Hill Climbing

W

Westy Steve

New Member
#1
#1
So, I got my Mini Baja up and running tonight and I had glowing stuff to say about it here:

http://www.oldminibikes.com/forum/b...bug-minibikes/29532-first-ride-mini-baja.html

But it made me wonder about something more "general". Has anyone here built a minibike specifically to be low geared so it can really power up hills? Or to kick butt off-road?

And has anyone taken your standard old-school minibike with a smallish motor and small (5 or 6 inch) wheels and geared it low? How did it work off road or on hills?

Steve
 
Oldsalt

Oldsalt

Well-Known Member
#2
#2
You'll need a jackshaft but it will be worth it. If you want a low gear first decide what the maximum speed needs to be. If we call that 15 MPH [I think thats fast enough for rough ground] and the rear tire diameter is 12.5 inches and the max. RPM is 4000. we can use the following formula to determine final ratio. Final Ratio = [4000 rpm X 12.5 tire dia.] divided by [15 mph X 336]. Solved shows a 9.92 final ratio is necessary if you agree on the 15 mph top speed and 4000 rpm. Makes sence because a 6 to 1 ratio is usually hard on clutches and will climb almost nothing. A 7 to 1 gives 21.3 mph [useing the above formula] and, as I understand you, is not 'really' low geared. I think 9 or 9.5 to one final ratio is what you are looking for. With the jackshaft you'll be able to easily and quickly change sprockets to zero-in on what fits your riding style. What is the number of teeth on the clutch and on the rear wheel?
 
jeep2003

jeep2003

#5
#5
the problem is traction youll need a wide grippy tire. a 4.10 wont cut it . My rupp has a 72 tooth sprocket and it wouldnt take too much more to make it awesome at hillclimbing. and thats with a clutch. with a bit more power than 5 and maby a tc youll be good to go. But a bike that actually looks like a hillclimber would be cool
 
steven Durham

steven Durham

#6
#6
Way back in time ( 1972 )there was a monster of a hill climb in the famous Saddle Back Motorcycle Park called the Matterhorn. A sign at the top had names of riders that had made the total climb up that killer cliff . Names like Malcolm Smith,Steve McQueen and one rider Jeff Ward and his ride up that hill was on a Bonanza Mini BIke with a Hodaka Ace 100 engine. I don't in any way think that it was a stock Hodaka motor but all in all still an incredible feat on a mini bike. So start from there and go and give the hills their due but remember what goes up must come down LOL
Steve :scooter:
 
1stlegendtx

1stlegendtx

Well-Known Member
#7
#7
steven Durham said:
Way back in time ( 1972 )there was a monster of a hill climb in the famous Saddle Back Motorcycle Park called the Matterhorn. A sign at the top had names of riders that had made the total climb up that killer cliff . Names like Malcolm Smith,Steve McQueen and one rider Jeff Ward and his ride up that hill was on a Bonanza Mini BIke with a Hodaka Ace 100 engine. I don't in any way think that it was a stock Hodaka motor but all in all still an incredible feat on a mini bike. So start from there and go and give the hills their due but remember what goes up must come down LOL
Steve :scooter:
Click to expand...
Back in the day I took one of the Saddle back rental Mini Enduros about 10 feet up the Matterhorn.:doah::scared:
 
Green Jelly

Green Jelly

New Member
#8
#8
My DB is geared pretty low, 12 clutch, 72 rear, and it'll wheelie a 240 pound man(my pops); it's climbed every hill we've gone after. I'll post pictures soon. :smile:
 
Oldsalt

Oldsalt

Well-Known Member
#9
#9
Green Jelly said:
My DB is geared pretty low, 12 clutch, 72 rear, and it'll wheelie a 240 pound man(my pops); it's climbed every hill we've gone after. I'll post pictures soon. :smile:
Click to expand...
I was responding to his quest to "be low geared" to "really power up hills".

At 6 to 1 [12 tooth and 72 tooth], and a 4 stroke engine haveing a power impulse every other revolution, means that you have 3 power impulses per revolution of the rear tire. With a 10 to 1 ratio the rear tire sees 5 cylinder fireings. That is only 66% more and will be necessary if he really wants to "power up", in my opinion.

The several Tote Gotes and etc. in my back yard, which are ment for serious grunt, all have double jackshafts to get low enough. As I recall a Boonie, wity the two speed jack shaft, was close to 9 in low.

Jeep mentions a torque-a-verter...that would be the way to go if the loot is available and availability was worked out. But a jack shaft would probably still be necessary. All I'm saying is that 6 to one is a relativey high ratio.
 
jeep2003

jeep2003

#10
#10
yup a jackshaft would be best and would make it easier to fine tune the ratio. low gearing is important but you also need speed to maintain momentum. a clutch is better at maintaining speed. a torque converter will slow you down when it gears down. its hard to say which would work best but im thinking clutch
 
steven Durham

steven Durham

#11
#11
The Matterhorn

1stlegendtx said:
Back in the day I took one of the Saddle back rental Mini Enduros about 10 feet up the Matterhorn.:doah::scared:
Click to expand...
So I guess that sparked a few memories for you. that hill had about 3 levels from the bottom to the top level one was a snap, level two could hurt you, and level three was pure insanity a vertical wall and a power sucking ride all the way.
Watched a guy climb the hill bottom to the top and then whipped the bike around and Bonsai jumped over the edge and rode it back down to the bottom.
Was there one on a hill climb event. unreal bikes got shot down left and right.
Steve :scooter:
 
steven Durham

steven Durham

#12
#12
Get a Rokon and forget needing power. In low gear the ratio was 84 to 1 and with a 9 HP West Bend 820 engine. I am talking the old Rokons from the 1970's. A fun bike to ride anywhere. Steve
 
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