Tyre pressures on 450h series 3

[luckyduck]

I have just had 2 new rear tyres from a UK Lexus dealer ( yes I know, but their price was competitive) -  they set the Bridgestone 235/55 R20 102V pressures at 36 psi (2.5bar) yet the handbook, Lexus website and door post label says pressure should be 2.3bar (33 psi) - which is right please?

[NemesisUK]

The pressures stated on the door post label.

My experience with garage set pressures has been they have all been set high.

That said how confident are you on the accuracy of your pressure gauge?

[Herbie]

One tyre fitter as opposed to three printed sources of information? I think you already know the answer.

[Farqui]

What were the pressures on the old tyres? Many fitters will check those to then determine the new tyre pressures.

Although you'd have thought a *ahem* Lexus trained tech would have set the pressure as per book. Although aren't the manufacturer suggestions just a minimum setting and you then need to factor in the tyres construction/etc?

There are other elements to consider, such as...

Did you both set/check the pressures using the same gauge? Some can vary quite a bit.

Do your new tyres have a softer sidewall? Different make/model? These may account for a few psi difference.

Maybe your old tyres were only wearing at the shoulders, so adding a few psi would even wear across the tyre.

[Herbie]

I'm not sure any of that really makes a difference Lee.

It may do to us as the drivers, trying to get a better ride or a few more mpg or whatever, but if you're involved in an accident the insurance company will take into account what's written in black and white because that's what the design engineers came up with as the best for the product.

I personally know someone who had altered the pressures for whatever reason and then hit a tree in an accident. No other vehicles or people involved, just himself, but the insurance company (or traffic cops, can't remember which) found the discrepancy during the investigations and he either got a reduced payout or none at all. It was about 15 years ago now and I really can't remember but it's always stuck with me that if you mess with pressures there may be unintended consequences, as well as whatever result you're trying to achieve.

[Lager shandy]

There is a tyre pressure range for your car look at the side wall this will give you the max pressure when cold say 50 psi then down to the minimum pressure recommended by lexus speed related and say load .so if your door sticker says 33 psi up to 80 mph that is your lowest pressure recommended by lexus for comfort and up to 50psi which is the safe working limit set by the tyre manufacturer but will be pretty a pretty harsh ride .so 50psi - 10% is really a starting point then drop down to a setting you are happy with . I have mine st at 38psi all round which I find is firm enough .  So 33-50 psi cold most people will look at the door sticker and choose a pressure on how fast they drive . I tend to drive a-b roads and like a firmer tyre .

[steveledzep]

The door post states 33psi for normal running and it also states 36 as an eco setting (presumably for more mpg).  I run my Pirelli Scorpion Verdes at 35psi all round.

[luckyduck]

Thanks guys - the tyre pressure gauge matches what the dashboard tyre pressures show - so I am happy with that. The tyres are the same all round. The old rears had to be replaced as the shoulders had worn more that the centres, so on balance maybe the fitter used a , and upped the pressures - I'll run it for a while and see how harsh the ride is, any change to mpg and wear marks on the tyres. Thanks.

Quote

 

 

[Farqui]

@Herbie the insurance company are looking after their own interests so I'm not surprised that they would look for ways to prevent or reduce a claim. Your pal must have had a specific reason why the claim was rejected and maybe it was a valid reason, albeit financially painful to them.

As I understand tyre's and their relevance to claims/the law...

• low tyre pressures can earn you 3 penalty points and insurers can use this against you in a claim, so definitely check your pressures regularly
• bald/bulging/badly damaged tyres are very bad, can earn you penalty points and are likely to invalidate your insurance
• tyres with too low a speed rating for the vehicle are a no no and are illegal in some countries.  higher rated tyres aren't a problem

You are allowed to vary your tyre pressures provided they still comply with the minimum vehicle and maximum tyre pressure ratings.

The recommended tyre pressure are cold settings that will increase after the tyres warm up once driven at speed.  So in theory once you're driving your tyres gradually become out of spec!

You are allowed to fit tyres from other tyre manufacturers provided they comply with the vehicle weight, rim size, width, speed rating, etc.  An extreme would be a budget tyre on a performance vehicle and nobody would bemoan and insurer reducing/eliminating a payout in this case.  So do all you can to eliminate any concerns later on.

If you had to fit the specific tyre and model to a vehicle then you'd be scuppered if the tyre was no longer in production/available to purchase.

There are so many variables involved that insurer's can exploit, it's a bloomin' minefield.

[NemesisUK]

7 minutes ago, Farqui said:

The recommended tyre pressure are cold settings that will increase after the tyres warm up once driven at speed.  So in theory once you're driving your tyres gradually become out of spec!

Not really as the specification is set at cold and set at a pressure determined so as to rise to a 'running' pressure.

[Teshoo Lama]

4 hours ago, luckyduck said:

I have just had 2 new rear tyres from a UK Lexus dealer ( yes I know, but their price was competitive) -  they set the Bridgestone 235/55 R20 102V pressures at 36 psi (2.5bar) yet the handbook, Lexus website and door post label says pressure should be 2.3bar (33 psi) - which is right please?

The manual cites both 33 and 36psi, with 36 being the "eco" option.

[Barry14UK]

There has to be a tolerance to allow for load and speed. Although a very different application, consider a bus that may have no passengers or be full with passengers standing (eeeer, sorry 'customers' in modern parlance).  There is no way of constantly adjusting inflation to load so pressures will not be nearer optimised as we have in cars where we can increase  pressure where we are to carry a heavy load or drive constantly at 70mph (if you can find a stretch without a 50mph speed restriction!).  Then you might lower pressures where a combination of snow and hills means more traction is required on occasion.  Normally, I tend to set my pressures to the middle of the manufacturers tolerances and make small adjustments if I find the crown or shoulders are wearing disproportionately.