1998.5 UP Speedo calibration and service manual tire size selection confusion?

[Chris O.]

 I'm just curious if you guys have any issues with your speedometer  when you compare it to GPS speed.
 I own my truck since 1999 and the speedometer was always off by about 5 miles when traveling at 70 it's actually 75.

I've been looking into the Chrysler shop manual and this stuff doesn't give me the correct tire revolution per mile, WTF?
Chrysler Shop Manual section 22.
TIRES/WHEELS 22.
BR/BE TIRES/WHEELS 22 - 9.
                                                                                                                               
                  SPECIFICATIONS

                  TIRE SIZE SUPPLIER REVOLUTIONS PER MILE

                  P225/75/R16      XL  GOODYEAR     716
                  P245/75R16   WRT/S  GOODYEAR  692
                  P245/75R16  LTX A/S  MICHELIN      691
                  P265/75R16   WRT/S  GOODYEAR  668
                  LT245/75R16 LTX A/S  MICHELIN     679
                  LT245/75R16 LTX M/S  MICHELIN    678 <--- My  DODGE RAM 1999 was set to this ?
                  LT265/75R16 LTX A/S  MICHELIN     648
                  LT265/75R16 LTX M/S  MICHELIN    652 <--- Currently running this tires and I'm still off.
                  LT275/70R17  WGSA  GOODYEAR 650
                  LT235/85R16   WAP  GOODYEAR   650
                  LT235/85R16 LTX M/S  MICHELIN    650 

Now I have a question if you guys have any issues with your speedometer  or did you calibrate your speedometer  with some type of programmer (Smarty, Chrysler DRB III or Hypertech ?).

[dripley]

Mine came with 265/75's and when new they are right on best I can tell. When they are about worn out I am about 1.2% off. This NOT checked with a gps but using mile markers on the interstate based on 100 mile distances. So thats not very scientific but is good enough for me and never felt I needed to do anything about it.

 My truck came with the 265's but the 245's were standard. If yours came with the 245's and you now have 265's that would explain it. 

 I got this from DT and it definitely does not agree with the manual.http://www.discounttiredirect.com/direct/infoTireMath.do?gclid=Cj0KEQiAperBBRDfuMf72sr56fIBEiQAPFXszcCOGEqylankr0xVtsMfoiV6--WVDId1XH0HPKPBJ9QaAtOu8P8HAQ&cid=3898ad0a-70d2-45b5-a8fc-00138672669d&ef_id=V7E2SQAAANi@sJ8w:20161127162832:s

[Mopar1973Man]

Be aware that tire size on the door label 99% do not match what the truck came with.

 

My 1996 Dodge 1500 came with 235/85 R16 tires and the door label states 225/85 R16. Then my 2002 Dodge Ram 2500 came with 265/75 R16 tires but states on the sticker that its 245/75 R16. You'll have to get a build sheet from the dealer to find out what the truck came with.

[Chris O.]

I think I solved my issue.

 

Long story short this is for my upcoming CCD bus OverHead gauge project.
I actually had a small bug in the coding which I believe is fixed now, just need to take the truck out for test-drive.

By the way i just implemented Tire Size Calculator in the CODE, auto calculates tire diameter and circumference based on a tire revs/mile.

 

[Mopar1973Man]

Now the other bug you CAN'T resolve is the GPH flow rate given by the ECM for MPG will be majorly off when you add a tuner and injectors. No way to correct that offset. Like my truck its off by 14.5% with +50HP injectors and the Quadzilla so on a stock overhead I would show 32-35 MPG.

[Me78569]

10 minutes ago, Chris O. said:

I think I solved my issue.

 

Long story short this is for my upcoming CCD bus OverHead gauge project.
I actually had a small bug in the coding which I believe is fixed now, just need to take the truck out for test-drive.

By the way i just implemented Tire Size Calculator in the CODE, auto calculates tire diameter and circumference based on a tire revs/mile.

 

I wish you would hurry up an get that to sale....I need one bad

[Chris O.]

 Yeah it's not ready yet but i'm going to need beta testers.
 Anyone interested ( Me78569, Mopar1973Man )?

 

@ Mopar1973Man 
 I don't think I'm even gonna bother with the fuel rate calculations Lie-O-Meter.

 

.I still need to implement the clock and inside outside temperature, fix details with the gauges.
 I'm also wondering if there is fuel temperature on the CCD bus?

 

Edited November 27, 2016 by Chris O.

[Me78569]

Sign me up I would kill to have that......  

 

 

[Mopar1973Man]

2 hours ago, Chris O. said:

@ Mopar1973Man 
 I don't think I'm even gonna bother with the fuel rate calculations Lie-O-Meter.

 

 

You can do it. It's mathed out from the MAP sensor. Then using offset percentage to correct. The ECM does not have GPH flow rates. 

2 hours ago, Chris O. said:

Anyone interested ( Me78569, Mopar1973Man )?

 

Put me on your list...

[Chris O.]

Both of you are on my list.
On the side note you would be include even if you said no,  you guys help so many folks around that is not even funny.
Just for that you deserve something out of the forum community, so as many other great active members on this forum.

[Mopar1973Man]

(Graciously bows) Thank you sir!

[Chris O.]

 Well we just got one more member for the beta test Dripley.

 

 So I've been thinking about some cheap enclosure project box i could get from Amazon or digikey.
 And just connect to the DLC diagnostic port, this would speed up the project a bit, at least for the beta test.

 

All we really need is 4 wires, the ground and the +12 volt ignition On [i don't think that's available on the DLC] and the two (CCD Bus +) and (CCD Bus -) wires.

[SilverMoose]

From a relative newbie to the site and to diesels I would love to be a lab rat for you.  I currently have the obdlink tweaked pretty good with 11 gauges on my dash.

 

Reguarding the tire size, I used the hypertech to calibrate mine to within 0.02 percent(0.8 miles over 400).  Of course gps verified.  I realized tire size and rev/mile will be different due to the load on the tire and the deflection caused by that. 

[Chris O.]

PM sent ...

[SilverMoose]

Sorry for the delay C O.  Responded to pm

[notlimah]

Wow don't know how I missed this thread! Definitely would like to see the finished project!

[Chris O.]

On 12/14/2016 at 6:36 AM, notlimah said:

Wow don't know how I missed this thread! Definitely would like to see the finished project!

Yeah me too.

 

@SilverMoose - np man I'm busy too.

With my boss recent death(1.5m ago), even my full-time job is in a limbo.
Well I only work for these guys since 1995,  i'm probably going to have to look for new job soon after New Year's.

On the bright side I did try to implement digital compass,  also need to redesign the main motherboard for the new microcontroller i have in mind, get new power supply figure out with auto shut down if there is no CCD bus activity.

 

 Here I am testing the digital compass and TFT brightness control:

 

 

At least the necessary parts are coming in for the beta test:

Here I got the triple axis magnetometer breakout  MAG3110 compass chip solder for testing.

Edited December 18, 2016 by Chris O.

[notlimah]

Wow! That looks awesome! Would this work for trucks that didn't come with the digital overhead?

 

btw

 

sorry to hear about your boss and job situation, hope it all works out for you!

[Chris O.]

Yes that's the idea but for the trucks already with overhead console it will be plug and play.

 

For truck that don't have overhead console installed by factory, a wire harness will be necessary to be installed,  the harness will enable you to make most of the connections needed. 

Edited December 23, 2016 by Chris O.

[Me78569]

The real question is if the overhead isn't there does the PCM have the flash needed?