Suitable Suspension Forks for 500-1000W conversion kit

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solbike   10 mW

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Suitable Suspension Forks for 500-1000W conversion kit

Post by solbike » Jan 19 2012 9:20pm

Does anyone know of a well known brand of suspension forks (preferably easily available in Australia) that is suitable for conversion with the typical axle and wheel nut size present on most of the direct drive motors (500W - 1000W)?
I do quite a few installations with the mini-motors (180-250W) on suspension forks because they nearly always slot into the moulded drop-outs due to the smaller axle width, washers and axle nuts but the larger powered motors do not do this on most modern day suspension forks. RST used to produce a steel variety on some of the older TREKS but I'm not able to get these anymore.
It's a pity SURLY don't do a good suspension fork for this purpose, any suggestions would be appreciated.

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by full-throttle » Jan 20 2012 2:00am

Matt,

1) Motors of this power level shouldn't be used on the front
2) No suspension is better than cheap suspension, especially if you're going to strap a 500-1000W DD motor onto it

Instead of looking for a suitable suspension fork I'd suggest you spend your effort on finding a suitable rear wheel motor

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by dogman dan » Jan 20 2012 7:48am

Hogwash. All you need to do is a proper intall, using two good fitting torque arms and c washers. I recomend the ones Justin designed, that you get at Ebikes ca. The forks will have to be filed deeper to use a 14 mm axle motor such as a 9c.


But it is true that many many many forks will not work right once the wheel is pulling the tubes out of alignment with 800w or so. They lock up when the motor pulls. All you can do is start buying forks and trying them. Likely you will be getting into pretty expensive forks before you find the type that work well. Not the $100 kind. If you can stand em, the $20 pinched tube forks can work, but 40 mm travel that sags to an effective 20 mm is hardly worth it. The cheap ones work because they are so sloppy they can't lock up.

I don't have a brand name to suggest. I do know my bike doesn't work well with RST Capa forks on it. So when I see a big bump coming, I have to get off the throttle so the forks work in the pothole. I need some better ones, but I keep putting my good forks on the dirt bike. :roll:

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by wesnewell » Jan 20 2012 10:58am

No, you should never ever put a hub motor on suspension forks. I don't even like the idea of putting them on non suspension forks. The forward/backward torque will damage all forks. On standard forks, the motion will damage the stem. On suspension forks, it damages both the suspension tubes and the stem. I'm using a front hub on my trike only because that's the only place for a hub motor, but I would never use a front hub motor when a rear one could be used. Just think about it. Would you grab your front wheel and start forcing it back and forth with a couple hundred pounds of force? Not unless your trying to remove the stem I hope. Conclusion. There are no suitable forks of any kind for a hub motor, and certainly no suitable suspension forks.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by Enpro » Jan 20 2012 12:00pm

You might want to look for something like this.
Image

It was my old norco street bike and i'm telling you there is a lot more than a 1000w hubmotor needed to break this fork.
Its an all steel fork though it has aluminum sized tubing.
Also look for a DH grade headset.

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by dogman dan » Jan 20 2012 12:21pm

Yeah yeah, all that force on the stem. Ever looked down when braking hard with disk brakes.

I don't deny that a 20 buck fork will wobble like mad. But don't try to convince me a decent DH fork is too weak. Too expensive sure, but not too weak.

You still have to get it right, and not crack the dropouts just tightening a nut on the wrong size washer. And double torque arms, good ones, not something cheeze whiz. It's not for a noobs first bike.

I've got somewhere around 8000 miles on front hubs with suspension forks. On a rigid fork, I've hit 49 mph, raced it, crashed it, the only problem was trying to corner the thing, not the 3000+ watts I was putting on the fork.

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by solbike » Jan 21 2012 9:33am

Hmm, still no super suggestions. I'm quite happy to install up to about 750W on the front as long as torque bars are put on and good chromo forks. I've not had a problem with running my bike with a 750/1000W kit but I'd like to get a good supplier of forks for even the 350W direct drive motors that have the larger axles and hubs. The Norco ones look good but alas no suspension. Will have to keep looking but any suggestions are welcome.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by Kingfish » Jan 21 2012 1:45pm

Image

Come on guys! Show some positive thinking & initiative :wink:

This is a Marzocchi 44 RLO Fork that I slightly modified to accept a typical M14 axle with 10mm flats. The stock fork accepts 9-9.5mm diameter axles (typical and common) so you're in for a bit of light-duty filing. The easiest method without going whole hog is to first mark the sides with Bluing-Ink. If you don't have that, a nice bright red permanent marker will do. Lightly file until the color is removed. Reapply, test-fit and look for the high points of wear, then gently file again: Rinse and repeat.

