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BIGGER TIRES.WHAT THEY DO TO SPEED LIMIT,TRASMISSION GEARING


 
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jiiim
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Joined: 16 Nov 2006

PostPosted: Fri Nov 17, 2006 2:27 pm    Post subject: BIGGER TIRES.WHAT THEY DO TO SPEED LIMIT,TRASMISSION GEARING Reply with quote

WHATS THE WORD ON PUTTING BIGGER TIRES ON MY 05 WRANGLER UNLIMITED ( TOOK OFF THE STOCK TIRES AND GOT SOME AN INCH BIGGER ER LEMME SEE ,,MMMM "TALLER"AS RELATED TO MY TRANSMISSION AS FAR AS GAS MILAGE AND ODDOMETER READINGS WILL MY AUTOMATIC TRANS CHANGE GEARS DIFFERENTLY,AND STUFF LIKE THAT,IMHAVING A TIME OF IT PUTTING IT INTO WORDS BUT I THINK YOU GUYS GET IT, THANKS JIM MT. VERNON VA.
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ehirner
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Joined: 01 Jan 2004
Location: Eastern PA

PostPosted: Sat Nov 18, 2006 5:52 am    Post subject: Reply with quote

Nothing changes as far as shifting. The 31s you put on are not that much bigger and you likely won't notice much of a difference. I know I didn't when I made the same upgrade. Now that I'm on 35s, there is a significant difference.
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TJ Apex
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Joined: 29 Jul 2005
Location: Mountains of SoCal. 6257 elev.

PostPosted: Sat Nov 18, 2006 1:03 pm    Post subject: Reply with quote

Since your tires are larger in diameter this would slow your speedometer down.
Example: Your speedo reads 60 mph, in reality your going 65.
Your basicly fooling the speed sensor in to thinking it's going slower, raising your top speed too.
Also, I have found that the faster you go the more the speedo is off.
At 60 mph indicated I'm going 66 mph, but at 65 indicated, I'm going 72.
At 35 mph and slower my speedo and GPS are dead on.
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ehirner
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Joined: 01 Jan 2004
Location: Eastern PA

PostPosted: Sat Nov 18, 2006 2:11 pm    Post subject: Reply with quote

TJ Apex wrote:
Also, I have found that the faster you go the more the speedo is off.
At 60 mph indicated I'm going 66 mph, but at 65 indicated, I'm going 72.
At 35 mph and slower my speedo and GPS are dead on.

That's because it is a percentage difference...not an actual MPH difference.
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TJ Apex
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Joined: 29 Jul 2005
Location: Mountains of SoCal. 6257 elev.

PostPosted: Sun Nov 19, 2006 7:38 am    Post subject: Reply with quote

ehirner wrote:
TJ Apex wrote:
Also, I have found that the faster you go the more the speedo is off.
At 60 mph indicated I'm going 66 mph, but at 65 indicated, I'm going 72.
At 35 mph and slower my speedo and GPS are dead on.

That's because it is a percentage difference...not an actual MPH difference.


your right, for my TJ it's off by 12% at 70 MPH, witch is my normal freeway speed, and most of my driving is on the freeway.
This is also how I figure my gas mileage.
I've been told that when you have larger tires put on your gas mileage goes down. THATS BS! If it does, It's only by a very small percentage, maybe a 1/2%, simply because you've added more rotating weight to your Jeep.
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02' Apex Edition,
2" BB, 31" BFG AT's
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T.O.W. Vehicle
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Joined: 15 Jun 2004
Location: Summerville, SC

PostPosted: Wed Nov 22, 2006 12:43 pm    Post subject: Reply with quote

Larger tires can affect several things. May or may not be too noticable depending on your gearing and size difference of the tires.

As mentioned above you'll need a new speed gear for the tranny unless you can talk the Dealer into changing/correcting your speedometer electrically (think this can be done on the 05's).

Didn't say what type of tranny you have but you may also find yourself with a small lost of power going uphill, i.e. shifting earlier than before.

If you get off road much a change in your crawl speed (4-LO) might be noticable as well (traveling faster).

How big the tire is in reference to the stock is the key. If you go from a 30" to a 31" tire you've only grown 1/2". There are ways to calulate this changes but it is a well know fact that as you grow, sooner or later, (depending on size) you'll be looking to regear the axles.
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nixt
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Joined: 17 Aug 2005
Location: Atlanta/Athens, Georgia

PostPosted: Wed Nov 22, 2006 2:48 pm    Post subject: Reply with quote

A guy that works for The Tire Rack told me that for trucks and SUVs you can differentiate in size by 15% before you really start having problems, but only 5% in cars. Of course some states don't require bumpers or the use of seatbelts in trucks but they'll ticket your ass in a car. Anyway, www.nagca.com has a great calculator that helps you figure out the exact changes due to tire size.
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