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Old 04-26-2015, 07:02 PM   #1
802mike OP
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Fly by Wire Quirk

I've only got several hundred miles on the '15 GSA and noticed something interesting. If I hold the throttle in on position and up or down shift, the RPMs change but the speed stays the same.

Has this been discussed before?
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Old 04-26-2015, 09:20 PM   #2
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Do you have the shift assistant installed?
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Old 04-26-2015, 10:52 PM   #3
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he must have ticked the CVT option.
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Old 04-26-2015, 11:03 PM   #4
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Unless I'm misunderstanding what you've written, if you hold the throttle position, and change gears (up or down), a bike's RPM's are going to go up on any bike, car, truck, etc...with a manual transmission until the gear change is complete.

The RPM's go up because you've taken the load off the engine so it's going to spin up until there's a load put on it again and it'll adjust accordingly.

The change in speed, or lack thereof, is going to happen more slowly vs. the time it takes you to change gears. Given enough time, your speed will change also if you hold the clutch in long enough because there's no power to the bike. With shift assistant everything happens much more quickly, but the same thing applies.

I'm assuming I'm reading your post wrong.
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Old 04-27-2015, 12:11 AM   #5
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I do have shift assist pro.
The speed does NOT change. As if I was using the cruise control.
The RPMs DO change though. As if I was using the cruise control.
Hope that's clear

So I'm going along at sixty MPH in fourth gear and without moving my right wrist I shift up, the revs change but the speed stays at sixty.
If I'm not moving my wrist the RPMs should stay the same and the speed change.

Does the same in other gears either shifting up or down.

802mike screwed with this post 04-27-2015 at 03:31 AM Reason: Ad explanation
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Old 04-27-2015, 02:04 PM   #6
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Quote:
Originally Posted by 802mike View Post
I've only got several hundred miles on the '15 GSA and noticed something interesting. If I hold the throttle in on position and up or down shift, the RPMs change but the speed stays the same.

Has this been discussed before?
Unless you go into a too high or low of gear, why would the speed change?
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Old 04-27-2015, 04:11 PM   #7
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The throttle position must be a hp rating. Shifting does not change the hp output there for the speed does not change. Computers!
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Old 04-27-2015, 04:54 PM   #8
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It took me a while to understand the OPs observation, but if throttle body butterfly valve position holds constant, and you change gears, bike should change speed; i.e. speed up or slow down... This observation indicates that the throttle body valve and the throttle position are not perfectly matched at all times under normal riding conditions; i.e. no traction control at work.

Maybe it's just me, but my non-GSAP 14GSA feels mildly unpredictable in regards to power delivery compared with my previous oil-head. Makes me kinda miss the predictable linear throttle to throttle body opening relationship.

Anyone know how the e-throttle actually determines the throttle body opening relationship? I've read the owners manual and I've seen speculation posted here (most notably about Dynamic ride mode), but nothing definitive.
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Old 04-27-2015, 04:56 PM   #9
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Quote:
Originally Posted by Crilly View Post
The throttle position must be a hp rating.


HP changes with RPM. HP = (torque * RPM)/5252 which is why the Torque and RPM curves always cross at 5252 RPM. He is saying that the speed is constant. I don't have shift assist, but have noticed that at moderate RPMs I can shift without rotating the throttle and the speed seems to stay more-or-less constant with only the RPM changing and no slow down due to engine braking.
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Old 04-27-2015, 05:10 PM   #10
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Quote:
Originally Posted by marchyman View Post


HP changes with RPM. HP = (torque * RPM)/5252 which is why the Torque and RPM curves always cross at 5252 RPM. He is saying that the speed is constant. I don't have shift assist, but have noticed that at moderate RPMs I can shift without rotating the throttle and the speed seems to stay more-or-less constant with only the RPM changing and no slow down due to engine braking.
Only available HP changes and if the load doesn't change you can keep the throttle in the same spot and change gears all you'd like. If the load changes IE: a hill then the torque and HP maps change. On a flat surface the engine doesn't care what RPM it's running.
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Old 04-27-2015, 05:19 PM   #11
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I rode again today and it certainly does hold the speed. It might be more to do with the shift assist than the fly by wire.
I happened to notice because I'm breaking in the bike, changing gears and varying the RPMs a lot.

Here's a reply I got in another forum:
"I asked a bmw tec and he said that's proper and the way it's supposed to be. Some sports cars also have it including the new M3/4. It called rev matching. Designed to make up and down shifts seamless and not jerky."
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Old 04-27-2015, 05:24 PM   #12
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Quote:
Originally Posted by asnowmobiler View Post
Unless you go into a too high or low of gear, why would the speed change?
I guess this is hard to get your head around.

I change gears, I do not move my wrist, the speed stays the same, the RPMs change.

In a normal world, the RPMs would stay the same and the speed would change.
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Old 04-28-2015, 10:37 AM   #13
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Quote:
Originally Posted by 802mike View Post
I guess this is hard to get your head around.

I change gears, I do not move my wrist, the speed stays the same, the RPMs change.

In a normal world, the RPMs would stay the same and the speed would change.
It is for me too
When you say "In a normal world..", what are you referring? What's your reference? IME, it's the opposite of what you're stating.

Quote:
Originally Posted by thirsty 1 View Post
Only available HP changes and if the load doesn't change you can keep the throttle in the same spot and change gears all you'd like. If the load changes IE: a hill then the torque and HP maps change. On a flat surface the engine doesn't care what RPM it's running.
I agree with this statement.

FWIW, in my ride into work over the past few days (120 miles rd trip) I've tried what you've explained and when using the GSAP, RPMs change but speed does not on mostly level/straight sections.

The only way I could get speed to change while holding constant throttle was when RPMs dropped into the low 3000's out of optimum rev range. Here engine response is slower (I.e. Just like if you're in too high of a gear and give it gas, it gets luggy). If I kept RPMs above 3500 I could shift between 4-5-6th gears all I wanted and ONLY RPMs would change by @400 for each shift.

IMHO, this is not a 'quirk' but normal.

As an aside, I also realized for myself how often throttle position changes because holding constant throttle (not the same as constant speed over varying terrain) took a lot more concentration than I thought. And when non-GSAP'ing I'm blipping and rev matching so naturally that constant throttle is only a theoretical exercise.
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Old 04-28-2015, 10:37 AM   #14
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Hmmmmmmm......it sounds like you have an electric motor for power, not a gasoline engine.
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Old 04-28-2015, 02:59 PM   #15
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They could have implemented a different control algorithm where you provide a velocity or power reference by using the throttle.

I think they had implemented velocity reference on the tesla.
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