Headshake and tire pressure

**FastJohnny** · 10-02-06, 05:24 PM

A little while ago I posted about how I almost crapped my pants at full lean when I got what I can only describe as a "weaving headshake" from the front wheel.

Then on a group ride I took a corner hot and had to lean way over and it happened again. This time I ran wide into the oncoming lane and almost hit a truck hauling a horse trailer.

Actually... The chicken strips on my front tire, while small, are in an almost sawtooth pattern. Not smooth looking like everyone elses I see.

This weaving headshake has me scared to do any kind of spirited cornering since the 2nd time it happened, since I know I was light on the bars that time and kept my head. I did manage to get it back over into my lane this time without what I thought would be certain death, but I missed the front of that truck by about 5 ft.

I thought my tires felt especially soft today and realized I havent checked my air pressure since late June. They were at 27 PSI and they call for 42 PSI. Yes Im an idiot.

I got on the back and it was a night and day difference, it felt so much lighter and flickable. I took a nice sharp slow corner somewhat hard and no sign of headshake.

Could this have been the cause?

**Josephd14** · 10-02-06, 05:28 PM

Without a doubt, i went a while one time without Checking my pressures, and then finally did, and they were around the same PSI as yours.. Night and day like you said.. Now i check them every other Gas Fill up or before a ride, i keep a Tire pres. gauge in my tool pouch under my seat now...

**black** · 10-02-06, 07:11 PM

check your front suspension settings

**OreoGaborio** · 10-02-06, 08:10 PM

I've ridden w/ less than 25lbs a few times and it didn't do anything funky like that. Something's fishy.

**Zolden** · 10-02-06, 08:43 PM

When I bought my bike I noticed a plug in the rear tire down the road, thought nothing of it. Few weeks of riding and apparently the bitch started leaking. I didn't realize it at that point and saddled up and went riding. When I took a turn at anything over 30mph it felt like the rear wheel was going to fall off - it was all sluggish and slow and splashy as hell. 25 psi in a tire that is supposed to have 38. It was pretty scary the way the bike acts under that situation.

The leak is so slow that I can just refill it every few days and ride, but when I get back from school I assume I'll need a new tire.

**Paul_E_D** · 10-03-06, 07:44 AM

That could easily have caused your problem. work your way back to full lean in safe conditions and verify that there's no shake. Also, watch the wear pattern. If it straightens out, you're good to go.

**FastJohnny** · 10-03-06, 09:39 AM

Originally posted by black
check your front suspension settings

Suspension is something Im not to confident about messing with. Anyone in the Springfield area wanna check it out for me? I have tools and beer! ]

**black** · 10-03-06, 09:41 AM

when I mean suspension I mean check to make sure your right and left settings are the same

same number of clicks etc

**number9** · 10-03-06, 10:10 AM

What kind of tires call for 42psi? That sounds kinda high.

I rode with a front tire at 20psi, at regular speeds and conditions there was virtually no difference. I also rode (for about 100ft) with a rear tire at 3psi on a separate occasion, but you could DEFINITELY feel that. The bike took heaps of pressure to roll (i.e. pushing it out of the driveway), and once it was rolling it didn't want to change direction easily; and when it did it wanted to lay down on the ground.

**Awesome** · 10-03-06, 10:32 AM

Originally posted by black
when I mean suspension I mean check to make sure your right and left settings are the same

same number of clicks etc

The suspension works as a system, the left and right do not need to be the same. you can mix settings, spring weight, whatever you want. I believe the new suspension penski is testing has compression on one side and rebound on the other.

**RSVMILLE661** · 10-03-06, 11:11 AM

What Jay said. Seacoast Aprilia built a race spec Mille' with a 10k Ohlins front end. One fork was compression the other was rebound. It is supposedly the same front end Eric Bostrom uses on his race set up bikes.

**black** · 10-03-06, 11:19 AM

on my zx6r, there was settings for each fork... When I had this same exact scenario.. i checkthe settigns... there was something ridiculous like 7 clicks of rebound on fork , the other had like 1

**Manny** · 10-03-06, 01:52 PM

Originally posted by number9
What kind of tires call for 42psi? That sounds kinda high.

The book for my Daytona recommends 42 for the rear...

**SilverDragon** · 10-03-06, 02:03 PM

Originally posted by OreoGitorio
I've ridden w/ less than 25lbs a few times and it didn't do anything funky like that. Something's fishy.

Pete, you talkin about race tires? If so, throw it out the window. Street tires (well most) hate to be at 25psi or less. I would say at LEAST 32 each for a street tire. My R6 calls for 36/36 stock.

**OreoGaborio** · 10-03-06, 02:11 PM

Yeah i guess that's true, i WAS on supercorsas. But this was on the street, so technically they're street tires

Then again, i've had my pilot powers down well below 30psi w/o any issues while on the street. Just felt mushy.

Bottom line, tire pressures are the easiest thing to change and his are obviously off... so put em back up to proper street pressures & see what happens.

