How Do You Ride Through A Crest Apex At Racing Pace?

[Spaghetti]

I've asked this question various times to expert riders but I always get evasive answers of the kind "stay light on the handle bars" or "the bike is designed to handle it". I know I shouldn't front load the bars, what I want to understand is how the bike is going to react and some physics explaining it. Crest apexes are thorny because the front becomes very light right after the top of the hill. The fear is that, with enough speed, the front could lift off the ground while still at max lean (different than straight hills where a wheelie is a lot more manageable). Can the bike crash in this situation? Should I cut the throttle enough to insure the front sticks to the ground?

Turn 2 at NJMP Thunderbolt is the best example I have, followed by turn 1 at NJMP Lightning. I've seen other tracks with this kind of turns (NYST, Laguna...), just can't remember exactly which turn number. Looks like track designer love to put at least one blind/crest apex at each track.

[Kevin Kane]

I love T2 at NJMP [my avatar is in that corner]; you really have to trust you've got your turn point set because it is truly blind. It is also like T2 at Sonoma (Sears Point) which is even more blind if that is possible or T8 at Mid-Ohio. Since I am not an "expert rider" I can't offer you anything of substance here but I have learned that even with a lightened front end at the crest of any hill, throttle control is how you manage to keep your bike planted thru ANY corner. I also think that for a rider to "lift" the front tire in a corner (including the crest of a rise) the rider has to be adding a lot of throttle to do that - but the back tire is carrying the load in the corner anyway so the bike will hold its line with the lightened front. How many times have you seen Moto GP riders with their front tire off the ground at lean?

[csmith12]

Do a search here for a thread named "crests", I asked the same question some time ago.

 

To sum it all up though, it goes like this...

 

Get your turn in point, apex, and exit point solidly set. (the exit is the key here, because you can't see the true exit due to the crest)

These points define your line through the corner.

Check your throttle control through the crest area.

 

Now the answer...

If you are pinned? - Check your shift points. Some riders short shift to keep the bike out of peak power band over the crest to keep the front somewhat down and the rear solid. Some riders, change their gearing... I think it's silly because all that does is mostly change the shift points if the crest is the only reason to change gearing. Some even drag the rear brake lol.

 

Not pinned but aggressive? - Some riders pause the throttle roll just at the crest but most likely it's a throttle control or turn in point issue. Could also be a good turn in point but the angle of attack at that point could be somewhat off (track position).

 

Funny that Kevin mentions Mid-Ohio. I am a coach there and I hear this question quite a bit, but more so for the crest at 10a. If your pace is Intermediate or so and the rider has the confidence, they will be heavy on the throttle because then entry speed was too slow. After they work on the turn in point, quick flick, line and throttle control, they enter the corner faster. Which in turn makes their throttle roll smoother over the crest, now the problem isn't as pronounced and it feels more acceptable to the rider. 9 times out of 10... the problem isn't the crest, it's with the corner entry and throttle control but mainly... riders simply overbrake which starts the whole mess... Also, to apex at the top of turn 8, is a pretty good amount off the race pace line at that track and requires lazy steering to hit that line.

 

So ask yourself when coming to terms with a crest and your heavy on the gas. Could the issue be on entry instead?

 

Will the bike automatically crash? Naw... google "The Mountain" Those cats get 2 wheeled air over the crest with a good amount of lean angle. There is a bunch of science that I don't understand but proves the bike steers with the rear. Maybe the CSS coaches can add more here to shed more light.

 

Should your roll out or pause the throttle roll to keep your wheel on the tarmac? Does that adhere to throttle control rule #1?

[spike]

Cadwell Park . I personally think throttle control rule 1 would still hold true.

[Spaghetti]

So what I'm gathering so far is --throttle control! make sure the front adhere to the asphalt to maximize traction--

That's fine, but let's brake it down further:

 

- Why in the next turn 3 at NJMP (after the chicane), many expert/racers wheely there? Where is the throttle control and traction there?

- Assuming best is to keep the front tire in contact with the asphalt, how do you know when you have reached the optimal balance between acceleration/speed and traction? When the front feels "very light" just before lifting or when the front feels a "little bit" light? Or when it's down solid to grip the asphalt, pressuring the suspension?

 

In other words how do you balance acceleration and grip to optimize speed on a crest apex corner? What about straight crest? And where is the acceleration crash point, assuming line/exit room is not an issue here?

[rchase]

I roughly remember part of one of Keith's books with a topic called "steer for the rear" which might be some good reading. Essentially what it says is the actual steering is handled by the rear tire. The front tire sets the lean angle. Once the lean angle is set what is the front tire actually doing other than riding along?

