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Speedometer Recalibration


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Well, the 4th GT500 tire and wheel that I bought should be here on Monday or Tuesday...FINALLY...FedEx lost one and shipped it all the way to Salt Lake City to their lost and found department and had a hard time determining that it was mine...morons!!!

 

Anyway, I digress....I'm wondering if I will need to have the speedometer adjusted since I'm going from the 235 50 R 18's to the 255 45 R 18 on the front and 285 40 R 18's on the back...or will it be so minimal that I won't need to worry about it? Anyone have any idea? I know others have done this switch on here...Input appreciated!

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Carl looking at the chart of specifications here are your tire numbers. I don't know if a re-cal would be necesscary.

 

 

Current tire: 235/50/18 Tire dia. 27.2" Rev's/mile at 45 MPH 759

 

New Front: 255/45/18 Tire dia. 27.0" Rev's/mile at 45 MPH 801

New Rear: 285/40/18 Tire dia. 27.0" Rev's/mile at 45 MPH 771

 

There is a difference but I would think too little to warrant a re-cal. The rears are very close. But I'm not an expert. Hopefully this info will help if you call a local tire specialist.

 

Roger

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Carl looking at the chart of specifications here are your tire numbers. I don't know if a re-cal would be necesscary.

 

 

Current tire: 235/50/18 Tire dia. 27.2" Rev's/mile at 45 MPH 759

 

New Front: 255/45/18 Tire dia. 27.0" Rev's/mile at 45 MPH 801

New Rear: 285/40/18 Tire dia. 27.0" Rev's/mile at 45 MPH 771

 

There is a difference but I would think too little to warrant a re-cal. The rears are very close. But I'm not an expert. Hopefully this info will help if you call a local tire specialist.

 

Roger

Here's a nifty tire calculator...

 

http://www.1010tires.com/tiresizecalculator.asp

 

Roger is (again) on the money here, and in my past experience, tires have to be within 1" in overall diameter to avoid triggering Traction Control, ABS warnings and making a speedo correction necessary. I checked too, and your numbers look good.

 

235/50-18 = 27.25" tall

255/45-18 = 27.03" tall

285/40-18 = 26.97" tall

 

My speedo is off by 2 MPH. 2 MPH slower, and I haven't made any tire changes to the stock dimensions, so, there appear some "wiggle room". However, you won't know for sure until you try.

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Thanks to both of you, Roger and Mac...You two are the two people on here that I trust more than anyone else, and I've never met either one of you, but your information is so precise...I thank both of you, and looking at your numbers, I'll give it a whirl and see what happens...the numbers look awfuly close, so I think I'll be ok...

 

BTW, being an ex officer, it's hard for someone like me to trust someone else, but like I said, you two guys are ALWAYS right on the money with your information! Keep up the good work you two! We don't want to lose either one of you guys!

 

Carl

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Not a problem, my friend. Glad I could help.

 

Roger is very bright and very "up, on his SGT game".

 

We don't often agree, but that's more about how we got there, than the end result.

 

Happy motoring, shout out when you need help?

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