Alta Redshift MXR and MX on a Dyno - Riding Maps Demystified

[Kurlon]

Torque is either calculated based on RPM and the rate the drum accelerates, or if the dyno has a z-cell it can direct measure rear wheel torque.

 

[Philip]

How is torque at the motor measured on the dyno?

No problem, I am glad to explain. Normally the dynos measure the HP that is required to spin the dyno's drum (HP at the rear wheel). They also measure the RPM by reading a spark plug wire. You can already plot the HP vs RPM accurately.

From the ratio of the dyno's speed to the engine's RPM it is easy to infer the total gear reduction ratio and the effective wheel radius combined. If you do it right, the HP will equal the Torque (measured in ft-lbs) at exactly 5,252 RPM.

With the electric you cannot easily measure the RPM. But we can measure the rear wheel circumference and get all the gear ratios from the owner's manual. This also allows to convert HP into Torque. Again, if you do it right, the HP will equal the Torque (measured in ft-lbs) at exactly 5,252 RPM.

The key with such calculation is to have the correct wheel circumference and the gear ratios, else the torque numbers could be a bit off. But the max HP numbers will be accurate regardless because they are measured at the dyno and their values do not depend of gear ratios.

 

[Kurlon]

'Accurate' on a Dynojet dyno is a bit of a misnomer... as is applying an SAE correction factor to an electric bike but I'll let those slide. Now repeatable I'll go for.

 

[Scotter]

How would dropping the front sprocket on the MXR to 12 in Map 3 impact the results and efficacy below 30MPH as well as battery life versus riding in Map 4? I utilize Map 3 for the majority of my track riding, but feel it is under-powered down low compared to my KX 450F and hitting jumps out of a corner is still a concern as I am still developing confidence on the Alta.

 

[Philip]

How would dropping the front sprocket on the MXR to 12 in Map 3 impact the results and efficacy below 30MPH as well as battery life versus riding in Map 4? I utilize Map 3 for the majority of my track riding, but feel it is under-powered down low compared to my KX 450F and hitting jumps out of a corner is still a concern as I am still developing confidence on the Alta.

The stock front sprocket on the MXR is already 12. Are you asking what would happen if you install a smaller or a larger front sprocket?

You should try Map 4, if you need to clear jumps. Your only get 37hp in Map 3. Of course it would feel underpowered.

 

[Speedkills]

I wonder if there is an easy way to measure power draw, and map it up to dyno numbers to generate an efficiency map, to better understand what rpm range our altas are most efficient in, and how bad the efficiency drops off as we move out of the ideal range? If the difference is big enough, I might include gearing for range in my tradeoffs as well as heat and usable powerband.

 

[Scotter]

Thank you and yes, I meant to state smaller on the front sprocket. The only area I feel the Alta is under powered is coming out of corners with a short run to a large (50-plus foot) jump. I only have an hour on the machine, so still trying to adjust to the torque versus harder hit of a gas engine. Map 3 works well in all areas of a track inclusive of straights, sandy areas and jumps except for short runs out of a corner for larger jumps.

A dealer suggested reducing the size of the front sprocket, thus getting the bike into the "meat" of the power sooner instead of running in Map 4 which will very quickly diminish the battery charge.

I find I am completing a 30 minute moto, then being forced to charge the battery for 30 to 45 minutes before I can ride again, so diminishing the charge further is a concern and my assumption is riding in Map 4 will have an adverse impact on the battery life.

The dyno info is fantastic and very useful in understanding where the power is delivered, thank you for providing.

 

[bsatt69]

Try level 4, I felt the same way when trying to ride track in anything but level 4. It would be interesting to see a graph of the motors efficiency vs rpm. I would guess that it is does not vary much, especially between the rpm ranges that changing 1 tooth on front sprocket would cause. Hitting a big jump out of a corner takes a lot of power regardless of engine rpm. I have found that track conditions vary the battery life a lot. When it is softer I am less than 30 minutes on a charge, when it is packed I can get close to 40.

 

[Philip]

Thank you and yes, I meant to state smaller on the front sprocket. The only area I feel the Alta is under powered is coming out of corners with a short run to a large (50-plus foot) jump. I only have an hour on the machine, so still trying to adjust to the torque versus harder hit of a gas engine. Map 3 works well in all areas of a track inclusive of straights, sandy areas and jumps except for short runs out of a corner for larger jumps.

A dealer suggested reducing the size of the front sprocket, thus getting the bike into the "meat" of the power sooner instead of running in Map 4 which will very quickly diminish the battery charge.

A smaller front sprocket will feel more like riding in the 1st gear where a second is needed. More wheelspin at low speed, then it will top out and become the same as before. You will still have only 37hp max, you will just waste more energy to wheelspin.

There is no free lunch. If you need to go faster to clear that jump, you need to use more horsepower. Try Map 4.

 

[blbills]

This may not be the right topic but has anyone done an endurance test between a 14t on Map 4 vs 12t on Map 3?

Would be interesting to find the result!

 

[strider]

So here's a bit of trivia regarding EVs. The rate of acceleration does not affect the amount of energy needed (Assuming no wheelspin). Unlike an ICE where accelerating rapidly requires revving higher with larger throttle openings that consumes more fuel, you do not consume more energy accelerating an EV quickly vs accelerating slowly.

Therefore, Map 4, by itself, does not use more energy than Map 1. If you rode the bike around in Map 4 the same way your rode it in Map 1 you will use the same energy.

