Are Suspension Forks always bad for Front Motors

[stiffi]

Hello,

Somewhere along the line I got it in my head that all Front Suspensions were bad for front motors. Is this true? Or if the fork is steel is it still okay?

I am looking at this bike for a new build with a Ebike-kit 500w motor. Would it work?

http://www.dickssportinggoods.com/product/index.jsp?productId=29203336

 

[Ykick]

My experience with steel "pogo spring" forks - they're totally fine for motor axle although any real suspension operation is never gonna happen.

I recently revisited one of my old bikes with steel suspension fork and a small gear motor. It can be tight clearance for the motor to fit inside the dropouts but if it fits, it works just fine.

 

[wesnewell]

Putting a motor on the fork is not a good idea at all, and it's worse with suspension fork. Simply geomtry proves that. The fork is like a chicken breast bone, It doesn't take much to snap because of the angle of pressure a front motor puts on the fork.

 

[Drunkskunk]

The answers to your questions are No, it's not always bad, and yes, that would work if you're careful.
As for that bike, No, not a good idea. Nishiki made bad bikes 20 years ago. So bad they went out of business in 2001. Then Raleigh bought the name and continued the fine tradition of selling bottom end bikes at bottom end process. In other words, they had some low end bikes, but wanted to tap the really low end market without soiling their brands, so they have the Nishiki. The only good thing i can say about it is that It's a step too high up the quality ladder for Walmart. But it is still a BSO, not a real bike.

I'm not just hating on the bike for no reason. When you convert a normal bicycle to an Ebike, you're suddenly putting many times more power through the bike than it was ever designed to handle. Consider that a normal human in good shape puts about 100 to 150 watts while riding. While storming up a hill, they might pump out 400 watts for a few moments. lance Armstrong might be able to double that while on drugs. Now consider a low end ebike kit with a 36v battery limited to 20 amps can pump out 720 watts peak power. How fast do you think Lance could destroy a bike like that riding hard? And you have that kind of power with the twist of a wrist. Now consider that to get that power, you have to double the weight of the bike. And if you want a front motor, you're putting the power through it in a way the parts were never designed to handle at all.

And that's a low end power kit. Most people want more power and it's very easy to get. But the bike needs to be able to handle it, and a low quality bike just won't.

The doesn't mean you need to spend a fortune on a bike to make an ebike. A $50 bike may be all you need. It just needs to be something of reasonable quality and strength. A well used Trek 800, or Specialized Rockhopper for instance. Yard sales are a good source for dusty bikes that were bought, rode twice, and forgotten. Craigslist is another great source. Since you'll be stripping parts and altering the bike to convert it anyway, buying new rarely makes sense for an Ebike.

Also, if you really want a front motor in a bike that works well, skip the front shock bikes. Any fork with steel parts is going to ride worse than a normal steel non shock fork. if you want a front shock, consider a rear motor.

 

[John in CR]

Putting a motor on the fork is not a good idea at all, and it's worse with suspension fork. Simply geomtry proves that. The fork is like a chicken breast bone, It doesn't take much to snap because of the angle of pressure a front motor puts on the fork.

Apparently you never considered how much force braking can put on forks. :wink:

The main concern wrt front wheel hubbies is torque arms to bear the tremendous force the motor axle applies to the dropouts. It can easily snap fork dropouts right off. Think of the consequences of your front wheel suddenly becoming disconnected from your bike.

The other concern is a failure resulting in plug braking, and sudden unexpected strong braking on the front wheel could have disastrous results. I've backed off from my strong opinion in this regard, despite most of my controller failures during testing resulting in plug braking. It's motor dependent. With geared hubbies it's not a risk because they freewheel. With high speed motors the risk is small because the force is small. Slow wind motors are the greatest risk, because the braking force will be stronger, though that is offset by the fact that since they have high motor inductance and can't handle high current, they're far less likely to blow a controller and short the phases.

I've yet to see a torque arm you can buy that I would trust on a front motor install, but fabbing one yourself is pretty easy using fairly crude metal working tools.

John

 

[MadRhino]

IMO, a front motor is not a good idea, suspension or not. The only advantage of a front motor is ease of installation. If you are gonna spend the time to do a proper hub motor build on a suspension fork, you might as well build on the rear and have a safer bike, that rides much better, with upgrade perspective as a bonus.

