Regearing speedo... to cut down on speeding...

[RatLabGuy]

Ok, so, I just got another speeding ticket yesterday, thats 2 in < 2 months.
Now the obvious solution here that I am trying to work on is *slow the hell down*. The problem is that I honestly do not realize I am going that fast.

In order to help me with this, I'd like to remake my speedometer. The most obvious problem (besides my impatience) is the gear ratio error from the larger tires (205s). While the error is not a massive %, it's not trivial for me to keep up with it and constantly re-calibrate in my head. And, most of the time I just forget it. W/ only 5k on the Pirellis, re-sizing is not an option.
The other thing that bugs me is the relative scaling of the speedo. I know you guys that do track runs may need it, but why this thing reads up to to 140 mph is beyong my comprehension, since there's no way the stock vehicle could do anywhere near that. This creates 2 problems for everyday drivers like me. First, the numbers only go up by 20s, and the big ticks by 10s. You have to pretty much guess at where, say, 55 is. I find that very annoying.
Second (and more relevant here), it means that a 10 mph difference is only about 1/2" deflection of the needle.Also, this means that you have to be going 70 to just hit the vertical point. Psychologically this is very bad b/c it really shows how much faster you *could* be going... if it topped out at 85, it's much more obvious when you're near the "top", plus each change would be more clear. I want a speedo that really emphasizes increases in acceleration etc.

The point of all this is, I'd like to swap in a face that tops out at, say, 90 or 100. Key is a replacement that looks nice. I see 2 ways to do it. 1 - dig around and get an aftermarket speedo and try and fit in there and calibrate it, or - 2 - replace the face, and modify the incoming signal so that it reads correctly. I'm worried about the odometer, though... I don't want my mileage off by 35%!
I'm just starting the research now, so I'm open to ideas/suggestions. Some things that come to mind - Are the odo and speedo feeding off the same signal? What kind of signal is it, just voltage from a speed sensor? I get the impresion (from a How To) the odometer is actually in the PCB, and not the LCD in the face, yes? Any suggestions on a recalibration unit to do the conversion? Etc etc.

Thanks guys!

 

[i12drivemyMP5]

205 what? 205/40/17 made mine say 60 when really doing 59.4. 215/40/17 woulda been 60.2 when speedo says 60. These are vs. 195/60/16 factory size. Larger outside diameter slows speedo, smaller makes it fast.

 

[pasadena_commut]

This creates 2 problems for everyday drivers like me. First, the numbers only go up by 20s, and the big ticks by 10s. You have to pretty much guess at where, say, 55 is. I find that very annoying.

http://www.miata.net/garage/tirecalc.html

I doubt your speed is off by more than 2%, which is not enough of a difference to earn a ticket except maybe in the pickiest of speed traps.

I'm with you 100% on the speedometer markings though. Silly thing reads linearly up to 140 mph and I've never been (much) over 80 in mine, so nearly half the range on the dial is wasted in normal driving. How hard would it have been to put in the missing ticks? Paint isn't that expensive. On the flip side, that's the way it is, and disassembling the dash to get to the dial seems like way too much work compared to the resultant gain. It would probably be easier to plug in some sort of aftermarket speedometer that works off the diagnostic port under the dash.

 

[5PADZAM]

Switching from 195/50r16 to 205/50r16 changes your speedometer by exatcly 1 mph (1.7%) at 60 mph. In other words, if your speedo says you are doing 60, then you are actually doing 61. at 30, you are doing 30.5. This is assuming that our speedometers are exactly calibrated to the stock tire size. No way you are getting tickets for 1 mph difference. I would say that you would have gotten tickets with the stock size tires. Like you said yourself, you should just slow down. Also, use your cruise. Works for me.

I don't understand your difficulty in judging where, say, 55mph is. If you are researching a custom speedo setup, maybe you should look into a digital one. Then you wouldn't have any question about how fast you are going. As for me, I like the way my speedo looks. If it only went to 85 it would look cheap to me for some reason. Maybe I drove too many cars from the 80's, but I hated that about those cars.

 

[pasadena_commut]

I like the way my speedo looks. If it only went to 85 it would look cheap to me for some reason.

