fitting a motorcycle fork onto a bike?

neptronix

neptronix

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Has anyone here ever fit a motorcycle fork to a 1 1/8 headtubed bicycle frame? I've got a motorcycle junkyard nearby and i've noticed that these forks seem to have headtube diameters around 1 - 1/8 inches, but didn't have a caliper on me nor did i know if there would be some complications..

Some of these forks are in the 5-10lb range and have a lot of nice squish to them.. the used forks are cheap and some of them have 150mm front axles... seems like a cool idea to use one. Anyone done it; and how did you do it if so?
 
Your google-fu is stronger than mine.. i couldn't come up with anything at all.

Thanks :)
 
I can pick up one of these for under a hundred bucks.. sounds like an awesome solution for a cargo bike if i can find a shorter one that has 150mm dropouts or less. I'm sure i saw some at the junkyard with around 150mm dropouts.

A motorcycle front wheel wouldn't be hard to come by there either..
 
neptronix said:
Has anyone here ever fit a motorcycle fork to a 1 1/8 headtubed bicycle frame?
Click to expand...

No, not on a modern bike, but back in the early to mid 1970's when me a about 20 other kids in my neighborhood were converting our Schwinn Stingray's into what would be the precursor of modern mountain bikes, (cutting our sissy bars and tucking them under the banana seat, changing out the handle bars with home made "crossbar" type bars, ....as the trend was back then,) one of the neighborhood kids had an older brother who knew a welder. So with some of our hard earned allowance from mowing lawns and other house work, we paid the welder to modify a Stingray frame to house a set of Honda 90 motorcycle forks. They worked well as the welder did a fine job, and we thought it looked great but, it made the bike very heavy and slow to peddle and nobody wanted to ride it with such weight. It got really heavy when we put a heavy knobby motorcycle tire on the rim. Alas, the poor bike lived the rest of it pitiful life in the junk pile behind Rick's garage until we were in collage and his Dad finally got rid of all the junk.

:D
 
All the links to find motorcycle fork adapters i see are dead.. :/
 
I have seen two examples right here on ES iirc they were Honda cr80 Forks

Whiplash has purchased pitbike forks for his latest build might want to pm him and get the skinny

Best of luck

KiM
 
neptronix said:
All the links to find motorcycle fork adapters i see are dead.. :/
Click to expand...
Ya - sorry 'bout that - I didn't check 'em - I thought the adapter concept was what was important.
Member blackarrow has a build with CR80 forks as well... not much detailed info on a quick glance, tho...
Also brief mention of adapters here: Fresh Full Suspension Build, but the thread sort of drops...

maybe PM these folks....
 
take a look at my greyborg build.. THe headtube is 44mm.. There's a bit of a writeup there
http://endless-sphere.com/forums/viewtopic.php?f=6&t=38846&start=75 pages 3 and 4.

have a read post and questions and I will try to answer them. but basically, I had to get my steering tube machined down to fit the 23.5 and 22mm taper bearings, however if you buy a fastace fork with 23.5mm at the base and 22mm at the top it might just work straight up.... the next problem is the length of the head tube. motorbikes must have longer head tubes. you may be able to fix this with washers as spacers..

Andy
 
I'd be thinking along the lines of cutting the headtube off the pitbike frame. Then welding to a bike frame.

On my longtail, the front forks are still some pretty cheap short travel ones. So much less weight up front, it's working fine. Better rear suspension seems to be the need I have. So maybe all you need is some entry level rockshocks up front, or something similar. But for the motorcycle tire, a motorcycle front fork sounds ideal.

I'm not getting much out the rear shocks, just some rim saving mostly, and a bit better ride on washboard dirt. Most of the better ride is just from being long, and fat cruiser tires. As Chalo would say, the shocks are more decorative than anything. However, saving my rim and spokes on the bigger potholes makes it worth it to me. The extra weight is not an issue on the cargo bike, so I don't really care about that.
 
dogman said:
But for the motorcycle tire, a motorcycle front fork sounds ideal.
Click to expand...
Yep - it sounds like an interesting off-the-shelf means to approach a cross-over vehicle that is on the way to motorcycle without the full motorcycle frame commitment.
 
dogman said:
I'd be thinking along the lines of cutting the headtube off the pitbike frame. Then welding to a bike frame.
Click to expand...


