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Old 11-16-2020, 10:36 AM   #16
Frame Maker
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Two additional comments about chassis design that I have come to understand...

First, no matter how good the chassis is designed, individual riders will want change things to fit their riding style. When Shawn and Tom were racing the AK-1s I had the bikes initially set-up identically. As we began sorting the bikes and getting the details dialed in, each rider had their own tire preferences as well as gearing preferences making each bike highly competitive for each rider. The following year I let Zoran take one of the bikes for the season. Even though Shawn and Tom won many races and nearly a championship, Zoran thought the bike was too soft for his riding style and he immediately replaced springs to make the bike stiffer at front and rear. He just had a different preference.

The other thing I recall is our second race weekend happened to be the first time each rider had their own dedicated bike to race. It was a Sears Point event and both riders did very well getting podium finishes in 500 Twins. Needless to say, they were very happy with how the bikes worked. Towards the end of the day on Sunday we began to notice some mysterious bright dust appearing on the rear / left side of the bike. After closer examination we determined that in the rush to assemble the bikes Friday night before the race weekend, the rear wheel on one (maybe both) bike was WAY out of alignment. The wheel was point as far to the right as possible without rubbing on the swingarm. This resulted in the chain wearing the sprocket badly on one side thus creating the bright dust. But the odd thing was that neither rider had noticed anything odd with the way the bikes handled. If it was noticeable, they just adapted and rode the bikes the way they were.

Because of these experiences, I'm convinced that good motorcycle design is more art than science.... and the areas that are science, aren't an exact science.
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Old 11-16-2020, 05:28 PM   #17
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Great info. There is a common thought that there are 2 types of rider/racers: The first is someone who needs to have their bike setup perfectly to be competitive or win a race. If not perfect, they fight the bike and finish poorly. The second is the rider/racer who can adapt to any short comings, and ride the bike to it's maximum, despite this. It sounds like the two gents who rode your bikes are of the second type.
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Old 11-22-2020, 04:39 PM   #18
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Part 2: the 2019 detour

Screenshot-from-2018-04-24-03-22-44 by andbike, on Flickr

My original plan was to utilize the 2019 Dirtbag Challenge as my motivation to build the first prototype bike. I also had an idea for a crazy dual-shock girder front-end that I also wanted to build. So the plan was to build the prototype for 2019 DBC, then add the crazy front-end to the prototype bike for DBC 2020... but that didn't go as planed.

DBC 2019 came many months earlier than anyone expected. Although Dirtbag has no official date and varies year to year, it has traditionally been fall or early winter months toward the end of the year. 2019 DBC was announced early summer catching many people (myself included) off guard. I normally like to have my Dirtbag builds designed and planned well in advance of the "GO". Wanting to build a ground up prototype, I was not prepared for the early announcement.

I quickly came up with an alternative plan... for 2019 I'd build the crazy front-end and install it on an existing RZ350 frame. Then hold off on the prototype frame till 2020. To make the build schedule worse, I had an out of state dual sport ride planned for early summer, so that came right at the beginning of the build window and would take a week out of my build schedule. Oh, and I still had CAD work to do to finish up the front-end design before I could begin building. Then to top off an already tight schedule, I'd be using a frame that hadn't been titled and I'd be building a bike from spare parts... so this meant extra DMV, CHP, and brake and lamp inspections to deal with. Okay, game on!



my dual sport ride exploring the back roads of northern Vermont with three good friends. I rode a rented BMW GS700. We rode some very technical class 4 (basically jeep/ATV trails) and I was still able to return the GS without a scratch, although extremely dirty

20190719_104857 by andbike, on Flickr

20190720_124931 by andbike, on Flickr

20190720_104530 by andbike, on Flickr



CAD work for the girder fork...

