Speed-O Fix

[GBall]

Help I need some help I have been woundering why when I go 70 mph I keep pushing folks down the road wanting them to get out of my way. i was going down the road the other day and my wife was behind me in her car and called me and asked how fast I was going I told her 70 she no way more like 78 plus. Well I do not have stock tires as you can fihgure I have 265/85R16 I think stock are 75/R16. So how do I get this fixed easy without going to a smaller tire. I like the big one's. Let me know if you have any ideas for me. Thanks

 

[Mick2500]

Gball,

Mentally add 10% to your speedo reading. That's what I do.



Mick

 

[BV]

Abbott Enterprises

Abbott Enterprises makes a speedometer correction box or you can use a tire calculator and adjust accordingly.



http://www.abbott-tach.com/index.html

http://www.thisoffice.com/calc_tire3.html#tire_code

 

[Steve St.Laurent]

I do the same as Mick - I've had larger tires on all my trucks for the last 9 years and I never corrected any of the speedos. In your case you're off by about the same as me - 10%. I've verified it on my truck by pacing with a number of friends and found that to be accurate. It's real easy - just add the first digit of your speed to the speed and you'll be close enough. 55 mph indicated is 55+5=60 mph, 65 mph indicated is 65+6=71 mph, 70 mph indicated is 70+7=77 mph. A side benefit of this is your warranty will last 10% longer .

 

[GBall]

Thanks folks for your help guess I will have to do a little math in my head. This is a good reason my wife will not want to drive MY TRUCK!!!! O tooo Bad Honey Thanks again

 

[raw]

speedo fix?

I don't know if this would work on the ram but here goes! I recently installed a white face gauge type kit on my 2k GT Mustang. I had to remove the speedo needles, tach needles,etc. .

After installing the white face gauge decal, and putting the gauge housing back in the dash , minus the clear glass cover. (by the way I used a fork to carefully pry the needles loose from the gauges) and minus needles. Anyway to make a long story shorter,

I went down the interstate with a buddy. I had a GPS unit showing how fast we were going. So at say 60 mph, I let him hold the wheel while I gently pressed the speedo needle back to the speedo stem. pointing it to 60mph. Presto ,correct speedo reading.

Wasn't that hard, but you will have to have the use of a GPS, Also I am not sure, but will the clear gauge lens come off so the

gauges can ge accessed????

 

[Bigramguy]

Moving the speedo needle will only correct it for the speed at which it was set to. The speed change from tires\gears is not linear,it more like a percentage. At 20 MPH if your change was 10% it would be 2 MPH,and at 85 MPH it would be 8. 5 MPH. If you moved the needle up by 8. 5 MPH,it would be correct at 85,but 6. 5 MPH fast at 20 MPH. It does help if you regularly cruise at one certain speed.

 

[Dennis Garrett]

Crawl under the truck, and find where your speedo cable goes into the tail of the transmission. Pull the plastic gear out & look at the marking, it probably has a 32 tooth gear, & you might need a 36 to slow down the readings in the cab. I had to do that on my 97 when it was new, it was about 10% fast on speed & odometer both. Cost me about $12. 00 & 5 minutes of my time.

 

[Big White Beast]

Can't the dealer reprogram tire size???

I know when I had my rear gears changed I went to the dealer to get the speedo reset. (Silly me its run from the rear end, But shame on the dealer for not knowing this!!!! )



I know they can change the speedo to a certain tire size. Not sure what it was. Call and find out.



Just my 2¢ worth...



Garrett

 

[CJ Johansson]

Originally posted by Dennis Garrett

Crawl under the truck, and find where your speedo cable goes into the tail of the transmission. Pull the plastic gear out & look at

Nope, not on a 98 or newer! With the 98's they use the pickup in the differential to get your speed, no gears to change. From there, it goes into the computer, which decides where to put the speedo needle.



Can it be changed in the computer. Well, maybe. The actual answer is yes, with some exceptions. Apparently, there are only a limited number of settings, which correspond to certain tire sizes. If you're outside these settings, you're out of luck and will have to do math or use the Abbott box.