I'm pretty sure that is what LFP did on the latest edition of his death bike. It turned out really nice.

Thinking back, I think he used a fork off of a Zero.
 
neptronix said:
Some of these forks are in the 5-10lb range ...
Click to expand...
Come on, go there and weight them just for fun.
The lightest of all DH racing forks is the Boxxer WC Solo Air, at 5 lbs 4 ounces for 8 inches of travel. Weight of a fork includes the crowns and axle.

Off road motorcycle forks are much heavier with an average of 3 times the weight, so they use a bicycle fork on pro trial motorcycles to build them lighter. Road forks are bigger and heavier, with shorter travel. If you find a high end carbon road fork off a motorcycle, it will be in the 15 lbs. Moped forks are sh*t, yet weight much more than bicycle forks.
 
Well, the weights that i felt with my hands were a guess. But this motorcycle junkyard is full of things from the 1970's - 1990's, and some of the forks felt very light; like a low end bicycle suspension fork ( these probably came off of kid sized motorcycles or 50-100cc jobbers.. )

http://www.chopcult.com/forum/showthread.php?t=28853

Anyhow, this lists the diameter in MM of the upper tubes for each of the shocks in a motorcycle fork. I know that dual crown bicycle forks have tubes between 25mm and 35mm. Motorcycle forks range between 27mm - 45mm and up.

I'm envisioning a hybrid fork - you take an old and abused dual crown fork; remove the stanchions/tubes ( whatever they are called ) and insert the motorcycle shock legs into the dual crown fork, and tadaa..

Bonus points: add a side-side brace, as many motorcycle forks seem to not have those. But maybe with the wider diameter axles that come on motorcycle forks/wheels they are not needed.

I just measured my vintage Rockshox Judy.. 28mm shock tubes.. bummer. I wonder how many 27/30mm tube dual crown bike forks exist. If they can be purchased used and broken for little $, they would be perfect.
 
I looked at the chopcult list and didn't see anything on that list like what we had back in the day. What we did was have one of our dads cut off the head-tube of an old Honda 90. He worked at a local body and fender shop so he knew how to use a torch on steel. The welder then cut the head tube off the Schwinn Stingray frame, refined the cut on the Honda head-tube and welded it all together. As I recall, we paid the welder $100.00 dollars in 1972 money. The front end of that bike stood tall and as mentioned was heavy.

If you really want to do it, sounds like picking the forks you want and asking the junk yard if they can cut the head tube off as well, or just buy the forks and have a local mechanist fabricate a head-tube and baring cups for the forks to fit into and then weld that to a frame.

As a side bar, I have read that tandem bikes have 33mm headsets.
 
I wish i had the means. I have a chromoly frame and no machine shop around. I need something that is relatively plug and play.

I'm convinced that it can be done with some head-bashing instead of investing into tools and labor time ( I don't know anyone of anyone capable, so.. ). I also don't want a permanent alteration done to an otherwise good frame.

So when i have a chance, i'm going to bring a caliper to my motorcycle graveyard and my local bike co-op. Unless someone can find some adapters or other useable stuff that can be bought.

So far, everything i've seen has required some custom fabrication.
 
neptronix said:
Well, the weights that i felt with my hands were a guess. But this motorcycle junkyard is full of things from the 1970's - 1990's, and some of the forks felt very light; like a low end bicycle suspension fork ( these probably came off of kid sized motorcycles or 50-100cc jobbers.. )

http://www.chopcult.com/forum/showthread.php?t=28853

Anyhow, this lists the diameter in MM of the upper tubes for each of the shocks in a motorcycle fork. I know that dual crown bicycle forks have tubes between 25mm and 35mm. Motorcycle forks range between 27mm - 45mm and up.

I'm envisioning a hybrid fork - you take an old and abused dual crown fork; remove the stanchions/tubes ( whatever they are called ) and insert the motorcycle shock legs into the dual crown fork, and tadaa..

Bonus points: add a side-side brace, as many motorcycle forks seem to not have those. But maybe with the wider diameter axles that come on motorcycle forks/wheels they are not needed.

