Front / Rear Weight Distribution

[spgtech]

Last Friday I was doing a trackday in preparation for the weekends racing and I had the front end washout. Specifically, I was doing fast for me but comfortable laptimes, was keeping stable lean angle, had started the roll on some time back, and was just at the apex of the corner when the front started skipping out and then let go at about 50mph.

 

As with the other front end washout I had earlier in the season, several people told me I need more weight forward, which seems contrary to the CSS teachings I've learned in Lv1-4. The local suspension guy did clarify it a little by saying that if the front end tucks, it is from too much weight forward, but if the front wheel skips or chatters that it needs more weight to keep it from understeering. It seems to me that if the problem is sheer lateral traction, that more weight is a bad thing, but I can at least wrap my mind around the idea that if the problem is vertical weight holding the front in contact with the pavement, that weight forward could work.

 

As before, bike is Ninja 250, so no throttle wheelies out of the corner to account for.

 

So, the question of the day (maybe more for the coaches) is how to incorporate some forward bias into the previously learned techniques (perpetual hook turning comes to mind), and if this is a direction worth exploring.

 

Thanks in advance for any input.

-Sean

[Adam06]

Hi Sean,

 

For the front to tuck whilst you were rolling on the throttle, some other input would have had to occured ie, a steering input, weight in the bars, a checking or rolling off of the throttle etc etc....

 

I don't have the book in front of me, but Twist of the Wrist II covers the technical side of this point in a chapter titled "Steer for the rear".

 

Do you have a copy of that book to refer to?

[spgtech]

Hi Adam,

 

Thanks for the reply. I do have a copy of the book and will re-read that chapter.

 

To be clear, the front did not tuck/turn in but rather started skipping and then let go. There wasn't much that was changing at that part of the turn as far as throttle, lean, or steering. Since I don't remember if it was that lap or one before, I might have "settled" my body position in and down (further off the bike) shortly before. SInce originally posting, I have also taken a closer look at my front tire and determined the edges have some flat spots worn on them and should probably be replaced.

 

I was more curious if a skipping front tire indicated need for more weight forward instead of less. Kind of challenging keeping everything balanced just so...

 

-Sean

[faffi]

Could the front fork have been fully extended or rebound damping be too firm? Both would prevent the wheel from following dips in the road, which again will cause a lack of grip in a grip/slip manner.

[spgtech]

Rebound was if anything, a little on the soft side, and I think the fork was where it should be (mid travel), but I suspect it quickly went to full extension as it started to skip. I remember looking down and seeing my front wheel moving away from me and thinking "oh sh.." just before it let go.

-Sean

[Hotfoot]

Last Friday I was doing a trackday in preparation for the weekends racing and I had the front end washout. Specifically, I was doing fast for me but comfortable laptimes, was keeping stable lean angle, had started the roll on some time back, and was just at the apex of the corner when the front started skipping out and then let go at about 50mph.

 

As with the other front end washout I had earlier in the season, several people told me I need more weight forward, which seems contrary to the CSS teachings I've learned in Lv1-4. The local suspension guy did clarify it a little by saying that if the front end tucks, it is from too much weight forward, but if the front wheel skips or chatters that it needs more weight to keep it from understeering. It seems to me that if the problem is sheer lateral traction, that more weight is a bad thing, but I can at least wrap my mind around the idea that if the problem is vertical weight holding the front in contact with the pavement, that weight forward could work.

 

As before, bike is Ninja 250, so no throttle wheelies out of the corner to account for.

 

So, the question of the day (maybe more for the coaches) is how to incorporate some forward bias into the previously learned techniques (perpetual hook turning comes to mind), and if this is a direction worth exploring.

 

Thanks in advance for any input.

-Sean

 

I'm curious, on what track and which turn did this occur? Was there anything on the track surface, like bumps, ripples, or seams that would have affected front wheel grip, or exercised the suspension? Was it downhill, off-camber, or did it have a change in camber? It sounds like you are looking for a more general solution but I still don't feel like I understand what caused the washout this time, or last time.