 

On high powered bikes it's quite common for the front wheel to lift under heavy acceleration exiting corners. Wheelies had bothered me in the past because of the perception of the steering and braking being lost. You can set the front wheel down very quickly by shifting, slowing your roll on or lightly dragging the rear brake. Once you get used to them they are a lot of fun. Even short shifting one of my bikes at certain tracks gives me a small "micro wheelie" under full power. I recently rode at a track where a friend of mine always did a wheelie coming out of a certain turn. The first few times it happened to me as my speed increased I tried to stop it. I eventually found it was more work trying to prevent the wheel from lifting and a lot more fun to just let it happen lap after lap.

 

Will you crash? That depends on the bike. Most of the modern 1L bikes have wheelie control that keeps things sane and keeps you away from the tipping point where you go backwards. Beyond that it's all up to the traction profile of the tire and the situation you are presented with on the track. It's certainly possible to crash but is it likely based on the specific situation? That's something you have to feel out for yourself and make your own decision on.

 

I think the most important advice that's been given though is to maintain a light grip on the bars. If you do get the front unloading slightly or even fully lifting it prevents you from losing control of the bike with a tank slapper. It's important to keep in mind that the bike wants to remain stable when it's moving and it's our inputs that tend to make things go wrong. Motorcycles are somewhat of a paradox. A machine that's at rest is completely unstable and will fall over. At speed it helps the rider out by correcting issues on it's own and does not even need a rider on board to remain balanced and travel in a straight line.

 

My advice? Ease into it and see what the bike does when the front end gets light. If it's still stable increase your speed as long as you remain comfortable. If you aren't comfortable don't do it. It's costing you attention. There's plenty of other places on the track to make up that time.

[csmith12]

I roughly remember part of one of Keith's books with a topic called "steer for the rear" which might be some good reading. Essentially what it says is the actual steering is handled by the rear tire. The front tire sets the lean angle. Once the lean angle is set what is the front tire actually doing other than riding along?

 

Chapter 13

[Hotfoot]

I've asked this question various times to expert riders but I always get evasive answers of the kind "stay light on the handle bars" or "the bike is designed to handle it". I know I shouldn't front load the bars, what I want to understand is how the bike is going to react and some physics explaining it. Crest apexes are thorny because the front becomes very light right after the top of the hill. The fear is that, with enough speed, the front could lift off the ground while still at max lean (different than straight hills where a wheelie is a lot more manageable). Can the bike crash in this situation? Should I cut the throttle enough to insure the front sticks to the ground?

 

Turn 2 at NJMP Thunderbolt is the best example I have, followed by turn 1 at NJMP Lightning. I've seen other tracks with this kind of turns (NYST, Laguna...), just can't remember exactly which turn number. Looks like track designer love to put at least one blind/crest apex at each track.

 

The riders you ask about this probably give you evasive sounding answers because there is no EXACT answer, too much depends on you and your bike and your setup. You will only be able to find the limit for YOU by approaching the turn with gradual, incremental increases until you find the limit for you or your bike.

 

There is a lot of good info in the posts above - stay relaxed on the bars, have great reference points, steer for the rear, etc.

 

Generally speaking, the most likely outcome to too much throttle over the crest is that you will run wide. Or, you could trigger your SRs, which could make you tense up on the bars. Causing the front wheel to lift should not itself cause a crash (although it could contribute to running wide, due to decreased traction with less tire surface on the road), but if you are hanging on the bars you can get a rough landing when the wheel comes down, or head shake as it comes up. Extremes of those could potentially cause a loss of control or a crash.

 

(One specific warning - pay attention to throttle and lean angle. Some riders, when they feel the bike get light over a crest, unconsciously lean the bike over MORE to try to keep it from running wide. The combination of rolling on, increasing lean, and decreased traction over the crest can exceed traction limits quickly and with little or no warning. Be careful not to add throttle AND lean angle simultaneously.)

 

If your current amount of speed/throttle is causing you to go offline or is triggering SRs, shifting up a gear to reduce acceleration, using a less aggressive roll-on, or just going a bit flat on the throttle to reduce the amount of lift over the crest are all good potential solutions.

 

Regarding the comment about throttle control rule #1, keep in mind that a primary purpose of the throttle control rule is to optimize handling by maximizing traction and keeping the suspension in its best operating range. You are looking for an ideal weight balance of 40% front, 60% rear; would rolling on hard enough to launch the front wheel in the air over the crest and top out the suspension accomplish that goal?

 

Would paying attention to the weight transfer through the crest help a rider determine how much throttle roll-on is ideal for that turn?

