MPH off?

[SoundQ SVT]

In my experience, there are 2 possible reasons for the speedo to be off...

First has to do with the ratio used to measure how far 1 revolution of your tire actually goes. An error here would indicate a greater amount of mph error the higher your speed. The error would be explained in terms of a constant percentage, for example 4%. 4% error at 50 mph would be 2 mph. 4% error at 100mph would be 4 mph off. Non-stock wheels and tires can contribute to this error.

The second possible reason is that the calibration to zero may not be correct. In this case, the mph difference is constant throughout the range, but since the speedo was off at 0, it will be off by the same amount regardless of speed.

Of course, it is possible to be impacted by both errors at the same time.

In my SVT with the aftermarket wheels and tires (215/45/17) the speedo is dead on at 20, 30, and 40 mph (didn't measure higher because I was in town) based on my GPS unit.

In my Explorer with stock drivetrain, the speedo is off by 2 mph regardless of speed (speedo says 20, 30, 40, 50, or 60 and I am really going 18, 28, 38, 48, or 58 respectively). This indicates the correct speedo ratio is used, but the zero calibration was off.

Anyway, just thought I'd throw my $0.02 in....

 

[PurpleMystique]

In my experience, there are 2 possible reasons for the speedo to be off...

First has to do with the ratio used to measure how far 1 revolution of your tire actually goes. An error here would indicate a greater amount of mph error the higher your speed. The error would be explained in terms of a constant percentage, for example 4%. 4% error at 50 mph would be 2 mph. 4% error at 100mph would be 4 mph off. Non-stock wheels and tires can contribute to this error.

The second possible reason is that the calibration to zero may not be correct. In this case, the mph difference is constant throughout the range, but since the speedo was off at 0, it will be off by the same amount regardless of speed.

Of course, it is possible to be impacted by both errors at the same time.

In my SVT with the aftermarket wheels and tires (215/45/17) the speedo is dead on at 20, 30, and 40 mph (didn't measure higher because I was in town) based on my GPS unit.

In my Explorer with stock drivetrain, the speedo is off by 2 mph regardless of speed (speedo says 20, 30, 40, 50, or 60 and I am really going 18, 28, 38, 48, or 58 respectively). This indicates the correct speedo ratio is used, but the zero calibration was off.

Anyway, just thought I'd throw my $0.02 in....

and the third and BIGGEST reason any normal car will have an error in the speedometer reading is the error inherent in any mechanical/electical measurement system.

The standard for American cars is +/- 4% error. If the max resolution of the speedometer is 5mph, a design stage uncertainty analysis reveals that at 60mph the speedometer could be off by up to +/- 3.46 mph.

 

[boogieq]

I think new manufacturers overrate the speedo reading, such that you think you are going faster than you are.

 

[Big Daddy Kane]

On a totally different note, what always fried my eggs was having a separate key for the ignition as well as the door. And unlike Ford, who provides a convenient two sided key for fumble free operation, the General didn't see fit to do this.

Ford had seperate keys up until the mid-90s also. Of course, they made more sense because the ignition key also operated the doors, where as the seperate key was for the trunk/glove box. No need for a valet key since you just keep the trunk key.

What I really hated was how Chrysler used an upside down ignition switch cylinder. Did they just want to be different?

 

[LauraSVT]

Ford had seperate keys up until the mid-90s also. Of course, they made more sense because the ignition key also operated the doors, where as the seperate key was for the trunk/glove box. No need for a valet key since you just keep the trunk key.

What I really hated was how Chrysler used an upside down ignition switch cylinder. Did they just want to be different?

I never minded having a separate trunk key. Both my SHOs, as well as my Taurus MT-5, were like that. Think they went to one-for-all PATS keys in '96.

Regarding your Chrysler comment -- Car and Driver recently had an article about all the nonsense items they're including in vehicles these days, including, in some cases, the elimination of the traditional, yet perfectly fine, key. They said, "Better is better, but different is worse." I think they're right.

 

[Big Daddy Kane]

Regarding your Chrysler comment -- Car and Driver recently had an article about all the nonsense items they're including in vehicles these days, including, in some cases, the elimination of the traditional, yet perfectly fine, key. They said, "Better is better, but different is worse." I think they're right.

I've read that people with the MS6 GT have mixed reviews of the keyless ignition on it.

Jay Leno on Popular Mechanics noticed the biggest kicker of keyless ignition:

But it seems as though a lot of this technology serves no real purpose. Take keyless ignition. You don’t have to use the key to get into the car or to lock it--or to start it. My Z06 has keyless entry. One of the guys from my shop drove off in it, and I had the keys in my pocket. I thought he’d get stuck, but he didn’t. Of course, if he’d turned the car off, he couldn’t have restarted it. There was probably a warning light flashing, but he didn’t notice. Me, I’d rather just use a key

Source

So imagine some punks breaking into your Z06 (maybe the MS6 too) and just chilling, waiting for you to come close enough to start it and drive away!

 

[PurpleMystique]

I've always thought of that too...like if you go to a restaurant and get a window seat looking at your car on the street...only to see it taken because you're close enough for the keyless ignition.