TwistGear Helical
Performance System
 

 

 

 

Johnson Engineering
100 Blake Road
Denver, IA 50622
(319)984-9298
(319)984-9299 fax
info@twistgear.net

web site map

 

updated February 24, 2003

Faster, Smoother, Stronger, Quieter!

Designed and Manufactured Exclusively in the USA!

tg kit

 

 

“Do you ride a five-speed? As a professional Harley mechanic, I’ve heard all the “Go Fast” hype on every engine and trans combo you can imagine, but I’ve seldom been satisfied when I used them in my own bikes.

When TwistGear caught my eye I decided to try it in my Roadglide® 95-inch TC. The close ratio 1st – 4th gear gave me a hole shot that really surprised the Hot Dogs I ride with, but 5th gear's the same as always.

In plain talk, I was just as quick as the guys with the smaller sprockets, but at 85 mph I was loafing along at 3,400 rpms while they were spinning like crazy at 4,000!

TwistGear really works – I highly recommend it to anyone who wants real performance without sacrificing comfort.”

WC
El Paso, Texas


What Is TwistGear?

TwistGear is a close ratio 5th-gear replacement system containing significant features and advantages not found in other designs. TwistGear fits 1991-up Evolution and Twin Cam 88 5-speed transmissions, and older 5-speeds back to 1985 with an appropriate conversion.

TwistGear features include reduced transmission noise, computer enhanced ratios (1st-4th), easier 5th-gear shifting, and significant improvement in gearbox reliability due to major improvements in bearing and shaft design.

Installation is straight forward, nearly identical to a fifth gear R&R, and can be accomplished in the frame, and without modifying the case. Depending on whether or not primary or final pulleys or sprockets are swapped, you'll either retain stock performance in 5th-gear combined with major acceleration gains in first through fourth, or stay with stock acceleration curves while significantly reducing engine RPM in fifth for comfortable cruising. Imagine...six speed performance in a five-speed gearbox, without the expense, noise, or wear and tear of an overdrive! (Fifth gear remains an ideal 1:1 direct drive ratio.)

1) Helical Cut vs. Straight (Spur) Cut Gear Teeth

The main reason helical cut gears haven't been used in American v-twins is the cost to manufacture, but the benefits clearly outweigh the expense. Not only do helical gears mesh more smoothly than spur gears, which have no helix or twist to ease engagement, they also increase the contact ratio. The result is superior tooth strength and reduced transmission noise.

TwistGear tooth strength is further enhanced by a high pressure angle and increased gear width. The helical gear twist delivers a face contact ratio of 1.1, resulting in at least 1 tooth in contact at all times. The involute gear profile gives a contact ratio of 1.4, resulting in at least 1 tooth in contact at all times. Together, there are at least two gear teeth in contact at all times.

2) Stock vs. High Performance Effect On Bearings

High and moderate horsepower applications generate lateral movement of the main gear inner drawn cup bearing, which will eventually work its way out of the main drive gear with predictably disasterous consequences.

TwistGear's main gear replaces the use of this low-cost stamped shell needle bearing with a high performance caged roller bearing capable of much higher load and torque than either OE or aftermarket bearings. Retained by snap rings on both sides, movement in the bore is eliminated. In addition our caged bearing features 3.5 mm diameter heavy duty rollers, with three times the load bearing capacity of standard 2.5 mm diameter needles.

Conventional transmissions use deep-groove ball bearings in the trapdoors, which aren't always up to the task. Both stock and modified engines benefit from Johnson Engineering's exclusive four-point ball bearings in both trapdoor locations. The radial capacity of the four-point ball bearing is double that of deep groove designs, while the shoulder design allows for complete control of axial thrust.

3) Rugged One-Piece Countershaft Design

countershaftConventional five-speed countershafts and gears are two separate pieces, resulting in a skinny cross-section between the splines and teeth roots, and a high stress concentration factor of 1.7 — not exactly the ideal design for transferring gobs of big inch engine torque to a sticky rear skin on a hot summer day at the strip and you're counting on riding home with a nifty time slip.

TwistGear's unique one-piece fifth gear and countershaft, precision machined from a solid chunk of forged steel billet, has an ideal stress concentration factor of 1.0 for superior fatigue resistance and built-in strength right where it's needed. The result is a gear and shaft so strong, we guarantee it for an entire year against defects when used according to instructions!

4) Quicker Shifting, Lower RPM’s

Replacing a stock ratio 32/17 early style or 41/22 (1.88 or 1.86:1) 5th-gear set with TwistGear's unique 41/20 (2.0:1) ratio helical gears delivers 10% shorter 1st through 4th for a true close ratio transmission. The result is better than six-speed performance minus the fatigue of shifting, the expense of a new transmission, and the noisey operation, coupled with greater reliability.

If it's lower cruising RPM’s and improved gas mileage you're looking for, a pulley/sprocket change is all that's required. In short, you control the acceleration, comfort, and economy characteristics with TwistGear and your choice of transmission and/or wheel sprockets.

5) Easier Shifting Equals Better Performance

Better shifts result in faster acceleration and longer transmission life. Shifting into 5th-gear is much smoother due to increased clearance on the main drive gear dogs, which are back-cut for positive engagement. Porting the dogs is no longer necessary for high-speed shifts.

These are just a few of the highlights detailing the revolutionary TwistGear close ratio helical transmission system. Get more details on our expanded tech page and our How Ratios Work page. Also available in WideGear configuration for fat tire conversions.

SportGear™ and TwistGear® are trademarks of Johnson Engineering, Inc. Buell™, Dyna™, and Sportster™ are trademarks of the Harley-Davidson Motor Company. No affiliation with the Harley-Davidson Motor Company is implied or inferred.