E-trike Aluminum vs steel frame

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coinmaster   10 W

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E-trike Aluminum vs steel frame

Post by coinmaster » May 04 2018 9:33pm

I'm planning to order a KMX trike kit next month for my cyclone 3000 and I'm trying to maximize range efficiency. I plan on riding about 14,000 miles per year.
I can either buy the steel or aluminum kmx venom frame, of course I'd want to go with the aluminum frame because it's lighter and will give me more miles but I've heard aluminum frames are prone to stress over time. What is the practical truth in this scenario? Is aluminum going to be a bad long term investment with a high powered rear motor?

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Re: E-trike Aluminum vs steel frame

Post by dogman dan » May 07 2018 6:41am

Well, once you have a motor helping, a few grams weight is meaningless. I have no idea which frame is stronger, but absolutely do not let weight be the decision maker, unless you have to carry the thing to the second story.

I'd go steel myself, simply because I weld (badly) and would be able to start frankenstien triking the thing. Adding stuff like sturdy racks, or a tow hitch. And, if need be, repair a broken frame.

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Re: E-trike Aluminum vs steel frame

Post by parajared » May 09 2018 11:04am

I own a steel KMX Typhoon and appreciate that I was able to wire feed mig-weld a rear rack and side mount battery box to mine. If you own a TIG welder you can weld stuff to an aluminum trike and we should note that there are plenty of no welds required solutions to panniers, rear rack, battery boxes too.

Weight matters because it takes less power to accomplish the same mission. If you require less power you require less re-enforcement, (less beefy torque arms ect...) and if you require less power you need less battery, and if you need less battery you don't need as large/heavy of a battery box. I think you will appreciate the elegance of a build optimized for the very lightest weight... but lets be realistic here, I bet you would also appreciate a build that can cruise along efficiently for distance but if needed but also crank out a couple kilowatts of joyride material at the minor expense of having a little extra battery/re-enforcement/motor weight. You might need a few kilowatts if you are hauling a load of camping gear with you.

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Re: E-trike Aluminum vs steel frame

Post by parajared » May 09 2018 11:44am

I'd go steel myself, simply because I weld (badly) and would be able to start frankenstien triking the thing. Adding stuff like sturdy racks, or a tow hitch. And, if need be, repair a broken frame.
I ended up having to weld my trailer hitch to my trike. The way that InStep trailers make their hitches does not play nice with KMX + hub motor.

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Re: E-trike Aluminum vs steel frame

Post by MadRhino » May 09 2018 10:44pm

I am not a trike rider. All I can tell is about bike frames and how they ride. You say high power, that has a very different meaning for different riders. So I prefer talking speed and terrain. Riding fast and hard, alu frames are much better because they are stiff. Good alu frames of course. Steel frames are twisting and bending at high speed,on rough terrain especially. Some say steel does bend but not break. I say you don’t care, after your frame distortion had sent you off course and broke your bones.

Both steel and alu have their advantages and weaknesses. Steel is easy to mod and repair, best for custom works. Alu is lighter and stiffer, best for performance. There are exceptions, for some expansive steel frames are made very stiff, and some very robust alu frames can be welded and mod without any problems.
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Re: E-trike Aluminum vs steel frame

Post by dogman dan » May 10 2018 5:57am

Couldn't agree more with that. High performance riding on or off road requires the best frames. And typically, that is not steel these days. Or cheaper aluminum, as in the wall mart bikes. I don't think the steel kmx frame is cheesy, flexy mild steel though. But I really don't know. If its chromoly, then its more spring like steel.

I did assume your need was sub 40 mph, on paved. The more info I/we have about what kind of riding you are wanting to do, the less stupid my answer gets. All we know at this point is you want high power and efficiency. Uhh right. Basically the only way to get long range from a limited size battery is to ride lower power and speed, regardless of how high power the motor may be. Think of driving your one ton truck, its not going to get good mileage running 80 mph. At 50, much better. Same deal with any e bike, the best speed to maximize range without going turtle speed, is about 18 mph. Astonishing how much more efficient that can be than 20 mph. Above 20 mph, wind drag just eats your battery up.


RE the weight, it does matter. but a 6 pound difference in frame weight may not do shit to change your overall efficiency, mainly because you weigh 200 pounds. Yes, measurable difference, but a very low percentage overall. You would feel that extra weight a lot more without a motor of course, but 300w will take a 350 pound bike and rider to that 15-18 mph speed that is so efficient.


One of the problems with bikes or trikes in general is that they are built to handle well up to about 30 mph. So if your intent is to go 50 mph continuously, frames can wear out fast. They may crack, or just get limber so that control suffers.

