Front Vs. Rear Weight Distribution

[spgtech]

So, I have started racing 250 Ninja's, and have taken some CSS schools. After the last race weekend, I was about 9 seconds a lap slower than the race leaders, and I was feeling pretty stable with my level three body position, and throttle roll on for a nice rear weight bias.

 

After reviewing the video footage from my bike and of the winners bike, and also talking to my Novice Mentor (the race winner incidentally), I have developed some confusion over the ideal weight placement. Specifically, the 1st and second place riders are using a very old school, crossed up style. This is said to be done purposely to get their weight forward to keep the front wheel from pushing out of the corner. While I understand that a forward weight transfer gives more lateral force on the front wheel, it also gives more downforce and traction as well, so some good along with the bad. Since the bike only has 30 horsepower, the roll on gives a nice weight bias, but not much more for exit drive. As a result, there is an effort to maximize speed throughout the entire corner, which may require a different riding style than with a more powerful bike.

 

For the most part, I figured that I was happy working along with my current course, and leaving the front wheel riding to others, I have two reasons that this has caused me some deeper thought.

 

First, these guys are darn fast.

 

Two, on the colder Seattle track, my rear tire looks like I have just been riding around the street. Not much shredding at all, and much "nicer" looking than it was after a day at Willow. The front however looks very chewed up, and with a little more of a glossy, melted appearance, this looks far worse than it did after several days at willow. This is causing me to wonder if I am starting to work/slide the front, and if there is some change I should make to my riding style to even out the workload.

 

Again, the default action is to continue with the rear bias, and wonder... That said, I am curious if there is ever a point where the increased traction of a front weight bias positively offsets the increased lateral force. If I had to guess, I would think that lean angles greater than 45 deg would favor the rear bias for front wheel traction, and more upright riding would favor the front bias.

 

Thanks in advance for any input.

-Sean

[bradvanhorn]

So, I have started racing 250 Ninja's, and have taken some CSS schools. After the last race weekend, I was about 9 seconds a lap slower than the race leaders, and I was feeling pretty stable with my level three body position, and throttle roll on for a nice rear weight bias.

 

After reviewing the video footage from my bike and of the winners bike, and also talking to my Novice Mentor (the race winner incidentally), I have developed some confusion over the ideal weight placement. Specifically, the 1st and second place riders are using a very old school, crossed up style. This is said to be done purposely to get their weight forward to keep the front wheel from pushing out of the corner. While I understand that a forward weight transfer gives more lateral force on the front wheel, it also gives more downforce and traction as well, so some good along with the bad. Since the bike only has 30 horsepower, the roll on gives a nice weight bias, but not much more for exit drive. As a result, there is an effort to maximize speed throughout the entire corner, which may require a different riding style than with a more powerful bike.

 

For the most part, I figured that I was happy working along with my current course, and leaving the front wheel riding to others, I have two reasons that this has caused me some deeper thought.

 

First, these guys are darn fast.

 

Two, on the colder Seattle track, my rear tire looks like I have just been riding around the street. Not much shredding at all, and much "nicer" looking than it was after a day at Willow. The front however looks very chewed up, and with a little more of a glossy, melted appearance, this looks far worse than it did after several days at willow. This is causing me to wonder if I am starting to work/slide the front, and if there is some change I should make to my riding style to even out the workload.

 

Again, the default action is to continue with the rear bias, and wonder... That said, I am curious if there is ever a point where the increased traction of a front weight bias positively offsets the increased lateral force. If I had to guess, I would think that lean angles greater than 45 deg would favor the rear bias for front wheel traction, and more upright riding would favor the front bias.

 

Thanks in advance for any input.

-Sean

I don't race, 250's or otherwise, but here are my first impressions:

- They ride crossed up to add more weight to the front to prevent pushing? My understanding is pushing is most often caused by overloading the front end. If there is a problem with pushing, why would you want to add more weight forward if the front is already overloaded? It seems to me you are daring to make the slide even worse.

 

- They are fast? No criticism of those riders, but just being fast does not mean it is being done most effectively. I recently quoted a former MotoGp world champion, someone who obviously can go fast, who thinks you can steer the bike with the footpegs. Most of us disagree, and believe the no-BS bike pretty clearly disproves the idea.

