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Discussion Starter #1
I extended my swing arm 14 inches, but haven't ridden it yet. Does anyone have any experience with this much extension? What will I have to change on the rear shock? Thanks
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looks like a hill climber...… I'm guessing you will need to stiffen the spring significantly. that is a lot of leverage
 

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Discussion Starter #5
I mount a suitcase behind the seat, load it with gear and go dirtbike camping. All that weight hanging off the back end makes it hard to climb. After flipping it a couple times I vowed to get the tire under the suitcase.

The front tire is a rear IRC M5B EVO 130/80-18 soft terrain.
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Discussion Starter #7
I can bottom it out by pushing the back of the bike down with my hand. I guess that's normal when you have that much leverage? I've got a yellow spring in there, with a stock shock.
 

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You've changed the wheelbase and rear suspension geometry, because of the distance between the rear wheel and the swing arm pivot point now, you've turned sag into pure squat.

You may need to look into custom coils and rear suspension options, while there is a rear stock shock back there, it already struggles to handle the compression from 200lb+ riders, with the geometry change, the stock shock and spring ain't gonna cut it.

Troll mentioned hill climbers, they vastly extend the swing arm as you did for a longer wheel base for more squat and stability to enhance rear tire traction while maintaining straight line stability. Keep in mind these custom machines run some insanely beefy rear suspension to maintain the swing arm angle.

One of the issues you are going to run into with that wheelbase is turning, while you will be extremely stable upright in straight lines, the longer wheel base is not going to respond as well to steering input, because the geometry changes you made make the bike want to stay upright and straight.

A good example is moto racing, those longer swing arms are adjustable and are used to balance that difference in rake they have to maintain their agility while compensating for squat from the longer swing arm.

I would talk with some custom shock companies and see what your options are, if you can get them to tell you the specs you need for your setup, maybe you can hunt down a rear shock that is set up to do the job.

I found a video that may help explain... Start at 5:40 for rear suspension stuff...

 

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Discussion Starter #9
Thanks for the reply Big Blake.

I read about the research and effort you put into your TW Marvin Shaw rear shock. Do you think a Banshee shock similar to yours might make mine ride-able? Do you think the red 19kg/mm TW spring available thru Procycle would be a waste of money to try on my stock TW shock body? Do you know what I should do to the front fork suspension to help?
 

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I see a lot of rice-rockets zooming around with long swing arms. You may want to research what they have to do to make them rideable.
 

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I see a lot of rice-rockets zooming around with long swing arms. You may want to research what they have to do to make them rideable.
I agree with Apolloha as far as the easiest route to possibly finding a solution that is affordable. The big bucks are gonna come out getting a hill climber shock, or custom ones made. However, if you find a street solution that'll get you by, all bets will probably be off once you start slamming it around off road.

When it comes to selecting a shock, I chose the marvin Shaw shock because they were able to replicate the shock height (I wanted the bike to stand about an inch taller) using the banshee shock as a template and since they build shocks for ATVs, it could accommodate all of the "mass" I have cultivated over recent years (400ish lbs worth).

You need a shock that can control the force of the longer swing arm during compression, and a seriously beefcake coil for rebound.The shock design I dialed with Marvin Shaw was for a stock length swing arm with measurements that limit travel for such and sprung for my weight.

You may be able to work with MSS or another shock company like race tech or local shops, but you are going to need to work on the math, figures like length of travel for the shock (I.e. taking the rear shock out, moving the rear swing arm and tire up and down and measuring using reference points to find out how much travel you want and where the shock needs to stop the swing arm from moving upward any further), rider weight or rider weight with gear/giant box, every rider and bike is different.

I would advise against a banshee shock because of the need to limit travel and a bump stop just getting destroyed with all that leverage coming down on it.
 

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Thanks for the reply Big Blake.

I read about the research and effort you put into your TW Marvin Shaw rear shock. Do you think a Banshee shock similar to yours might make mine ride-able? Do you think the red 19kg/mm TW spring available thru Procycle would be a waste of money to try on my stock TW shock body? Do you know what I should do to the front fork suspension to help?
As for the TW spring, I don't know for sure, but I'm almost positive it will not be the right spring for the application.

Depending on your weight, you might be able to get away with the TW shock if you can find The right spring to handle the rebound without pogo sticking (being way too stiff).

As for front, I went all out and enlisted my friend to help me with the drilling and cartridge emulator installation. Again, depending on your weight, maybe try the stiffer fork springs first. But before you purchase the cartridge kit you might want to enlist a mechanic that is willing to do the work for you, unless you are comfortable drilling out your rods and setting up the emulators.
 

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Discussion Starter #13
Thanks for the replies. I'll do some more reading and see what the rice-rockets with extended swing arms are doing and I sent Race Tech and Cascade Innovations an email asking for help. I'll wait and see what they say.
 

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While not necessarily applicable to a 14" swingarm extension here is some older information pertaining to spring length and stiffness and their effect on ride height. Something like the longer progressive wound Blaster spring looks attractive but despite it's larger 11mm coil diameter might still need about double the spring constant to replicate the suspension characteristics of the stock swingarm.

Need Rear Shock Info
 

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I assume the swing arm fabrication is not complete and once finished will not retain the visible bow. The stresses seen off-road might justify some additional gusseting to stiffen the structure hopefully reducing any tendency to deform or bend over time.
Looks like a fun machine to take dirt bike camping. Hope it all works out well. These machines are so versatile it is always nice to see a somewhat new direction taken.
 

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Discussion Starter #16
It's not welded yet, so I'll try to get the bow out before I weld.

I never thought about it breaking.... I don't jump, and only hit huge bumps by accident, haha.

Thanks for the reply and the link. Good info!
 

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Doubt it would break, just might flex a bit. :)
That, like the Duro ATV tire, might improve the ride in the rough stuff.
Here's wishing you many a good camping trips. You certainly have gobs of gorgeous woods and impressive water features just north of you. Very nice country!
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Discussion Starter #18
Race Tech makes custom shocks. It sounds like the custom shock they make is called a G3-S. They send you this form to fill out. So, with the measurements and I think he said 800 bucks, you got yourself a shock. (I didn't ask him what if it doesn't fit or work). I'll fill out the form and send it in, and see what they say.
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A stiffer spring seems more of requirement than any changes in the shock valving or physical dimensions. An $800 shock could be nice but it would still need an appropriate spring to correct what is likely excessive sag and too soft a spring rate due to approximately doubling the measurement "G", distance from lower shock mount to axle.
Should you elect for a custom shock explain to RaceTech that you are not racing so that they can assist you in a set up for your intended use.
 

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Discussion Starter #20
Well, like a lot of you guys know, a guy on the hillclimber forum said with the 14 inch extension, it would be pretty much impossible to flip it going up a hill, but I'd stop half way up because the tire would be spinning. He said I'll loose a lot of traction when I extend it that far. He didn't think I would be happy on the trail with a 14 inch extension, for one reason, because the turning radius will be much greater. So, unfortunately, I'll probably settle with a considerably shorter extension, maybe 5 inches?

Anybody's input would be appreciated.
 
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