Hi,

I have a 2008 G37S Coupe 5AT. My speedometer is off 7km lower then the expected speed. I went to the stealership and they took it out for a test drive with their computer connected to my car. They also confirmed that the speedo was off and needed to change my whole cluster. They were asking almost 1500$ to get it replaced. I was thinking to put a different tire size so it equals to the speed im going at. What tire size do you suggest I put on. Im running on oems on 19". Thanks!

 

The way I see it, there are three ways of thinking:

1) The speed difference may get worse or fluctuate. If this turns out to be the case, your only option is to fix it (though perhaps you can find a used cluster, junkyard maybe?).

2) The speed difference is going to be constant and not change. If this seems to be the case, I don't see why you'd even bother messing with the tires. Just mentally keep in mind that your sped-o is reading 7kmh too low and compensate.

3) Screw having a speedometer, just get a GPS unit and use that for speed.

 

Just get another cluster from ebay. I seen them from $29 up to $200.

 

Ok thanks for the feedback. Got someone willing to do it for 400$ including setting up the current mileage of the car.

 

for changes in rims and tires, here's a post i wrote up:
https://www.myg37.com/forums/brakes-...ires-rims.html

 

Just a FYI, your not allowed to change the dash cluster with the speedo.

It has to be sent to a place in Washington, D.C. Not sure if its dot, or some other govt agency.

Ran into this problem in 1996, they were mandating all used speedo, be sent out to avoid owners from tampering with the mileage.

Example the 1996 j30t I bought had its dash replaced at dealership at 55k.
Person puts only 6k on new dash sells the car at auction.

Now the car is titled with only 6k on the odo, see the problem.

I put 50k on it only read 56k, when I signed the odo statement had to cetofy true mileage of 116k.

This was one year before it was mandatory ,at least in NY.

Yes we all know someone who rolls odo, but it is not worth the trouble & could get you in a heap of trouble with the law.

 

Yeah i heard something about that also. thx for the info!

 

I had a friend that bought a rav4 with a new cluster in it, the mileage on Carfax was at 110k but the odo in the car read 46k.
I'm sure you can change it, but the mileage won't match like risky said.

 

I also have this exact same problem, 2008 G37S Coupe 5AT, running OEM 19's. I verified with a portable Garmin GPS and a phone app that there's about a 5-8km/h difference in displayed speedometer readings and actual speed (I'm from Canada). It doesn't make sense that wheel size would affect the readings (since its stock sizing), which leads me to believe it's a calibration error. A concern I have is that this would somehow affect/inflate the overall odometer reading.

Other than replacing the cluster, are there any other potential fixes?

 

I think what you guys are experiencing is normal. Drop the OCD's and move on lol

 

I can't help it

 

Mine did the same thing... I think mine was just from putting different size wheels and tires

 

Speedo's never read 100% accurate. I have been 'told' (read into that what you will) that the manufacturers are allows +/- 10% on their speedo accuracy. Seems crazy to me but that it what I was 'told'. So if the reading is out by 7kph when doing 70kph, possibly this is normal. If it is out by 7kph when you are not moving......then you have an issue.

To be honest, I would just be happy to know how inaccurate the speedo is and can then keep that in the back of my mind when driving. Unless it was WAAAAY out, I wouldn't waste the money having it fixed.

 

The higher my speed the more difference it shows. Once my speedometer was showing 200km/h, when my speed was actually on 160km/h

 

Great! That should keep you safe.