If you get crazy with the file (or have someone else do it that doesn't have a clue) your fork will fail as happened to me on my previous ebike:

Image
Story here.

Assembly required that I place one large thin washer on the inside next to the motor to protect the metal interfaces. The axle has a very low shoulder where the flats terminate, and eventually this will dig into the strut, so placing a large thin washer on the inside (both sides) spreads the load out and inhibits maring. This will create a very tight fit, however it can be accomplished with care.

Next, I used Lawyers' Lips as the next washer exterior of the strut: It's thick, it fits nicely into the well of the mount, and can be installed/removed with without huge difficulty. The fit will be tight and I suggest applying a bit of lithium grease beforehand. Then comes the torquearm, and there should be room for another washer before the nut. Personally, I mounted a torquearm on both sides.

Common torque arms are fine in most cases if the power output is reasonably low and you're not into racing. I crafted my own cos I wanted to test a theory with about 2 hp programmed to each wheel. I took this ebike on a long journey: The front suspension at the mounting point was never an issue. After 1500 miles, my shock displayed slightly unusual play (related to the huge load), but it wasn't enough to stop me or warrant replacement and I continued on home. I've put over 3400 miles on the shock and it's still going strong.

Just invest in a quality DH shock and you'll be fine. Heck - I ran with the 1st model RockShox on my previous ebike for about a year before it failed, and that was because I couldn't find parts to R&R.

Bottom line: Have faith and apply yourself! Experiment. Be conservative: Run with two torquearms :)

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by solbike » Jan 21 2012 9:01pm

I'm aware that there are quite a few modifications that can be done to existing suspension forks to secure the front hub motors a lot better but I'm just looking for a production line set that needs no filing at all, is good quality, chromo (preferably) and the motor just slots straight in with room to add a torque bar. I'd like to be able to recommend a set to customers who want to maintain the front suspension or revert to it and be confident of their quality and no need to modify. RST had a set that came out years ago but I can no longer get them in bike shops so was wondering if there is another one around that someone may know of that is widely available. The picture here is from my girlfriend's bike that has the forks I was talking about, they had a nice steel protrusion at the end of the fork that made them quite suitable for kit installs. This set has done about 20-30km a day for 3-4 years. The forks are still fine (though a bit leaky) and the only replacements have been an upgraded tube battery and a bunch of brake pads. Australia has a cruddy 200W motor limit law which is sometimes a blessing in disguise. The mini-motors slot into nearly any modern fork without modifications and battery failures are much lower when using this motor - also range is fantastic. Still looking for suggestions...

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by solbike » Jan 21 2012 9:39pm

I see suntour now have an "ebike" set of suspension forks. Anyone have any opinion on these ones?
http://www.srsuntour-cycling.com/dstore ... 26%27.html

Will have to get a sample and see how adequate.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by amberwolf » Jan 22 2012 2:51am

"alloy monocoque" lowers according to the site. means they are aluminum so can/will break dropouts.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by neptronix » Jan 22 2012 3:14am

Those are probably designed for weak power, still; not the hardcore folks here at ES :)

After breaking my suspension fork in half during a 3mph crash, and watching it flex as i hit the brakes when i had 180mm avid disc, there is no way in hell i would go with a front motor. Not for any serious kind of power use.

A suspension fork that is particularly overbuilt might survive with the right torque arms, etc. But most are designed for the lightest weight and most travel possible - 2 things that go against stiffness of a fork.

