Determining distance travelled per rotation of the driveshaft

[Atropia]

I may be oversimplifying, but can't you just change your odometer to km and just mentally move the decimal over a few places?

Not really, lots of reasons. Number one being the navigator needs to manage the trip. I have to focus on the driving (off-road). The comp also lets us back off distance if we blow past a turn and have to turn around. To get the most points you have to be the most accurate. the rally is eight days, 10 hours a day. And we live out of our vehicles. I can’t do any math after day 5 because my brain is fried. That’s why I’m not the navigator

also, odo only measures tenths. The rally comp goes down to hundredths.

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[Atropia]

Hey! We were past math already, all solutions must include duct tape and zip ties, or other things found in your household junk drawer.

Hahaha you should see my “oh shit” box the day we cross the finish line!

 

[Atropia]

Put a long zip tie on the driveshaft and count the whacks.

Ok - now THIS is brilliant!!!!

 

[GATORB8]

Not really, lots of reasons. Number one being the navigator needs to manage the trip. I have to focus on the driving (off-road). The comp also lets us back off distance if we blow past a turn and have to turn around. To get the most points you have to be the most accurate. the rally is eight days, 10 hours a day. And we live out of our vehicles. I can’t do any math after day 5 because my brain is fried. That’s why I’m not the navigator

also, odo only measures tenths. The rally comp goes down to hundredths.

Who/what determines what the accurate distance is?
Sounds like you need to calibrate to that. For example, if it was GPS, you should calibrate to a GPS reading.

 

[Atropia]

Who/what determines what the accurate distance is?
Sounds like you need to calibrate to that. For example, if it was GPS, you should calibrate to a GPS reading.

We do. Sort of. Given lat/long each morning. The director determines the points, we determine how we find them. Not all coordinates have visual confirmation (like a flag). If your too far off, you can lose points.

Navigator plots the points. Then we determine the route. Then she measures the distance of the legs of the route using map rulers. Maps are 1:24000 to 1:200,000 - depending on which map the director gives us.

 

[Left Field]

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One way to get an accurate distance per tire rev is to duct tape a 2' level horizontally on your wheel.

Duct tape a stick or stiff wire on your bumper securely that reaches almost to the ground.

Mark that starting spot on the ground, then move the vehicle until the tire rotates exactly one turn, and verify it again with the level. Mark the second point and measure between the two points.

You'll get best results if you have a long tape (100') and can measure 10 wheel turns, then divide by ten to get the average distance.
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Lol. I’m willing to try all the numbers!!
I’m not tracking your theory though. That would only work if one tire rotation equaled one driveshaft rotation. And that simply can’t be. I run both 37s and 35s and I don’t cover the same distance per rotation. What am I missing from your approach?

As @GrimJeeper points out, an accurate tire circumference (distance traveled per tire aka axle rev) is key. The above suggestion is to get an accurate distance per tire rev.

From there you can divide by your axle ratio to get distance per driveshaft rev.

 

[Atropia]

*************
One way to get an accurate distance per tire rev is to duct tape a 2' level horizontally on your wheel.

Duct tape a stick or stiff wire on your bumper securely that reaches almost to the ground.

Mark that starting spot on the ground, then move the vehicle until the tire rotates exactly one turn, and verify it again with the level. Mark the second point and measure between the two points.

You'll get best results if you have a long tape (100') and can measure 10 wheel turns, then divide by ten to get the average distance.
***************




As @GrimJeeper points out, an accurate tire circumference (distance traveled per tire aka axle rev) is key. The above suggestion is to get an accurate distance per tire rev.

From there you can divide by your axle ratio to get distance per driveshaft rev.

Ahhh got it. Thank you!

 

[Left Field]

What units will your trip computer provide for distance? If 'Feet' that could work well, and perhaps allow you the best possible accuracy.

Find a quiet road with mile markers (or any place with an accurately known distance). Stop lined up with a marker and zero your trip computer.

Drive a mile (or better yet 5) and line up with the new mile marker.

However many miles you drove, multiply by 5280 ft and compare that with your trip computer distance. That comparison will give you the exact correction factor you need.

For example:
You drive 5 miles = 26400 feet. Your trip computer says 27399 feet.

The correction factor would then be 'actual ft' /' indicated ft' = 26400 / 27399 = 0.96354

If you have entered 498mm as the calibration on your trip computer, correct it by multiplying with the correction factor: 498mm x 0.96354 = 480mm

Re-test, it should now be spot-on.

If your trip computer doesn't have feet but gives accurate miles (preferably at least two decimal places) that works too, just do the same division as you used for feet (above).

 

[BigGreen]

This is what I imagine is going to happen with all our accurate measurements:

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