Why 2 throttle cables

[ilanr1]

I saw that there are 2 throttle cables that exists on various models.

On my tracer 900 GT 2019 model year , the first is to pull in order to accelerate and the second is to break the cruise control operation - there is a small micro switch that is doing this operation when you push the throttle.

So only one cable is enough in a non cruise control models.

Second think about a less friction on the throtle movement ...

Any thoughts please.

Thanks

Edited January 21 by ilanr1

[jdub]

I'd read many years ago the second (closing) cable's purpose was for safety. In case the opening/main cable hung up and/or the carb/throttle body plate stuck open, rolling off the throttle would ensure the second cable closed the slide/throttle plate. Some have removed that second cable and ride with no issues on various bikes, and I thought about doing it on my DRZ when rerouting the cables during some bike mods but figured it doesn't hurt being there.

Edited January 21 by jdub

[ilanr1]

We are dealing here with throttle bodies that have throttle position sentor , accelerator sensor etc.

 

[RaYzerman]

It's as jdub says, the return cable is there for safety purposes.  Best leave it installed.

[kilo3]

If your worried about the friction or throttle pull, a few have lightened the spring on cable carrier to great success:

https://www.tracer900.net/topic/3442-reducing-throttle-effort/#comment-39568

[bwringer]

4 hours ago, ilanr1 said:

We are dealing here with throttle bodies that have throttle position sensor , accelerator sensor etc.

Right, but up to that sensor sitting on the throttle body, it's a purely mechanical system, not even a throttle closed switch. So between the grip down to the TPS, you still need the mechanical redundancy, or at least Yamaha thinks so. This may be a regulatory requirement as well, although I'm not sure about that. 

The worth of this added complexity is debatable, of course; this is a very low-percentage failure. The most common issue with throttle cables by far is human error; botched installation, adjustment, modifications, or maintenance. Second would be failure at high mileage; if the "open" cable breaks or begins to fail, the loose or frayed wires could conceivably jam in the housing and cause the throttle to stick open.

In any case, you always have the kill switch.

If everything is in good shape and reasonably well adjusted, the "close" cable changes the feel and friction very, very little. The "open" cable gets all the wear and stress.

As noted above, there are some who have modified the spring with satisfactory results. And there are many vintage and custom bikes blatting around trouble free with a single throttle cable. It's not a common issue.

There are some bikes where all the electronics for the TPS are in the twist grip housing, so it's just wires heading to the ECU. Pretty much every car for a long time has been throttle by wire, with the sensor electronics in the accelerator pedal assembly. That's a very harsh environment, but these sensors are generally quite reliable.

One issue with motorcycles may be that a simple tipover could easily damage this expensive part. Then again, there's considerable other evidence that manufacturers don't give the slightest thought at all to tipover survival or expense.

I'm honestly not quite sure why Yamaha decided to use a hybrid system like this. 

[piotrek]

4 minutes ago, bwringer said:

Right, but up to that sensor sitting on the throttle body, it's a purely mechanical system, not even a throttle closed switch. So between the grip down to the TPS, you still need the mechanical redundancy

...just for clarity, that mechanical linkage is between the throttle tube and the APS. It in part controls the opening of the throttle, indirectly via ECU. The TPS is mechanically linked to throttle plate shaft and reports to the ECU on position. 🙂

[bwringer]

On 1/21/2024 at 11:35 AM, piotrek said:

...just for clarity, that mechanical linkage is between the throttle tube and the APS. It in part controls the opening of the throttle, indirectly via ECU. The TPS is mechanically linked to throttle plate shaft and reports to the ECU on position. 🙂

Excellent point! Thanks for the correction.

[skipperT]

On 1/21/2024 at 8:21 AM, bwringer said:

.

I'm honestly not quite sure why Yamaha decided to use a hybrid system like this. 

Initially when YCC-T was introduced on the R6 in 2005 (or 6), it was to give the rider a conventional throttle cable “feel” while riding, instead of the rider’s experience of twisting a hollow tube connected to a sensor. Fly-by-wire wasn’t common on bikes back then. 

-Skip

Edited January 23 by skipperT

[jeff_s]

Cables work well in tension, not so well in compression.  Isn't the 2nd on there so you can "pull" to both open and close the throttle?  Otherwise you're relying on springs for the closing force.  Yeah, springs are pretty reliable, but...

So, as other said, the real question is why these have ANY throttle cables..

[ilanr1]

Even with 1 cable there is enough tension...