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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: necromonger on July 28, 2013, 02:00:29 pm

Title: spedo gear ?
Post by: necromonger on July 28, 2013, 02:00:29 pm

what color spedo gear do I need for 16 inch tires trans is a sm465.

Title: Re: spedo gear ?
Post by: Irish_Alley on July 28, 2013, 04:16:19 pm

16" rims? What gear ratio do you have

Title: Re: spedo gear ?
Post by: necromonger on July 29, 2013, 07:14:34 am

I will pull the pan and let you know.because I don't have a clue.

Title: Re: spedo gear ?
Post by: Irish_Alley on July 29, 2013, 07:57:03 am

You said 16" tires but that don't sound right. What's the numbers on the tire

Title: Re: spedo gear ?
Post by: necromonger on July 29, 2013, 06:19:46 pm

235/70/16

Title: Re: spedo gear ?
Post by: necromonger on July 29, 2013, 06:20:39 pm

rear is a 3.73

Title: Re: spedo gear ?
Post by: rich weyand on July 29, 2013, 08:44:13 pm

The original tires on the 1978 K-30, per the chevy brochure, were 31x9.50x16.5.  That's a 31" tire.  The 235-70R16 is a 29" tire.  Your speedometer right now with the shorter tires should read 31/29 high, or about 7% faster than you are really going.

That assumes the rear-end ratio was not changed since new.  3.73:1 sounds like the stock ratio. 

Not sure which speedo gear is in there now, so hard to tell you which one to switch to.