Speedometer gear recomendation

Blue68Coupe · 11-03-2006, 09:08 AM

I just wanted to get everyone's thoughts on speedometer gear selection. I have a 1968 289 with a C4. I just installed a set of 3.55 gears. My rear tires are 24inches tall 14 inch rims.

My math says a 21 tooth gear would be best but I am being told a 20 tooth is best.

Anyone have any thoughts?

Rev · 11-03-2006, 04:39 PM

Try the one that your math says is correct. Then test it next to a known correctly reading car. If you have to, you can then get the other one. They are only about $10 each. That's the way I did it.

Rev

pearce9906 · 11-24-2007, 12:03 PM

There is a formula to figure out what gear you need.....

ring gear x speedometer drive gear x tire revolutions per mile / 1000

this will give you the driven gear tooth number

11-03-2006, 09:08 AM	#1
Blue68Coupe 68 Coupe 289 Join Date: Apr 2005 Location: North carolina Posts: 44	Speedometer gear recomendation I just wanted to get everyone's thoughts on speedometer gear selection. I have a 1968 289 with a C4. I just installed a set of 3.55 gears. My rear tires are 24inches tall 14 inch rims. My math says a 21 tooth gear would be best but I am being told a 20 tooth is best. Anyone have any thoughts? __________________

11-03-2006, 04:39 PM	#2
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	Re: Speedometer gear recomendation Try the one that your math says is correct. Then test it next to a known correctly reading car. If you have to, you can then get the other one. They are only about $10 each. That's the way I did it. Rev __________________ '66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi. O.B.C. #2 '66 coupe

11-24-2007, 12:03 PM	#3
pearce9906 Registered Member Join Date: Nov 2007 Location: OHIO Posts: 20	Re: Speedometer gear recomendation There is a formula to figure out what gear you need..... ring gear x speedometer drive gear x tire revolutions per mile / 1000 this will give you the driven gear tooth number

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