Reply With QuoteMissus has a mitz colt with low profiles, in the book it says 35 psi........if that helps?!
My son has his first car and is fitted with aftermarket wheels with low-profile tyres. He asked me yesterday about the pressures and I've no idea.
The recommended pressure in the handbook is 31psi but should this be changed up or down because of his tyres/wheels?
Missus has a mitz colt with low profiles, in the book it says 35 psi........if that helps?!
On all my cars I've always inflated to 30psi, over the years I've seen recommended pressures (in handbooks) range from 30 - 36psi... so figured the lower end would be a safe rule of thumb.
Priority would be to see if he's insured. If those wheels/tyres haven't been declared he wont be. If you can give the tyre make/model and size I'm sure someone can advise.
What's the model of car and size of tyres?
You should wait for Cilla's exposition on the perfect gas law, temperature, altitude, volume, weight and how many birds one is boffing on the back seat to get the correct answer.
I've always gone for 30PSI as a safe rule of thumb for a normal passenger car. I had different pressures front/rear on my LR Disco but that's the only time I've strayed from the rule.
Are they fitted to a model higher up in the range as that would be a good starting point (unless it has a massively heavier engine). If you look on Michelin you can select the car/tyres and it shows you the recommended pressures.
The cold pressure is meant to (I think) 30% lower than hot but I would start with as close as you can get to the manufacturers suggestion - my car has several sizes & loads listed on the door arch so the manual could be a good place to try too.
I think I'd start by checking in the manual if front and rear are the same pressure. With tyre pressures I tend to play around regardless of what the manual says but I always maintain gaps front to rear (as in if in the manual the fronts are 29 and the rears 36, I don't just pump up all the tyres to 30).
It's important to keep any tyre/wheel combination to within 1% of original circumference as supplied by manufacturer, will alter handling and speed readings, have a look at this site, http://www.alloywheels.com/Tyre_Calculator
and put new wheel/tyre sizes in, as stated above Insurers should be notified of any changes from original specifications.
Check the manual or on the inside of your fuel filler cap cover - but 30 does it for most normal cars.
Check the aftermarket tyre manufacturer's website.Originally Posted by Kingstepper
Not sure if it's the same for cars, but for caravans you work it out by looking at the max load rating for the tyre, divide weight of vehicle by number of tyres and see what percentage of the tyres max loading you are using, then multiply the tyres max pressure by that percentage. Seems logical. So if each tyre is rated for 500kg, car weighs 1500kg, you are using 75% of the tyres max load, therefore inflate to 75% of the tyres max allowable pressure.
Brighty
^^ This. DO NOT guess or 'just use 30', correct tyre pressures are vital to all of a cars important functions.
Braking, handling, acceleration, fuel consumption and ride all rely totally on correct tyre pressures.
Set when cold i.e. car having stood overnight and out of the sun. Get a good gauge. Check weekly.
Last edited by london lad; 31st March 2015 at 11:34.
It should say on the tyre
That wouldn't take weight of car in to account though. You'd want more air in the same tyres on a 2000kg car than on a 1000kg car. Pressure on tyre will be the max for that tyre, not necessarily what you want to put in them on your car.
Brighty
Not sure if anyone else have seen the growing phenomena of yoofs buying typically old hot hatch type cars, seriously lowering them, to the point of there being very little clearance and putting wheels with low profile tyres on that are too big for the car, necessitating alteration to the geometry of the wheel (I've seen some road cars with more camber than an Indycar) and the body work being beaten out to accommodate the over size wheel. I've also seen the opposite, usually on old Golfs/Polos, where a smaller size wheel with quite large tyres are used. With lowered springs this lowers the car even further. Looks like a go kart. In both examples I've thought the handling would have been horrendous and likely dangerous.
I have low profile Michelin Pilot Super Sports on my car and they run at 38psi, try a car forum specific to the car that your son has.
I ran my car at 32psi until I checked up on it, the extra psi makes a big differance to the performance and handling.
Last edited by CaptainSlow; 31st March 2015 at 11:37.
Set the fronts to 24psi and the rears to 50psi to teach him car control.
A quick check is available here:
http://www.tyre-pressures.com
AFAIK the pressures for low-profile are the same as standard.
R
Ignorance breeds Fear. Fear breeds Hatred. Hatred breeds Ignorance. Break the chain.
But not on public roads, please (in any country) - whether or not this was intended tongue in cheek
You're right - 50psi in the fronts and 24 in the rear - can't get into much trouble if you understeer everywhere.
The correct tyre pressure will be exactly the same as that stated by the car manufacturer for that particular car.
The tyre pressure is connected to the weight and spec of the car, regardless of tyre size, unless he's got monster truck tyres on it of course.
