Jump to content

tank slapper


Recommended Posts

Took my '03 HD in for service today. For a loaner motorcycle, I grabbed a fellow officer's '09 FLHP. He is reassigned to another shift so his bike is seldom ridden. A little background on this bike. New, in-service 6 months ago, 4500 miles, 96 cubic inches, six speed, ABS along with HD's new for '09 FL frame. This frame features a redesigned, stiff chassis and the now trendy wide rear tire. I noticed the front, original tire was heavily cupped with wear bars showing in the low areas. No damage history that I know of. Bike is flawless and under warranty.

I barely could pull out of the parking lot, I thought the bike was going to pull me over. Steering is very heavy and the steering wanted to throw me to the pavement during low speed turns. Checked air pressure and found pressures were 10 pounds low. Inflated tires and rode it again. The handling improved but steering still very heavy, lots of counter steer needed while leaning. It felt as if I let go of the bars while leaning, the front end would immediately turn full lock. No inherent stability like my '03.

Rode on a smooth straight roadway and noticed the tires sang and buzzed like snow tires, especially during braking. Steering becomes more stable at higher speeds. Steering still felt funny though. Something not quite right.

While in third gear, 40 mph, I let go of the handlebars with the throttle closed. As the bike slowed between 40-and 35 mph, an oscillation slowly began which became progressively more intense as the front shimmied back and forth. Only grabbing for the wildly out of control bars regained control of the front end. Did it a few more times and each time same results, bike would have gone down with a wild tank slapper if I had not grabbed the bars to stop the oscillations.

Took it back to the dealer where my '03 is being serviced. Service manager said it could be a loose steering head. He too was concerned about the unusual front tire wear. He suggested I continue riding it and swap it out for my '03 when it is finished. He admonished me not to let go of the handlebars in the meantime.

Any suggestions from motorcycle engineers as to what is going on here? I am aware of rake, trail in the design of motorcycle steering. Is this an inherent design flaw or something else. I did not notice or feel any clunks or noises in the steering head while riding.


Link to comment
Paul In Australia



I think the front tyre is telling you something for sure. maybe a front wheel not quiet round or out of shape? Or maybe the bad cupping ( due to long tme under inflation) produces this oscillation on this model.



Link to comment
Dennis Andress

I like the service managers about a loose steering head. Front to rear wheel alignment is something I'd check too. Bottom line for me is to have these things checked ASAP. How do you feel about riding a cage until your bike is ready?



Link to comment

Wheel ballance is what sticks in my head. It'll be worse at certain points while not noticible at others. I know from cages that front tires out of ballance seem fine at 80 or 82MPH. Get down around 65 and they can feel like they'll rip the front end off.

Link to comment

Bob, lots of bikes will go onto a front wheel oscillation at a specific speed range.. Front tire wear might have been the driver on that particular bike but it wouldn’t have gone into a wobble if the bike didn’t have a natural tendency in that tire rotational RPM & speed range..


As the service manager suggested it might have had a loose steering head bearing as that can add to the wobble.. Again it wouldn’t go off there if the bike didn’t have a natural tendency in that speed range..


My personal GoldWing (as well as a lot of others) have a VERY BAD front shake at 40-45 mph.. If allowed to go unchecked it will quickly turn into a tank slapper (I have had that happen a few times).. The bike will wildly jump up & down as the bars slam from lock to lock.. The bike won’t go down but it is very difficult to hang on wile it is jumping around as you can’t re-grab the bars as they have just too much energy to grab while slamming around..

If I can get to the rear brake & dump off a little speed it will quiet right down like nothing happened.. Same with speed up a little (can’t get to the throttle with the bars jumping around though).. Honda’s fix (if you can call it that) is to add tapered roller bearing in the steering head & tighten the hell out of them.. My contention is: bearings are meant to be bearings & not friction brakes.. I have lived with the front end shake for many many mile & just don’t let go of the bars at 40-45 mph.. Otherwise you can ride it for miles no handed at 100+ mph.. I guess I would rather have the problem at 40-45 mph than 90 mph..


