Speedometer Gear Reference Chart?
02-28-09, 09:11 PM
#1
Speedometer Gear Reference Chart?
I picked up some wheels that have brand new tires on them but they are 205/55R16. So they are 24.8" tall vs the stock 23.2" tall. They appear to fit, but the speedo will be off. Rather than replace new tires with new tires....
With the stock 3.900 rear gear.
So does anyone have a gear reference chart that I can find the proper speedo gears? Is there an aftermarket for such a thing?
Thanks
-Paul
With the stock 3.900 rear gear.
So does anyone have a gear reference chart that I can find the proper speedo gears? Is there an aftermarket for such a thing?
Thanks
-Paul
02-28-09, 09:21 PM
#2
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02-28-09, 10:57 PM
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...Man, I didn't know we could get speedo gears for our cars. If I wouldn't have known this I'd pick out some different tires, but I just ordered tires three days ago. Good timing.
03-01-09, 11:13 PM
#4
This one works good for me:
http://www.car-videos.net/tools/speedrpm.asp
Just look up the gear ratio for your car, enter it and the size tires you want and it will tell you what speed you are showing on the speedo vs, your actual speed.
http://www.car-videos.net/tools/speedrpm.asp
Just look up the gear ratio for your car, enter it and the size tires you want and it will tell you what speed you are showing on the speedo vs, your actual speed.
03-02-09, 08:43 PM
#5
This one works good for me:
http://www.car-videos.net/tools/speedrpm.asp
Just look up the gear ratio for your car, enter it and the size tires you want and it will tell you what speed you are showing on the speedo vs, your actual speed.
http://www.car-videos.net/tools/speedrpm.asp
Just look up the gear ratio for your car, enter it and the size tires you want and it will tell you what speed you are showing on the speedo vs, your actual speed.
That kind of defeats my quest for finding speedo gears. I like to have my gauges accurate and easy to calculate MPG. Besides, who wants to have a chart next to their speedo and explain that to an officer?! :O)
03-03-09, 07:44 AM
#6
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***That kind of defeats my quest for finding speedo gears. I like to have my gauges accurate and easy to calculate MPG. Besides, who wants to have a chart next to their speedo and explain that to an officer?! :O)***
For gods sake kid use your brain. Your speed will be not true to the new tires by "X" mph. Do you need a chart to remember one (1) number.
I could take you by the hand & explain further but I'm afraid it wouldn't sink in.
For gods sake kid use your brain. Your speed will be not true to the new tires by "X" mph. Do you need a chart to remember one (1) number.
I could take you by the hand & explain further but I'm afraid it wouldn't sink in.
03-03-09, 09:52 AM
#7
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***That kind of defeats my quest for finding speedo gears. I like to have my gauges accurate and easy to calculate MPG. Besides, who wants to have a chart next to their speedo and explain that to an officer?! :O)***
For gods sake kid use your brain. Your speed will be not true to the new tires by "X" mph. Do you need a chart to remember one (1) number. I could take you by the hand & explain further but I'm afraid it wouldn't sink in.
For gods sake kid use your brain. Your speed will be not true to the new tires by "X" mph. Do you need a chart to remember one (1) number.
I could take you by the hand & explain further but I'm afraid it wouldn't sink in.He is aware that the new tires will change his speedo. And I'm sure like any of us he could remember something like 'it is off by X @ X speed'. The point he is saying is that he doesn't want to have his speedo off. This will also throw his Odo off and will make it hard for him to calculate MPG, and would just be a pain. That is why he is asking if he can buy some speedo gears to correct the thing.
Like I originally said, I didn't know these were availible. Its a complicated subject, as those other mazdas that might have a correct reading for such a tire may have a different final drive ratio. I don't think you are going to have much luck with this. IMO you shoulda shopped a bit better and found tires that weren't so tall. Where'd you get 16"s in a 4x110 anyways?
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03-03-09, 10:42 AM
#8
I have a Garmin GPS in my RX7 and used that to confirm the accuracy of my speedo.
It'll give you a real-time speed calculation automatically, based upon your actual geospacial movement, regardless of your tire size.
It may suffice until you convert your gear ratio.
It'll give you a real-time speed calculation automatically, based upon your actual geospacial movement, regardless of your tire size.
It may suffice until you convert your gear ratio.
03-03-09, 10:51 AM
#9
Good grief David. The math is not an issue. These tires will slow the speedo by 6%. I can do the math but it'll be rather annoying driving down the road constantly multiplying my mph by 1.06. The speedo will be off by a percentage it's not just a matter of adding or subtracting a single number.
Back on topic. Looks like the trans up to and including 83 use a 17 tooth course green gear. All other teeth count are numerically higher for the later years steeper butt gears and are a fine gear offset differently.
I bought the wheels because they. Looked good IMHO. They are 4x4.5(114.3). I'll be getting wheel adapters to mount them at the spacing I want. The tires were included and cost no extra over what I've seen the bare wheels go for. There is a speedo shop in town that builds a conversion box to adjust the speedo math for about $60. I might do that until the tires wear down vs $400+ for a new set of tires with the proper profile.
Back on topic. Looks like the trans up to and including 83 use a 17 tooth course green gear. All other teeth count are numerically higher for the later years steeper butt gears and are a fine gear offset differently.
I bought the wheels because they. Looked good IMHO. They are 4x4.5(114.3). I'll be getting wheel adapters to mount them at the spacing I want. The tires were included and cost no extra over what I've seen the bare wheels go for. There is a speedo shop in town that builds a conversion box to adjust the speedo math for about $60. I might do that until the tires wear down vs $400+ for a new set of tires with the proper profile.
03-03-09, 01:09 PM
#10
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you might want to check your speedo/odo meters BEFORE you do anything. there is no spec for the 1st gen (ive got the book in front of me) but the FC spec is 5%...
so at 90 mph the speedo can read 90-94.5, at 30 it can read 30-32 etc etc
so at 90 mph the speedo can read 90-94.5, at 30 it can read 30-32 etc etc
03-03-09, 02:40 PM
#11
What do you mean "spec"? All the speedometers are calibrated to a certain pulse setting. Then the drive and driven speedo gears do their work and are chosen based on tire size and rear ratio.
Mine seems to be pretty darn close based on mile marker readings.
03-03-09, 04:50 PM
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its a 5% margin
so actually 2% off with the tires might still be within spec
i do agree with you that mazda speedo's are pretty good, my bmw is horrible
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