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

[macribs]

So I got response from BlackArrow. He thinks a dirt bike fork is wrong move, and he would not have used such fork for another build.
Well that was the cold hard truth. He had to modify alot to make cr 80 fork work and even rebuild internals of legs to make fork more rigid.

So I guess stronger springs for DH fork is what is needed.

 

[sigimem]

Go for a Pit bike fork.
http://www.ebay.com/itm/Fork-Forks-FASTACE-AS-01-XR-CRF50-50-KLX-DNM-SDG-SSR-PIT-BIKE-Marzocchi-V-FK06/200756639380?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D29381%26meid%3Dc7d409d7d5ed4455b25c4e6e89758214%26pid%3D100005%26rk%3D2%26rkt%3D6%26mehot%3Dpp%26sd%3D330954338897&rt=nc
something like this. There is one user who is using it in a bycicle.

I don´t get the whole Bike vs Moto rims+tyres thing it´s an easy choice IMO If you run over 3kw and(!) put a lot of stress on your rim (Hubmotor and offroading/ Weight and Curbs) You go for moto tyres+rims. If you want to pedal and run lower power and lower stress bike tyres+rims are a better choice

On my FS with a 9kg Hubmotor the moto tyre in the back has proven far better in terms of handling and damping when going over curbs than the bike tyre. Also it has more rolling ressistance and acceleration when pedaling is slower. I prefer the motor tyre for my 4kw Hub offroad Setup.

 

[macribs]

Edited after new info came to the thread.

 

[macribs]

Well seems this settle things. As you see in the video there are both jumps and rough terrain. Works well even for us big guys. I guess the weight issue for DH forks in fact was more of a myth then the very truth.
I got this from a big guy rider on a stealth Fighter. :

I am struggling with weight issues guys. Seems my 300lbs will set most DH forks to the test, and also will not allow for motoX wheel/hub.

I am 35 pounds lighter, than you, not a huge difference, and I find that the Marzocchis, Fox 40s, and MRP Grove forks are all more than up to the task for serious off roading. Now I know I couldn't ride the Shore with MTB stuff, but short of that, good to go.
Here is a vid of the type of riding I do, I am running the RST R1 in this vid, not now though, just trying to show that components selection can work for the bigger guys like Macribs and I.

[youtube]xbG4ZILyR_I[/youtube]

 

[macribs]

@sigimem - so what kind of spokes and hub are you using for the front wheel? In the back I assume you are using moto spokes?

So now I've decided not to have the weight penalty of a motocross fork. It seems quality forks will do just fine for me.
But I would still like to avoid pinch flats, have more secure feeling from using moto rim + tire. Back at least due to heavy hub motor. And the back rim I think I should lace with moto spokes due to hub motor + weight. What do you think, bicycle spokes or moto spokes for rear wheel?

If I do a moto rim/tire in the front as well - what bicycle hub (heavy duty hub?) and what spokes gauge do I choose?

 

[LegendLength]

So now I've decided not to have the weight penalty of a motocross fork. It seems quality forks will do just fine for me.
But I would still like to avoid pinch flats, have more secure feeling from using moto rim + tire. Back at least due to heavy hub motor. And the back rim I think I should lace with moto spokes due to hub motor + weight. What do you think, bicycle spokes or moto spokes for rear wheel?

I think it's a good choice to avoid the mx forks. Downhill forks are made for large dropoffs, especially the high end ones. I think they are a lot cheaper too compared to dirt bike forks.

For the rear wheel lacing, maybe have a look at what people have done with the cromotor builds. It is a very heavy motor compared to the more common 9C so you might be able to find some good information about people's experiences with cracks etc.. Otherwise it seems to be a bit of a hot topic (spoke size)

 

[Ch00paKabrA]

It is my opinion that you have made the right choice by just using a mountain bike fork. The real expensive forks are great and there is nothing bad to say about them. After doing my research, I settled on the Marzocchi Drop Off Triple. This is an entry level fork so if you are going to do serious off-roading, then it is not the one for you.

There are a few advantages to it though. It is damn simple to build and rebuild. It is old school oil bath and the Any Marzocchi 32mm oil seals will work so you can use Marzocchi motocross seals for about $10.00 for the pair. To help handle the excess weight of the battery, you just need to put a second spring and spacer in the left tube. Compression is adjustable with air in both Stanchions. If you want to run a dual motor set-up, there are 9mm QR drop out lowers kicking around.

