Texas Two Step Taco

teazer said:
Not really. You want a flatter (or flat) profile to get more rubber to the ground when you make enough power to need it. MT don't list a compound for the 3210 front tire but they do specify 35-40psi.

I wonder if you wouldn't be better with say an Avon AM26 or Bridgestone BT45 street tire for that rim. The bike doesn't weigh much and has less than 60 rear wheel HP and I suspect that you would be fine with one of those. I am starting to think I might be better off with one too.

The Phat Trakka made over 80 rwhp and never broke loose the BT45 I had on it. Of course I'm not too fast off the line, but it's worth thinking about. Or just lace a fatter rim on. Mikes XS sells a 2.5 rim that might work better, but rather than keep spending, why not focus on getting it running and then see what needs to be changed if anything. (that was a note to myself as you might have guessed).
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Oh we are going to ride it this weekend! I am just thinking online. Lol

Very excited and highly competitive. I have been talking to Airtech and their owner use to drag race a Kawasaki 350 Bighorn. They said the same thing about having less contact patch and suggested launching in second gear.

You may want to check out Sava/Mitas MC50 120/90-18 is 12.5 lbs and has a soft racing compound and a 27.5” diameter.

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I am going to play with the air pressure on the slick first.

BTW Mickey Thompson tech support said their compound is unlisted but is more inline with a car tire compound. They have never heard of someone trying to use the 2.75-18 for a rear tire. I guess they don’t have friends sending them videos of Thai motorcycle drag racing.


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That's interesting. Not familiar with that tire.

Wher are you racing? Not going to 131 in Michigan with BB by any chance?
 
Brodie said:
Weighs less than I do! Good effort.
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Thank you. Bought a good scale instead of weighing it with a bathroom scale and am a little disappointed. Now we have an accurate baseline. The good news is we removed most of this off the rotational mass. Original Bultaco Bandido was 251 and the Montadero was significantly heavier than that. Drop the tank and tail and we are 217.


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Texasstar said:
John do you have rubber isolators on your head stays?


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No, rubber is exactly the wrong way to go, it needs to be as rigid as possible. The vibrations originate from the engine but are passed on to the frame which resonates along with it (remember everything is a spring, or tuning fork). We need to very firmly brace that open frame loop to stop it amplifying the engine vibrations - like clamping the tines of a tuning fork together. The forces are high so the brace needs to be strong - those lightweight factory head stays like the one you showed often crack, and when they do the vibrations increase very noticeably. Vibration control starts with finding a suitable balance factor but doesn't end there - the frame is the other half of the equation. One other thing I have found is that rubber mounting all the accessories - like batteries, ignition boxes, fuel pumps, tanks, air boxes and so on - not only protects these things but it also helps dampen the frame vibrations a little as well, like passive dampers.
 
John Murray said:
No, rubber is exactly the wrong way to go, it needs to be as rigid as possible. The vibrations originate from the engine but are passed on to the frame which resonates along with it (remember everything is a spring, or tuning fork). We need to very firmly brace that open frame loop to stop it amplifying the engine vibrations - like clamping the tines of a tuning fork together. The forces are high so the brace needs to be strong - those lightweight factory head stays like the one you showed often crack, and when they do the vibrations increase very noticeably. Vibration control starts with finding a suitable balance factor but doesn't end there - the frame is the other half of the equation. One other thing I have found is that rubber mounting all the accessories - like batteries, ignition boxes, fuel pumps, tanks, air boxes and so on - not only protects these things but it also helps dampen the frame vibrations a little as well, like passive dampers.
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So it is important to also put a stay on the front two studs?


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Texasstar said:
So it is important to also put a stay on the front two studs?


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Not really - I attach to the three rear studs of the head but so long as it's solidly connected it doesn't matter how you do it. The arrangement you have looks like it would work well.
 
idahofrank said:
John, besides your LSR setting, what's your background.
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Questioning my credentials eh? So you should! :)

I'm a machinist by trade but have spent the last 30 odd years working with exploration drilling companies, first as a mechanic and then as a maintenance manager. But my favorite period was the few years I spent as an R&D Manager up till about 2016, again for a drilling company. I'd always been involved in designing and building specialized equipment and rigs from scratch and enjoyed it, so when we found that there were generous government subsidies for R&D it was only natural we'd take advantage of them.

One thing that really struck me with this work was the importance of what I call the human aspect of technical projects. What I mean is this: you can have the most technically proficient person in the world running the project but if he can't stay focused and properly manage his time, people and resources then the project is doomed. He also needs to be able to distinguish good advice from bad, fact from fiction. Doesn't matter if it's a drill rig or a race bike or car, if you can't allocate your time and money to where it'll give the most return then it'll fail or never be finished. The internet forums are full of tales like this. Sometimes it's hard to do what needs to be done rather than what you want to do.

I'm not really a car or bike nut; I just have a keen interest in engines. I found out long ago I have practically zero talent as a rider or driver and that I'd be better off sticking to tuning. So I've spent a lot of my own time doing that, built my own flow bench and bike dyno, spent a lot of money and barked up a lot of wrong trees. I always say one good test is worth a million internet opinions. And it's fun. At the moment I'm still working on the Metralla - just made a new crank and cylinder head for it and almost finished an injection system that may see some nitro in the near future. Another project that is almost finished involves adapting a DOHC 4 valve Barra head onto a 6 cylinder Holden pushrod engine that will hopefully go into a front-engine dragster.

