Tank slapping

[Moonshot_1]

Just got new to me Interstate (99). All was good till tonight when she started some tank slapping when I took my hands off the bars. Not real drastic but a pretty good shimmy. Different roads seemed to have significant effects from virtually no shimmy to fairly substantial. I can feel no shimmy when my hands are on the bars and the shimming stops immediately when I simply touch the bars.

Bike has only 49k and in near pristine condition. It has led a very sheltered life.

Previous owner put on a Dunlop front tire and it has an Dunlop Elite tire on the rear. Both tires are relatively new with less than 1k on the front and not much more on the rear.

Tire pressure in the front was 33 on a warm tire. Added air and it improved the situation some. Will dbl check when cold.

Question- Are Dunlops prone to tank slapping a bike around? Or am I looking at a new set of head bearings in the near future?

Thoughts please.

Added note, I just got this bike on Tues. (6-9-15) Test drove it prior, rode it home 150+ miles
and probably 300 miles in addition. I've rode it with "no hands" on a number of occasions to check for this very thing during the test drive,  plus giving my hands a break during the ride home and the miles since. Solid as a rock till tonight. (6-15-15) No incidents to account for the change.

[Firefighter]

Don't think I can help much, but any bike can have tank slap under certain conditions. I have found web sites on the subject. My 2000 IS with 50,000 miles will sometimes have a hands off wiggle at certain speeds or wind direction. Tires do make a difference as I have had tire combinations that do or don't cause this. Tire pressure, and bike loading also allow this slap. It is not dangerous because it will never do it with your hand on the bars, and I doubt it would upset the bike with your hands off. Research on youtube and you will find info that will put your mind at ease. You do need in my opinion to increase your tire pressure or you will have cupped tires that wear out too soon. I am running 40psi up front and 45 in the rear car tire.     Firefighter

[R J]

Mike, I'd run 45# in the front and 49 to 50#'s in the rear.

That is just my opinion.

You could jack the pressure up and give it a whirl.

RJ.

[Jopson]

Yes tires do sound a bit soft I'm running 42# front and rear.
Front is a metzler 880. Back is a Bridgestone excedra max MC tire

[PhredValk]

My 99 IS was like that when I got her. Rock solid as long as I had at least one hand resting on the bars, but shimmied like crazy if I let go at hiway speeds. Went from Dunny E3s to a D404 rear bias on the front 30K ago and nary a wiggle since.
Fred.

[Jess from VA]

This is almost always a front tire issue.  Air and/or wear and/or balance (or out of round).

Go up to one pound under Max psi printed on the sidewall (cold) and I bet it disappears (unless really out of balance or out of round or damaged... lift the front and spin to see something)

[Bighead]

A cupped rear tire will give you the same symptoms.

[Michvalk]

Mine did that until I re-torqued the steering head bearings. Handle bar mounted fairings puts a lot of extra weight on the front, and they need to be right.

[Novavalker]

Your steering head bearings need to be replaced.

[longrider]

Couple of things come to mind here.  Honda revised the air pressures in the op manual many years ago.  We here all agree that 40 - 42 in the front and 40- 42 in the rear is where you need to be.  Your front is most likely cupped from running too low for too long.  Maybe you do need steering head bearings but the bike should be put up on a lift to check if they are indexed.  If not they should be adjusted to specs(7 ft lb I believe on the IS).  I usually set mine just a hair tighter.  Change out the rear shock bushings.  Either or all of these should improve the handling as well
Warren

[Challenger]

Exact same description I gave when I posted about a shimmy and shake with no hands., 99 I/S with fairly new Venom on front. Tire looked good and balanced. Take one hand off bars and relax the other and "Katie bar the door." Switched front wheels with the STD and could run triple digits with no hands. Installed new Metz and all is good.  YMMV

[97BLKVALK]

Couple of things come to mind here.  Honda revised the air pressures in the op manual many years ago.  We here all agree that 40 - 42 in the front and 40- 42 in the rear is where you need to be.  Your front is most likely cupped from running too low for too long.  Maybe you do need steering head bearings but the bike should be put up on a lift to check if they are indexed.  If not they should be adjusted to specs(7 ft lb I believe on the IS).  I usually set mine just a hair tighter.  Change out the rear shock bushings.  Either or all of these should improve the handling as well
Warren

 

[Paladin528]

40-42# in a tire?  What is the max pressure rating on the tire?  Mine are MAx 41 psi at max load (1200lbs) putting 41 psi in a cold unloaded tire would be a very dangerous venture. loaded would put the tire above it max pressure rating which will degrade performance and cause uneven wear.  My recomendation would be around 38psi max.  Of course it depends fully on the tire.

[salty1]

Couple of things come to mind here.  Honda revised the air pressures in the op manual many years ago.  We here all agree that 40 - 42 in the front and 40- 42 in the rear is where you need to be.  Your front is most likely cupped from running too low for too long.  Maybe you do need steering head bearings but the bike should be put up on a lift to check if they are indexed.  If not they should be adjusted to specs(7 ft lb I believe on the IS).  I usually set mine just a hair tighter.  Change out the rear shock bushings.  Either or all of these should improve the handling as well
Warren

 

When your ready get rid of the Dunlops. My $0.02 worth.

[Gryphon Rider]

40-42# in a tire?  What is the max pressure rating on the tire?  Mine are MAx 41 psi at max load (1200lbs) putting 41 psi in a cold unloaded tire would be a very dangerous venture. loaded would put the tire above it max pressure rating which will degrade performance and cause uneven wear.  My recomendation would be around 38psi max.  Of course it depends fully on the tire.

