Why is my speedometer off with stock size tires?

Bbrayden85

Bbrayden85

TJ Enthusiast
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I just bought a new tj, and the first thing i did before i even bought it was look at the build sheet. And saw on there it was optioned with 30” tires stock. And i was excited and it has 30” tires on it. But after a couple weeks of driving, i realize the speedometer is 3-4 mph off, and the little sticker in the doorjam says the tire size is 225/75r/15. So did jeep just not change anything not even the speedo gear and just throw bigger tires on it? Im just confused, is this the case with anyone else?
 
The little sticker on your doorjamb should list several sizes of tires given that Wranglers shipped with several sizes from the factory.

If you want to calibrate your speedometer, it's a simple thing to do... know your axle ratio and tire size and select the correct speedometer gear tooth count from the chart on the webpage linked to here. It take nothing more than a 1/2" wrench and 5 minutes to change the speedometer gear. http://www.4x4xplor.com/speedo.html

Make sure to rotate the speedometer gear housing to the right position so the new speedometer gear with its different diameter will engage the pinion gear underneath it. If you don't the speedometer won't work afterward.
 
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Jerry Bransford said:
The little sticker on your doorjamb should list several sizes of tires given that Wranglers shipped with several sizes from the factory.

If you want to calibrate your speedometer, it's a simple thing to do... know your axle ratio and tire size and select the correct speedometer gear tooth count from the chart on the webpage linked to here. It take nothing more than a 1/2" wrench and 5 minutes to change the speedometer gear. http://www.4x4xplor.com/speedo.html

Make sure to rotate the speedometer gear housing to the right position so the new speedometer gear with its different diameter will engage the pinion gear underneath it. If you don't the speedometer won't work afterward.
Click to expand...
Thats the weird thing. It only lists the one size. And yea i went through the speedometer gear change on my other tj
 
Buying anything used can get in a quagmire...
What number owner are you....
What did the previous owner(s) do?
Let's spitball a second...
What if a second owner...
What if a first owner....
Called a tire store and they installed stock tires.

Build sheets most times are NOT what some person specified but rather a build sheet the dealer specified for the lot. Most people buy one from the lot and don't want to wait 8 weeks or more build time.
(Unless it's one of the stupid
pre-spec units the mfg sends you...there you get what they send you for the lot)
 
Rubicon88 said:
Buying anything used can get in a quagmire...
What number owner are you....
What did the previous owner(s) do?
Let's spitball a second...
What if a second owner...
What if a first owner....
Called a tire store and they installed stock tires.

Build sheets most times are NOT what some person specified but rather a build sheet the dealer specified for the lot. Most people buy one from the lot and don't want to wait 8 weeks or more build time.
(Unless it's one of the stupid
pre-spec units the mfg sends you...there you get what they send you for the lot)
Click to expand...
I am the second owner. The first owner kept it bone stock. Zero modifications
 
Rubicon88 said:
If using the mile markers you must use a percentage.
3 percent of 60 mph is 1.8 mph
Thats nothing.
Not suggesting you're doing it wrong but just letting you aware in doing the mile marker thing.
Click to expand...
So if a stock TJ had 30,s put on in the factory by request then would they have adjusted the speedo drive for the difference? Or would they not have bothered. The Sahara came with 30,s so the speedo drive/gear must have been different to stock unless it was insignificant enough not to bother?
 
Fishtaco said:
So if a stock TJ had 30,s put on in the factory by request then would they have adjusted the speedo drive for the difference? Or would they not have bothered. The Sahara came with 30,s so the speedo drive/gear must have been different to stock unless it was insignificant enough not to bother?
Click to expand...
Listen I'm not sure what the OP has going on.
He insists there is no tag on his door threshold showing anything other than 225's

Yet he says looking at the build sheet it states a 30" tire option was included.

I used to order new Jeeps for the lot and honestly it was so long ago I just don't remember some of the auto deletes with certain packages, etc...

I'm not sure what he's got going on with it.

I mentioned to him that who knows what a previous owner(s) did to it. He said he's the second owner and the first owner did nothing to it.


??????????
 