 

In regards to your suspension, does your bike go where you point it, and hold a consistent line, or does it have any tendency to want to run wide? When you do a hook turn, do you get a noticeable hook or not get much of a response from the bike? Do you feel like you have to hook it all the time to hit your apexes or exit point?

 

Were both of your washouts in left turns or rights, or was it one of each?

[Cobie Fair]

Hi Adam,

 

Thanks for the reply. I do have a copy of the book and will re-read that chapter.

 

To be clear, the front did not tuck/turn in but rather started skipping and then let go. There wasn't much that was changing at that part of the turn as far as throttle, lean, or steering. Since I don't remember if it was that lap or one before, I might have "settled" my body position in and down (further off the bike) shortly before. SInce originally posting, I have also taken a closer look at my front tire and determined the edges have some flat spots worn on them and should probably be replaced.

 

I was more curious if a skipping front tire indicated need for more weight forward instead of less. Kind of challenging keeping everything balanced just so...

 

-Sean

 

Sean,

 

I'm interested to make sure we really get the correct reason for this.

 

Definitely raises some questions, and Hotfoot asked a few, answering those to start could help narrow this down. Interesting that you bring up this point as I just had a converstaion with Keith on this subject...another rider was concerned about losing the front (had done so in a very fast turn). My first questions will be: what lap was this in the session, did it happen the lap before, was the pace the same (as far as you can tell)?

 

Body positioning can change the weight bias on the bike, but we were just measuring it yesterday, and a rider moving around (dramtically) makes a pretty small change in the overall weight--like less than 1 per cent on a liter bike.

 

Shoot us some more info on this, let's see what we can sort out.

 

CF

[Crash106]

I have a theory (and with my theory and five bucks, you can buy a cup of coffee). Anyway, here goes. You said, "... (I) was keeping stable lean angle, had started the roll on some time back, and was just at the apex of the corner when the front started skipping out ..." (emphasis added)

 

Is it possible that you did a great job of rolling on the throttle and had, in fact, taken the bike to the limit for speed, lean angle and traction? Then, because it is so natural that you almost can't help it, you tipped the bike in a little at the apex? If you were nice and smooth and stable, you might have been comfortably at the limit of traction, then almost unconsciously asked for just a b-i-t more lean angle at the apex.

[Crash106]

Oops. Never mind.

[spgtech]

 

I'm curious, on what track and which turn did this occur? Was there anything on the track surface, like bumps, ripples, or seams that would have affected front wheel grip, or exercised the suspension? Was it downhill, off-camber, or did it have a change in camber? It sounds like you are looking for a more general solution but I still don't feel like I understand what caused the washout this time, or last time.

 

In regards to your suspension, does your bike go where you point it, and hold a consistent line, or does it have any tendency to want to run wide? When you do a hook turn, do you get a noticeable hook or not get much of a response from the bike? Do you feel like you have to hook it all the time to hit your apexes or exit point?

 

Were both of your washouts in left turns or rights, or was it one of each?

 

 

Hi Hotfoot,

You and Cobie will probablyget a longer answer that you hoped, but here goes:

 

The track is Pacific Raceways near Seattle, (the old SIR). It was in turn 9 which is a long LH sweeper, no camber, old pavement with exposed rocks like marbles, surface is a little bumpy but nothing horrible. Others do go around it much faster than I do, I am still building speed slowly. The race winners in the 250 class are occasionally hitting 1:48s I hit a 1:57 in my last race (for a 2.25 mile 10 corner, reasonably techincal track). This was a 70 degree day, on a trackday and I was having a good session. I had done several :57s and a :56 in the lap before the crash. I had smoothed out my lines on the backside of the track so the laps felt pretty easy.

 

The washout last time occured when the track was not wet but not fully dry, on a 45 degree morning and I was on my dry tires. On my 4th lap (with pre-warmed tires) I quick flicked it into turn 6 (right hand) and the front tire never grabbed, the bike went straight to the handlebar and continued straight off of the track.