Since it is old school, there are plenty of disadvantage to them as well. first off, they are have 32mm stanchions. they are oil bath. Marzocchi does not make replacement parts for them any more. The rebound adjustment is internal so it is hard to get to.

Did you look at the 19" M/C rim thread yet? there is a lot of good info in it.

 

[Drunkskunk]

And now you've come full circle. You got off on the tangent thinking you needed a massive hub to take the abuse of the massive spokes you thought you needed to fit your heavy duty rim. to do so, you'd need a massive fork capable fo fitting that hub, but also of handling the massive increase in unsprung weight. to fit that fork you might even need to modify the frame, and we never got into discussing if that light weight frame would be strong enough to support such a heavy front end.
It's a never ending spiral, and many of your threads have gone that way, but it's a fun mental exercise.
What you need, and what you think you need are at odds with each other. The question you might want to ask is what wheel would the forum recommend for your bike?




if you want to use a DH fork, (And I agree they're better for bike) you will have problems fitting a motorcycle hub, so you need a bicycle hub. that means building your wheel up with bicycle spokes.
Fitting 19" light weight MC rims with bicycle spokes is a known combo that works well. an alternative is the 48 spoke tandem wheels Chalo mentioned.

Or just go with a normal 36 spoke bicycle wheel running 14 or 15 gauge spokes like every other extreme cyclist.
Think you're going to be harder on your bike than these guys?
[youtube]vbLLqaa9ksw[/youtube]

 

[macribs]

if you want to use a DH fork, (And I agree they're better for bike) you will have problems fitting a motorcycle hub, so you need a bicycle hub. that means building your wheel up with bicycle spokes.
Fitting 19" light weight MC rims with bicycle spokes is a known combo that works well.

Or just go with a normal 36 spoke bicycle wheel running 14 or 15 gauge spokes like every other extreme cyclist.
Think you're going to be harder on your bike than these guys?

No I didn't watch that video before, I've been watching this video. And that's when I started to look for heavy duty parts.
And I figured I don't want that to be me going 60 mph. Look how the mtb tackles weight

[youtube]hLIQjgrg_b4[/youtube]

 

[macribs]

It is my opinion that you have made the right choice by just using a mountain bike fork. The real expensive forks are great and there is nothing bad to say about them. After doing my research, I settled on the Marzocchi Drop Off Triple. This is an entry level fork so if you are going to do serious off-roading, then it is not the one for you.

There are a few advantages to it though. It is damn simple to build and rebuild. It is old school oil bath and the Any Marzocchi 32mm oil seals will work so you can use Marzocchi motocross seals for about $10.00 for the pair. To help handle the excess weight of the battery, you just need to put a second spring and spacer in the left tube. Compression is adjustable with air in both Stanchions. If you want to run a dual motor set-up, there are 9mm QR drop out lowers kicking around.

Since it is old school, there are plenty of disadvantage to them as well. first off, they are have 32mm stanchions. they are oil bath. Marzocchi does not make replacement parts for them any more. The rebound adjustment is internal so it is hard to get to.

Did you look at the 19" M/C rim thread yet? there is a lot of good info in it.

Thx.
Will take a look at the 19" motorcycle rim thread. Puh. 33 pages long. Well all I got is time now a days

I will keep my eyes open for good deals on DH forks.
In the mean time I will look into what spokes and hub to use for front wheel and what to choose for rear wheel.

 

[johnrobholmes]

Here is what all they guys building 45 to 60mph bikes get from us-

regular 36h downhill hub of some sort, dmr revolver is popular for the price
13g spokes with matching nipples for a moto rim, 3 cross lacing
19" moped weight rim, I now carry the MMP front 19" that is matched for front MTB hubs and lighter than a motorcycle rim
19x 2.25 to 3" front tires depending on needs. I personally like the shinko 244 and 241, but that thread just linked has lots of info too.



I've built and helped facilitate hundreds of these style front wheels over the years and haven't had one reported spoke or hub failure come back to me, besides a stick in the spokes sort of accident. The only damage I have personally experienced was when using oversized spokes (11g) into a regular hub and motorcycle rim. The hub flange cracked within a few hours of riding and jumping down stairs.

