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The Tire Rack's Tire & Wheel Forum
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Old 12-01-2010, 02:28 PM   #21
DangerousMind
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Quote:
Originally Posted by MasterC17 View Post
That's exactly what I was thinking except 255/40's on the front - the same as what they came with from the factory except wider. Is there any reason they were taller in the front from the factory? Was it to compensate for the smaller diameter?



Thanks but I already have two sets so I think I'm good for the moment



I have 4 18x8.5 Rear ZHP Wheels. I have two mounted w/ 255/35/18's and two unmounted. I am proposing that I mount two 255/40/18's on the unmounted ones and put them in the front. Why not 255/35/18's? Because the factory had 40's in the front. What I'm confused by is why, and is it fine to do the same. Honestly, I can't afford another set of wheels and tires atm. I'll be selling my all-seasons and other wheels once spring comes. Unless I find a set of Apex 18's for $700 I'll be keeping the ZHP wheels.
The 40 is the sidewall aspect ratio, which is a percentage of the width in cm. A 225/40 is 225cm wide and the sidewall height is 40% of 225, or 90cm. A 255/35 is 255cm wide and the sidewall height is 35% of 255, or 89.25cm. A 255/40 would have a sidewall height of 102cm, resulting in a 1" taller tire and some serious rubbing issues with that width. 255/35/18 all around is the correct combo
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Old 12-01-2010, 02:41 PM   #22
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Originally Posted by MasterC17 View Post
I am proposing that I mount two 255/40/18's on the unmounted ones and put them in the front. Why not 255/35/18's? Because the factory had 40's in the front.
WOW


You realize the second number is a ratio of the tire width.

225/40 = 90mm
255/35 = 89.25mm

255/40 = 102mm


That's why. You want to track your car and you don't even know the basics on how to read tire sizes?
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Old 12-01-2010, 03:10 PM   #23
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Originally Posted by DangerousMind View Post
The 40 is the sidewall aspect ratio, which is a percentage of the width in cm. A 225/40 is 225cm wide and the sidewall height is 40% of 225, or 90cm. A 255/35 is 255cm wide and the sidewall height is 35% of 255, or 89.25cm. A 255/40 would have a sidewall height of 102cm, resulting in a 1" taller tire and some serious rubbing issues with that width. 255/35/18 all around is the correct combo
Thank you, I understand now.

Quote:
Originally Posted by Penguin Koolaid View Post
WOW


You realize the second number is a ratio of the tire width.

225/40 = 90mm
255/35 = 89.25mm

255/40 = 102mm


That's why. You want to track your car and you don't even know the basics on how to read tire sizes?
Sorry, completely forgot it was a ratio rather than a measurement. I never quite understood the second number. I do and have known what the first and third numbers mean, my bad. Should have gone and looked. /thread

Last edited by MasterC17; 12-09-2010 at 02:21 PM.
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Old 05-12-2011, 02:25 PM   #24
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Well, this seems like the perfect place to ask my question, as it pertains to the ZHP wheels:

Current setup:

Rear fenders rolled

18x8 F
225/40/18

18.8.5 R
255/35/18

My question is, how much of a stretch do I need if I plan on dropping the car on either H&R Sport springs or on Eibach Sportline springs? (I realize they both have different drop specs, so let's air on the side of caution and go conservative)

I currently have 10mm F and 15mm R spacers, and I would like to push to 15 mm F and 25mm R, giving me an approximate ET of about 32F an 26R

How much of a stretch do I need to get basically flush? I was thinking of going with 225/40/18 in the back, but have no idea what size to get for the front (215/40/18?)

Any help is GREATLY appreciated!
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Old 05-13-2011, 09:23 AM   #25
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^^Anyone?

Want to try and get my answer in here as opposed to starting a new thread
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Old 05-13-2011, 10:22 AM   #26
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Originally Posted by DJ Reminisce View Post
giving me an approximate ET of about 32F an 26R
18x8 225/40R18 et32 Front when dropped will have no issues.

18x8.5 255/35R18 et26 Rear when dropped should be okay if you roll your fenders and dial in a tad more negative camber.
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Old 05-13-2011, 10:32 AM   #27
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Originally Posted by Penguin Koolaid View Post
18x8 225/40R18 et32 Front when dropped will have no issues.

18x8.5 255/35R18 et26 Rear when dropped should be okay if you roll your fenders and dial in a tad more negative camber.
Thanks man

I really thought the tires in the front would have an issue with the stock tire size?

