mjbalogh's Chopper/Bobber '81 GS750LX

[mjbalogh]

That's definitely do-able. At that point, you'd probably wind up having to spring the seat just to make sure you don't slide off the back end. Chopping and dropping the back end does provide some swoop, although not to a radical point. Just to where you're sitting a bit down "in" the bike.

One of my future winter projects will be to fab the frame into a full hard tail, but it's not a major priority. This winter will be getting all of the performance mods in-place, and maybe (if I have enough time, painting/coating the engine). I'm probably looking at another year until I get time to really fab a new frame for her.

 

[Ironriot]

Just thinking aloud here but an aluminum frame would be wicked bad@ss. And not to mention would be light as hell. Although whether it would be strong enough is whole nother story

 

[Mark M]

Just thinking aloud here but an aluminum frame would be wicked bad@ss. And not to mention would be light as hell. Although whether it would be strong enough is whole nother story

Well, I hate to burst your bubble, but aluminum isn't significantly better than steel as a frame material and has a number of disadvantages for the garage builder compared to steel. But it would be unique and look different. If you're more concerned with the esthetic value than the performance value, then a custom aluminum frame would be a very cool piece.

Mark

 

[Ironriot]

Well, I hate to burst your bubble, but aluminum isn't significantly better than steel as a frame material and has a number of disadvantages for the garage builder compared to steel. But it would be unique and look different. If you're more concerned with the esthetic value than the performance value, then a custom aluminum frame would be a very cool piece.

Mark

Wouldn't argue with it being harder to work with especially welding. But I would assume lower weight plus rust resistance would be pretty badass

 

[Mark M]

Wouldn't argue with it being harder to work with especially welding. But I would assume lower weight plus rust resistance would be pretty badass

To get the same rigidity from an aluminum frame, the weight has to be very similar to steel. Aluminum is 1/3 the weight and 1/3 the stiffness of steel, so it often ends up a wash. It does lend itself very well to production manufacturing methods though. As for corrosion resistance, ask anyone living near salt water how well aluminum does in that environment.

I'm not trying to be an ass, but the myth that aluminum is so wonderful keeps on going and going... It's not better than steel, so much as it is different, with different properties and characteristics that still must be managed to produce the desired result. I think a really nice steel spine frame would make a great custom machine, putting the engine on display very well and being pretty easy to do at home as well. My personal opinion on that one, of course. Some of the Spondon and Over Racing aluminum tube frames have looked awesome as well, so they can all be done right with the proper effort and equipment.

Mark

 

[Ironriot]

To get the same rigidity from an aluminum frame, the weight has to be very similar to steel. Aluminum is 1/3 the weight and 1/3 the stiffness of steel, so it often ends up a wash. It does lend itself very well to production manufacturing methods though. As for corrosion resistance, ask anyone living near salt water how well aluminum does in that environment.

I'm not trying to be an ass, but the myth that aluminum is so wonderful keeps on going and going... It's not better than steel, so much as it is different, with different properties and characteristics that still must be managed to produce the desired result. I think a really nice steel spine frame would make a great custom machine, putting the engine on display very well and being pretty easy to do at home as well. My personal opinion on that one, of course. Some of the Spondon and Over Racing aluminum tube frames have looked awesome as well, so they can all be done right with the proper effort and equipment.

Mark

Salt water kills steel also if you want to argue that point but I get ya. I figured it would be a cool choice because well every performance car manufacturer in the world make frames and body panels from aluminum for weight savings. Plus i think it would look badass and be a good conversation piece but either way it was just an opinion and thought

 

[n1elkyfan]

What would be really cool but almost impossible is a titanium frame.

 

[mjbalogh]

Thanks for the thoughts on the frame. I'll probably stick with steel as it's what I'm used to working with, but I won't be coming to a final decision on what other frame mods I'll be making for a while.

 

[Mark M]

What would be really cool but almost impossible is a titanium frame.

Why almost impossible? It TIG welds OK, but material sizes would be limited. Now THAT would be exclusive and different... It is the ultimate exhaust system material, as well.

Mark

 

[TheCafeKid]

To get the same rigidity from an aluminum frame, the weight has to be very similar to steel. Aluminum is 1/3 the weight and 1/3 the stiffness of steel, so it often ends up a wash. It does lend itself very well to production manufacturing methods though. As for corrosion resistance, ask anyone living near salt water how well aluminum does in that environment.

I'm not trying to be an ass, but the myth that aluminum is so wonderful keeps on going and going... It's not better than steel, so much as it is different, with different properties and characteristics that still must be managed to produce the desired result. I think a really nice steel spine frame would make a great custom machine, putting the engine on display very well and being pretty easy to do at home as well. My personal opinion on that one, of course. Some of the Spondon and Over Racing aluminum tube frames have looked awesome as well, so they can all be done right with the proper effort and equipment.

Mark

Another quality with aluminum that would probably deter someone from building a frame of it is that aluminum, unlike steel, has a finite number of vibrations/bends in its lifespan before it breaks. Now that may be in the billions in certain situations, but it would really suck to suddenly have your frame snap under you should you hit a good jolter on a rigid frame like a chopper/bobber generally has.

