an inflation-pressure of 3.4 Bar be used for a Fabia Mk 4's rear tyres when the car is has onboard 5 people (of an unknown weight) and 5 suitcases (of an unknown weight) represents a worst case scenario when each of the rear tyres will be carrying 615kg. That the car's rear axle's maximum permissible load of 800kg would now be exceeded by 430kg is quite another matter (!!) but at least, if the tyres were inflated to 3.4 Bar, they might survive that level of ill treatment.

 

Sorry, I'm confused by this. If the rear axle maximum load is 800kg and the tyre will carry 615kg, then the two tyres on the axle will be able to carry 1230kg, well in excess of maximum tyre load. Or am I missing something?

As I understand it that's what Derek is saying.

He is just commenting that in theory the max weight that the tyres can cope with is well over that of the rear axle.

 

In practise though the additional weight of two more passengers and especially two more suitcases is rather arbitrary due to a lack of space! And if calculated as if it was possible would surely show that the weight is well short of the 800kg capacity which in itself is low due to the factor of safety allowed for in calculations.

 

This does indicate to me that the stated tyre pressures for the increased load of passengers and luggage are above what is required and it is therefore fine to run at slightly lower pressures to give a more forgiving ride. I usually drive (Not in a Fabia at the moment) with two or three in the car and so use the lower pressures stated and only increase the rear pressures, but not to the max stated in the table, when going on longer journeys with more passengers and luggage.

 

The size and weight of car needs to be taken into consideration here though as a smaller, lighter car with smaller tyres is going to be affected more by any increase in weight and more consideration needs to be given to tyre pressures with regard to this.

 

In an ideal world the actual pressures required should be calculated and appied before the start of any journey as the weight of passengers and luggage can vary wildly and can't be covered accurately by a simple table.

 

In reality though the table should be used as a starting point and then common sense applied to arrive at safe and comfortable tyre pressures above the minimum values stated. Unfortunately for many motorists common sense is sadly lacking. When filling up the other week there was an oldish Jag at the nearby pumps and all tyres looked very soft, even with the car empty. The driver was obviously oblivious to this.

Edited 11 August, 20241 yr by VAGCF

3 hours ago, Routemaster1461 said:

If the rear axle maximum load is 800kg and the tyre will carry 615kg, then the two tyres on the axle will be able to carry 1230kg, well in excess of maximum tyre load. Or am I missing something?

 

Offset weight.

 

I think you may have meant to write "maximum axle load" and not "maximum tyre load".

The sticker on my MK4 Fabia suggests 2,5 bar front and rear for partial load and 2,7 front 3,4 rear !!! full loaded... Seems to me very high for everyday/normal use resulting in harsh ride. I believe these have been set mainly for max fuel economy reasons. Tried a 2,3 front and back and the car feels much better to me. Maybe i will add 0,2only in rare cases of full load.

The psi difference between 2.5bar and 2.3bar is roughly 3psi.

I inflate my 2009 Skoda Roomster's tyres to 2.2bar (front and rear) and, if its front tyres' pressure has reduced to 2.0bar, I can recognise a 'softening' in the car's ride-quality shortly after setting out on the badly maintained roads around where I live.

So, if you rate ride-quality over fuel economy, use 2.3bar instead of 2.5bar.

For +35 years all my previous vehicles suggested an 2,1 -2,3 bar as “optimal” pressure and i find hard to believe that suddenly something has radical chanced leading Skoda to suggest 12 -40% higher (the 3,4 bar suggestion for rear/ loaded is unprecedented and in some cases may reaches the max allowed pressure of some tire manufactures…).

The only reason i could think of is an agonizing and stupid effort for max fuel economy despite the sacrifice of all other aspects.

Specially as living in Greece where the roads outside of highways are very bad maintained, i will never exchange a much softer, better feeling, and safer ride for a slight (if any…) fuel economy of just 0,5-1%...

Generally speaking, after all these years i have concluded that 2,1-2,3 bar is the “sweet spot” for every day driving on low and medium loads with a possibly slight increase of 0,2-0,3 in rare cases of full load and/or driving long trips in highways with speeds above 130 km/hour.

That i am following to my MK4 regardless what sticker says

@fabiamk4man Back 35 or even 20 years ago what sort of width & profile of tyre was on cars about the weight of a Mk4 Fabia?

26 minutes ago, Evolution13 said:

@fabiamk4man Back 35 or even 20 years ago what sort of width & profile of tyre was on cars about the weight of a Mk4 Fabia?

Not much different as you may image. 

Specially from 2000 and up most higher tier superminis and almost all class c passenger cars were fitted from factory with 15 – 16 inch rims with tires of 185-195-205 width of 55/60 ratio and they weighed more or less the same as a today’s MK4 (most class c even more…).

4 of my previous passenger cars manufactured after 2000 (2 superminis and 2 class c) were no different than the 16 inch -195/55 of my current MK4 and in all of them the manual suggested 2,1 – 2,3 as optimal pressure (with a slight increase in full load cases).

Location location location then, and different world regions and climates.

