Sprocket sizes VS speed

#21
Max-torque is the route for a cheap china clone pred engine!
OldMiniBikes Warehouse has 3/4", #35 chain Max Torque clutches in a wide variety of sprocket sizes, from 10T to more than 20T.

12/60 worked great on my Fimco, racing on the slightly less than 1/8 mile indoor oval last weekend. It jumped off the line and still had good top end speed w/lightly modded 212 Predator, no governor, 4.10 x 3.50 -6 tires, 120 lb rider. We won the race going away.

Now I'm building up my old Ruttman for a larger outdoor track. The race line around the Castle Rock, Wash., oval is a bit over 1,400 feet long, or 1/4+ mile. The corners are broad and it should be possible to go flat out just about all the way 'round with a good rider. Bike will have 6" wheels, no jackshaft, an engine w/similar mods to the Fimco, and a light weight rider. Taller gearing will be in order, but I'm not sure if I want to get a TAV. I can just pop on a new clutch w/bigger sprocket and not have to mess w/rear sprocket (60T), and retain the clutch brake. 13T-15T on the front gives a ratio range of 4.6 - 4.0. Do you think that I'll toast the clutch? It only needs to last one race day, perhaps three 6-lap sessions (practice, heat race, and main event).
 
#22
Couple of points here:

Max Torque sells sprockets for their clutches of a wide variety of teeth options. OldMiniBikes carries them. They also sell replacement hubs for the larger-toothed versions. You don't have to buy clutches to change gear ratios.

When over loading the clutch like you are discussing, remember that heat is your enemy. Also, you can swap out the original silver unpainted garter spring for the 2500 RPM engagement "green" spring, or the 3100 RPM engagement black spring. Now days, I do not even use silver springs on my MT clutches.

Even if you are using a stock Max Torque clutch (SS) on a 3 to 5 HP vintage bike, if you are "heavy" ie heavier than the 85 pound 12 year old it was all designed for, you will love the way that the green spring engages and launches.

The "rule of thumb" of 5 or 6 to one ratios are ball park. The amount of torque of a specific engine at engagement, through acceleration is not even a factor in those "calculators," but of even more importance is the weight of the rider/bike.

The difference between a 120 pound rider running a 12-60 ratio on 12" OD tires and me with twice that weight is everything. I do have bikes with that ratio, and they are slugs off the line. My grand sons on the other hand grab the throttle and pull a wheelie.

Top speed calculators are factored for down hill, wind at your back, best case scenario. And I don't know what is so exciting about 40 MPH on a mini bike, when it takes a long time to get there.

@Tom S. yes, you will burn the bushings, but you "could" show up at the track with an extra bushing, snap ring pliers, and a driver and run the practice laps, then rebuild the clutch. Takes minutes. Also, swap out garter spring, (to practice rebuilding the clutch and get your tooling down) to a black spring, since you'll be WOT, "and" running at a high geared ratio.

Two cents worth. I've been buying up used MT clutches and rebuilding them. Have all my little specialty tools made, etc. Something I enjoy doing.
 

Np02

New Member
#23
Couple of points here:

Max Torque sells sprockets for their clutches of a wide variety of teeth options. OldMiniBikes carries them. They also sell replacement hubs for the larger-toothed versions. You don't have to buy clutches to change gear ratios.

When over loading the clutch like you are discussing, remember that heat is your enemy. Also, you can swap out the original silver unpainted garter spring for the 2500 RPM engagement "green" spring, or the 3100 RPM engagement black spring. Now days, I do not even use silver springs on my MT clutches.

Even if you are using a stock Max Torque clutch (SS) on a 3 to 5 HP vintage bike, if you are "heavy" ie heavier than the 85 pound 12 year old it was all designed for, you will love the way that the green spring engages and launches.

The "rule of thumb" of 5 or 6 to one ratios are ball park. The amount of torque of a specific engine at engagement, through acceleration is not even a factor in those "calculators," but of even more importance is the weight of the rider/bike.

The difference between a 120 pound rider running a 12-60 ratio on 12" OD tires and me with twice that weight is everything. I do have bikes with that ratio, and they are slugs off the line. My grand sons on the other hand grab the throttle and pull a wheelie.

Top speed calculators are factored for down hill, wind at your back, best case scenario. And I don't know what is so exciting about 40 MPH on a mini bike, when it takes a long time to get there.

@Tom S. yes, you will burn the bushings, but you "could" show up at the track with an extra bushing, snap ring pliers, and a driver and run the practice laps, then rebuild the clutch. Takes minutes. Also, swap out garter spring, (to practice rebuilding the clutch and get your tooling down) to a black spring, since you'll be WOT, "and" running at a high geared ratio.

