Motocross fork or DH fork for heavy rider w/heavy bike?

macribs

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Jul 22, 2014
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I took the advices I got to heart and used a good quality DH fork rather then a motoX fork to keep the weight down and to avoid using m/c hubs and spokes in the front. I ended with FOx 40 RC2. Saved around 7 kilo on the fork alone. Then add in m/c spokes, brakes and hubs and there should be more then 10 kilos saved by using DH fork. And a lot of that extra weight from m/c parts will be unsprung to make it even worse.

Others thinking the same as I did and want to look for money savings deal or go real heavy duty by using m/c forks - rethink. One m/c component easily leave you in the need of choosing more m/c parts and you will suffer a big weight penalty. I have spoken to several members that did go for motoX or pitbike forks and no one is truly happy with their choice. And they would not go down that route one more time.



Edited:

I am currently looking for a motocross fork for use with the Vector frame. That way I can use motocross hub and wheel to in the front end. I know it will increase the weight but I see this option as the only durable and problem free route for a 300 lbs rider.

I know motocross forks on e-bikes have been done before. BlackArrow did at build. And a few others I think.
e-bike with CR 80 fork.
Looks good that bike - and the fork does not appear to be out of proportion.

So if you have any idea on what is needed to fit a motocross or motard fork to a bicycle pls let me know.

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Why the heck would you use 11g spokes on a bicycle? Are you also planning to fill your shocks with concrete, and replace the springs on your seat with solid blocks of steel?

That's a motorcycle spoke. look at motorcycle hubs and rims. But if you're looking to get things right the first time, then you're waaaaay off course already.

Lets start with the basics here. A spoke is a torsional spring. It's job is to be springy, and help distribute the load of the bike all the way around the rim. Spokes are superior to mag wheels because they they can share the load. when one spoke stretches, the spokes beside it also stretch, sharing the force of the impact or load. when you hit a rock in the road, all 36 spokes, top and bottom take the force of that impact, distributing the force all around the wheel and hub.
If the spoke is too thick, it can't stretch. it can't share the load, and puts all the force on one localized area. either the hub or the rim has to take all that force around the spoke hole. And it will fail. It Either cracks the hub, tears out of the rim, or crack's it's own head off.
 
For the same reason they use bigger spokes on motorcycle wheels, car wheels, etc. The thicker they are, the stronger they are. Spokes don't stretch. Not even the really thin ones. At least not to any degree in a bike rim. The rim can flex. The tire can flex. but the spokes don't and shouldn't. That's just a myth. They provide tension between the hub and rim. They may appear to stretch if they aren't tensioned properly, but they don't stretch. Most people can't even stretch a plastic straw, much less a SS spoke. I don't know how or where this myth got started, but it's BS. Using thinner spokes will not make a stronger wheel. That's just nore BS.
 
Drunkskunk said:
Why the heck would you use 11g spokes on a bicycle?

That's a motorcycle spoke. look at motorcycle hubs and rims. But if you're looking to get things right the first time, then you're waaaaay off course already.


Well I will be using a moto cross front rim - would it not make same to also use moto cross spokes?
I might be wrong as it is my first build but what I do know is that for 100lbs e-bike with a 300 lbs rider any double rim bicycle rim will crack, and fail sooner rather then later. And because of that I need to figure out a way to use a motoX rim with a DH fork.

Are you saying that I should use bicycle spokes and hub on a motoX rim?
 
Avitt said:
There are bicycle rims which are targeted for tandem use (example is the Velocity Chukker). Those should work fine for you heavy guys.


I tried to check but it seems that the prices are extreme for heavy duty tandem wheels.
Seems for the price of just a front wheel with a hub I can get a used motocross wheel, calipers, rotors and fork. :D

The price landed on 550 $ laced and trued. Too expensive I think.
 
If you go all motorcycle parts, it will work, but adapting the axle is going to be trouble. The first problem is the axles that most of them use. Some are 12, some 15, some 22, some are different sizes depending on which side. The second is the width. You need 100mm for that fork, and most of those hubs are wider. Adapters could be made, but with a heavy wheel like that, best to say F*-it and mount a CR85 or similar fork as well.
 
I read about one that used pit bike forks - thing is was that green cruiser bike with midmonster motor.
Has anyone tested those pitbike forks and how well they work for e-bikes?

They are cheap, and rotors and calipers are cheap too. But I have no idea of they can handle a 300 lbs rider.
 
