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Location:
Brisbane
Registered:
July 2002
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right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 10:12
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Im just wondering what right tyre rpessures are for wear and performance... atm I think they are all sitting on 36 psi?.. can anyone tell me what good pressures are. these are expensive tyres and I dont want them to die too quick.
Car is gz10 soarer, around 1200kg.
17 inch rims that are all wrapped in 235/45/rz17 Dunlop Formula FM901's.
Any help is much appreciated
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Location:
Brisbane
Registered:
February 2003
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 10:47
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I run 215x40x17's on my GT4. 1400kg and AWD... I run 42psi all round.
My tyres (Firenza ST03) are rated with a max pressure of 51psi at 487kg.
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Location:
Melbourne
Registered:
October 2003
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 11:35
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I'd be getting in touch with the tyre manufacturer. btw I don't believe the weight of the car has anything to do with the correct tyre pressure. Calling a tyre/wheel shop is ok, but you migh get some new guy on the phone and you want to be confident with the figures, who better than the people who made them. Just look for dunlop in the yellow pages.
hope it helps
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Location:
NSW, East Coast
Registered:
July 2003
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 11:43
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I think the correct pressure is labelled on the side wall of the tyre isn it.
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Location:
Melbourne
Registered:
October 2003
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 11:52
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| FKN16V wrote on Sun, 04 January 2004 22:43 |
I think the correct pressure is labelled on the side wall of the tyre isn it.
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on some higher profile tyres it is. but now days some extremely low profile tyres are printed with only the brand and model on them, not even the size of the tyre.
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Location:
Sydney
Registered:
January 2004
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 13:22
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is there a trend with higher pressures in lower profile tyres? If so, anyone know of the main reason for this?
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Location:
Canberra
Registered:
August 2002
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 13:47
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i run the same sized tyre as you, and mine are on 48psi all round. 
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Location:
Brisbane
Registered:
July 2002
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 13:53
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atm ive got 36 all round.. i think ill ring dunlop tomorrow
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 14:09
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the lower the profile of the tyre, the higher the pressure should be. for 45s, 40psi or even a little under would be fine - depends how much you value your comfort
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Location:
Brisbane
Registered:
June 2003
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 14:16
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i run about 32-34 on my ma61 tyres..seems to work a treat, too high psi makes them hard and your car feels like shit
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Location:
Melbourne
Registered:
October 2003
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 14:40
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| HighRolla wrote on Mon, 05 January 2004 00:22 |
is there a trend with higher pressures in lower profile tyres? If so, anyone know of the main reason for this?
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Note: Aspect ratio (AR) is the more professional approach to describing the profile of a tyre, as the sizes '45' '50' are in respect to the width of the tyre.
With lower profile tyres you obviously have much less room from the ground to the hub. So at 32psi it wouldn't take much to push a tyre with an AR of 40 to the hub and cause damage, and possibly a blowout. So you need to up the force acting on the inside of the rubber to make sure the tyre walls are able to absorb the 'rock'/'Rail track' on the road given the lower distance it has to travel.
Given that
Force = Pressure / Area
to increase the force you need to up the pressure OR decrease the area. We've already decreased the surface area as it is by lowering the AR so therefore increasing the pressure is the way its done.
I can't say for certain that what I have said is the way it is, But after reading the question I thought I'd try an answer using physics. Hope it helps
Cheers.
PS.(The best way to understand (Pressure = Force / Area) is to think of someone standing on your foot with flat soled shoes, and then doing it again with high-heels. ie:stilletos with a surface area of around 1cmx1cm sometimes
The force remains the same (the weight of the person) but with a smaller cross sectional area on the stilleto the pressure goes up (basic mathematics). And as you would expect being stood on with stilletos hurts more due to the greater pressure.)
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Location:
Brisbane
Registered:
July 2002
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Re: right tyre pressures for 235/45/17's?
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Sun, 04 January 2004 23:49
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i jsut rang beaurepairs... they said run 32....
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Location:
Brisbane
Registered:
February 2003
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Re: right tyre pressures for 235/45/17's?
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Mon, 05 January 2004 01:04
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| Jag7799 wrote on Mon, 05 January 2004 09:49 |
i jsut rang beaurepairs... they said run 32....
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Tell them they are dumb.
Seriously, 32psi is fine in your girlfriend's Barina... .not in your performance car on 45 series rubber.
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Location:
Canberra
Registered:
December 2002
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Re: right tyre pressures for 235/45/17's?
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Mon, 05 January 2004 03:49
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Pump them up so they are not so flat on the bottom. 
Works for me.
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Location:
Montrose, VIC
Registered:
May 2002
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Re: right tyre pressures for 235/45/17's?