[Spaghetti]

Causing the front wheel to lift should not itself cause a crash (although it could contribute to running wide, due to decreased traction with less tire surface on the road),

 

Good point! I never thought about the increased arc due to the loss of front tire traction.

 

 

 

(One specific warning - pay attention to throttle and lean angle. Some riders, when they feel the bike get light over a crest, unconsciously lean the bike over MORE to try to keep it from running wide. The combination of rolling on, increasing lean, and decreased traction over the crest can exceed traction limits quickly and with little or no warning. Be careful not to add throttle AND lean angle simultaneously.)

 

 

 

Good warning! Perfect example of why riding on track without the right knowledge can do bad. It's easy to rush to put down the front in this case.

 

Regarding the comment about throttle control rule #1, keep in mind that a primary purpose of the throttle control rule is to optimize handling by maximizing traction and keeping the suspension in its best operating range. You are looking for an ideal weight balance of 40% front, 60% rear; would rolling on hard enough to launch the front wheel in the air over the crest and top out the suspension accomplish that goal?

 

 

OK, but then what about the wheelies I see professionals do all the time on straight hills. The front lifts off the ground often in races. Where's the 60/40 balance there? Not even close. My guess is that rear tire traction is higher than 60% anyway, so it's better to maximize acceleration/speed vs. front grip?

[Spaghetti]

My advice? Ease into it and see what the bike does when the front end gets light. If it's still stable increase your speed as long as you remain comfortable. If you aren't comfortable don't do it. It's costing you attention. There's plenty of other places on the track to make up that time.

 

Thanks, sounds good, but this "feel comfortable" needs to be digged in further. I have another thread ready to go...

[Hotfoot]

 

OK, but then what about the wheelies I see professionals do all the time on straight hills. The front lifts off the ground often in races. Where's the 60/40 balance there? Not even close. My guess is that rear tire traction is higher than 60% anyway, so it's better to maximize acceleration/speed vs. front grip?

 

How close do you think you are to the limit of traction when NOT leaned over? The only force on the tire when accelerating in a straight line is the driving force from the engine. How much does the front tire contribute to accelerating the motorcycle?

 

The throttle control rule is for corners, to get the BEST possible traction and handling in a turn. If you have an abundance of traction, maximizing weight distribution may not be the priority, and you may in that case be focused on maximizing acceleration.

[rchase]

 

My advice? Ease into it and see what the bike does when the front end gets light. If it's still stable increase your speed as long as you remain comfortable. If you aren't comfortable don't do it. It's costing you attention. There's plenty of other places on the track to make up that time.

 

Thanks, sounds good, but this "feel comfortable" needs to be digged in further. I have another thread ready to go...

 

 

Sounds like an interesting thread. I have struggled with "feeling comfortable" on the bike myself and it was not just a question of ergonomics.

[tmckeen]

It's interesting timing with this thread, as I just happened to crash my bike on this exact kind of corner last week.

 

From my experience I can add that the margin for error on this kind of corner is less than on most other corners, and the feedback that you might normally get as you approach the traction limits of the bike will be reduced or nonexistent.

[Kevin Kane]

Tyler;

Not to jack this thread but 1 - are you OK? and 2 - what corner?

[Spaghetti]

The throttle control rule is for corners, to get the BEST possible traction and handling in a turn. If you have an abundance of traction, maximizing weight distribution may not be the priority, and you may in that case be focused on maximizing acceleration.

 

Very enough, makes sense.

[tmckeen]

Tyler;

Not to jack this thread but 1 - are you OK? and 2 - what corner?

 

Sadly I suffered some major contusions and bruising to my ego, and considerable hemorrhaging to my bank account, and I cut my knee loading the bike back into the trailer.

 

This is why I push myself on the track and not the street, I was able to dust myself off walk away from what would have been a MAJOR accident on a public roadway with nothing more than torn up leathers.

 

Turn 3 at "The Ridge Motorsports Park" I'm using the upper part of 3rd gear there so I'm guessing its 60+ mph corner

[Hotfoot]

Wow, Tyler, bummer. Glad you are ok! What actually caused the crash?

[tmckeen]

Unfortunately I'm not entirely sure.

 

Obviously, I did something different on that lap because bikes don't just crash on their own but without some DAQ info to review, or video footage to look / listen too I can't say for sure. I didn't feel like I did anything different that lap. Didn't get any feedback from the bike before it happened, and couldn't really say if I lost the front or rear first. I talked it over with a few coaches throughout the day but couldn't nail down any major specific cause. The things I do know for sure is that I lost the bike at the very crest of the turn, I went back to look for some missing hard parts and inspected the crash marks on the pavement. It was the end of a session and I had already completed a few laps at pace, so my tires were warmed up. I had switched from Q3's to GPA-Pro's that morning, so I was using a different, but better, tire than I had the previous 3 days.