If you get a chance ride another newer Harley with better tires to see if they all do that or just that one.. I have a little older ElectraGlide & it also has a front end oscillation & that one is at 85-88 mph.. Not a tank slapper type but a fairly slow side to side waddling type oscillation that always feels like it could get worse at any second but never does.. If I tighten up on the bars it does get worse though, as long as I stay loose it just walks around a little but never gets any more severe.. At a little over 90 mph it cleans right up..




Link to comment

I contend that many bikes/models will show head shake when the throttle is "chopped" at 40 mph (or there abouts) when no hands are steadying the bars. My '85 R80RT would do this with either worn front tire or brand new rear with average front tire. I replaced (well, had the dealer replace) the steering bearings and had my metal bending cousin make me a special 35 mm box wrench (cut tool kit's wrench in half and welded a 3/8 inch drive socket) so that I could torque steering bearings easily (without removing handle bars).

Funny the Alb dealer, when I first reported this (bike was newish and warrenteed), gave the same advice as yourself, i.e., "keep your hands on the handlebars". Just the same, knowing that it would only happen with "chopped" (suddenly closed) throttle gave me a little piece of mind.


Best wishes and watch out for the two wheeled bucking broncos,


Link to comment

A badly cupped (fat) front tire on a heavy bike will exhibit all the conditions you described. Chances are the previous rider neglected tire pressures for such a long period of time that the tire is now junk.


Replace it and re-ride. I'll bet your conditions improve.


Hard to believe steering head bearings alone. You can check by centerstanding the bike and push bars from lock to lock. Notchiness or play in steering indicate such a problem. You may also notice clunking from the steering head area, even while on the road going over road irregularities. Perhaps factory forgot preload on the bearings, if applicable.


Not familiar with the HD, so just general info Bob.


Good luck, and hold on... :grin:



Link to comment

It is the tire, coupled with the front end geometry. Seems to have some relationship to rake and trail and what is strange is it only happens under trailing throttle. I have had any number of bikes do this to me. Even those equipped with a steering damper.


High mileage bikes sometimes get notchy steering head bearings but that is more the cause of high speed wobbles than this particular thing.


Going back to the root cause, a badly cupped tire doesn't grip the road like a new, round one will. It will grab differentially on the high spots and that can cause a reaction in the steering. 35-45 mph seems to be the key speed and most of the tires have pretty much the same rolling radius.


On my Sprint, the BT-020 tires would start to do this once I hit 6000 miles. The PR2s on there now don't do it even though they are over 15K miles at this point. They are cupped much less though.

Link to comment
My R1100RT would do that with certain tires when the front was badly worn and cupped like you described.


+1. I've had several bikes that did that with badly worn front tires.

Link to comment
  • 1 month later...
Thanks for the replies, I will let you know what HD does to fix the problem. My bet is on the tire too, we will see.


Ever find the problem?


My 09 work bike is close to 9,000 miles and both tires look great. Never noticed any wobbles, either...

Link to comment

The dealer put a new front tire on under warranty. It seemed better but I was glad to return to my '03. The bike could be a 103 too, might have been wrong about the 96. The bike is parked and used presently.

Link to comment
The dealer put a new front tire on under warranty. It seemed better but I was glad to return to my '03. The bike could be a 103 too, might have been wrong about the 96. The bike is parked and used presently.


That '09 is definitely a 103 as that's the only engine H-D has used in police motors since they went to the 96 in 2007. Whatever the problem is with this particular bike, the problem is not "inherent" to the new model/frame. I've ridden several of the new bikes and they didn't exhibit any of the issues you describe.

Link to comment

I had something like this on my 2005 1200RT and my post on the subject got similar advice to what you have had here. In my case the culprit was simply that the front tyre had worn down to the minimum 1mm but other members also recommended checking tyre pressures.........


I do not want to sound as though I'm preaching but there is another lesson here. With any pool car or bike it is worth assuming that someone has not been doing their "daily" checks (who checks tyre pressures daily anyway?). If you had come off the bike the first thing the department would carry out is a check on the bike and use the low tyre pressure and wear bars showing to argue that it shouldn't have gone out at all..... Don't know where you would have stood for any injury claim?


Case of real world meets departmental regs - and yes, there but for the grace of God go a lot of others.


Safe riding.



Link to comment


This topic is now archived and is closed to further replies.

  • Create New...