Internal Grip Heaters

September 2011 coming home from a long trip, a multi-day cool spell (5.5 deg. C) had numb fingers despite thinsulate gauntlets. This got me thinking about grip heaters. I've never much liked the kind that go under or over the grips, particularly that the wiring rotates with the throttle and gets in the way of the throttle lock.

Ordered some bits and pieces from eBay to fabricate grip heaters internal to our hollow bars. The Concours bars are aluminum, so they conduct heat nicely. I thought this idea was original, but it seems the concept is already established  for motorcycles and snowmobiles (Symtec Heat Demons, Polly).


Prototype 1

The first bench setup consisted of a couple of 7.5 ohm 10W tubular axial lead resistors in series in a spare left handlebar, dissipating a total of roughtly 14W from a battery conected to a charger. The resistors had an air gap of maybe 1/8" to the inside of the bar, so by both conduction and convection, heat could escape in any direction, including sideways then out thru the switch or the bar end. The resistors got hot but not much came out through the grips.
The heat all has to get out to the atmosphere somehow, and I intially thought that only the power level was significant while internal physical configuration didn't matter. But getting the heat to go where you want is the trick, with as little as possible elsewhere. Ideally the heat should flow directly outward from the resistor, thru the bar grip and glove and into the hand.

Prototype 2

Aluminum has a much better thermal conductivity than air. So I bought some 25W aluminum-clad resistors and filed them to just slide/fit inside the bar, with an extra longitudinal groove to pass the insulated return wire. It helps to file the rough edges off the inside-bar tube weld to ease insertion.

The resistors make good thermal contact to the bar, reducing the air gap to essentially zero and this yielded much better results. A single resistor is also a more concentrated heat source than 2 resistors in series.

Convection transfer is largely eliminated, except from the resistor ends. For conduction, the thermal resistance directly outward thru the aluminum sleeve, bar and grip is lower than any sideways path through the air to either the switch or the bar end. There's less sideways loss, so for the same 14W of bench test power, more heat gets to the hand.

The aluminum resistor is rated at 25W. Nothing melted or shorted. One little irony is that these resistors run cooler because there's a better heat path to atmosphere.

Installed Version

The installed version uses ~10 ohms on the right/throttle side, giving 19.6W, 1.4A @ 14V nominal. The left side uses ~14 ohms giving 14W, 1A. The additional power on the right is to compensate for higher sideways heat losses due to the thermal resistance of the throttle tube and air gap.


Mechanically, the tricky part is handling the return wire. It's in a tight groove between the resistor and the bar, and has to be impervious to high temperature. To prevent current flowing through (and ruining) the steering head bearing, it cannot make electrical connection with the bar.

The return lead is a few inches of #20 GA solid bare copper wire, inside a high-temperature (good to 600 deg. C) insulating sleeve. At the far end, heat-shrink tubing covers the resistor connection and the insulating sleeve. At the near end, an insulated stranded wire is soldered to the solid return lead, with heat-shrink over the sleeve, connection and insulation. The stranded connection to the resistor is also heat-shrunk, and the two leads are taped together for protection.

I decided to install the on-off switch in the ignition switch bezel to allow actuation with the left hand while the right is on the throttle. This minimizes the number of wires which bend when the bars are turned, only the main 12V hot and ground wires. The DPDT switch was just a smidge too big to fit there, so I ordered a narrower SPDT switch.

Drilled a 1/4" hole in the ignition switch bezel about 1" forward of the back edge. Epoxied the orientation washer that came with the switch to the underside of the bezel. Used one more 1/4" washer as a shim under the bezel to adjust the switch height protruding above the bezel to match the waterproof switch cover height. The cover threads onto the switch and directly down onto the bezel top.

Switched 12V is obtained from pin 8 of the J-Box. Routed the 12V power source and ground wires under the tank, along the cable to the ignition switch, terminating in connectors under the top triple clamp, left side. Wired the switch under the bezel with a connector to the 12V source under the triple clamp and connectors to deliver 12V to the heaters.

Drilled 3/16" holes in the plastic inside bar caps for the heater external leads. A dab of RTV on the wires to keep water out. Stuffed a bit of fiberglass into the bar at each end of the resistors to control convection losses and keep the heat focused on the grip area.

Routed the heater wires immediately forward, then outwards under the brake/clutch switch, down the outside of the bar risers, then under the upper triple tree. Negative leads connect to ground wire connectors under the triple clamp, positive leads sneak up into the bezel connectors. The right heater negative wire passes under the ignition guard bracket, between the ignition switch and the top triple clamp to get to the ground lead on the left side.


The switch is small and the cover black, doesn't spoil the stock look. Most of the wiring is hidden, you can just see the wire poking out the inside bar ends.

For me, hand discomfort starts around 5 deg. C and below. Got things ready in the cold garage over the winter for a test ride in the spring. First ride of the season was a Mar. 27/2012 evening ride around Ottawa at 3 deg. C., deliberately using normal (thin) riding gloves rather than (thick) insulated gauntlets.

The heat effect is warmth rather than sizzling, just enough to reduce the pain in the fingers. Because of the aluminum bar mass, the heat takes a while to become noticeable. If it's cold enough for heaters to be necessary, they can stay on all the time - no need for a variable controller.

Nov. 2012 Update

Well, November was 'good' here in Ottawa in the sense that the roads were dry and the temperatures hovered around +2 deg. C., so I had plenty of chances to use the grip heaters. With 14W on the left and 20W on the right, the left would warm up more quickly (more direct heat path) and the right more slowly (trickling through both the throttle tube and the grip). However, after a few miles, the right became hotter than the left. Still not so hot that I had any urge to turn off the power. And my hands decided that they preferred hotter to not so hot.

So a modification is planned. I'm changing the left resistance to 10 ohms to give the same 20W power as the right. The resistor has been ordered and received, installation planned for over the winter. Fortunately, most of the work can be done in the warm basement instead of the freezing garage.