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Author Topic: So when going up a few sizes in tires do you need to change the PSI.  (Read 996 times)

Offline Zombie

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So when going up a few sizes in tires do you need to change the PSI.
« on: April 11, 2011, 03:56:15 pm »
So I went up a few sizes on tires. 205/50-R17 -> 235/45-R17.
The tires came mounted and pressured at the max for the tire, something like 50 psi.
I put them on, drove around for a bit, it felt nice and tight. Later I dropped the psi to the recommended 32.
The drop in pressure made a noticeable difference in driving feel.
Regardless do I always run the recommended PSI marked inside the door or do I have to go higher because the tires are wider?

Cheers Z
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Offline articsteve

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #1 on: April 11, 2011, 04:01:10 pm »
32 psi in 235/45/17  on rims meant for 205/50s  ???     Fine if you drive like a grandmother.

Me, I'd keep them at 40 psi minimum.   Max would be 44.      50 psi is too much. 
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Offline tpl

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #2 on: April 11, 2011, 04:09:46 pm »
The way I read Zombie's post:  "The tires came mounted and pressured at the max for the tire, something like 50 psi."   they are on appropriate rims.

But I do agree that 32 psi intuitively feels low.     38-40 seems right as long as the tread is flat across the width of the tire under load.
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Offline ktm525

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #3 on: April 11, 2011, 04:11:30 pm »
It's also tire dependant. For the first few weeks keep experimenting between drving feel/smoothness/sidewall rolling etc.

Some auto parts shops will sell a pad that will show the pressure of a tire tread to confirm under/over inflation.


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Offline Zombie

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #4 on: April 11, 2011, 04:28:57 pm »
No I want up from a 7" to an 8" rim.
So I was correct to assume I need to go up in pressure when you go up in size. Any rule of thumb?
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Offline tortoise

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #5 on: April 11, 2011, 04:29:10 pm »
"Paging Capiracer, Capiracer to the Tire Talk phone."
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Offline ktm525

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #6 on: April 11, 2011, 04:36:20 pm »
FWIW I like to run pressures just below where ride comfort is compromised. Works for me although if I notice abnormal wear (either center wear or even wear on the outer edges) then I will adjust accordingly.

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Offline Sir Osis of Liver

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #7 on: April 11, 2011, 04:38:33 pm »
Quote from: Zombie on April 11, 2011, 04:28:57 pm
No I want up from a 7" to an 8" rim.
So I was correct to assume I need to go up in pressure when you go up in size. Any rule of thumb?

I don't think that's correct for a couple of reasons. The higher the tire pressure, the smaller the contact area with the road. Over the long term, too high pressure will wear the centre line of the tire.

Most of the cars I've owned recommended somewhere handy to 32psi (220kPa). I would stick with the recommended tire inflation level on the door post.
« Last Edit: April 11, 2011, 09:34:47 pm by Sir Osis of Liver »
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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #8 on: April 11, 2011, 04:53:05 pm »
32 will save your rims.  I'd run 32, 45 if you are on the track for that extra stiff sidewall
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Offline Zombie

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #9 on: April 11, 2011, 05:05:48 pm »
Quote from: wing on April 11, 2011, 04:53:05 pm
32 will save your rims.  I'd run 32, 45 if you are on the track for that extra stiff sidewall

What if I run 32 front, 45 rear??

I think I actually currently have them set to 35 because 50 felt so good.
Well there was also the swapping out the winter tires nostalgia so maybe it is all in my head.
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Offline articsteve

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #10 on: April 11, 2011, 06:28:55 pm »
So I was correct to assume I need to go up in pressure when you go up in size. Any rule of thumb?

As the side wall shrinks the psi usually climb.

The 32 psi on the door frame is for the stock tire.  Most every manufacturer places a whimpy psi rating there so the "ride" is "nice".

Personally I would not enjoy aggressive turns running 32 psi with the resulting mushy sidewall.

What was the purpose for the wider rims and tires?  Looks  :)
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Offline vdk

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #11 on: April 11, 2011, 06:32:01 pm »
FWIW I run 38PSI
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Offline rrocket

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #12 on: April 11, 2011, 06:34:59 pm »
I'd run 36-38.  Or so.
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Offline EV Dan

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #13 on: April 11, 2011, 06:36:42 pm »
Depends on the make of your tires...
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..and wether you feel like calling a few (dozen) tire dealers and shops..
« Last Edit: April 11, 2011, 06:38:35 pm by DanYanoff »
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Offline ajay

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #14 on: April 11, 2011, 07:17:28 pm »
Look on the inside of your door - ( stays the same as far as I know )
OR
go 6 - 8 lbs less than max rating on the tire . ( 6 for better handling , 8 for better gas mileage )

OTHERWAY around oops
« Last Edit: April 12, 2011, 07:42:45 pm by ajay »
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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #15 on: April 11, 2011, 07:36:04 pm »
32 front 45 rear could make for some interesting handling
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Offline rrocket

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #16 on: April 11, 2011, 08:04:47 pm »
Quote from: wing on April 11, 2011, 07:36:04 pm
32 front 45 rear could make for some interesting handling

Formula Drift, baby!!
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CatsEye68

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #17 on: April 11, 2011, 08:14:16 pm »
But are they Hercules Tires G5000Z (235/45ZR17) tires? Perhaps you should call a number of dealers and ask about the pressures.
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Offline Zombie

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #18 on: April 11, 2011, 09:18:45 pm »
They are handkook ventus v12 EVO max performance tires.
The wider rims were to better accommodate wider tires.
I'm going for better handling but looks were part of the equation as well.
I'm just trying to figuere out what pressure I should run but I guess I'm just going to have to figure it out.
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Offline ajay

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Re: So when going up a few sizes in tires do you need to change the PSI.
« Reply #19 on: April 12, 2011, 03:37:18 am »
Winter is different from summer , don't forget that .

Zombie , I can ask my aftermarket wheel guy, he knows his stuff . You're running aftermarket rims ? What make etc and how much do they weigh ? 
   I have your tire info . Also it's a 08 wrx - went from a 7 to an 8 inch rim (17 inch)


« Last Edit: April 12, 2011, 06:16:23 am by ajay »
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