The big Stark Varg supermoto information topic

[Johnny Depp]

I don’t know how this guy was able to fit a 16t front sprocket as on my ex theres no physically possible way to mount that big of a sprocket without making contact with the aluminum motor case. I only know because i already tried, lol..

Probably a grinder, for sure have to remove the chain guard.

 

[AL_V]

I don’t know how this guy was able to fit a 16t front sprocket as on my ex theres no physically possible way to mount that big of a sprocket without making contact with the aluminum motor case. I only know because i already tried, lol..

Probably removed the front chain guard, see photo (shown with 14T):

 

[Phantom]

Now that i see its not limited to any certain speed, the real enemy hear is obviously finding better cooling alternative for the motor/controller etc. Finding a way to front mount a set of radiators from like a traditional IC bike or attatching external heat sinks….something. This Florida heat/humidity just saturates the power system so dang fast! Even if your only doing a mildly spirited ride with 15t/45t gearing.

This gets me thinking. Move the current radiator to the front and then that would free up room for the charger. Has to be obvious to Stark cause there is not many options and I was really surprised by how small the radiator is and where it’s located

I hear the rumors of the next stark being a supermoto but I wouldn’t hold your breath. They did a sale of $2k off which tells me sales are weaker than expected so this means they need to be careful rather than create another model. Hope I’m wrong.

For those having this overheating issue. The first thing I’d try is to increase air flow to the radiator. Seems like if you modify the rear wheel well plastics with some holes or slots, that would make a meaningful difference. Air flow in seems ok but can’t get out.

When I mounted my charger off the rear subframe, it looked like if you removed the radiator, the space left behind could fit the charger. The cable from there to the charging port could get shorter and the incoming power cord could fit in the remaining space.

Front radiator should be doable but front plastics would need to be expanded wider. Maybe twin radiators? One on each side of the frame spine?. Maybe need to buy a spare radiator and pump and give it a try.

I think if it was a little wider in the “tank” area, that would not be a problem for street. Maybe off-road this narrowness is nice. Don’t have much experience there.

Sad to read about the issue others are having cause these bikes are amazing. I’ve had some phone issues but nothing that power cycling didn’t clear.

Curious to see if I have any issues when my street wheels arrive. So far no issues I can tell but the dirt wheels are fun only up to about 60mph on the road. Then the imbalance is just not worth tolerating for long.

 

[Erwin P]

They did a 2K sale because the new model was comming, wich is now around the old price. This is pretty much standard in industry.

Supermoto won't be a huge investment though. Design some 17' wheels, some lower and firmer suspension, different handlebar and you could call it a day. The frames and Drivertrain could remain the same.
But since most SM's would be for on the street they really should integrate the charger in there somewhere.
Nicest would be if it was all interchangeable with the EX. Buy some parts and be able to mount the charger on the EX.

 

[Johnny Depp]

I think Tesla has a more sophisticated cooling method, channeling coolant through heat sinks that the batteries are mounted on? If the Stark is to be a race bike, pushed to the limits on a road track, the current setup won't get it done. A few band aids like better airflow or repositioning the radiator will likely help some, but it's likely going to end up like an Alta with an overheated battery too often.
There must be a way to enhance airflow in the current location of the radiator? Holes in the side panels?

 

[Bernardo]

I did some calculations on the bikes powertrain, bearings, electrical and mechanical losses
and a simulation of the torque, motor rpm and speed realations.
That all fits pretty good to the dyno tests on youtube.

at the end, at full power, the losses reach almost 8kW.
and 90% of it end up as heat generated within the powertrain.
so ... no wonder its getting hot.
and the installed cooler is far away from 8kW coolingpower.

do not wonder about the low torque values at this examle.
they are the values at max. motor speed.
and power = torque * rmp. so as one value rises the other shrinks
as one can see on the chart.

hope the translations of values are adequate.
and metric - of course ;-)

Greez

Bernardo

 

[Johnny Depp]

I did some calculations on the bikes powertrain, bearings, electrical and mechanical losses
and a simulation of the torque, motor rpm and speed realations.
That all fits pretty good to the dyno tests on youtube.

at the end, at full power, the losses reach almost 8kW.
and 90% of it end up as heat generated within the powertrain.
so ... no wonder its getting hot.
and the installed cooler is far away from 8kW coolingpower.

do not wonder about the low torque values at this examle.
they are the values at max. motor speed.
and power = torque * rmp. so as one value rises the other shrinks
as one can see on the chart.

hope the translations of values are adequate.
and metric - of course ;-)

Greez

Bernardo

View attachment 14464

View attachment 14465

Glad you summarized that, because it's weird science. Looks like the chain is the biggest friction. Luckily as a dirt bike, overheating doesn't seem to be a problem. My fan runs a lot, not sure that means much?

 

[Theo]

I think Tesla has a more sophisticated cooling method, channeling coolant through heat sinks that the batteries are mounted on?

Here are some of their solutions applied to some recent models, @11:32

Notice how the cooling system should be made in such a way that It doesn’t short the cells.

power = torque * rmp

I’m sorry for being pedantic but this formula written like this has confused me so many times over the years before I found out the true one.
Actually power (W) = torque (Nm) * rotational speed (radians/second) = torque (Nm) * rpm * 2π / 60 seconds

On the other hand I really like your idea to assess the heat generated by losses, but I wonder how much of the heat generated by the gears and bearings in the powertrain ends up heating the inverter, I guess not so much of it. One concern could be that that heat may affect the magnetism of the permanent magnets, but it would take hundreds of Celsius degrees to do that thanks to rare Earth metals.