Do consider rear conversions. There are many benefits. A broken rear mount will not send you over the handlebars, it won't have traction issues, and it won't give you a funny steering feel if you have a particularly heavy front hub motor. Most hub motors also have really poor disc brake side cover machining, so that's a downside if you want to run disc brakes in the front - where they are most critical since the front brakes take more stopping power than the rear, just like a car.
Last edited by neptronix on Jan 22 2012 3:18am, edited 1 time in total.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by neptronix » Jan 22 2012 3:18am

By the way, surly forks are stunning. I wish they'd make a sus. fork as well, but it would probably weight 10 pounds ;)

There are stronger suspension forks out there, but you will want to experiment and see how it goes. Aluminum lowers are probably what you want to stray from, since it likes to snap suddenly rather than give a warning sign like steel. I'm not sure how magnesium reacts.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by Diamondback » Jan 22 2012 7:55am

i have an ezee front geared hub motor on my bike.

it has just on 1000W ( 1100W if you let it run to the full 20A limit of the controller)
i have limited mine to 15A (780W) via the CA, and it's fitted to a suntour suspension fork.
i have twin torque arms, and the proper c washers installed.

i have over 1800km on it now, and no signs of anything going wrong so far.
the hub was a perfect fit, no filing needed.

and it has a disc brake too.

i usually pedal up to a few km/h before i open the throttle, just to limit the biggest lump of torque
on the forks.

im not 100% sure what the model number of the fork is, but it was standard fitment to a 2010
Apollo trace urban hybrid bike.it has 80mm travel (i think, from memory)

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by dogman dan » Jan 22 2012 8:42am

Currently my primary commuter bike is set up with a cheap RST Capa alloy fork. Like I said, it sucks, but the primary reason for having it is I can get off the throttle when a big bump is seen, then it functions normally and I can ride over a speed bump or whatever without breaking spokes and bending rims. So it rides more like a rigid fork under power, but anytime I roll back the throttle, I get 80mm for the big pothole.

But no affordable alloy suspension fork is going to be very good. Previously I had a better fork on th bike, but it was fairly worn when I got the bike, and it did not work well at all after a year with the motor on it.

Your only solution for a fork is going to be a very expensive one, overbuilt for real trail riding. Nothing in steel will be that good. So the question is, can you get what you need from a piece o crap steel lowers suspension fork, like a Zoom? It may be good enough for your needs if it's just for street. If you plan on trail riding, you are barking up the wrong tree, unless the front motor is going on a bike that already has a rear motor.

If you dig deep enough, threre is an ancient thread about a guy who built new steel dropouts for his suspension fork. The dropouts clamped to the fork lowers using a tube shaped sleeve. So that is perhaps the "best" front suspension fork option. Still gonna bind the forks on cheaper forks though. I personally don't see the point since a good well fitted set of torque arms is plenty for 1000w.

When I put 3000+ watts on the front forks of a racing bike, I had to weld tabs to the forks to support the torque arms better. So at some point, even good torque arms can get ripped off the fork if they are secured by hose clamps. But two good torque arms are plenty good for 48v 20 amps, which puts out 1200w at the peak spike.

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by gurshark » Feb 11 2013 1:16pm

dogman wrote:Currently my primary commuter bike is set up with a cheap RST Capa alloy fork. Like I said, it sucks, but the primary reason for having it is I can get off the throttle when a big bump is seen, then it functions normally and I can ride over a speed bump or whatever without breaking spokes and bending rims. So it rides more like a rigid fork under power, but anytime I roll back the throttle, I get 80mm for the big pothole.

But no affordable alloy suspension fork is going to be very good. Previously I had a better fork on th bike, but it was fairly worn when I got the bike, and it did not work well at all after a year with the motor on it.

Your only solution for a fork is going to be a very expensive one, overbuilt for real trail riding. Nothing in steel will be that good. So the question is, can you get what you need from a piece o crap steel lowers suspension fork, like a Zoom? It may be good enough for your needs if it's just for street. If you plan on trail riding, you are barking up the wrong tree, unless the front motor is going on a bike that already has a rear motor.

If you dig deep enough, threre is an ancient thread about a guy who built new steel dropouts for his suspension fork. The dropouts clamped to the fork lowers using a tube shaped sleeve. So that is perhaps the "best" front suspension fork option. Still gonna bind the forks on cheaper forks though. I personally don't see the point since a good well fitted set of torque arms is plenty for 1000w.

