Trials Bike Question

[Chris41X]

I don't know much about Hodakas yet and don't know about any differences in frames and cases. I'd like to build a trials bike to fool around with and for AHRMA trials and wondered what frame and engine are the best starting point. I would plan on making the engine as big as I can ( up to 175cc). Any suggestions about which parts to use on something like this would be a great help. I've looked at the PABATCO paper on building a trials bike.

[Bullfrog]

Chris:

If you are planning on competition riding and are in the eastern half of the country, then a slightly shorter wheelbase - Ace frame starting point might be better than the longer wheelbase - Wombat/Combat Wombat frame starting point which I'd recommend for the western half of the country. Eastern trials tend to be just a bit tighter, so tight turning, shorter wheelbase machines may have a slight advantage there.

Any of the street/trail Hodie 125cc engines would be a good starting point. The only 125cc cylinder which wouldn't be useful is the Super Combat cylinder. The Combat Wombat cylinder would have to have a reed valve added to work well, but then would work just fine. An "off-the-shelf" cylinder for trials work would be the Wombat 03 cylinder. It was stock with a reed valve and has excellent port timing for trials work. If you are interested in running a piston port engine - the Wombat 94 (all iron) cylinder is your best choice.

While folks have created some mighty fine trials machines with the large bore Hodaka engines, that is a more complicated route to follow -- because most such machines have squeezed the large engine into an ACE or Wombat frame which requires considerable effort.

Ed

[Chris41X]

Thanks Bullfrog, I live in the middle so trials can have either western or eastern depending on what part of the state it is in. The AHRMA trials are in the eastern part of the state so a shorter wheelbase would probably be best. I knew Hodaka had a lot of parts interchangeability but I didn't know if the frames changed over time and models. My original thought was to build a BSA Bantam based bike but they are hard to come, Hodakas are a little easier to find and I don't have to order parts from overseas. Now to find a cheap frame and engine to work with.

[bobwhitman]

Frames are so common, you shouldn't have to pay much at all (free?). Forks, shocks, etc can usually be scrounged economically. Any motor (90-125) can easily be fitted to any frame with no or minimal mods. Have fun!
Bob

[junker2k]

I guess my first post did not get posted so here we go again.
I have built trials bikes using the ace, wombat and toad frames. I would use the wombat frame, it gives you more room to ride than the ace frame. I would not use the toad frame again it seems nothing is in the right place when I modified the frame. When you use the ace frame and a good motor the bike gets very jumpy. The two best and must do mods is changing the steering head angle and moving the foot pegs back and down to just above the bottom of the frame. The biggest mistake is trying to get a much ground clearance as you can, this makes the bike very unstable. Draw a line between the front and rear axle, if you keep the top of foot pegs on or below this line the bike becomes very stable. I use a 125 motor with some very good mods to make it work at low RPM's but will jump when it is time to go.
But like Bob said just have fun building you bike.
Jack K

[Chris41X]

Thanks Jack, I should have thought about the CG issue with raising the ground clearance but didn't. Same as a bicycle, if you go above the axle line it becomes unstable. I plan to make an Otter type bike and will be changing the steering tube angle and moving the rear loop up out of the way as well as relocating the pegs. May add some gussets also. Are Hodaka frames mild steel? Will a 4.00 x 18 fit in a stock swingarm? This is a do it yourself project so trying to keep it kind of simple. I really like some of the things they've done on the other side of the Atlantic with Bantams, Cubs and C15s. The goal will be to update it as much as possible while still being able to use it in AHRMA.

[junker2k]

The 4.00 x 18 tire will fit the stock wombat swing arm. The only add gussets I have added was under the seat area, like the super combat frame. I would add a picture of my trials bike but I don't have a clue. Bob or Ed, Help.

[socalhodaka]

Jack Kelly has wrote a guide to building a trials bike in the Resonater.
Volume 1 # 13
Volume 2 # 2
Volume 2 # 2

You can access these back issue in the members only area of the Hodaka Club website.
Kelly

[Camman]

I have pictures of my trials bike build. Send me your email address and I will send the pictures to you.