 

[wesnewell]

Putting a motor on the fork is not a good idea at all, and it's worse with suspension fork. Simply geomtry proves that. The fork is like a chicken breast bone, It doesn't take much to snap because of the angle of pressure a front motor puts on the fork.

Apparently you never considered how much force braking can put on forks. :wink:

Yes I considered ti. But it's a different force than the motor acceleration. It compresses the the fork because of the weight shift to the front. A motor acceleration force is just the opposite. A front motor just deosn't make sense. If it did I'd use one, It's certainly easier to mount.

 

[dgk02]

I put a front kit on a Schwinn ClearCreek comfort bike. The problem with using more expensive bikes is that it's tough to find better bikes that don't have an aluminum fork, and that's supposed to be a problem with front wheel kits. Since a magnet held, I figured the fork was ok (but still asked here to check). And I put on a top quality torque arm. I'm only using a Q100 motor with 36 volts, so it isn't exactly a speed demon, and the only time I exceed 20mph is if I'm going downhill, and I'm not comfortable going much faster than that on any bike.

The motor doesn't weigh much, but I also wanted to distribute the weight better than a rear wheel motor, since the battery is in the back rack. And I've had issues with another bike with a heavy motor in the rear, lots of broken spokes and even the axle (very expensive in a BionX setup). I did break one spoke on this bike (in 8 months or so) and it was the rear wheel.

I'm certainly exceeding the design requirements, both in speed and duration. I've probably taken it 3000 miles already. But the acceleration of that motor is pretty puny, and I just can't see how that slight pulling is going to snap a fork or even the dropouts. I do check it at least weekly.

And they sell a lot of these kits. I would think that we'd be reading a lot about front wheel failures if they were happening.

 

[Russell]

Invariably good front suspension forks are going to be made from lightweight alloys which are not at all suitable for a front hub motor installation. I’m a big fan of small front geared hub motors used for assist and an inexpensive suspension fork with steel lowers work just fine for such an application. Presently my favorite E-bike (I have 3 right now) employs such a low cost fork. Due to high stiction it does little for comfort except to dampen the bigger hits from potholes and driveway entrances but it does have decent dropouts. I don’t even bother with a torque arm.

If you plan on using the bike off-road I would not recommend putting a big direct drive motor on the front but for a street/path bike it would be ok especially with the stock EBK 22A controller.

-R

 

[Punx0r]

IMO put the motor in the rear where it belongs.

 

[stiffi]

Are all motors interchangeable for Front and Back? Why are some sold as "Front hub" or "Rear hub"?

 

[Drunkskunk]

Rear motors have mounts for the gears, and come in the normal widths for a multi geared bicycle, which is 135mm.
Front motors don't ave any place to attach the gears, and the axle is the most common front axle width, 100mm.

 

[Paderolis]

When I attempted to install a FHM on my 2010 Trek 4300, I found the dropouts were too small for the axle so I filed them until it fit. The stock fork is a Spinner 100mm with lockout. The filing weakened the fork and when I attempted my first test run the dropouts snapped off! This wasn't even full power as one of the hall sensors in the motor was inactive. I must admit at the time I didn't know that a torque arm was recommended or that any conversion over 500W is recommended for a rear wheel conversion.
I replaced the suspension fork with a basic steel fork and the hub motor fit right in with no modification, but found out later the motor was not running on full power due to the inactive hall sensor. The motor was 48V 1000W configuration. I now have a 48v 1000W RHM installed on the same bike and love it! I just wished I had read up more and done this initially, I would have saved my front suspension fork! Now the bike has no suspension but I really dont miss it... yet!

 

[RLT]

My first build on a hundred dollar Walmart Mongoose full suspension mountain bike survived some hard miles carrying ~300 pounds of me and batteries. It was 2WD, with up to 2KW occasionally going through the front motor mounted on Mozo steel forks with home made torque arms. Obviously the 2000 watts pumped through the rear motor at the same time changed the dynamics of the situation, but I never had a worry about the forks breaking, even on dirt trails. Of course I wasn't doing jumps or doing other crazy stuff with it.

The next bike though, even with no motor on them, I didn't trust the front suspension forks at all, despite them being steel too. Even mild braking would flex them noticeably.