When I put 3000+ watts on the front forks of a racing bike, I had to weld tabs to the forks to support the torque arms better. So at some point, even good torque arms can get ripped off the fork if they are secured by hose clamps. But two good torque arms are plenty good for 48v 20 amps, which puts out 1200w at the peak spike.
I just got an RST Capa with a 1" steerer for my old Bridgestone MB5 ebike, and ordered a BB7 with 200mm rotor. After ordering the 200mm rotor, I checked the RST website, and they say 160mm rotor max. What risk am I running if I use a 200mm rotor? Fork failure? Wheel coming out of dropout? Can I stick with the 200mm, will 180mm cut it, or should I just go with 160mm to be safe?

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by dogman dan » Feb 11 2013 6:37pm

Since its a junk fork, I'd say stick with the 160. It may be strong enough for more, but I can't see any reason to think so.

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by Samd » Feb 12 2013 9:14pm

There are still some cheap STEEL clunker forks with 50mm travel about in Australia that have carbon steel dropouts - therefore they can handle the initial jerk/torque that comes >750W hubs.

But as for modern magnesium/alloy dropouts on forks I'll concur with full-throttle, they are brittle like a biscuit when subjected to sudden changes in torque and forward/back cycles.

Unless you want take the extra efforts of Kingfish - when it comes to dual drive with lots of power on a proper frame setup he is the man. But I assume solar bike want a simple commercial product for customers, without selling them large torque arm solutions and a supplementary dental plan.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by miro13car » Feb 15 2013 12:34am

it only imagination tells you what happens to suspention fork holding 1000W motor during acceleration , such force will for certain stress fork terribly.
Even like dogman wrote can lock fork.
Such force of course depends on control method used to control motor, but if controller allow "to jerk" front wheel you are asking for trouble

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by Kingfish » Feb 15 2013 11:27am

Both of my wheels pull 2 hp each at WOT for speed-testing. On cross-country that value is closer to about 1.72 hp/1.3kW each. In the summer of 2011 – On the Road, I had about 1500, maybe 1700 miles on the Marzocchi 44 RLO fork when I pulled into San Francisco. Concerned that the fork might be failing from too much weight and abuse I took it to a local bike shop: There the guy tried to tell me it was bad and I should spent $1500 to replace it. I considered it – but something he said had me check one other factor, decided it was fine as is – and instead rode that bike back to Washington for a total of 2515 miles. Since then I’ve put another 1200+ aggressive urban 2WD miles on that fork. Not been a problem, and no need to adjust it.

The trick – as previously stated, is to have quality torque arms. In my case I expect the axle will fail before the shock. I also would like to think the employment of Cane Creek 110-series Headset has had a good effect keeping things snug tight and wear to a minimum. Not long ago during the 2012 summer rework I inspected the frame from tip-to-tail looking for stress cracks and any other signs of fatigue – but found nothing other than normal wear from debris. Both front and rear shocks are holding pressure and there are no obvious signs of leakage. That said, I rarely take my bike off-road or jump curbs. Still – it sees a lot of activity riding in the margins of the road.

To conclude, invest in quality equipment to reduce the risk of critical failure to the lowest possible level. I am constantly wary of loose-fitting components; most of the focus has been on the rear suspension – and except for squeaky brakes, I am very grateful the fork has not been a part of that, knock wood. :)

Safe travels, KF
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by Aktung » Jan 17 2022 6:09am

I use a 1000w front wheel drive on my Giant Sedona LX. I use this bike 7 days per week on average 20km per day. I've done about 25,000km on the bike. The forks on this bike are fortunately strong without modification. Its all about the thick strong drop outs. This is the critical part in my opinion.
My previous Sedona had a different fork with smaller drop outs. I had a very scary experience. I descended a large hill reaching speeds of about 60km/phr. I came to a gentle stop at an intersection. I got off to walk the bike (which I never do) the front wheel fell off. I couldn't work out what had happened, I tried several times to put the wheel back into the drop outs but the wheel would not stay. I then realised the drop outs had snapped off. I dodged a bullet.

My current bike is brilliant. I stumbled on this thread in search of stronger forks. Although my current forks have been great I still am haunted and would love steel forks with very strong drop outs.

I use 203mm disc with 4 piton callipers. The bike is brilliant, I love it.