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Re: E-trike Aluminum vs steel frame

Post by parajared » May 10 2018 10:16am

Think of driving your one ton truck, its not going to get good mileage running 80 mph. At 50, much better. Same deal with any e bike...
Yeah but internal combustion motored examples don't compare quite right. I think a "one ton truck" lets say a F-350 with an empty weight of 6000lbs will chug along at about 13mpg whereas a Tacoma with some rocks in the bed to equal the same weight of 6000lbs would probably get about 17-ish mpg. Gas engines take get exponentially more inefficient simply from being larger in size. Say for example with your aerodynamic drag comparison, Lamborghinis are super aerodynamic but they still only get about 10 mpg.

BLDC motors don't take an efficiency loss in the same way that ICE motors do. You can take a rather beefy e-bike, something capable of putting decent power and still get 10wh/mi with it. Weight seems the only penalty you take from going larger motor/esc compared to gas motors where large motor seems to mean weight gain and also efficiency loss.

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Re: E-trike Aluminum vs steel frame

Post by eCue » May 10 2018 5:36pm

Im a weight weenie with bicycles with ebikes Im finding its a different world where durability is paramount not lightness.

Steel frames have stronger drop outs and absorb shocks / vibrations better providing a plusher ride then Aluminum frames.
Although Aluminum frames have good lightness with acceptable durability in this case the extra weight of the Steel frame is minimal. Probably only 5 lbs difference in weight.
I like light bikes and am using a Aluminum Mtb frame myself (750w peak) all the same I would choose the steel frame for a trike build or any other high powered ebike.
Even though the aluminum trike frame is likely well built.. I still like steel better in this case as trikes have more frame stress then conventional bikes making cracks more likely to develop. As mentioned Steel is easy to repair or weld mounting tabs etc. on if desired.


Looks like a lot of fun

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Aluminum would be trick Steel would be real :D
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Re: E-trike Aluminum vs steel frame

Post by novaraptor » May 20 2018 3:10pm

Last year, I purchased the KMX Cobra and added a 1kw hub motor. My main reason for going with the Cobra was because of the ease of
modification of the Chromalloy steel and the higher weight limit. So far, I've been totally pleased with the trike. Fits through most regular doors, pedals easily enough, and on throttle only cruises at about 17mph with the 48v 15ah battery in 750watt mode. Calculated range suggests around 36miles, and I believe that should be fairly close. I've only actually ran it around 30 miles at 14mph or so and had power left. I'd go with the steel, but I've never tried the alum.
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Re: E-trike Aluminum vs steel frame

Post by wturber » May 20 2018 4:17pm

I wouldn't worry about stressing the frame over time issue one bit. I'd trust that the makers have done the appropriate engineering to make that point moot. Many folks seem to get fixated on the fact that there is no fatigue limit for aluminum while not giving appropriate consideration to these two things.

1) Engineers who design aluminum bike frames are well aware of fatigue limit of aluminum and take it into account when making their designs.
2) If stressed beyond a certain point, steel frames also have a fatigue limit. They only escape the fatigue limit issue if they are never stressed beyond that point.

There is a stress test posted online where conventional lightweight bikes that use different materials were put through tens of thousands of stress cycles. They did this until either the frames failed or the cycles hit their limit of 200,000. And while certainly not an exhaustive test, the conclusion was that for lightweight bike frames from reputable makers, the steel frames were generally the least robust - even though the other frames weighed substantially less. This wasn't so much a matter of material, but was almost surely more a matter of the engineering and construction was used to make the various frames.

https://www.sheldonbrown.com/rinard/fra ... e_test.htm

The KMX specs suggest something possibly similar or related in that their aluminum frame trike has a maximum load of 300 lbs while the steel bike frames all max out at 209 lbs. That suggests to me that the aluminum frame is probably more "over-engineered" (and stiffer) than the steel frames. The quality of the engineering and construction are more important than the material chosen when it comes to durability. And how can a lay person judge the engineering and construction quality well? So people tend to judge based on what they can clearly see and that's the material that is used ... which really doesn't tell them anything important regarding actual real world durability.

I'd choose the material based on other factors as previously mentioned. Things like whether you intend to modify the frame, frame flex, weight, frame dimensions, and so forth.
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Re: E-trike Aluminum vs steel frame

Post by eCue » May 21 2018 1:12am

Chomo is the frame material of choice mostly do to its flexibility
Anyhow I had to check it appears the people at KMX trikes have engineered the alum and steel frames for the same capacity , which makes sense.