An aluminum bicycle hub plays very nicely with 13g spokes or thinner. The moped size rim and tire distributes the force along spokes more evenly, so the unit is far stronger than what can be done with bicycle rims and 13g spokes alone. This build of wheel I've jumped down the same stairsets as the other, and continued riding hard for countless hours over the years without any signs of wear or loss of true.

 

[Chalo]

I've been watching this video before I started to look for heavy duty parts.
And I figured I don't want that to be me going 60 mph. Look how the mtb tackles weight

Both those bikes look like big-box garbage. Caveat emptor.

For what it's worth, I won't test ride most of the bikes I repair, because I don't want to hurt them. I don't worry about my own bikes, though. And I don't use motorcycle parts.

 

[sigimem]

I think the spokes in the rear wheel are 3mm. The same spokes as in the bike rim just different nipples.
Front wheel is a normal bike wheel 32 spokes SUN ringle rim.

Go for the parts JRH tells or get the wheel made by him

DH Fork will do the job Pit bike fork might be a little cheaper maybe not as good. Motocross fork weighs in about 10kg+ not needed. DH Fork 200mm about 4kg, Pit bike fork 200mm about 6kg.

I am still building and planing a mid drive with high power for offroad use due too studying and other things I am not nearly as far as I planed to be and the big project is on for years now.
Planing is very unsatisfying go for it.
I have a blast riding my Hub motor bike with crappy components.
In the end it´s just a ebike and you probably won´t compete in a race with it. So build it and enjoy it maybe you will make some mistakes but you rebuilt it and learn.

btw if your giving me that you want to make it right the first time speech you might as well include it in your signature

 

[macribs]

Here is what all they guys building 45 to 60mph bikes get from us-

regular 36h downhill hub of some sort, dmr revolver is popular for the price
13g spokes with matching nipples for a moto rim, 3 cross lacing
19" moped weight rim, I now carry the MMP front 19" that is matched for front MTB hubs and lighter than a motorcycle rim
19x 2.25 to 3" front tires depending on needs. I personally like the shinko 244 and 241, but that thread just linked has lots of info too.



I've built and helped facilitate hundreds of these style front wheels over the years and haven't had one reported spoke or hub failure come back to me, besides a stick in the spokes sort of accident. The only damage I have personally experienced was when using oversized spokes (11g) into a regular hub and motorcycle rim. The hub flange cracked within a few hours of riding and jumping down stairs.

An aluminum bicycle hub plays very nicely with 13g spokes or thinner. The moped size rim and tire distributes the force along spokes more evenly, so the unit is far stronger than what can be done with bicycle rims and 13g spokes alone. This build of wheel I've jumped down the same stairsets as the other, and continued riding hard for countless hours over the years without any signs of wear or loss of true.

That really makes sense. And saving some weight on the front rim using moped rims rather then motox rims is also nice.
Yeah the breaking of hub flanges I have seen in one thread here, but you have control on that part by using thinner spokes. And as it seems to work I for all of you customer too I will take your advice.

Tks for your advice.

 

[Hugechainring]

I didn't make it through every post, but I did note this is an opinionated topic.

I was in the same boat, so to speak, at one time. It's not the weight (I'm about 190lb), but my desire for heavy duty that lead me to purchase a used Yamaha YZ85 front end for a build. However, after evaluating all the pros and cons, (one of them being the need for a custom set of springs) I decided to part with the front end and stick with the DH forks. My concern was mainly with the brakes, not so much anything else. After actually using some of the better brakes, I realized I was overcompensating.

This is my opinion on the subject, in general terms, based on my own experience, and the documentation of others.

You are concerned with the wrong end of the bike. The rear wheel, with the added weight of the hub motor, is the one that takes the beating, regardless of your mass. This is assuming that you ride over ruts, potholes, do a little off-road, etc. The weight of the hub motor, being un-sprung, puts a tremendous amount of stress on the rim. No amount of spring or shock dampening can make up for this. The tendency of off-roaders to run low tire pressures, risking a tire bottom out against the rim just makes the issue worse.

Take a look at the Stealth thread. There are lots of examples of rim failure, and they are all on the rear.

1) The motor is huge.
2) The spokes are huge
3) The rim is not-so-huge.

My personal Stealth has several stress cracks, only on the rear rim (The one with the 30lb motor and 9 gauge spokes).

The riders that are upgrading are doing so on the rear, not so much the front. Many are sticking with the stock front 24" DH rim. Others are upgrading the front so to get heavy duty tires that don't pinch flat. I don't think you will find an example of somebody taco-ing a front rim.

