Why is my speedometer off with stock size tires?

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.
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Also its one i trust because its the one chris posted in a forum. Also everything on there is also on the window sticker
 
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All vin numbers matching. No im not in idiot like rubicon88 seems to think. Just a genuine question.
 
Yes it says on the sticker the size on the door jamb. Then it says optional equipment 30” tires. Thats where im confused whether they didnt change the speedo gear, or something else going on
 
So looked at mine , I didnt even know there was one each side, I only ever see the one with the vin emissions codes and build date on the body.
Mine other one is on the right door and says all 3 sizes 215 /15 225/15 and 225/16 all 7 inch wide.
So if the Rubicon was the only one with 16,s and they got 30" tires I wonder why on my door it says 225/16?
 
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Fishtaco said:
So looked at mine , I didnt even know there was one each side, I only ever see the one with the vin emissions codes and build date on the body.
Mine other one is on the right door and says all 3 sizes 215 /15 225/15 and 225/16 all 7 inch wide.
So if the Rubicon was the only one with 16,s and they got 30" tires I wonder why on my door it says 225/16?
Click to expand...
Mine does not have that. Weird. It only has the one i pictured up above and lists thenone tire size.
 
Bbrayden85 said:
Yes it says on the sticker the size on the door jamb. Then it says optional equipment 30” tires. Thats where im confused whether they didnt change the speedo gear, or something else going on
Click to expand...
Bbrayden85 said:
Mine does not have that. Weird. It only has the one i pictured up above and lists thenone tire size.
Click to expand...
your sticker also only says "215/15" not 225/15 which I thought was the standard for the sport?
I am sure somebody will know?

https://www.quadratec.com/c/reference/tire-size-calculator
 
Bbrayden85 said:
View attachment 261205View attachment 261206View attachment 261207View attachment 261208
All vin numbers matching. No im not in idiot like rubicon88 seems to think. Just a genuine question.
Click to expand...
Nobody suggested you were an idiot and nothing could be further from the truth.
I'm very curious to exactly what happened here and why the discrepancy.

You stated from the get go that your Jeep had 225's..when it's 215 on your tag. It also shows 215 on your window sticker.
Your Jeep would've come with Canyon wheels with that 30" tire option. Canyon's are 8" wide. Your tag isn't even showing those as it's showing the stock 15x7 wheels.

You said you were 3-4 mph off. Ok...but you didn't define that. As in 3-4 mph off at what mph?
If you're just a constant 3-4 mph off no matter the mph...that's not tire related.

If it's a tire discrepancy you'll be a percentage off throughout the MPH range. (Different mph off at different mph)

Clearly your Jeep is showing it should've had 30" tires and canyon wheels.
That said I've been around many TJ's...hell i used to order new ones for the dealership and I honestly can't tell you if every single one on the door tag always indicated the correct tire. I'd think they would (probably a law) but I never paid attention to every single one I've been around.

Did someone err when printing out the door tag during the build in 2002?
Anything is possible.
Hell the factory service manuals have misprints in them.

Did Jeep put a speedo gear in for a 215 tire since that's what the tag calls for?

It's really hard to know exactly what happened here.

If you're concerned with getting the speedometer accurate and you're a percentage off in the mph range then it's definitely tire related. For a 30" tire I believe you need a 28 tooth speedo gear since you have 3.07 gears in the axles.

Maybe others will chime in if they've noticed a discrepancy between tag and actual factory build on their rig too.
 
Rubicon88 said:
Nobody suggested you were an idiot and nothing could be further from the truth.
I'm very curious to exactly what happened here and why the discrepancy.

You stated from the get go that your Jeep had 225's..when it's 215 on your tag. It also shows 215 on your window sticker.
Your Jeep would've come with Canyon wheels with that 30" tire option. Canyon's are 8" wide. Your tag isn't even showing those as it's showing the stock 15x7 wheels.

You said you were 3-4 mph off. Ok...but you didn't define that. As in 3-4 mph off at what mph?
If you're just a constant 3-4 mph off no matter the mph...that's not tire related.

If it's a tire discrepancy you'll be a percentage off throughout the MPH range. (Different mph off at different mph)

Clearly your Jeep is showing it should've had 30" tires and canyon wheels.
That said I've been around many TJ's...hell i used to order new ones for the dealership and I honestly can't tell you if every single one on the door tag always indicated the correct tire. I'd think they would (probably a law) but I never paid attention to every single one I've been around.

Did someone err when printing out the door tag during the build in 2002?
Anything is possible.
Hell the factory service manuals have misprints in them.

Did Jeep put a speedo gear in for a 215 tire since that's what the tag calls for?

It's really hard to know exactly what happened here.

If you're concerned with getting the speedometer accurate and you're a percentage off in the mph range then it's definitely tire related. For a 30" tire I believe you need a 28 tooth speedo gear since you have 3.07 gears in the axles.

Maybe others will chime in if they've noticed a discrepancy between tag and actual factory build on their rig too.
Click to expand...
The 225 was a typo I didn’t realize until later. Apologies
 
Rubicon88 said:
Nobody suggested you were an idiot and nothing could be further from the truth.
I'm very curious to exactly what happened here and why the discrepancy.

You stated from the get go that your Jeep had 225's..when it's 215 on your tag. It also shows 215 on your window sticker.
Your Jeep would've come with Canyon wheels with that 30" tire option. Canyon's are 8" wide. Your tag isn't even showing those as it's showing the stock 15x7 wheels.

You said you were 3-4 mph off. Ok...but you didn't define that. As in 3-4 mph off at what mph?
If you're just a constant 3-4 mph off no matter the mph...that's not tire related.

If it's a tire discrepancy you'll be a percentage off throughout the MPH range. (Different mph off at different mph)

Clearly your Jeep is showing it should've had 30" tires and canyon wheels.
That said I've been around many TJ's...hell i used to order new ones for the dealership and I honestly can't tell you if every single one on the door tag always indicated the correct tire. I'd think they would (probably a law) but I never paid attention to every single one I've been around.

Did someone err when printing out the door tag during the build in 2002?
Anything is possible.
Hell the factory service manuals have misprints in them.

Did Jeep put a speedo gear in for a 215 tire since that's what the tag calls for?

It's really hard to know exactly what happened here.

If you're concerned with getting the speedometer accurate and you're a percentage off in the mph range then it's definitely tire related. For a 30" tire I believe you need a 28 tooth speedo gear since you have 3.07 gears in the axles.

Maybe others will chime in if they've noticed a discrepancy between tag and actual factory build on their rig too.
Click to expand...
Thats the weird thing. It does have the original canyon wheels on it. The only thing is the door jamb sticker and the speedo being off. I will have to check if it is off by 3-4 at all speeds or not. If its mph off would the culprit be my sensor the gear is on? Or the guage cluster
 
Take speed readings at a couple of different points and note the difference.

If you have the speedo gear for the small tires, you should be going faster than the speedo is reading.
 
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