[socalhodaka]

I have pictures of my trials bike build. Send me your email address and I will send the pictures to you.

Share them here, no secrets. We like photos.

[bchappy]

For anyone that hasn't posted a picture just click "Quick Reply" then "Full Editor" and then "Upload attachment" then Browse for the photo on your computer. You just have to be in "Full Editor" to do anything other than a plain text comment. There is a size limitation so it will let you know if it is too large.

[rdbrooks14]

Here is an ACE 100 version of a trials bike.

The TADPOLE - A baby Bullfrog...



I did most of the common modifications BUT I did NOT cut the frame and modify the fork angle. I just kicked the back end up with the KDX shocks and got the 24 degrees that way.

Ed doesn't like the geometry of the TADPOLE but I like it and have had great success with this bike.

Note the line between pegs and axles.

Started as this when I got it...



All this for 600 bucks with the cool CORRECT ACE Pipe that Hodaka SPEC'd back in the day in their pamphlet:




Progressed to this.... How about that fancy hand bent front fender mount? LoL





Here is how it ended up with Progressive KDX style shocks and gusseted swing arm and lowered, even more, pegs..



Running the bike is a Trails in the East... Does very well but I am no any good at trials so who really knows....






So there are some ideas!

Three things I would do that really matter is get QUALITY Radial Trials Tires, put weight on your flywheel, and run CAM 2 to keep bike cool. These things really made a difference for me when competing in trials events.

Bob in MD

[junker2k]

This is my trials bike , it has had a few mods done to it.
Jack K

[rdbrooks14]

Yep just a few! Looks great! Ah if I could use a torch or weld! Mine is a shoestring budget project. You bikes and Jay's are tech art!

[RichardMott]

Hey, with everyone posting photos of their trials bikes, I couldn't resist the posting of my Spyder. Ace 100 B+ with 24 mm mikuni, Webco head, reed valve, wieghted fly wheel, extended swing arm, chain tensioner, Clarke tank, 64 tooth rear sprocket, IRC trials tires. This baby will climb a tree. In fact I have tried to. Not on purpose though. Bringing it to HD2014.

Rick Mott

[Chris41X]

Thanks for all the great information everyone. This will be a very low budget build. I have a small cheap frame jig for the steering head figured out, will just need cones or something to enter it. I may have what I need in my stash of bicycle stuff. Can anybody tell me what the id of the steering head is? Has anybody tried oxy-acetylene welding on one of these frames or should I seek out someone that can TIG it? What is the stock angle on the steering heads? As I'm going to build it cheap I will probably use the 13.5 inch Fox Shoks that I have, I'm guessing that I will want to rebuild them with very light weight fluid in them, any thoughts? I guess I can change the ports in while I have it apart also. What about fork choices? Are the stock hubs ok or do most change them for something else? Chris

[junker2k]

Frame jig? Just cut the main frame back bone where it is welded to the loop just below the seat area. The tube is most likely rusted on the inside a bunch. Now heat the two down tubes just below the steering head, when hot grab the back bone where you cut it and lift till you get 24-25 degrees. Cut the back bone pipe out and add a new one. Gas welding is all right if you know what you are doing but never I mean NEVER braze the frame. If you are going to braze the frame just save the time and use super glue, it is about the same thing. The Hodaka forks will work just fine with a little lighter oil in them, but there are better forks out there that can be used. I use a different set of forks. The Hodaka wheels and hubs are fine but they need to be 18 on rear and 21 in front. The conical hub on the front seems to be better but if you don't use that type just turn the front wheel around and have brake plate on the left side. Like Kelly posted here if you go to the Hodaka club web site and look at the Resonater.
Volume 1 # 13
Volume 2 # 2
Volume 2 # 2
This should be just what you are looking for and if you still have questions I will be more than glad to try to help you out. I sure don't have all the answers but I sure can help you not make the mistakes that I made building the first 7 Hodaka trials bikes.
Jack K

[Chris41X]

I was going to use a simple jig to make sure the steering head stayed square with the swingarm mount points. I should be able to use the same jig to do work on the swingarm and keep it lined up. I was going to use square tubing to form a simple jig to hold the steering head in position while it was welded. I will join the club soon and be able to access those articles.

