rim sizes?

[EZZY]

i had 18" in 1998. i was able to get it engineered because the gross weight of the car was over 1200kg (according to the engineer).
the speedo calibration test was about $60 back in the late '90s. have no idea what it's cost now.

[Zdster]

There is no need to have your speedo recalibrated just because you increase wheel size. Just use a tyre size calculator to determine the change in your speedo (http://www.miata.net/garage/tirecalc.html)

[EZZY]

There is no need to have your speedo recalibrated just because you increase wheel size. Just use a tyre size calculator to determine the change in your speedo (http://www.miata.net/garage/tirecalc.html)

if this was directed at me...
thats because i need to present the speedo calibration test report to the engineer, so a engineers cert can be issued.

[J-Rome]

I've got 18's on my EK. Where can I go to get an engineers certificate?(I'm in Northern NSW)

[EZZY]

check the RTA website, from memory there should be a list of RTA approved signatory engineers available to issue you an engineers cert.

[J-Rome]

LOL, well cars actually registered in QLD so i guess i gotta check the DOT site. Cheers mate

[OMG.JAI xD]

i heard it doesnt ma tter what rim size you have, as long as the diameter n width stay the same in ratio to your old one :/

lol .. apparently I AM the tyre guy .. doin evrythin myself .. got machine at work .. just need to know if itll fit right etc .. :/

[EZZY]

i heard it doesnt ma tter what rim size you have, as long as the diameter n width stay the same in ratio to your old one :/

you heard wrong....

[omgitsmatt]

so i bought 17s for my civic ( 4x100-114.3 ) but not sure what size tyres i should be looking at. ie ?/?/? if that makes sense

[EZZY]

205/40 or 215/40 (at the most)

[OMG.JAI xD]

can anyone tell me if 17x7 n 17x7.5 will change what tyres you get?

obviously theres gonna be some differences .. someone tell me .. i know all the diameter aspect ratio rim size details on tyres n sht.
just gotta know if it does matter what tyres are for which width :/

[SeverAMV]

only a small width would really limit what tyres you can get. most tyres can be stretched if theyre not far enough (this is a trick some people do over here to keep the tread under the guard to keep it legal). for 215-235, i dont think it would make much of a difference. for 245 and more, it would be noticeable.
just remember that contact patch only affects grip in wet weather, only the compound matters in the dry. wider tyres in the dry will only help it cool better, wont make it grip more (unless you're going from stretched to regular, then its noticeable in cornering).

@omgitsmatt - whats the width of the rim? should tell you on the inside.

@OMG.JAI xD - width generally doesnt matter, its more so the diameter of the tyre.

@Zdster - yup, dont need speedo recalibrated. all factory speedos are usually 2 degrees higher than the actual speed, so when your speedo reads 100, you're actually going 98 (a trick by car manufacturers to reduce the chance of collision). so if you bump up the rim size by the 2 inch rule, youll normally be getting your speedo spot on.