Tire sidewall math

[jarhead]

Hey everyone,
I am a little stumped on tire sidewall dimensions.

If a 295/40-18 has a 4.6 inch sidewall, does that mean the amount of tire showing is 4.6", or does it include the bead hidden in the wheel?

Thanks!

[dontlifttoshift]

An 18" wheel actually measures a little over 19" in diameter. Actual visible sidewall on that tire would be approximately 3.85" depending on rim design.

[jarhead]

Thanks Donny!

[71OLDS]

Hmmm those #s seem way too high in my opinion. I have found this:

https://tredwear.com/dealer-application/

to be very accurate.

Just plug in width mm (295) and Height % (40) and click on calculate - for any diameter (17, 18, 19 etc) a 295/40 tire your "usable" sidewall should be around 2.4"

For a sanity check since this is MUCH lower then what you guys are saying. Here's a pic of my old 305/45/18s w/1" tall glued on RWLs. If you plug in the 305 and 45 and calculate you will see it shows 3.15" Here's a close up:



If those letters are 1", I think 3.1" looks correct just eyeballing the pic and there's no way a 295/40 is going to be more than 2.5" of sidewall at the max.

-Joe

[dontlifttoshift]

A Falken RT660 295/40-18 has an overall diameter of 27.4"

Even if the face of an 18" rim measures 20" that still leaves 7.4"/2 = 3.7"

That calculator doesn't give you visible sidewall height It gives you available sidewall height on which you can put a sticker on successfully.

[WSSix]

You should also keep in mind that sizes aren't exact even though there's supposed to be math behind it all. For instance, not all 315's are the same width. I use Tirerack and Discount Tires website to check overall diameter of a tire I'm interested in to confirm it's what I am expecting. You'll also need to look at the tire and maybe read reviews if you're wanting a squared off look or a rounded look to the tread and sidewall intersection. It's a pain, lol.