Gear Ratio Benefit of Grubee Belt Drives

Mike St

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Jun 16, 2008
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726
Grubee allows the selection of a 4:1 belt drive, where I believe all the
Chinese belt drives are 5:1. This small option of 4:1 brings the top speed
of 4 strokes to reach in the 30's mph, easily by choosing the right
drive sprocket and wheel sprocket. Example: running at 6800
rpm, with a 4:1 belt drive and a 10T drive sprocket, and 41T rear
wheel sprocket calculates to: 31.9mph. A 5:1 belt drive lowers
the top speed to mid-20's.
 

Sidewinder Jerry

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Mar 14, 2011
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3,260
Grubee allows the selection of a 4:1 belt drive, where I believe all the
Chinese belt drives are 5:1. This small option of 4:1 brings the top speed
of 4 strokes to reach in the 30's mph, easily by choosing the right
drive sprocket and wheel sprocket. Example: running at 6800
rpm, with a 4:1 belt drive and a 10T drive sprocket, and 41T rear
wheel sprocket calculates to: 31.9mph. A 5:1 belt drive lowers
the top speed to mid-20's.
I have a shifter bike. Just because I shift to a higher gear ratio doesn't mean I'll go faster. You must have the horse power to propel you at the higher ratio. For example say my tachometer reads 7000 rpm at WOT shifting to a higher ratio will cause the rpm to drop where my speed remains the same but now the engine is being strained more.

Other factors to consider when it comes to speed is total weight, aerodynamics, rolling resistance, engine performance, weather conditions and terrain surface/gradients.
 

DieselTech

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Sep 18, 2021
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My grubee trans is the 5:1 model, designed to be used in conjunction with the grubee 10G shift kit. I'm running 9/36 gearing with a top speed of 26-32 mph depending on gps unit used to check speed.
 

Sidewinder Jerry

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Mar 14, 2011
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My grubee trans is the 5:1 model, designed to be used in conjunction with the grubee 10G shift kit. I'm running 9/36 gearing with a top speed of 26-32 mph depending on gps unit used to check speed.
What size tires are you using? Also here we're talking about level ground speed only. GPS speed apps can be very inaccurate. You'd be better off getting a quality bicycle computer for knowing your speed.
 

DieselTech

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What size tires are you using? Also here we're talking about level ground speed only. GPS speed apps can be very inaccurate. You'd be better off getting a quality bicycle computer for knowing your speed.
26×2.1 continential tires, yes gps phone app. I got a trail tech vapor but have yet to install it. Yes all was level ground speeds.
 

Sidewinder Jerry

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Mar 14, 2011
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A modded out hausheng 142f engine.
So 6800 rpm is where your max hp is.

(6,800×26×π)÷(1,056×5×(36÷9))=26.2989385016

Which means going faster than this on level ground, at least one of the following conditions exist: your GPS speed app is wrong, you're a lite weight and the lower hp at a higher rpm is still able to propel you, you're actually going down a slight grade, your tire's true diameter is larger than 26" or you have a very strong tail wind behind you.
 

DieselTech

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Sep 18, 2021
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So 6800 rpm is where your max hp is.

(6,800×26×π)÷(1,056×5×(36÷9))=26.2989385016

Which means at least one of the following conditions exist: your GPS speed app is wrong, you're a lite weight and the lower hp at a higher rpm is still able to propel you, you're actually going down a slight grade, your tire's true diameter is larger than 26" or you have a very strong tail wind behind you.
So if I have that same setup with a 11-34 freewheel, & buy a grubee shift kit, what kinda speed is a guy looking at? Can I pick up some speed with installing the grubee 10g shift kit. I could do the math, but you always seem way quicker at doing it. 🤣😂🤣 What speeds in conjunction with what gear you have selected? Thanks Sidewinder!!!
 
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