Some pitbike forks may work. Most pitbikes are child sized and use small forks. Some are adult sized and use a bigger fork but small wheel. and then some use normal wheels. There is no Generic fork size, so no way to give an absolute answer. If you look around enough, you'll probably find something.

You might check with this guy... who's user name I can't remember, though I can remember his real name... Ask him what fork and wheel combo he used.

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Thx I will look him up, I remember his avatar but can't remember his nick :)

Edited: Found him. Willow was it.
 
I have looked for several pit bikes fork. And one of them is 83.8 cm from axle to crown. With 8" travel. Adjustable.
The fork Willow uses for his trike is a Chinese fork by the brand name Zinmoto.
I think in comparison the Dnm USD 8 is 75 cm axle to crown.

Think I should just go for this pit bike fork? I mean is it possible to swap springs if fork is too soft for my 300lbs?
 
That fork might work for you, depending on what you do with the rest of the bike. Are you drawing up plans yet?
Springs aren't universal. you can only change them if the manufacture makes some in different spring rates, or they just happen to be the same size as another that does, and if the design of the fork isn't sealed.
 
Thx. Yeah buying a fork that I can't upgrade if needed seems like an uncertain route so maybe look into motoX forks.

What about motoX forks - will they fit the vector frame? Will a motocross crown fit the Vector steering tube without machining or welding? Is there adapters or something like that that can make motocross fork work with 1.1/8" bicycle steer tube?

Head tube for 1.1/8-inch non-integrated steering tube, 130 mm in length.
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There isn't anything standardized with motorcycles. to fit a 1 1/8th head tube, you would need a steering tube with a 1 1/8th straight taper tube. but different bikes use different tubes, and not all are straight taper. you can pretty much count on making parts and welding. That's why I suggesting going to Willow, or someone else who has done it. Find out exactly what parts they used. Otherwise, you're going to have to be inventive.
 
I found this pic, I think it is the very first Phasor. Early Alfa testing. Carbon fiber frame and dirtbike fork.
How he made fork work I don't know. But looking at the pic it seems he just lowered the top clamp down the legs.
Could it be that simple?

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I forget that dude's screen name, too. But they built the frame, they could have put any head tube in it they wanted. Or it could have been one with a 1-1/8th straight taper steer tube, or they made an adapter. Ask him.

As for lowering the top clamp, that's not it. both top and bottom clamps have been lowered. the height is adjustable some on this style fork. they may have wanted a lower ride height, or different angle on the front end, or quicker steering response. Lots of reasons why people adjust the fork height.
 
wesnewell said:
The rim can flex. The tire can flex. but the spokes don't and shouldn't. That's just a myth. They provide tension between the hub and rim. They may appear to stretch if they aren't tensioned properly, but they don't stretch.

Read and understand about Young's modulus, and stop polluting this forum with your plainly idiotic misinformation. It's bad enough that you are so ignorant; please don't encourage others to adopt your ways.

Everything stretches or compresses when subjected to forces; there are no exceptions. In the case of bicycle spokes, this stretch is important to maintaining the integrity and reliability of a wheel.
 
Don't be stupid, you can't put enough force on a SS bicycle spoke to stretch it to any degree. Just not possible since the force is divided between at least 50% of all the spokes on the bike wheel. You can see flex in the rim, and possibly in the nipple and head, but you aren't going to stretch the spoke. Nor do you want it to stretch. What does happen is that the tension on the spokes in the upper part of the rotation increases as the wheel turns and tension on the lower spokes decrease. If the spokes stretched, you'd have to constantly re tension them.
 
macribs said:
Avitt said:
I tried to check but it seems that the prices are extreme for heavy duty tandem wheels.
Seems for the price of just a front wheel with a hub I can get a used motocross wheel, calipers, rotors and fork. :D

The price landed on 550 $ laced and trued. Too expensive I think.

Apples to apples, please. For the price of a new motocross wheel, calipers, rotors, and fork, you can probably buy at least a couple of nice used tandem bicycles.

The least expensive way to get a new heavy duty tandem grade disc wheel is to buy a 48 hole Alex DM24 rim for $25, 50 double butted spokes from Danscomp.com for $20, a 48 hole front disc hub for the lowest price you can find (here's one for $68), and build it up yourself using Sheldon Brown's or Jobst Brandt's instructions.

If you don't need a disc brake, you can get a good 48 spoke wheel, handbuilt, complete with tire and tube for $125.