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Mon, 05 January 2004 04:08
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After screwing round with 235/45 17s on the commodore, I found 38 seems to be about the best balance of grip, control etc. (who gives a toss about ride!! ) Of course, different brands of tyre could be SLIGHTLY different too... 
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Location:
Eskilstuna, Sweden
Registered:
May 2002
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Re: right tyre pressures for 235/45/17's?
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Mon, 05 January 2004 07:21
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I run 45 psi in my 205/40s. A little under the maximum set for the tyre on the sidewall. Works great, the low profile tyre does not have to loose to much pressure before they look flat and I don't like the idea of the rims eating drt.
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Location:
Melbourne
Registered:
October 2003
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Re: right tyre pressures for 235/45/17's?
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Mon, 05 January 2004 08:18
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| Jag7799 wrote on Mon, 05 January 2004 10:49 |
i jsut rang beaurepairs... they said run 32....
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 Exactly why I suggested it was risky calling your local dealer, unless of course you trust them. And go straight to the manufacturer.
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Location:
Menai area of Sydney
Registered:
June 2003
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Re: right tyre pressures for 235/45/17's?
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Mon, 05 January 2004 11:19
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T APLUS 22 - In my humble maths training, to be a ratio, AR has to have a numerator and denominator. So yes, Aspect Ratio relates to the tyre width but as the percentage ratio of the height to the width. So a 245/45 tyre has a nominal tyre width of 245mm and a nominal height off the rim of 245mm x 45% = 110.25mm. I say nominal because actual height depends on tread depth which obviously changes during the life of the tyre.
Also, in my humble physics and/or maths training, lowering the AR shouldn't reduce the area over which the force of the car's weight is spread as in using a lower profile tyre one normally uses a larger rim to maintain the overall diameter of the wheel.
In fact, one would expect the surface area to increase because of the wider tyre profile. Too wide and you can easily aquaplane on a wet road because not enough force is being applied over the contact patch to push the tread through the water layer on the road to make contact with the road surface - and water gets trapped as it can't escape quick enough.
The correct tyre pressure will be determined by experience with a given tyre on a given car as other factors such as tyre wall strength come into account in how much air is needed to resist bottoming the rim.
Sorry to be a killjoy but it pays to get to know your car and experiment with pressures above and below the 38psi suggested in previous posts. Watch how far around the edges that the tyres scrub on the road with the different pressures and driving styles.
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Location:
Brisbane
Registered:
July 2002
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Re: right tyre pressures for 235/45/17's?
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Mon, 05 January 2004 13:18
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ill see what max is on sidewall
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Location:
Melbourne
Registered:
October 2003
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Re: right tyre pressures for 235/45/17's?
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Mon, 05 January 2004 19:28
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| Scorpion wrote on Mon, 05 January 2004 22:19 |
T APLUS 22 - In my humble maths training, to be a ratio, AR has to have a numerator and denominator. So yes, Aspect Ratio relates to the tyre width but as the percentage ratio of the height to the width. So a 245/45 tyre has a nominal tyre width of 245mm and a nominal height off the rim of 245mm x 45% = 110.25mm. I say nominal because actual height depends on tread depth which obviously changes during the life of the tyre.
Also, in my humble physics and/or maths training, lowering the AR shouldn't reduce the area over which the force of the car's weight is spread as in using a lower profile tyre one normally uses a larger rim to maintain the overall diameter of the wheel.
In fact, one would expect the surface area to increase because of the wider tyre profile. Too wide and you can easily aquaplane on a wet road because not enough force is being applied over the contact patch to push the tread through the water layer on the road to make contact with the road surface - and water gets trapped as it can't escape quick enough.
The correct tyre pressure will be determined by experience with a given tyre on a given car as other factors such as tyre wall strength come into account in how much air is needed to resist bottoming the rim.
Sorry to be a killjoy but it pays to get to know your car and experiment with pressures above and below the 38psi suggested in previous posts. Watch how far around the edges that the tyres scrub on the road with the different pressures and driving styles.
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Scorpion
well, quite humble. if you'd check with your local dealer it is called a ratio... however no-one said anything about being a constant ratio. Its simply a wording of AR to describe the size of the tyre. A larger width on the tyre will actually change the overal height of an inlflated tyre, even if the profile remains the same.
And as for the second comment, well you might want to read my post again, I was talking about the total surface area of the tyre... not the area keeping contact with the ground. If you don't understand what I mean, then pm me and I'll go into more detail. So, there was no killjoy, just a miss-informed post in some respects, and if you aren't sure what your talking about when trying to disprove someone else, then maybe its best not to try and put holes in others statements.
[Updated on: Tue, 06 January 2004 08:28]
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Location:
Brisbane
Registered:
July 2002
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Re: right tyre pressures for 235/45/17's?
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Tue, 06 January 2004 00:22
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doesent say anything about max rpessure on side of the tyre
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