The key to energy efficiency with an Alta is minimizing wheelspin. The more power you have in Map 4 causes most people to spin the wheel more and waste more energy. For that reason, going up in the front helps minimize wheelspin as it decreases torque at the wheel while also giving you more headroom on top speed.

The consensus here is to go to a 14T front and run Map 4.

 

[snydes]

A dealer suggested reducing the size of the front sprocket, thus getting the bike into the "meat" of the power sooner instead of running in Map 4 which will very quickly diminish the battery charge.

I would disagree with the idea that map 4 will get you much less range. It's all about that right wrist. Sure, if you go around blowing off the rear tire the whole time then yes. I have been using map 4 pretty much exclusively at this point.

Therefore, Map 4, by itself, does not use more energy than Map 1. If you rode the bike around in Map 4 the same way your rode it in Map 1 you will use the same energy.

Precisely!

 

[OneLapper]

I would disagree with the idea that map 4 will get you much less range. It's all about that right wrist. Sure, if you go around blowing off the rear tire the whole time then yes. I have been using map 4 pretty much exclusively at this point.

Precisely!

I agree. I have seen no real range difference in my ST loop by riding in different modes. The more I roost my buddies, the less the range. No roosting, no real difference noticed in range for each mode.

 

[TCMB371]

Thinking I'm going to try a 13T front like the EXR on my MXR. It should put the initial torque ramp somewhere in between the current map 4 and map 3.

 

[Philip]

So here's a bit of trivia regarding EVs. The rate of acceleration does not affect the amount of energy needed (Assuming no wheelspin). Unlike an ICE where accelerating rapidly requires revving higher with larger throttle openings that consumes more fuel, you do not consume more energy accelerating an EV quickly vs accelerating slowly.

I had to Google this one because I did not understand what the assumptions had to be for this to be true.

Does rate of acceleration affect the amount of energy used to accelerate?

So, if we have no wheelspin, no rolling resistance, no aero drag, then yes, it would take the same amount of energy to get from 0 to 60mph quickly over 60 feet, or slowly over 1 mile.

But if you add back all the real forces, then going faster, or longer, or accelerating harder will always cost you. If you want to have your battery last longer, then going slower is the default recommendation.

 

[OneLapper]

And the faster you accelerate, the more quickly you use the energy stored in the battery cells, the more the battery pack heats up, the higher the inefficiencies of the electrical system. I had to google this one too.

 

[strider]

This is absolutely an academic exercise. That was why I prefaced it as trivia. Most of us are taught with ICEs that you should accelerate slowly for best efficiency. With an EV the rate of acceleration doesn't change the amount of energy consumed. Now if you accelerate quickly and therefore spend more time at a higher rate of speed you will consume more energy.

My point was related to Map 4 consuming more energy than lower Maps. That is true with an ICE when you spend more time in lower gears. It is not true with an EV when ridden the same way. The point of maps is to help the human control the power.

And the faster you accelerate, the more quickly you use the energy stored in the battery cells, the more the battery pack heats up, the higher the inefficiencies of the electrical system. I had to google this one too.

Resistance goes down as heat goes up. Tesla has a max performance mode that actually heats up the batteries. This is not good for the health of the batteries which is why the bike limits power when the batteries get hot.

Also, I'm being pedantic, but it's the length of time at speed, not the rate of acceleration that determines the energy used.

Take the below curves. Speed on the left axis, time on the bottom. Assume the area under the curves are identical. With an EV, the energy used would be the same, with an ICE, the top curve would consume more fuel than the bottom one.

   __________
  /
 /
/

        _ ------------
    _ -
_ -

 

[TCMB371]

The top curve wouldn't always consume more fuel than the bottom one for an ICE. It really depends on where in the BSFC map the engine is operating at to achieve the speed. Typically a gas ICE is most efficient at about 85% load (roughly 3-5" hg) near the point of maximum torque output.

I used to be a hypermiler back when gasoline was $5/gallon, and actually had an article written about me where i achieved over 100mpg on a Ninja 250 just through riding technique. There was a concept of pulse and glide where you would do all your acceleration inside the most efficient range on your engine's BSFC map, and literally shut off the engine and let it coast back down (in neutral) until you were ready to accelerate again. This technique is partly why CVT transmissions are often more fuel efficient; because they allow the engine to operate inside the most efficient BSFC range more often, instead of climbing through the RPM range like a typical manual or automatic transmission needs to do.

With electric motors, it generally doesn't matter how hard you accelerate. It is when you over accelerate and need to use your brakes that you lose efficiency. Regenerative braking helps solve that human inefficiency, though. That said, every electric motor does have a point of maximum efficiency. However, even the point of least efficiency is vastly more efficient than an ICE.

 

[Altaracer929]

Thank you Philip for all your dyno work on the MX & MXR including gearing changes. Really opened our eyes, showed all of us the maps are the same except map 4. Now I know the only real difference between MX & MXR is faster charge times and map 4 horse power explosion on MXR. I agree if your buying the MXR it's to ride map 4's horse power & better suspension. With 14T gearing in map 4 slowly rolling your throttle staying hooked up throttle control smooth and easy no wheel spin using all that massive pulling torque like its a 260 lbs. 690 KTM ICE. Your right hand controls everything on these bikes. I am selling my ICE bikes now, looking to buy a used Alta MXR.

 

[Philip]

I am selling my ICE bikes now, looking to buy a used Alta MXR.

Hurry up! I thought you were an Altaracer already!