# Gear reduction/Titan50 to bike cassette

Discussion in 'Rack Mounted Engines' started by TWalker, Dec 16, 2008.

1. ### TWalkerGuest

Ive done some searchin because I dont wanna ask whats already been answered but...I really get confused when it comes to gear reduction.

I have a rack mount which has the 5:1 PTO>10 gear output>10/10 Jackshaft>to 44 tooth drive gear very nice works well.

I want to try running a chain down to a standard bicycle rear cassette (say 22 tooth gear) roughly a 1/3 to 1/2 the size of the 44 tooth standard chingen sprocket.

Here is a video of a guy who did it but I dont know what reduction he used but you get the idea...mines just a rack mount.

• What additional reduction would I need?
• Any thoughts? I pretty much can figure it out if I know the proper reduction but suggestions are welcome.

Last edited by a moderator: Dec 17, 2008

2. ### duivendykGuest

The original reduction was 5x(4.4)= 22.Most casettes are
14to28t ,midrange around 20,so you need at least a reduction of 4 from PTO out to the 20 t sprocket on the cassette,resulting in an overall reduction of 20.At 5k rpm your road speed would be 75x 5/20=19mph at mid range.For instance you could use 10/20t to the jack shaft and 10/20t from jack shaft to casette.If you try to put all the reduction in the drive from the jack shaft you end up with a 5t output sprocket (impractical).

3. ### TWalkerGuest

Ah headache...I'm an A/B student in college and have 120+ IQ so I'm not totally dumb but...

So are you saying I could increase the size of the jackshaft sprocket? I'm thinking I need smaller sprockets to compensate for the move from the 44 tooth down to the mid-range 20 cassette.

gear reduction totally confuses me. :sweatdrop:

Thanks

Edit: Ok, so if I have a 10t engine drive gear and I connect that to a 20 tooth on the jackshaft and then a 10t as a final drive gear; I have .5:1 and 2:1 which would mean?

I add 10t and then I take away 10t so I'm at 1:1 because they cancel each other out? Doesnt make sense because im at 1:1 already with three 10t sprockets in a row.

Does anyone have a tutorial on this because Ive tried the calculators and it doesnt help either.

Last edited by a moderator: Dec 16, 2008

I think Dui is saying you need to go from a 10t on your engine, to a 20t on the jack. Then a 10t off the jack to a 20t rear gear. I could be wrong (wouldn't be the first time). But it sounds about right to me.

While we're on this subject, has anyone tried running off a rack-mount to the front crank ala SBP Shift Kit? I like the shift kit, but I worry about getting too far out in the wilderness with the HT.

6. ### 5-7HEAVENGuest

Okay college guy, here's some simple algebra or ratio and proportion, which is how you solve gear reduction problems.

In ratio and proportion, 5:1 aka 5/1.

5/1 (gearbox on engine) X 10/10(10t on engine/10t on jackshaft) = 5/1 X 10/10 = 5 x 1 = 5:1.

44t on wheel sprocket/11t on jackshaft sprocket = 44/11 = 4:1

5/1 x 4/1 = 20/1 or 20:1

If you reduce the 44t sprocket by 50%, then you need to DOUBLE the engine side of the jackshaft ratio. The 5:1 needs to be bumped to 10:1. Change the jackshaft sprocket that connects to the engine to 20t.

For every 20 engine revolutions per minute(20 rpm), the bicycle wheel spins one time around (1 rpm). For every 2,000 rpm, back wheel spins 100 rpm.

7. ### TWalkerGuest

I have both sitting in my house and I lined up a chain last night to how it would line up and it seems pretty doable. I decided though to go another route. One reason being that the tension on the chain is no longer verticle on the mount I have it would now being diagonal.

Thats not the only reason but the main one. But it seems like it would work fairly well if your willing to have that long chain stretched out near your leg on the outside chain ring.

8. ### TWalkerGuest

Did I mention I focus on arts at school? :dunce:

Ok I ran the numbers through a gear ratio calculator (see screenshots below) and yes indeed you are correct, running a 20t sprocket on the jackshaft keeps it exactly the same when running to a 22t cassette sprocket.

Very nice...thanks very much!

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Last edited by a moderator: Dec 16, 2008
9. ### 5-7HEAVENGuest

I'm a Sociology major myself, 3.67 GPA , 120+. :grin5:

10. ### TWalkerGuest

3.17 here...I struggle with Algebra...not trying to say I'm super smart, just not a total idiot.

Actually I'm a pretty sad case, I'm over 40 years old and my main focus is the women in college...

The way you just lay that stuff out is impressive.

11. ### 5-7HEAVENGuest

Walker, we have a lot in common...

I'll be 62 and women are awesome distractions in school.

I didn't get too far past algebra, but that ratio and proportion I learned in 7th grade was priceless knowledge.:detective:

God bless the \$4 calculator.

12. ### duivendykGuest

The Jack shaft has an input sprocket and an output sprocket,if you increase the size of the input sprocket you increase the reduction from the PTO,for instance 10t on the PTO out and 20t on the jack shaft gives you an overall reduction of 5x(20/10)=10 to the jackshaft.Allways multiply INPUT to/OUTPUT from, (20/10 in this case), for each reduction !.If you then have a 10t output sprocket on the jackshaft, driving a 20 t mid sprocket on your cassette, you pick up an extra 2 to one reduction for a total reduction of 20, 5x2x2,which is about what you had originally,I hope is that clear now?.Sprockets smaller than 10t are hard to come by and also lead to rapid chain wear.IF you did not change the input sprocket on the jackshaft to 20t but kept it at 10,you would have had to reduce the output sprocket on it to 5t for the same overall reduction (don't exist to my knowledge).It is well known that IQ by standard measurement paradigm is poorly correlated with mechanical ability&insight,I'm not at all sure what,if anything it really measures,verbal ability?.you seem to prove this point.If you want to relate engine rpm to roadspeed here is my handy-dandy formula:
S= 0.075x rpm/reduction,for instance rpm 6000 ,reduction 20
S= 0.075x6000/20 or S=22.5 mph.(26" wheel) Sociologues with access to a calculator should have no problem with this.

Last edited by a moderator: Dec 17, 2008
13. ### 5-7HEAVENGuest

IQ is strictly potential.

I liken it to HORSEPOWER! that needs to be harnessed.

As a senior in high school, I sneaked a peak at the IQ figures in my class of 25 students. :detective:

The straight-A, honor roll, valedictorian had an IQ of 100, which is normal for an average person. I was floored!!

I also gained MUCH greater respect for that nice guy who maximized his potential. I kicked myself for barely passing.

I've been a 5.5 hp Kawasaki engine on a push trailer all my life. Wasted power with 2:1 gears, just getting by.

Now I'm finally getting my gearing problems sorted...at age 62.:grin5:

We ALL get smarter hanging out with fellow MB ers here.:idea:

14. ### duivendykGuest

Conceivably you might get smarter, at least be better informed.The problem overhere is that the smarter kids have far to easy a time in school.In Europe and Japan they sort you out by ability in grade school and then you go on to different types of schools,where you have to work at your ability level. There is a lot of competition to make it to the top schools.No slacking off and just getting by in High School,that's for sure!