JRH has good advice, and a lot of experience. Take it from him (and think about your rear wheel build)

You could go to a full moto front end, and it would be bulletproof, but you are adding a lot of unnecessary weight, and integration is not seamless. There are many mechanical issues, and factory Japanese forks are usually too tall.

Current DH forks and tire/rim/hub assemblies are quite strong. The best advice I could give is to choose the proper spring rate for your front end. Either too stiff or too soft has the potential to transfer unnecessary stress to the wheel. I am actually using a "soft" spring. There are three springs stiffer above that, for heavier riders.

The best deal I have found in general is the Rockshox Domain RC, either in 180mm or dual crown 200mm. Prior year models can be had for less than $400USD (NOS). They have steel stanchions and are crazy strong. They pair well with the DMR Revolver hubs JRH mentioned, and cheap parts and springs are readily available.

Good luck with your build.

 

[johnrobholmes]

Best bet on the rear for hard riders is a 17 to 19" moped rim and spokes suitable for the hub flange, generally 13 or 12 for aluminum and 11 through 9 for steel. Unless you need rim brakes, then you are pretty much SOL.

 

[macribs]

Well I finally came to my senses and took your advice people. Ended up with a Fox 40 RC2.
Looking at it and lifting it it seems both sturdy and light. Glad I didn't end up with a motox fork.

 

[minde28383]

Old topic... but still im glad ive found it.
Maybe someone like me will go thouth topics looking for ideas so ill share my thoughts regarding my ride.

Few moments ago I was between two options:
dnm m200 pit bike fork (6kg) with mc wheel and mc parts (whole front end) or
regular double crown hd bicycle fork - dnm usd8.

My biggest concern was and is front brakes. With bicycle 203 rotor and oil brakes i still feel that its week part of powerfull 60kg ebike regarding its capabilities to performe good in long descends. If i hadnt already purchased new regular one sided front hub i would definetly go for double sided hub - two 203 rotors. But maybe its just me who wants to brake so powerfuly.
Nevertheless I will use 32mm width 26'' Alex rim with kenda 3'' tyre which is cruiser type tyre. I wanted bigger wheel especially in the front. So thats how it will be. Obviuosly ill stick to bicycle fork. I need no additional 7kg or even more kgs in front by using pit bike fork.

Nevertheless If somebody will decide to use pit bike fork. Note that they come in variuos leanths from 600mm to 800mm so basically they tend to be little bit on shorter side compared to bicyle double crown forks but might be even longer so there are quite a few options in the market. For ex DNM m200 750mm or PS 770mm forks but as i didnt find who uses them i cant tell if they are comfort ride for ebikes as these are intended for small offroad motorcross and by my humble opinion these might be not quite plush compared to quality bicycle hd forks therefore might need to change oil or spring adjust needed.

 

[macribs]

Well I going back to the original idea of mx fork. Reason for that is mainly due to rider and bike weight. I am a husky rider and I do tend to ride hard. I had the Fox 40 axle snap a few weeks back and that really got my thinking of safety. Lucky for me the axle snap happen in slow pace when I landed a wheelie a little abrupt. But that axle could have snapped in 60 mph going down a back road gravel road and that would at best have caused serious pain. Or worse.

I've replaced with custom axle so I know the new one is tougher. But mx fork also let me use serious brake rotor and calipers. I've warped that 242mm rotor of my old Hope Mono 6Ti due to heavy breaking on long descent. Then new hope 3 v4 seems to work well but honestly at the speed we frequently ride and with the weight of rider+bike I think the added weight of a mx front fork/brake/wheel is a small price to pay to keep riding hard without upping the risks.

 

[robo4]

Hi all
I used a set of pitstar pro forks and hub and I think they are very good for the purpose
they ride really well and are about the right weight spring for the weight of the bike
each to their own but I would use them again if I could find another set cheep

I haven't got headlight shroud on any more which changes the look
I currently don't have a rear brake and the pitstar single disk is awesome for pulling stoppies

 

[minde28383]

How many more of you turned to mx/mc/pit bike forks?

I recalled ebay order of my double crown bycycle fork. I'll keep seeking to test few setups before making decission about the fork to use.
Bicycle fork is too wheak but somehow a lot of us ride them 50mhp and even quicker and don't report any issues. Maybe that's the nature of them. They accept how it is and ride it.