I just measured my vintage Rockshox Judy.. 28mm shock tubes.. bummer. I wonder how many 27/30mm tube dual crown bike forks exist. If they can be purchased used and broken for little $, they would be perfect.
Click to expand...

Moto frames are the way to go. 'Street' fenders have extra bracing between the forks. If you don't want to use the fender, consider retaining the portion that has the bracing.
 
Why bother? Unless you doing a 60mph build, mc forks and wheels are overkill and add a lot of weight.

My forks on the ke100 weigh 15lbs. complete 19x2.75 tire and spoked wheel is 15lbs. I have a set of r6 forks that are 20lbs. There are tons of used MTb forks available at the community bike shop and they aren't worth more than $10. Not big travel, but how much do you need?
 
Well, i think i mentioned this before, but i've got a big heavy cargo bike that will be regularly loaded down. Cargo bikes put more weight of the rider up front, thus most ordinary suspension forks will exhibit lots of sag in that condition. A motorcycle fork is more up to the job - or an expensive damping fork with very hard custom springs or tuning - but i'd rather not throw down $500-$1000 for that.

I would not mind a heavy front end on this bike whatsoever. A motorcycle fork would simply be better for the job - and cheaper since i have access to piles upon piles of used ones on the cheap.
 
There is no way I threw down that much for either set of Marzocchi bomber forks that I have. Look hard enough, you might find a good air adjustable fork for under $300. Then you can at least pump it up hard enough to not have excessive sag.

I didn't put the bomber fork on my cargo bike for two reasons, the older one is cut too short, and I needed the longer new one for my dirt bike which also has a long head tube. As it turned out, my build is still pretty light on the front wheel, even with battery in the triangle. It's the rear shocks I would have liked to modify to use old school motorcycle shocks like those still used on pit bikes. I'd do that if I was welding a frame from scratch.

But using a bike fork takes you back to not so easily using a motorcycle tire. Not just grab one from the junk yard anyway.
 
To avoid alignment issues when rewelding the Moto head tube on, cut the bike head tube down both sides and remove the front part, then, squeeze the moto tube in place, don't pry the remaining part open, and weld that along the cut area. You can also raise or lower the longer Moto tube before welding it in place. Cleanup would be much easier and just as stout an install as original.
 
dogman said:
Look hard enough, you might find a good air adjustable fork for under $300. Then you can at least pump it up hard enough to not have excessive sag.
Click to expand...
That is the way to go if you have a lot of weight on the front. Even paying the price for a good air fork is well worth it if you ask me. They are very light weight with the widest tuning range, and they ride better than any motorcycle fork. Their only down side is frequent maintenance, but the rebuild kits are cheap and servicing is quick and easy.

When you have a heavy cargo bike with the extra weight of batteries and motor, I see no good reason to f**k with a heavy motorcycle fork that will be hard to fit, and won't ride as good after all. If you would build a chopper with a lot of power, then you might have a good reason to use a motorcycle fork.
 
Hey Neptronix,

I did this on my 'Cafe Gus' build. All that is required is to change the stem in the bike triple tree to a stem from a bicycle fork. You can buy the stems on their own. I just wrecked some old forks for it. There are some pictures on my build log. http://endless-sphere.com/forums/viewtopic.php?f=28&t=31705&start=25

Here is the bad news. The bike stem is actually bigger than the moto one. You need to turn out the triple tree slightly. You may be able to do this by hand, it would take some patience and skill...

Good luck with it.

D
 
I have used Pit bike forks on a pair of my builds for the extra braking power and cause i am cheap. You should just go to the junk yard with some measuring tools and see what will work, i managed to get both forks for around $100 each including some shitty 21" wheels that i reused the hubs and spokes from the 21" moto rim to lace a wide aero 26" bike rim too(Almost perfect fit, spokes were a fraction short so i drilled out the spoke holder on the hub by 5mm giving me enough to get the right amount of threads engaged). Also came with the full brake setup, had to space out the brakes to fit the larger 21" wheel avaliable disc sizes. The other i left as a 17" moto wheel.

DSC_0295.jpg
 
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