Maximum Permissible Speedometer Error

[mryakan]

So if the sensor is in the transmission, it is reading the rear wheels.

I highly doubt that BMW has purposely set the speedo reading high to account for tire/wheel changes that are not the stock size. That's not their problem if an owner makes changes that are "not approved".

If I look at my tire pressure sticker, it list many sizes. Both 16" and 17". Mine came stock with 235/45-17. It also allows 225/55-16 which is the size I use for my winter tires. Do the math and the 16's are a larger diameter tire. When these are installed, the speedo reading is much closer to actual than the 17's. I'm thinking that this is the factor that explains the difference.

Ah, I didn't pay attention to him saying front, usually you want all tires to roughly have the same rolling circumference (or within1-2 %). In any case, I still think BMW possibly goes a bit overboard to protect themselves against litigation even with people who put non OEM sizes. Maybe that is one more question for the engineers.

[gtxragtop]

I still think BMW possibly goes a bit overboard to protect themselves against litigation even with people who put non OEM sizes. Maybe that is one more question for the engineers.

Think about this a bit. A manufacturer SPECIFIES the acceptable tire sizes that may be used on that vehicle. Now, your suggesting that they are trying to cover their liability against someone who does not follow the recommended sizing? No, it does not work that way. If it went to court, it would get thrown out instantly. They are covering variances in the sizes they spec including wear, inflation pressure and the fact that not all tires of the same size are the same diameter.

[ddsski]

My Lotus is the same way. I have to set speedo at 81 to do 75. Europeans are pretty fu%^ed up on this one, Giant PIA as I fully believe in doing the 74.9 thing on the highway. 10+ gets you tickets, under 10 there are plenty of others. been told this by multiple cops over the years. Yes, there are always going to be a few Officer penis's out there (usually in little podunk towns)
On the other hand, my Jag is dead on and so far, my X5 seems qiute accurate based on similar travel times to other vehicles including my Ascender (American) Haven't done the mile marker test yet on the X5.

$50000+ vehicles with intentionally inaccurate speedos is just plain stupid. In Germany, if they really want you to go that slow, set speed limit at 15 KM/hr instead of 20km/hr or maybe they did this to speedos cause all of the sign in the country signs are inaccurate. So much for German precision