Having bigger tyres = speedo reading correctly?

sublime19 · Post by **sublime19** » Wed Jun 21, 2006 6:21 pm

Gonna buy 18" rims soon, and somebody told me I gotta make sure my new tyres won't cause my speedo to read incorrectly,
anybody know of ways of making sure it doesn't give the incorrect speed?

I'm sure this is something that's overlooked often cos most people I mentioned it to didn't even know about it

FTO338 · Post by **FTO338** » Wed Jun 21, 2006 6:32 pm

Mr President show us a website on it before, but i don't have the link on this computer. So you just have to wait till he reply.

But yeah if you don't have the correct size tyres, it would be out by a fair bit. You still be out but only 1-2kmph

khunjeng · Post by **khunjeng** » Wed Jun 21, 2006 6:34 pm

there was a link I posted a while back they had an aplet for claulating your tyre size based on stock rim/tyre size. serach for that somewhere.

juts in essence...18s will require 40 profile i assume.

rnbboi · Post by **rnbboi** » Wed Jun 21, 2006 8:41 pm

u guys must be referring to this site

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

im out by 2 kmph with my current setup...

Post by **Bennoz** » Wed Jun 21, 2006 11:41 pm

Thats the one ^

sublime19 · Post by **sublime19** » Thu Jun 29, 2006 4:14 pm

I just want to verify something:

According to the site - If I get 215x35R18 with 18" will this be the best setup for my speedo to read the speed correctly?

Is the reading of the speedo based purely on which type of tyres are used when getting 18"?

Post by **Bennoz** » Thu Jun 29, 2006 11:30 pm

sublime19 wrote:I just want to verify something:

According to the site - If I get 215x35R18 with 18" will this be the best setup for my speedo to read the speed correctly?

Is the reading of the speedo based purely on which type of tyres are used when getting 18"?

No, its based on the tyre size - diametre to be specific. the '35' series is the tyre height there, a '45' series would be larger & throw your speedo out etc

sublime19 · Post by **sublime19** » Thu Jun 29, 2006 11:47 pm

Ahh i c.. well I used that calculater, and when my speedo reads 100, i'll actually be doing 101.3

Now if this really is the case with 215/35 then my problems are solved

Thanks for clearing that up as always Ben!

Damn I gotta find a Q that you DON'T have an answer to one of these days

Post by **Bennoz** » Thu Jun 29, 2006 11:49 pm

35 series is what I should have gone for on my 18's... they wont rub. I went with 45's & they rub & my speedo is out!

downside is - it'll be a rougher ride....

sublime19 · Post by **sublime19** » Thu Jun 29, 2006 11:55 pm

Hmm so does that mean your speedo is out by about 6 - 8 K's

Post by **Bennoz** » Fri Jun 30, 2006 12:09 am

Not quite that bad... by my estimates about 3-4kms

sublime19 · Post by **sublime19** » Fri Jun 30, 2006 12:14 am

ah ok i was going by the calculator thingo

Post by **Bennoz** » Fri Jun 30, 2006 12:17 am

Also gotta factor in manufacturer variance. Most of the time your doing 60 on stock wheels your actually doing 57 or 58 etc... so I spose you'd be right with 7-8 kms!

sublime19 · Post by **sublime19** » Fri Jun 30, 2006 12:27 am

ahh.. well I'll stick to 35, safest bet for me

By the way, I was talking about this to some guy at work, about buying new rims and my speedo readin incorrectly and he goes "just get a white marker and put lines where your car hits 40 ks, 60ks etc"
and im thinkin to myself "riiiiight... it's not like my speedo is gonna flip upside down, it'll still read the same!"

sublime19 · Post by **sublime19** » Fri Jun 30, 2006 9:49 am

I just noticed the rims I want are 18*7.5 ... not 18*8 aghh... why must there always be problems!!!!
can i still use 18x8" 215x35R18?

bobz · Post by **bobz** » Fri Jun 30, 2006 10:04 am

Well Michelin on their web site recommend a rim betwee 6.5 and 7.5 inches wide for their 215 tyres.

So the rims your thinking of buying should be OK.

BobZ

sublime19 · Post by **sublime19** » Fri Jun 30, 2006 3:17 pm

bobz wrote:Well Michelin on their web site recommend a rim betwee 6.5 and 7.5 inches wide for their 215 tyres.

So the rims your thinking of buying should be OK.

BobZ

thanks for that BobZ, I just dont wanna do my research, show up there and get a different tyre size which totally puts me off my speedo!

sublime19 · Post by **sublime19** » Sun Jul 02, 2006 9:56 pm

well looks like i was worrying for nothing, got 215/35 with my new rims w00t!

1600 = paid extra for Kumho tyres i'll post a pic when i can find my stupid digital camera