Offroad-Express

Hi Team,

Any Jeepers here recalibrated their electronic speedo when fitting larger tyres? What did you use? Who did you go to? I'm looking at the JayCar option but not 100% convinced this will work.

Cheers,

JP

Anything electrical in Nelson may do a Kit, but being a Jeep there may be some "off the shelf" options in the US already available...

What Jeep is it? If it's a TJ, a simple gear picks up speed from transfer case. Grand Cherokees are different.

Superlift make a correction unit that I used in the past. Very easy and accurate.

Thanks for the advice - my truck is a 2003 Grand Cherokee CRD. From what I understand I need to intercept the signal from the ABS sender.

jonboy80 wrote:Thanks for the advice - my truck is a 2003 Grand Cherokee CRD. From what I understand I need to intercept the signal from the ABS sender.

I'll search and see what can be found. I know one solution is for the dealer to reflash the PCM with new tyre size. But whether dealers in NZ do that is what I don't know.

TJ wrote:

jonboy80 wrote:Thanks for the advice - my truck is a 2003 Grand Cherokee CRD. From what I understand I need to intercept the signal from the ABS sender.

I'll search and see what can be found. I know one solution is for the dealer to reflash the PCM with new tyre size. But whether dealers in NZ do that is what I don't know.

I've heard this too, however many have said it can only be changed to factory size settings eg. going from 235/65R17 to 245/70R16.

I've looked about and found that Pin13 from the ABS module sends the VSS signal to the speedo, I'm going to try the JayCar option soon to see if the signal can be modified.

if its an analogue speedo the easiest way is to make up a new sticker with the 10, 20, 30 40 etc in the correct places and stick that on the faceplate over the old numbers, you'd be surprised how original and good or better you can get it to look with a bit of time spent on paint or whatever program you use on the computer, if your diesel and need the odometer to be accurate you may not get away with that method, otherwise google is your friend lots of people have done different speedo drive gears adaptors etc and spent a few hundred bucks getting it sorted

Drive it and compare it to a GPS . Most things over read by 7 % .you might find its actually more accurate with bigger wheels

derk wrote:if its an analogue speedo the easiest way is to make up a new sticker with the 10, 20, 30 40 etc in the correct places and stick that on the faceplate over the old numbers, you'd be surprised how original and good or better you can get it to look with a bit of time spent on paint or whatever program you use on the computer, if your diesel and need the odometer to be accurate you may not get away with that method, otherwise google is your friend lots of people have done different speedo drive gears adaptors etc and spent a few hundred bucks getting it sorted

Pros: Get more KMs out of RUCs

Cons: ABS thinks you are doing 100 when you are actually doing 112 (for example), need to check if i'm gonna run into issues braking with larger tires

sirLachlan wrote:Drive it and compare it to a GPS . Most things over read by 7 % .you might find its actually more accurate with bigger wheels

Yup, will try this tomorrow - hopefully Jeeps are woefully over-reading so I'm within the threshold for my cert

So the speedo is out by 10%. 50kph on the dash is 55 on the GPS, 100kph is 110 on the GPS.

I am attempting to fit the JayCar module this week, looks to be the same set-up as many US based speedo calibration modules.