20190704 RZ350 frame assembly 2019.1 by andbike, on Flickr

20190704 RZ350 frame assembly 2019.2 by andbike, on Flickr



And the donor RZ350. The frame was an ex race bike that had been cut in a few places, so no restoration value. It was gifted to me by BARF's very own KPKE. The pipes were also a BARF donation... thank Butch! Engine is from a Banshee and found on CL for $500. The DRZ/supermoto wheels and GSXR600 forks (would end up on the 2020 build) were inherited from a good friend who had passed away a year earlier. FUCK CANCER

20190629_084606 by andbike, on Flickr

Back from Vermont and with CAD work completed the construction begins, starting with lots of small turned parts...

20190705_193536 by andbike, on Flickr



Laser cutting is outsourced to sendcutsend.com. They have a great service making it very easy to upload files. Prices are excellent and parts arrive at your door a few days later...

20190727_102558 by andbike, on Flickr


CNC parts are from a secret Chinese vendor... and are dirt cheap! I often wonder how they can even afford the material at the prices they offer. The parts pictured were around $800 total. I love these guys (actually a gal that I deal with)

20190727_103447 by andbike, on Flickr

From here its lots of tube bending, cutting, notching, fitting, welding, and stuff coming together...

20190727_180633 by andbike, on Flickr

20190728_092855 by andbike, on Flickr

20190728_153706 by andbike, on Flickr

20190728_170512 by andbike, on Flickr

20190810_134138 by andbike, on Flickr

20190810_153715 by andbike, on Flickr



With the crazy front-end on the bike, I'd need to do something odd at the rear to balance the aesthetic...

20190811_104525 by andbike, on Flickr

To be continued...

Last edited by Frame Maker; 11-22-2020 at 05:03 PM..
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Old 11-22-2020, 07:25 PM   #19
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I can't quite visualise it, but it appears from angles of upper and lower arms, that wheel-axle is moved rearward when fork is compressed upwards?
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Old 11-22-2020, 10:17 PM   #20
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Originally Posted by DannoXYZ View Post
I can't quite visualise it, but it appears from angles of upper and lower arms, that wheel-axle is moved rearward when fork is compressed upwards?
In that photo the top linkage hasn't been adjusted to final length so its a bit exaggerated... but yes, a "J" shaped travel path is common for girders. The nature of a girder you'll never get a true linear path. Always an arc of some sort. Even though that may seam odd, it really doesn't do anything weird when riding. I have two bikes with girder forks and both are a blast to ride.
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Old 11-22-2020, 11:19 PM   #21
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Yeah, that's what I thought, sum of two sine-functions. That J-path seems more optimal as that motion creates progressive action to shock? Also doesn't push bike backwards as much when hitting a bump for smoother action.

Progressive motion is unicorn in fork-design which couldn't be done previously (due to mis-match between spring-rate vs. damping-rate at different displacement amounts). Also matches wheel-motion to spring-rate & damping ratios between front & rear better. Extremely innovative, wow!!!

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Old 11-23-2020, 06:10 PM   #22
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I think modern suspension design has been trending away from progressive actuation (that was popular in the 80s and 90s) and now more linear... but with more control over low speed and high speed damping.

Anyway, all possible benefits of my design are lost in that my design is heavy and not very refined. It works okay, but un-sprung mass is high so bumpy roads aren't very fun. I was happy that it worked well for 350 miles of riding for Dirtbag.
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Old 11-25-2020, 11:12 AM   #23
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Part 2: the 2019 detour (continued)

With the crazy girder completed, I now move to the middle and rear of the bike. For the front I followed closely to my CAD design. The rear would be much more "figure it out as I go" with a few simple goals in mind...

- utilize R6 tank and seat
- keep the ergos as comfortable as possible (have learned this lesson from past DBC bikes that were VERY uncomfortable)
- make sub-frame strong enough for rear shock loads
- create some type of utility rack (DBC now requires two nights of camping, so need to attach tent and sleeping bag on the back)
- try to add some design details to the rear to accent the front
- and of course provide a place to mount a tail light and license plate

So with these goals in mind I begin the fabricate a rear sub-frame figuring out the details as I go...

