ATC 250r suspension tech

[loganm]

Not that I was just waiting to be unbanned, but s doesn't get much traffic and I need more input on this...

Started with this:



Used every clamp I could find and an old jig table to keep it as straight as possible:





It's +10". So 24 1/4" ish. It is LONG, but, I effectively doubled my suspension travel with the stock shock, effectively putting it at ~9+" Someone on another forum told me that 1.5 .120 wall HREW would bend if I jumped at all, so the 1" flat bar on the top and bottom should help prevent that a bit.

I hanmered the carrier out cutting it off and welding it on and installing the new bearings, so I reinforced it a bit. BEFORE the new bearings were installed.




This is full compression.




I also modified the chain tensioner. I'm not sure if this design will hold up, I'll just have to run it and see how it works.




As for the front suspension, seeing as every pair of 85 forks on ebay seem to be bent, I'm going with inverted forks. Either a Honda VTX triple clamp, or I'm seeing if my friend can make me a set. I like the rake on the stock design, some of the inverted fork trikes I found on google seem to have the forks too vertical for my liking. Hitting a tall square edge bump would put a lot of stress on the fork tubes instead of the springs absorbing the hit. I'm 6'1, 225+ in full riding gear, I think USD forks would be a good investment.

I still need to find an extended brake line. 40" is what I measured for the entire length of the line. Seeing as the parking brake didn't previously work I'm not too worried about keeping it. My hubs are also ed. I think I want a smaller more modern atv tire and definitely a bit wider rear end.

Feel free to point out any glaring flaws in the design I overlooked.

[barnett468]

It's +10". So 24 1/4" ish. Someone on another forum told me that 1.5 .120 wall HREW would bend if I jumped at all, so the 1" flat bar on the top and bottom should help prevent that a bit.

I hanmered the carrier out cutting it off and welding it on and installing the new bearings, so I reinforced it a bit. BEFORE the new bearings were installed.

I'm 6'1, 225+ in full riding gear,

Feel free to point out any glaring flaws in the design I overlooked.

You would have been far better off using rectangular tubing.

Your swingarm will flex like a rubber band in a hard turn or whenever a high enough force is applied more to one wheel than it is to the other.

I would add more reinforcement braces/gussets.

Your flat plates will do very little to increase resistance to bending . They would have made it more resistant to bending if you would have stood them on their edge as shown on the arm below.

Just lay the same size piece of flat metal on the floor with a 2 x 4 on each end and stand on it, then place it on its edge with a vice holding each end and stand on it . Obviously it will be a little stronger because it is welded to the swingwarm but not be very much.

[loganm]

When the swingarm bends, the bottom piece SHOULD be under tension and the top under compression forces. But I'm not an engineer, so I don't know all the technical details. I will see how this one works, if I build another I'm planning on having a new carrier machined and building out of DOM tubing, which is almost twice the strength of HREW. The stock swingarm by comparison is made out of thin gauge steel, but it is very short.

[El Camexican]

I like the rake on the stock design, some of the inverted fork trikes I found on google seem to have the forks too vertical for my liking. Hitting a tall square edge bump would put a lot of stress on the fork tubes instead of the springs absorbing the hit. I'm 6'1, 225+ in full riding gear, I think USD forks would be a good investment.

The longer you make the swing-arm the tall the rear of the trike will be. That will decrease the rake of the front and make the forks "more vertical". If you use USD forks that are longer than the stockers you may be able to get the angle back to what it was, but the trike will be taller. Don't worry about the stress on the USD forks, anything 43mm or larger will out last your frame if it comes to one or the other bending. You'll want a stiffer rear spring for that longer swinger as well if you plan to jump it.

I still need to find an extended brake line. 40" is what I measured for the entire length of the line.

Spiegler. Call them, give them the length, banjo size and angle and tell them what color you want. The banjos are adjustable which makes things a lot easier when building something.

definitely a bit wider rear end.

The wider you go the more leverage you'll be putting on that swing-arm which (don't take this the wrong way) I'm glad you'll be testing it and not me

[loganm]

I can jump on the rear grab bar and bottom out the suspension... But I fully expected that. Even with the preload maxed out. Now, I'm running chinese 22" ballon tires. They were brand new when I bought the trike, but I've wanted to go down to 20s or 18s, which will lower the rear 1-2"

I'm shooting for about the same stance as stock with me sitting on it. As it is right now it leans forward quite a bit under its own weight. I did some rough measureing today and with USD forks and a stock size front tire I should be at the ideal ride height front and rear. Maybe a little tall for my liking. But smaller tires and some suspension tuning should help with that.

[barnett468]

When the swingarm bends, the bottom piece SHOULD be under tension and the top under compression forces. But I'm not an engineer, so I don't know all the technical details. I will see how this one works, if I build another I'm planning on having a new carrier machined and building out of DOM tubing, which is almost twice the strength of HREW. The stock swingarm by comparison is made out of thin gauge steel, but it is very short.

Again, rectangular stock will be far better.

Your swingarm will be just as flexy if you build the carrier out of DOM.

The thickness of the stock swingarm is irrelevant since you are making yours 10" longer AND using wider tire spacing, however, the stock swingarm can be thinner because it has a massive box section reinforcing it.

You said you are not an engineer and asked for help so that's what I'm trying to do.

[loganm]

If I remember correctly the ticket said it was A513 1.5"x11 gauge HREW tubing.