KMX coyote weighs 17.5 kg / aluminum Frame:
Folding TIG Welded Aluminium Box Frame with Aluminium Front Boom. Maximum Weight Limit:130kg / 286 lbs

KMX Typhoon - 18.9 kg / steel with aluminum front boom ,capacity 210lb off road 300lb on road use.

venom aluminum ~ Maximum Weight Limit:
95kg off Road, 130kg / 286 lbs on road.

kolt TIG Welded Steel Box Frame with Aluminum Front Boom Maximum Weight Limit: weighs 19.5
95kg off road, 130kg / 286 lbs on road.

The steel frame trikes weigh 2kg / 4.4 lbs more then the aluminum frame

More consideration (Quote from Sheldon browns article )

Steel is not so sensitive to stress risers, and is more tolerant of minor damage. Also, surprisingly, steel frames have less of a problem with corrosion than many aluminum frames. Certainly, steel rusts, but only slowly. Some aluminum alloys commonly used in bicycle frames, on the other hand, are rather vulnerable to so-called “grain-boundary corrosion,” which can work its way quickly through the material and so, lead to failure.
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Re: E-trike Aluminum vs steel frame

Post by Buk___ » May 21 2018 2:22am

wturber wrote:
May 20 2018 4:17pm
I wouldn't worry about stressing the frame over time issue one bit. I'd trust that the makers have done the appropriate engineering to make that point moot. Many folks seem to get fixated on the fact that there is no fatigue limit for aluminum while not giving appropriate consideration to these two things.

1) Engineers who design aluminum bike frames are well aware of fatigue limit of aluminum and take it into account when making their designs.
2) If stressed beyond a certain point, steel frames also have a fatigue limit. They only escape the fatigue limit issue if they are never stressed beyond that point.
Your faith in distance strangers is touching.

Would you agree that Airbus SE are probably fairly competent and diligent engineers; working in a highly regulated industry and subject to intensely regulated and highly specified design and testing requirements?

If so, read this(pdf)

When those designing and maintaining structures for use in one of the most thorough tested and scrutinized industries on earth can have failures; what guarantee of a mom&pop manufacturer getting it right every time?

Its not just about taking it into account; sourcing good quality materials; storing it correctly; cutting it correctly; welding it correctly; destressing it correctly; suface finishing it correctly; et.al.

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Re: E-trike Aluminum vs steel frame

Post by wturber » May 21 2018 3:51am

eCue wrote:
May 21 2018 1:12am

More consideration (Quote from Sheldon browns article )

Steel is not so sensitive to stress risers, and is more tolerant of minor damage. Also, surprisingly, steel frames have less of a problem with corrosion than many aluminum frames. Certainly, steel rusts, but only slowly. Some aluminum alloys commonly used in bicycle frames, on the other hand, are rather vulnerable to so-called “grain-boundary corrosion,” which can work its way quickly through the material and so, lead to failure.
And that's kinda my point. The issue is far more complex than "aluminum or steel" due to material fatigue limits. BTW, I didn't find the on/off road specs for the steel frames when I looked on the manufacturer's site. And the manufacturer's site mentions hi carbon steel, not CroMo steel. CroMo steel would be more corrosion resistant than hi carbon steel. I think it is a fair bet that when the Sheldon Brown article mentioned "steel" they were not referring to hi carbon steel but the more exotic and expensive CroMoly steels commonly used on lightweight steel framed bikes. I didn't find any info on the aluminum alloy being used by KMX. But I'm frankly not sure that any of this really matters if the frames are painted and otherwise treated appropriately.

When it comes down to it, I think the OP might be better off sending his question the the people making these trikes who have specific knowledge about how they are engineered. Tell them what he intends to do. Tell them he is going to buy one of their trikes - it is just a question of which one. And let them say which one is likely the best overall choice ... and why they think so.
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Re: E-trike Aluminum vs steel frame

Post by eCue » May 21 2018 10:03am

Was surprised with the frame material testing results but is good news for the carbon and aluminum frame owners.
The riders / members of the trike forums would be a good source for frame pros and cons. Long distance riders may choose the steel frames for its comfort and easier repair whereas others may be interested in as light as a trike as possible.

The pages I read called the steel Cromo in one high carbon in the other.
The steel was likely too flexible for the boom so its aluminum
The steel back half probably ride smooth with the aluminum boom to keep the pedaling sturdy flex free with good torque

A quick Video on frame materials

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Re: E-trike Aluminum vs steel frame

Post by eCue » May 21 2018 10:38am

A deeper look

Last edited by eCue on May 21 2018 10:41am, edited 1 time in total.
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Re: E-trike Aluminum vs steel frame

Post by eCue » May 21 2018 10:40am

What is Chromoly and what does 4130 mean

http://indybikemechanic.blogspot.ca/201 ... -mean.html
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Re: E-trike Aluminum vs steel frame

Post by parajared » May 22 2018 3:36pm

I've hauled about 75lbs with mine if that helps...