 

For the suspension, the bike is reasonably well setup, goes where it is pointed and responds well to hook turns. I don't always hit my apexes but it is a combination of either insufficient reference points for turn in, lazyness to make mid turn corrections, or not wanting to make lean corrections once I have started the throttle roll on. I would be very happy to lean more after roll on, but it is something I stop myself from doing since I have been told a few times that it is not a good idea as a result, I usually stick with the line and if it takes me a little wider, I usually have a bit of margin left. There are some areas of the track where I have had an awful time finding RPs which would help some of the above. Possibly equipment related, I was running my tires around 28/29 cold when others run as low as 25/25 (Bridgestone 003rs), and my tires have a bit of wear on the sides. I have since replaced them.

 

For general riding style, I am a huge fan of the CSS, 1 cheek off, lock onto the tank, sit back a little on the seat, quick flick in and relax the upper body to let the bike handle the rest. That said, this is my first season racing, and I have had several people including my assigned mentor (and the first place holder in the 250 class), tell me that I need to get further off the bike, and that I need to get my weight forward to keep the front from pushing. In my 6 days down at Streets and my races since, my knee has never touched down. Close but not there yet. As a result, I have been experimenting with slightly further off the seat, knee against tank, calf on bodywork, weight a little further down and slightly forward. Mostly I don't feel as comfortable with it since my lock on is not as solid, and it is hard to stay relaxed on the bars, and it is hard to not use the bars a little bit to keep from rotating forward.

 

I would be very happy to revert back to the earlier BP, trust the bike to lean a bit more and figure my knee will touch down with more lean angle when it's good and ready.

 

Current goals are:

Not wash out the front again anytime soon

Maintain a stable BP with stable weight distribution

Get a knee down for the additional angle reference and stability it affords when sliding

Drop my laptimes 5 seconds by the end of the end of the season

 

Re-reading TOTW2 and re-watching same, there is an emphasis on not hanging off too much because it tightens the rider with all the associated problems. I know the bike recovers from slides much more comfortably for me if I'm not too far off, and I cannot ride as relaxed with the deeper hang-off.

 

In an earlier thread, (when I dropped it before); http://forums.superb...?showtopic=2921, I posted a picture of the hang-off style which is winning the races. Those bikes are pretty uprignt and I do have a certain curiosity if I can hang off less, and still get the knee down before running out of traction. I also know of another rider who rode the winners bike, and indicated that the front started to chatter, and that they had to shift their weight forward to stop it, when on their own bike they would usually move weight back to stop it. Same make of bike but different tires and suspension setups.

 

So, my current plan is based on the assumption that I ride better with the CSS method, and that it does make sense to me. So, next weekend at PortlandI will try:

A new front tire in a stickier compound (for confidence, my last get-off hurt)

A smooth, fast and grippy track (PIR)

A more moderate BP

More lean angle as necessary

Try to have the tires and the knee on the ground at the same time

 

Cobie; to put the fore/aft weight shift in perspective, I am talking about the difference between butt settled back in the seat, inside knee out to the side, outside knee in the tank cutout, vs: thigh up against the tank, inside knee slightly forward, outside knee off the tank and upper body in a nice hook turn position. Hard to believe it is only one percent, but I would agree it's subtle. Still seems like throttle would make more difference, but the winning riders go through a lot of corners (including some turn ins) with the throttle opened or pinned. Maybe there is a point where the forward weight counters a greater than ideal roll-on?

 

Thanks to all for your ideas.

-Sean

[Hotfoot]

OK! All that information DOES help, a lot. Your post was very informative, and leads me to some more questions.

 

First, have you ever tried lowering the front end of the bike a bit? If you are having a bit of trouble consistently getting to your apexes, and finding yourself wanting to lean it over a bit more after getting on the throttle, and hooking it often, it makes me wonder if you are fighting a bike setup issue where the front end is riding a little high, making the bike less responsive on steering (and, maybe, not carrying enough weight in front). Really this is something you would just have to experiment with, slide the forks up in the triple tree a little, and ride it, and see how it feels. If you get it too low, it may start to feel twitchy or you may get headshake. A lot of it is personal preference, my husband likes a very stable bike that takes a lot of effort to turn, and I like mine so quick to steer that he finds it scary and unstable to ride. But in my mind, lowering the front would have a LOT more impact on getting more weight on the front end than making adjustments in your body position.