In regards to the rears, I already have my fenders rolled, but was told that if I wanted to get to et26, I'd have to get a small stretch? Ideally, I'd love to keep as much rubber to the road as possible, but would LOVE to get the rims to sit almost flush.

So basically, you're saying my stock tires should clear even if I drop? What is the most negative camber I can run in the rear with the stock components, -2?

Thanks so much for the reply man, I'm putting together my final suspension list as we speak, and since I need to replace my tires soon, I'll probably do those shortly after

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Old 05-13-2011, 10:32 AM   #28
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^ You sure about that? When I had the ZHP, I had some rubbing in the rear with 18x8.5 ET35 running on 235 width tires. Rear camber was -2.1 iirc. I had a minor drop (maybe .75"). I don't think I would've been able to push it out another 9mm and put on a wider tire.

I do agree that the front would be fine.
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Old 05-13-2011, 10:43 AM   #29
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Originally Posted by Penguin Koolaid View Post
18x8 225/40R18 et32 Front when dropped will have no issues.

18x8.5 255/35R18 et26 Rear when dropped should be okay if you roll your fenders and dial in a tad more negative camber.
Quote:
Originally Posted by TerraPhantm View Post
^ You sure about that? When I had the ZHP, I had some rubbing in the rear with 18x8.5 ET35 running on 235 width tires. Rear camber was -2.1 iirc. I had a minor drop (maybe .75"). I don't think I would've been able to push it out another 9mm and put on a wider tire. I do agree that the front would be fine.


I wasn't planning on getting anything wider, those are my stock tire sizes. If anything, I thought I'd need a stretch to like 225 in the back to get em to fit. Did you have your fenders rolled?

Thanks for your feedback everyone! I only have one chance to get this right when I buy tires lol
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Old 05-13-2011, 01:27 PM   #30
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Looks like I'll need to create a separate thread for this topic to get some more input lol
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Old 10-01-2011, 11:27 PM   #31
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Originally Posted by MrMotorwerk View Post
Get 4 ZHP rear wheels and run 255/35/18. That would be the best setup.
Kris runs this setup on his ZHP sedan.
Little bit of a thread revival, but do the fronts need spacers with the rear ZHP 18.5 rears on them? I'm looking to go square with 4 rears all the way around.
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Old 01-15-2013, 05:36 PM   #32
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Another thread revival here.

I've only had my ZHP for 3 days now but I can see I'd probably like to increase the tire size to fix the speedo error (reads faster than I'm actually going) and also to get more cushion under me for a slightly more civilized ride. I know some wise guy will probably pipe up that I should not have got a ZHP if I don't like race mode. Well, there is so much to like about the ZHP, I don't see any harm tweaking a little.

So here's my idea. When I get new tires I go from:

Fronts Rears
225/40/18 255/35/18

to

225/45/18 255/40/18


I do not believe that change will confuse the DSC. It will increase actual speed by about 4%.

How does this sound? Has anybody did it?

Last edited by Dave1027; 01-15-2013 at 05:37 PM.
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Old 01-15-2013, 05:57 PM   #33
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Why do people put taller tires up front?mine is setup that way just never knew why.

Does it just provide better grip when the tire rolls?
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Old 01-15-2013, 06:01 PM   #34
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Originally Posted by HBizzo88 View Post
Why do people put taller tires up front?mine is setup that way just never knew why.

Does it just provide better grip when the tire rolls?
If you are asking about the ZHP in particular, they are not taller in front. Even though they have 40s in the front and 35s in the rear they are still the same overall height.
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Old 01-15-2013, 06:04 PM   #35
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If you are asking about the ZHP in particular, they are not taller in front. Even though they have 40s in the front and 35s in the rear they are still the same overall height.
Just in general. Why not 40's all around. Typically I see 35's in front and 30's on the rear. Just wondering the reason behind that.
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Old 01-15-2013, 06:12 PM   #36
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It's because if you go 40 all around and go wider in back then the back 40s will be taller than the fronts and would roll at a different rate making the DSC throw an error. It's because the 40 number is not the height measurement but the ratio. This is why the 225/40/18 is the same height as the 255/35/18.

Look at this converter http://www.discounttire.com/dtcs/infoTireMath.dos
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Old 01-15-2013, 06:19 PM   #37
HBizzo88
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Originally Posted by Dave1027 View Post
It's because if you go 40 all around and go wider in back then the back 40s will be taller than the fronts and would roll at a different rate making the DSC throw an error. It's because the 40 number is not the height measurement but the ratio. This is why the 225/40/18 is the same height as the 255/35/18.

Look at this converter http://www.discounttire.com/dtcs/infoTireMath.dos
Interesting, thanks!
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