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Re: E-trike Aluminum vs steel frame

Post by eCue » May 23 2018 10:16am

My first aluminum frame more then 25 years ago was a team edition Canondale rigid mtb with solid fork that felt like a vibrator on the hands with tiny sharp vibrations nearly shaking the hands off the bars at speed down hills.
At 30 mph it felt bad at 50 mph it was life frightening on long smooth packed gravel hills
I bought a fs RM element after one year on the Cannodale. shocks softened the aluminum ride perfectly.
The previous 5 years before this was riding Columbus tubed road frames that felt nice at speed. The steel forks "noodle" absorbing shocks

My current ebike a aluminum Quintanna Roo panamint mtb with a manitou front air shock rides nice.
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Re: E-trike Aluminum vs steel frame

Post by AF7JA » May 23 2018 1:52pm

Image

My "Heavy Solar" was stolen after my ride from Kansas to Utah. I am thinking about abasic rebuild. Fortunately the panels and charge controller were off the trike when it was stolen; so I have some of the expensive parts. For V.2 I am thinking of putting the panels on a trailer. I had a problem with them on top of the trike, it was a bit too top heavy. I will still have some sort of frame on top, if for no reason than to support a sunshade.

I am thinking of going with a KMX trike this time. First, it is cheaper. Second, I think the square tubing will be easier to attach things to. For my application I don't see much advantage to going with aluminum; however, that may be subject to change.
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Re: E-trike Aluminum vs steel frame

Post by AF7JA » May 23 2018 2:24pm

Yours was a inspiration for mine. As you saw, I went Aluminum instead of PVC, I will not say either is better, they are just different. I think you were looking for higher speeds than I was.
parajared wrote:
May 22 2018 3:36pm
I've hauled about 75lbs with mine if that helps...

Image
To clarify, in the post above I said:
For my application I don't see much advantage to going with aluminum
In that sentence I was talking about the bike frame, not the solar panel supports.

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Re: E-trike Aluminum vs steel frame

Post by parajared » May 23 2018 2:53pm

I am thinking of putting the panels on a trailer.
Putting the panels on a trailer is a perfectly sound idea.
I went Aluminum instead of PVC
Also a good idea. PVC sucked! Way too floppy.

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Re: E-trike Aluminum vs steel frame

Post by wturber » May 23 2018 3:34pm

eCue wrote:
May 23 2018 10:16am
My first aluminum frame more then 25 years ago was a team edition Canondale rigid mtb with solid fork that felt like a vibrator on the hands with tiny sharp vibrations nearly shaking the hands off the bars at speed down hills.
My first aluminum frame bike was my Trek 1400 - a road bike that I bought nearly 30 years ago. It rode fine on roads where you'd ride a road bike with 100 psi tires and felt plenty stable at over 40mph going downhill on I-17 from Sunset Point to Phoenix, Arizona. I still have and ride the bike. It was designed differently than the Canondales of the day, using smaller diameter, double butted aluminum tubes that were bonded, not welded.
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Re: E-trike Aluminum vs steel frame

Post by eCue » May 24 2018 12:09am

The Cannodale had some fat tubes with a fat front fork. The front end was so light could barely keep it on the ground pedaling up hills , was constantly popping wheelies with it.
I *think* the aluminum fork beats the rider up more then the frame tbh
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Re: E-trike Aluminum vs steel frame

Post by dogman dan » May 25 2018 6:59am

FWIW, I wasn't comparing types of one ton truck. Just using that example because in larger gas vehicles the difference in mileage by speed traveled is more dramatic. For sure, the chevy one ton I once owned was anything but aero. The Toyota would have been better, even in 1989.

You see the same thing in my 400cc scooter. Almost 75 mpg at 45 mph, 50 mpg at 80 mph.

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Re: E-trike Aluminum vs steel frame

Post by eCue » May 25 2018 3:12pm

Now I have not tested this yet maybe you guys have but its my thinking running at top rpm will give the most miles per AH. It's how I understand the ebike.ca motor calculator so have been running at top speed / rpm as much as possible. If the wind is calm its flat out both ways if not its flat out one way and 3/4 or 1/2 speed the other way. Its seems to be working well doing this , My 12AH battery drops from 54.6 to 50v after 36K.
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