Would ZR1s cause my speedo to be off a lot?
06-01-2009, 04:52 AM
#1
Would ZR1s cause my speedo to be off a lot? After the install of my ZR1s my speedo reads 4-5 mph slower on radar then in the car. According to the tire calculator it should be off no more than .4 mph with 285s in the back. 235s were my stock size. Could this be a gearing issue? My axle was replaced about a year ago, not sure if the gearing changed. Any help would be appreciated
06-01-2009, 05:17 AM
#2
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Depending on that tire calculator, it might have told you the diameter of the tire. Compare that with what your actual tire diameter is...this will rule out anything with the tire. If that matches up, then it would only leave an axle/gearing issue.
Obviously the ZR1's themselves are not the cause.
Obviously the ZR1's themselves are not the cause.
06-01-2009, 05:55 AM
#3
Depending on that tire calculator, it might have told you the diameter of the tire. Compare that with what your actual tire diameter is...this will rule out anything with the tire. If that matches up, then it would only leave an axle/gearing issue.
Obviously the ZR1's themselves are not the cause.
Obviously the ZR1's themselves are not the cause.
06-03-2009, 05:37 PM
#5
The wheels themselves won't have any effect of your speedometer. I assume that you also changed the tires at the same time, so any change in the "overall diameter" of the complete package, will, indeed have an effect on the speedometer reading. Unless you changed the rear gears also, any change you have will be due to the tires only.
06-03-2009, 05:45 PM
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285 refers to the width of the wheel. Width has no effect on your speed. However, if you went from 16" wheels to 17" or 18", then your speedo will be off, due to a larger diameter. You need to get a programmer or scanner to adjust it
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06-04-2009, 01:53 PM
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Just went to the site and used it. Same results as you. The calculator could be wrong. When I upgraded the programmer fixed my problem. Have you installed new gears? Messed with the tune at all? Those could be other issues
06-04-2009, 02:50 PM
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You need to see what gears you have. You can tell by highway rpms. Get on the highway and see what speed you're going at @2000 rpms. If you're going 67, you have 3.23s. If you're going 80, you have 2.73s. WS6s came stock with 3.23s, check the door code GU5. Do the highway test and you can see what you have, then can diagnose from there.
06-04-2009, 06:24 PM
#13
Secondly, simply changing the OD of the wheel won't necessarily change the speedo reading, as the OD of the tires can be juggled to maintain the same overall OD. For example, a 205/75/14 tire, a 215/65/15 tire, a 245/50/16 tire, and a 275/40/17 tire were all available on Firebirds/Camaros between 1982-2002. They were all pretty much the same OD, despite the 3 different wheel diameters.....
06-04-2009, 11:50 PM
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You need to see what gears you have. You can tell by highway rpms. Get on the highway and see what speed you're going at @2000 rpms. If you're going 67, you have 3.23s. If you're going 80, you have 2.73s. WS6s came stock with 3.23s, check the door code GU5. Do the highway test and you can see what you have, then can diagnose from there.
If he actually measured the diameter (like I mentioned vs. using a calculator) then this will work. Otherwise those readings will be just as far off as his speedo.
The problem with the discount tire (and other) calculators is they are approximate. a 275/40 tire from one manufacturer and a 275/40 from another could vary by quite a lot. Do a search for 315's in this forum and you will see a guy comparing goodyear vs a few others and they are GROSSLY different in width...even tho they all claim 315.
Best bet is to actually measure the tire radius and compare to stock. once thats been ruled out it is definitely the gearing and you can do the highway test.