FJ62 speedometer accuracy; stock 4.11 gears and 31" tires (1 Viewer)

[Spook50]

So today while driving home from work I turned on the GPS speedometer app on my phone (GPS Speedometer and Odometer on a Galaxy S9+) to compare it to my OEM speedo. Surprisingly, my factory speedo was almost perfectly accurate. Most deviation was at 80MPH (highest speedo I reached) and my phone showed 82MPH. The slower I went, the less the error. This is funny because going from the stock 28" tires to 31" without regearing should throw it off by 9.3% when you do the math, which I had gone by since I first put 31" tires on at 215K miles. In my case, real world comparison says different. I'm going to try a couple other GPS speedo apps to see if their accuracy is the same.

Just a little gee whiz info I thought I'd share.

 

[OSS]

Yeah they're highly inaccurate. On my FJ60 with 31" tires and stock 3:70 gears, my speedo showed about 10% faster than actual (should have shown 10% slower) but my odo showed 10% lower which was correct

 

[Spook50]

Might have to look at finding a shop to refurbish my speedo to read accurately. I know there's one in Spokane and mechanical eddy current speedos can be tweaked within reason to read accurately.

 

[Seth S]

I’m right about 8% error on distance and about 10% on speed with 31’s.

 

[Spook50]

So it looks like my speedo is actually pretty accurate as far as speed, but when comparing my odometer to what I measured on my GPS this morning it showed a 15.7% error. Odometer showed 18.2 miles and the GPS showed 21.6 miles. I don't know if this correction can be taken up by any modification to the speedometer assembly itself though, beyond simply rolling the odometer forward to the current mileage on the vehicle. It'd be nice, but I think the only way I'm going to get close to accurate again will be through changing the speedo drive and driven gears or regearing my diffs. If I'm going to regear my diffs I'll go ahead and upgrade to 33" tires at that point and regear for those.

Cool thing though is that means my fuel economy is actually much better than I thought it was. The last tank I ran I calculated 13.7 MPG but refiguring it was actually 14.5 MPG, so that's pretty neato.

 

[4Cruisers]

Fro one of @POTATO LAUNCHER's posts:

"I have done this recently to my 60 on 35s. @Dixon Santana pointed me to Commercial Speedometer Service in Sacramento, CA. Use a gps based speedometer to figure your actual speed vs. what the stock speedo reads. Call and talk to Chuck, tell him what you drive, how much change is needed and he will send you an inline correction part that takes less than 2 minutes to install for around $80 to your door. Awesome service and my speedometer is dead on.
One banana job with everyday results."

BTW, this is still on my list of things to do.

 

[Spook50]

Fro one of @POTATO LAUNCHER's posts:

"I have done this recently to my 60 on 35s. @Dixon Santana pointed me to Commercial Speedometer Service in Sacramento, CA. Use a gps based speedometer to figure your actual speed vs. what the stock speedo reads. Call and talk to Chuck, tell him what you drive, how much change is needed and he will send you an inline correction part that takes less than 2 minutes to install for around $80 to your door. Awesome service and my speedometer is dead on.
One banana job with everyday results."

BTW, this is still on my list of things to do.

I'd like to get it dialed in right, but I'm suspecting any adjustment to either the speedometer magnetic coupling inside the gauge or the gearing driving the odometer will affect the other. I think what I'll do is just run with it for now, and once I go to 33" tires and regear to 4.56, then send it off to be refurbished and dialed in.

 

[POTATO LAUNCHER]

I'd like to get it dialed in right, but I'm suspecting any adjustment to either the speedometer magnetic coupling inside the gauge or the gearing driving the odometer will affect the other. I think what I'll do is just run with it for now, and once I go to 33" tires and regear to 4.56, then send it off to be refurbished and dialed in.

Seems like a bunch of work for a simple solution.

 

[Spook50]

Seems like a bunch of work for a simple solution.

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The tires and gears are coming eventually. I'll just wait until they're on and the drive ratio is back close to factory before I send out my speedo.