Correct speedo gear

[Flyinbrian72duster]

904 with 3:55 with 195/70/14 from what I've seen on a chart it should be a 39 tooth is that correct

 

[Dana67Dart]

Is the car drivable now with the setup you listed?

If so fire up a GPS and go for a drive. Record what the speedometer says and what the GPS says. From that and the current number of teath you can calculate the ratio of old number of teeth to new number of teeth.

 

[SGBARRACUDA]

Your tire should be 24.75" tall? If so you need a 37 tooth gear.

 

[Cliff'sDodge]

Your tire should be 24.75" tall? If so you need a 37 tooth gear.

I've seen GPS Speedometer apps free for the iPhone and Android. It's a good way to dial it in!

 

[dartfreak75]

Here is the chart @moparmandan sent me

 

[69_340_GTS]

Tire is almost 25", so closest gear is 37 tooth.

 

[Dana67Dart]

OK admittedly nit picking here.... what is the tire dia with full body weight on it? (also new vs 1/2 used vs tread bare tire will have an effect all be it small) The gps method will get you the closest and you can decide if you want to be a tad over or a tad under. if the gears were $5.00 each I would say buy a couple and experiment till you are happy but at 40-60 each you want to get it right first time.

 

[Flyinbrian72duster]

Looks like a 37 tooth thanks

 

[69_340_GTS]

You can change the tire diameter by changing the air pressure in it. But the real thing that matters is the tire's circumference. So weight on, or off, the tire won't matter. You can't change the circumference of the tire by placing weight on it. The distance around the tire will be the same whether perfectly round or oblong in some way. And the speedometer works off of distance traveled compared to time (miles/hour). Besides, how accurate do you think you can get it? Your choice of gears is not finite. Many times the exact gear needed falls in between what's available in whole numbers.

 

[MoparMike1974]

The charts are usually accurate but I have seen some speedos that are out of wack and you have to swap the gears to find what works the best. I use a gps ap on my phone, its really accurate.
My dart sport is a few mph off. I swapped gears back and forth but found its off one way or another so I made it read faster than what im really going to help prevent speeding tickets. Its only about 3 mph but thats as close as it can get.

 

[Dana67Dart]

You can change the tire diameter by changing the air pressure in it. But the real thing that matters is the tire's circumference. So weight on, or off, the tire won't matter.

good point. Slapping forehead!