Tank Slapper or Head Shake on Supermotos

[Z3n]

Some say 690 SMC doesnt need a damper. I find that ridden on rough roads like Mines/Mt Hamilton/Santa Cruz goat trails hauling ass the GRP damper I have on, has saved me from many a tank slappers and jolts from fucked up pavement while leaned over. Its peace of mine
I've ridden it without damper speed over 100pmh with no headshake at all. Might have to put a little more weight on front tire to prevent the shakes like coming over turn 10 I think @ Thunderhill.

I also have a street legal 450 EXC i converted to SM that used to get shaky and squirrly on the tight twisties cause I wasnt riding it SM style I rode it more sportbike style which doesnt work tooo well with dirt bike suspension. I added GRP damper and road it SM style now it is solid on any corner.
Definitely need to have your suspension set up , if your suspension isnt set up properly all the steering damper and fancy shit you put on isnt going to help you feel confident on the bike.

I had the opposite experience...my 690 was rock solid anywhere. My DRZ400SM (converted S model) was unstable in a lot of places though...S and SM models have different offset on the triples and geometry setup.

Headshake problems are almost always related to either tire wear/pressure/profile, unbalanced tires, suspension setup, or some combination of the 3. You'll get headshake on anything that'll transfer a significant amount of weight back on the throttle, especially if you weight the bars too much.

On the triple digits, my KTM hit a solid, verified 116 at the track. Dead stable.

 

[Gary856]

My DRZsm is awesome on any goat road in the SC mountains, so I thought it would be great going over 17 too. Wrong! From Los Gatos going uphill on 17 toward Bear Creek Rd, the DRZ feels surprisingly stiff and nervous at 60-65 mph. When I rode the same route on my YZF600R, it felt totally planted and so much better!

On a flat freeway, the steering of the DRZsm also feels a little twitchy. Now and then I would grab the bar and give it a slight shake on purpose to see what it would do, and I would feel the whole bike twitching. It's not a real problem to me; it's just feels different from "regular" bikes.

 

[EEEliminator]

Own at least two bikes.

I've had 2 bikes before the only problem is I only rode one, maybe they were too similar. 1000cc sport bike and a tard are pretty different, so...

I had the opposite experience...my 690 was rock solid anywhere. My DRZ400SM (converted S model) was unstable in a lot of places though...S and SM models have different offset on the triples and geometry setup.

On the triple digits, my KTM hit a solid, verified 116 at the track. Dead stable.

I'm interested in the KTM 690 although I don't know how it would hold up in daily use. From what I've been reading they seem to have a lot of little quirks, nothing major though. That fact that it looks to be discontinued is a bit of a turn off though. I don't think a DRZ is going to have the power I'm looking for coming off of a newer liter bike.

 

[kingmoochr]

I need to figure out if I want something for tight twisty roads and around town riding vs something that can handle extended periods of time on the highway and long sweeping turns. Given the degrading road quality on many roads and lack of interest in triple digit speeds makes a motard intriguing.

I have no problem pushing my 630 under me or leaning off in the fast sweepers from San Gregorio going up to La Honda (granted I have never done those at ludicrous speed, on my 996 or any other bike - 80/90 max). Bike feels perfectly stable at 80 miles an hour on 101, 1, and 280. I've got more practice now, but I definitely feel more comfortable going up the rest of 84, and I am doing it faster than I was.

Can you pin it at 60 and be at 100+ in 2 seconds? No, its not that bike. Can you ride down 5 to LA and not want to kill yourself? No, its not that bike (granted, there are lots of TE630 owners who have taken them great distances). Can you reasonably, comfortably ride to any fun roads in the Bay Area? Yes, it does that fine. Can you tear up any fun road in the Bay Area as fast/faster than a sprotbile? Most definitely, it IS that bike. You can even commute on it if you don't mind being a sail on the freeway.

This is my experience with the SMS630. Just as the 650R/GS500 != a CBR/GSXR, not all supermotos are created equal. There ARE ones that will do what you want. Don't buy a converted dirt bike. Go for a 600cc, non-race spec factory sumo and you have the best bike for all sorts of fun in the Bay Area. You can even track it for 40 bux a pop at Infineon arty

 

[ScottRNelson]

Interesting that this subject should come up on the eighth anniversary of my tank slapper crash.

I wrote about it at the five-year anniversary. That might provide some insights into what can cause a tank slapper, for those who are interested.
http://bayarearidersforum.com/forums/showthread.php?t=268088

I'm still crash-free. arty

 

[Z3n]

I've had 2 bikes before the only problem is I only rode one, maybe they were too similar. 1000cc sport bike and a tard are pretty different, so...



I'm interested in the KTM 690 although I don't know how it would hold up in daily use. From what I've been reading they seem to have a lot of little quirks, nothing major though. That fact that it looks to be discontinued is a bit of a turn off though. I don't think a DRZ is going to have the power I'm looking for coming off of a newer liter bike.

http://www.advrider.com/forums/showthread.php?t=566295

2 guys with 37k on their 690 enduros they're riding RTW...no serious issues that weren't caused by them, and they're not even using the expensive oil.

