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Additional weight/ rear shock RM

2K views 5 replies 5 participants last post by  ChiefHelm 
#1 ·
Have a '17 RoadMaster and I would like to change the rear shocks to carry additional weight. Is this possible? Any recommendations are welcom.
 
#2 ·
My gut feeling is this is not commonly requested so you might be blazing new ground, if true,
I feel any solution you find could become your custom one-off Frankenstein bike.

the RM should have a fox mono-shock in the rear. I think its 700lb but I wouldn't bet on that.
I would start by getting part# and calling fox for its published specs
things like total length, compressed length, number of lbs needed to compress, yadda yadda.

Once you know those specs find a similar dimension shock with 300lbs more capacity.
a quick google shows 1000/1250/1500/2000 mono shocks exist but no idea if they would "fit".

An issue you might face is MC tire manufacturers design tires for bikes that exist.
you already have one of the heavier bikes made so there might not exist MC tires rated for the weight
you are trying to get too.

Also just because you address rear suspension doesn't mean you can ignore front, I have no idea how you beef that up.

good luck.
 
#3 ·
Between the misses and I we put about 625 lbs sitting on the bike. Normally run about 135 to 140 of air pressure on the rear shock. Gives a comfortable ride and don't have any issues of bottoming out the suspension. I believe the max rated load on the RM is 450 lbs. The only issue is you need to run a bias tire out back, the radials do not have the max load rating to carry that weight. You needing to carry more than that? Dean
 
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#4 ·
I’m looking into changing only the spring on my 14 Vintage. I’m running the air shock. The current spring is 400 lbs (the stock manually adjusted shock spring is 450 lbs and the shock has about an inch less travel) I’m thinking about going to a 525 or a 550 lbs spring. (Measurements need to be taken while the bike is in a chock. With the rider and without. Sag rates are measured. It’s a two person job). I’m not interested in carrying more weight. I’m looking for a better ride. I want to set the rear for me, with out adding any air to the shock. Then when I ride two up or add gear for a long trip. I won’t have to add as much air to the shock. Hopefully that will result in a ride that’s not as stiff. When I had my Ducati 999, I had my suspension adjusted for me by a pro (who knew what they were doing) and it made a big difference in how the bike handled. It was noticeably better.

Suspension is much more complicated than it seems. I’ll be talking to someone who knows more than I do before I make changes.

You don’t want to exceed the Gross Vehicle Weight of the bike.
 
#6 ·
I’m looking into changing only the spring on my 14 Vintage. I’m running the air shock. The current spring is 400 lbs (the stock manually adjusted shock spring is 450 lbs and the shock has about an inch less travel) I’m thinking about going to a 525 or a 550 lbs spring. (Measurements need to be taken while the bike is in a chock. With the rider and without. Sag rates are measured. It’s a two person job). I’m not interested in carrying more weight. I’m looking for a better ride. I want to set the rear for me, with out adding any air to the shock. Then when I ride two up or add gear for a long trip. I won’t have to add as much air to the shock. Hopefully that will result in a ride that’s not as stiff. When I had my Ducati 999, I had my suspension adjusted for me by a pro (who knew what they were doing) and it made a big difference in how the bike handled. It was noticeably better.

Suspension is much more complicated than it seems. I’ll be talking to someone who knows more than I do before I make changes.

You don’t want to exceed the Gross Vehicle Weight of the bike.
Smart response. Do what you want with the shock, but never surpass the GVWR of the bike. The tires, axles, bearings, frame, and all load bearing parts are designed to handle the GVWR and none of us can know which component is the weakest link.

To have a safe load, you have to make sure the bike doesn't squat too much in the rear or the steering will become loose. Plowing into a turn could lead to a crash. You also have to make sure you don't exceed the tire and axle ratings for the front or rear. Finally, you have to make sure that you are not exceeding the GVWR. If you're within all three load ratings for front, rear, and GVWR, a rear shock upgrade to eliminate squat is a sensible addition. It's also a good way to transfer a bit of weight from the rear to the front since a passenger and tour pack mainly only load the rear axle.

With that said, the axle ratings on a Chieftain are lower than the respective tire load ratings. I think it is 500# front and 885# rear. It would be nearly impossible to have a 1385# load distributed exactly this way. There have been hundreds of thousands of uneventful miles logged with overloaded rear axles, but I don't want to be a test mule. If I really wanted to be technical about it, I would weigh both axles on a truck scale when fully loaded 2up with gear. Since that isn't practical, I keep my load below the GVWR and only pack very light stuff in the tour pack or sissy bar rack since that is behind the rear axle.
 
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