Speedometers don't have to be linear (although the vast majority of them are.) The range 90-140 MPH could be greatly reduced in size and frequency of tick marks and the other parts stretched out a bit. So that in the range where one does care about reading the speed (generally 30-75 mph) the thing could be read accurately quickly, and outside that, it wouldn't be quite so accurate or quick to read. For me, I'd like to be able to tell 72 from 65 at a glance, ditto for 34 vs 25 - those are the sorts of speed ranges where knowing your actual speed can help you avoid a ticket. Conversely, the actions of the highway patrol officer aren't going to be much different if he catches you going 95 instead of 110.

 

[RatLabGuy]

I'm sorry, I think you guys are missing my point. This isn't intended as a debate about how much error I have. I went from 195 to 205 width (5% - 10/195) w/o chanaging aspect ratio, so that should be the error in total circumference too. I never said I'm getting pulled BECAUSE of the error. I'm getting pulled b/c I have a lead foot. However not SEEING the actual speed I'm going is making it worse. Both times pulled, the speed stated by the PO has been about 4-5% more than what I saw when I made that that quick glance down we all do when we pass a cop.
It's all about ratios and psychology. Having a digital speedo dosn't help the problem. I want to be able to really emphasize the rato of how faster I am going from one point to the next - e.g., more space between useable point. Having the needle 3/4 of the way around at 75mph helps in making it LOOK like I'm already going too fast. Basically trying to fool myself into not pushing it as much.

 

[RatLabGuy]

Speedometers don't have to be linear (although the vast majority of them are.) The range 90-140 MPH could be greatly reduced in size and frequency of tick marks and the other parts stretched out a bit. So that in the range where one does care about reading the speed (generally 30-75 mph) the thing could be read accurately quickly, and outside that, it wouldn't be quite so accurate or quick to read. For me, I'd like to be able to tell 72 from 65 at a glance, ditto for 34 vs 25 - those are the sorts of speed ranges where knowing your actual speed can help you avoid a ticket. Conversely, the actions of the highway patrol officer aren't going to be much different if he catches you going 95 instead of 110.

I agree! Missed your post while I was replying....
Many times the difference between 70 and 75 is a ticket!

 

[BondoBob]

The Flat Earth Society tried for a time in the 1980s to get all car makers to limit their speedometers to 80MPH thinking (as you do) that if the needle is WAAAAAY over there, you'll slow down. It's busted logic, as it made people simply try to make the needle wrap around to the stop at 0MPH.

If you want to stop speeding, then stop speeding. It isn't the tires fault, it isn't the gauge's fault - it's the driver's fault. Unless you are getting nailed for 61 in a 55MPH everytime, you are driving too fast and need to back it down.

Why not do what racers do and mark the face of the speedo where 55MPH is with a red line!

 

[5PADZAM]

http://www.miata.net/garage/tirecalc.html

I doubt your speed is off by more than 2%, which is not enough of a difference to earn a ticket except maybe in the pickiest of speed traps.

I'm with you 100% on the speedometer markings though. Silly thing reads linearly up to 140 mph and I've never been (much) over 80 in mine, so nearly half the range on the dial is wasted in normal driving. How hard would it have been to put in the missing ticks? Paint isn't that expensive. On the flip side, that's the way it is, and disassembling the dash to get to the dial seems like way too much work compared to the resultant gain. It would probably be easier to plug in some sort of aftermarket speedometer that works off the diagnostic port under the dash.

Sorry, I guess I did miss your point. I didn't realize that you were talking about a psychological aspect.

 

[P5SurchJunkE]

I used to get a lot of tickets for a variety of different speeding infractions. One thing I did is I bought a cheapo radar detector, you know the kind that goes off when you pass every other store or bank along the road and drives you insane. It's a constant reminder to check my speed. I haven't been pulled over in almost 4 years since I bought it. I used to get pulled over on average of once a month. It has paid for itself time and time again.

 

[Beau M]

Speeding in a P5... is that possible?

 

[RatLabGuy]

The Flat Earth Society tried for a time in the 1980s to get all car makers to limit their speedometers to 80MPH thinking (as you do) that if the needle is WAAAAAY over there, you'll slow down. It's busted logic, as it made people simply try to make the needle wrap around to the stop at 0MPH.

If you want to stop speeding, then stop speeding. It isn't the tires fault, it isn't the gauge's fault - it's the driver's fault. Unless you are getting nailed for 61 in a 55MPH everytime, you are driving too fast and need to back it down.

Why not do what racers do and mark the face of the speedo where 55MPH is with a red line!