**FastJohnny** · 10-03-06, 02:26 PM

They are Dunlop D208's. The tire says to inflate them to 42 PSI cold.

The bike felt better today, but I didnt get it anywhere near full lean, so I dont really know if the problem is cured.

Like I said I dont know what the hell Im doing when it comes to suspension. I'll probably take the bike to a Suzuki dealer and make sure it has the stock settings.

**OreoGaborio** · 10-03-06, 02:31 PM

there's TONS of info about suspension on the net.... do some reading & edjamakate yerself.

Here... took me 2 mintues to find these decent links:
http://www.gostar-racing.com/club/mo...ion_set-up.htm
http://www.carbibles.com/suspension_bible_bikes.html
http://www.webbikeworld.com/motorcyc...ks-suspension/

i'm sure there's better ones out there... i just did a quick google search, skimmed those over & posted em as examples.

**benVFR** · 10-03-06, 02:37 PM

Speaking of tires recommended to be set at 42psi.

That's probably a recommendation for sport-touring tires on heavier bikes.

My VFR's recommended pressures are 36/42.

Running it 30/30 is absolutely not a problem with any tires I've tried.

I run 32/33 on the street right now. So the front is not to far out of wack but I know running the rear >10 psi lower then recommended is not a problem.

There's certianly nothing mystical about having different stuff in the legs of the forks. Tons of mountain bikes are built that way, and they're not uber-gear. (Though a lot of MTB gear is in fact better then lots of what is available OEM on motorcycles.)

**FastJohnny** · 10-03-06, 02:51 PM

Thanks for the links, im going to check my downloaded repair manual and see what they have to say about the suspension. The back end does look jacked up on my bike, and I remember the guy I bought it from saying that he had ridden his wife on the back of it once or twice, and they were not small people.

No sport tourer, it's a 2004 GSXR 600.

**benVFR** · 10-03-06, 03:41 PM

Check the position of the forks in the triple tree... that should definitely be in the service manual.

Lots of people who don't know what they're doing seem to like to raise the forks in the clamps, dropping the front end and messing with the geometry.

**FastJohnny** · 10-03-06, 04:10 PM

Thanks man.. Will do.

**FastJohnny** · 10-04-06, 04:05 PM

OK.. The Owners Manual actually had information on how to adjust the front shocks and some for the back. Basically I was able to set everything back to stock except for the rear spring.

Wow.. The damping rates were all fucked up. The front springs (I think thats what they are) where good, but the dampers on the top and bottom were somewhere like 3 turns out. Stock settings call for 1 3/4 turns out.

The rear was fucked! Same deal, Big screw was like 4 turns out, called for 1 3/4. Small screw was like 5 turns out calling for 1 3/4.

The manual wouldn't tell me the stock settings for the rear spring. Stating "You can adjust the rear shock, but we suggest you bring it to a Suzuki Dealer as it requires a special tool."

I have the special tool. It's a big flathead screwdriver, a framing hammer and a steady hand.

DOES ANYONE KNOW THE STOCK SETTING FOR AN 04-05 GSXR 600'S REAR SHOCK?

There are 5 or 6 threads showing depending on which side I look at. Which is pretty close to what there picture shows.

Regardless, the bike sits more level (the tail end used to be much higher) and when I bounce on the seat there is much less movement. It feels SO much easier to turn in on, and I find myself accelerating harder earlier in corners. Not to mention it's so much more flickable. My balls tingled the first time I had to swerve around a pothole and felt the bike move gracefully underneath me. With it sitting flatter it's less weight on my wrists, which is good.

I had no idea a couple adjustments would make such a huge difference, or that my settings were so far off. Thanks for pointing me in the right direction!

**benVFR** · 10-05-06, 09:12 AM

Be REAL careful adjusting the preload collar with a screwdriver & hammer.

The tool is probably only $10-20. That is crap that Suzuki didn't include it with the bike but you should go get one.

Ideally you'll want to adjust it for riding 2-up or carrying luggage on a trip. If you "adjust" it too many times with a screwdriver you could trash the collar and have it stuck in the wrong position.

**number9** · 10-05-06, 10:21 AM

Originally posted by benVFR
Be REAL careful adjusting the preload collar with a screwdriver & hammer.

The tool is probably only $10-20. That is crap that Suzuki didn't include it with the bike but you should go get one.

Ideally you'll want to adjust it for riding 2-up or carrying luggage on a trip. If you "adjust" it too many times with a screwdriver you could trash the collar and have it stuck in the wrong position.

+1. Buy the tool. The stuff I have seen people do to suspension threads, you wouldn't believe...

**benVFR** · 10-05-06, 10:36 AM

I say that cause I wore mine out WITH the proper tool.

Friggin Honda.. they made the collar out of very soft material.

But I got it replaced under warranty with a shock with hydraulic preload. No more tools.

Headshake and tire pressure

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