Can Tire Size Make The Speedometer Be Off?

[HondaBoy]

i wanted to know if the size of the tire can make a difference on our cars with the speedometer. i know on some cars it does, and some it doesnt. i ask this because when im going 40mph, it feels more like 30 or 35. the original size for our tires one 13in rims is 185 70 R13. now what i have on there is a 175 70 R13. the diameter is smaller than what is supposed to be on there. this is why i think it may make the speed off just a bit. maybe im just used to going fast. i think the tire size should be 175 80 if its gonna be that skinny of a tire. im hopping i can get some other tires put on. i want 195 60 R13. im gonna stay on my 13s for now. but if any of yall have the same thoughts about ur 3gee, tell me.

[johndej]

yeah, it can make the speedo off. lol, go drive at one of those cop things that tells you your speed and sometimes takes a pic if your speeding, you can prob tell by what those things say.

[Jims 86LXI HB]

Originally posted by HondaBoy
i wanted to know if the size of the tire can make a difference on our cars with the speedometer. i know on some cars it does, and some it doesnt. i ask this because when im going 40mph, it feels more like 30 or 35. the original size for our tires one 13in rims is 185 70 R13. now what i have on there is a 175 70 R13. the diameter is smaller than what is supposed to be on there. this is why i think it may make the speed off just a bit. maybe im just used to going fast. i think the tire size should be 175 80 if its gonna be that skinny of a tire. im hopping i can get some other tires put on. i want 195 60 R13. im gonna stay on my 13s for now. but if any of yall have the same thoughts about ur 3gee, tell me.

Yes is sure does make a differance. Some famous sizes that are incorrect are 195/50-15 (correct is 195/55-15) and 205/40-16 (correct is 205/45-16)

175/70-13 is 2.4% undersized, speedo showing 60mph while your really going 58.4mph

195/60-13 is much worse, 4.2% undersized, speedo showing 60mph while your really going 57.5mph

Use this web site to check how size's your thinking about stack up against the stock size for rolling diameters.

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

[88accordlxcarb]

How would one fix the speedo with new tires? Would have to do something with the computer?

[86AccordLxi]

Since the speedometer is cable driven, there's really no way to fix an incorrect speedo. I'm running an incorrect tire size (205-40 16) and i know that the speedo is off about 2 mph at 60mph. You just have to learn to compensate basically.

Alex

[HondaBoy]

well i didnt get good info from my mom. i told her to drive about 35 and wave to me when she was there. i think she was driving a bit faster, but neway, my speed said about 45. well i will just have to kinda estimate. i think its actually a bit less off than 10. neway thanx for the info.

[bobafett]

hahah there is no way they are gonna be that much off unless you are runinng tricycle tires.

just drive 58mph and u will be going 60, thats easy enough.

[Justin86]

I have 205/40/R17 and at 60mph it is really like 62.8mph.

[HondaBoy]

hey i checked 2day with my friend. i was on the cell with him and he was following me. we were both going 40mph on the speedo. so i guess it was just feeling like i was going slower than i realy was. well i know some cars are different how their speedo is connected to the tranny or somewhere else. also my car seems to be doing the right speed since i disconected my battery when i was puttin in new spark plug wires. when i reconnected the battery it seems to have reset? i dont know but it seems to be normal. well more suggestions are good to post here

[Jims 86LXI HB]

Originally posted by Justin86
I have 205/40/R17 and at 60mph it is really like 62.8mph.

That's odd, that size is the proper plus size, thier really close to oem diameter. 1.1% different, true 60mph would read 60.7mph.
For your to be reading that much off would mean your speedo had some accuracy issue's before you put the tires on.

[guaynabo89]

About the radar police stand idea.


I'm running 205/45/17 tires which I know make the speedo about 2 mph off.

When I drove by one of those police radar stands The speed displayed by the stand was right on the money with my speedo.


Now when I drove by with my 91 Accord on stock wheels and tires there was a 2 mph difference in the speed displayed by the stand and the speedo in the 91.


Just leads me to ask, Was this perticular stand in need of adjustment or is radar detection just off in general?

[87lxi accord]

radar detection always completly accurate.

[guaynabo89]

Well if its completely accurate than Honda speedos are off by two mph.

I have three Accords and it did the same with all three.

[HondaBoy]

well i guess i was wrong cuz my speedo is like pretty much correct. ive been driving on the freeway here and i was doing the right speed. so i guess i was feeling like i was going slow? thats wut everyone is telling me. i guess its cuz i worry about stuff like that.

[Grant2k]

that's why i like my 205/50/15s. the diameter is .1 inch off. when my speedo reads 60 i'm doing 59.7.

the stock instumentation that cars come with is just not always accurate. they really aren't persicion instruments.