Rear end speed
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Joined: Aug 2016
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Rear end speed
Hi all.
I just wanted to check something - my truck should have 4.10 gears in the backend as it has axle code '35'. It's wearing 205/85R16s on it, with a tire height of 30.4".
at 50mph (80km/h), the tach shows 2250 rpm. Various calculators I've checked suggest the engine should be running at ~2350RPM with 4.10s in it.
This isn't a huge difference, but I'd be curious why this is. Is the tach possibly wrong?
Also, the speedometer is off - when my GPS tells me I'm doing 50mph, the Speedo is showing 43 mph. This is about double the error you would expect from a 4% change in tire diameter (stock tires are supposed to be 235/85R16).
I just wanted to check something - my truck should have 4.10 gears in the backend as it has axle code '35'. It's wearing 205/85R16s on it, with a tire height of 30.4".
at 50mph (80km/h), the tach shows 2250 rpm. Various calculators I've checked suggest the engine should be running at ~2350RPM with 4.10s in it.
This isn't a huge difference, but I'd be curious why this is. Is the tach possibly wrong?
Also, the speedometer is off - when my GPS tells me I'm doing 50mph, the Speedo is showing 43 mph. This is about double the error you would expect from a 4% change in tire diameter (stock tires are supposed to be 235/85R16).
Logistics Pro
Joined: Aug 2010
Posts: 3,716
Likes: 583
From: Chillicothe
What year is the truck? If it's old enough to have a cable driven speedometer the speedo could be off. Also tire and rim combo. Mounting a tire on too wide of a rim shortens the final tire height.
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