 

[arkmundi]

Alright, there seemed to be chorus saying a rear mount is "better". But I don't understand why. Is there some physics I don't get at work here? When I built my Heinzmann 500 watt eBike on a Gary Fisher bike, it was the option sold me and I didn't question it then and still don't. But I'm into my second build and have not yet made a purchase of motor.

 

[dgk02]

Bikes are designed to have the power from the rear, and the front wheel is meant to be pushed by that power and to steer. Just look at all the metal connected to the rear wheel, and compare that to the front. But that's not saying that a relatively small amount of power pulling the front wheel is going to rip the front of the bike off. And then there is the issue of whether a shock is more likely to break than the plain fork.

I'm not aware of any studies of what happens when force is applied to the front wheel; all we can go by are the reports from the people who are actually doing it. I don't see many reports of broken forks, shocks, or dropouts.

For me, the battering that the front wheel takes is mostly from riding on NYC streets. Of course, the front is designed to take punishment in that direction.

 

[Ykick]

"better" is a relative thing. But I can assure that people won't really understand until they live with both for a while. Rear motors are nice when you want/need to pop the front wheel up over a curb or something. It's also handy if/when you might want to "walk" your bike through doorways with it up on the rear wheel. In many ways it simply feels "better" and more natural than a bike with heavy front wheel.

Power application is also more like a front wheel drive car - torque steer type stuff. And more likely to fornt wheel spin when you harness significant power.

All that said, there's legitimate reasons for front motors too. Not messing with gears and generally less daunting installation. Big heavy battery on rear rack I'll tend to accept a front motor wheel when I can't stash the battery in the triangle or middle of frame. Wheel dishing is another bitch with rear motors - couple that with HUGE weight, rear motors begin to become maintenance liabilities.

Honestly, the BB drives may be the future of all this stuff? I haven't had the pleasure yet but I plan to ask Santa for a Bafang this year...

Bottom line is you're not going to go wrong with ANY eBike. Accept the fact that it takes some time, trial & error to understand what the different "types" can do. All of us wound up with more than one anyway.

 

[arkmundi]

"better" is a relative thing.... All that said, there's legitimate reasons for front motors too. Not messing with gears and generally less daunting installation. Big heavy battery on rear rack I'll tend to accept a front motor wheel when I can't stash the battery in the triangle or middle of frame. Wheel dishing is another bitch with rear motors - couple that with HUGE weight, rear motors begin to become maintenance liabilities.

I can say for a fact that its the rear wheel where all my headaches lie, because of the weight. I'm a heavy dude riding a heavy bike, what with my 20ah 36V battery load. I've gone through several tires, tubes and rims, which tend to get destroyed over time. The idea of distributing the weight to the front wheel in my mind seems like a good idea. And I'm still rolling with the original wheel build done for me fully laced into an Alex rim. And no sign of any damage to the fork or drop-outs yet.

 

[Avitt]

Data point of one, here...

I run a MAC10 with 500-1500W of power on the front wheel, with no concerns.

But there are a few caveats: I've replaced my aluminum fork with a high quality Tange steel fork. I use 2 torque arms. And probably most importantly, I don't use a throttle - it's PAS only. What this means is that the bike is always in motion when the power comes on. The motor is never pulling at full power from a dead stop, so the forces on the fork and head tube are significantly reduced.

The PAS setup also means I don't have any unfortunate front wheel drive surprises, since there's no power when I'm not pedaling.

 

[arkmundi]

When I did the installation of the Heinzmann 500 watt motor on my front fork, I confess I had some concerns. First, it was too tight a fit and I ground down the insides of my fork to squeeze it in. So what was that going to do to weaken the fork? Then I also thought the motor might pull out of the drop-outs. But it came with good nuts and I tightened them down well. So neither of those concerns has materialized yet. I'm still good with a front hub motor mount.

 

[dogman dan]

Opinions vary. I have run 8000 miles with zero problems on 1000w front motors with suspension forks. Some were cheap steel, some cheap alloy, and some medium cost alloy.

With major modifications to the fork, I've run 4000 w on a solid steel front fork. That was fun, but tricky if you got on the power in a corner.

But it's no coincidence I have no ebikes assembled and running today using a front motor. For many things, rear works best. One of those things is having the front shock actually work.

