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Old 08-28-2009, 06:18 PM   #1
kman25i
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Default New wheels and tires. Correct pressure

I got Enkei rpf1 17x7.5 with Hankook Ventus V12 Evo 225/45 rubber from Tirerack.

I'm putting them on tomorrow morning on a stock 2010 2.5i impreza hatch. They are inflated obviously and I emailed Luke but he didn't get back to me.

What should they be inflated to front and back for normal daily driving.

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Old 08-28-2009, 06:33 PM   #2
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I have a performance biased view on this subject.

With that removed for the moment, the best input I have is to start on the high side of the mid-30's and work down 1 psi at a time.

38/36, 36/35, 35/33, 35/32, 34/32 ( Examples only )

Any of those combinations F/R would be fine for daily driving on that tire. Play with it and find what works for your tastes.

I personally recommend having the rear lower by 2-3 psi, but that's just me. I run 45/42 cold, but I would not attempt that on your setup.

One more opinion in a sea of too many.

Travis

Last edited by UFOpilot; 08-28-2009 at 06:34 PM. Reason: Addendum
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Old 08-28-2009, 07:50 PM   #3
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I'll try that thanks.
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Old 08-28-2009, 09:58 PM   #4
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As long as it doesn't exceed the max pressure stated on the tire.

I forgot to mention that part.

Travis
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Old 08-29-2009, 09:51 AM   #5
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Quote:
Originally Posted by UFOpilot View Post
I have a performance biased view on this subject.

With that removed for the moment, the best input I have is to start on the high side of the mid-30's and work down 1 psi at a time.

38/36, 36/35, 35/33, 35/32, 34/32 ( Examples only )

Any of those combinations F/R would be fine for daily driving on that tire. Play with it and find what works for your tastes.

I personally recommend having the rear lower by 2-3 psi, but that's just me. I run 45/42 cold, but I would not attempt that on your setup.

One more opinion in a sea of too many.

Travis
My rule of thumb is:

Use 80-85% of the max inflation as listed on the tire sidewall as a start with 2-4PSI differential front (higher) to rear (lower).
More differential allows the rear to get loose easier, less differential tends towards understeer.
Adjust all 4 tires to give the ride you desire.

If you look at the OEM Potenzas and apply my "rule" you get the numbers listed in the owners manual.
But, on a different tire (like Pirelli P-zero Nero like mine) the "owner manual pressures" make the tire too soft.
Using the 80-85% rule gives the sidewall more support and is closer to their design specs.
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Old 08-29-2009, 02:55 PM   #6
kman25i
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Ok just finished putting them on. We measured the pressure before we put them on and they were at 35psi (all of them). With them on the car the front tires look "flatter" than the rear.

Now how do I go about inflating them to the recommended psi? I'll start with 38/36 and see how that goes. I've heard people mention cold pressure so does that mean I have to get up at 4am or something and go to a gas station and do it then?
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Old 08-29-2009, 04:27 PM   #7
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....simply adjust them in the morning or before you first drive the car for the day (when they are relatively cool). However, if you park it outside consider the fact that if one side of the car is facing the sun, the pressures on that side may show a variance (increase) as compared to the others that were shaded. ....in other words, if you adjust pressures at that point, they may be off once you begin driving (when all of the tires start to get up to operating temp).
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Old 08-29-2009, 04:45 PM   #8
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Quote:
Originally Posted by Kean View Post
....simply adjust them in the morning or before you first drive the car for the day (when they are relatively cool). However, if you park it outside consider the fact that if one side of the car is facing the sun, the pressures on that side may show a variance (increase) as compared to the others that were shaded. ....in other words, if you adjust pressures at that point, they may be off once you begin driving (when all of the tires start to get up to operating temp).
+1

Tire pressure changes ~1PSI for every 10*F in change in temp.

In the summer, checking with an ambient temp of say 65*F is fine, mid winter up north the ambient temp may be 30*F.
The pressure change/*F is still the same.
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Old 08-30-2009, 09:27 AM   #9
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Thanks for all the help everyone. I got up at 7am and checked all the ties. They were all at 31 psi. I drove to the Shell 1k down the road and put 36 front 34 back in there.
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Old 08-30-2009, 05:03 PM   #10
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Hopefully you are enjoying your car. Pressure is a great fine tuning tool.
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Old 08-31-2009, 02:47 AM   #11
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Quote:
Originally Posted by Charlie-III View Post
My rule of thumb is:

Use 80-85% of the max inflation as listed on the tire sidewall as a start with 2-4PSI differential front (higher) to rear (lower).
More differential allows the rear to get loose easier, less differential tends towards understeer.
Adjust all 4 tires to give the ride you desire.

