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Discussion Starter · #1 ·
Long time ago I replaced the OE 17-inch wheels and 205/45R17 tires with a set of 16-inch König wheels and 225/50R16 General tires; kept them at the 29 PSI recommended on the door jam.

I recently came across this tire pressure calculator: Tire Pressure Calculator

According to this calculator, I am currently over-inflating my tires:
  • OE tires: 205/45R17; recommended PSI = 29
  • Current tires: 225/50R16; recommended PSI = 22

Does 22 PSI sound correct for a wider, taller tire?
 

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22 sounds rather low for a modern tire that's not being used in a 4wd all terrain IMHO.
 
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Discussion Starter · #3 ·
Yeah, 22 PSI does seem low, doesn’t it.
 

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Hi "Aldo Lad"....SteveP and I had a good chat about this subject very recently....the conclusion was that 29 psi "IS" the correct tyre pressure for the 124 Spider as no matter what the circumstances are your volume of required air for normal driving conditions for our car remains constant. Yep, the air pressure is raised in a fully loaded tin box car or when winterised and left standing but 29 psi is the baby. Some guys..."Young "Arthur" for one have happily driven at 32 psi for years in their Spider and got mega- miles out of the tyres, so little wear effect, but at 22 psi so well under inflated...I don't think so Mate, Cheers
ron
 
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To know the real answer you need to know the weight on each axle. I haven't weighed my Spider, but it is stock and the weight doesn't vary much when loaded vs. unloaded.
My GTI on the other hand can carry 4 people and luggage vs. just me. The tire pressure on the doorjamb is for a fully loaded vehicle, not a lightly loaded one. So, I weighed the car, front axle, rear axle, whole car. Then I consulted a tire load chart I found online. With the Load Index (92) in this case and the axle weights (2015#F, 1520#R) I came up with 29psi Front and 21psi Rear versus the door sticker of 37psi F/R. I thought 21psi too low and wanted some margin for adding a passenger or two, so I settled on 33F/25R as a safe compromise. And the ride is much better than 37F/37R.

With your axle weights and tire Load Index (on the sidewall) I can look up recommended pressures. I printed out the tire load chart years ago and cannot find it online.

Mike
 

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Discussion Starter · #6 ·
Aight, you guys convinced me: 29 PSI it is.
 
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