Hi Guys and Gals,

Needed new tyres all round along with full wheel alignment and rear brake pads so booked the motor in at the weekend at Merit Tyres in Hazlemere, High Wycombe.

Opted for the Dunlop Lexus Sp9000's MFS tyres as couldn't make my mind up between these and the Goodyear F1's. And received an excellent service from Merit's. Phoned up last week to ask for a quote. Was told tyres would be £126 all in, 4 wheel alignment would be £50 and rear pads would be £77.

Phoned back two days later to confirm and when the guy asked what I was quoted, I said £126 and he said, I can get them down to £111 (rarely hear of a company actually 'trying' to get the price down unless specifically asked).

Got the car down there, brakes ended up at £72, another £5 off and when it came to wheel alignment, he managed to get the toe adjustments and something else but the camber adjustments just wouldn't budge but he got an improvement. Still, he gave me a discount again cos he couldn't get it absolutely spot on.

So all in all, excellent service and pricing (in my opinion).

Only one thing that made me nervous, they have filled my tyres with nitrogen instead of air. Apparently, its better solution all round, less leakage and other benefits and they will check and refill FOC if required. Just not heard of this before. Is this a good idea?

F1 teams use Nitrogen.

Aeroplanes use nitrogen in there tyres because it is an inert gas in case of blow outs

Just checked out the website for the garage that did it and it says:-

Police forces across the country carried out roadside surveys to check tyre pressures
On average they found 75% of tyres checked had incorrect tyre pressures
Road Traffic Accident Statistics show that 86% of tyres have incorrect pressures
Tyres filled with Nitrogen will maintain their correct pressure for longer, because Nitrogen doesn't leak through the tyre's structure. Normal compressed air contains Oxygen and water vapour, both of which permeate through the tyre casing.

Why use Nitrogen?

Better road holding
Longer tread life, up to 25% increase
Reduced fuel consumption, up to 5% reduction
No corrosion to the inside of the wheel

I used to have a motor bike that used Nitrogen, didn't know that was the reason though!

Isn't that slightly disingenuous? The implication is that it's the nitrogen that offers these benefits, whereas surely in reality it's the maintenence of the tyre at the correct pressure that does so, irrespective of whether that is done with nitrogen or just air. Perhaps nitrogen may help those who don't check their tyre pressure very often.

Indeed, these aren't actually benefits at all - they are to be expected from any correctly inflated tyre. ie you don't GAIN a 25% increase in tread life; you simply don't suffer a 25% LOSS in tread life should you have the wrong pressure. Also be interesting to know how the 25% was derived anyway.

He's got a good point!!

Nitrogen filled tyres don't go down as quick as the reason this happens is to do with the oxgen thingys in the air escaping through the rubber compound.

They are supposed to be more stable over temperature. Usually garages charge about £5 per tyre though to fill em up! Got a good deal there then.

There was an article in a paper not long ago about this.

what about if you need to top one up can you mix it .

as for mixing nitrogen with air there is no reason why you cant, but u have to be aware that u will be diluting the nitrogen - % depends on the amount of inflation required.

As for aircraft the reason we use it is because nitrogen expands less than air when subjected to heat - ie a tyre going from 0 -> 200mph in a split second, as well as it being inert. we are allowed to put 5% of air into a nitrogen filled tyre is so required.

Ermm. Isn't air 80% Nitrogen?

Yes it is, but its also 19% oxygen, which supports combustion. Not good on aircraft! Or any vehicle for that matter!

well not that it matters at 30 ish psi ( compared to 200psi) but that 19% of oxygen will heat up a bit quicker and thus is less stable, hence once there is a bit of heat in the tyres the presures will change at a greater rate than that of a tyre with nitrogen in.

erm escuse my ignorance but...

we are discussing the combustable properties or air in the tyres not being very good near aircraft

dont the planes fly in air ?

but - you dont get many tyre explosions when the plane is flying, well i have never seen or heard of any in 9 years of being in the industry, and atmospheric air is not at 200 psi.

When you look inside the glove (who keeps gloves in here? CDs and Polo mints box, perhaps?) at the recommended pressures, you have three choices. As I only use the car with me, or me and my graceful partner, in, and I don't exceed 150kms/hr too often, I use the 'lesser' of the pressures, though it seems to me that a higher rating will result in less wear(?) but less grip, which is fine as I tend to cruise rather than race (I have a Series 3 LS400, bought for comfort, though fast on M-Ways) If I was a boy racer (who would call themselves that anyway?) I'd have a 200? Perhaps Helium would be better, as It would make the car a little lighter? (Include the spare?)
Anyone got a spare set of wheels for an LS400 in good cond? Or even better, a chrome set?
Chris at cskelton@madasafish.com in Bristol, U.K.

I filled mine up with Helium. Trouble is, my car keeps floating off now