Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

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Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by mbgjt1 » Jan 06 2021 5:51pm

Hi everyone,

I am in the process of ordering the wheels (front and rear).

QS205 V3 3T hub motor will be laced in 17" rim. However, I am not sure what the width of the rim should be.

Looking at most dirt bikes, it looks like they have a 21" by 1.6 front wheel size, and a 19"2.15 rear wheel size.

Should I be going for a 2.15" diameter on the rear wheel? Would this offer the best balance of strength, grip, and maneuverability? The total bike weight and rider weight will be around 200kg.

The bike will be running at 25kW so allot of power to the rear wheel, does this mean the wider the better, so I get better grip?

Riding will be 60% on street, 40% off road (fire trails etc.)

Thank you in advance.

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by Yermommy » Jan 06 2021 5:56pm

I think 25kw is a little too high for a 205. You might want to look into getting a 273. Sorry I can't comment on the correct rim width.

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by markz » Jan 06 2021 7:38pm

17 comes in 1.40, 1.60, 1.85 (WM2), 2.15 (WM3) and larger.

You need to figure out what tire size (width) you want and choose appropriate rim width.

It is also a good idea to find out if 17" is a common size or go with 16 or 18". There seems to be plenty for sale in 17" but you also have to see what the tire availability in 17" is, which seems like theres a good selection. Then you need to find out what size spoke you want to use, and if the nipples will fit the rim holes.
Last edited by markz on Jan 07 2021 4:55pm, edited 1 time in total.

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by 999zip999 » Jan 07 2021 12:49pm

Are you going to have QS laced the rims ? Yea want to see your tire choice.

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by anddan » Jan 07 2021 5:27pm

Did you mean 2.5 kw, 25000 watts is way above the 3000W rating of the QS205, you could possibly run 2.5 kw on the QS205 with a temperature sensor and a display (cycleanalyst) to monitor the heat.

Andrew

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by amberwolf » Jan 07 2021 5:52pm

Shortcircuit911 ran *peaks* of over 20kW on one of these motors, but also broke both axle ends off (I have that motor here now for experiments). If the 20kW+ was continuous, rather than an occasional peak, the motor wouldn't be able to dissipate the heat, and would probably fail. It also probably would be saturated when in operation at the really high power levels, and making more heat than motive power out of it, compounding the problem. :(

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by MadRhino » Jan 07 2021 8:22pm

anddan wrote:
Jan 07 2021 5:27pm
Did you mean 2.5 kw, 25000 watts is way above the 3000W rating of the QS205, you could possibly run 2.5 kw on the QS205 with a temperature sensor and a display (cycleanalyst) to monitor the heat.

Andrew
2.5 kw is only 2500 watts, which is conservative with a motor that is rated 3000 watts continuous. In fact, this 3k rating is on a test bench. When riding, some cooling from air flow does make it able to take a few hundred watts more continuous power. We can’t overpower much the continuous rating, but short bursts can be very high, up to 10 times the continuous rating with some hub motors in ideal situations.
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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by mbgjt1 » Jan 07 2021 11:45pm

Yermommy wrote:
Jan 06 2021 5:56pm
I think 25kw is a little too high for a 205. You might want to look into getting a 273. Sorry I can't comment on the correct rim width.
hi there, it should be fine in very short bursts (under 10 seconds)

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by mbgjt1 » Jan 07 2021 11:46pm

999zip999 wrote:
Jan 07 2021 12:49pm
Are you going to have QS laced the rims ? Yea want to see your tire choice.
yup, I can't decide whether to have QS lace my rims or just do it myself.

The only option width they offer is 17" by 1.6".

I'm not sure what the difference between the 1.6, 1.85, and 2.15"... what are the advantages and disadvantages of each

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by mbgjt1 » Jan 07 2021 11:47pm

anddan wrote:
Jan 07 2021 5:27pm
Did you mean 2.5 kw, 25000 watts is way above the 3000W rating of the QS205, you could possibly run 2.5 kw on the QS205 with a temperature sensor and a display (cycleanalyst) to monitor the heat.

Andrew
Hi Andrew,

25kw would be run for a very short amount of time...

What tire size are you running?

