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Ok as some of you know from another thread I posted, my tyres were seriously over inflated from pick up in July, only just checked them and have corrected as per the label in the door.

But...... Wait for it....... I thought this would improve my mpg, oh no, it has dropped

NOT a happy bunny
 

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When you have the pressure too high it bulges out the centre of the tyre which means you have less rolling resistance (therefore better economy) but it also means you wear your tyres out quicker - overall you lose out because you have to replace your tyres more often. Over inflation is not dangerous as such but if your pressures are excessively high then you actually reduce the contact patch on the road and you'll have less grip (but that's probably more theoretical than in reality). Obviously there is a limit before the thing explodes though!Overall, it's best to go with the manufacturers recommendations but I wouldn't worry about varying it a couple if PSI either side. For example, if you change your tyres for another brand the sidewalls might be less rigid and a few extra PSI might be a good idea.I would always err on the side of more pressure because it is definitely dangerous to have them too low. Too low and the side walls of the tyres flex and get hot which leads to blow outs on the motorway.Altering your pressures can be a good thing, for example 'Economy freaks' run high pressures to get better MPG, having lower pressures can help in snow and hill-climbing events, and reducing the pressure a little before a track day means your tyre pressures aren't too high when you get them really hot when you're caning it around the bends.Sorry, I'll stop, I'm boring you now!!
 

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You need to be careful with tyre pressures - if they aren't inflated to the manufacturers recommended pressures, then you are breaking the law. However, the manufacturer is the tyre manufacturer, not Nissan - if you change brand, you may be able to get the pressure from the manufacturers web site (certainly used to be the case with motorcycle tyres, but if not a call/email to their technical department will give you the answer) and the tyre manufacturer may well have a pressure with an allowance of a couple of psi either way.

Additionally, if you have a serious accident, the police often check tyre pressures to see if that contributed to the cause of the accident - potentially you could find your insurance company arguing with the claim if the pressure is out.

Also, don't forget pressures are measured cold, but a sudden change in temperature can affect the pressure - would have to be a fairly large change though.actd2012-08-01 12:23:31
 

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Just as an added remark it is not just Nissan, when I puchased my Ford Ranger, apparently at the time built on Mazda's pick up production line it had 45 Lb psi in all four road wheels, they should have been 30 psi. before finding this out it was as twitchy as hell on the back end. Much more sure footed when I lowered the pressures.I would rather burn fuel than have an accident. How I miss that old girl now for the tip runsTc
 

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Just checked mine - showing 36 all round when hot, so fronts may be under when cold. Hope that doesn't affect the go-kart handling when I correct them :-D
 

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I take that back - I can keep the Juke pointing in the right direction, something I've never been able to do with a go-kart :)
 

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Car companies over-inflate the tyres in the factory and your dealer should set them to the correct pressures during the PDI. I hadn't thought of asking the tyre manufacturer about the correct pressures. If they can supply than info then people could contribute to a new thread on here for everyone's benefit
 

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it's something i learned years ago when riding big bikes, tyre pressures are very critical to how a tyre handles and feels and different manufacturers have different recommended pressures.
 

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It does make sense. Like I said before, different tyres have different strength side walls. It just never occurred to me that the manufacturers went to the bother of deciding what pressures work best on each car. Or maybe they just know what percentage to adjust the manufacturers figures by.
 

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Just got round to checking the tyre pressure after having it for 5 days. Continental Contisport Connect 5 225/45/18 were up at 3.1 bar. Tyre website recommended 2.4 bar. How to wreck a good tyre in one easy lesson. Dealers are fuds.
 

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actd wrote:You need to be careful with tyre pressures - if they aren't inflated to the manufacturers recommended pressures, then you are breaking the law. However, the manufacturer is the tyre manufacturer, not Nissan
Is that really true? Can you provide a link to a source?The UK Highway Code says:
Tyres MUST be correctly inflated to the vehicle manufacturer's specification for the load being carried. Always refer to the vehicle's handbook or data.This clearly refers to the vehicle manufacturer's specification, not the tyre manufacturer's. The use of the word MUST indicates that this is a legal requirement - but where is that enshrined in law? I can't find it. The only reference in law I can find is in the Road Traffic Act 1988, Section 41: Construction & Use Regulations. Regulation 27 section B states it is an offence to drive a vehicle if "the tyre is not so inflated as to make it fit for the use to which the motor vehicle or trailer is put". This does not say who decides what pressure is suitable, and mentions neither the vehicle nor the tyre manufacturer. It seems so vague as to be worthless - the sort of thing a half decent lawyer could drive a coach and horses through.
 

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It's a collaboration between the two with the OEM tyres, but any other tyre manufacturer will recommend their own pressures as they (and not the car maker) will have tested the tyres, or have tables to refer to based on weight (and probably some other factors), though chances are the pressures will be close to that of the car manufacturer. If the tyres are under or over inflated, then this will show in the tyre wear, with the outer edges (under inflation) or middle (over inflation) wearing more quickly. With motorbikes, the tyre manufacturer will (or used to) suggest a pressure, with a recommendation that the pressure should not vary by more than 10% from that - in my days of old on a motorbike, I used to run at a slightly lower pressure from the suggested pressure as if definitely felt better, but it really did depend on the rider.
actd2013-05-24 16:32:52
 

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It probably varies across manufacturers...when I was talking to Michelins tech support about tyre pressures for a BMW they said the recommended pressures were nothing to do with them they just supplied the OEM tyres. The (EDIT: BMW) handbook recommends the same pressures regardless of which OEM (or non-OEM) tyre was fitted, despite for instance the Continental OEM tyre having a "softer" sidewall (EDIT: than the Michelin) and benefiting from a few extra psi.The handbook pressure are always going to be a compromise of various factors - I tend to prefer a few extra psi to stiffen the sidewall and improve turn in.

Kid Groucho2013-05-25 10:44:01
 

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I've always gone by tyre manufacturer recommendation. A lot of/all? tyres have the max PSI/Bar written on the wall, I'm not saying inflate right up to this though (and now I read this bit of my post again I don't know why I thought this was relevant). Just out of curiosity has anyone done any testing at various pressures to eek out the most MPG?

TheShield2013-05-25 08:13:30
 

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TheShield wrote: Just out of curiosity has anyone done any testing at various pressures to eek out the most MPG?
Tried to but on the Juke it isn't that easy.With the winter tyres on I got no grip when I inflated the tyres. I had to go back to, or near to, standard pressures to be able to drive away from my home. With higher pressures I was stuck in the drive.With summer tyres on and higher pressures I did detect some small improvement in economy but difficult to quantify how much was due to tyre pressures and how much due to other factors. Before reaching any conclusion I noticed that the tyres were wearing more in the middle and I dropped the pressures again.The only outcome is that I decided the Juke is not a car where it is possible to raise the pressures by any significant amount.
 
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