Reply With QuoteI thought we were talking about fiestas,your talking about something which would obviously need to be more accurateOriginally Posted by Tinker
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I thought we were talking about fiestas,your talking about something which would obviously need to be more accurate
I really hope you are not serious
LOL I think this is actually the attitude some people really do take to tyre pressures.
ALL cars are only connected to the road by 4 very small oval patches of rubber and all cars obey the laws of physics. If you hit the brakes at 40mph with severely over or under inflated tyres your stopping distance WILL be longer.
After doing routines on fire appliances at every change of watch for 32 years I'm happy that I'm riding around on correctly inflated tyres.
F.T.F.A.
Generally speaking (and within limits) softer tyre pressures will increase grip for acceleration and braking, whereas harder pressures increase stability and reduce rolling resistance. Manufacturers tyre pressures are chosen to be a balance between those two things and tyre wear. So running under-inflated tyres should actually reduce your stopping distance.
Last edited by Groundrush; 1st April 2015 at 12:27.
A friend mentioned to the main dealer that his brand new Legacy seemed to be riding a bit harshly. The dealer asked what the tyre pressure was. 38psi as per the manual. The dealer said he'd check. He phoned back to say that Subaru started printing one copy of the manual for the US and the UK. In the US the tyre pressure was 38psi but in the UK it should be 34. Once set the car rode more comfortably. Tyre wear and handling are good.
Especially with wide low profile tyres, under inflation will cause the centre of the tread to have insufficient contact pressure with the road and over inflation will force the tyre to run on it's centre with less contact pressure on it's outer edges. Under inflation can also cause excessive side wall flex and overheating. There are also uneven ware issues. For a road car neither is good.
This thread has me now got paranoid about my tyre pressure.
Last edited by KurtKlaus; 1st April 2015 at 14:04.
That's a good thing :-)
That's only part of the story London Lad. Within limits the footprint of the tyre contacting the road will increase as tyre pressure decreases. This allows more of the tyre to deform around the surface of the road which increases grip during acceleration and braking. It is a well known trick used by drag racers to get off the line faster. It doesn't help in the corners because it allows too much lateral flex, but it does in a straight line. Under/over inflation will affect tyre wear in the way you suggest to be sure but it takes hundreds if not thousands of miles to start to adversely affect on road tyres, whereas race tyres can be destroyed in a few laps through incorrect inflation although that is usually more to do with temperature. Simply stating that under-inflated tyres will increase stopping distance may well be incorrect depending on the specifics of the situation. I spent 10 years as a race mechanic, we put a lot of effort into optimising this kind of stuff.
Last edited by Groundrush; 1st April 2015 at 14:25.
I hear what you say and don't disagree but I did state that I was referring to road cars; where deflating enough to get what is effectively the start of the side wall on the road is not a good thing!
That's not under inflated, that's flat.
Pmsl
OK well lets put it this way. If you under inflate a road car tyre enough to get it to, in your words 'deform around the surface of the road' in a straight line, then when cornering, bits of the tyre are going to be in contact with the road that shouldn't be.
There is no valid reason for under or over inflating a road tyre on a road car for use on a normal road.
I'm not being pedantic but there is such a lot of misinformation on the net about road tyres and tyre pressures and it's so important to safety.
I wouldn't agree with this at all, if we are talking a race car with a relatively short tyre life and a large budget then it probably applies, but reading what Groundrush has written it doesn't seem to be about under pressure but more about finding the optimal pressure, an overinflated or under inflated tyre will not have the optimum contact with the road, in the case of under inflated it also generates heat which will significantly shorten tyre life through sidewall damage and bead wear.
Lower profile will generally need a higher pressure to keep the rim off the floor due to the shorter sidewall, wider tyres typically need less pressure but this gets complicated when you go lower and wider, do not go with a rule of thumb.
I would not use the recommended pressures for the car unless that model has a 'hot version' that uses the same or very close sizes, I would probably go to the tyre manufacturers website and get some recommendation from that and find a similar sized car that has those tyres and take an educated guess somewhere between the 2 pressures.
Once you have a pressure make sure that you maintain it and regularly inspect the tyres for wear across the tread, you are looking for even wear, accelerated wear in the middle and its too high, the edges its too low (if you see one edge then he is probably either trying too hard around roundabouts or there is some misalignment)
Check them cold with a reasonable gauge (spend a fiver) and don't trust garage tyre inflator gauges and you'll be OK.
Last edited by Daffy; 1st April 2015 at 15:08.
Wise words indeed!
I really hope so too.
As for guessing the ‘tyres don’t leak’...
R
Ignorance breeds Fear. Fear breeds Hatred. Hatred breeds Ignorance. Break the chain.
I'd also look at your sons car insurance if he has non standard wheels and tyres and is in an accident they may not pay out.
Has anyone posted a Queen video yet?
"Bite my shiny metal ass."
- Bender Bending Rodríguez
This is what happens when you pump up your tyres to 30psi all round.
That looks nasty. How did you manage to bring it to a controlled halt?This is what happens when you pump up your tyres to 30psi all round.
Did I never tell you amongst other things I'm a highly successful racing driver with razor sharp reactions? No?
Looking after your tyres can save your life.
Yeah I have recently bought one of these as well. I also got a 12v to mains converter so I could plug it into the mains rather than have to use the 12v socket in the car and I also use it for my motorbike.
I love my Ring. Wouldn't be without it. I'm always showing it to friends and other motorists.
Best play on words I have read for some time.
Why not ask a tyre specialist the question? Any reputable tyre dealer should be able to advise.
As for tyre gauges, the ones I`ve found ost accurate are the old-style pneumatic 'pencil' type. I don`t trust anything else
Paul
True. But you don't need to kill yourself with the stress of worrying that they're a couple of psi above or below the recommended pressure!
Look on the side of the tire. It should be there, under "MAX LOAD".
That is NOT the correct running pressure; it's the max the tyre can be run at, not what it should be run at for any given car weight / type
Absolutely spot on, I was going to post that a while back. I've had one since being in the trade and still use it today. Never once gone out of calibration and fits in your top pocket.
Gotta say I can't believe this is still running. Seems to be lots of hand wringing and talk about what is a couple of psi. As been stated you're not instantly going to drop dead because your tyres are a few psi out.
We're talking about a Honda with slightly lower profile tyres on not a bloody Ferrari or other 200+mph super car. Just fill it with what the the recommended psi says and then forget about it.
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