Celica Forums General Discussion General Speedometer correction

Ok, so I was cruising by one of those mobile radar stations that tell you how fast you are going. I had cruise set at 55, but the machine said I was doing 48. I do have 17 inch rims with low profile tires, but I matched them up so the overall diameter of them is very nearly equal to the stock wheels and tires. Also, I did disassemble my gauge cluster to do the LED conversion, if that might disrupt the calibration of the speedometer.

My question is this: Is there a way to make my speedometer read correctly again? I went to a calibration shop today, and it turns out the mobile radar station was right. It's about 6 mph off where it should be. The guy said since the car is so new (2002), there is no way they can correct the cluster to read correctly. He said there isn't anything on the market that can help me. His final analysis is that I have to just mentally know that my speedometer reads 5mph faster than what I am really traveling.

take off your needle. tunr ur car to acc i belive leave for leik 20 sec it will calibrate then put needle back on. now if its becasue of your tires i dont know

A lot of my friends say that they give all cars a 5mph more then what the car is saying, thats why when you are cruisin 70 on a 65 and a cop clocks you in you wont get pulled over only if the cop isnt a dick, correct me if im wrong! But yea ive notcie the same thing a while ago since i got new gauges and 17" rims.

Yeah, I read somewhere that the DOT almost requires police to give a 5 MPH leeway, and usually when you read the guidelines for speeding fines, they start at 5 MPH over.

They can pull you over still, since you ARE above the speed limit, but they'd probably just give you a warning.

I had a friend at a P.D. clock me at 130, my car read 125. 100 was 113 on radar. The gun is less than a year old! I wonder what 55 realy is?

Yeah, radar guns need to be calibrated often, and with the right tuning fork. I think if I ever get pulled, I'm gonna ask when the last time the gun was calibrated. I figure that's my only fighting chance.

My stock '00 has always been 5mph fast, even after the RJAutoworks upgrade.

Radar is only accurate under the most perfect of circumstances. Radar measures the speed at which the object is traveling to or from the gun... which means to get a perfect reading, you'd have to be directly behind of in front of the object. If the gun is even slightly off from the plane on which the object is moving, the reading won't be fully accurate.

Oh yes, also...

Most factory speedo's are set a hair on the safe side, maybe 2-3% below the actual speed.

I have the same problem with my 01' celica GT. It started after I put an overlay on instrument panel & had to remove needles. It's never been the same since. I've tried the acc method 20x but it still reads 7mph over the actual. When stopping you can see the speedo go to 5mph pauses then after you've stopped it drops to zero. Does anyone else notice this? I've had a friend set his cruise & travel along side me & it's definatley off. We have school radar that posts your speed as you travel by(over by 7mph). I also have low profile tires & kept the same overall diameter as stock so this is not the cause. Only other option which I've heard discussed here is to get a GPS unit & while driving with cruise set have someone put needles on to the speed on the GPS(dangerous). I think most people who have taken off there gauges have this problem but really haven't noticed like a few of us have. Don't worry, you're not the only one that this bothers.

True, but if the radar gun is at an angle to you the error will be in your favor - it will read slower than you are actually going.

i was just wondering this same thing it feels like i am going slower than i really am but i have never messed with my gauges all i have is 17' rims, why would these change anything just becasue of rims

I have this exact same problem!! So I know I'm not the only one.


That's not a bad idea. But I don't want to be the first to try it. It's risky, but a feasible idea.