Speedometer Calibration

I have a question regarding speedometer calibration, hopefully someone can throw me a bone here. I resized my tires from stock 215/70/15 to 235/75/15 and i regeared from 3.31 to 3.73. I installed the hypertech speedometer calibrator but that didnt do much. I have read and agree that the stock toyotas run high a little high for there numbers. Its seems that when i went to the larger tire it became normal but when i regeared it got all screwy again. The calibrator i think did nothing really except put it to stock or throw it way outa wack lol i have no idea how fast im going now, i know im going slower but i have no idea by how much. any info or ideas that would help me figure this out would be great. Its not a big issue or driving me crazy i would just like to figure it out.

 

gps

 

yeah did that, was going like 80 said 67. same thing at a cop stationed mph radar, going like 40 said 27 i was like no way thats true gf mother went thru it last night at 30 sure enough it said 30 i was like dammit lol

 

dealer should be able to correct it, The chevy dealer has to calibrate our police car speedometers every 6 months.

 

Maybe your dealer will be different, but mine told me they couldn't do that. I got a ScangaugeII and calibrated it using the directions in their manual. You should get an idea from using the same forumla. Here's an excerpt from the manual

I think if you change both tire size and gear ratio, you add the results of the two equations for the total % that your speedo is off.

Edit: Been doing the math, but it doesn't seem to add up with your numbers above, maybe I'm doing it wrong. I'd think the GPS would be your best bet or using the mile markers on the freeway.

 

I did the calculations above came up with 28% thats adding 5% from the stock thats toyota already off. I had the gps out yesterday was going 80 gps said 73, when i was going 30 said like 26. I am going to have to figure this out with the hypertech speedo calibrator. Has anyone used these and am i doing something wrong with it??
You can adjust your speedo with the scanguage II??? if thats so add +1 to scanguage for being awesome

 

Looks like the Scanguage II displays the speed it does not appear to change the speedometer calibration.

 

I have stock P245/75R16 tires..and my speed is off simular to yours according to my GPS , im wondering if that is standard from Toyota?

 

Toyta have a margin of acceptable error in the speedo...It's like 5% or 10% at any speed. It is a cheaper/less specific digital to analog converter and helps keep them out of trouble when folks make modifications to the car
SO some error is just inherent to the system- Start changing tire size and gearing and you'll change what that error is.

 

You should come up with a negative number since your speedo reads faster than your actually going. I got -5.6% but that didn't line up with your previous post. With your above speedo showing 80 and using the -5.6%, then the actual speed/GPS should have been reading 75, which is much closer. All of this is good in theory and tolerances can be off in so many places. Like Brunes said, changing tires and gears will cause any error in the speedo to change as well. I don't know much about the hypertech, but I'd just adjust it to match the GPS or police radar.

Yeah and unfortunately the Scanguage can't reprogram you speedo, but it can display an adjusted speed.

 

I calibrated my speedometer by upgrading the original 215-70-15s to 235-70-15s. Now the speedometer and GPS agree.

When you put the 3:73s in and changed the tires you threw everything off. Good luck getting it sorted out.

 

yeah lol, its all f*d up. It runs bad ass now but i have no idea how fast im going and the trip is off like 1 mile per 10

 

Get a GPS unit and check what your error is. If you don't want to buy one see if a friend will let you borrow his for a day. Then you can know what your adjustment needs to be. My speedometer read 3 MPH fast before I used the TW Tire Size Calculator to see what would bring things to a proper reading.

 

I drove mine with new bigger tires this morning with the GPS. It is off 2.5 mph from 30 to 70. So I am going to print up some small font numbers and tape them to the speedo at the true MPH. I can do it neat and pretty so it does not look like a Jerry Rig.

 

i did a sync with my gps and my scangauge. the scangauge needed to go -3%. the numbers don't seem to add up( speedo reads 70 when my actual speed is 63) but now my sg speed is the same as my gps speed, which i have heard is suppused to be dead nuts correct. ps. i have the stock 245 dunlops on a 4x4, not sure what the gears are at.

 

good idea brp.

 

stick on numbers? just use the gps.

 

depends on how accurate the gps is too. they are still not accepted here for land surveys.

 

So your old tires have a sidewall height of 150.5 mm and the new tires have a sidewall of 164.5 mm... I am thinking of going to 215/75-15 on the next set (161.25mm sidewall), this will keep the same tire width with a slightly taller sidewall and overall diameter. Won't be enough to match the GPS like yours did but close enough for me. I just don't want to set the cruise at 65 and actually be going 60.

 

Im planning to replace my stock tires 215/70/15 to 235/70/15 with my stock rims 15x6 . Did you have a rubbing issue?

Thanks,