St185 gt4 - rims - 17 inch - what profile tyre

**-==L=a=N=c=E==-** · 31-01-2006, 04:27 PM

Originally Posted by UMP-man

how do u calculate this speedo accuracy thing.
i've got 225/45s on a 17x7" wheel.
could someone tell me how far out my reading might be?

Use this link
http://www.miata.net/garage/tirecalc.html

Stock tire size is 215/50/15
Your tire size is 225/45/17

Your speedo is out by 6.4%, so when your doing 100km/h your actually doing 106,4km/h

Ticket country *shudders*

**UMP-man** · 31-01-2006, 05:28 PM

another reason why i should put my 16s back on.
when i had my 16s on my speedo was only 2.6% out.

**SilverGhost** · 31-01-2006, 06:01 PM

im running 225/40/18's on my 185, not sure what the load rating is but i remember it being around 560kg so that must make it 88.

speedo wise im doing 104 with my speedo sitting on 100

**Classique71** · 01-02-2006, 12:35 PM

Anyone have an idea on the cost to get a speeedo recalibrated ?

**-==L=a=N=c=E==-** · 01-02-2006, 01:39 PM

Originally Posted by Classique71

Anyone have an idea on the cost to get a speeedo recalibrated ?

Permanent pen $5

OR

You can get a speedo calibration kit from jaycar. Wire it in, and then adjust the little dials the percentage the speedo is out by.

**Aust162** · 01-02-2006, 03:19 PM

speedo recalibration can be pretty expensive. i had a rough quote of between $90-220

Once you know how far out it is you will remember it

Most dyno's tell you the speedo reading, so at your next stage of mods (dyno) you will know.

**Classique71** · 02-02-2006, 12:44 PM

might see if i can look at a reduction box for the mechanica lspeedo side of things - probably just as easy that way

seeing id save upwards to 500 bucks foir the rims - paying an extra 1- 200 hundred to get the speedo calibrated for the cheaper size tyres might be a good thing

**Toobs** · 02-02-2006, 12:52 PM

The speedo is electronic is it not?
I'm pretty sure it is on mine anyway.

**-==L=a=N=c=E==-** · 02-02-2006, 03:05 PM

The speedo is an electric unit on the ST185 and ST205. If anything i think a reduction gear system would be more expensive requiring some custom mounting job to make it all work properly.

Unlike the gizmo i was talking about, you can adjust it on the fly in percentages. So find a mate with a stock car, follow him at say 100km/h and set your speedo in the cabin. And your done.

Well, that's how i would do it anyways.

**Toobs** · 02-02-2006, 11:47 PM

I'm sure Witzl would build you one of the pulse adjuster kits from Jaycar... he's already got the hand controller so he could just set it and send it down to you.
Considering all you are doing is changing tyre sizes it will only be one value for all points on the scale.

**JustCallMeOrlando** · 03-02-2006, 12:24 AM

The speedo corrector uses small pots and not the hand controller.

**Toobs** · 03-02-2006, 10:18 AM

I was thinking about the digital pulse adjuster kit, I forgot about the speedo corrector.
Speedo corrector is even easier to build... only a handful of components on the board.

**JustCallMeOrlando** · 03-02-2006, 10:34 AM

Ah okay. Yeah, it looks pretty simple

Mind you, they're all simple given a bit of time.

**RyleyMA61** · 07-02-2006, 11:36 AM

try this thing out!

it kicks arse

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

**Classique71** · 07-02-2006, 08:06 PM

hmss - pretty sure the st185 has a mechanical hookup onto the st205 box .. im pretty sure we turfed the electronic sender ..

Ill be checking this out on friday when shes back on the hoist for finishing touches and measurements ..

be SO cool if i can get away with 45's - makes this tyre swap actually affordable !