Ford Powerstroke Diesel Forum banner

Speedo error on actual speed

589 views 3 replies 2 participants last post by  RUFFSTUFF 
#1 ·
So I stuck some 20" KR rims on the '08, using the 275/65-20 tires. Stockers were 275/70-18. I programmed the CTS with the 20" sizes and it reads 3% slower than the speedo. Programming the 18" tire gives a 5% slower reading. So I got to wondering if the speedo was off. I had a popo friend shoot me today, and the speedo is dead on with his laser gun, which was certified last week. I got screwed out of 5K miles on the 100K warranty:mad:
 
#2 ·
<---- waiting patiently for a version of this story that makes sense.
 
#3 ·
Installed CTS.
Speedo reads 10% faster than CTS when set for stock tires.
Installed 20" KR rims.
CTS reads 5% slower than speedo on corrected tire size for 20" rims.
Speedo reads correct by laser detector

Deduction: speedo is 10% faster than actual speed on stock 18" tires so warranty expired 10% quicker than it should have.

I hope that version makes sense. I'm in Italy sitting on the shore getting drunk. Maybe that helps:dunno::woot:
 
#4 ·
Woohoo! Well unless your CTS has a GPS function I'm sorry to say that using the tire size will not be accurate unless you get really lucky.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top