Help me with my van speed please. Because I have different motor and trans, plus tires, the spedo is off

[funboy6942]

Spedo in car reads a steady 60mph, I time from mile marker to next mile marker a consent 54 seconds between markers. How fast am I really going??

TIA!!

 

[Freshgeardude]

im too lazy to do the math. something like 61 or 62 I think

 

[yelo333]

So then speedo * 1.11111... = your real speed (You were going 67mph)

If you want to go 60, set speedo to 60/1.1111=54mph

Edit: 54 seconds per mile, want miles/hr.
1/54 = miles per second
1/54 * 60 = miles per minute
1/54 * 60 * 60 = miles per hour = 66.66667mph

 

[funboy6942]

Originally posted by: yelo333
So then speedo * 1.11111... = your real speed (You were going 67mph)

If you want to go 60, set speedo to 60/1.1111=54mph

Edit: 54 seconds per mile, want miles/hr.
1/54 = miles per second
1/54 * 60 = miles per minute
1/54 * 60 * 60 = miles per hour = 66.66667mph

So 60 is actually 67mph in real speed so my spedo is a good 7mph off.

If this is true, I thank you very much for your time, and its what I was needing to know so I dont get a ticket. I was safe for speed on highway is 70 I was on

 

[Zenmervolt]

Originally posted by: funboy6942

Originally posted by: yelo333
So then speedo * 1.11111... = your real speed (You were going 67mph)

If you want to go 60, set speedo to 60/1.1111=54mph

Edit: 54 seconds per mile, want miles/hr.
1/54 = miles per second
1/54 * 60 = miles per minute
1/54 * 60 * 60 = miles per hour = 66.66667mph

So 60 is actually 67mph in real speed so my spedo is a good 7mph off.

If this is true, I thank you very much for your time, and its what I was needing to know so I dont get a ticket. I was safe for speed on highway is 70 I was on

Speedometers are rarely off by a fixed amount, rather they tend to be off by a percentage. It looks like yours is off by about 11%.

Also, this thread is getting moved into the Garage.

ZV

 

[SparkyJJO]

Can you get it calibrated? Not sure what year/make/model the van is or what powertrain you put in it but sometimes that kind of stuff can be reprogrammed in the computer so the speedo responds correctly.

 

[NutBucket]

Shouldn't that be a quick fix with a different gear for your speedo cable?

 

[Billb2]

Originally posted by: NutBucket
Shouldn't that be a quick fix with a different gear for your speedo cable?

Uh, they haven't been using those for the last 20 years or so. It's all electronic.

 

[funboy6942]

One, thanks Zemmers for moving the thread, my bad,, brain fart

two, no computer to program because it is analog, IE-Cable and rod

Tgree not sure if I can change gears on it because it has a digital, to analog adapter on it as it sits now. How that POS works, no fn clue, which its why it is easier if I knew exactly how fast Im going when the spedo is reading 60, when I got exactly one mile, in 54 seconds

 

[BlackTigers]

Funboy. The way I fixed mine was kind of...ghetto? but it worked.

My speedo was off by some weird numbers. 3MPH high at 25, about 4MPH high at 35, and somewhere in the range of 6/7MPH high at 55.

I took my instrument cluster, and removed it until I got to the needle. I pulled the needle off, and drove alongside a car that was moving at a set speed (a GPS in your car will work better for this). I slapped the needle back on as soon as I set the cruise to keep up with him. It's almost perfect now, maybe 1MPH off or so.

 

[Zenmervolt]

Originally posted by: BlackTigers
I took my instrument cluster, and removed it until I got to the needle. I pulled the needle off, and drove alongside a car that was moving at a set speed (a GPS in your car will work better for this). I slapped the needle back on as soon as I set the cruise to keep up with him. It's almost perfect now, maybe 1MPH off or so.

That will only work for a single speed.

As I mentioned earlier, when a speedometer is inaccurate because of tire size, it's a percentage inaccuracy and not a fixed mph inaccuracy. If it reads 55 when you're really going 50, then it's reading 10% high and will read 33 when you're going 30, 22 when you're going 20, and 77 when you're going 70.

If it's off by 10% and you re-set it to read 50 when you're going 50, it will only be accurate at that speed. At 70, it would read 72, at 30 it would read 28, and at 20 it would read 17. This is likely to encourage speeding in residential areas (because below 50 mph the speedometer would read less than your actual speed) which is where speeding has the worst consequences.

ZV

 

[BlackTigers]

Originally posted by: Zenmervolt

Originally posted by: BlackTigers
I took my instrument cluster, and removed it until I got to the needle. I pulled the needle off, and drove alongside a car that was moving at a set speed (a GPS in your car will work better for this). I slapped the needle back on as soon as I set the cruise to keep up with him. It's almost perfect now, maybe 1MPH off or so.

That will only work for a single speed.

As I mentioned earlier, when a speedometer is inaccurate because of tire size, it's a percentage inaccuracy and not a fixed mph inaccuracy. If it reads 55 when you're really going 50, then it's reading 10% high and will read 33 when you're going 30, 22 when you're going 20, and 77 when you're going 70.

If it's off by 10% and you re-set it to read 50 when you're going 50, it will only be accurate at that speed. At 70, it would read 72, at 30 it would read 28, and at 20 it would read 17. This is likely to encourage speeding in residential areas (because below 50 mph the speedometer would read less than your actual speed) which is where speeding has the worst consequences.

ZV

Oh, good point - I forgot about the tires.

When mine was off it was because I replaced the lights to LED's in my cluster, so I just had to reset the needle in that fashion. The tire size makes it difficult.

