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mrhusker

Adjusting 1998 C5 Speedometer

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mrhusker

I have a question for anyone that might be able to help out. I recently changed my wheels and tires and the rear tires are taller then what I had on it previously so the speedo is off a little bit. When cruising 75 on my gauage it's really going close to 80 according to my gps. I have a hypertech programmer I purchased a long time ago just for this purpose. I've tried 3 different times to get it to read correctly but it just won't change the computer to accept the new tire height for some reason. It says it writes the new program but in actuality it doesn't change anything. I'm giving up on the programmer and was wondering if anyone had a tech2 to change it for me? Or maybe let me know what it would take to get it to read right? I would like to have it read the right speed so the wife doesn't forget and get a ticket if she ever drives it. I've thought about taking it to Joe at Classic and that's still an option.

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Extender32

I wonder if the speedo is gear driven? If so, then you'll need to visit a speedo shop to have the gearing changed. I took Julies to https://www.dicksspeedotach.com/ when we changed out her turbo 350 for the 700R4.

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MidNiteFury01

HPTuners can help you solve that, if not a Tech II is your next best bet. A trusted dealership or speedshop can help you with that. Just remember, your speedometer is only accurate at 1/2 tread life of OEM tire sizes. From 10/32nds to the wear indicators there is a speed & revolutions per mile difference of ~3%. There is no gear to change. I need to change the tire sizes in my ride too. I'm off where at 80, actually I'm only doing 77. 

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mrhusker

Thanks for the info. I'll get in touch with Joe at Classic tomorrow morning on my way home from work. Just frustrates me that the hypertech didn't work....

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mrhusker

Found out some more info on this subject if'n anyone cares. 

 

My car has a custom tune in it that NicD installed quite a few years ago. Been a great tune and I have nothing to complain at all about that. I also bought a hypertech tuner to be able to change the speedometer when and if I ever needed it. I got in touch with Nic as I tried 3 or 4 times to get the speedo to read correctly. He told me that the hyoertech came out before the custom tuning really took off so it doesn't know what to think about the custom tune. So it just plays stupid and doesn't really write anything to the computer. It acts like it does but actually won't. So I'll have to get with Nic and have him change it for me. This sucks because I bought the hypertech to avoid having to bother him with something so trivial. But I guess I'll have to because the stock tune will never be reinstalled. 

 

Got an appointment on the 25th around 4 pm at Joe’s shop.

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