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by mbgjt1 » Jan 07 2021 11:50pm

amberwolf wrote:
Jan 07 2021 5:52pm
Shortcircuit911 ran *peaks* of over 20kW on one of these motors, but also broke both axle ends off (I have that motor here now for experiments). If the 20kW+ was continuous, rather than an occasional peak, the motor wouldn't be able to dissipate the heat, and would probably fail. It also probably would be saturated when in operation at the really high power levels, and making more heat than motive power out of it, compounding the problem. :(
damn! I have the Qulbix Q140r frame.. any idea what the max torque I can handle on it is?

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by Chalo » Jan 07 2021 11:54pm

mbgjt1 wrote:
Jan 07 2021 11:47pm
25kw would be run for a very short amount of time...
It still over 8X the power rating. How many other things would you do that with? Car? Cordless tool? Coffee machine?

"Hi, product support? I ran my new 60W desk lamp at 500W for a very short amount of time, and it failed. Will you replace it under warranty?"
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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by markz » Jan 07 2021 11:55pm

Would depend on the quality of the materials used for the rear swing arm, hinge point/frame and the quality of the welds. I doubt Qulbix spent to much time or money in engineering, quality standard assurance testing, stress testing then what the major bicycle brands have done over the past 5 decades for simple pedal power. Ramp up the power to motor levels, that testing is even more required.

That goes for any and all Enduro style EEB ebike frames, kits and complete bikes for sale.
As a matter of fact, I bet Walmart bicycle shaped objects have more money funneled into appearence alone but lets also include design, engineering and QC of said BSO's.

I bet the Qlbix can handle a ton of power but it wouldnt take much to beef up the rear end. Just hope the power levels doesnt twist or bust the hinge point when something does go wrong.
mbgjt1 wrote:
Jan 07 2021 11:50pm
damn! I have the Qulbix Q140r frame.. any idea what the max torque I can handle on it is?

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by mbgjt1 » Jan 08 2021 12:13am

Chalo wrote:
Jan 07 2021 11:54pm
mbgjt1 wrote:
Jan 07 2021 11:47pm
25kw would be run for a very short amount of time...
It still over 8X the power rating. How many other things would you do that with? Car? Cordless tool? Coffee machine?

"Hi, product support? I ran my new 60W desk lamp at 500W for a very short amount of time, and it failed. Will you replace it under warranty?"
fair point, but many QS205 owners are running them at this sort of power for short bursts and it seems to be ok. I guess as long as the temperature of the motor is monitored then it may be ok

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by mbgjt1 » Jan 08 2021 12:15am

markz wrote:
Jan 07 2021 11:55pm
Would depend on the quality of the materials used for the rear swing arm, hinge point/frame and the quality of the welds. I doubt Qulbix spent to much time or money in engineering, quality standard assurance testing, stress testing then what the major bicycle brands have done over the past 5 decades for simple pedal power. Ramp up the power to motor levels, that testing is even more required.

That goes for any and all Enduro style EEB ebike frames, kits and complete bikes for sale.
As a matter of fact, I bet Walmart bicycle shaped objects have more money funneled into appearence alone but lets also include design, engineering and QC of said BSO's.

I bet the Qlbix can handle a ton of power but it wouldnt take much to beef up the rear end. Just hope the power levels doesnt twist or bust the hinge point when something does go wrong.
mbgjt1 wrote:
Jan 07 2021 11:50pm
damn! I have the Qulbix Q140r frame.. any idea what the max torque I can handle on it is?
Very true, when I emailed them they said the rear swing arm was tested at 200Nm of torque but I think the QS205 might be able to handle a bit more.. I may take it to a local machine shop and ask how I can beef up the swing arm, at the point of connection to the motor.

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by amberwolf » Jan 08 2021 12:36am

mbgjt1 wrote:
Jan 08 2021 12:13am

fair point, but many QS205 owners are running them at this sort of power for short bursts and it seems to be ok. I guess as long as the temperature of the motor is monitored then it may be ok
And some of them have broken axles. ;) (though this is probably not *solely* from that)

Another issue is as I said before--saturation. That means there is a point at which the motor is no longer turning the extra input power into torque, but instead is just making heat out of it. That's different for each motor design, so you'd have to ask the manufacturer for this point for the specific motor you wish to use. It's also not just a cliff, but a curve where it gets worse and worse until at some point more heat is made than torque for the same power increment, so you'd need this data from them as a chart that you could use to determine where that point would be in your particular system.