 

[funboy6942]

OK, really quick before my pills kick in and Im fucked for the day.

If 1 minute in a mile = 60

Wouldnt it be safe to say then if I did it in less time, I would add every second under 60 seconds as a mile per hour?

60
-54
=
6

so if 54 seconds pass me up a mile, then Im really doing 66mph, even though my speedo shows Im only doing 60 and so forth, provided I have mile markers to go by to figure speed.

But if this is right, then I know IM 6mph faster then what is shown, and since all I ever do is 5 mph over any speed limit, 59 on the speedo would be 65 for for real, and that gap will get close to actual speed on speedo the slower I would be going, so if it reads 30mph, Im doing either 30-32mph for real, and only effects highway speeds really to give it a gap of x seconds per mile larger cuz Im faster.

Or am I wrong, and wont make much sense to me anyway right now, pills are kicking in so a yes or no, or really short, non math answer will have to be given, Im off to lala land for the day now

Also need to remember[/]
Im not using stock tires, motor, OR TRANS, ot trans cable for that matter, so it all must be done per seconds going by in one US mile, to give me a actual true MPH no matter what my needle says. But then once I can figure it out can guestimate my speed then using my speedo, know how fast Im doing when it reads 60.

 

[BlackTigers]

Originally posted by: funboy6942
OK, really quick before my pills kick in and Im fucked for the day.

If 1 minute in a mile = 60

Wouldnt it be safe to say then if I did it in less time, I would add every second under 60 seconds as a mile per hour?

60
-54
=
6

Well let's say you did it in 30 seconds.

That's actually going to be 120 miles an hour.

60-30=30
60+30 = 90
90 != 120.

Not quite.

 

[funboy6942]

Originally posted by: BlackTigers

Originally posted by: funboy6942
OK, really quick before my pills kick in and Im fucked for the day.

If 1 minute in a mile = 60

Wouldnt it be safe to say then if I did it in less time, I would add every second under 60 seconds as a mile per hour?

60
-54
=
6

Well let's say you did it in 30 seconds.

That's actually going to be 120 miles an hour.

60-30=30
60+30 = 90
90 != 120.

Not quite.

Of course not, you never factored in what my speedo is saying, and THATS what I would be adding the extra seconds to.

so if my spedo says 90 on it, did the mile in 30 seconds (as general fart), Id add them 30 seconds to what my spedo says, meaning Im really going 120 miles per hour

 

[Demon-Xanth]

Just call it 10% and you'll be fine.

10=11
20=22
30=33
...

 

[Zenmervolt]

Originally posted by: BlackTigers
When mine was off it was because I replaced the lights to LED's in my cluster, so I just had to reset the needle in that fashion. The tire size makes it difficult.

Yeah, it's a pain to work on the instrument cluster. I've had to pull the speedometer on my 951 several times (stupid old cheap VDO odometer gears disintegrating) and I'm thankful that it has an internal stop pin. As long as I line the needle up with the "0" on the gauge face when I put it back on, it's set.

ZV

 

[kalrith]

Originally posted by: funboy6942

Originally posted by: BlackTigers

Originally posted by: funboy6942
OK, really quick before my pills kick in and Im fucked for the day.

If 1 minute in a mile = 60

Wouldnt it be safe to say then if I did it in less time, I would add every second under 60 seconds as a mile per hour?

60
-54
=
6

Well let's say you did it in 30 seconds.

That's actually going to be 120 miles an hour.

60-30=30
60+30 = 90
90 != 120.

Not quite.

Of course not, you never factored in what my speedo is saying, and THATS what I would be adding the extra seconds to.

so if my spedo says 90 on it, did the mile in 30 seconds (as general fart), Id add them 30 seconds to what my spedo says, meaning Im really going 120 miles per hour

I don't think that would work. Let's plug in some numbers and see where it gets us (assuming your speedo is off by 11.11%). The first number is what your speedo displays, and the second number is the actual speed you're traveling (rounded to whole numbers to make it easier).

• 60 * 1.11 = 67
  70 * 1.11 = 78
  80 * 1.11 = 89
  90 * 1.11 = 100
  100 * 1.11 = 111

Now let's calculate them with your method. The first number is what the speedo reads. The second set of numbers is the subtracting the time it takes to travel a mile from 60. Again, I'm rounding to simplify the math.

• 60 + (60-54) = 66
  70 + (60-46) = 84
  80 + (60-40) = 100
  90 + (60-36) = 114
  100 + (60-32) = 128

As you can see, that method is pretty close at 60 mph, but it doesn't work for any other speed.

 

[hanoverphist]

Originally posted by: Zenmervolt

Originally posted by: funboy6942

Originally posted by: yelo333
So then speedo * 1.11111... = your real speed (You were going 67mph)

If you want to go 60, set speedo to 60/1.1111=54mph

Edit: 54 seconds per mile, want miles/hr.
1/54 = miles per second
1/54 * 60 = miles per minute
1/54 * 60 * 60 = miles per hour = 66.66667mph

So 60 is actually 67mph in real speed so my spedo is a good 7mph off.

If this is true, I thank you very much for your time, and its what I was needing to know so I dont get a ticket. I was safe for speed on highway is 70 I was on

Speedometers are rarely off by a fixed amount, rather they tend to be off by a percentage. It looks like yours is off by about 11%.

Also, this thread is getting moved into the Garage.

ZV

this. my truck is about the same % off, i have to remember to subtract rough estimates for 35, 45 and 65 roads i drive on. not too hard to do, i usually do 10% + 1 for a basic guide. havent gotten any tickets or camera flashes so far.