Front end bounce - Honda CRF1000L Africa Twin Forum
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post #1 of 33 (permalink) Old 07-05-2019, 02:55 PM Thread Starter
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Front end bounce

So I recently got new wheels from Honda with the new spokes, so used the chance to do my Tubeless conversion with 3M tape and sealant and put on some Pirelli Scorpion Rally STR's. Super happy with the tires, have already tested a bit offroad and they work amazingly on the road. Give loads of confidence.
BUT
I feel sometimes like the front end is bouncing/vibrating too much. This is especially apparent between around 25-45mph. Below or above this, it seems to disappear. If I take my hands off the bars between 25-45, the bars shake and wiggle quite a bit. Feels like going over a very consistently rough road. What could this be?


I don't think it's the tires because they aren't that aggressive. I had the wheels changed and balanced at Honda so that should be ok.


Could Honda have given me wheels where the spokes aren't adjusted properly? Is a bouncing feeling a symptom of having spokes that are too tight maybe? When I ping them, they sound more on the dull side than high pitched, which is what got me wondering. But then if it was a bounce from the spokes not being right, this probably wouldn't go away at higher speeds, it would get worse.


Happy to be told it's just the tires. It's my first bike with non street tires. Thanks

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post #2 of 33 (permalink) Old 07-05-2019, 03:23 PM
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My 2017 DCT does the same thing. No matter how I tried to adjust the forks, I haven't been able to stop it to my satisfaction. These are not my first fully adjustable forks, so I have experience with this and yes I even take notes. I also checked the balance of the stock front tire and it was off just under a 1/2 oz, so I fixed that. Still bouncing. Now I have new springs on order from Cogent. I may also increase the weight of the oil in the forks to better compensate for my sevlte 255 lbs frame. I'll report back when I have more.
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post #3 of 33 (permalink) Old 07-05-2019, 03:44 PM Thread Starter
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Quote:
Originally Posted by Allen Orazio Jr. View Post
My 2017 DCT does the same thing. No matter how I tried to adjust the forks, I haven't been able to stop it to my satisfaction. These are not my first fully adjustable forks, so I have experience with this and yes I even take notes. I also checked the balance of the stock front tire and it was off just under a 1/2 oz, so I fixed that. Still bouncing. Now I have new springs on order from Cogent. I may also increase the weight of the oil in the forks to better compensate for my sevlte 255 lbs frame. I'll report back when I have more.
When you checked the balance did you also check the trueness of the rim?
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post #4 of 33 (permalink) Old 07-05-2019, 11:50 PM
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Not specifically, but I did not notice any out of roundness when I had it on the static balancer. I have done enough tires over the years that I'm sure I would've noticed any. I did balance it out and it didn't make any difference. I really believe that the springs are too weak, flacid in the small movement zone and correspondingly the dampening can't control the bounce. When, the forks hit a bigger bump the dampening works well enough. Maybe even just a thicker fork oil might do the trick. If you compare any of the aftermarket springs to the stock Honda ones you will find a much more robust spring.
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post #5 of 33 (permalink) Old 07-10-2019, 08:58 AM
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My 2019 ATAS manual is doing the same
thing. In the 30 mph range the bike bounces up and down. It smooths out at higher speeds but it doesn’t seem to be a normal thing.
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post #6 of 33 (permalink) Old 07-10-2019, 11:43 AM
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Every 21 inch front wheel bike I personally have owned does the same thing just like my 2016 does. I don't know why.
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post #7 of 33 (permalink) Old 07-10-2019, 02:13 PM Thread Starter
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So I've found a bit of a flat spot on the rims, which is likely to be giving the bounce. Although still weird that it doesn't bounce at all speeds. The tire is perfectly balanced. Honda don't seem to think adjusting the spokes will round out the flat bit. Seems it could be a factory issue with the mold, or possibly the tire I have. Not sure what to think but Honda don't seem keen on adjusting the spokes and in a bit hesitant to try myself... definitely didn't have this with the original tires and rims though so has to be one of the two

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post #8 of 33 (permalink) Old 07-11-2019, 09:53 AM
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Make sure the front axle is seated properly and that the forks are not binding. I recently replace the tires and had the same thing, along with the front end popping up from a stop, I went thru the front wheel mounting procedure again making sure to really compress the forks before tightening the pinch bolts and they are both gone.
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post #9 of 33 (permalink) Old 07-11-2019, 10:52 PM
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Find exactly what mph it starts doing it - then upshift and see if the speed it is doing it at changes. If it does - then the engine vibration is matching with the wheel vibration and they are amplifying each other. Make sure your air pressure isn't too high.
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post #10 of 33 (permalink) Old 07-12-2019, 09:11 AM
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Yesterday I changed out the front springs with the .72 kg springs from Cogent Dynamics. Being close to the 260 lbs weight that Cogent lists on their web site for the .82 kg springs I initially ordered the .82's. Speaking with Cogent I learned that the .82's have been replaced with .80's because people found the .82's to be to stiff. While discussing my riding style, back roads, nothing hard core off road, Cogent felt that I would be better served with their .72's. While I was changing the springs I also changed the fork oil to a 12.5 weight, achieved by mixing one quart each of 10w and 15w. Result, I'm very pleased. The front is much tighter with less fork dive. The bike corners much better, the forks feel stronger with less flex. The bounce that I was experiencing has been greatly reduced, I still need to tweak the rebound and compression to see if I can dial it in more. Next time I change the fork oil I may try a straight 15w. The Cogent springs are a straight swap out, you don't need to change anything else. They are also a much beefier straight rate rather than the the wimpy Honda progressives. Finally, at 255 lbs the .72's are plenty strong for my purposes and I can't imagine needing the .80's.
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