Gear Ratio and Speed **Update: Now there are pics!!**

[Silverbullet28]

Alright, I have got a quick question for anyone who knows anything about gear ratios and how that equates to speed. This is the information I have been given:

Engine Sprocket = 17 teeth
Rear Sprocket = 34 teeth
Rear Tire = 56 in(Circumference)

Now what would the speed be at 2500 RPM?


Here is what I did.

RPM/Gear Ratio = Axle Speed
2500/(34/17) =1250 RPM

Circumference of Tire * Axle Speed = Inches per Minute
56in *1250 rpm = 70000 IPM

(IPM/12)/5280 = Miles per Minute
(70000 IPM/12)/5280 = 1.10 MPM

MPM * 60 = Miles per hour
1.10 MPM * 60 = 66.29 MPH


Does 66.29 MPH seem right to you guys, or did I do something wrong? This question is from someone I know who is building an Odyssey, and that seems a little bit fast. Any help would be appreciated. 🙂

- SB

 

[Silverbullet28]

**Pics for help **

Jamie Pressly 1
Jamie Pressly 2
Jamie Pressly 3
Jamie Pressly 4

Gotta bribe you guys to get advice even.. 😛

- SB

 

[BreakApart]

Your calculation does not seem fast at all.

With the info you provided:
Front sprocket 17
Rear Sprocket 34
Tire size approx 18"
RPM 2500

What your missing here is the ACTUAL drive ratio from the gear box if it has one. The sprocket gearing is called the final reduction ratio. Without the gearbox ratio 1st gear, 2nd gear, etc, etc, you are assuming a 1-to-1 ratio from crank to front sprocket, which on a motorcycle is approx 5th gear, or on my truck is approx 4th gear. So 60mph on 18" rims with your info sounds about right.

 

[Silverbullet28]

Thanks BreakApart, just wanted to see what someone else thought before I told my friend what I came up with. Danke. 😀

- SB