I have 285/45/22s on the car curtesy of the previous owner and am wondering if they should be inflated to the same pressure as shown on the door jamb chart.

Strange because I tried this site https://tiresize.com/pressure-calculator/ and it says the pressures should be reduced to 28fr and 31r.

I reduced the tyre pressures accordingly and am not surprised to find that it goes over bumps and manholes much smoother but I must say I'm quite surprised.

Does this sound right?

This is from an L405 but shows the same pressure for all sizes under normal load and only a small difference under heavy load -

Although those tyres on the chart, even though they are different sizes, I would have thought that they all have the same rolling radius.

According to a tyre size comparison, the wheels and tyres on my car have a 7% larger diameter and are 12% wider. Apparently with more volume of air the pressure needs to be less.

I suppose the only way to know for sure is a chalk test but I am wondering if anyone found the same results, ie lower pressure with larger tyres.

I would say to compensate for more compliance in a higher sidewall the pressures need to be a bit more? 2012 TDV8 Vogue (L322)

285/45R22 I don't believe is a standard LR tyre size so will be significantly different and makes your speedometer way out, compared to standard.

As in Alistair's picture, for 22inch wheels the standard sizes are 275/40 and if you increase the width you need to reduce the aspect ratio to keep tyre diameter etc consistent. 2017 4.4 SDV8 Autobiography
2012 4.4 TDV8 Westminster - Gone, but not forgotten

I know they are not a standard tyre but they are brand new Contis and I feel I should use them until they wear out rather than throw away €1500 of good tyres.

I have adjusted the suspension with Gap tool so there are no clearance issues, just want to set these up properly.

I'd simply adjust to taste - too high a pressure and the ride will get harsh and too low a pressure and the handling will get unpredictable. Main thing is to have higher at the rear to preserve some directional stability. Worth also dialling in the new size into your CFF - instrument pack to get both a usable speedo and help the ABS and gearbox behaviour. The rolling radius - ABS is easy to work out but the last value in the list is for the speedo and you lower the number when you increase the tyre size. On my 255/55 R20 I had to drop digits and you may have to drop 4? 2012 TDV8 Vogue (L322)

Unfortunately, the Gap tool does not have this setting on L322s. My speedo reading and fuel consumption are thus lower than they should be due to the slower rotating wheels.

Ah the settings must be just for the 2010 facelift models?
At least you have a V8 to overcome the effective later gearing. 2012 TDV8 Vogue (L322)

jazzdude wrote:

I have 285/45/22s on the car curtesy of the previous owner and am wondering if they should be inflated to the same pressure as shown on the door jamb chart.

Strange because I tried this site https://tiresize.com/pressure-calculator/ and it says the pressures should be reduced to 28fr and 31r.

I reduced the tyre pressures accordingly and am not surprised to find that it goes over bumps and manholes much smoother but I must say I'm quite surprised.

Does this sound right?

As I said they are Continentals and I was originally running them at the pressure as shown on the door, ie 2.3 /2.5. It was crashy over the bumps which is why I looked further into the pressures.

I only tried the lower pressures today and the car instantly felt softer over the speed bumps and potholes but I have not gone out onto a highway yet to see how the handling is.

To be honest, if this size works out I'm considering sticking with them as they offer the same amount of tire wall height as the 255/50/20s that are standard. I am hoping that the replica Overfinch alloys that the car came with will thus not be too fragile and might resist the odd pothole.

Rob99 wrote:

285/45R22 I don't believe is a standard LR tyre size so will be significantly different and makes your speedometer way out, compared to standard.

As in Alistair's picture, for 22inch wheels the standard sizes are 275/40 and if you increase the width you need to reduce the aspect ratio to keep tyre diameter etc consistent.

I've been driving around all morning with the 28/31 pressures and although the car feels smoother, the steering is heavy.

I am trying out a midway point between the above and the door pillar spec to see how that goes.

You've got overfinch wheels on yours by the looks of it. Heres a pic of the overfinch tyre pressure sticker on door pillar of mine, you could try these pressures and see what you think.

Very easy to find the correct tyre pressure for any tyre on any car......

Inflate the tyres to the pressure you think....

Drive 20 miles down a motorway.

Stop and immediately check again.

It should be 4psi higher than the first pressure.

Drive home and let them cool overnight before trying again....

Ambient temp should be 15-20C

 Pete

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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
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