[Bruce Young]

Hello, Hodaka Trials world, I have a question about the different size and brand of tires and tube you all use. I am asking to try and extend my knowledge into the diff. types of Hodaka use for future reference. What tires work best for beginners and experts. Thanks Bruce Young Hodakaparts.com IDAHO

[junker2k]

The tires are the same for nov or experts. 2.75x21 inch front and 4x18 inch rear. As far as brand is best, that is like asking witch is best ford or dodge. Good tires cost money from $75 to +200 per tire. If you stay with the top 3 makers you can't go wrong but if you try to go cheap that is just what you end up with. Cheap tires that do not work!!!
If anyone is interested in building or just trying a updated vintage Hodaka Trials bike, After the Hodaka days trials, Jay, Ed, Mark and mine along with a few others are more than willing to let you try ours out and ask questions. You can ask questions any time.
Jack K

[Bruce Young]

Thank you Jack, what I was trying to determine, not only the size,s used but the Brands of tires most use. IRC, Bridgestone, and other low end priced tires or the Michelin, Pirilli, Dunlop, or Metzler, these companies, also make two diff. tire, compounds for trials use.
Pro and non Pro compounds. Sticky or not so Sticky type compounds or tread designs.
I now cost is a factor, but I was trying to determine what most use, by Brand in the Hodaka world of trials. Thanks again, I plan to do more detail questions at Hodaka days, because I now how popular this riding can be. Bruce.

[junker2k]

Bruce, most of the real trials tires used on the Hodaka's and modern trials bikes are Michelin, Dunlop and a few use IRC. I would say these are the main brands tires. I have used both the mich and Dunlop, at my ability I can't tell much difference but the Dunlop has stronger side walls and that means less sidewall cuts in the rocks. Maybe Jay L. at his ability could tell a difference. The other thing is the Dunlop's are about $100 cheaper per set and I'm cheap. The chicken choker tires (chin sing (sp)) are just plan junk!!!!! You want the tires as sticky as possible. I can tell the difference with new tires but I'm not like the very good riders that change tires ever 3-5 rides, maybe every 3 years or so. Sometimes you can find a pro rider that changes tires every 5 rides and buy them from them cheap.
One thing I should say about the Hodaka Days trial is this is intended to be a fun event for the lower classes and to get many people to give it a try. We want people to have fun and not get hurt and enjoy the ride. But the upper two classes, things start getting harder and they are there to show what the bikes and riders can do with the old bikes. Ride what challenges you but never over your head.
Jack K

[Bruce Young]

Thank you, Jack that info is actully what we where looking for. With you info, I can now determine what is needed to help supply the Trials riders with new shoes for thier bike.
I have a source that sell both Micelin and IRC so that gives me a couple of options to look at.
I really appricate the help and I am sure you have helped others out there with the same questions, that are building trials bikes, using Hodaka pieces. There are so many options one can go with a Hodaka. See you at Hodaka Days Thank you again. Bruce Young

[rdbrooks14]

At the risk of going up against a trials guru... I do not believe you are going to get a GOOD trials tire for 75 bucks... Unless there is a killer sale. You really need MODERN Radial Trials tires... Worth the money. Most sizes are metric now of course so you can find something close to the Specs above in a metric tire... I, and most, have extended swing arms so tires a little bigger do fit. Not that you really need one much bigger for bikes this size...

[junker2k]

You are right about good trials tires but the front tires start around $100 and the back is more. I have not seen much of a choice in tire sizes in the good modern radial tires, 2.75-21 and 4.00-18 . Michelin does make a lite trials tire, you save a few grams and they cost more. I could not tell any difference on a modern bike so I sure I would not see anything on a vintage bike. Also a lot of the radial tires are tubeless
tires, not a big deal just put a tube in and bead locks.
Jack K