Rubicon88 said:
Listen I'm not sure what the OP has going on.
He insists there is no tag on his door threshold showing anything other than 225's

Yet he says looking at the build sheet it states a 30" tire option was included.

I used to order new Jeeps for the lot and honestly it was so long ago I just don't remember some of the auto deletes with certain packages, etc...

I'm not sure what he's got going on with it.

I mentioned to him that who knows what a previous owner(s) did to it. He said he's the second owner and the first owner did nothing to it.


??????????
Click to expand...
I have to agree. My 04 build sheet says 30" tire option and my door jamb sticker says 30x9.5r15.
 
Nomader said:
I have to agree. My 04 build sheet says 30" tire option and my door jamb sticker says 30x9.5r15.
Click to expand...
My new to me 2005 LJ still has what are probably the original tires 30"/9.5"/15" Goodyear Wranglers. They measure less than 29" sitting on the truck. Metric 225/75/15 are 29.3" nominal dimension but probably closer to 28" measured on the truck.
 
roverhi said:
My new to me 2005 LJ still has what are probably the original tires 30"/9.5"/15" Goodyear Wranglers. They measure less than 29" sitting on the truck. Metric 225/75/15 are 29.3" nominal dimension but probably closer to 28" measured on the truck.
Click to expand...
225/75/15 are 28.29. 245/75/15 are closer at 29.47" according to tire calculator on garage buddy app.
 
roverhi said:
My new to me 2005 LJ still has what are probably the original tires 30"/9.5"/15" Goodyear Wranglers. They measure less than 29" sitting on the truck. Metric 225/75/15 are 29.3" nominal dimension but probably closer to 28" measured on the truck.
Click to expand...
Nomader said:
225/75/15 are 28.29. 245/75/15 are closer at 29.47" according to tire calculator on garage buddy app.
Click to expand...
Correct...

But this isn't about actual mounted measurements rather a tag on the door threshold showing 225's but the OP says his build sheet shows 30" tire ...which would also have included a wheel package.

Perhaps he looked at a build sheet from a 3rd or even 4th party and it's not accurate.?.

All the above said...

His speedo wouldn't be off 3-4 mph throughout the entire mph range unless it's just off by that much regardless.

Tire size differences and speedometer variances are off by a percentage.

The difference between
a 225 vs a 30"
@20 mph would be about 1 mph
@60 mph it's around 3.5 mph
@90 mph around 5.5 mph

I didn't see anything stating where he's off by 3-4 mph @ a certain mph but if he's off 3-4 at 60 mph that makes sense.

Maybe it never got 30" tires from the factory in reality hence the tag saying 225 and speedo reading for a 225.
 
Rubicon88 said:
Listen I'm not sure what the OP has going on.
He insists there is no tag on his door threshold showing anything other than 225's

Yet he says looking at the build sheet it states a 30" tire option was included.

I used to order new Jeeps for the lot and honestly it was so long ago I just don't remember some of the auto deletes with certain packages, etc...

I'm not sure what he's got going on with it.

I mentioned to him that who knows what a previous owner(s) did to it. He said he's the second owner and the first owner did nothing to it.


??????????
Click to expand...
Yes. Thats why im confused and wondering if jeep didn’t bother with the correct speedo gear. Its bone stock. And no there is no other size listed. I dont know what’s confusing. It has the original window sticker and shows the 30” tire option.
 
Rubicon88 said:
Correct...

But this isn't about actual mounted measurements rather a tag on the door threshold showing 225's but the OP says his build sheet shows 30" tire ...which would also have included a wheel package.

Perhaps he looked at a build sheet from a 3rd or even 4th party and it's not accurate.?.

All the above said...

His speedo wouldn't be off 3-4 mph throughout the entire mph range unless it's just off by that much regardless.

Tire size differences and speedometer variances are off by a percentage.

The difference between
a 225 vs a 30"
@20 mph would be about 1 mph
@60 mph it's around 3.5 mph
@90 mph around 5.5 mph

I didn't see anything stating where he's off by 3-4 mph @ a certain mph but if he's off 3-4 at 60 mph that makes sense.

Maybe it never got 30" tires from the factory in reality hence the tag saying 225 and speedo reading for a 225.
Click to expand...
It did come with a wheel package. That is also listed.
 
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