There are a few threads floating around where riders are having problems with high speed wobbles. I found out the hard way that the 18/21 combo with a 180 rear tire does not seem to work on the 09 + frames. I upgraded in 2 phases. 1st, the 21 front with the stock 16 rear. no issues, at any speed. A few months later, I decided to swap out the rear to match the front. Went with a 18 as that seemed to be a popular combo. I did not get a chance to test the set up until Daytona in March. I had dont the 120r Crate upgrade over the winter so I was breaking in the bike/motor in Daytona but notice when putting the motor thru its paces, I got a head shake/wobble when I got north of 80mph. I thought it was the road/wind ect. Traffic and cops being what they were for bike week, I kept the speedo from getting out of hand. Fast forward to this summer, lots of 2 up touring, kept speed down with wife on back but every one in a while the front end felt loose. The ah ha moment came when I did the annual boys trip, running pretty hard out of the gate and on a straight road I am catching up to the pack, look down and see 83mph, and I get as close to a tank slapper as one can get with out flying off. Guys behind me thought I was having a wheel fall off. I save it but had a pretty tense weekend not being able to get up to speed.
Before anyone says, 80 is too fast for a bagger, you get run over in the midwest with highway speed posted at 65-70mph if your not doing 80 or better.
If you have read this far, here is the payoff
I tore the bike down, looking for something that was "off" checked the fall away and tightened the head bearing 1 click. took both front and rear wheels off and had tires removed to check for broken belts, swing arm bushing, motor mounts, everything I could think of. Found nothing... Started doing some research on the internet and found a couple of others with this same problem. I tried my buddys 17 rear and guess what, no wobble. Put the 16 stocker on, no wobble.
I called my wheel supplier, Jason at Coastal Moto and no questions asked, he sent me a new 17 inch rear with new rubber (200 metz) no cost and 2 day air. No more wobble. Costal Moto and Jason rock. Great customer service above and beyond what was expected!!
I hope anyone that has a death wobble on their bike finds this thread and looks at their wheel set up 1st before thinking something else is wrong.
Lots of 18/21 combos out there, no disclaimer that they might not work on 09 bikes (with 180 rear tires). I hope this post help someone in the future and can save some time/money chasing down their wobble.

 

Yeah, I'll stick to my 16's.

 

Thats very interesting about the 21/18 combo. Lots of guys on here have this setup so will be curious to get their opinions.

 

From what I have seen and the people I have talked to, it seems to be a problem for the 09 (new frame) and up bikes. 18/21 on pre 09 do not seem to be a problem...

 

My buddy has the same problem. Almost lost it chasing me down on my Dyna last week. We just lowered the front end 1" to see if it would take care of the problem.

Prior to the 180-18, he was running a 200-18. The problem was even worse. You could see the bike weaving down the road at 70, probably 2" weave, but noticeable.

 

First, I'll NEVER chastise someone for going 80+, 90+, 100+, etc. on their bagger. With that being said...I have an 21/18 combo and have been 110+ (according to the speedo) and not had a "death wobble" or "bar slapper". BUT...I have complained about a wobble in high speed sweepers, but again...no way near a death wobble or bar slapper.

And, just for the record...I was at that speed last night on my way home. Some punk in a truck kept F&%kin' with me so I left him behind.

In summary, I'm fine in a straight away...but not a long high speed sweeper.

 

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What kind of tires. You using? Are they same brand Bias or radial ? So we can help more

 

Tire brand on aftermarket set up are Metzler (ME880). When I was running the stock rear and the 21 front, it was the stock Dunlop in rear and Metzler in front. all tires are radial

 

1st radial is not good for a heavy bike. .it makes bouncy ride because it's softer , less side wall especially the low profiles, you can go to tire shop ask them if you test one. So you will see how soft it is. Stand up the tire push it down . The tire will deform , with less force imagine your 800 pounds bike sitting on it , it will bounce ,up and down causing you to loose control .wobble . Then ask for a bias tyre . I bet it will need you to put more weigh on it to deform. I thnk Harley makes 180/70/18 that's what you need. 2nd .wider rear tires is not good to match with 21 front . On High speed turns . Cause
when you turn you are loosing tire alligment .front and rear are using different angle . Wide vs skinny . Straight ways no problem. I had this problem before With my 07 and 09 .keep away from lo profile rear tires I hopethis will help you