The DRZ will feel a bit like a scooter, although I won't deny that that is part of the appeal.

I rode my 690 750 mile days, no problem. The PO did an 850 mile day on it. I sold it with 12k and fully expect that it would go 50k no problem.

 

[russ69]

Headshake can be caused by many things. On the V-Strom, it can be caused by the unfortunate combination of:...

A head shake (not a wobble or a weave) is usually caused by a lightly loaded front wheel. The cure (if there needs to be a cure) is to put more weight on the front, that can be done a number of ways. Less gas, raise rear ride height, lower the front, more rear spring, more rear compression damping, etc.

 

[ScottRNelson]

A head shake (not a wobble or a weave) is usually caused by a lightly loaded front wheel. The cure (if there needs to be a cure) is to put more weight on the front, that can be done a number of ways. Less gas, raise rear ride height, lower the front, more rear spring, more rear compression damping, etc.

Those solutions don't help much when it is caused by going over some sort of bump that temporarily gets the front wheel off of the ground. Especially if it happens during acceleration.

 

[stan23]

The geometry on supermotos and lightness of them will always feel a little uneasy when going in a straight line at high speeds. That's normal.

Every SM i've ever owned was a little nervous going 100+mph on a straight line. I wouldn't call it headshake, but if you slap the bars hard enough, it's pretty easy to induce a nerve racking experience.

 

[louemc]

A head shake (not a wobble or a weave) is usually caused by a lightly loaded front wheel. The cure (if there needs to be a cure) is to put more weight on the front, that can be done a number of ways. Less gas, raise rear ride height, lower the front, more rear spring, more rear compression damping, etc.

What is this "less Gas" thing, spoken of?

 

[Wack]

I had the opposite experience...my 690 was rock solid anywhere. My DRZ400SM (converted S model) was unstable in a lot of places though...S and SM models have different offset on the triples and geometry setup.

Headshake problems are almost always related to either tire wear/pressure/profile, unbalanced tires, suspension setup, or some combination of the 3. You'll get headshake on anything that'll transfer a significant amount of weight back on the throttle, especially if you weight the bars too much.

On the triple digits, my KTM hit a solid, verified 116 at the track. Dead stable.

My 690SM has 2" less travel then the SMC but no head shake issues under any condition encountered so far. The 690's are lardier then the race reps with plates but go 3,000 between oil and filters and 6,200 between valve adjustments. Tom at Moore and Sons thinks that the 690's will be good for at least 60,000 miles, I'm 25 percent of the way.

 

[Z3n]

My 690SM has 2" less travel then the SMC but no head shake issues under any condition encountered so far. The 690's are lardier then the race reps with plates but go 3,000 between oil and filters and 6,200 between valve adjustments. Tom at Moore and Sons thinks that the 690's will be good for at least 60,000 miles, I'm 25 percent of the way.

My guess is a slightly more conservative 50k, but I still think the 690 engine will do the distance!

No question though, the 690 SMC is the best street sumo available. More HP than most of the race reps, more weight, but long intervals and a rock solid engine.

 

[russ69]

Those solutions don't help much when it is caused by going over some sort of bump that temporarily gets the front wheel off of the ground. Especially if it happens during acceleration.

Yes, there will always be a condition that will excite a head shake. However, I have seen more than one rider/tuner ignore the obvious problem and end up on the ground. If you can apply a solution to reduce an issue you are better off. Even on the street, you will save some skin if you try to find a workable solution. If your bike shows a tendency to shake it's head, please do something before you end up having a big "moment".

 

[ratpick]

Own at least two bikes.

You sir are a GENIUS!

 

[Dr. Evil]

Bike mass and mass distribution are also a factor in headshake. True supermotos have to be going pretty fast and vibrating pretty hard to headshake, because there's comparatively little mass and inertia with respect to something like a Dorsoduro or Hypermotard.

 

[corndog67]

I've got an XR650L that has been lowered 2 inches, came with a 19"/17" combo on the wheels, the guy I bought it from was worried about putting a 17 on the front causing it to be too twitchy, but I did anyway, and it's a little nervous on the freeway, but it's never shook on me. But it's an XRL, so it doesn't have the quickest steering to begin with anyway.

 

[rrrdbw]

My guess is a slightly more conservative 50k, but I still think the 690 engine will do the distance!

No question though, the 690 SMC is the best street sumo available. More HP than most of the race reps, more weight, but long intervals and a rock solid engine.

They crash very well also.

 

[1RUN]

Hahahahaha hypermotard is not a true motard.

this ^

 

[louemc]

Hahahahaha hypermotard is not a true motard.

Everyone is free to have an opinion on that...But..."True"?...

Motards are very size-able, to the track they are used on...
Motards that are sized to a little track that's set up in a parking lot with excursions into dirt sectons on the side of the pavement....are not the same motard that rocks the back roads.

It shouldn't take a Rocket Scientist to keep the Rocket in the Crotch Rocket.