speedo gear when going to 17's

jammer84_03

New Member

Nov 30, 2003

468

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May 16, 2007

#1

• May 16, 2007

• #1

been searching but to no real help. i did the spaw to five lug and 17's to replace the 4 lug 15's i had. i have the stock 2.73 gears (do to the gearing in the tremec i have i dont need to up the rear end gear). now my question is, under highway speeds roughly 70-80 mph, my speedo is anywhere between 5-10 mph off. is there any speedo gear i can put in to correct this?

 

Mustang5L5

That is…until I whipped out my Bissell

Mod Dude

Feb 18, 2001

43,238

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Massachusetts

May 16, 2007

#2

• May 16, 2007

• #2

You shouldn't need a speedo gear if you use the correct size tires. On the Mustang, the correct tire size with 17's is either a 245/45/17 or a 275/40/17. If you have either one of these tire sizes on the rear then there is no change in speedo gearing due to the overall diameter of the tire being the same.

Now if you use a different tire size, then it's a different story.

What size are you running??

 

jammer84_03

New Member

Nov 30, 2003

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May 16, 2007

#3

• May 16, 2007

• #3

the 275 40.....just a bf g-force kd

 

jammer84_03

New Member

Nov 30, 2003

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May 16, 2007

#4

• May 16, 2007

• #4

actually i think it is a 45

 

Mustang5L5

That is…until I whipped out my Bissell

Mod Dude

Feb 18, 2001

43,238

17,923

224

Massachusetts

May 16, 2007

#5

• May 16, 2007

• #5

Well then that's your problem. A 275/45/17 is an inch taller than the 275/40/17 you should be running. So your speedo is slow by 5-8MPH around 65MPH.

Only way to fix it is to run the correct tire next time.

 

jammer84_03

New Member

Nov 30, 2003

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May 16, 2007

#6

• May 16, 2007

• #6

got ya.... sounds right though. going to a 275 with a nitto though

when i replace these i mean with the new tires i will have the right sidewall