Is Honest John correct?

Linas.P · January 10, 2017

I found it weird to suggest that underinflating tires can give any advantage to anyone. I often find Honest John advice correct, but suggesting to run 30PSI without even considering manufacturer recommended pressure or sizes is plainly dumb. Maybe OP can provide link, where HJ suggest that (I am just wondering what is background for such claim).

I treat recommended pressure as indicative - something which is going to be correct for 90% of use cases and you should stick with them if you are running stock tire sizes. Based on load it can be adjusted, but more often than not pressure needs to be increased and not decreased e.g. I run slightly higher pressure on IS250 R17, because over the years I have noticed that tires tends to wear outside under Lexus recommended pressure indicating that it is too low, but even then I run like 38 instead of 36, not 30 instead of 38.

GSLV6 · January 12, 2017

He's wrong *EDIT.....If he's actually said that and could be encouraging people to inadvertently break the law, and possibly invalidate their insurance.

As has already been stated, the manufacturer's recommended pressures are based on axle loading and always stated as cold pressures. The recommended tyres will have a specified load rating, and there is a margin on inflation at which this will be optimal for a specific axle weight. Under inflation can mean that the tyre won't make it's recommended load rating, it will overheat, especially at speed and sidewall deformation will affect both cornering stability and braking stability. Any accident could see your insurance company refusing to pay out and as far as the police are concerned, you could also be committing a traffic offence by not ensuring that you were running your tyres at correct (safe) pressures. Slight over inflation will reduce rolling resistance because the tyres wont be deforming as much and wasting energy transferred to them as heat, as happens with under inflated tyres but there are no grip advantages nor really much in the way of mpg advantage over the correct inflation. lexus publishes what it calls "Eco" inflation pressures. These tend to be at the upper end of the recommended settings for your vehicle for the reasons above. eg with the RX450h, "Eco" inflation setting is 36psi with 19 inch tyres, front and rear, and minimum recommended pressures are 33/35 rear/front split. Under inflating by just 5psi can have marked effects on fuel economy as well as handling. when I picked up my RX recently, all tyres were 5 to 6 psi under inflated (despite the fact that this was an "approved used vehicle and ought to have been checked). Now that the tyres are at correct pressures, I am expecting a few mpg more as well as improved stability.

Edit *Long story short: If HJ has recommended under inflation, then his advice is best ignored, and could be viewed as dangerous advice.

Verbout · January 12, 2017

I've just checked and inflated all my tyres with my new compressor.

One of the front and rear tyres were well under inflated, oops.

I drove it this morning with the correct, and Lexus recommended, pressures, what a nice difference. Drove beautifully.

royoftherovers · January 12, 2017

4 hours ago, GSLV6 said:

He's wrong and he's also suggesting that people break the law, and possibly invalidate their insurance. What he says is brainless, uninformed, ignorant rubbish.

As has already been stated, the manufacturer's recommended pressures are based on axle loading and always stated as cold pressures. The recommended tyres will have a specified load rating, and there is a margin on inflation at which this will be optimal for a specific axle weight. Under inflation can mean that the tyre won't make it's recommended load rating, it will overheat, especially at speed and sidewall deformation will affect both cornering stability and braking stability. Any accident could see your insurance company refusing to pay out and as far as the police are concerned, you could also be committing a traffic offence by not ensuring that you were running your tyres at correct (safe) pressures. Slight over inflation will reduce rolling resistance because the tyres wont be deforming as much and wasting energy transferred to them as heat, as happens with under inflated tyres but there are no grip advantages nor really much in the way of mpg advantage over the correct inflation. lexus publishes what it calls "Eco" inflation pressures. These tend to be at the upper end of the recommended settings for your vehicle for the reasons above. eg with the RX450h, "Eco" inflation setting is 36psi with 19 inch tyres, front and rear, and minimum recommended pressures are 33/35 rear/front split. Under inflating by just 5psi can have marked effects on fuel economy as well as handling. when I picked up my RX recently, all tyres were 5 to 6 psi under inflated (despite the fact that this was an "approved used vehicle and ought to have been checked). Now that the tyres are at correct pressures, I am expecting a few mpg more as well as improved stability.

Long story short: Ignore Honest John's advice. It's unlawful and dangerous advice at worst, a grossly negligent statement on his behalf.

I am not saying that you are wrong Paul, nor am I saying that you are correct, nor am I a lawyer and nor am I a technical expert on anything, but I am saying that it is important that one is aware of the law of libel.

Regards

John

Malc · January 12, 2017

aaaw c'mon, he's a journalist ............

Malc

Rabbers · January 12, 2017

There is so much specialist information and advice available to us today that it has become difficult to tell if it is accurate

or free of vested interests or misleading or misguided or simply wrong. So, unless we make a habit of questioning everything

we read, see and hear, which for some of us would quickly lead to mental exhaustion or a permanent state of indecisiveness,

we need, whenever in doubt, to set a limit on the economic damage and personal aggravation we would be willing to tolerate

after acting on information that might prove wrong even if purveyed by entities who, justly or unjustly, have acquired a guru-like

status. To suggest that tyre pressures should be set lower than those recommended by a car's manufacturer is a case in

point. In order to find out if the advice is unsound you would need to constantly monitor the outer-tread wear that will

normally result from under-inflation and then re-inflate in order to stop further wear before you are forced, hopefully not

after a suffering a blowout, into the not inconsiderable expense of buying a new set of tyres. If you are not bothered by

the potential expense and risk to yourself and others and possibly your car, you should by all means go ahead and experiment

with HJ's advice.