Diesel engine cars usually specify a higher pressure at the front because of the added weight of the diesel lump. Similarly, if you're fully loaded with 4-5 adults and a boot full of luggage, the pressures will all have to be increased.
EDIT: As others have said though, check the tyres are the correct size with the new wheels to keep the rolling ratio the same as the original wheels and tyres or he might find himself coming unstuck. If the tyres are wrong then the speedo will be wrong.
Last edited by Onelasttime; 31st March 2015 at 14:00.
Thanks everyone for your input. The car is a Honda Civic 1.4 (2005). Obviously not a performance car but it looks quite 'cool' for his first car.
He's at work at moment so I don't have the tyre details.
That makes sense and we might just go with that. I'll also get him to look on the various car forums.
Someone mentioned insurance. He has had a 'box' fitted and the installer did look around for any modifications which would invalidate the insurance but didn't mention the wheels.
I would double check with the insurer on this. They will look for any way out they can not to pay a claim and undeclared modifications, such as aftermarket wheels, will void the insurance. Better be safe than sorry
I'm ferrying my middle bairn to Uni and back twixt Durham and Oxford regularly, so it's a fully packed C4 Picasso one way and an empty one in the other direction, a trip of 250 miles each way. I've invested in a digital 12V compressor, run from the car. Simply preset the desired pressure, attach , start, and it shuts off automatically once the pressure is reached. It's a godsend for adjusting the pressures quickly and accurately, when reducing there is a bleed valve on the connector. A plus has been that it makes the chore so much quicker and easier than with a foot pump that I can do all of the family fleet in @ 30 mins every week. I bought a Ring after some reesearch, and got it from my local Screwfix, could have saved a couple of quid online, but it's just around the corner if I have any problems with it. It can also be used manually and has a couple of lights on it. http://www.screwfix.com/p/ring-autom...ight-12v/65414
F.T.F.A.
Thanks for that, I’ll be getting one later this week.
R
Ignorance breeds Fear. Fear breeds Hatred. Hatred breeds Ignorance. Break the chain.
The only downside with all small compressors of that type is that they get hot and so heat the air they are pumping into the tyre and make the inflation inaccurate.
If you want to be spot on buy a good gauge, the best you can afford. THIS is what a lot of F1 teams used to use up until a few years ago and it's spot on, expensive but not mental money for something so important and the makers (M A Horne) offer a recalibration service. THIS is a well proven gauge and considerably cheaper. Now go and pump up your tyres with what ever takes your fancy but put them about 7PSI over the correct pressure. Leave them over night (to settle to ambient temperature) and first thing in the morning check and deflate to the correct pressure with your good gauge.
You can't go wrong with 30 in any car tyre,I've had alsorts of cars and different size wheels,at the end of the day were not talking racing cars are we
A consideration if flat, but for a top up, most of the air in the tyre will be at ambient temperature.
Sorry but that is so wrong. You could be talking about under or over inflation by anything up to 50%, that makes a massive difference to contact patch size, rolling resistance and tyre wall flex. Setting a tyre that should be at 45 to 30 PSI is simply very dangerous.
Try my suggestion and see how much difference it makes, you will be surprised.
As has been previously mentioned, declare the exact wheels and tyres to the insurance company. Most insurance companies take a dim view of alterations and 'non-standard' kit and this needs sorting and clarifying asap. You know what most insurance companies are like, they will wriggle like greased worms on a spiked hotplate given the slightest opportunity!
take the wheels off and replace with the original specification wheels, and while your at it, rip of the boot spoiler, and remove the Recaro seats from the 1.2 litre fiesta
So basically you'll never know what the correct pressure is because it'll be different if you've got 5 people in the car rather than 1
For everyday driving, that first pressure gauge is way overkill. Ideal if you regularly track a car mind.
I would leave them at the manafactures spec and just keep on eye on tyre wear. Lower profile tyres are generally a bit firmer in the side wall so I wouldn't be raking the pressure up too much.
Regarding tyres hot/cold. It's always better to check your pressures when colder as it is simply more accurate....but again it's really not worth wringing your hands over , We carry out vast amounts of quality checks on our technicians and as a general rule of thumb tyre pressures can vary a few psi when hotter. Your not talking about an F1 car here.
I've just put two new tyres on the front of my car, and the two that came off had a few mm left in the middle of the tyre but the inner and outer shoulders were gone. I checked the pressures fairly often, and inflated to the manufactures recommended 2.2 bar, but looking at the tyres, the pressure was too low. So I would suggest, tinkering a bit either side of the recommended figures.
Oh, and as others have said, definitely inform the insurance company of the aftermarket alloys.
Depending on the car, that could be down to the castor angle wearing the tyres out during town work.
With regards to the OP, assuming they are around the 17 to 18'' mark, 32psi should be about right for an 05 plate civic.