If you have enough room for a motocross wheel in your rig, you have enough room for a 65mm fatbike rim with 2.5" or larger tire. The Origin 8 double-walled fatbike rim comes in 32 or 36 hole drilling, retails for about $60, and laces up to all kinds of cheap and readily available hubs, like this one that retails for $18.

Using motocross wheels on a bicycle makes about as much sense as using car wheels.
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(Deleted duplicate post.)
 
wesnewell said:
Don't be stupid, you can't put enough force on a SS bicycle spoke to stretch it to any degree. Just not possible since the force is divided between at least 50% of all the spokes on the bike wheel. You can see flex in the rim, and possibly in the nipple and head, but you aren't going to stretch the spoke. Nor do you want it to stretch. What does happen is that the tension on the spokes in the upper part of the rotation increases as the wheel turns and tension on the lower spokes decrease. If the spokes stretched, you'd have to constantly re tension them.

You're being oblivious again. It's spokes that DON'T stretch enough (because they are too thick) that require frequent retensioning. If they aren't elastic enough, they go slack as you roll over them and the nipple gradually unscrews. If they are thin enough and therefore elastic enough, they don't go slack and thus they stay tight.

Normal double butted spokes stretch about a millimeter under normal spoke tension. This is enough to follow normal deflections inward at the rim without slackening.

Please, do yourself and this forum a favor and read Jobst Brandt's book. You can probably find it at a public library.
 
Wow Chalo I hope that isn't your auto bike. Good for over 300lbs I guess and even JohnCR would have room for batteries and a monster motor. Only safe at a top speed of 18mph would be a problem at 10,000 watts.
Plus forget about spoke breakage. A winner.
Somebody had to much time on there hands.
 
macribs said:

That looks like a terrible mountain bike fork. What you're looking for is an old Marzocchi Monster T:

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1 1/8" straight steerer tube. 40 mm stanchions. It was a repurposed trials motorcycle fork originally, iirc.

I used to run one on my downhill bike way back when:

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Chalo said:
Apples to apples, please. For the price of a new motocross wheel, calipers, rotors, and fork, you can probably buy at least a couple of nice used tandem bicycles.


Sure but I intend to buy used moto parts. So it will be cheap.

The least expensive way to get a new heavy duty tandem grade disc wheel is to buy a 48 hole Alex DM24 rim for $25, 50 double butted spokes from Danscomp.com for $20, a 48 hole front disc hub for the lowest price you can find (here's one for $68), and build it up yourself using Sheldon Brown's or Jobst Brandt's instructions.

I will look into that. Thanks Chalo.

If you don't need a disc brake, you can get a good 48 spoke wheel, handbuilt, complete with tire and tube for $125.


Disc brake is a given for an 60 mph e-bike. Safety first.


If you have enough room for a motocross wheel in your rig, you have enough room for a 65mm fatbike rim with 2.5" or larger tire. The Origin 8 double-walled fatbike rim comes in 32 or 36 hole drilling, retails for about $60, and laces up to all kinds of cheap and readily available hubs, like this one that retails for $18.

Fatbike wheels has no place in a 60+ mph e-bike I think. I find those wheel/tires to be most of all a hype for all but the beach cruising crews. And not for riding in snow, for that they are Hopeless. :D


Using motocross wheels on a bicycle makes about as much sense as using car wheels.


Well for many that might be true but for I have fat ass and a heavy bike. I am certain the total weight will be close to 400 lbs.
I really can't see any DH rims and forks that will deal with the stress. Not to mention tires and tubes. I go this moto parts route for durability and safety.
 
Toshi said:
That looks like a terrible mountain bike fork. What you're looking for is an old Marzocchi Monster T:



1 1/8" straight steerer tube. 40 mm stanchions. It was a repurposed trials motorcycle fork originally, iirc.

I used to run one on my downhill bike way back when:


I've seen different Monster T for sale. Some with 300mm travel. That seems to be dirt bike territory. And some monster T with 200mm travel. Do you know which one of those came from a trail motorcycle? And as it seems like the Monster T was discontinued a few years ago do you think parts might be a problem? Like seals, springs etc?

A 48 spoke wheel must be able to handle a lot of weight, right? I will try to look and see if there are some 48 holes rims that will withstand abuse. The pedalac link it said nothing about width, weight of the rim or how strong it was so I think they dismissed themselves.
 
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