Anyhow it doesn’t surprise me that some Vargs overheat when used racing on asphalt.
Josh Hill, in a video, hit a thermal limit and explained, in the comments, that the problem was possible to occur only to pro level riders. Never occurred to me. A user of this forum who was a former professional MX rider had overheating problems.
The EX is capable of delivering so little continuous power that it’s less than 11 kw and therefore here in Europe it can be ridden with the same riding license as power restricted 125cc bikes, probably because of overheating.
Still some people have enjoyed doing supermoto anyways.

 

[Erwin P]

The EX is capable of delivering so little continuous power that it’s less than 11 kw and therefore here in Europe it can be ridden with the same riding license as power restricted 125cc bikes, probably because of overheating.
Still some people have enjoyed doing supermoto anyways.

Yes and no. There is a "bug" in the way this power is tested. For a certain amount of time the bike is tested at full throttle. I believe for something like 15-20 minutes although i have to look that one up.
Then after that time they look at the last number. If the test is 20 minutes and it makes 50kW at 19 minutes, but 10 at 20 minutes, 10 it is.
Also if they would use partial throttle in their testing so it doesn't overheat or drain the battery the continuous power would be much much higher.
If the test is 20 minutes, top speed 160 km/h that allready is 53km. Close to max range at that power so the battery wipl have lost most power anyways.

There are chinese bikes taking advantage of this. They are programmed to be limited after exactly the right time.

 

[brongle]

I think Tesla has a more sophisticated cooling method, channeling coolant through heat sinks that the batteries are mounted on? If the Stark is to be a race bike, pushed to the limits on a road track, the current setup won't get it done. A few band aids like better airflow or repositioning the radiator will likely help some, but it's likely going to end up like an Alta with an overheated battery too often.
View attachment 14461 There must be a way to enhance airflow in the current location of the radiator? Holes in the side panels?

FWIW I don't think the battery is really a limiting factor (at least with the new 7.2kwh pack), it's the inverter and motor which will eventually heat-soak and cause throttle cut-outs. I've pushed the EX pretty hard and I've only seen max battery sensor temps of 115F (46C) and that was after a 2KW charging session from 20% in a 100F garage, immediately followed by heavy street riding in 90+ temps. The cells in the EX pack are probably rated to discharge up to 60C, and with a realistic safety margin I'd imagine the bike cuts out somewhere in the 50-55C range. There are some benefits to having control over the pack temperature especially when it comes to charging/discharging performance, but even then I imagine Stark doesn't wanna accept the complexity and risk of developing an actively cooled pack.

I think if the SMX model is to be competitive they will need to redesign the drivetrain cooling system and likely move the radiator into airflow (like others have suggested). The system already works pretty well for its size, but it just can't keep up with the rate of heat soak you get when pushing high RPM.

 

[Bernardo]

Yes and no. There is a "bug" in the way this power is tested. For a certain amount of time the bike is tested at full throttle. I believe for something like 15-20 minutes although i have to look that one up.
Then after that time they look at the last number. If the test is 20 minutes and it makes 50kW at 19 minutes, but 10 at 20 minutes, 10 it is.
Also if they would use partial throttle in their testing so it doesn't overheat or drain the battery the continuous power would be much much higher.
If the test is 20 minutes, top speed 160 km/h that allready is 53km. Close to max range at that power so the battery wipl have lost most power anyways.

There are chinese bikes taking advantage of this. They are programmed to be limited after exactly the right time.

Hola!
In Europe, at least in Austria, the stated power in the license paper is the max continous power during a period of 30min.
the procedure is the same for cars and bikes.
the instantaneous power is not a factor.

A 16 year teenager can drive a bike with max 11kW in Austria.
thats ok with ice bikes.
the stark has 9kW in the license.
and our kids can ride rocketbikes nowadays.

as VW has shown some years ago with their emission limiting test mode.
things may easily be constructed in the right way to pass those tests.

 

[Erwin P]

Same here in the Netherlands. I just was unsure of the time. But 30 minutes makes it even more ridiculous.
You need to be 18 here for the A1 license. But i think A1 riders with no previous MX experience have no business being on the street with a Varg Alpha.

 

[Johnny Depp]

FWIW I don't think the battery is really a limiting factor (at least with the new 7.2kwh pack), it's the inverter and motor which will eventually heat-soak and cause throttle cut-outs. I've pushed the EX pretty hard and I've only seen max battery sensor temps of 115F (46C) and that was after a 2KW charging session from 20% in a 100F garage, immediately followed by heavy street riding in 90+ temps. The cells in the EX pack are probably rated to discharge up to 60C, and with a realistic safety margin I'd imagine the bike cuts out somewhere in the 50-55C range. There are some benefits to having control over the pack temperature especially when it comes to charging/discharging performance, but even then I imagine Stark doesn't wanna accept the complexity and risk of developing an actively cooled pack.

I think if the SMX model is to be competitive they will need to redesign the drivetrain cooling system and likely move the radiator into airflow (like others have suggested). The system already works pretty well for its size, but it just can't keep up with the rate of heat soak you get when pushing high RPM.

My quick fix today. If mud is a worry, a strip of duct tape seals it back.

 

[Bernardo]

any changes in behavior?
what does the backside of the radiator looks like?
Is there any space that air may travel freely.
or is there an thermal short circuit?

Bernardo

 

[TheJ0rma]

My EX dispalys a battery warning icon when it starts cutting power on track. Don't know what temp is actually causing the power limitation.