understanding tyre sizes - caldina needs new rubber

[steve74]

hey guys. im currently running standard 15 inch wheels on my gtt caldina with 205/60/15 tyres. I have a set of 17 x 7.5 wheels but im unsure of what tyres to fit? My understanding is for every inch in wheel size you increase the first number by 10 and drop the second by 10.

so therefore

205/60/15 becomes 215/50/16 becomes 225/40/17

is this correct?

if not what tyres should i be running? what do you other caldina owners run?

[Mr.Phreak]

viewtopic.php?t=62515

Specifically the middle one

[postfach]

Tyre sizes go like this:

width/profile/wheel diameter

The profile is the sidewall height, and is a percentage of the tyre width.

If you want a tire for your 17" rims that has the same rolling diameter as your 15" rims, then:

Wheel Diameter =15" = 381mm
Sidewall Height = 205 x 0.6 = 123mm
Overall Diameter = 381 + 246 (123x2) = 627mm

New Wheel Diameter = 17" = 431.8mm
Sidewall Height = (Overall Diameter - New Wheel Diameter)/2 = (627 - 431.8 )/2 = 97.6mm

You probably want to use a tyre that will fit nicely on the rim, so you would pick a size close to the width of the rim, maybe slightly larger.

7.5" = 190.5mm

So, maybe use 195's, then to work out what profile, you would do:

Sidewall Height/Tyre Width = 97.6/195 = .501 = 50%

From that we have, Tyre Width (195) Profile (50) Wheel Diameter (17) = 195/50r17

[postfach]

Or, you could use this tool

http://www.miata.net/garage/tirecalc.html

[steve74]

ok, i used the tool, to keep them same outer diameter as standard i ended up with either

245/40/17 or 215/45/17

the 245 is probably a bit wide im guessing?

so i guess the 215 is my best option?


thanks for the links, i must have spent a few hours last night searching.

[postfach]

Yeah, 245 is 55mm wider than the rim, so way too big, 215 should work ok but it might look a little balloon-ish.

[85AW20v]

But then on 215's, there's probably no way that you'll ever curb your new rims

[Twolitre]

Nothing at all wrong with a 215 on a 7.5" rim
Sure it's not "phat stretched drift look" but this is a Caldina after all.
I'd go for the 215/45/17

[Lloyd]

As above. 215s are about right on a 7.5 width rim. I has 215s on a 7 inch rim and they were about perfect, low profile also. Price up a few options close to that size as prices can vary a lot between the perfect fit for you and a slightly different but much more common size

[sergei]

I have 225 on 7" rim and it looks fine.
Having slightly wider tyre than rim is fine, it is a problem when you run other way around.

[steve74]

Cheers guys, thanks for the help. i have seen some good deals on trademe, seems you can pay anywhere from $130 to $300 a tyre.

Ive seen some good deals on federals and some asain brands? and Mag and turbo currently have a tire deal on, not sure what brands but will look into it sooner rather than later. warrant due on the 15th.

[Twolitre]

Never heard a bad thing about Toyo T1-R's and not as expensive as some but still out of reach for most people but plenty of other tyre threads to search through on these forums.

[fuel]

it is a problem when you run other way around.

Says who?

[tsoob]

215/45/17 is perfect for a caldina, you could run a 225/40/18 or a 215/40/18 or 225/35/19 or a 225/30/20 if ya got the nuts to go that big haha.

[tsoob]

I have 225 on 7" rim and it looks fine.
Having slightly wider tyre than rim is fine, it is a problem when you run other way around.

haha rubbish, i have fitted a 205/40/17 onto a 9.5" rim, and regurlarly do it on a9" for adams BMW

[Bling]

Cheers guys, thanks for the help. i have seen some good deals on trademe, seems you can pay anywhere from $130 to $300 a tyre.

Ive seen some good deals on federals and some asain brands? and Mag and turbo currently have a tire deal on, not sure what brands but will look into it sooner rather than later. warrant due on the 15th.

I would stay away from those brands tbh. Sure you'll save some money now... but with winter coming you don't want to be rolling rubbish tyres in the wet. A good tyre is the difference between stopping and rear ending someone thats stopped suddenly in front of you.

Do a search on here for good tyre brands and go with quality.

[Mr.Phreak]

haha rubbish, i have fitted a 205/40/17 onto a 9.5" rim, and regurlarly do it on a9" for adams BMW

Just because you can, doesn't mean you should

[tsoob]

Cheers guys, thanks for the help. i have seen some good deals on trademe, seems you can pay anywhere from $130 to $300 a tyre.

Ive seen some good deals on federals and some asain brands? and Mag and turbo currently have a tire deal on, not sure what brands but will look into it sooner rather than later. warrant due on the 15th.

I would stay away from those brands tbh. Sure you'll save some money now... but with winter coming you don't want to be rolling rubbish tyres in the wet. A good tyre is the difference between stopping and rear ending someone thats stopped suddenly in front of you.

Do a search on here for good tyre brands and go with quality.

Yep you are dead right, give me a pm if you like ill quote up for you.

remember most of the time with trademe you have to pay to have them fitted and balanced as well, (costs $100 for a set of 17/18 inch rims)

[fuel]

Federal SS595s are a pretty decent price given the price of them, the 535 is the budget version to compete with NS-1s, Bridgestone MY-01s etc.

$100 is really on the steep side to fit and balance a set of tyres - I don't think I've ever paid more than $40 to do a whole set when I swap semi slicks onto my rims for the track.

[rollaholic]

yeah most tyre places round here seem to do them for 10 or 12 a rim