HELP!!! Front End Wobble - Wrist Twisters
 
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post #1 of 11 Old 08-09-2009, 10:09 PM Thread Starter
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HELP!!! Front End Wobble

Lengthy Read Please Help!!!

Last week I installed a Penske Shock on the rear, and ever since I have had a major problem when exceeding the speed limit. I would like opinions and thoughts on what the issue may be.

When traveling at 115mph+ the front end starts to get a wobble at 125 the wobble gets to where it is shaky and begins to get unnerving, and I haven't attempted to go faster. Before switching out the shock I had maxed out the Top Speed of my bike a few dozen times easily maybe more, and never had any problems. The bike always felt solid to me and never had a wobble.

The wobble is similar to the feeling that your front tire gets right as it looses traction when pulling a wheelie, or right in the purgatory when the front wheel is only a few inches from the ground.

I have not changed anything on the bike for at least a month before installing the rear shock. So it has to do with something in conjunction with the rear shock. I maxed the bike out a day before the Penske was installed and had no problems at all.

I measured the overall length of the stock VS the Penske from eye to eye, and the Penske was right barely shorter than the Stock.

I know the rear is adjustable in ride height, and will probably adjust the shock to be taller on Tuesday, but all input is appreciated.

***Disclaimer...I know the speeds quoted are unsafe for street riding, but it has been a personal choice each time to do so. I also know that the speedo is not 100%, and don't care I am merely quoting what it indicates on a 17/45 setup. End Disclaimer***

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post #2 of 11 Old 08-10-2009, 09:40 AM
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Am no expert but I would try the adjustment and if the prob continues put the old one back on.. Whatever you feel you would gain from the new shock isn't worth a non handling bike ..




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post #3 of 11 Old 08-10-2009, 09:47 AM
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Quote:
Originally Posted by zookmor View Post
***Disclaimer...I know the speeds quoted are unsafe for street riding, but it has been a personal choice each time to do so. I also know that the speedo is not 100%, and don't care I am merely quoting what it indicates on a 17/45 setup. End Disclaimer***
You forgot to put in something about wheelies....

I am no expert with suspension. However I noticed when I added more preload to the rear of my bike at higher speeds it seemed abit shaky. As I would assume the suspension was unable to adjusted to the numerous lil bumps you hit at high speed at a rate that was fast enough to keep the bike stable.

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post #4 of 11 Old 08-10-2009, 08:12 PM
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Set up that shock!
https://wristtwisters.com/links/12615...ion-setup.html contains links to a couple articles on this subject. Read them until you understand what's giong on, then adjust the rear shock. I'm willing to bet every adjustment is way off.

Give it a go and if you still have a wobble it indicates a problem with the shock or an incorrect installation of something associated with the rear end somewhere.

Rob

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On the other hand, if it has not been done never assume it is impossible to do it.
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post #5 of 11 Old 08-10-2009, 08:31 PM
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I had a similar issue when I bumped my rear shock two clicks tighter, I brought it down one click and it cleared up a bit. Probally to tight I'd guess, how much do you weigh?

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post #6 of 11 Old 08-10-2009, 08:50 PM Thread Starter
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Haven't gotten to the bike yet, but I am pretty sure that the rebound was to high on the rear, but would that really create the issue of front end wobble?

I weigh 200lbs, and had the stock shock 1 click away from max, and the screw 2/3rds the way towards hard. When I switched to the 900rr setup I noticed the loss of weight up in my tail, and almost felt like that little bit of weight was to much lost and that I needed to soften up the rear 1 click for comfort, but never had any handling issues.

The Penske shock is set up for a 185lb. rider, and I figure that the weight saved by removing the high mount exhaust is helps to make up the difference in my weight.

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post #7 of 11 Old 08-11-2009, 01:16 AM
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This is an obvious check but make sure you haven't lost a wheel weight up front... the front tire could be out of balance.

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post #8 of 11 Old 08-11-2009, 07:32 AM
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Go to a reputable motorcycle shop that can do suspension set-ups (unless you want to learn to do it yourself, with the help of a friend). I would go to a shop, and watch and learn how they do it.
It could be a number of things... sag, springs, rebound, compression... even pre-load.

I had the same problem with my bike when I ran the front straight at TWS. I have an Ohlins HRCS Rear, with RaceTech internals up front. I knew it was suspension, and the rear was probably too soft vs. the front. I brought it in immediately, and went straight to the suspension guys. I paid $30 to have them tweak it out. Got back on the track, and all was great!

IMO, the best place to do this is at the track, because you can set it up, get on the track to safely test it out, then bring it back to tweak it till it's perfect. I had already had my suspension set-up prior, but apparantly it need a little more tweaking to get it right.

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post #9 of 11 Old 08-11-2009, 02:54 PM Thread Starter
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Thanks for everything so far everyone. I would love to go do a track day and get it tweaked as I go, but I just paid this semesters school tuition out of pocket, and now I am trying to come up with book money.

I plan to continue tweaking myself and slowly try to get everything good. Is it possible to go to a track day as a spectator, and still get them to setup my suspension?

Also Rob or someone who has redone the forks and has the suspension set up. Can you measure the distance between the top of the fork seal up to the bottom of the triple tree for me please.

When I did the 1kg springs I left the spacers the same(I knew that was an immediate mistake), but a few other people said it had turned out alright for them. The front end was way to tall, so I raised the forks at the tree to drop the nose a little, and it worked until I got the rear shock.

Today I cut down the spacers in the forks by 1cm, and put them back in and put the forks back close to stock positioning in the triple tree, and I have 13.8cm between the top of the fork seal and bottom of the triple tree. Before cutting the spacer I had that distance down toe 10.5cm, and I still felt like the nose was just a tad high due to the rear being a tad bit lower. I feel like I need to raise the rear, but not entirely sure if that is a wise idea. Guess it cant hurt at this point.

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post #10 of 11 Old 08-11-2009, 08:33 PM
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I know the answer! Top of seal to bottom of triple, on my bike, is 4-1/2"

I measured because I was trying to make that d*mn Brutale headlight fit, so it wouldn't hit the top of my fender at full compression!

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post #11 of 11 Old 08-11-2009, 08:41 PM Thread Starter
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Quote:
Originally Posted by Rob919 View Post
I know the answer! Top of seal to bottom of triple, on my bike, is 4-1/2"
Thanks Rob 4.5" is roughly 11.5cm and I was at 10.5cm earlier today, but right now I am sitting at 14cm and .5cm raise up out the top.

I went for a ride after all the work today, and it was a little better, and the head shake/wobble was pushed back about 10mph, but still present must keep working, but work and school is about to interfere.

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