So I guess I have some engine experience. Does that mean I know what I'm doing? God, no!
 
This pic shows the light head steady on my Metralla (I like yours better!) and in front of that you can see two jacking screws that jack up against the frame from the head. It's surprising how much the frame flexes up with just a little bit of jackscrew force, and while the original purpose was to help keep the engine together it also further reduced the vibration. I think the preload applied to the frame reduces the tendency of it to "ring". Probably not necessary for your application but it worked well for me and might be an option should you ever need it.
jackscrews.jpg
 
John, Not questioning your credentials. I can see how it came across like that now. Sorry.

I just wanted to know because you are the real deal.

I have learned "stuff" from you, Teazer and others on this site. I am old but I like to learn! Thank you.
 
idahofrank said:
John, Not questioning your credentials. I can see how it came across like that now. Sorry.

I just wanted to know because you are the real deal.

I have learned "stuff" from you, Teazer and others on this site. I am old but I like to learn! Thank you.
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Don't be sorry Frank, I was just kidding ;)
 
John Murray said:
Questioning my credentials eh? So you should! :)

I'm a machinist by trade but have spent the last 30 odd years working with exploration drilling companies, first as a mechanic and then as a maintenance manager. But my favorite period was the few years I spent as an R&D Manager up till about 2016, again for a drilling company. I'd always been involved in designing and building specialized equipment and rigs from scratch and enjoyed it, so when we found that there were generous government subsidies for R&D it was only natural we'd take advantage of them.

One thing that really struck me with this work was the importance of what I call the human aspect of technical projects. What I mean is this: you can have the most technically proficient person in the world running the project but if he can't stay focused and properly manage his time, people and resources then the project is doomed. He also needs to be able to distinguish good advice from bad, fact from fiction. Doesn't matter if it's a drill rig or a race bike or car, if you can't allocate your time and money to where it'll give the most return then it'll fail or never be finished. The internet forums are full of tales like this. Sometimes it's hard to do what needs to be done rather than what you want to do.

I'm not really a car or bike nut; I just have a keen interest in engines. I found out long ago I have practically zero talent as a rider or driver and that I'd be better off sticking to tuning. So I've spent a lot of my own time doing that, built my own flow bench and bike dyno, spent a lot of money and barked up a lot of wrong trees. I always say one good test is worth a million internet opinions. And it's fun. At the moment I'm still working on the Metralla - just made a new crank and cylinder head for it and almost finished an injection system that may see some nitro in the near future. Another project that is almost finished involves adapting a DOHC 4 valve Barra head onto a 6 cylinder Holden pushrod engine that will hopefully go into a front-engine dragster.

So I guess I have some engine experience. Does that mean I know what I'm doing? God, no!
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There are many people in this world that are “starters” but very few finishers. I look for the finishers in my line of work. Starters are not usually finishers and vice versa. You need both to be highly productive. It is a rare talent to have both. I knew you were the real deal when I found your development of your bike online.

Right now there are 5 people telling me how wrong I am on Facebook for the way that the head stay is mounted but what they don’t know is that I listened to a guy who has built two of the fastest bikes rolling down the track at the moment. That is a Hobbs Racecraft design. Now I placed the tabs and it may be better to form a triangle up under the frame tube and have one mounting point. Triangles are strong. It is one thing to make it strong it is a totally different thing to make it strong and light. If the tabs crack I will make version two but the tabs are centered in the tubes. I went with two mounting points because it transfers the resonance to two different tubes instead of my testicles.

Also I am a firm believer that “the engine is ancillary to the pipe.” It all comes down to listening to the right people then applying. A wise man learns from others they say but a fool spouts off why it won’t work, a wise fool knows why it won’t work because he has tried it. Lol.

Every Bandido Montadero rider knows this is the only correct way to ride their Bultaco.
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I like that brace. It will help to stop the motor from moving side to side or front to back, but won't do much to reduce vertical motion. Johns solution is neat in that it puts all that force into trying to distort the whole frame structure, so he's spreading the vertical forces effectively. You could adapt your deign to work as a vertical mount and have both mounts.

If the two small tabs crack or tear the frame tube around the weld there are a couple of ways to make it much stronger. As the motor vibrates, it is trying to tear the tabs off and the weld typically will be harder and will tend to tear along the edge of the weld.

If they are longer where they are welded - wider triangle shape, the load is spread over a longer path. That's the simplest.

Next approach is a longer (taller) tab welded to a longer piece of half a tube. Weld the tab to the half tube which is fitted over the existing frame tube like a sleeve and then weld along the two long sides of the sleeve. That will create a longer stronger joint.

Or, put one tab on each side of each frame tube so they clamp the brace from each side of the short mounting tubes. Again, make the tabs a little longer and that will more than double the length of weld supporting the load on each down tube.

Any of those will also make the down tubes slightly stiffer and will tend to dampen resonance.

But for now, stop reading things on the internet and try it. Ultimately, it's all empirical at this point. A little science and a lot of trial and error. To get the ways that fail out of the way, they have to be tried and failed so they can be eliminated. Channel the spirit of Bert Munro.

And for a 1/8th mile run, I would try the small tank in front of the forks and either leave the stock tank on the shelf or make a carbon fiber shell for looks. It should help to isloate it from vibration a little better.
 
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