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Discussion Starter · #1 ·
Saw something you all might be interested in at tire shop today. I was getting Nitrogen put in my new OZ/Kumhos, and I told tech to put 2.7 bar (39psi). He asked me if I drove fast and I said yes. He said that was too little pressure for 18" wheels and showed me Michelin's chart.



For the S60R, Michelin reccomends 2.5 bar (36 psi) for 235/45x17" and 2.9 bar (42 psi) for 235/40x18". Most people on here always say run 36 psi. I wonder if underinflation is why so many people with 18" rims get damage from potholes?
 

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Re: Proper Tire Inflation for 18" vs 17" ("R" Kelly)

How does the load rating play into all of this, if at all? Notice that in the pic the load rating for the 18" tire is 90. If the load rating was 95 (as is with my current tires, Toyo, or with the stockies) would the pressure requirements be affected (less/more pressure)? I would imagine that with the higher load rating, you wouldn't need as high a pressure as 42 psi.
 

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Discussion Starter · #4 ·
Re: Proper Tire Inflation for 18" vs 17" (IwantaS60R)

Quote, originally posted by IwantaS60R »
How does the load rating play into all of this, if at all?

I noticed same thing, but my Kumhos are 95Y XL and right there in front of the guy when he made the comment. This is a high end tire shop, so you think they would know...
 

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Re: Proper Tire Inflation for 18" vs 17" ("R" Kelly)

That's interesting. I ran 38-39 psi for a while in my previous set of Rossos, and that pressure minimized a lot of the tramlining and rear-end issues. But when I went to change my tires, I noticed that the center of the tires were worn significantly more than the outer/inner areas . . . and TRUST me, I corner hard quite frequently.

So to get even tire wear, I've reduced the pressure to about 35-36 psi. The handling isn't quite as "crisp" or responsive at that pressure. But I've since installed eibachs and ipd track-spec sways, so the handling improvement from those two upgrades nullifies the drop in tire pressure.

42 psi . . . man, that just sounds high
 

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Re: Proper Tire Inflation for 18" vs 17" (R Salesman)

~41 is what I use with the PS2's. rear sometimes ~40.

The PS2's need it, the PZero's start to hammer a lot with these pressures.
 

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Discussion Starter · #9 ·
Re: (JimLill)

Quote, originally posted by JimLill »
http://apps.volvocars.us/owner...pg117

Jim, see I listened to you when you told me run 39 psi. (2.7bar).

I think the fact that Michelin reccomends higher with their Pilot line of performance tires is worth noting.

Also, 39 may be good for cold tire pressure when filled with compressed air, because pressure will build when tire heats up correct?

Because I'm running nitrogen (which doesn't expand with heat and anyone running expensive Pilot tires in Germany probably is as well), perhaps that is why they reccomend 42 psi?

More stuff to ponder...
 

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Re: Proper Tire Inflation for 18" vs 17" ("R" Kelly)

WAY too high.
We can argue this to death but Volvos HATE high tire pressires, all they will do is rattle apart.
I used 33-34 with 17's and PZeros
I use 36-37 with 18's and Michelin PS ALL SEASONS
I would go with 34-35, maybe 36 tops with 18's and Pzeros.
Michelins seem to want a couple of pounds higher pressure than Pirellis (softer sidewalls)
I forgo "ultimate" handing for a nice ride and good tire wear you WILL wear out the centers if you go 39-41 lbs of pressure
All pressures are cold, of course
 

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Re: ("R" Kelly)

Something else to ponder....

I have the goodyear's and I think they are 91 load, regardless. I normally run 36 psi and at Bedford autodrome, I had checked my hot pressure:

42 psi front

41.5 psi rear

So perhaps this is the recommended hot psi when filled with nitrogen.......?


Kevin
 

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Re: Proper Tire Inflation for 18" vs 17" (JRL)

Quote, originally posted by JRL »
WAY too high.
We can argue this to death but Volvos HATE high tire pressires, all they will do is rattle apart.

I would go with 34-35, maybe 36 tops with 18's and Pzeros.

I run 36 with the PZeros and it's jarring enough.....and this is the lower end of Volvo's recommendations. I guess it's a sacrifice for sidewall protection.
 

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Re: Proper Tire Inflation for 18" vs 17" (MagoonR)

I ran 36 in my Rossos and had a pair of blowouts due to potholes. I am now running 39 (filled with nitrogen) with my Michelin Pilot A/S and have been through 4 tires since November. Thankfully the roadside hazzard warranty has picked up the bill on all 4 Michelin replacements. Good news, I have made friends with the tire tech @ my local Costco and they now keep a pair of 18s in stock (for me)
 

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Re: Proper Tire Inflation for 18" vs 17" ("R" Kelly)

40-41 psi in the Toyos this spring and even the glovebox rattle is gone. Car has never felt tighter. http://********************/smile/emthup.gif
 

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Re: Proper Tire Inflation for 18" vs 17" (JRL)

Quote, originally posted by JRL »
WAY too high.
We can argue this to death but Volvos HATE high tire pressires, all they will do is rattle apart.
I used 33-34 with 17's and PZeros
I use 36-37 with 18's and Michelin PS ALL SEASONS
I would go with 34-35, maybe 36 tops with 18's and Pzeros.
Michelins seem to want a couple of pounds higher pressure than Pirellis (softer sidewalls)
I forgo "ultimate" handing for a nice ride and good tire wear you WILL wear out the centers if you go 39-41 lbs of pressure
All pressures are cold, of course

Not at all, and you are actively promoting unwanted tire blow out..
 

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Re: Proper Tire Inflation for 18" vs 17" (Johann)

Quote, originally posted by Johann »


Not at all, and you are actively promoting unwanted tire blow out..
Again, for the gazillionth time, this is for the US and our speed limits. No one drives a steady 110-120 here, you just can't, no room. You may do it for a minute or two but not for 20 minutes at a clip
I suppose if I drove like you I would run 50 LBS! YOU are the exception not the rule
Never had a blowout in my life, nail flats sure, but NEVER any tire trouble for no reason, EVER
 

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Re: Proper Tire Inflation for 18" vs 17" (JRL)

Quote, originally posted by JRL »
No one drives a steady 110-120 here, you just can't, no room.

Isn't that just ironic? With as big as the US is, we just don't have enough room to drive fast, lol!
 

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Re: Proper Tire Inflation for 18" vs 17" (R Salesman)

Quote, originally posted by R Salesman »


Isn't that just ironic? With as big as the US is, we just don't have enough room to drive fast, lol!

you guys have never been on I-95 have you
 

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Re: Proper Tire Inflation for 18" vs 17" (R Salesman)

My statement excludes Nevada and Montana and certain other Western states where some of us MAY have the chance to keep it at over 100 for periods at a time
 

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Re: ("R" Kelly)

Quote, originally posted by "R" Kelly »


Because I'm running nitrogen (which doesn't expand with heat and anyone running expensive Pilot tires in Germany probably is as well), perhaps that is why they reccomend 42 psi?

More stuff to ponder...

nitrogen does expand with heat....

its still a gas and still follows P V = n R T

your pressure will increase the same amount for a given increase in temp. whether you use air or "pure" nitrogen (IIRC, you go from 78.5% nitrogen in regular air to about 88-93% with the special filling)
 
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