Don't mean to be an arse, but as far as I am aware besides insurance companies and safety it is against the law to use a vehicle on the road with wrongly inflated tyres, Police can prosecute and fine + points PER tyre. There is DEFFINATLY no rule of thumb for preasure with even different models of same car having different pressures, DOUBLE check reliable sources ( handbook) aftermarket suppliers, tyre manufacturers etc and stick to them,
Whilst I imagine a driver could be prosecuted for having an unsafely inflated tyre I don't think the information suggested is that easy to find.
The handbook will only give a value for the standard wheel/tyre.
Tyre manufacturers may well give values for their tyres on a standard wheel/car.
Recommended pressures for aftermarket wheels that are perhaps 5-10 years old of unknown origin aren't going to exist.
Well that's certainly true
Registered to this forum to react.
Will copy text I saved and used for other fora , so can be a little of topic here sometimes.
Live in Holland ( Europe) and once got hold of the formula for calculating pressure for a load and went running with it. Now call myself tire-pressure specialist. Got much wiser about it and maximum load of tires in the years.
So will not introduce myself in a seperate topic, because I dont own a car on this forum, only react on tire-pressure related questions.
Tirepressure advice is all about load on tire and speed ( and sometimes about alighnment - camber angle).
So if you can give details of car and tires , I can calculate an advice pressure with some reserve for things like, pressure-loss in time, unequall loading R/L, incidental extra load, misreadings of pressure scales,and misyudging of weight, etc.
This is from tires next and can be read from sidewall:
Maximum load or loadindex.
Kind of tire to determine the AT-pressure/pressure needed for the maximum load up to maximum speed of tire, or if lower 160km/99m/h/reference-pressure, wich is not the maximum pressure of tire.
Maximum speed of tire, most given as letter ( Q=160km/99m/h,N=140km/86m/h fi)
If you have offroad or tires looking like that , with large profile blocs that cover a part of sidewall, also mention, they are allowed lesser deflection then a normal road tire, then the tire maker used to determine the maximum load (to my conclusion the case for the Bridgestone tires on Ford Explorer in the Ford/Firestone affaire).
If you cant find all of it give sises of tire and Loadkind, then I will google for it.
From car next and mostly can be found on same plate as the original pressure advices:
GAWR and GVWR ( Gross Axle/Vehicle Weight Rating)
But best would be to determine the real weights in your use on seperate tires or estimate it as acurate as possible, by weighing per wheel(pair) or axle.
Maximum speed , you dont go over for even a minute in your use, eventually different for different situations, for instance when towing or fully loaded.This apart from trafic regulations, if you drive faster then allowed give that speed. Nature punnisches with tire-failure, police only with a penalty.
Give all that and I will calculate and give a picture of one of my filled in spreadsheets in my answer.
If other then original tires, indead as is already answered other advice is needed, a stiffer tire ( fi C-load instead of P-tire) needs a higher pressure for the same load, or the other way around, has lower loadcapacity for the same pressure.
Greatings from a Dutch pigheaded self-declared tire-pressure-specialist.
Seems rather extreme calculation, but if you're keen to do it I'll dig out the data tomorrow - might(?) be interesting to see how your calc compares with other recommendations.
And welcome to the forum...
I'd intended to buy a guage to use alongside my pump in order to check the accuracy of the digital guage it has. The Autoexpress review section that rated my Ring compressor also tested some guages, so I'll be buying one of those. http://www.autoexpress.co.uk/accesso...014-group-test Once I determine if the pump guage is out either way I'll adjust my preset accordingly. The guage on the pump can also be used as independently of the pump, but a small hand held guage will be much easier for a quick check to see if an alteration up/down is needed. I've been setting the preset at 0.2BAR high to allow for the slight escape as the hose is removed, so I reckon I'm pretty much spot on.
Most cars quote pressures for 'driver only' and 'fully loaded' on the trye pressure plate usualy found on the door jam.
You can in mine. Porsche 911. 36 front, 44 rear.
My tires get pumped up every year when I take it in for a service.
Any more than that seems a waste of time.
I've never noticed the difference, pre and post service, so I guess my tyres don't leak.
I do have a fetish for quality tools. Having said that I've had it for 12 years and it's had hard use including being dropped and it's never let me down, it has a 7 year lithium battery so it's always ready to go, you can get all the spare parts and as I said before the makers offer a recalibration service. Compared to the cost of a watch it's a bargain. The serious track day boys use MUCH more expensive stuff with thermometers and logging etc.
The 'domestic' type electronic gauges you see in Halfords and the like can be very accurate but the sensors suffer from two things, lack of thermal compensation and susceptibility to going out of calibration due to impact. Baby it and keep it indoors and it will be fine. Don't forget to test the tyre first thing in the morning when its had no running, sun or re-inflation for a good few hours.
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