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Old 05-01-2012, 06:22 AM
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Switching 17's to 20's

I have stock 17's on my Laredo and I am thinking of getting a set of the polished stock 20's. will my speedometer be off and will I have to reprogram for the sized difference? anybody do this yet?
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Old 05-01-2012, 07:05 AM
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It will if you change your tire size. To correct this all you have to do is get a Superchips.
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Old 05-01-2012, 12:13 PM
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Re: Switching 17's to 20's

Can this be compensated for by a computer update with the dealer?
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Old 05-01-2012, 01:09 PM
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Re: Switching 17's to 20's

No can switch from 17 to 20 and the speedometer will be correct, maybe 1-2% +/- this is only if you use the correct size of tires (width and heigh).

They are a lot of calculators on the web that tells you how much will do with new sizes. Try some of them

http://www.web-cars.com/math/tiresize.html
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Old 05-01-2012, 05:21 PM
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Re: Switching 17's to 20's

Your dealer should be able to calibrate this for you if there is a change.
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Old 05-01-2012, 05:27 PM
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Re: Switching 17's to 20's

I dont know for sure, but I have a feeling that the total tire diameter and tire height is very close, if not identical between the different wheels available on the Grand Cherokee. I HIGHLY doubt that Jeep configures each vehicle differently depending on which set of wheels it has. Especially considering you can get the same model (Overland) with completely different wheel sizes. So I would assume that Jeep would install tires on the 17" wheels that are exact same diameter as the tires on the 18" wheels, or the 20" wheels.


So basically, what I am saying is that if you remove your original 17" wheels and replace with a set of OEM 20" wheels that has the original tire size on, your speedo will most likely be exactly where it needs to be.

James
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Old 05-01-2012, 07:22 PM
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Re: Switching 17's to 20's

Quote:
Originally Posted by JTS97Z28 View Post
I dont know for sure, but I have a feeling that the total tire diameter and tire height is very close, if not identical between the different wheels available on the Grand Cherokee. I HIGHLY doubt that Jeep configures each vehicle differently depending on which set of wheels it has. Especially considering you can get the same model (Overland) with completely different wheel sizes. So I would assume that Jeep would install tires on the 17" wheels that are exact same diameter as the tires on the 18" wheels, or the 20" wheels.


So basically, what I am saying is that if you remove your original 17" wheels and replace with a set of OEM 20" wheels that has the original tire size on, your speedo will most likely be exactly where it needs to be.

James
Agree 100%... Like James said, Theres diff wheels and tire combos for diff model levels. Highly doubt the jeep has to be calibrated to match the oem wheels and tires..
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Old 05-01-2012, 10:32 PM
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Re: Switching 17's to 20's

I believe if the overall diameter of the tire stays the same, your speedometer will show the same speed. Any increase in the wheel size will be offset by the decrease in sidewall height. So, I think you should be fine going from 17" to 20" as long as your overall diameter stays same.
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Old 05-01-2012, 11:33 PM
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Re: Switching 17's to 20's

Good choice in wheels. You're Grand Cherokee is going to look great!
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Old 05-02-2012, 12:44 AM
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Google miata.net tire calculator. I've always used that one.

And like was already said, if you keep the same overall diameter, it'll read the same.


Sent from a pay phone.
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Old 05-02-2012, 06:44 PM
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Re: Switching 17's to 20's

James is correct if the diameter stays the same. I just switched from the 18's to the Summit highly polished 20's today and the dealer said the speedo would not register different until 80 mph or so.
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