Tire Size Changed but Speedo way off...

MurderedJK

MurderedJK

Member
Okay guys so here is my weird problem. I upgraded my rigs tires from 33s Nitto TGs to the 35 TGs. I bought the Superchips Flashcal to adjust the tire size and correct the speedo. I measured the tire from the ground to the top of the tire which was I think 34 something. I completed the flashcal reflash and drove around and found that the speedo was at least 7MPH off. So I did some more playing and here is where it confuses me. I set the flashcal to reflash the Jeep back to factory settings which put the tire size at 30.75 or something. Well I drove around and found that this put the speedo at exactly what my GPS is showing at 35MPH and at 60MPH. I also found a radar box to double verify and again the stock tire size setting is more accurate at the speedo than the actual size of the tire... Is this strange or normal? I have a 2011 JKU Sport if that matters. :thinking:
 
StrizzyChris

StrizzyChris

New member
If you are talking about the in dash navigation GPS and the speedo, then they are always (at least on my 2013 with 430N) the same...even of they are wrong. I know garmin gps window suction style units measure speeds based on gps, but I am thinking the factory unit uses the speedo for its reading :thinking:

May want to read the instructions closely one more time and make sure the tuner is set accurately
 
jeeeep

jeeeep

Hooked
MurderedJK said:
Okay guys so here is my weird problem. I upgraded my rigs tires from 33s Nitto TGs to the 35 TGs. I bought the Superchips Flashcal to adjust the tire size and correct the speedo. I measured the tire from the ground to the top of the tire which was I think 34 something. I completed the flashcal reflash and drove around and found that the speedo was at least 7MPH off. So I did some more playing and here is where it confuses me. I set the flashcal to reflash the Jeep back to factory settings which put the tire size at 30.75 or something. Well I drove around and found that this put the speedo at exactly what my GPS is showing at 35MPH and at 60MPH. I also found a radar box to double verify and again the stock tire size setting is more accurate at the speedo than the actual size of the tire... Is this strange or normal? I have a 2011 JKU Sport if that matters. :thinking:
Click to expand...

I have a 2010 and I had to make the tire size closer to stock then the actual measured size. I checked it against my Garmin to check the speed accuracy and got it as close as I could. I did submit a trouble ticket to Superchips after this but never received a reply and as far as I am aware of, none of the recent upgrades have changed anything. FYI I still get BSOD when plugging the unit to my laptop for updates ..this issue was also never replied to as well.
All other functions seem to work as advertised but I'm leaning towards making a switch to the Bully Dog programmer.
 
OverlanderJK

OverlanderJK

Resident Smartass
That doesn't sound right. Are you measuring and setting the device correctly? My 35's were almost 33 exactly.
 
wayoflife

wayoflife

Administrator
Staff member
MurderedJK said:
Okay guys so here is my weird problem. I upgraded my rigs tires from 33s Nitto TGs to the 35 TGs. I bought the Superchips Flashcal to adjust the tire size and correct the speedo. I measured the tire from the ground to the top of the tire which was I think 34 something. I completed the flashcal reflash and drove around and found that the speedo was at least 7MPH off. So I did some more playing and here is where it confuses me. I set the flashcal to reflash the Jeep back to factory settings which put the tire size at 30.75 or something. Well I drove around and found that this put the speedo at exactly what my GPS is showing at 35MPH and at 60MPH. I also found a radar box to double verify and again the stock tire size setting is more accurate at the speedo than the actual size of the tire... Is this strange or normal? I have a 2011 JKU Sport if that matters. :thinking:
Click to expand...

You are NOT supposed to measure your tire to the top but rather, measure only to the edge of the shoulder, the point where the sidewall turns 90° and becomes the tread. On an advertised 35" tire, that should be closer to 33". Having said that, did you make sure to set your gear ratio too? If that is off, it will effect your speedo. I would double check both and try it again.
 
MurderedJK

MurderedJK

Member
wayoflife said:
You are NOT supposed to measure your tire to the top but rather, measure only to the edge of the shoulder, the point where the sidewall turns 90° and becomes the tread. On an advertised 35" tire, that should be closer to 33". Having said that, did you make sure to set your gear ratio too? If that is off, it will effect your speedo. I would double check both and try it again.
Click to expand...

Okay so I did my measurements based on what you said Eddie, and my speedo is right on. StrizzyChris, I have an aftermarket Navi as my rig did not come with a factory navigation system, so the speed reading is solely based on the GPS antenna reading (which is not always accurate but close). I guess the problem was when I was instructed on how to set the tire size, I was told to measure from the ground to the "level" top of the tire...:naw: Thanks for all of the replies and for them being so quick! :thumb:
 
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