Tyre Pressure Fabia III

[jemjem]

Hi

 

I’m hoping someone can help me with my query?

 

Soon after fitting 4 x Goodyear Efficient Grip Performance 2 (215 45R16 90 V) and whilst driving on the motor way, there was an alert to say that the tyres had lost pressure.

 

I went to Skoda garage and was told that there had been too much air (2.5) and they reduced all tyres to 2.1 and did a reset.

 

My previous tyres 215 45R16 86 H always drove well with 2.1 but the new tyres don’t feel quite right with it.

 

I called the tyre fitter to ask.  He said they should be at 2.3.

Do the tyres need to be inflated differently because of the change from 86 H to 90 V?

 

Also, I’ve noticed the speedometer on the car is giving a different speed to my Satnav since the tyre change.

 

Thank you

[freemansteve]

With any new tyres or pressure changes, the TPM system usually needs resetting. Quite normal. Don't forget it doesn't actually measure pressure, it just monitors rotation speed from all 4 wheels via the ABS, and looks for a discrepancy that might indicate a wheel is rotating (on average) a little faster than the others. (I.e. possibly lower on pressure).

 

You are running a configuration that means the rolling radius of the tyres has changed and this is why your speedo and satnav are now disagreeing more than normal.

 

 

 

Edited 11 June, 2021 by freemansteve

[matthall94]

9 hours ago, freemansteve said:

With any new tyres or pressure changes, the TPM system usually needs resetting. Quite normal. Don't forget it doesn't actually measure pressure, it just monitors rotation speed from all 4 wheels via the ABS, and looks for a discrepancy that might indicate a wheel is rotating (on average) a little faster than the others. (I.e. possibly lower on pressure).

 

You are running a configuration that means the rolling radius of the tyres has changed and this is why your speedo and satnav are now disagreeing more than normal.

 

 

 

I’m not sure how the OP’s tyre radius has changed when he’s fitted the same tyre size, it’s just the speed rating of the tyre has changed which has very little affect in the real world (tyres are rated much higher than the max legal limit of 70mph)

 

Some tyres use softer compounds which can make them feel low on pressure/air, Uniroyal rainsports are a popular soft tyre and even look visually under inflated the sidewalls are that soft. 

 

[KenONeill]

10 hours ago, jemjem said:

Do the tyres need to be inflated differently because of the change from 86 H to 90 V?

Not as such, but you may need a different pressure if you've changed make/model, and hence tyre construction. You do need to reset the TPMS having fitted new tyres.

[Ootohere]

The total Diameter / Radius might well have changed a bit.

 

First off the tyres coming off were a bit worn i assume. (I know you should never assume.)  The new ones are not.

Then tyres can be marked 213/45 R 16, but put a tape measure around different brands / types / season of tyres and the tape can tell the tale that not are all equal.

 

As to the GPS and the Speedo, lets assume again that the GPS is probably pretty accurate and the speedo does as nearly all do on OEM tyre sizes which is over read as in the speedo says you are doing 70 mph when actually you are at 67 mph.

[jemjem]

Many thanks for all your helpful comments.

 

I've upped the pressure from 2.1 to 2.3 and there's some improvement but they still don't feel as good as my previous tyres did.  I did do the reset.

 

The tyre fitter had them at 2.5, and I'm wondering whether to increase it to that.  If it feels good on the road at 2.5, I'm assuming it wouldn't cause a problem?

 

I have indeed changed the make of tyre and the tyres that were replaced were indeed very worn. (Even though I'd just had an MoT and they were passed).

 

[FabiaGonzales]

It's illegal to have a speedo which underreads your speed, so to take into account of that and how some people like to bump up the sidewall profile manufacturers will usually give a 5-6% margin.

 

It'll have shown a different speed before the tyre changed too, you probably just didn't notice it!

 

For tyre pressures as a starting point go from the recomended ones in the fuel filler cap label. From then on it's personal preference.

 

Bearing in mine i'm on 215/40R17 so different to you (different tyre size different pressure recomendations)

My old tyres i used to run 30psi (2.05 bar) as they were very harsh (i think they were possibly runflats) and that was the only way i could get any comfort at all.

If i ran my current tyres at the same pressure they're super quiet and soft but i lose a lot of feel in the steering, i set them to 35psi (2.4 bar) to try out, and they're still comfortable, but felt a bit skittery on rough road, ultimately i settled for 32psi (2.2 bar).

 

2.5 bar is 36psi and is fairly high, though as you're on 215/45R16 tyres you can get away with higher pressures as it makes up for the flex in the sidewall.

 

Don't go too low though, you'll overheat the sidewalls, have a blow out, and crash. Not the best thing to have.

Going too high can increase the chance of a blowout if you hit a particularly bad pothole, but at the same time it protects the alloys better. Too high is also detrimental to grip as it reduces the contact patch. Try to settle for a middleground.

[nta16]

Jemjem, who ever fitted your tyres should have told you or given you something written to tell you to take it easy on your new tyres as they need the "grease" run off them for the first about 100 miles or 200 if wet weather - and to have the wheel nuts/studs checked for tightness (torque) after the first 30-50 miles.

 

The Fabia driver's instruction handbook 'OPERATING INSTRUCTIONS' has "run in" so drive with care for the first 300 miles on new tyres. - http://manual.skoda-auto.com/004/en-com/Model/Fabia_NJ 

 

They need to settle, and will feel different anyway if they're different make and model of tyre, plus you've gone from 86 (weight index, 530kg each tyre) to 90 600kg each tyre) and from speed rating of H to V.

 

The 45 is the ratio of the sidewall height compared to the width of the tyre (as said earlier all measurements are nominal) that's only 97mm of sidewall on a 16" (406mm) wheels that's more about speed than comfort.  The modern trend for a good while back is to have large wide wheels with wide low profile tyres, these aren't best for comfort and ride (nor for the snow and ice) but it's the fashion, whether they're really needed or not.  The tread pattern changes also as a matter of fashion as well as design.

 

I can't find it now but I'm sure 2.1 was normal pressure for our factory 15" tyres but you could use an eco setting of 2.5 as this reduces the rolling resistance of the tyre, less for the engine to to push against and less resistance to the tyre rolling over the road surface so more mpg.

 

Tyre markings explained. - https://www.goodyear.eu/en_gb/consumer/learn/how-to-read-your-tire-sidewall-markings.html

 

Edited 1 July, 2021 by nta16
speeling and stuff