I found the forward pull of the motor on the cheaper alloy forks would jam them. So when a pothole was seen coming, you had to let off the throttle, then the shock would absorb the bump.

Really cheap steel forks would always work, but always work crappy. The best they can do. When the motor pulls on them, the fork is so loose fitted that the fork would tilt forward an amazing amount. But they way they are made, this will NEVER cause them to break. Not the cheap steel.

Any fork, suspension, non suspension, alloy or steel could snap at the stem where the steer tube meets the fork crown. But I never heard of it happening much. Crashes have been the reason for most of this kind of failure I have heard of. Not a motor just pulling. Disk brakes do load this part of the fork much more than rim brakes. A good suspension fork can handle it.


Snapping the dropouts of alloy forks is very common. You have to use two very good torque arms and c washers. The slightest flaw in the install can break the dropout like it's made of toasted bread.


SO WHY USE A FRONT MOTOR EVER?

I ran that 8000 miles because the bikes I was using had a Y frame. No place to carry the battery but a rear rack. So a front motor balanced the bike and resulted in much improved handling, and the ability to carry more cargo in back. It was a daily commuter, so some days I rode home with a gallon of milk, and a gallon of wine. Had I used a rear motor, I'd have had to carry that cargo in back pack. Not fun if it's 105 F out, to use a backpack.

The other reasons to go front are even more obvious. You might have a bike with no brakes at all if you remove the original rear wheel. Or you might want to keep a really nice internal gear hub. You could have a kooky shaft drive bike, or it could be a delta trike, that could only accept a front hub.

But if it's a normal bike, and you haven't bought the motor yet, GET A REAR.

 

[Punx0r]

I guess the answer is that for a low-power motor (250W), it's less of a performance/safety compromise fitting to the front wheel, but you'd also be much better off with a crank drive at that power level...

With high-powered motors, well, I think there's reason no one makes a front-wheel-drive motorcycle...

 

[MadRhino]

...
With high-powered motors, well, I think there's reason no one makes a front-wheel-drive motorcycle...

Well they did, but it was not a success. On a car FWD makes some sense because one can learn and control front slipping. On 2 wheels there are very few 6th sense gifted riders who can control a front wash, and most who tried to learn ended up in a high side crash.

 

[motomech]

...
With high-powered motors, well, I think there's reason no one makes a front-wheel-drive motorcycle...

Well they did, but it was not a success. On a car FWD makes some sense because one can learn and control front slipping. On 2 wheels there are very few 6th sense gifted riders who can control a front wash, and most who tried to learn ended up in a high side crash.

Having road raced motorcycles back in the '90's, crashing is something I know a bit about and loosing the frt. tire results in a face plant on the low-side. It happens so fast, there is no time for the tire to try a hook-up again, which is what happens on a high-side crash.
Fortunately, frt. wheel washouts were rare and much of the time, when the rear let's go, it can be saved.
So far in this thread, we have learned that putting a large DD motor of substantial power on a $200 bike with cappy steel forks is a bad idea, and somehow, it seems that some can draw the conclusion, that all frt motor installations are dangerous and should be avoided.
The fact is, a small low power motor works very well on the frt., with little or no adverse handling effects(some would argue, when traction is limited, it's an advantage).
Quality alloy forks, such that are found on mid-range mountain bikes for the last 15 years will easily take a > 750 peak Watt motor.
Care in installation, a torque arm and some Loctite is all that is needed.

Note; Pro road racers can slide the frt. tire at will to shorten the radius of the turn. This was pioneered by the great Freddy Spencer, he was the first to slide both tires entering a turn. The only time I could ever do it and not crash was on banked tracks. Riding a Honda RS125 GP bike on the steep banked Adams track at Riverside was great fun.
I have body problems today from frt. end washouts and what I call the "water-sking"syndrome. ï can save it, I can save it"and you don't let go-result-dis-located shoulder.

 

[wineboyrider]

I used a front hub motor for about a year on my Walmart cruiser bike and had no issues until I started upping the battery voltage and thus the speed and power into the front. It would have worked flawlessly except I was too lazy to tighten the torque arm on the front one day while it was raining and I face planted on asphalt going 30 mph ! LOL. Was a blast.