 

[Ironriot]

Another quality with aluminum that would probably deter someone from building a frame of it is that aluminum, unlike steel, has a finite number of vibrations/bends in its lifespan before it breaks. Now that may be in the billions in certain situations, but it would really suck to suddenly have your frame snap under you should you hit a good jolter on a rigid frame like a chopper/bobber generally has.

Brutal ok this I DIDN'T know. Yeah this would be a deal breaker for me

As for the titanium frame that would be badass as hell. I wouldn't know where to begin working with it though. And isn't titanium brittle? Where as steel and aluminum have a good amount of give and bend before they break

 

[TheCafeKid]

I dunno...i think (and this is total guess) titanium is definately LIGHTER than steel and possibly more maleable (sp?) but probably doesnt have the tinsile strength of steel. not sure tho im no metalurgist.

 

[Ironriot]

Titanium is lighter and in fact is supposed to be stronger or atleast as strong AS steel but I remember reading that it had properties like cast iron where when it is put under enough pressure it would break instead of bending like steel does. which brings us right back to the frame snapping. but i'm no metalurgist either maybe there are different alloys of titanium nowadays my information is a few years dated

 

[Commodus]

Typical titanium alloys are actually heavier than steel, but they are much much stronger - so you can use much less material and thus end up with a lighter construct.

Ti alloys can also be quite flexy so they are an excellent materal for frame construction, especially in a rigid configuration. Lots of high-end bicycles are ti. Well OK not lots but it's not uncommon.

 

[Mark M]

Typical titanium alloys are actually heavier than steel, but they are much much stronger - so you can use much less material and thus end up with a lighter construct.

Ti alloys can also be quite flexy so they are an excellent materal for frame construction, especially in a rigid configuration. Lots of high-end bicycles are ti. Well OK not lots but it's not uncommon.

Ti alloys weigh about 60% of steel, have very high strength and no fatigue endurance limits. Ti is also about 60% as stiff as steel, so it will give more deflection for the same load. This does lend it to bicycle frames and it is an excellent material for that purpose. Pure Ti is not that useful, but a number of alloys are around that give good toughness, strength and workability.

Just for the record, steel also has endurance limits the same as aluminum, but they are harder to find and steel is generally more forgiving in it's failure modes. Aluminum can cause issues with cracking, especially due to engine vibrations.

Our frames are almost never that highly stressed, they are designed with rigidity as the main criteria and almost any frame that is stiff enough is also more than strong enough for typical operational loads. Crashing is not included in typical loads, however. And local cracking issues around engine mounts and such can be a real headache for all frame types, regardless of how strong they may be overall.

Mark

 

[TheCafeKid]

Nice! We have a metalugist here to teach us the ways of the force!!! And i just realized, and appologise for the fact, but we totally jacked this thread with our talk of metals and what not...Sorry man

 

[Mark M]

Nice! We have a metalugist here to teach us the ways of the force!!! And i just realized, and appologise for the fact, but we totally jacked this thread with our talk of metals and what not...Sorry man

Actually, mechanical engineer. But I have spent enough time pondering cool bike stuff at work that I have come across lots of useful info.

I noticed the hijacking in progress, but I figured it was semi on topic since we were discussing frame mods and changes.

Back to the cool GS of the original post,
Mark

 

[klhilberg]

I yuo decide to go full rigid with your fram you should check out Black Widow Choppers. They will take your frame and do the rigid conversion for a pretty fair price. My buddy sent them his Yam XS650 frame and they did it for less than 300 buck with a 3inch stretch. The rigid conversion gave it about 35 degrees of rake w/o changing the neck.

 

[mjbalogh]

No worries about the thread derailment. It was still related to the thread, and I learned some new stuff. Always cool. Please, keep it up guys.

I've looked at Black Widow Choppers before. ~$300 to hard-tail the frame isn't a bad price at all. I just have a hard time handing things off that I used to do myself.

ETA: As far as progress goes, I've had some new parts come in. Nothing major, and not the tank that I have been waiting on for a week already. It's getting to the point where I'm just going to spot weld or braise the holes in the existing tank just so I can get the bike on the road before the snow falls. Plans for this weekend include fabbing the seat mounts, and a mounting bracket for the tail light to turn the existing light/plate combo into a side-mount. If everything works out, I'll post updated pics.

 

[Commodus]

Ti alloys weigh about 60% of steel, have very high strength and no fatigue endurance limits. Ti is also about 60% as stiff as steel, so it will give more deflection for the same load. This does lend it to bicycle frames and it is an excellent material for that purpose. Pure Ti is not that useful, but a number of alloys are around that give good toughness, strength and workability.

Just for the record, steel also has endurance limits the same as aluminum, but they are harder to find and steel is generally more forgiving in it's failure modes. Aluminum can cause issues with cracking, especially due to engine vibrations.

Our frames are almost never that highly stressed, they are designed with rigidity as the main criteria and almost any frame that is stiff enough is also more than strong enough for typical operational loads. Crashing is not included in typical loads, however. And local cracking issues around engine mounts and such can be a real headache for all frame types, regardless of how strong they may be overall.

Mark

Learning is good

Thank you.