speedo gear question

[wrangleramp88]

Hi , I just changed my tires to 225/75/15 from 255/70/15 but it came with 205/75/15 and it has 4.11 in the rear, dose any one happen to no what speedo gear i should use as far as how many teeth it should have. I have a 41 tooth that it came with, and a 39 tooth i used for the large size tires but not sure how accurate it was.

 

[TerryMason]

What type of Jeep?

 

[wrangleramp88]

02 jeep wrangler with a 4banger thats why i went to the tire size that i did ,the 4 dose not have enough power to turn a bigger tire like i would like it to. thanks

 

[Bounty__Hunter]

I would run the 41 and check it with a GPS speedo.

 

[LVRockCrawler]

if you dont have a gps speedo or someone to pace ya - you can alway get on an interstate w/mile markers - compare the markers with your odometer and do the math accordingly....

 

[jfrabat]

or just look up a chart; you can convert metric to inches in many sites. For me, the chart in Quadratec has been very accurate.

 

[wrangleramp88]

I found its off buy 2.5 MPH and that's not bad ,but it cant be fixed because a tooth is is worth 10% and I'm not off that much for the next gear to fix it

 

[jfrabat]

At 60mph, a tooth will ad about 3mph. In my case, I need a 44T speedo gear, but since only 43T is available, this is what I have, and I am off about as much as you are (although I got no choice to fix it unless I have a gear custom made; I rather save that money and invest on my 33" BFG MT's KM2 33X12.50R15 and use the speedo gear the jeep came with, which is perfect for 33" tires and 4.88 gears). At 70mph, I am off by by almost 5mph (speedo shows almost 75mph when my GPS shows 70mph...

 

[TerryMason]

Leave it as is, and get the speedo calibrated next time you get a speeding ticket. I've used that in the past

 

[wrangleramp88]

OK I'm a little confused again according to all the calculator devices i find on the net that tell me that my speedo is fast, when i go by the mile markers on the highway my odometer takes longer than the markers on the highway to go by ,not a lot but longer .

 

[TerryMason]

Try doing it 10 miles at a time. More distance may make it easier to judge.

 

[wrangleramp88]

Thanks for the tip off, over a span of 7 miles it said i was off by 2 tens to the (-) side like it suppose to be if your speedo is faster then it should be. Plus i took my wife car to work and her speedo is 2 tens less in distance than what mine is on the same trip.

 

[jtjwrangler]

Speedometer Gear Computation