50mph w/33"=what? (1 Viewer)

[PabloCruise]

Your speedometer is not pointing to true magnetic North


Ed

You need deguasing...

 

[PabloCruise]

some PO must have done something to my rig, because the speedometer reads the exact same speed as the GPS

You can replace the speedo gear w/ one that has a different tooth count...

 

[IDave]

Your speedometer is not pointing to true magnetic North


Ed

We have a local declination of 19 degrees!

 

[IDave]

Its not a linear relationship, so the speed is not offset the same amount ant any speed.

The relationship should be proportional, though, right? I mean, 0 mph should be 0 mph, then the error should be in a ratio of the actual tire diameter to the original tire diameter (of course, circumferance ratios would also work).

 

[FJ40zen]

I used hand held GPS and figured my correction factor for 33*12.5 MT's was 1.17

So 50 = 58.5 MPH

I agree. 1.16-1.2 x speedo reading. Depending on air pressure in tires/actual circumference difference and of course, the gps.

 

[Brian in Oregon]

What was your original tire diameter, and was the speedometer accurate with the original tires?

What's your gear ratio (usually 3.70 or 4.10)?

 

[Spud]

Original tire dia.?? I am not sure exactly what "stock" is on a 77'FJ40, Is it surely 29"?

Vehicle is new to me and came with 33's, so that is "my" original....

As far as gearing, I am not sure, it is stock gears.

I am driving it about 150 highway miles today. First extended drive it has been on, (lately). I did a whole bunch to fix it up and iron out all the messed up stuff from neglect and or PO busy hands. It is running great now, I am confident. It felt good doing 50, (which is closer to 60), so I wont be holding too many folks up behind me. At the end of the ride I get to 4wheel up the class 6 to my place...I am very excited to get it on.

 

[PabloCruise]

Sammy, I think you mean "Whether" vs "weather" in your sig...

 

[Vicm]

Don't you think that somebody should be selling a face plate that you can stick on the old speed plate for whatever size tire with the correct speed reading. I don't think it should be hard to do.
Thia maybe another dum idea.
Vic

 

[fjwagon]

It's about 6-7 mphs at 50 when I pass those speed things that tell you fast you are going.

 

[DSRTRDR]

You can replace the speedo gear w/ one that has a different tooth count...

I know, I know - every time my husband got a bigger set of tires on his truck, we went shopping for the speedo gear again (the first time I had to go with him since it fried while I was driving )

fortunately, my truck came already well adjusted

 

[IDave]

I know, I know - every time my husband got a bigger set of tires on his truck, we went shopping for the speedo gear again (the first time I had to go with him since it fried while I was driving )

fortunately, my truck came already well adjusted

I'm not sure there were ever stock speedo gears that work exactly for 33s, from all of the research I've done. However, I do have those that should be closest. I just need to drain the transfer case and do the swap. It will be interesting to see what happens.

https://forum.ih8mud.com/showpost.php?p=1754780&postcount=15

 

[projektdotnet]

I think was kept you out of speeding tickets was driving a 40 series......

Worked when I had my old ranger too and I buried the needle in that sucker before (speedo ends at 85MPH). I also had someone pace me side by side while using this method and it worked quite well because my math and his speedo both came to the same speed

EDIT: Although I agree it is not the most accurate estimation