With the old sub-frame removed, the main frame is cleaned up to erase any residue of the old sub-frame...

20190811_122915 by andbike, on Flickr


Oh look... there's a custom swingarm on there! I'll come back to that later.

20190811_135650 by andbike, on Flickr


Rear sub-frame begins with a long loop of tubing. The R6 tank is used to find correct placement to the main frame, and progresses from there...

20190811_192318 by andbike, on Flickr


I don't have a lot of pictures of the sub-frame construction... so magically its done. Rear tank mount, seat mounts, utility rails, and sheet metal wings to match the front. The wings have cut outs on the bottom that allow for bungy cords to grab along the edges, thus providing added functionality...

20190821_181200 by andbike, on Flickr

Okay, getting back to the swingarm. The original design intent is to utilize a TZR250 3XV swingarm on the custom frames. With that in mind, I decided to design a custom dual-shock swingarm with similar shape and geometry to the TZR arm. For shocks I'm using Ohlins shocks off a 90s era Yamaha snow mobile. These have been coming up for cheap on eBay (I guess snow mobile guys don't care as much for Ohlins parts as moto guys). Because they are for a snowmobile application, they are much stiffer than a similar moto shock. So my design takes the stiffer spring rate into account, thus the exaggerated mounting location. I will also replace the spring with aftermarket Hyperco spring that are a little softer.


Here are a few photos of the swingarm construction...

20190714_092405 by andbike, on Flickr

20190713_171958 by andbike, on Flickr

20190714_092320 by andbike, on Flickr

20190714_153808 by andbike, on Flickr


A few other detail include modifying and mounting the expansion chambers, foot controls, and lighting...

new cups to adapt the expansion chambers to the Banshee cylinders...

20190803_182844 by andbike, on Flickr

Bracing added to the upper linkage. The high bend is to clear the tachometer...

20190810_185445 by andbike, on Flickr

Tapping screw holes in all of the CNC parts...

20190809_160527 by andbike, on Flickr


Here are a few detail photos of the finished bike...
20200802_185627 by andbike, on Flickr

IMG_0661 by andbike, on Flickr

IMG_0662 by andbike, on Flickr

IMG_0664 by andbike, on Flickr

IMG_0669 by andbike, on Flickr

IMG_0679 by andbike, on Flickr

IMG_0685 by andbike, on Flickr
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Old 11-25-2020, 11:48 AM   #24
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Overall, I'm extremely happy with how the bike turned out. I'm only able to get in a very short ride before showing up Friday morning ready for 3 days of Dirtbag adventures and mayhem...

The completed bike...

20190901_070725 by andbike, on Flickr

20190901_070806 by andbike, on Flickr

20190901_070307 by andbike, on Flickr

20190901_070142 by andbike, on Flickr



Then its DBC time!

End of Revere Street, SF ready to go!

IMG_0655 by andbike, on Flickr



First gas stop across the GG bridge in Marin. For the very short distance, it used much more fuel than I expected. Hummm?

20190823_140636 by andbike, on Flickr


A few hours later and another gas stop we arrive for the night at Willow Creek Campground. I figure out the bike is getting around 10 or 12 miles per gallon. I'm not worried about gas, but I'm running pre-mix and I estimated enough oil for running at 20mpg. Now I'm worried about running out of 2-stroke oil.

20190824_084211 by andbike, on Flickr


I decide to do a daring fix. As the sun is going down and parked in a dirt lot, I'm going to attempt to move the needle clips in the carbs. I spread out my jacket as a catch blanket so if I drop the tiny clips they won't fall in the dirt and get lost forever. I work slowly and VERY carefully and get each clip moved two position to the top of the needles. With the carbs back together and the sun almost down, I take a quick test ride up hwy1 for a mile or so and return. The bike is running good and throttle response is the bit crisper. This is a good sign.