Your posts about pressures never mentioned which wheels / tyres.

You could have been on 18" and low profile.

Edited 7 November, 20257 Nov by Evolution13

fabiamk4man

If you read through the firt page of this thread, you'll see I mentioned that, for my 2009 Skoda Roomster, a 'car-fully-loaded' pressure of 3.2bar was advised for the rear tyres.

I can't see why you should find it surprising that, when a lot of weight is put on a car's rear axle, the pressure in the rear tyres must, for safety reasons, be increased accordingly. In normal 'lightly-loaded' use I use 2.2bar for the Roomster's front and rear tyres, but - if, behind the car's front seats, I have loaded 500kg of builder's rubble to take to the local recycling centre - it should be obvious that the 2.2bar will be too low to safely handle the load now being put on the rear tyres.

(It was also suggested earlier in this discussion that inflating to 3.4bar the standard tyres Skoda fits to Fabia Mk 4 cars might exceed the maximum pressure advised by the tyres' manufacturer, but it takes minimal research to confirm that this not so.)

Too much discussion for almost no reason…

Ever passenger vehicle I am aware of suggest around 2,1-2,3 bar for partial load with a slight increase of 0,3-0,5 bar in cases of full load (mainly increasing the rear tires). All above valid for “normal” size tires, for “normal “ cars, and for “normal” use.

It’s the first time i see 2,5 bar as recommended “minimum” pressure in a normal passenger car and also is the first time ever i see a very high 3,4 bar as a recommended pressure in general.

I already explained why this happens to my opinion, and after have driven the car under different situations and pressures i concluded that for a MK4 the best all around pressure is 2,2-2,3 bar when we take account all aspects of driving. But that’s only my opinion and everybody is free to drive his car in any pressure he likes…

I think you may be right that the pressures will, at least partly, be to do with stretching the miles-per-gallon. For decades the sizes of wheels and tyres has been about fashion, marketing and sales over practicality and need. Some are ridiculous sizes but that's fashion, and possibly machoism.

As you mentioned on Page 1 of this forum thread, Fabia Mk 3 cars' tyre-pressure sticker had three columns (as shown below)

The 3-people values in the 1st column are sometimes referred to (in VW Group-speak) as 'comfort' pressures, with the 3-people ECO pressures in the 2nd column providing potentially better fuel economy at the expense of a slightly firmer ride.

For the Fabia Mk 4, Skoda has reverted to a 2-column sticker and - having come across online requests for an explanation of how the 3-column sticker should be interpreted - I believe this is for simplicity's sake. And, for a 2-column sticker, it's understandable that ECO pressures will be provided for the 3-people loading.

I wondered, briefly, if the 3.4bar rear-tyres pressure specified on the Fabia Mk 4 sticker's 5-people column might be to counter oversteer in the event of a high-speed swerve being necessary, but concluded that it's merely close to the pressure needed when the tyres are subjected to their maximum design-load.

Manufacturers of commercial-vehicle tyres can provide tables showing the inflation pressure needed to safely support a defined load. So it's possible to weigh a loaded commercial vehicle and establish a suitable tyre pressure for each axle. To the best of my knowledge pressure-to-load tables are not available for car tyres, meaning that car manufacturers may assume a worst-case scenario, which seems to be what Skoda has done with their 5-people pressure recommendations.

For every 10°C change in temperature, tyre pressure changes by about 0.1bar (or 1 to 2 PSI) and the tyre industry reference temperature for providing tyre-pressure recommendations is 20°C. If a Fabia Mk 4's tyres are inflated to 2.5bar at 0°C, this will equate to around 2.7bar at 30°C. I once asked a Continental tyre technician about the quite common suggestion that car drivers should adjust tyre pressures to allow for summer/winter temperature differences, but he said "Just use the car manufacturer's recommended pressures irrespective of the weather".

I think the German engineers and their German ways of specifications think differently to us in the UK so for us to try to interpret what they might be thinking or actual mean with the restricted information they give is very difficult and perilous, just be grateful they put the steering wheel on right for us and don't expect too many more concessions.

The Japanese drive on the left like we do and like British stuff including when we used to make cars.

The title of this forum thread ("Correct Tyre Pressure?") begun in April 2024, suggests that the data on the Fabia Mk 4's tyre-pressure sticker may be incorrect, but there's absolutely no proof that this is the case.

The recommended pressures are indeed high, but that does not mean they are somehow wrong and, if Fabia Mk 4 owners choose to use lower pressures, there is nothing to prevent them doing so.

If driving on UK's poorly maintained roads at UK legal speeds, reducing the sticker pressures by 0.2/0.3 bar should be fine, but, if I were regularly cruising a Fabia Monte Carlo at 200kmh on a German unrestricted autobahn, I'd definitely choose to use the sticker pressures.

(During my 60+years of driving I've only come across one instance - with a motorhome - where I KNEW the recommended tyre pressures were wrong, plus one instance (with another motorhome) where the recommended pressures were questionable. Otherwise, I've used the recommended pressures as a guideline, not as an 11th commandment.)