How does the Boxster determine it's speed?

[KRAM36]

As the title asks. How does the 986 Boxster determine it's speed? I did a internet search and from what I could tell is it does it from the ABS sensor? Then I read a post that the systems takes into account all four ABS sensor speeds and gives out an average.

So I'm really not sure about this. Can someone enlighten me please on how the 986 Boxster determines it's speed?

[KRAM36]

I know that changing the tire radius will cause the speedometer to report an incorrect speed, well the factory set speed. I'm not sure if it's being based off the front tires or rear tires?

Anyone know?

[Boxstard]

By my mood and right foot!

[KRAM36]

Originally Posted by Boxstard

By my mood and right foot!

Yeah my mood and right foot also affects the speed my Boxster is traveling at.

How does the 986 Boxster determine the speed the car is traveling at?

[specboxCO]

I'm pretty sure it uses the right rear wheel speed sensor for the VSS signal.

Easy way to test, jack the car up, turn the igntition to run and spin the wheels. See which ones move the needle on the dash.

[KRAM36]

Originally Posted by specboxCO

I'm pretty sure it uses the right rear wheel speed sensor for the VSS signal.

Easy way to test, jack the car up, turn the igntition to run and spin the wheels. See which ones move the needle on the dash.

Jack up the car and see which wheel it reads the speed from? So nobody here knows for sure?

[Qmulus]

Originally Posted by KRAM36

Jack up the car and see which wheel it reads the speed from? So nobody here knows for sure?

Soooo, why does it matter? I can't say for sure, and I really don't care.

[KRAM36]

Originally Posted by Qmulus

Soooo, why does it matter? I can't say for sure, and I really don't care.

Why does what matter? The fact that people on the forums don't know the answer to this or that I want to know how the Boxster determines it's speed?

It matters to me because I am going to change the diameter of my tires and I want to calculate how far off my speed will be if the car judges the speed from the tire rotation speed.

Thanks for not answering the question and being a jackass for nothing.

[Qmulus]

Originally Posted by KRAM36

Why does what matter? The fact that people on the forums don't know the answer to this or that I want to know how the Boxster determines it's speed?

It matters to me because I am going to change the diameter of my tires and I want to calculate how far off my speed will be if the car judges the speed from the tire rotation speed.

Thanks for not answering the question and being a jackass for nothing.

You are quite welcome.

I think you will find that I am generally not a jackass, and go quite far out of my way to help people find answers that I often have no other use for. In this case it would have been nice to know the scenario before calling me a jackass for not helping. I don't like spending a bunch of time because someone was "just wondering", hence my comment. This actually piqued my interest last night and I even spent a half an hour of my time looking up exactly how it calculates speed. I looked in the Bentley, the factory (996) 911 Technical Introduction Service Information manual and called a friend that I thought would know as he sets uses this info in 911 and Boxster race cars. Why would such a jackass go to this trouble? Maybe he likes abuse.

Yes, of course the system uses wheel speed to calculate vehicle speed. That is the only way it could. Each "tone wheel" that the wheel speed sensors read has 48 teeth that is read by the ABS module. The ABS module then divides this down by eight and sends it to the appropriate module. The real question is does it use one sensor, does it somehow derive it from all of the sensors, or? Well, the answer, as far as I can tell is a bit tricky. It appears that there are two speed signals sent out. One from the right rear, and one from the left rear. The key is that it seems that the speed is derived from the rear wheels, not the front, so hopefully that answer is good enough. But hey, I am just a jackass.

[JayG]

Originally Posted by KRAM36

Why does what matter? The fact that people on the forums don't know the answer to this or that I want to know how the Boxster determines it's speed?

It matters to me because I am going to change the diameter of my tires and I want to calculate how far off my speed will be if the car judges the speed from the tire rotation speed.

Thanks for not answering the question and being a jackass for nothing.

just load waze or a speedometer app on your phone and you can easily see what your speed is relative to the speedo

And Qmulus is far from a jackass

[maytag]

Originally Posted by Qmulus

Soooo, why does it matter? I can't say for sure, and I really don't care.

And the winner of "most helpful and relevant post of the week" goes to......

Sent from my SM-G970U using Tapatalk

[Racer Boy]

KRAM36, you are the one being a jackass. Why don't you just move on?

