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Discussion Starter #1
Yesterday I noticed front end wobble. I was on I-80 in temperature of 28F. The tires are almost brand new at about 2600 miles on the bike. I have Woolich autotune so had made some tuning runs and associated changes to the ECU. I have not ridden much over the last month since the last ECU flash. While I was on the interstate last night, I decided to pin the throttle WFO and see how it runs in 6th toward red line. When I got to about 141 indicated speed, I started getting handelbar oscillations/wobble. Kind of scary but not quite tank slapper bad. When I got to about 146 they seemed to go away. I slowed back down to a legal speed. Then tried the same while leaning forward to see if weight distribution more over the front wheel changed anything. Maybe slightly it did, but overall seemed about the same. My third try, the oscillations seemed to stay at about 145-146, which is close to, if not where, I stopped.

In the past, used cupped front tires have caused wobble like this on another machine if I lightened the handlebars enough. New tires eliminated the wobble. Both tires are new (less than 100 miles) on the GSXS. I have verified pressure is ok. If tire pressure is correct (I go by sidewall, not Suzuki specs), not sure what else could cause this. I put a Puig windscreen on months ago. Tires are Shinko Verge 011 front Raven 009 rear. I think I only got the bike to 150 once before on the original tires. I don't remember a wobble, but not certain. Besides the tires, I cannot think of anything else that could cause this.

Has anybody gotten their bike up to 150?
Have you noticed a wobble?
On What tires?
 

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id noticed it often some days .. some days none,,after a few years i closed down my rebound a bit forks and shock ,,, seemed to help big time
 

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So many factors can contribute to that. Tire and wheel balance, fork trueness, chain alignment, headset adjustment, pitted headset bearings... Also, the F fairing has been designed to create more down force at speed. The nak'd doesn't. Seem like if you want to hit those speeds you might want to go with a steering stabilizer. ;)
 

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Sidewall pressure is the maximum for the tire not the recommended pressure. Did you try Suzuki’s recommended pressure? I run 32/36 on Metzeler Roadtec tires on a 2018 F but have not run up to those speeds.


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In all seriousness, you were riding in 28f temps....maybe coldly holding on??

As it is, I felt this was the most planted motorcycle I have ever been on, deep into triple digits.

Though, it wasn't freezing out either...
 

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was it windy. i had experienced some thing to that effect once , but it was due to it being windy , i constantly push the bike up to 150 , and as i said happend only once .
 

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Gritty, I don't think a steering damper is the answer.

There is something else causing the high-speed wobble. First you need to check wheel alignment. Then wheel balancing. Are the new tires/wheels balanced perfectly? Also, tire pressure - the side wall reco is for MAX cargo weight, try 32-32 if you are way above that.

Once the bike/suspension is dialed in, THEN you add the steering damper for increased stability.

Or easier yet - just keep it under 100!
 

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Discussion Starter #10
Or easier yet - just keep it under 100!
Phht! Silly you!

No, not perfectly balanced. I do all my own changes and just try to get it in the ballpark. I had weights fall off in the past without realizing it. So from my experience I never really noticed unbalance as an issue as long as it is close, so no not perfect.

Yes, I figure there must be something else. I will look at the suspension. I watched the Dave Moss video. Since i replaced the shock I have not verified sag. I did not hit a bump, though, either. So not sure how much it will matter. I go by sidewall pressure. Aftermarket tires, so have always used max sidewall whenever I check. Lowering to Suzuki recommended is a thought. (I'm lazy. It will get down there eventually :) ).
 

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The issue is pretty obvious. Gritty has severely over inflated those set of tyres. No wonder it goes crazy at high speed.
The maker of his tyres indicates it has W rating and a load bearing capacity of 520 lbs at the front. Didn't check the rear figures.

The Suzuki recommended rating for an 'average' rider load needs 36 Psi/42 Psi.
My Ninja 1000 has the same rating of tyre (an S22) and same load rating and has a front pressure of 42 Psi AT 520 on the front tyre by itself, never mind the rear.
With his ambient temperature, there would be thankfully little increase in generated air pressure in the tyres.
The contact patch on the road at 42 Psi compared with 36 would be lot lot smaller.

As he was 'pinning' it for the entire time of the acceleration burst, the rear suspension would be inclined to squat down a bit, further lightening the front end.
Any road is never dead smooth, so at a certain speed, the front becomes closer to airborne momentarily, and the head shakes happen.
Then if there's windscreens, luggage like boxes fitted, that's another lot of instability to be considered.

I drove a 6 tonne work truck once.
The workshop inflated the tyre's to the side wall rating of 95 Psi. The maker, Isuzu, had 60 as the recommended pressure. Some 30+ Psi too much
It subsequently skidded around like it was on ice on warm tarmac. When I complained to them, he remarked 'we always follow what's on the carcass'.
I told him to get another job before he kills someone, namely me and my Mates.

Rob.
 

