tyre presures and bigger wheels

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tyre presures and bigger wheels

dave

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i was told today by a dude that has good rep that rule of the thumb is 2lb/in(squared) extra for each inch bigger:)
 
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dave

dave

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helpimonfire said:
2lb or 2psi ?

i dunno how to work out lb's of pressure :eek:
um not sure it the bigger number of the 2 so if you had 15s at 29 an you fit 17s it will now be 33, will go look at pump :eek:
 

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Hello there fuzzy forum brother tell me the tyre size of the 17" is it 215/45/17 if so its 34 psi same on the stilo (y)
 
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dave

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there is no tyre size its a rule of thumb guide for fitting bigger wheels, the dude says the profile n with no matter, but if you change tow to slightly tow in then you add 4 not 2 :)
 
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wotnowarninglight

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The 16vt Coupe alloys on mine are 1/2'' narrower that Stilo 16's (6.5 vs 7.0) but the offset of the coupe wheels means my track is 0.7'' wider (coupe wheels stick out of the arches further than Stilo 16's). Started with Stilo 16's pressure of 2.1 bar = 30ish PSI and car feels great and sticks like glue despite budget tyres. Will just check tread after 1500 - 2000 miles and see how tyres are wearing and depending on results may alter tyre pressures.

By the way, even manufactures recommended pressure are sometimes wrong! With Favorits & Felecias Skoda say 27PSI F & 26PSI R - F turns in sharply and rear follows on a wider line eventually - tyres dont wear properly. Solution is 30 PSI all round for more responsive handling and even tyre wear (y) Sometimes its a case of trial & error / suck it & see etc.
 

hmallett

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Manufacturers give their ratings in conjunction with tyre manufacturers taking into account a variety of factors.
Eg, the 20V Turbo Coupe has pressures of 32psi rear, and 39 psi front. Many owners reported that they felt it was better at 32 psi all round. One owner contacted various tyre manufacturers, asking their opinion. I think it was Michelin who said that 32 psi all round would be ideal, if the car had a top speed of 100 mph. However, taking into account a 155 mph top speed, the reccomendation they gave was 39 psi. At higher speeds, 32 psi wasn't safe.
H
 
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dave said:
i was told today by a dude that has good rep that rule of the thumb is 2lb/in(squared) extra for each inch bigger:)

Up to a maximum of what though? That could put you up above the safe maximum for the tyre quite easily under load. I go to 32/33ish for everyday driving, mid 30s if I'm doing a longer/ faster journey though admittedly my car doesn't do 155mph :eek:
 
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I know the maximum is on the side of the tyre. But then you compare that with maximum levels in my job - it varies from an absolute safe maximum level to a licenced maximum level where the absolute safe maximum is way above that stated on the licence. Personally I wouldn't like to go near the stated maximum in case it was an absolute safety limit. This is why I'm asking.
 
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The maximum limit on my tyres (on steel wheels standard for Bravo/a) is 44psi. Assuming a standard recommended pressure under load at the rear of 36psi and folloing the above, change from a 14ins standard to 18ins wheel and you get to 44psi rear with a full boot(also assuming the maximum safe pressure on the new tyres is 44psi - anyone have any very low profile tyres for comparison?). Not that I'm planning this, obviously, just trying to fine tune the calculation and it's good to know the safety limits and margins of error of things like tyres :)
 
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dave

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36psi standard for a 14 inch rear, front wheel drive car seems a lot, my 17" tyres are low profile have a max of 40 psi standard presure on. my 15s was 29 front 28 rear
 

HP

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I'm not sure about this.

The PSI figure is exactly that, pounds per square inch. If you put wider tyres on - say 205 instead of 185 then you have far more rubber in contact with the road.

The weight of the car will be spread out more across the tyre, so the mathematical part of my head suggests a very slightly lower psi figure for wider tyres.

The diameter should make no difference at all, it's the size of the footprint that matters.
 
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dave

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fixitagaintomorrow said:
I'm not sure about this.

The PSI figure is exactly that, pounds per square inch. If you put wider tyres on - say 205 instead of 185 then you have far more rubber in contact with the road.

The weight of the car will be spread out more across the tyre, so the mathematical part of my head suggests a very slightly lower psi figure for wider tyres.

The diameter should make no difference at all, it's the size of the footprint that matters.
thats what i always told people until i went to this place, its most advance tyre fitters ive ever seen in my life:eek: seemed to know thier stuff, there was top motors in there inc 1 of them lhd lancias mmm. i would think they would soon go out of business if all thier customers tyres started to whear oput in the middle too quick
 

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The pressures within the tyres arn't that high.. Start looking at bike tyres... 60psi standard :D

Sorry I can't help beyond that. Try comparing similar size/weight on other cars for reccomended pressures.
 
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