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Patrick L. · 11-10-2020, 09:42 AM

Our speedo's are notorious for being 'way out of whack'. So you'll never know. 3:54 should give about 4mph more than the 3:78 at the same engine speed. The way I check my actual speed is to compare the speedo with a GPS. When mine [ 3:78] shows 40mph the GPS says 44. At 50mph the GPS says 57.

11-10-2020, 09:42 AM	#2
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Rear axle ratio and car speed Our speedo's are notorious for being 'way out of whack'. So you'll never know. 3:54 should give about 4mph more than the 3:78 at the same engine speed. The way I check my actual speed is to compare the speedo with a GPS. When mine [ 3:78] shows 40mph the GPS says 44. At 50mph the GPS says 57.