 

Second, what kind of suspension adjustment do you have available to you on this bike? I imagine you have explored these things already, but I'm going to ask anyway: is there any chance you are bottoming out your suspension at turn-in? That could certainly cause you to lose tire grip at the entry or maybe even later in the turn, especially if you are on rough track surfaces. Also rebound settings could be a factor - if the rebound is too slow and compression too soft the front could "pack" with a series of ripples and bottom out. Conversely, if rebound is too soft (too quick) it could pop up when you release the brake (as an example) and/or pogo up and down through the turn, compromising your tire grip. Either of this scenarios (high in front or suspension adjustment) could also account for difficulties with quick transitions, which I think you've mentioned in a prior post were a challenge.

 

I've been checking around a bit on this idea of there being "not enough weight on the front"; all the info I have found so far seems to come back to the idea of either a problem with the bike's attitude (too high in front or too low in back) or a suspension issue (front end bottoming out, or some other suspension component at the extreme top or bottom of its range, or some overreaction like a bouncing-around problem).

 

I don't think anyone will be able to give you a solid answer of WHERE to put the front height, you will just have to set aside some practice time to try it a few different ways and find what suits you. Lowering the front will reduce your ground clearance a little, but it doesn't sound like that has been an issue for you - plus it might help you get your knee down.

 

So maybe you're bike just needs an ATTITUDE adjustment. Have you tried having a stern conversation with it? Tell it if it doesn't knock this S**t off right now, you're going to trade it in on a new S1000rr. _

[spgtech]

"Have you tried having a stern conversation with it? Tell it if it doesn't knock this S**t off right now, you're going to trade it in on a new S1000rr. _"

 

Hi Hotfoot,

I think you have a winner there! But, I think before I go down the road of, "it's not me, its you..." with my motorcycle, I should make sure it's true

 

So, to answer your questions in no particular order:

 

The fork telltale showed approximately 8mm of travel left before they would bottom out. That said, our suspension guy (Barry of KFG / GP suspension), thought I should have more high speed compression and revalved my forks after the crash. The forks are not externally adjustable but are cartridge forks with shim stacks, so they can be pretty finely tuned. I think the rebound is a little fast, and have noticed the forks shooting out after trail breaking into a corner. Oddly, Barry thought that they were probably not to far off, and that while we would want to slow them down in the warmer weather, he would rather see them too fast than too slow. He also looked at the bike and wanted to leave the fork height in the triples alone (probably 3mm lower front end than stock), but had me lengthen the rear shock by about 4mm, which would add 5/8 inch of height in the rear. It didn't feel particularly good or bad in the next two races, but I since found my forks still had some twist in the triples (my fault), and a big slide in a wet patch halfway through the first race kind of reduced my comfort level for the rest of the day.

 

The bike tends to be on the easy initiation/nervous side, but it wiggles a bit and stops, it doesn't get worse and work into tank slappers or anything. Mostly there is a fair amount of frame flex which is not altogether bad, but takes a little getting used to. I resisted steering dampers until last session. I generally feel that anything which reduces the ability of the bike to sort itself out is not good, but Barry likened it to wearing earplugs when you ride. Just to "quiet things down a bit" and allow the rider to concentrate on other things. I gave it a try and do like it so far, but a little damping goes a long way.

 

I appreciate you checking around about the forward weighting. Perhaps the seemingly universal adherence to its importance that I'm exposed to, could be a very localized phenomenon.

 

Also, to complete the picture, the following link has some pictures from last months racing which show my generally low key BP...

 

http://www.darrenbeattyphotography.com/WMRRA/5-1-11/900/16880620_BHgMzL#1276460198_CmsZ4ZV

 

Thanks again for the reply.

