speedometer gear/VSS question

riceslayer302 said:

my friend bill, who you may know through josh bentley, has one of the only remaining connecticut SSP cars around. its 5 speed too!!

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Is he on here? SSPMustang.org

SSPs from the northeast states are all pretty rare. They never used many of them, and the elements rotted them away. A rusted out NYSP SSP just sold on eBay for $5K .

riceslayer302 said:

not sure, i dont even think he knows anything about the cars past, just beats the **** out of it.

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riceslayer302 said:

its a rare car though, i never saw an original SSP that was 5 speed

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California, Texas, and Florida all used 5 speeds, almost exclusively. They were the 3 biggest users of SSPs (about 5300 between them -- more than 1/3 of all the SSPs made).

Sorry for the thread hijack.

Before you order that 21 gear, consider this:
If you are reading exactly 80mph when you are actually running at true 60mph, your gears are off by 25%. If your speedo gear ratio is 2.857 (20/7), then you need to would need to step up to a 25 driven gear... 25/7 = 1.25% X 20/7. Since a 23T is the largest gear you can get, you will need to swap the drive gear as well. If you swap to a 6T drive gear, you would need a 21 or a 22 driven gear (actual needed gear would be 21.428). See how important it is to know just how far off your speedo is off? Also consider if you are going to change your tire height. This can have a big impact on accuracy.
Someone please check the math on this one...It's not one of my strengths!

Mr Grim said:

Before you order that 21 gear, consider this:
If you are reading exactly 80mph when you are actually running at true 60mph, your gears are off by 25%. If your speedo gear ratio is 2.857 (20/7), then you need to would need to step up to a 25 driven gear... 25/7 = 1.25% X 20/7. Since a 23T is the largest gear you can get, you will need to swap the drive gear as well. If you swap to a 6T drive gear, you would need a 21 or a 22 driven gear (actual needed gear would be 21.428). See how important it is to know just how far off your speedo is off? Also consider if you are going to change your tire height. This can have a big impact on accuracy.
Someone please check the math on this one...It's not one of my strengths!

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x/6 = 25/7

7x = 25x6 = 150

x = 21.429

Yep. Your math looks good to me. And a 25-tooth gear is what I initially came up with too.

How many of you thought you'd never use algebra in real life?

No matter what gear a calculator tells you is required, or what you mathmatically determine you need, be prepared to go up or down another gear. Every calculator, and all the math said I would need a 20-tooth gear. The 20-tooth got me close (about 5 or 6% off, as measured by radar), but a 21-tooth got me within 1%. Just a bunch of small variations in things like actual tire diameter (Do the manufacturers measure them on a 8 inch rim, or 9 inch rim? At recommended pressure, or maximum pressure? ), non-standard temperature when taking the speedo readings, etc., can be enough to throw the calculations off. Sometimes you'll need to choose between having your speedo read a little fast of a little slow.