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Old 11-24-2010, 06:06 PM   #1
vicious_fishes
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Member#: 158864
Join Date: Sep 2007
Location: Aussieland
Vehicle:
2003 GD w/EZ30 swap

Default tyre profile and handling

hi everyone,


i'm about to/thinking about moving tyre/wheel sizes to a smaller wheel but fatter tyre/taller profile. my question for all the nasioc'ers out there is how much of a difference did you notice moving between profiles (say from 16 to 17 inch wheels or, whatever) and what profiles did you move to.

for the record, i'm going from a 215/45 17 (3.8 profile) to a 245/45 16 (4.3 profile) and i'm just a little concerned if this is going to cause me squishy sidewall (or whatever) issues.


thanks in advance for all replies.
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Old 11-24-2010, 07:21 PM   #2
Back Road Runner
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Member#: 60082
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Chapter/Region: MWSOC
Location: Minnesota
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2004 Forester STI
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Flex has a lot to do with tire design. Size alone isn't going to tell you how a tire responds. Even of the same model, different sizes may be designed differently to maintain certain goals. Since you are very likely looking at a summer tire when you're looking at that size, you will already be getting a product that has relatively little flex. In fact I often suggest looking at upgrading suspension bushings too given the relatively high amount of squish they have in the system relative to a sport tire. If you're running a 205/70/R16, most of the flex you feel is from the tire. If you're running a 245/40/R17, most of the flex you feel are from the various bushings in the suspension and steering systems. Heck, even chassis flex starts to become noticeable because these sport tires are so firm.

Two suggestions:
1) Run higher tire pressures. A lot of the tires I've run on my car seem to be more ideal near and around 40psi. Depending on the tire, this may or may not be a sizable factor.
2) If squish is seriously important to you, you should start looking into upgrading the various rubber bits of the car. Grab an ALK for the front to upgrade the front arm suspension bushing. Upgrade the steering rack bushings to keep the rack in place under harder corner loads. These two part do a whole lot to really lock down the front end. Upgrade the rear lateral links and trailing arms to lock down the rear end. If you plan to or have upgraded the suspension, firmer tophats or a swap to camber plates might be useful. You can even start looking at chassis bracing as a final step to the process by getting at least a rear strut tower brace and front fender braces. All of these things really solidify the chassis and handling turning the car into a very responsive and very precise device rather than the mush lump of dough it is in stock form.
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Old 11-24-2010, 09:42 PM   #3
vicious_fishes
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2003 GD w/EZ30 swap

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Quote:
Originally Posted by Back Road Runner View Post
Flex has a lot to do with tire design. Size alone isn't going to tell you how a tire responds. Even of the same model, different sizes may be designed differently to maintain certain goals. Since you are very likely looking at a summer tire when you're looking at that size, you will already be getting a product that has relatively little flex. In fact I often suggest looking at upgrading suspension bushings too given the relatively high amount of squish they have in the system relative to a sport tire. If you're running a 205/70/R16, most of the flex you feel is from the tire. If you're running a 245/40/R17, most of the flex you feel are from the various bushings in the suspension and steering systems. Heck, even chassis flex starts to become noticeable because these sport tires are so firm.

Two suggestions:
1) Run higher tire pressures. A lot of the tires I've run on my car seem to be more ideal near and around 40psi. Depending on the tire, this may or may not be a sizable factor.
2) If squish is seriously important to you, you should start looking into upgrading the various rubber bits of the car. Grab an ALK for the front to upgrade the front arm suspension bushing. Upgrade the steering rack bushings to keep the rack in place under harder corner loads. These two part do a whole lot to really lock down the front end. Upgrade the rear lateral links and trailing arms to lock down the rear end. If you plan to or have upgraded the suspension, firmer tophats or a swap to camber plates might be useful. You can even start looking at chassis bracing as a final step to the process by getting at least a rear strut tower brace and front fender braces. All of these things really solidify the chassis and handling turning the car into a very responsive and very precise device rather than the mush lump of dough it is in stock form.
thanks a lot. handling mods are rear chassis X brace, RCE yellows/sti struts, front strut brace, rear strut brace, front fender brace, alloy LCA's.

what you're trying to say though, is that tyre deformation shouldn't be too much of an issue? i.e uneven contact patch etc.

i was already planning on upping the pressures - something along the lines of 38F, 35R psi i imagine should do the trick.
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Old 11-25-2010, 07:43 AM   #4
vicious_fishes
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Location: Aussieland
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2003 GD w/EZ30 swap

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any other users report their experiences?
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Old 11-25-2010, 08:11 AM   #5
sniper1rfa
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Member#: 141040
Join Date: Feb 2007
Chapter/Region: NESIC
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Tire deformation will not be a major problem with those. It will be more than the 17's, but not enough to worry about and certainly not enough to make the swap worthless.
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Old 11-25-2010, 06:12 PM   #6
sc00by4life
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What wheels do you currently have. a 215 to a 245 is a big jump.
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