The next morning we fill up with gas in Jenner. The little country store happens to have 2-stroke oil (for garden tools I presume), so I stock up. Turns out, day-two fuel consumption is now closer to 20mpg and bike is running really good! I get to Point Arena (our lunch stop) about 20 minutes ahead of the main group. The suspension is working well and the bike is super fun to ride at a rigorous pace up hwy1.

20190824_113256 by andbike, on Flickr

From Point Arena we head inland with our final destination up in the Mendocino National Forrest at a remote beach the locals call "Hippy Rock". And the place is literally noting but rocks! This is where we spend the night.

48625182226_769b8a8584_o by andbike, on Flickr

20190824_182007 by andbike, on Flickr

Sunday we would make our way back through Clear Lake, Napa, and back to Oakland for the usual DBC "return and burn" festivities. We would ride about 350 miles for the weekend and other than the rich fuel condition on Friday, the bike ran perfect and was an blast on the many twisty roads we would take. I couldn't be happier...

20190825_162131 by andbike, on Flickr

20190825_163258 by andbike, on Flickr

Burn-out debris compliments of BARFs very own Cheez

20190825_164445 by andbike, on Flickr
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Old 11-25-2020, 12:12 PM   #25
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But wait, there's more!

In the days and months following Dirtbag, I would make some short rides out Mines Road to the Junction...

dirty rat bike 4.1 by andbike, on Flickr

dirty rat bike 1 by andbike, on Flickr

And then some BIG NEWS... the bike is invited to be shown in The One Motorcycle Show in Portland. For those who have never been, the One Show began 11 years ago as a very small local moto show to highlight local Portland builders. Over the years it has grown in size and prestige. It is now one of the best custom motorcycle shows in the country and entry is by invitation only. This would be my 6th bike to be in the show. This is just fantastic!!!


Its early February so rain and snow are very possible. I would build a giant box on the back of my daughters truck to keep the bike covered during the journey.

20200204_135903 by andbike, on Flickr


The view outside the Veterans Memorial Colosseum, Portland OR. Their largest venue to date...

20200208_154459 by andbike, on Flickr


All set up and the gawking begins.

20200208_124629 by andbike, on Flickr

For the first time the organizers have added indoor dirt track racing making this an epic event!

Racers lined up ready to race in their best racing gear!

20200208_153153 by andbike, on Flickr

20200208_210201 by andbike, on Flickr

I always enjoy my time in Portland meeting with old friends and often making new friends. I'm not sure what will happen next year with C-19 rules, but I hope to be back to The One Show sometime soon!

20200209_125302 by andbike, on Flickr


Again, a very big thanks to KPKE and Butch for the donated parts!!! ...and CHEEZ still owes me a bike wash

Last edited by Frame Maker; 11-25-2020 at 12:28 PM..
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Old 11-25-2020, 02:14 PM   #26
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Great write up. I ran into an old friend of yours in Eureka today. Chaz Lord. Old RZ guy, and a 2 strike friend of mine.
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Old 11-25-2020, 03:27 PM   #27
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Great write up. I ran into an old friend of yours in Eureka today. Chaz Lord. Old RZ guy, and a 2 strike friend of mine.
Thats funny... I bought some RZ parts from a guy in Santa Rosa a few weeks ago, and of course we both know Chaz. I guess there was a time when if you had an RZ350 on the west coast, you'd end up doing business with Chaz. I remember going into the shop behind his house in Santa Rosa and it was filled floor to ceiling with RZ parts. Then he had a huge pile of bare frames behind the shop. He's a good guy. I like Chaz.
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Old 11-25-2020, 03:34 PM   #28
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A bike wash might could happen.

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Old 11-25-2020, 03:47 PM   #29
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A bike wash might could happen.

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Old 11-25-2020, 04:57 PM   #30
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