Standard Speedo Variance

Jono · Post by **Jono** » Wed Jul 18, 2007 4:52 pm

Hey guys.

Does anyone know how much our speedo's are out by when doing 100km/hr
on the stock 205/50/16 tyres.

Im thinking of getting rt615's in 225/45/17 which would be about +3.7km/hr according to our speedo vs the miata calculator. though i havent yet got a speeding ticket on my current 215/45/17 which is +2.3 km/hr

Post by **aza013** » Wed Jul 18, 2007 5:22 pm

well I know my speedo is out by 3km/h at 100 and I am running 235 /45 /17s as per dyno speed check
as for stock rims sorry could not tell you but they did say it was a standard setting for the car but but they could be wrong

JOeJOe · Post by **JOeJOe** » Wed Jul 18, 2007 5:56 pm

I have stock rims, i'm out by 2km.

onnzo · Post by **onnzo** » Wed Jul 18, 2007 6:09 pm

I have stock rims/tyres and im out by about 6kp/h.

This is tested with my GPS and those speed checkers on the highways (my GPS is pretty much spot on with the radar)

Onnzo

Jono · Post by **Jono** » Wed Jul 18, 2007 6:43 pm

when you say your out are you + or - ?

harry90 · Post by **harry90** » Wed Jul 18, 2007 6:58 pm

yea ive noticed those speed radar things that actually show your speed now a lot more often !!

Delvance · Post by **Delvance** » Wed Jul 18, 2007 7:23 pm

I've checked mine against my GPS and it's spot on. I seem to remember being very close to a radar checker too once. Standard size tyres.

Grue · Post by **Grue** » Wed Jul 18, 2007 7:56 pm

Those radar guns always have me at 1-2km/hr under what my speedo says. 215/40/17's. Near enough for me!

onnzo · Post by **onnzo** » Wed Jul 18, 2007 9:37 pm

onnzo wrote:I have stock rims/tyres and im out by about 6kp/h.

This is tested with my GPS and those speed checkers on the highways (my GPS is pretty much spot on with the radar)

Onnzo

My speedo under reads by about 6kph.

Richy · Post by **Richy** » Thu Jul 19, 2007 8:49 am

i ve got the rt615 225/45/17.....before i bought them, i checked on

www.miata.net/garage/tirecalc.html

this profile should be 0.4km/hr faster than stock..

(anyone correct me if i am wrong...thanks)

FTO338 · Post by **FTO338** » Thu Jul 19, 2007 9:49 am

Remember the calculation is base on 100kmph. So you won't find much different on low speed.

mr-charisma · Post by **mr-charisma** » Thu Jul 19, 2007 10:56 am

Check at the bottom of this page for a general idea..
http://www.myfto.co.uk/fto_performance.htm

Jono · Post by **Jono** » Thu Jul 19, 2007 3:33 pm

Thanks Charisma, but i dont think the actual speed at 70 is 70 on our standard tyres.

Richy · Post by **Richy** » Thu Jul 19, 2007 3:38 pm

when i bought my car, had an inspection done....it stated that at 60, my car is going 60 (gps satellite check)...

Jono · Post by **Jono** » Thu Jul 19, 2007 3:39 pm

richy was that for standard tyres?

kid_dynamite · Post by **kid_dynamite** » Thu Jul 19, 2007 3:52 pm

Jono wrote:Thanks Charisma, but i dont think the actual speed at 70 is 70 on our standard tyres.

The FTOs I've driven on standard suspension/rims/tyres have been pretty close.

If you're worried that it's significantly off get it checked &/or calibrated by an instrumentation / speedo place. I don't know who the ones up in QLD are, but in NSW if you get it done they can issue a certificate which you can use as part of engineering certificate if you choose to.

Richy · Post by **Richy** » Fri Jul 20, 2007 4:43 pm

richy was that for standard tyres?

yep. it WAS all stock when the report was done...

always feels cool when passing speed camera traveling 60 and see other cars slow down to around 50 (as per my speedo)...nice time to take over others too...

Post by **aza013** » Fri Jul 20, 2007 4:49 pm

never trust the cameras my mate got done in a school zone he was doing 50km/h but the thing is the time was 5:30 so it was a standard 60zone then so go figer school zone stops at 4:30

So thats why PPL slow down for speed cameras