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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by MadRhino » Jan 17 2022 10:48am

Aktung wrote:
Jan 17 2022 6:09am
I use a 1000w front wheel drive on my Giant Sedona LX. I use this bike 7 days per week on average 20km per day. I've done about 25,000km on the bike. The forks on this bike are fortunately strong without modification. Its all about the thick strong drop outs. This is the critical part in my opinion.
My previous Sedona had a different fork with smaller drop outs. I had a very scary experience. I descended a large hill reaching speeds of about 60km/phr. I came to a gentle stop at an intersection. I got off to walk the bike (which I never do) the front wheel fell off. I couldn't work out what had happened, I tried several times to put the wheel back into the drop outs but the wheel would not stay. I then realised the drop outs had snapped off. I dodged a bullet.

My current bike is brilliant. I stumbled on this thread in search of stronger forks. Although my current forks have been great I still am haunted and would love steel forks with very strong drop outs.

I use 203mm disc with 4 piton callipers. The bike is brilliant, I love it.

Tony
Good that you now have a reliable fork. Very few are. Don’t replace it unless you find the same type in a better condition. Still, ebikes are much better rides with a rear or mid motor. That is because like horses, a good bike need to be light in hand and powerful on heels.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by Chalo » Jan 17 2022 11:49am

Aktung wrote:
Jan 17 2022 6:09am
Although my current forks have been great I still am haunted and would love steel forks with very strong drop outs.
Steel suspension forks? No you don't. Steel when used in suspension forks is only a sign of cut corners and shoddy quality.

Are you using a front hub motor with suspension forks? If so, don't do that. It's asking for bad trouble. It doesn't matter how thick the dropouts look. They're made of cast aluminum or magnesium and they're intolerant of being pried open the way your motor is doing.
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Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by dogman dan » Jan 18 2022 5:46am

Broken dropouts are usually from not using proper c washers and really good torque arms on a front hub install on a suspension fork.

My best advice, is replace the bike. Get one that is more suitable for a rear motor on it, rather that prematurely wear out or break expensive front forks. My eventual solution was going to longer bikes, which don't need suspension for paved riding, and carry the batteries better. I was lengthening steel frames 6-9 inches. Cheaper than newer bikes, and more practical for commuting than a converted MTB.

You might be stuck with front hub on that bike, like if its got an IGH in back you want to keep. If so, you just got to do a decent preflight on the thing each day. Let a nut get loose, it will break your dropout.

Well, I never found a great suspension fork for use with a front hub motor. But for various reasons, I did nearly all of my commuting to work for 4 years on a front hub bike, limiting it to 1200 peak watts. 22 amps controller, 9 continent style 500w direct drive motor. Mostly I wanted to keep my 9 speed rear gear cluster, and back then rear hubs were hard to find affordably.

I never broke a dropout. Half of this was using pogo stick, piece of crap steel forks that come on a bike shaped object. I just needed some help with the rough pavement. In the deserts in the USA, huge heat cracks hump up the pavement every 20 feet or so, similar to riding over a 2x4 in the road every 20 feet.

Later on, I put a few different aluminum forks on the bikes after upgrading the bike frame. None did well. The pulling force on the fork tended to lock up the fork, so I had effectively a rigid fork over the heat cracks. If I saw an actual pothole coming I had to get off the throttle so the fork would work through the pothole or curb hop.

I was just kind of stuck with this, because of the bike frames I could afford at that time. I was bike commuting because my car was dying, and too deep in debt to fix or replace it.

Put that front hub on a cruiser or something with a cromoly front fork. Get a rear hub for your current bike. A motor will be cheaper in the long run, than ruining expensive forks.

HillCruiser   100 mW

100 mW
Posts: 46
Joined: Jan 19 2022 8:56pm

Re: Suitable Suspension Forks for 500-1000W conversion kit

Post by HillCruiser » Jan 30 2022 10:15am

Dogman wrote:
"My eventual solution was going to longer bikes, which don't need suspension for paved riding, and carry the batteries better."

This is really a gem hidden in a long post.

I bought an old Electra Cruiser 7 for $100 when I was overwintering in Fl two winters ago.

It's a longer bike without any suspension but rode like an '63 Cadillac (sadly it needed about the same amount of power from the pedals), so I hauled it back to Canada and put a 1000w rear wheel kit on it.

I love that bike and I gotta say that longer bikes are best!
(Not to mention the beautiful curves on the beach cruiser tubing but I digress...)

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