-Sean

[Cobie Fair]

I'm a bit behind on this discussion now, but a few points:

 

What's the reason you are being told you need to hang off more? Are you running out of ground clearance?

 

The washout you had: cold morning, some moisture (possibly on the track), pre-warmed tires will cool down some, and it was a right hand turn on a left hand track...do I have that correctly summarized?

 

Is this more difficult than "tire not fully warmed on that side?" There are many tracks on cold days that have little time on one side, and the tire never warms all the way. I'd consider this, let me know what you come up with.

 

Chattering front: for sure talk to the guys at GP, but 1 riding question: does it happen all the time (in the same turn), at the same pace?

 

Best,

Cobie

[spgtech]

I'm a bit behind on this discussion now, but a few points:

 

What's the reason you are being told you need to hang off more? Are you running out of ground clearance?

 

The washout you had: cold morning, some moisture (possibly on the track), pre-warmed tires will cool down some, and it was a right hand turn on a left hand track...do I have that correctly summarized?

 

Is this more difficult than "tire not fully warmed on that side?" There are many tracks on cold days that have little time on one side, and the tire never warms all the way. I'd consider this, let me know what you come up with.

 

Chattering front: for sure talk to the guys at GP, but 1 riding question: does it happen all the time (in the same turn), at the same pace?

 

Best,

Cobie

 

 

Hi Cobie,

 

I think I'll have to chock up the first washout to the "...can we quick flick on a cold track or if the track is wet?....NO!..." I was still not on any record setting pace, but it is a series of corners which can all be taken without ever backing off of the throttle, so I think I quick flicked a transition, in questionable conditions, while accelerating through the corners (and therefore not adequately loading the front).

 

Latest washout, probably 6 laps into the session, on warmed and warm tires. After a lot of thought, and with a bit of hesitation, I'm leaning towards a combination of; worn front tire, 5 psi too high of pressure, even speed through the turn, and something to upset the bike (most likely some movement or not being fully relaxed on the inside bar). The throttle was cracked open, but the gps track from my lap timer shows a pretty constant speed in the corner. I got on the gas early, but the corner takes probably 5-6 seconds to complete, and I may not have been maintaining enough acceleration to keep the weight back, and may have overloaded what little front tire contact I had.

 

As far as hanging off more, no, I am nowhere near running out of ground clearance. I think it is well intentioned "advice" based on me not having my knee anywhere near the ground, and being slower than the race leaders. There is also a prevailing opinion that being on the gas without a corresponding forward weight shift will understeer the front and push it wide in the corner (obviously once you break the back end loose it's a different discussion). I generally disregarded this front weighting and figured that it made little sense to me, but after having the front push out of a corner, I felt the matter deserved a little consideration, even if it doesn't make a lot of sense to me. When my suspension guy said "tucking the front is too much weight forward, pushing the front is not enough...", that was at least some supporting information, from a different source, who has many race wins to his credit over the years.

 

And no, that didn't happen every lap in the same place. I actually though I was taking a pretty easy lap and going a very comfortable speed in the corner; then it went push-push-push-release in less than 1/2 second.

 

Thanks for the input.

-Sean

[Cobie Fair]

this is what I'd look in to:

 

(most likely some movement or not being fully relaxed on the inside bar).

 

CF

[spgtech]

this is what I'd look in to:

 

(most likely some movement or not being fully relaxed on the inside bar).

 

CF

 

Yes, I find that adjusting the nut behind the handlebars is usually the best place to start...

 

-Sean

[Jasonzilla]

It's always struck me as weird that too much weight on the front tire is what makes it go and people always say you need to weight the front more.

[bradvanhorn]

It's always struck me as weird that too much weight on the front tire is what makes it go and people always say you need to weight the front more.

I know there are situations where getting the front too light can cause problems, but I kept having nearly the same thought as you. Why get more weight to the front unless the conditions are getting the front way too light, as opposed to keeping with the more CSS textbook 40% - 60% front to rear (once on the gas in the corner)?