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Old 12-28-2004, 09:59 PM   #1
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Calculating Speed

I'm trying to calculate the speed of my car. I found this speed calculator online and I'm not sure if it's right. I also don't know the gearbox ratio of my motor. I have a Trinity Monster Stock, 93T Spur, 18T pinion, and 24mm wheels. The maximum RPM I got from the specs page at Trinity that is 21000RPM's.

Is there a set formula to figure this out?

I attached an image of the app with my numbers in it.
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Old 12-28-2004, 10:11 PM   #2
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try www.gearchart.com
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Old 12-28-2004, 10:29 PM   #3
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Default Re: Calculating Speed

Quote:
Originally posted by jigga21
I'm trying to calculate the speed of my car. I found this speed calculator online and I'm not sure if it's right. I also don't know the gearbox ratio of my motor. I have a Trinity Monster Stock, 93T Spur, 18T pinion, and 24mm wheels. The maximum RPM I got from the specs page at Trinity that is 21000RPM's.

Is there a set formula to figure this out?

I attached an image of the app with my numbers in it.
What's the car you have and the tire diameter?
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Old 12-28-2004, 10:35 PM   #4
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X-Ray T1FK. I saw an article in a mag about an electric car clocked at 46MPH. I'm trying to learn how to calculate gear ratios, and how to tweak my cars speed. Plus it wouldn't hurt to know how to make it that fast.
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Old 12-28-2004, 10:40 PM   #5
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Quote:
Originally posted by jigga21
X-Ray T1FK. I saw an article in a mag about an electric car clocked at 46MPH. I'm trying to learn how to calculate gear ratios, and how to tweak my cars speed. Plus it wouldn't hurt to know how to make it that fast.
Assuming the 1.77 internal ratio is being used and the tires are the same as mine (63.5 mm in diameter) the theoretical top speed is only 17 mph.
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Old 12-28-2004, 10:45 PM   #6
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63.5 mm in diameter? I think my tires are 24mm. Is 17MPH the fastest you can get in this car or just with your setup.
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Old 12-28-2004, 10:48 PM   #7
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Quote:
Originally posted by jigga21
63.5 mm in diameter? I think my tires are 24mm. Is 17MPH the fastest you can get in this car or just with your setup.
24 mm is how wide your cars rims are dude, I mean the distance from the top of the tire to the bottom when viewed from the side.

You have to know, the gearbox ratio (in your case 1.77) the number of teeth on the pinion and spur (you've given those) the rpm of the motor (you gave that as well) and the tire diameter to calculate the possible top speed.
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Old 12-28-2004, 10:50 PM   #8
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I guess that would change things.
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Old 12-28-2004, 10:51 PM   #9
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Default Hell no.....

Quote:
Originally posted by jigga21
I guess that would change things.

But is 17MPH the fastest it can go?
But you might want to think of using a larger pinion with that spur. Others here will know what's good for that motor.
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Old 12-28-2004, 10:53 PM   #10
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unless you know the rpm the motor is achiving under the load of driving the car, you are wasting your time.

venom make a speed meter which is mounted in your car. this would be the easiest way of discovering the speeds you are achiving...
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Old 12-28-2004, 11:05 PM   #11
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Default I think I'm understanding more.

One more question. I checked HPI's website for the wheel sizes and the only spec I see is 24mm. How do I know the size, like mabuchi540 stated?
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Old 12-29-2004, 10:24 PM   #12
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Wow i have a top speed of 31MPH
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