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Glad you've got it nailed down to the obvious solution. What else could it be? :rolleyes:
 

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Discussion Starter #14
I would definitely check chain alignment. Mine was not perfect from the factory. I bought one of these handy dandy tools (Profi Laser Cat)
In the past, I used trammel points I picked up from somewhere to make sure the rear axle is parallel to the swingarm pivots. Trammel points mounted on square tubing centered on the swingarm pivot and centerline of the axle on the chain side then check the right side to make sure the distance is equal. The factory markings may not be that accurate. That should get the rear sprocket parallel, I believe. Maybe check both ways because I also have a precision straightedge used to get my jointer tables coplanar after putting a shelix cutterhead on it.
 

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I would definitely check chain alignment. Mine was not perfect from the factory. I bought one of these handy dandy tools (Profi Laser Cat) and it is fabulous for checking alignment. Cheaper tools work quite well too in my experience.
Just wondering, after using the alignment tool did you then check if the wheels were in line.
I used an alignment tool like yours, but not Laser, then found the wheels were out of line. Suggesting a problem with the frame some where. The bike has never been in an accident other than falling over while stationary.
I check alignment using two parallel pieces of fine cord off the rear tyre anchored to a pair of axle stands.
I preferred to have the wheels in line so did a reset. Did 30,000 miles on original chain set which still looked good.
 
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@dekker I haven't checked wheel alignment other than eyeballing, but I've never had any handling behavior that concerned me. The markings on my GSX are accurate for as chain alignment (confirmed by the Laser tool), but I've had bikes before that were way off. I'm sure a wheels out of alignment or an untrue frame could contribute what @gritty describes.
 

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The issue is pretty obvious. Gritty has severely over inflated those set of tyres. No wonder it goes crazy at high speed.
The maker of his tyres indicates it has W rating and a load bearing capacity of 520 lbs at the front. Didn't check the rear figures.

The Suzuki recommended rating for an 'average' rider load needs 36 Psi/42 Psi.
My Ninja 1000 has the same rating of tyre (an S22) and same load rating and has a front pressure of 42 Psi AT 520 on the front tyre by itself, never mind the rear.
With his ambient temperature, there would be thankfully little increase in generated air pressure in the tyres.
The contact patch on the road at 42 Psi compared with 36 would be lot lot smaller.

As he was 'pinning' it for the entire time of the acceleration burst, the rear suspension would be inclined to squat down a bit, further lightening the front end.
Any road is never dead smooth, so at a certain speed, the front becomes closer to airborne momentarily, and the head shakes happen.
Then if there's windscreens, luggage like boxes fitted, that's another lot of instability to be considered.


I drove a 6 tonne work truck once.
The workshop inflated the tyre's to the side wall rating of 95 Psi. The maker, Isuzu, had 60 as the recommended pressure. Some 30+ Psi too much
It subsequently skidded around like it was on ice on warm tarmac. When I complained to them, he remarked 'we always follow what's on the carcass'.
I told him to get another job before he kills someone, namely me and my Mates.

Rob.
that makes alot of sense although i keep my air pressure (more or less)at the recomended rating , i notice that professional riders tend to put less that the rating , because of different road or weather that they are riding .i dont recomend to anyone to lower there tire pressure , because everyone rides different i tend to keep mine where i want it , but thats just me
 

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Thinking back to road racing and track day experiences, (FastTrack Riders) the Dunlop guys recommended psi numbers less than 30 for traction on litre superbikes.
Over 30 psi is going too high for traction, unless the rider is super heavy, like with a passenger??
I lived with wobbles accelerating hard onto the main straight to the banking at Ontario, pushed on thru to 150. A steering damper will solve the problem, Ohlins is the best.
At 150 the contact patch is too small at "standard" air pressures, and traction is reduced by lift at the front. Braking probably settles things down by getting load on the front.
Drop the pressure for fast riding, cornering and straight line, accept faster wear as the price to pay.
I always run 28 to 31 psi "cold", 70 to 80 ambient, ambient temp will change measure psi significantly. I see about 34 psi "hot", after a ride. The only psi that matters is when the tire is working for you, a tire temp gage would be good the see if the tire is at a working temp. Cold tires will take you down. .
Finally, riding at 150 mph at 20F, are you serious??
 

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Discussion Starter #19
At 150 the contact patch is too small at "standard" air pressures, and traction is reduced by lift at the front.
Interesting. Thanks.

Finally, riding at 150 mph at 20F, are you serious??
It was almost 30, c'mon stop exaggerating.
Colder weather=more dense air, more horsepower better for top speed.
 

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Discussion Starter #20
Just read this in Kevin Cameron's book "Sportbike Performance Handbook". Copyright 1998, p. 103, in chapter 12 covering suspension, "Therefore, if you have instability, consider any recent tire changes you have made".
BAM! (all emphasis mine).

Probably would not have posted this thread if I read this last week. My original post above included "The tires are almost brand new ". However, good for discussion purposes.
 
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