I never said it was the tires fualt, or the gauges fault. This is a problem that *I* have, and I am trying to help myself work towards doing something about it. i'm sorry, but "just stop" is useless advice. When people try to kick other habits (alcohol, smoking, nailbiting), you do not say, "just quit, what's the big deal?". No, you find measures to allevaite the urge and help make the transition easier. Ultimately it is indeed up to the person, but the transition can be greatly cushioned, resulting i na higher probability of success. THAT is what I am trying to do for myself.

Re: a lot of work/money - perhaps. Probably. But.... just 1 ticket cost at least $200 + the unsightly record, not to mention insurance risks. I am not scared of a challenge.
We had a cheapo radar detector for awhile. We found that it lulled us into thinking it was OK to speed (which it i not), and since it went off all the time, just became annoying. A good suggestion, though.... that wasa long period of no tickets....

Re: speeding in a P5 - of course you can. They don't ticket you for accelerating too fast, lol.... in both cases I'd had plenty of time to get up to cruising speed, so it could just as well have been a VW Bus.

 

[Beau M]

Take the radar detector one step further. Mabey hook up your door chime to go off when you go over 60. Or a stun gun in your seat

 

[rednecks_r_us]

Just put some duct tape over the right side of your speedo and then you won't see the 80 - 140 mph.

Get a GPS and read your speed there.

 

[Tom03es]

So it seems to me that it's the driver that's broken- not the speedo, not the tires, not the car, not the space/time continuum. Therefore, instead of trying to fix those outside factors, why not try to fix the nut behind the wheel? If a couple $200 speeding tickets aren't enough to get you to slow down, then I don't know what will. I seriously doubt that a custom, one-off speedometer will do anything. Just keep doing what you're doing. Eventually, you'll get so many speeding tickets that your license will get taken away and you won't be able to drive anymore without risking jail time. So you see, the problem will eventually take care of itself.

 

[P-Funk!]

^I know it sounds harsh - but it really is true. I have the same tire-induced error - indicated speed is off (but smaller tire circumference 'raises' indicated speed above actual (indicates higher speed than reality) albeit by a small amount*. The larger tires on my Durango indicate lower speeds than actual (indicates lower than true speed) ).

But the problem was the throttle actuator!

It wasn't until i was faced with losing my job (potentially) that i really committed to change my evil ways.

Just be aware - especially if you find yourself the fastest car in traffic (or the only one)!

You CAN slow down. People do beat addictions.

* picture two identical cars driving down the road - but one has smaller tire circumference from a lower aspect ratio tire on the same rim - the smaller wheels make that car spin its wheels faster to pace the other car. This is reflected in the speedometer showing a higher rate of travel.

 

[pasadena_commut]

Just be aware - especially if you find yourself the fastest car in traffic (or the only one)!

On the highway I usually try to be about the 3rd or 4th fastest car, in the group of cars more or less around my own. Except not when there are a lot of lead footed loonies about - if everybody else is driving like a maniac the goal becomes to try to look like the only sane driver on the road. Also to let the crazies go by before their wreck becomes my wreck. In other words, drive as fast as possible subject to the two conditions: that speed is safe; and the Highway Patrol Officer will always pick somebody else first to pull over. The hypothesis is if the officer sees one car passing another, he will generally ticket the faster of the two, even if both were speeding. Unless both were going dangerously fast, then he'll nab whichever one he can get since he'll assume they were racing.

Either the strategy works or I've been extremely lucky, as I've never had a speeding ticket in over 30 years of driving.

Edit: Also no accidents other than the three times I've been rear ended while stopped at lights or stop signs.

 

[16902]

This reminds me of my wife who sets her alarm clock ahead 10 minutes so that she makes sure to get up on time. Of course, she knows what time it really is and instead of setting her alarm for 10 minutes before she needs to get up, she sets the clock 10 minutes fast with the alarm at the same time. When it goes off she says, "Well, it's 10 minutes fast so I can hit snooze, and still get up on time."

So are you trying to outsmart yourself or outdumb yourself?

 

[P-Funk!]

^BWahaha! Brilliant!

 

[dharman]

(lol) My girlfriend does the same thing. Never understood that one. The only way I could see it working is if someone else changed the time on it without you knowing.

Here is the answer.

When approching speed that you may feel is too fast:

A) lightly lift right foot off of pedal until desired speed is obtained.

B) Two words " cruise control"

or

C) Let the wife drive