Putting the max pressure in a tire that is not at max loading is not dangerous, i.e. you are not risking having the tire fail.  The downsides to having a tire over-inflated for the weight are that the ride will be harsher, and a car tire will wear more in the middle than at the sides of the tread, and thus will wear out faster.  A motorcycle tire will wear less and the bike will turn easier with higher pressure.  Assuming the tire pressure is within the range of proper inflation pressures (vehicle lightly loaded and vehicle fully loaded) the difference in pressure between an unloaded tire and a fully loaded tire is insignificant, a small fraction of one PSI.

https://www.youtube.com/watch?v=wOHSJ7zUBIA

[Jess from VA]

Gryph, this has always been my understanding: (really talking heat more than load, but I suppose a higher load results in more and/or quicker heat)

The MAX PSI printed on the sidewall must take into account that a cold tire heating up will gain a few PSI (I rarely check pressures hot, but it seems to only go up 4-5psi) (not talking full load semi tires, but bikes and cars).  

I really doubt tire manufacturers would print a max psi on the sidewall that required consumers to do the math and testing to discover how many more lbs the tire pressure goes up when fully heated up and then to reduce pressures accordingly from max psi (when checked cold), so it is never exceeded, however hot.  Esp with all the liability issues and giant class action lawsuits against them in years past (see the Firestone 500 story).  And tires should/must be checked cold, not hot, as a base constant.  Whether or not this is optimal for wear, stopping, handling, etc, it seems to me running a max psi printed on a sidewall (checked cold) should never be dangerous for any reason.  (Not optimal does not equal dangerous)

I do think one should not exceed max psi on the sidewall (cold), and it should be taken as the upper limit when deciding what pressure is optimal for wear, stopping and handling.  

My experience is that car and bike manufacturers tend to recommend lower than optimal psi based on their own liability concerns, and better wear and handling are achieved somewhere between their recommendation and the max psi printed on the sidewall by tire manufacturers.

Better stopping may occur at a bit lower pressure, but being at or near max psi never caused my bike to slide under hard braking (with good tread) on any tire.  I have slid a bike under emergency braking, but believe that was a function of speed and HARD breaking, not psi.

Finally, it is well known that grossly underinflated tires are subject to very high and possibly dangerous heat (probably higher heat than could ever be achieved at max psi on the sidewall)

Your thoughts?

  

[Gryphon Rider]

Gryph, this has always been my understanding: (really talking heat more than load)

The MAX PSI printed on the sidewall must take into account that a cold tire heating up will gain a few PSI (I rarely check pressures hot, but it seems to only go up 4-5psi) (not talking full load semi tires, but bikes and cars).  

I really doubt tire manufacturers would print a max psi on the sidewall that required consumers to do the math and testing to discover how many more lbs the tire pressure goes up when fully heated up and then to reduce pressures accordingly from max psi, so it is never exceeded, however hot.  Esp with all the liability issues and giant class action lawsuits against them in years past (see the Firestone 500 story).  And tires should/must be checked cold, not hot, as a base constant.  Whether or not this is optimal for wear, stopping, handling, etc, it seems to me running a max psi printed on a sidewall (checked cold) should never be dangerous for any reason.  (Not optimal does not equal dangerous)

I do think one should not exceed max psi on the sidewall (cold), and it should be taken as the upper limit when deciding what pressure is optimal for wear, stopping and handling.  

My experience is that car and bike manufacturers tend to recommend lower than optimal psi based on their own liability concerns, and better wear and handling are achieved somewhere between their recommendation and the max psi printed on the sidewall by tire manufacturers.

Better stopping may occur at a bit lower pressure, but being at or near max psi never caused my bike to slide (with good tread on any tire).  

Your thoughts?

I agree, check the tire pressure cold and don't worry about the increased tire pressure as it heats up from use, or from sitting in the sun.  To try and guess differences in traction at different pressures and temperatures is more than can be expected of anyone other than racing pit crews.  On clean pavement we (on Valkyries) run out of cornering clearance before we run out of traction, even with tires inflated to maximum, and as far as braking/acceleration traction vs. tire pressure is concerned, I'll let someone else produce the data.

[gordonv]

Also, who cares what the manual says the max air preasure should be, it ONLY applies to the OEM tire that was on the bike when it was first sold. Who is still riding on that same tire?

Who knows if that same tire sold today has the same PSI max rating printed on the side?

It's already been said, manufactures tell us to check the psi when cold. You can top it up to the max. They know it will increase by a max of 5psi when hot, and have taken that into consideration.

My 88' GW, I pulled a E2 off of it. Are they even still available? Went to an Austone TT and getting a Bridgestone Excede Max for the front.

[Gryphon Rider]

Also, who cares what the manual says the max air preasure should be, it ONLY applies to the OEM tire that was on the bike when it was first sold. Who is still riding on that same tire?

Who knows if that same tire sold today has the same PSI max rating printed on the side?

Most of the time you want to use the vehicle's tire inflation sticker, not the maximum pressure indicated on the sidewall, to determine the correct pressure for the same size of tire, regardless of manufacturer or model of tire. A particular tire could be used on many different vehicles, each with different recommended pressures. There are special cases, like with our Valkyries, where a plethora of user experience has determined that a different pressure works better. This is an exception, not the rule.