Now for the "maybe" part. Even if you're in the acceptable ranges, your local stealer... uhh... dealer might not be able to reset things. When I went to a bigger tire size, I asked the dealer about changing it and was told that they used to be able to do it, but DC sent the new programming upgrade to their programmer and it removed the ability to reset for tire size. They didn't know why or if they would ever get it back, just that it was not possible to do anymore. This was shortly after the big fiasco with Ford and Firestone and all those tire problems they were having, the speculation was that by not allowing speedo changes for different size tires, DC could limit litigation by not "allowing" the use of tire sizes other than what was originally on the truck.



-cj

 

[work2muchplay2little]

If you want to go the electronic correction route - about $150 from Abbott, it's pretty straight forward. Just installed one on my 1999. Do a search for Abbott in the Products/Accessories forum in the last 2 months and you'll find a detailed installation procedure I posted. I really like mine, especially knowing it's accurate throughout the range, oil change intervals are on time, etc.

 

[JHerrlich]

I mounted a GPS on my dash. I'm kind of anal about having the most accurate readings possible. I realized a couple of weeks ago that I don't even look at my speedo any more. I'll glance at my tach and then at my GPS' speed and never at my speedo.

 

[Yellowlab]

along with that... if you dont change the speedo, im sure that the mileage would be off as well as the gas mileage. So I wonder what my real gas mileage is now that I have the new tires on??

 

[Dennis Garrett]

Gball's truck is a 98 12 valve. Did the change in speedometer drive come with the 98 1/2, 24 valve? I thought the 98 12v trucks use the same trans & speedometer drive as the 97's?????/

 

[Todd G]

I have found that at an indicated 75 mph on the speedo, my GPS reads only 77 mph. Thats with 33" tires. Makes me think my speedo was way off stock. I think almost all speedo's are way off at speeds over 70 mph. I'd suggest testing with a GPS before messing with it.

 

[Slick]

I had a 98 Dakota that I put bigger tires on. I was told by the tire store that the dealer could calibrate for the tire size through the truck computer. So I went to the dealer and they looked in there manual and it had listed settings for different size tires and their rpm(rpm-revolutions per mile). I had increase to 255's and it wasn't listed. Man did that cause confusion. Well they did not like me telling them how simple it was to set the proper rpm's so they did it their way and it was much worse than before. A few days later I wrote out the math for them so they could see how many rpm's my 255's would turn in a mile. I measured the circumference of the tire it was so many inches (I don't remember the specific numbers)and then you divided that to how many inches in a mile and it gave you how revolutions the 255's would turn in a mile!!! SIMPLE Then they entered the rpm's into the computer and WELLA we were right on. Since this is all through the speedo it corrects the miles per hour also. Don't know if it can be done on the Rams that way or not but if it can be done by computer and you know your revolutions per mile it is simple. Sorry to be so long winded!!!Hope this will work for you.

 

[swamp rat]

Fuel mileage and bigger tires.

You can use the same %'age that the speedo is off to multiply the registered mileage to get the actual miles driven.



Say your odometer has registered 625 miles and the speedo is 8% low. Multiply 625X1. 08=675 actual miles driven.



Then do your usual miles/gals. for a more accurate MPG rating.

 

[pcorssmit]

The problem with measuring the circumference is it does not take the loaded radius of the tire into effect.



The best way (since I don't have a GPS) I've found is to use the mile markers on the highway. Note your milage as you pass one, then note the milage 10, 20 , or 100 miles or whatever down the highway (the farther you go, the better), then find the difference (percentage).



On my '97, I did this and then applied the % off that I was to my speedo drive gear, found out I was 2 teeth off (I run 255/85s), went to the stealer and got one for $12. I don't know if the '98 12 vavles use the same setup or not. Also don't know if this makes the auto trans mad (it would only do it on an electronic trans, I never paid attention since I have a stick).



Pete

 

[Slick]

The loaded circumference is never taken into consideration when you are clabrating. Best you can do is measure with the tire mounted on the truck also make sure the pressure in the tire is what you nornmally run (as we all know that too can change by heat build up) But I can say that by using that formula and checking the the mile markers you are about as accurate as you can get. My Dakota was auto but again I state that I do not know if the Rams are capable of this method. The shifting of the trans was not affected at all.

 

[GBall]

Well it took me a day or two to figure out the my fuel millage is up 10% better than I thought. I am now getting about 20 mpg not bad fora big A truck. My buddies keepa asking why I got a Diesel truck and I keep tell them millage and power this kinda stuff just blows them away. I love it Just a FYI folks