 

Perhaps I was just a little tense on the inside bar and when the front got light I made a unwanted steering input, or perhaps I just turned the bike too much based on the tire change that morning. I'm just not sure, I know I did something, but nothing sticks out as something I majorly screwed up.

[Kevin Kane]

Oh man Tyler, I was haunted by a low side that nobody saw so I could never piece it back together. Ironically after it happen I swore off brand x for GP-A'S and never had a phantom crash again (I crashed racing but I knew why each time). When the 211 GP-A'S arrived I was surprised and skeptical of the recommended rear cold pressure of 22 but I never argued with Will - ever!

Good luck with sorting this out. From one CW to another, it's especially difficult if you crashed at a School because your team needs to adjust their corner coverage to finish out the event.

[rchase]

Tyler,

 

Sorry to hear about the crash. You and the bike will mend quicker and easier than you think!

[Hotfoot]

Unfortunately I'm not entirely sure.

 

Obviously, I did something different on that lap because bikes don't just crash on their own but without some DAQ info to review, or video footage to look / listen too I can't say for sure. I didn't feel like I did anything different that lap. Didn't get any feedback from the bike before it happened, and couldn't really say if I lost the front or rear first. I talked it over with a few coaches throughout the day but couldn't nail down any major specific cause. The things I do know for sure is that I lost the bike at the very crest of the turn, I went back to look for some missing hard parts and inspected the crash marks on the pavement. It was the end of a session and I had already completed a few laps at pace, so my tires were warmed up. I had switched from Q3's to GPA-Pro's that morning, so I was using a different, but better, tire than I had the previous 3 days.

 

Perhaps I was just a little tense on the inside bar and when the front got light I made a unwanted steering input, or perhaps I just turned the bike too much based on the tire change that morning. I'm just not sure, I know I did something, but nothing sticks out as something I majorly screwed up.

 

Do the new tires have a stiffer carcass than the prior ones? Going from Q3 to GPA-Pro it seems like they could. Did you make any suspension adjustments along with the tire change? I find myself wondering if maybe the new tire was less compliant to the road and maybe either sprung you up a little more over the crest or did not flatten out as much as the Q3 (giving you a smaller contact patch) when the bike was light over the top. I'm not sure how much difference there is between those two tires but sometimes when going to a more aggressive tire the suspension needs to be softened a little to compensate.

 

Another question - how much were the tires scrubbed in? Any chance you leaned it over onto a "fresh" part of the tire that had not yet been scrubbed in?

[tmckeen]

After spending 2 days at Streets methodically working though the schools suspension drill worksheet I came to the grand conclusion that the clickers and adjusters on my stock shock do absolute diddly squat, so I I didn't do anything to the bike other than switch the tires. I was running them at pretty low pressure, 20 PSI hot in the rear based on advice from a coach in the pits, so they should have flattened out pretty good.

 

The tires have 4 Code RACE days on them already so they were plenty scrubbed in and were hooking up well in my previous session and for all of the session leading up to the crash. The tread on the right side of the tire was almost down too but not flush with the wear bars so I don't feel like they were "shot" either.

 

Like I said, it happened very quick with no warning or feedback so I have very little data to go on, but I'm pretty sure the cause was the rider and not the machinery.

 

 

From one CW to another, it's especially difficult if you crashed at a School because your team needs to adjust their corner coverage to finish out the event.

 

I'm not sure how you guys do things but here in SoCal unless your a "Transport" that's just one less person who needs relief. I would have been really bummed if I had cost everyone their Bar for the day though.

[khp]

Apologies for trying to get back on (thread-) track.

 

What is it with crests that are making them a problem? Well, it's not that you're riding on a slope in itself, but the change in slope.

From physics, we know that the amount of friction available, is proportional to the force between the two objects and the coefficient of friction.

 

If the tires hit an increase in slope (e.g. starting going up a hill), the tarmac is "pushing up" on the tyre (and suspension), effectively increasing the force between the tyre and the tarmac. Conversely, if you hit decrease in slope, there is less force keeping the tyre and the tarmac together. So in this case you have less friction. A classic case where this goes terribly wrong is when a rider comes just over a crest and find something blocking the path, so the rider grabs the front brake just as the front tyre has gone over the crest, causing the front wheel to lock up due to the lowered friction and down he goes. Personally, I've seen this a couple of times.

 

The point i'm trying to make here is that you'll have reduced friction available when you go over the crest (first on the front, then the rear tyre), and if you're (very) close to using all your 10 dollars worth of friction in making a turn at the same time, you might just go bankrupt.