Speedo Gears
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Speedo Gears
Here we go again. My speedo is off by 20% so it seems that I need to change the speedo gears. I have a 19 tooth gear in there now. How many gears do I need to makup the 20%. There was a post a while back talking about percentages per tooth.. but of course I can't find it.
Thanks in advance.! :cheers:
Thanks in advance.! :cheers:
Guest
Posts: n/a
Re: Speedo Gears (Fevre)
Thanks for the input but I'm color blind.. I thought it went by teeth.. I have a 19 tooth gear now.. Since it was determined that I have a 20% variance.. 20% of 30mph would be +6mph.. 20% of 60mph would be +12mph.. How many tooth gear would you use? The local dealer said to try a 21 tooth gear and see how that works.. Said they weren't too expensive. I rather get a concensious here before buying anything..
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Re: Speedo Gears (Koz)
You're dealing with a gear ratio. The percentage calculation won't work here. I'll write it again: EACH TOOTH REPRESENTS 5MPH. This is whether you are travelling at 10 mph or 100 mph. If your speedometer is registering 5mph faster than your car is travelling, you need to slow it down by adding one tooth or in your case going from 19 to 20 driven teeth. For the in-between ranges, the recommendation is that you go to the next gear that will mean your car is slightly slower than the speedometer reading.
It's hard to say which way you need to go as far as teeth. Is your speeometer faster or slower than your actual speed?
It's hard to say which way you need to go as far as teeth. Is your speeometer faster or slower than your actual speed?
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Re: Speedo Gears (gerry72)
You're dealing with a gear ratio. The percentage calculation won't work here. I'll write it again: EACH TOOTH REPRESENTS 5MPH. This is whether you are travelling at 10 mph or 100 mph. If your speedometer is registering 5mph faster than your car is travelling, you need to slow it down by adding one tooth or in your case going from 19 to 20 driven teeth. For the in-between ranges, the recommendation is that you go to the next gear that will mean your car is slightly slower than the speedometer reading.
It's hard to say which way you need to go as far as teeth. Is your speeometer faster or slower than your actual speed?
It's hard to say which way you need to go as far as teeth. Is your speeometer faster or slower than your actual speed?
I used one of the stationary radar detectors that flash your speed when you drive by. I was doing apx. 36 on speedo when it read 30 but on the highway I have to do apx. 65mph to keep up in 55mph traffic. That's where I got the 20% variance from.. :confused:
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Speedo Gears (Koz)
I'm with Koz, the relationship would be proportional not linear. For simplicity say the gear in the trans has one tooth and the drive gear has 10 so it takes 10 revolutions of the trans gear to make the drive gear rotate once, add 1 tooth to the drive gear and you have slowed it by 10% since now it takes 11 revolutions of the trans gear to make the drive gear rotate once. If it took 60 revolutions of the trans to register 60 mph with 10 teeth, adding the one tooth would cause it to take 66 revolutions. At 30 mph it would take 33 revolutions with the added tooth keeping the 10% relationship.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Re: Speedo Gears (Koz)
If your speedometer is registering about but no more than 10 mph fast at around 60mph you need a 21 tooth gear. You can do the math for the ratios but what you're trying to achieve is a cable rotation of 1000rpm for exactly 60mph indicated and actual velocity.
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Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Speedo Gears (gerry72)
It's 5mph per tooth. Once you know how many teeth you need you just look up the part number and head to your Chevy dealer's parts counter.