You can't recognize it when someone is trying to be helpful, but needed clarification on what you were asking for. I wasn't sure just what you were looking for either.

And you continue to bury yourself.

Go ahead and blast me, it won't be me that looks like a fool.

[KRAM36]

Originally Posted by Racer Boy

KRAM36, you are the one being a jackass. Why don't you just move on?

You can't recognize it when someone is trying to be helpful, but needed clarification on what you were asking for. I wasn't sure just what you were looking for either.

And you continue to bury yourself.

Go ahead and blast me, it won't be me that looks like a fool.

You already made yourself look like a fool with this post, no need for me to blast you. Why don't you just move on?

[morgal48]

Reading prior posts by those involved in this leg wetting contest might bring to light who the jackass is. Don't have a dog in this fight, but that may be a reasonable solution for those that really need to be right.

[Qmulus]

Well, I gave a snarky remark, and Kram responded. No biggie. I asked my 18yo daughter if she thought I was a jackass, and she said no. That is all that matters to me.

As I see it, there is only one important piece of information and that is does the speedo calculate speed off of the front or rear wheels. From everything I can see, it is the rear (doesn't matter which, the tires better be the same size). So, if you go with a larger tire, which will make the car accelerate slower, your actual speed will be higher than indicated by the percentage increase in tire circumference which is easily calculated.

The actual way the cluster calculates your speed basically is by taking the number of pulses (6 per tire rotation) over time and using a calibration factor based on tire size displays the speed in digital and analogue form. This method is analogous to gear ratios in an old mechanical speedometer.

There a jumper location in the fuse box with the signal that has pulses corresponding to speed that is used by the things like the radio (speed based volume), top control (so you don't open the top at speed), PSE (closes the exhaust flaps at certain speeds), etc.

That is all from me. I have a sick '01 Boxster S cluster sent to me from the land down under to fix. It is a real PITA at the moment. Probably, one reason why I came here in the first place for a distraction...

[maytag]

Originally Posted by Qmulus

Well, I gave a snarky remark, and Kram responded. No biggie. I asked my 18yo daughter if she thought I was a jackass, and she said no. That is all that matters to me.

We should all be so lucky..... (That our kids at 18 don't think we're a J/A, )

So I have a question:
I know on my enthusiast-level Durametric tool, there is a tab for the cluster. I haven't explored it whatsoever, and I'm not where I can anytime soon. Does anyone know if that function / tab will allow changes like speedometer calibrations? My other "Tuner Tools" (think SuperChips) allow for this, but that's a different sort of functionality.

waddy'all know?

[KRAM36]

Originally Posted by Qmulus

Well, I gave a snarky remark, and Kram responded. No biggie. I asked my 18yo daughter if she thought I was a jackass, and she said no. That is all that matters to me.

Have two daughters myself, thankfully they are out of the house and married.

People around here are freaking about about me calling your post a jackass reply. Can people not be honest around here? That and they seem to equate my reply as a constant, but it was only about your post, not who you are in whole 24/7.

Anyways I'm glad you did stick your head into this thread as now we have some useful information and thank you for that. I figured it wasn't an easy answer or JFP in PA would have posted the answer already.

Thanks again.

Originally Posted by maytag

We should all be so lucky..... (That our kids at 18 don't think we're a J/A, )

So I have a question:
I know on my enthusiast-level Durametric tool, there is a tab for the cluster. I haven't explored it whatsoever, and I'm not where I can anytime soon. Does anyone know if that function / tab will allow changes like speedometer calibrations? My other "Tuner Tools" (think SuperChips) allow for this, but that's a different sort of functionality.

waddy'all know?

Nah, the Durametric won't let you do anything like that. About the only thing it will do along that line is turn on the OBC to the cluster. So if you put in a 4 stalk column, you can scroll through the extra information the OBC will now be displaying to the cluster.

[JFP in PA]

Originally Posted by maytag

So I have a question:
I know on my enthusiast-level Durametric tool, there is a tab for the cluster. I haven't explored it whatsoever, and I'm not where I can anytime soon. Does anyone know if that function / tab will allow changes like speedometer calibrations? My other "Tuner Tools" (think SuperChips) allow for this, but that's a different sort of functionality.

waddy'all know?

No, you need the PIWIS for that.