I agree that mine could use more triangulation between the tubes, but, the real question I have is how hard of a hit will it take before the swingarm actually BENDS, not just flexes.

Also, if you notice on the stock swingarm, the shock mounts are actually welded to the carrier, so VERY unlikely that it will bend. You would be snapping axles off before that swingarm breaks. Mine however has a lot more leverage acting on the tubing itself due to the design.

[El Camexican]

Pre-load has no effect on bottoming out and DOM is not necessarily stronger than ERW tube. The strength depends on the grade of steel and shape either is made of.

This A513 11ga. (.108 - .120") you mention is typically grade B (55KSI) and close to .118" thick if made in the USA and .110" thick and grade A if imported. If from Mexico, or South America the KSI will be at least 44, if Turkey, or China 36 on a good day.

The grade is what's important, but few if any mills use grade C coil to make ERW tube thinner than 3/16". When you get into DOM then you start finding higher strengths in smaller sizes, usually rounds only. Once you're set on a design you may want to use 4130. It comes in a wide variety of sizes that would be perfect for you, plus its very strong. Unfortunately it's not cheap and MIG welding it isn't recommended.

[barnett468]

..the real question I have is how hard of a hit will it take before the swingarm actually BENDS, not just flexes.

Well, my guesstimate is that the first time you land on a hard flat surface off a 5 foot or higher jump, it will turn it into scrap metal.

[loganm]

It's a moot point. If it breaks I'll build another one, stronger. Build it and break it until everything is stronger than my riding abilities.

Pre-load has no effect on bottoming out and DOM is not necessarily stronger than ERW tube. The strength depends on the grade of steel and shape either is made of.

This A513 11ga. (.108 - .120") you mention is typically grade B (55KSI) and close to .118" thick if made in the USA and .110" thick and grade A if imported. If from Mexico, or South America the KSI will be at least 44, if Turkey, or China 36 on a good day.

The grade is what's important, but few if any mills use grade C coil to make ERW tube thinner than 3/16". When you get into DOM then you start finding higher strengths in smaller sizes, usually rounds only. Once you're set on a design you may want to use 4130. It comes in a wide variety of sizes that would be perfect for you, plus its very strong. Unfortunately it's not cheap and MIG welding it isn't recommended.

I don't want to use chromoly for cost reasons. And because of heat-treating. It is far more work than I am capable of. I think with 1" 1020 DOM and a truss-style swingarm it would be far stronger than anything I'm capable of breaking.

[barnett468]

It's a moot point. If it breaks I'll build another one, stronger. Build it and break it until everything is stronger than my riding abilities.

If you break it or bend it bad enough off a big enough jump, you won't have any riding abilities because both your legs will be broken or the cartilage will be shredded.

The intelligent thing would have been to ask for help designing it BEFORE you built it instead of building it and then asking for people to "point out the glaring flaws" in your "design" and then not listening to them and telling them their suggestions are "moot points".

[onformula1]

Since the swingarm has be commented on, I think you next concern would be-

The rear shocks compression & rebound damping, spring rate.
The frame flexing, flexing of the adjustable swingarm pivot bolt.
Chain derailing and tension.
Overall handing on the trike.

Plus 3" is about max on a first gen, unless you only dirt/sand drag.

[loganm]

Since the swingarm has be commented on, I think you next concern would be-

The rear shocks compression & rebound damping, spring rate.
The frame flexing, flexing of the adjustable swingarm pivot bolt.
Chain derailing and tension.
Overall handing on the trike.

Plus 3" is about max on a first gen, unless you only dirt/sand drag.

Mine is a plus 10. See how I more than tripled your "about max". I'm setting records.

Jokes aside, my options for shocks are limited. Most everything nowadays has a rising rate linkage. This does not, the spring is progressive rate. Is the stock shock worth rebuilding or would I be better off finding a more modern dirtbike/atv shock on ebay and using a progressive rate spring?

Overall handling is a complete shot in the dark at this point, which is why this swingarm is a rough prototype and not a show quality master of engineering... It will take a lot of time and work to dial it all in.

How do you see the swingarm bolt flexing to the point it becomes a problem? Frame flex could be an issue, no way of telling until I ride it. As for chain tension I will have to get it into riding condition before I decide if a roller/spring tensioner and chain guide are necessary.

If you break it or bend it bad enough off a big enough jump, you won't have any riding abilities because both your legs will be broken or the cartilage will be shredded.

The intelligent thing would have been to ask for help designing it BEFORE you built it instead of building it and then asking for people to "point out the glaring flaws" in your "design" and then not listening to them and telling them their suggestions are "moot points".

So you've done this before then? Can I see your swingarm, I would like to take some "design features" as notes. If you don't have anything constructive to say, or if you're just mad that I have no reservations about hacking up vintage 3 wheelers... :

[loganm]

Here are some more facts. The rear grab bar will in fact bend and break well before 1400lbs. Ask me how I know, or wait for pics... I would say at most I had 1000 lbs on the rear end. The swingarm was just starting to bow. I do agree with barnett that it may be too flexy especially with an uneven landing

And with the preload maxed out the spring bottoms before the shock. Backed it off a bit and netted me another inch of travel. Maybe the stock shock will work with a rebuild and stiffer spring.

[DohcBikes]

Adds 10+ swingarm, touts the gain in suspension travel.

Because, um, long swingarms are great for jumping.

Cmon guys, this dude is a pro fabricator, there's not a single thing you could teach him.