Home :: GUIDE - BIG WHEELS gearing solution 2:1 Reduction Jackshaft

GUIDE - BIG WHEELS gearing solution 2:1 Reduction Jackshaft

GUIDE - BIG WHEELS gearing solution 2:1 Reduction Jackshaft



Sure, big wheels can look great, and most of all give fantastic ground clearance - allowing the use of your vehicle off-road, on the beach or in boggy and bumpy terrain.  Normally the first thing our clients think of when designing an off-road vehicle is how much ground clearance they can achieve.  This isn't a bad thing - ground clearance is fantastic for the most part, but it all falls apart when searching for compatible gearing on a stationary engine.

Typically, most stationary engines will have a 3/4" or even a 1" crankshaft - in the case of 9hp and larger engines which are commonly used on off-road recreational vehicles. 

The biggest problem that arises with larger wheels is when using a standard centrifugal clutch s that in order to get a gear ratio that won't destroy the transmission it is necessary to have a rear sprocket that is almost the size of the rear wheels, meaning all the effort designed into the vehicle for ground clearance is wasted.  (Not to mention the fact that anything over about 280mm needs to be custom made, or some sort of incompatible pitch needs to be used)

With the advent of the humble torque converter this issue is halved, by using around a 3:1 reduction initially, it's possible to run a sprocket about half the size of the rear wheels and in most cases you'll have a working vehicle.  (YOU CAN READ MORE ABOUT TORQUE CONVERTERS BY CLICKING HERE

However, this does come at the cost of diminishing value, since as the engine revs build, the torque converter shifts to a longer ratio meaning at 3500rpm on a typical stationary engine, if your engine is actually strong enough to get there, it will take a long time and you'll be going so fast it would be downright dangerous . 

What will happen in most cases is that the belt willl wear and slip, ending in a smokey and stringy or broken belt, and a significant loss of fun-time.

These are great on karts with small wheels like the one below:


Don't worry though, there is a way to solve the issue.  With our new range of reduction jackshaft kits you can now shorten your ratio again by 2:1, allowing you to take advantage of increased acceleration witout compromising top end speed (since you wouldn't actually achieve anything like a top speed anyway otherwise).  The reduction jackshaft kit is avialable in #35 and 420P pitches so that it will connect to most projects running mainstream kart chain.

The reduction jackshaft kit will change a typical 3:1 reduction on a torque converter, to a starting reduction of 6:1 providing you with strong acceleration with very large wheels.  The final drive ratio will be reduced by 2:1, giving you good acceleration all the way to top speed, and a top speed that is actually usable and reachable.

By combining one of these incredible 2:1 reduction jackshafts along with a suitable torque converter from our range you'll be able to achieve a ratio that will allow you to use a sprocket between 1/3 and 1/2 the size of your rear wheels reliably!