FWIW, based on what I've personally seen and experienced of various motor manufacturers, I'd expect less structural failures in the QS motors than any of the other DD hubmotor brands except Ultramotor (TDCM). But there are still various things in their designs, like still using flatted axles for torque transmission, with sharp-cornered transitions between the varying diameters of the axle sections, that are asking for the same kinds of failures every other such motor design has had, and the risk of such failures is higher the more torque you ask of it.
mbgjt1 wrote:
Jan 08 2021 12:15am
I may take it to a local machine shop and ask how I can beef up the swing arm, at the point of connection to the motor.
The motor axle design is the main problem with torque transfer. Change the axle out for somethign that transfers torque thru an arm, not axle flats, and make the swingarm match, and you'll have a much more reliable system.

THere are various threads about this problem, including design studies by Justin_LE and others on systems to correct this severe design flaw.

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by MadRhino » Jan 08 2021 4:44am

mbgjt1 wrote:
Jan 08 2021 12:13am
Chalo wrote:
Jan 07 2021 11:54pm
mbgjt1 wrote:
Jan 07 2021 11:47pm
25kw would be run for a very short amount of time...
It still over 8X the power rating. How many other things would you do that with? Car? Cordless tool? Coffee machine?

"Hi, product support? I ran my new 60W desk lamp at 500W for a very short amount of time, and it failed. Will you replace it under warranty?"
fair point, but many QS205 owners are running them at this sort of power for short bursts and it seems to be ok. I guess as long as the temperature of the motor is monitored then it may be ok
Performance has a cost, and no guarantee. There is a development cost, and reliability compromises. We need to find out the limits, and decide how close to the limits we are willing to accept the risk. Then, we can optimize our build to achieve the best performance out of this limit. Looks simple, but high goals can cost a lot of time and money.

Using motorcycle components is accepting a performance compromise for better reliability, or lower maintenance cost. Choose your rims and tires for weight. Motorcycle wheels are rated for much higher load and speed than ebikes will ever need, thus the weight penalty is counter productive, performance wise.
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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by fatty » Jan 11 2021 3:12am

mbgjt1 wrote:
Jan 06 2021 5:51pm
QS205 V3 3T hub motor will be laced in 17" rim. However, I am not sure what the width of the rim should be.
I never understand this. The 140 takes a 26" x 90mm tire. Why compromise tire size (fundamental) for gearing? Get the correct wheel&tire and fix gearing with Kv and battery volts. Or better yet, mid-drive and fix gearing with.. actual gears.

21" moto rim with MH90-21 or 80/90-21 tires are equivalent 26" x 90mm bike. Plenty of tires in those sizes to choose from.

Get strong dimpled rims in your desired diameter. Width is tertiary concern, if at all.
Bucnahan's for REWM22136 EXCEL WM2 (1.85) x 21" ALUMINUM RIM - 36 HOLE
Last edited by fatty on Jan 11 2021 3:20am, edited 1 time in total.

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by fatty » Jan 11 2021 3:19am

MadRhino wrote:
Jan 08 2021 4:44am
Using motorcycle components is accepting a performance compromise for better reliability, or lower maintenance cost. Choose your rims and tires for weight. Motorcycle wheels are rated for much higher load and speed than ebikes will ever need, thus the weight penalty is counter productive, performance wise.
I last agreed with this, and generally still do. But for 200kg at 25kW? That is a motorcycle.

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Re: Rear wheel & rim size, what is the best moto rim width to go for? QS205, 25kW

Post by MadRhino » Jan 11 2021 1:23pm

Yep, 200 kg is definitely too heavy for an ebike, when seeking performance especially. That is something that had been discussed. I don’t like using motorcycle wheels because my bikes are in the 40-45 kg of weight. Yet I can understand that some do, for many reasons. Then I recommend building their wheels with front Trial motorcycle rims, that are stiff alloy and light weight. I also recommend choosing tires for light weight, because no ebike is going to ride the speed that robust motorcycle tires are rated for. The problem with motorcycle wheel weight, is it does make for the need of even more weight, in batteries notably; and the performance loss, in braking distance especially.
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