Speedometer is off!

saved2live · 11-02-2009, 10:38 PM

*I wasn't sure where exactly to post this, so if it's in the wrong spot MODs feel free to move it.*

Okay, for the longest time I had 18" wheels. About a month ago I went back down to 15" wheels and ever since, my speedometer has been waaaaay off. I'm talking like 7mph off. On the freeway my speedometer will say I'm going 90mph when I'm traveling with the flow of traffic. So unless EVERYONE else on the freeway is doing 90mph, something is off.
I don't know what could be causing this? I did notice that my car is lower than it was with the 18s. (I'm on S-Techs). I also have to get my camber corrected as well.

Any thoughts? Thanks guys.

awinter · 11-02-2009, 10:41 PM

What size tire are you running? With a 195/50/15 you are 1" shorter in diameter than the OEM wheel/tire combo. This will give you a false odometer reading +/- 5mph (going 80 mph by speedo yet navi shows 75 mph). Plus, at the higher speeds, the OEM wheels are off as well by 1-2 mph as the speedo was set for the wheel combo used by the bB in Japan.

saved2live · 11-03-2009, 12:28 AM

Okay that makes sense. I'm running 195/50/15 tires. So basically to solve this problem I just need to run the stock size tires? I guess that's no biggie. I'll just have to live with the issue until it's time for new tires.

ketchup_xb · 11-03-2009, 12:31 AM

i too had a problem when i was running 17"s for awhile. but just make adjustments, youll be alright.

bkb68 · Yesterday, 11:44 AM

There are probably some other combinations that will work (general rule of thumb is to stay within 5% of OEM specs), but your best bet is to go with the 185/60-15 stock if the speedo/odometer accuracy is important to you.

saved2live · Yesterday, 11:47 AM

I think I'm going to go with the 185/65/15 since they make the car to the bB specs.

Black_Sheep_xB · Yesterday, 12:01 PM

Yeah.. when I got my 17's I made sure the rim/tire combo was within a mm or two of the oem overall diameter.. no issues here. I check myself with those roadside radars all the time (we have many).. always on the money.

wask0 · Yesterday, 12:32 PM

Correct me if im wrong, but if you can get your hands on a Scangauge, i believe it can adjust the tire size.

PCH · Yesterday, 01:16 PM

Yes you can dial in the actual speed on Scangauge.

HaoleXB · Yesterday, 05:13 PM

mine was that way when i was running my sportmax on 195/50/15 . i kinda liked it because it made me drive slower cuz the speedo said i was going faster!

Downside. . . . .. racks up more miles on the odometer since the wheels are spinning more times!