Tire size calculator?

[Danjam]

Sorry if this has been covered before, but I can’t find my exact situation through searching. I have a 2018 Civic Si sedan on Eibach Pro Springs and have ESR SR06 18x8.5 +30 on the way. I thought the stock tires might fit without rubbing, but now that it’s lowered, doesn’t look like it. Does someone know of an online tire calculator that I could use to see what tires I need. Now I’m also wondering if I should have gone 18X9.5 +35 instead.

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[arpypat]

https://www.willtheyfit.com/

 

[arpypat]

If you want to know the math, the offset calculation is taken from then centerline of your wheel to it's mounting hub face. 0 offset would be the centerline is inline with the hub face. Positive offset means the hub face is closer to the outer edge of the rim. Negative offset means the hub face is closer to the inner edge of the rim.

The Si OEM wheel is 8" wide with offset of +50

Your 8.5" wheel is 0.5" or 12.7mm wider than OEM. The outer edge of the rim to the centerline would be 6.35mm closer to your fender if the new wheel offset was +50, but since it's +30 (more negative) your new wheel is now 26.35mm closer to your fender.

The same math on a 9.5" +35 wheel:
1.5" (38.1mm) wider
15mm more negative offset

(38.1/2) + 15 = 34.05mm closer to fender

20-25mm closer to the fender is what you want to shoot for if you want to be flush with the fender. Anything more than that will be poking out past the fender.

 

[justasimpleman]

Since we’re talking about this...

Anyone know the stock offset on 2020 ex wheels?

I’m upgrading soon to 18x8 40 offset with 235/40 18. I’m assuming there won’t be an issue.

 

[jayy_swish]

Since we’re talking about this...

Anyone know the stock offset on 2020 ex wheels?

I’m upgrading soon to 18x8 40 offset with 235/40 18. I’m assuming there won’t be an issue.

Offset will not be an issue, but check to see your speedometer error % compared to stock

 

[jayy_swish]

Sorry if this has been covered before, but I can’t find my exact situation through searching. I have a 2018 Civic Si sedan on Eibach Pro Springs and have ESR SR06 18x8.5 +30 on the way. I thought the stock tires might fit without rubbing, but now that it’s lowered, doesn’t look like it. Does someone know of an online tire calculator that I could use to see what tires I need. Now I’m also wondering if I should have gone 18X9.5 +35 instead.

Go 255/35r18 won’t have any issues. It’s what I run and I’m on sportline springs. And will have almost basically no speedometer error (-1 or -2 mph off max, but that’s at high speeds). I had the same stock Sport wheels: 235/40r18 on 18x8 +50.

 

[justasimpleman]

Offset will not be an issue, but check to see your speedometer error % compared to stock

Thanks dude! Looks like it will be a very minor difference, which I’m not worried about.

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