Braking/Suspension issues - questions - Yamaha R6 Forum: YZF-R6 Forums
 
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post #1 of 8 (permalink) Old 05-17-2013, 02:10 PM Thread Starter
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Braking/Suspension issues - questions

Ok. This may not be the best place to ask (maybe more of a suspension ?) and it may be a bit premature but I am having some issues with the rear end moving around under heavy braking. It doesnt matter if the rear tire is new or old and I have tried taking preload out of the shock and messed with only the shock rebound.

Bike specs are:
Front end - .925 springs, Traxxion valving
Rear end - JRi shock, dont remember spring #, eye to eye length was set by JRi

I have never paid anyone to set the bike up nor have I measured sag, so I dont have those numbers. That being said I will probably have the suspension guy work with me at a track day June 1-2, but I wanted to get some r6-forum input.

To the real question. Can someone give me an idea of some shock rebound, compression, and sag numbers? Or anything else to try. Thanks.

Sloan
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post #2 of 8 (permalink) Old 05-17-2013, 02:21 PM
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In for the responses.
FWIW I recently made some suspension changes and now the back end moves a little when braking hard on a slight decline, which I'm sure serves to unweight the back tire.


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post #3 of 8 (permalink) Old 05-17-2013, 03:07 PM
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Re: Braking/Suspension issues - questions

I would think you'd want to add spring to the front end to slow down or reduce weight transfer under braking.

How's your downshifting? Are you dumping the clutch or letting it out slow and smooth?

I'm slow and unskilled though - so take it with a big grain of salt. Definitely curious to see what DanQ or Melk or Chief have to say about it.

Last edited by Fallis; 05-17-2013 at 04:09 PM. Reason: Braking.
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post #4 of 8 (permalink) Old 05-17-2013, 03:45 PM
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Re: Braking/Suspension issues - questions

Where is your fork height at? The lower the front, the more it puts weight on the front, and that leads to this issue. So does being too grabbby on the brakes, so you may need to work on being smoother there. You could also try slowing down the fork compression (more damping).

While you should definitely measure your sag numbers, I don't think that is the issue here. Hard braking is going to put both ends of the suspension near the end of their travel. And if it's not doing that then it would actually be helping you keep weight on the rear.
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post #5 of 8 (permalink) Old 05-17-2013, 08:13 PM Thread Starter
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Re: Braking/Suspension issues - questions

Forks are flush. More spring in the front doesn't sound like a bad idea.

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post #6 of 8 (permalink) Old 05-17-2013, 08:37 PM
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Re: Braking/Suspension issues - questions

Quote:
Originally Posted by mmmfishrighton View Post
To the real question. Can someone give me an idea of some shock rebound, compression, and sag numbers? Or anything else to try. Thanks.
unfortunately, i don't have any numbers for you, but i had my suspension refreshed and upgraded over the winter, then tuned at the track by the same guy. bike still wiggles like you describe when i'm braking hard and downshifting.

a suspension tech can help get everything set up right, but i think the rear will always move a bit for you. i've gotten used to the bike moving under me...


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post #7 of 8 (permalink) Old 05-18-2013, 07:18 AM
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Re: Braking/Suspension issues - questions

Is it moving up/down like you are going for a stoppie or side to side sliding?

I'm not the most help, but I've been having to do my own research on my bike as my 600 was eating rear tires like nobody's business and the the rear on mine was giving me a form of vibration/lifting up that prevented me from doing anything with the bike until it stopped it....then I could turn in. On video it looked like I was riding a rumble strip, even though I wasn't. Some people called it chatter, I don't know - and I'm not good enough to do a stoppie! I paid the suspension guru at the track day organization $80 for a "set up" that offered NO help - so don't go with Superbike Suspension. Now that I know more it makes me mad he didn't help me and took my money.

I'm 125 pounds and had the stock 10.8 shock spring on the rear and had NO sag AT ALL, even though on paper he said I did - and I didn't even know what it was before; I just took his word for it, even though none of my problems went away.

As for tire wear, I was chewing up rear tires on a 600 way faster in 1 day than a 1000 could in 2 days on the old spring that SSB couldn't figure out why - from talking with the tire guy, I was "spinning" up the rear tire, for example, 10 inches, but every 8 inches the bike moved.

My research led me to a lighter spring (9.8) from Race Tech and then I had Thermosman at my most recent event go over it for a very fair $40.... where I still didn't have any movement from the bike whether I'm sitting on it or not
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He mentioned a "collar" and to get it from Race Tech.

I got in touch with Race Tech just yesterday and learned I need 2 "collars" for the shock and that will allow me to set the preload... because right now I'm topped out as I understand it.

Not sure what year bike you have or what year bikes these collars are needed, but in sum Thermosman got it spot on. I'm finally on my way to some correction! I believe he's in Georgia but not sure what all events he attends. Good luck!

p.s. my bike still moves under heavy braking, but now it's more side to side but it's nothing that freaks me out or prevents me from riding the bike out.

Sherry
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post #8 of 8 (permalink) Old 05-24-2013, 02:17 PM Thread Starter
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Re: Braking/Suspension issues - questions

Thanks for the thoughts. I'm going to put a smaller rear sprocket to lengthen the wheelbase. Hopefully this will help.

Sloan
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