david2u

I have a GS3 (2001) with 215/60/16 as summer tires.

I just put on a set of 225/55/16 blizzak's.

Does the different tire size effect the speedo and the Odo??

Maybe it's just me, but I seem to be going slower than what the speedo says.

altaf

No it shouldn't. Your tire size is correct... its the same as the 16" for the GS4.

GS400_PUSHER

Yeah I think you just have to get use to the low profile tire. there use to be a link here where you could put in your new tire size and it would tell you that type of info. Does anyone have that link......

Mean Gene

David - Your speedometer reads off your ABS sensors on the wheels so as long as U don't drastically deviate from the factory overall tire diameter, things will remain accurate. FYI - the stock 215/60/16's have a diameter of roughly 25.2" while the 225/55/16 combo U R using now show to be 25.0". Not enough difference here to matter, IMHO. Enjoy the ( hopefully ) better traction of the Blizzaks this winter!!

duster

As Mean Gene says...not much difference. Speedo will read 1.6% too fast. So when it reads 60, you are really travelling at 59.1 mph.

Here's the site http://www.miata.net/garage/tirecalc.html

bitkahuna

iTrader: (20)

It's actually not clear WHICH speed is right, because the FACTORY 16 and 17" tires are quite different in size but the GS has no way to compensate, so who knows which tire size would give the 'right' speed. But as has been said, it's not major either way unless you put tires WAY beyond either factory size.

dipstick

For what it is worth, I saw an article somewhere that had compared speedo error among cars, and the Lexus GS4 with stock 225/55/16 wheels was reading about 1 mph fast. I think the nominal o.d. for this tire would be 25.74, so you could compare using nominal o.d. for other tires.

david2u

Just wanted to thank all that answered my question.

I'll try to find one of those roadside speed monitors to see what it really says!!

dipstick

You can check it using the mile markers alongside the highway. Set the car right on 60 mph and time from one mile marker to the next. If it takes 59 seconds, your speedo is reading 1 mph fast. If it takes 61 seconds, it is 1 mph slow. This will work ok up to 2-3 mph error.

Lexus of Manhattan

I also noticed that based on the stock size 215/60/16 tire, both 225/55/16 and 235/45/17 tire are not as closely matched as you think...Observe:

Specification Sidewall Radius Diameter Circumference Revolutions Difference
215/60-16-------5.1 in---13.1 in--26.2 in----82.2 in-------771 / mile--- N/A
225/55-16-------4.9 in---12.9 in--25.7 in----80.9 in-------783 / mile--- -1.6%
225/50-17-------4.4 in---12.9 in--25.9 in----81.2 in-------780 / mile--- -1.1%
245/50-17-------4.8 in---13.3 in--26.6 in----83.7 in-------757 / mile--- 1.9%
235/45-17-------4.2 in---12.7 in--25.3 in----79.6 in-------796 / mile--- -3.2%
245/45-17-------4.3 in---12.8 in--25.7 in----80.7 in-------785 / mile--- -1.8%
255/45-17-------4.5 in---13.0 in--26.0 in----81.8 in-------775 / mile--- -0.5%


Ed