Two cents worth. I've been buying up used MT clutches and rebuilding them. Have all my little specialty tools made, etc. Something I enjoy doing.
so am i getting from this that even using a max torque clutch will still burn out at a 12 - 48 ratio just as bad as it would burn out a cheaper clutch at the same ratio?
 

I74

Well-Known Member
#24
No jackshaft. Straight from the clutch to the sprocket attached to the hub and not an axle. I believe the diameter was just past 12 inches on the rear wheel. Taking a look at some pictures I had it turns out the clutch on it is a max torque so I might be able to get away with having a 46 or 48 without it pooping out just yet.
OK,,
I was pretty much spot on with your current 12 - 60 combo.
That puts you @ 5 -1.

Let's now figure your rough top speeds & different ratio options.
Am going to calculate this stuff with figuring an RPM of 5000.

First,
with your current ratio @ 5000 rpm's, that puts the top speed @ around 36mph.

Next,, lets figure 12 - 46.
That is a ratio of 3.83 - 1, & a speed of 47 mph. ''You would smoke the clutch in short order with this set up'' !!

And then,, 12 - 48.
Ratio is 4 - 1, with a speed of 45mph, ''still going to smoke the clutch''...

Lastly,,
Changing out the gear on the Max torque clutch drum to a 13t, & running your 60t sprocket, would put the ratio @ 4.615 - 1
Top speed @ just under 40 mph.
That ratio is the highest I would run.

I personally would just stay with your current set up.

I
 
#27
so am i getting from this that even using a max torque clutch will still burn out at a 12 - 48 ratio just as bad as it would burn out a cheaper clutch at the same ratio?
The only thing that "burns" out is the bronze oil lite bushing. It gets hot quicker that it normally would, the oil disappears and it starts wearing fast. There really isn't anything else that gets destroyed. (in a sintered metal clutch) I'd be more concerned warping a clutch housing with one of those clutch brakes, than I would about losing a bronze bushing. All of it can be replaced.

I've never used the Chinese knock offs, so I can't compare. It's not rocket science. The only problem I see with what you are trying to do, is having a really crappy take off and acceleration. Who cares if you burn out a bushing? Just replace it.
 
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#29
OK,,
I was pretty much spot on with your current 12 - 60 combo.
That puts you @ 5 -1.

Let's now figure your rough top speeds & different ratio options.
Am going to calculate this stuff with figuring an RPM of 5000.

First,
with your current ratio @ 5000 rpm's, that puts the top speed @ around 36mph.

Next,, lets figure 12 - 46.
That is a ratio of 3.83 - 1, & a speed of 47 mph. ''You would smoke the clutch in short order with this set up'' !!

And then,, 12 - 48.
Ratio is 4 - 1, with a speed of 45mph, ''still going to smoke the clutch''...

Lastly,,
Changing out the gear on the Max torque clutch drum to a 13t, & running your 60t sprocket, would put the ratio @ 4.615 - 1
Top speed @ just under 40 mph.
That ratio is the highest I would run.

I personally would just stay with your current set up.

I
Your saying that 4.615:1 is the highest ratio you would run doesn't make much sense, most run a higher ratio than that. I think you are confused about what is a higher and what is a lower ratio. 6:1 is a higher ratio than 5:1, 5:1 is a higher ratio than 4:1, 1:1 is the lowest possible ratio. The greater the difference between the numbers, the higher the ratio.
 

I74

Well-Known Member
#30
Your saying that 4.615:1 is the highest ratio you would run doesn't make much sense, most run a higher ratio than that. I think you are confused about what is a higher and what is a lower ratio. 6:1 is a higher ratio than 5:1, 5:1 is a higher ratio than 4:1, 1:1 is the lowest possible ratio. The greater the difference between the numbers, the higher the ratio.
In the 40 + years that I was a mechanic, the lower the number, the higher the ratio,, meaning -'' higher gearing''.
Example,,
In drag racing ect., a 4.11 gear would be lower ratio ,''lower gearing'' & a 3.55 would be higher.
That's just the way it's always been worded.
 
#31
In the 40 + years that I was a mechanic, the lower the number, the higher the ratio,, meaning -'' higher gearing''.
Example,,
In drag racing ect., a 4.11 gear would be lower ratio ,''lower gearing'' & a 3.55 would be higher.
That's just the way it's always been worded.
Yes, higher/lower gear/gearing have been common terminology for a very long time (I'm old, so I know). Thing is, higher ratio = lower gearing, lower ratio = higher gearing. That's just the way it's always been. ;)

http://www.badasscars.com/index.cfm...ct_id=398/category_id=13/mode=prod/prd398.htm

http://www.mossmotoring.com/the-highs-and-lows-of-differential-gear-ratios/
 
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I74

Well-Known Member
#32
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