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Discussion Starter #1
The TI Hatch with the 18" wheels and Michelin tires requires 39lbs of air pressure per tire (see the chart on the inside of the drivers door frame). That was a new one on me.

I tried 35 lbs in them today just for grins to see the difference and I immediately noticed more slop in the handling and more road noise. Most likely a reduction in mileage also.

Not sure for the sedan or the Hatch without the handling package.

Looks like I'll be doing lowering springs next. Probably the Eibach's.
 

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Good stuff. Our 17's say 35psi. Interesting on the 39 psi on 18's.
 

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39 is nothing special for a performance summer tire, my Potenzas called for 41PSI
 

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I talked to Michelin customer support about the 39PSI and he said it is critical to keep the Pilot Sport 3 at that PSI
 

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Discussion Starter #5
I talked to Michelin customer support about the 39PSI and he said it is critical to keep the Pilot Sport 3 at that PSI
Did he mention what factors make it "critical"?

I'm curious now, since every performance tire I've ever owned has called for 35psi. I've run Z-rated Pirellis, Goodyear Eagles, and several models of BFG and they all called for 35psi max.

I run BFG's on my Mustang at 32 just to soften the ride a bit, but even with a much heavier car and stiffer suspension they still call for 35lbs.
 

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I think it's possibly because of the 40 series sidewall. It will cause less deflection in sidewall and stop a pothole from possibly bending the wheel.
 

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You should be following the Ford recommended tire pressure, not the tire manufacturer. My Saab recommended 42psi front and 38psi rear... and the tires were all the same size.

Posted via FF Mobile
 

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You should be following the Ford recommended tire pressure, not the tire manufacturer. My Saab recommended 42psi front and 38psi rear... and the tires were all the same size.

Posted via FF Mobile
A difference in tire pressure front to read is done to help the care get closer to neutral handling. In my 3 Series, to help with oversteer I'd run the rears 3 pounds more than the fronts. So maybe the same situation with your SAAB.
 

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I think it's possibly because of the 40 series sidewall. It will cause less deflection in sidewall and stop a pothole from possibly bending the wheel.
Ding Ding Ding. Would not recommend lowering springs if you live in an area with potholes, you'll be replacing tires & rims.
 

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As the profile of a tire gets lower it's load carrying capacity goes down. So in general low profile tires require more air pressure than the same cross section in a taller profile. For example the numbers below are for the same model and rim size Dunlap SP tire.

225/55-17 1819 lbs
225/50-17 1653 lbs
225/45-17 1356 lbs

Lots of the low profile high performance tires are rated for more than 50 psi.
 

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Ding Ding Ding. Would not recommend lowering springs if you live in an area with potholes, you'll be replacing tires & rims.
why would lowering effect the wheels and tires if you hit a pot hole.... doesnt matter if you are 3 inches off the ground or 3 foot off the ground your tires and wheels stay in the same spot
 

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why would lowering effect the wheels and tires if you hit a pot hole.... doesnt matter if you are 3 inches off the ground or 3 foot off the ground your tires and wheels stay in the same spot
When you lower a car you let the body drop relative to the wheel center. This brings the upper suspension connecting point (shock top) down so you have less wheel travel from curb to full compression (jounce).

Less travel = less energy absorbed by springs/dampers = higher force once you hit full compression. [:0]
 

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Moved to "Wheels, Tires, Brakes & Suspension - Sponsored By Tire Rack"
 

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When you lower a car you let the body drop relative to the wheel center. This brings the upper suspension connecting point (shock top) down so you have less wheel travel from curb to full compression (jounce).

Less travel = less energy absorbed by springs/dampers = higher force once you hit full compression. [:0]
Well that sounds like stuff you learn beyond highschool.... I didnt make it that far...lol
 

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The best way to lower a car is to replace the steering knuckles with ones that position the hub higher. This way the suspension geometry is not effected and you do not loose jounce travel. The down side is you now have to take into consideration clearance because the tire will be further up in the fender at full travel.
 
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