What speedo gear to use with 28" tires?

[John Larkin]

With 3.42 gears, I'm seeing a ~9% variance in road speed vs. speedometer reading with 28" tires, confirmed by the C=2¶r formula (that ¶ is pi, hehe). Is there a speedo gear that can correct this? I'm not planning on going back to 26" tires.

 

[MeanBuicks]

John, I'm headed out the door or else I'd figure it up for you.

See this page for assistance: www.tciauto.com/tech_info/speedo_gears.htm

 

[John Larkin]

27.07 teeth so says the calculator. That makes sense being that the blue speedo gear stock as 30 teeth according to the chart (10% more than the recommended black gear as compared to my roughly 9% needed calibration). Now to figure out where to get a black gear.....Thanks Greg!

 

[TR Custom Parts]

Anyone know the proper GM part# for the black gear. Are these the small size speedo gears that were common to older GM trans or are they huge with a metal sleeve in them. My GM dealer wasn't much help when I told him I needed a black speedo gear for a 2004r. John, would you happen to know it?

 

[MeanBuicks]

Contact Bruce.

I bet he has one.