If you look at the OEM Potenzas and apply my "rule" you get the numbers listed in the owners manual.
But, on a different tire (like Pirelli P-zero Nero like mine) the "owner manual pressures" make the tire too soft.
Using the 80-85% rule gives the sidewall more support and is closer to their design specs.

just curious where you found this info? if this is true, then my previous few tires would/should be 40+psi each according to this rule.
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Old 08-31-2009, 10:31 AM   #12
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A percentage rule can't be applied. Some tires have large max PSI, others not so much. For example my RE-01R's say max 40.
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Old 08-31-2009, 08:48 PM   #13
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Originally Posted by wrxSIN View Post
just curious where you found this info? if this is true, then my previous few tires would/should be 40+psi each according to this rule.
Which tires do you have that are over 60 psi max pressure, and what valve stems did you get to run those ? Holy **** that is a lot.


Quote:
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A percentage rule can't be applied. Some tires have large max PSI, others not so much. For example my RE-01R's say max 40.
Yeah, my R1R's are 50 psi max, which by the 80-85% rule would put the "sweet spot" at 40 and 42.5 respectively for low and high end. They actually run really nice at 45/42. I must say though that I did the calculation at 85% on several max pressure amounts from the last few sets of tires, and it was pretty close to what I was running, or at least within fine tuning range. Also at 85% your REO1R's would be 34 psi. I would guess it's within a few psi of where you run them. I am not validating the system, as I have a different method, just stating it seems to be in the ballpark.
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Old 08-31-2009, 11:41 PM   #14
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Quote:
Originally Posted by UFOpilot View Post
Which tires do you have that are over 60 psi max pressure, and what valve stems did you get to run those ? Holy **** that is a lot.




Yeah, my R1R's are 50 psi max, which by the 80-85% rule would put the "sweet spot" at 40 and 42.5 respectively for low and high end. They actually run really nice at 45/42. I must say though that I did the calculation at 85% on several max pressure amounts from the last few sets of tires, and it was pretty close to what I was running, or at least within fine tuning range. Also at 85% your REO1R's would be 34 psi. I would guess it's within a few psi of where you run them. I am not validating the system, as I have a different method, just stating it seems to be in the ballpark.
40+psi = 50psi max.
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Old 09-01-2009, 12:22 AM   #15
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Quote:
Originally Posted by UFOpilot View Post
Also at 85% your REO1R's would be 34 psi. I would guess it's within a few psi of where you run them. I am not validating the system, as I have a different method, just stating it seems to be in the ballpark.
It's true. I like them at 35/32...
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Old 09-01-2009, 12:45 AM   #16
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Quote:
Originally Posted by wrxSIN View Post
40+psi = 50psi max.
....max cold pressure.
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Old 09-01-2009, 08:52 AM   #17
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Quote:
Originally Posted by wrxSIN View Post
just curious where you found this info? if this is true, then my previous few tires would/should be 40+psi each according to this rule.
It's a rule I just came up with over the years.
Partly from looking at "owners manuals tire pressures" vs sidewalls, partly from doing my own tire pressure tuning.

I have seen too many times people go from, say, a RE-92 to a Pirelli P Zero Nero and run the stock tire pressures.
On the RE-92 it has a max inflation of 44 (IIRC) vs the Nero max inflation of 51.

Using the original tire pressures leaves the Nero way too soft and people complain about the handling.

I run my Nero's @ 46 front 44 rear for daily driving.

Sooo.......my "80-85%" rule gets you reasonably close, adjust to taste. Just don't use the tire pressures listed in the manual once out change out tires to something different (or even changing rim diameters).
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Old 09-01-2009, 07:12 PM   #18
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Quote:
Originally Posted by wrxSIN View Post
40+psi = 50psi max.
Ah, right. Like my R1R's, 85% = 42.5 I did "quick math" estimating in my head, and obviously, my head sometimes doesn't work right.

I actually do run mine at 45/42 cold, and with -2.5 front camber I get right into the little indicator on the top of the sidewall.
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