Possible to create an overdrive gear?

[JayinTexas]

Just kind of brainstorming recently and wondered how possible it would be to create some type of an overdrive gear. For instance, I've downloaded the plans for the Marauder and an going to build it as my first project. But something that I thought that would be interesting to add would be a really big, oversized gear to use when going down moderate hills. Think of it.....head down a hill and when you hit your last gear (typical 21 speed setup), then throw it into the overdrive gear and really pull some speed out of it. Of course it would be useless going uphill and probably on flats. Still, I wonder how this could be accomplished?

Jay

[Sparky]

sure, of course you could. just add a higher gear somewhere. a tiny sprocket on the rear or a bigger one on the front. or a 3rd sprocket in the middle.

but then... people can easily get uprights to 50 mph with regular gearsets. so i wonder if its worth it. how fast do you plan to go?

[gbbwolf]

Guy on ebay sells some overdrive thing never looked at it much but saw it there when looking for a freewheel the other day.

I just think If you find the biggest chainring you can find for the front set of cranks you be cruising.

I just have the typical 18 speed setup on most mountain bikes.
And when I hit 18 I am moving pretty dang good.

Can't imagine what I could do with a real crankset in front with one of those monster third chainrings.

But then again My chain is jumping gears in the rear because of the bearings in the freehub.

That's why I was on ebay looking for a mega-range 7 speed.

Nelson

[SirJoey]

The fastest I've ever gone (that I could measure) on a bike was on my first bent, in 1985. I started at the top of this monster hill, exactly 1 mile from the bottom. Since I didn't know how fast I'd end up going, I didn't even pedal AT ALL. I was afraid to!

Starting from a dead standstill, & only coasting, I maxed out at 42mph, according to the bike computer. It was exhilirating, but a little intense, since I wasn't sure how fast I was gonna end up going before I reached the bottom.

http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif

[gbbwolf]

Assuming a standard 52 tooth chainring and a 11 tooth rear cog, at 110 crank RPMs (assuming you have the legs) calculates to about 40.2 MPH driving a 26" rear wheel. And assuming you do have the courage to exceed 40 MPH on a 'bicycle', just how much thought have you given to the shear ineffectiveness of most 'bike' brakes at that speed?

Leave it to papa to know exactly, I think papa builds way more bikes than he tells anyone about LOL.

He probably needs a vacation too.

And Just because you can build something doesn't mean you should.

Nelson

[robertwb70]

Yeah you'd have to either do a mid drive or a big gear in the front because you're pretty much stuck with an 11 tooth on the back as the smallest you can get.

Use one of those 36" rear wheels and you can get a little extra speed.

[JayinTexas]

Hey folks,

Nope, had not put much thought into the brakes. To be honest, I'm not sure what my top speed has been. I ride a hybrid bicycle which is basically a road bike with front suspension and tires that have slightly more meat on them than a road bike. I have a daily 42 mile commute to work (21 miles one way) as long as it's not raining....it rarely does here.

I want to build the Marauder and use it as my commuter bike....my commute is 99% all highway riding with virtually no travel within the city streets. The highway consists of mostly flat roads with just a few hills that have only a moderate incline at best. The trip home is the fun part with most of the riding either on flat roads or downhill riding. If it were possible to incorporate some type of a really big gear, it would be awesome to get the bike up to the 40's or 50's. What I think would be cool, is that some of these hills, while having moderate declines, are very long with some stetching out for a couple of miles. When riding on a decline on one of those hills and shifting into a overdrive gear of sorts, just imagine how long a high speed could be maintained.

I know, this is mostly just crazy thinking but you never know when to ditch those ideas until you ask questions.

Jay

[TheKid]

Thanks Papa. I think a lot of us who are thinking SPEED don't take the brakes into consideration. I was told that the reason hydraulic discs were introduced was to improve the braking at high speeds. The theory is that more pressure can be put on the calipers with less effort.
I don't believe that hypothesis. All my experience with cars tells me that the only way to increase stopping power is to increase the area of contact on the disc. That's why Toyota stressed this improvement in their ads. Hydraulics do require less hand pressure, so they make braking less strenuous, but unless the discs and pads are engineered with a greater area of contact, the stopping power will not be significantly increased.

[AtomicZombie]

Unless you are this guy...

http://www.muscleandstrength.com/gallery/data/515/Mr_Legs_tom_platz.jpg

or have this on your bike...

http://www.speed101.com/images/sept/SamTheRocketMan_VarnaDiabloAtWedStart2001.jpg

Any kind of up geared overdrive system or front chainring over 52 teeth will be a waste of time. You may get the odd backwind and massive hill, but in reality that kind of speed is out of reach for mere mortals like us.

Brad

[Grant]

[quote=AtomicZombie;7798]Unless you are this guy...

http://www.muscleandstrength.com/gallery/data/515/Mr_Legs_tom_platz.jpg

That looks painful:confused: -grant