PCM · January 12, 2017

On 07/01/2017 at 9:28 AM, opsmajor said:

Happy New Year

In nearly all his 'advice' in the DT Honest John advises ignoring manufacturer's recommended tyre pressures, e.g. 35/38 psi, and, unless we are doing 100 mph all the time, run on 30/30 (he says all his cars are on that). What do you say?

Krs

Mike

Please provide citations/links as to where he says this...

GSLV6 · January 12, 2017

3 hours ago, royoftherovers said:

I am not saying that you are wrong Paul, nor am I saying that you are correct, nor am I a lawyer and nor am I a technical expert on anything, but I am saying that it is important that one is aware of the law of libel.

Regards

John

You have a point John. I haven't seen where he's said this, but the point being made is that it's not something that can or should be open to interpretation. Tyre pressures, in relation to an axle loading, speed and tyre geometry, are a known quantity in engineering terms and tyre manufacturers are very careful to specify correct application and use. IF HJ has advised that tyres are under inflated, then at best, that can be viewed as irresponsible advice, or ill-advised. However, your point stands and until someone can point to where he's said that, then obviously, my comments above are out of order, albeit technically valid (my engineer's hat on ). I have edited the comments accordingly.

opsmajor · January 13, 2017

My apologies. I thought this subject would be of wider interest to all ther Forum so put my below reply in Wheels & Tyres. So, PCM, here's your 'citation' from HJ.

Mike

Yesterday I asked HJ to clarify his advice and received this reply: "As I incessantly point out, tyre pressures rise by up to 4PSI when the vehicle is used and the air inside the tyres heats up. Obviously if you set the cold pressures at 38PSI, the pressures could rise to 42PSI in use and that could result in a serious crash."

NemesisUK · January 13, 2017

Does the man not comprehend that the manufacturer has factored in the increase in temperature and pressure in setting their cold inflation figures????

Does he genuinely believe he and he alone has discovered this apparent flaw in the recommended tyre pressures???

Linas.P · January 13, 2017

I would add, that without knowing in which context HJ said that is hard to say how valid is his advice. Maybe that concerns Fiat Panda which requires 32PSI and which he personally drives and has discovered that car performs better when he inflates R14/195/65 at 30PSI and not 32... But if he states that 30PSI is universal pressure for all cars then it is clearly bonkers...

Glover · January 13, 2017

Hi all

I'd definitely recommend following the Lexus handbook/information plate re tyre pressures. After all Lexus designed the car and computer modelled it, built prototypes and tested them, built pre-production vehicles and tested them in extremes of temperature, in snow, ice, and rain on different surfaces cobbles, gravel, smooth tarmac and that ultimate test for any vehicle British roads. They've tested them at high speed, harsh acceleration and braking, twisting mountain roads, fully loaded and driver only etc.. They've liaised with tyre manufacturers and designed suitable wheels. After all that they will know the optimum tyre pressures and will have allowed for the fact that tyre pressure increases as the tyre heats up.

I really like Honest John but in this particular case I'd trust Lexus 100%. And the icing on the cake. Would Lexus put lives and their reputation and profits on the line by giving inaccurate information. Buy the best tyres you can afford, inflate them to the correct pressure, test the pressures regularly and with luck (because Sod's law works on all machinery!) you'll be fine.

GSLV6 · January 15, 2017

On 13/01/2017 at 7:23 PM, Glover said:

Hi all

I'd definitely recommend following the Lexus handbook/information plate re tyre pressures. After all Lexus designed the car and computer modelled it, built prototypes and tested them, built pre-production vehicles and tested them in extremes of temperature, in snow, ice, and rain on different surfaces cobbles, gravel, smooth tarmac and that ultimate test for any vehicle British roads. They've tested them at high speed, harsh acceleration and braking, twisting mountain roads, fully loaded and driver only etc.. They've liaised with tyre manufacturers and designed suitable wheels. After all that they will know the optimum tyre pressures and will have allowed for the fact that tyre pressure increases as the tyre heats up.

I really like Honest John but in this particular case I'd trust Lexus 100%. And the icing on the cake. Would Lexus put lives and their reputation and profits on the line by giving inaccurate information. Buy the best tyres you can afford, inflate them to the correct pressure, test the pressures regularly and with luck (because Sod's law works on all machinery!) you'll be fine.

+1

Lexus, nor any other manufacturer, are stupid enough to quote cold temperature pressures and neglect frictional heat increasing PSI. They all factor that in. The point HJ makes is really out of context, especially when he neglects to differentiate between lower profile tyres (requiring higher pressures to maintain their specified load ratings) and non-low profile.

You are more likely to result in a crash from under inflation, not over inflation. There's a good factor of safety built into the hoop stresses generated from over inflation in the specification of the radial banding. If he is refusing to revise his opinions, his reputation will be tarnished and that would be a shame because he does provide a lot of good reviews.

dutchie01 · January 15, 2017

I have an uncle that really knows a lot about cars and always gives honest advice. I met him last night at a birthday party and he told me that driving without seatbelts is much safer. It seems easy to bypass the warningsystem so the annoying beep will be silent. What do you think, shall i follow his advice??

NemesisUK · January 15, 2017

Yes, it's called Darwinian selection ...

royoftherovers · January 15, 2017

38 minutes ago, dutchie01 said:

I have an uncle that really knows a lot about cars and always gives honest advice. I met him last night at a birthday party and he told me that driving without seatbelts is much safer. It seems easy to bypass the warningsystem so the annoying beep will be silent. What do you think, shall i follow his advice??

The Dodo DID NOT WEAR SEAT BELTS...... and look what happened to him !

Regards

John