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View Full Version : upgraded to 18's - make more changes?



Weejie
01-10-2005, 06:10 PM
i just got some 18's - but it seems like my speedometer is all whacked. i'm wondering if going from the oem 16" 5-spoke from my '96 to an 18 with 225 40's will alter the speed read-out.

is there something i need to do to fix that?

JMG
01-10-2005, 06:20 PM
it shouldn't be that huge of a problem considering low profile tires should keep the rolling diameter pretty close.

infinity20k
01-10-2005, 06:24 PM
Were do you go to change it? or how do you change it yourself

Weejie
01-10-2005, 06:31 PM
i could have changed it myself, but i had a local tire shop do it. infinity, you and i live where the snow flies. i just didn't feel like sitting out in the snow and freezing my a$$ off...

Weejie
01-10-2005, 06:32 PM
my bad - you're probably talking about changing the speedo, huh...??

HotSauce
01-10-2005, 06:47 PM
I believe there is a pinion gear that needs to be changed, to correct the speedo, for different diameter tires.

Kruat
01-10-2005, 06:50 PM
But the overall tire size is the same. It must be something else, put the 16's back on and see if that fixes it.

infinity20k
01-10-2005, 06:52 PM
ya man but thats kool ya its to cold to do anytihng outside

Weejie
01-10-2005, 06:52 PM
again - it's nothing too dramatic. it just feels like i'm going faster than i probably am. speedo says 65 but it feels faster. i'll run it until mr. occifer pulls me over with tickey tickey

WatchMeFlyBy
01-10-2005, 07:03 PM
shouldnt make that much of a difference..maybe a couple mph either way at most.. I went from 16" to 20" on my infinity Q45 and i never had any problems... like JMG said... the lowpros should even it out fairly close enough...
AL

AudiMV
01-10-2005, 09:01 PM
http://www.miata.net/garage/tirecalc.html

HAVE FUN.......

Chard
01-10-2005, 09:28 PM
darn, u beat me to it. i was going to post up that link.

you'll be surprised at how different the sizes are, even taking into account the lower profile tires.

Easy way to tell... I can fit my 17" S4 rim in my spare wheel well but not my 19" spare. Also, stand your 16 next to your 18 and you'll see that the 18 is significantly taller. It doesn't mess with your speedo that much though. Should be around a few MPH slower than you are actually going.

Fartsniffer
01-11-2005, 10:06 AM
it'll mess with your speedo and its also an arguement you can use to fight a speeding ticket, i did it once.
you just have to go to a shop that specializes in speedos and get it calibrated.

Weejie
01-11-2005, 12:04 PM
Originally posted by AudiMV
http://www.miata.net/garage/tirecalc.html

HAVE FUN.......

thanks for the link. i guess it's not much of a difference after all. good to know.