 

- Your front tire is shredded and your back tire is clearly not? It seems to me this follows in the same fashion as my first thought. You appear to be working the front very hard, and the proposed solution is to add more weight forward and work the front tire even more? My thought is just the opposite, get more weight to the rear.

 

Good luck

[Crash106]

Sean,

 

First of all, I'd like to complement your choice in racing bikes. Everything I've heard tells me the little Ninja is a very reliable bike. They're also affordable and light and don't normally shred a set of tires every time you take off the tire warmers. I don't race either, but like to think I would have enough sense to start on the 250 Ninja.

 

Second, I agree with what Brad told you: your tires are telling you something.

 

Could you be over-braking? Are you turning with too much throttle on, or adding gas and lean angle? Could you be carrying too much weight forward, especially when braking hard? Are you waiting too long to roll on the throttle? Are you braking hard but stiff arming the bars instead of gripping the tank? Maybe it's something as simple as needing more room to slide your bum back when braking.

 

I imagine that choosing the Ninjet allows you more chances to ride and sort it out. I look forward to hearing what you learn.

[Jasonzilla]

I'm not sure that riding a 250 requires that grossly a different technique than the others. There has to be a reason your rear tire is looking good and your front is chewed, as was previously mentioned. You may want to look at where you're getting beat. If you seem to be making up time going into the corners and getting beat at corner exit, you could be burning into the corners, using the ever dreaded in fast/out slow technique. That would also explain the front tire being chewed and the time disparity you're dealing with. It could have you getting on the throttle later and sparing your rear tire. Also, if you're on the throttle properly, pushing the front OUT OF a corner should be the last thing on your mind.

 

I'd say stay with the proper body position as well. Being crossed up and weighting the front out of a corner isn't going to help any. While crossed up isn't good in general, weighting the front tire while giving a steering input will benefit you turning (making it quicker), while weighting the front during exit won't help you get out of the corner faster.

 

 

You can also be getting lazy on your quick turn. That could have you struggling to get the bike turned, causing it to push as you're trying to make the corner and even getting you stiff on the bars, then delaying your ability to get back on the throttle. My last experience at CSS taught me that we can get lazy on things when we don't pay that much attention to it during practice.

 

Any way you can post that video?

[Jasonzilla]

Sorry. Double post.

[faffi]

If you have enough power to seriously lift weight from the front tyre, it will unload and understeer. Climbing closer to the front wheel will increase the load again, allowing the tyre to dig in and deliver grip again. So it's a balance act between having enough weight on the front for the tyre to steer and enough weight on the rear to allow it to drive. Since modern tyres offer so much grip, chances are that the rear will have enough grip to unload - or even lift clear off the ground - the front tyre well before spinning out of control. Hence fast riders will try to shift their weight forwards when accelerating out of turns.

 

Why you front is chewed up is not something I can tell you. Perhaps taking a few pictures of it and post it in the Tires section would be a good idea; a skilled tyre specialist will be able to tell if the wear stems from wrong tyre pressure, poor suspension settings or even poor technique.

[fossilfuel]

I was very interested to read this about your problem with the front tire and weight bias....

"the 1st and second place riders are using a very old school, crossed up style. This is said to be done purposely to get their weight forward to keep the front wheel from pushing out of the corner" I would think if you want to prevent the front wheel from pushing out of the corner, one should decrease lean angle and the best way to do that is to get the riders weight forward and to the inside. It doesn't seem to me that the crossed up style is the best way. I suggest viewing Moto3 for reference.

 

"The front however looks very chewed up, and with a little more of a glossy, melted appearance, this looks far worse than it did after several days at willow. This is causing me to wonder if I am starting to work/slide the front, and if there is some change I should make to my riding style to even out the workload."

You said you were nine seconds a lap slower than the race leaders. What kind of tire issues are they having?

 

"This is causing me to wonder if I am starting to work/slide the front, and if there is some change I should make to my riding style to even out the workload." If you were sliding the front you would definitely feel it and you would not be nine seconds slower than the race leaders. Maybe it's a pressure or alignment issue?

[Jasonzilla]

Once we're in the corner, done with our initial steering input and on the throttle, the rear tire is doing the steering. That's easily demonstrated every time a rider is coming out of the corner, wheelies, and remains in a turning position. The rear tire is steering the bike. That's also why the rear tire is more chewed. Your issue is with the front having too much pressure. You'd really have to be riding poorly for corner exit and underweighting the front to be the issue here. Crash mentioned it could be because you are waiting too long to get back on the throttle, and that's the only thing I can see being an issue coming out of a corner having the front tire worn and not the rear.

