[jimbo]

speedometer gear or whatever it is called that you can change to correct the speedometer after getting different gears. anyway would the dealer have what i need to get my speedometer accurate after going from 235/75/15 tires and 3.55 gears to 33inch tires with 4.56 gears

thanks for any help

 

[Ram]

When I changed up from 29 inch diameter tires to 31's, I "swagged" the teeth count that my speedo gear should change and posted it on the board. Some one came back with a formula as to what gear it should be and I was not off. I just came to the size I needed differently! I seem to remember that the formula had the teeth count of the speedo gear. Do you know what size you have now that went with the last set of tires which ran accurately? I'll try and find that post.

 

[Ram]

Ok, I know that my post was back between Aug 2003 and Jan 2004 and I can't get the search, or page back feature to get that far back in time. Sorry! Hopefully some one who has answered my post in the past will chime in and let us know again!

 

[mrpeal]

best way i can tell you is get your truck to 60 mph true speed, at that point you can calculate actual correction needed. 60 mph is the sae mandated setup to allow the speedometer to run at 1000 rpm. so get either a gps or a known accurate car beside you doing 60 and see what your speed reads, if it is too fast figure out how much. then you need to pull your existing gear and count teeth. lets just say at 60 true speed your speedo reads 50. your 10mph off but on the slow side, you would want to take teeth away from your tooth count. so say your stock gear is a 30 tooth, each tooth is worth around 3mph. so you would want to take 3 away giving you a 27 tooth gear. which are available cheap via www.ring-pinion.com extension 5533, just tell em jamie told ya to call. lol. jeremy will get you a gear. good luck

jamie

 

[Hoss54]

Go to http://www.bgsoflex.com/speedo1.html and put your info into the spaces provided, and it will figure it for you. There are gears available, just have to count the teeth on the drive gear first, and go from there. Amazing what you can find, when searching for a transmission mount.......everything but what you are looking for.......

 

[Duffy]

Here's the fomula that you requested
first you need to figure the driveshaft rpm at 60
speed x gear ratio x 336 / tire diameter
60 x 4.56 x 336 / 33 = 2786 ( or about )
take that number and devide it by 75
2786 / 75 = 37 tooth gear needed
each tooth on the speedometer gear is equal to about 3 mph.
speedometers cost about $12 at the dealership.

 

[440Ramcharger]

Duffy has it.
What I have used and works for me is the following:
Drive down the freeway using a GPS and have the GPS read 60 mph.
Read the value of your dash speedometer, if your speedo reads HIGHER than 60, you need to go with a gear that has MORE teeth. Like Duffy said, each tooth of the speedometer gear is about 3 mph at 60 mph. Use a gear with LESS teeth if your speedo reads LOWER than 60 mph. And again, 3mph per tooth of the speedo gear.

 

[Ram]

Here's the fomula that you requested
first you need to figure the driveshaft rpm at 60
speed x gear ratio x 336 / tire diameter
60 x 4.56 x 336 / 33 = 2786 ( or about )
take that number and devide it by 75
2786 / 75 = 37 tooth gear needed
each tooth on the speedometer gear is equal to about 3 mph.
speedometers cost about $12 at the dealership.

Thats it, Thank you Duffy