 

Weight should be maintained by BP and is placed forward and down from initial steering on to help with the steering input, then kept there to not upset the bike while accelerating out of the corner, and maintaining a good balance between front and rear. Then it can be used as leverage to pick the bike up coming out (see pick-up drill). While it helps keep the wheel down some at this point, I don't see how good throttle control in this instance wouldn't be better advised than putting MORE weight on a tire that is obviously already being worn more than the rear. I'm not sure even sitting upright on a 250 (still bad BP) would get the bike to wheelie if you're applying the throttle correctly. Unless you want to. Then you'd still be putting more stress (read wear) on the rear tire.

 

Too much throttle will more than likely be the culprit making you run wide coming out of a corner than not properly weighting the front. Either way, you wouldn't be having the chewed up front tire issue from underweighting the front, as it would underweighting it means less pressure and less wear.

 

Eirik and Fossil brought up a good point: how's your set-up? Is your bike set up? Can you post pics?

[spgtech]

Thanks for all the replies.

 

Here is a picture of the 1st and second place finishers and the BP I was referring to. I'll try to get a picture of me up there sometime soon. I generally try for a 1 cheek hang off, use the hook turn position to get weight forward as needed, and generally keep my weight back and my knee stays off the ground.

 

I agree that what I have been told about the weight on the front to keep the front from sliding is something which makes sense when we are upright for braking or turn in, but seems to make less sense the more the bike leans over. While I have had some instances of the bike noticeably pushing the front, they are rare and usually relate more to track condition than other less noticeable influences. Pushing the rear out at the corner exit is much more common and comfortable.

 

Bike setup is decent, but I was running slightly lower (1psi) pressures than normal for the colder track. Running Brigestone BT003 RS tires, the Front 27, Rear 28 cold (I know it sounds backwards, but that gets them both up 4-5 psi when hot, higher pressures in front won't let it come up as much). Otherwise front comp/rebound is a little lighter than I might want, but close. Rear seems about right.

 

Mostly it was the combination of a faster rider mentioning that weight forward was important on the Ninjette, coupled with the difference in tire wear between the front and rear that left me a little confused. Usually my front tire looks pretty smooth and my rear looks like it has been pushed around a bit. Maybe it could be that my pressures were a little too low for the day.

 

-Sean

[fossilfuel]

Thanks for all the replies.

 

Here is a picture of the 1st and second place finishers and the BP I was referring to. I'll try to get a picture of me up there sometime soon. I generally try for a 1 cheek hang off, use the hook turn position to get weight forward as needed, and generally keep my weight back and my knee stays off the ground.

 

I agree that what I have been told about the weight on the front to keep the front from sliding is something which makes sense when we are upright for braking or turn in, but seems to make less sense the more the bike leans over. While I have had some instances of the bike noticeably pushing the front, they are rare and usually relate more to track condition than other less noticeable influences. Pushing the rear out at the corner exit is much more common and comfortable.

 

Bike setup is decent, but I was running slightly lower (1psi) pressures than normal for the colder track. Running Brigestone BT003 RS tires, the Front 27, Rear 28 cold (I know it sounds backwards, but that gets them both up 4-5 psi when hot, higher pressures in front won't let it come up as much). Otherwise front comp/rebound is a little lighter than I might want, but close. Rear seems about right.

 

Mostly it was the combination of a faster rider mentioning that weight forward was important on the Ninjette, coupled with the difference in tire wear between the front and rear that left me a little confused. Usually my front tire looks pretty smooth and my rear looks like it has been pushed around a bit. Maybe it could be that my pressures were a little too low for the day.

 

-Sean

Nice picture! I don't think your friends are crossed up. On the 1-10 Larry Pegram scale, I would say they are a 4.

[spgtech]

Good to know. They certainly have more of the MotoGP hang from the knee instead of the CSS 1 cheek off, thigh contacting side of tank thing happening. Also, the guy on the right rotates his hips in and forward to keep as much weight on the front as he can.

 

Attached is a picture of my front and rear tires, both on the right side (due to better lighting, track only has 3 rt turns). After looking more closely at the front, I am thinking it's looking more like low pressure.

 

-Sean

[fossilfuel]

Sean,

Those tires look great! Don't worry you've got plenty of tire left.