Suspension And Rear Tire Under Braking

[Hotfoot]

Hi y'all,

 

Looking for some ideas from the forum. As you know I am doing this Academy competition and we had a round this weekend. I was on an upgraded suspension, and I am very happy with it. We also lowered the front of the bike a little (dropped the triple down lower on the forks), which sharpened up the handling and REALLY like how that feels, it turns very quickly and gives me a lot of feedback in corners.

 

However, with that change I am having challenges under hard braking, the back tire is not staying in contact with the pavement, causing a lot of rear instability (wagging or coming around) or lifting totally up in a stoppie. I tried raising the front of the bike back up and that fixed it but I didn't like how the handling changed in corners so I put it back.

 

I want to fiddle with the rear suspension to try to improve the situation (preferably without messing around with the front settings because they are GREAT). Any suggestions? Should I speed up rebound to keep the tire more in contact? Should I soften compression so it doesn't get bounced up as easily and is more compliant? Change rear tire pressure? Just a LITTLE bit more rear traction would be enough to keep the back from coming around and that's what I am trying to accomplish.

 

I am already doing all I can with my body to manage it - sitting back farther, staying relaxed in my arms (I learned quickly that ANY tension in my arms causes the rear wheel to lift right up dramatically), braking earlier and more gradually, etc., but I have had to extend my braking distance noticeably and it is affecting my lap times and leaving me open to late passes entering corners where I was not having that problem before.

[khp]

Hotfoot, you're having a delicate balance here. Lowering the front will make the steering quicker, but will also move more weight over to the front and make the bike easier to make stoppies.

 

Have you considered if you can raise the rear instead? either by shims or by extending the shock itself?

Like you're saying, you really want the rear shock to extend quicker and further than it does right now. Since rebound affects the wear quite a lot, I would be reluctant to mess too much with that, but instead consider to either have less preload (so it sinks deeper) or maybe have a softer spring. If I remember the discussions on the forum right, you're not a particularly heavy rider, so it might be OK to remove a bit of preload without sacrificing too much in the other end.

 

I'd try giving my local suspension guru a call - in your case that would be someone like Dave Moss, I presume.

[Hotfoot]

Hotfoot, you're having a delicate balance here. Lowering the front will make the steering quicker, but will also move more weight over to the front and make the bike easier to make stoppies.

 

Have you considered if you can raise the rear instead? either by shims or by extending the shock itself?

Like you're saying, you really want the rear shock to extend quicker and further than it does right now. Since rebound affects the wear quite a lot, I would be reluctant to mess too much with that, but instead consider to either have less preload (so it sinks deeper) or maybe have a softer spring. If I remember the discussions on the forum right, you're not a particularly heavy rider, so it might be OK to remove a bit of preload without sacrificing too much in the other end.

 

I'd try giving my local suspension guru a call - in your case that would be someone like Dave Moss, I presume.

 

Hm, good ideas. I always balk at raising the rear because I am short and don't want to make the bike ANY taller than I have to. But sometime we have to sacrifice comfort for performance.

 

Preload is a great idea and pretty simple to try.

 

Good point about the wear on rebound; I suspect the rebound is a bit too slow anyway, so I think I'll start with making that a little quicker to see if it helps, and I'll just see how it feels and keep an eye on the tire wear. If it doesn't help or the tire wear suffers, I'll try preload next.

 

Thanks for the feedback - this gives me a starting point, and I am still interested to hear feedback from others if you have thoughts on the subject.

[rchase]

Have you considered changing the springs in the front? It's worth exploring different options there.

[Hotfoot]

Have you considered changing the springs in the front? It's worth exploring different options there.

Yes, I did change them and this was day 1 riding on the new setup. The front end is GREAT, perfect, so I am trying to adjust the rear without messing with the front.

[rchase]

Flipping the shock eccentric will raise the bike considerably. I'm tall and it's downright awkward riding my well setup S1000RR. It's worth it though. When the bike is underway it's a non issue.

[khp]

 

Have you considered changing the springs in the front? It's worth exploring different options there.

Yes, I did change them and this was day 1 riding on the new setup. The front end is GREAT, perfect, so I am trying to adjust the rear without needing with the front.

 

 

Hotfoot,

 

If you added 1-2 mL (milli-liter, one thousands of a Liter) of oil, you will have a slightly more stiffer air-spring, which should mainly have an impact when the fork is most compressed.

I tried adding ~10 mL of oil to my forks, in order to reduce the max travel of my forks, and I found that that gave me ~15mm less travel - more than I wanted. So if you're going to add oil to the forks, try adding a very small amount at a time and see how much difference it makes.

 

Speaking of fork travel - how far are you from bottoming out the forks?

 

I would still try to reach out to Dave Moss or someone similar, if I were you.

 

Kai

[csmith12]

I had the same issue on my 08 r6.

 

Hotfoot, assuming your braking and downshifting techniques are great. Then, I would focus on 2 things; rear rebound and front compression. Your braking technique will have a strong influence on your suspension setup here. If you're fast and sudden on the brakes to load them up, then you are more prone to collapse the front due to a very fast weight transfer. Your suspension settings on the brakes much match your application skills. A common and improper solution to this would be to simply add more rebound to to the rear to help keep the rear on floor. While your rebound could in fact be too slow, make sure it is not too fast as to accent a jumpy/floaty by the rear shock rebound pushing up the rear during braking. My gut feeling is you need to work with a suspension guru to setup the bike to your riding style vs some generic numbers or "common" settings. If I were a betting man, I would bet they will add preload and/or adjust compression damping in the front too better manage the weight transfer per your application.

 

Lastly, there comes a point where you must start to enjoy the lifting and sliding around, as you shouldn't sacrifice corner feel, feedback and rideability for the 300/350ft of braking feel and feedback. Let's face it, even with a perfectly setup bike, scrubbing 100mph in 300ft is a fairly violent affair.

[Hotfoot]

My downshifting technique is GREAT, my braking technique is good but could always be better; I am not abrupt with it but I am braking very hard in a coupIe of places on the track. I did catch myself being a bit tense in my arms a few times and of course that GREATLY increased the tendency of the bike to stoppie.

 

I am working with Jeremy Toye and he is very knowledgeable on setup. The bike suspension is set up for my weight. I am using most of the travel in front, going down to about 8-10mm from the bottom, which I'm told is ideal for my particular fork setup. Setting up for my style is a little challenging as I am rapidly changing my pace and laptimes during this Academy competition - on Saturday my settings felt great but then I went two seconds faster, then three, and suddenly the front started feeling soft. We increased compression damping and the front was more supportive but the back end became very unstable (somewhat the opposite of expected, actually). The general consensus seems to be that I need to firm up the front to make the rear more stable but we tried that three different ways (compression, preload, and moving the forks back down) and in every case my laptimes suffered - preload and compression made the rear worse, change the front height made braking better but lost cornering feel and slowed the transitions a lot.

 

I think this is a key statement: "you shouldn't sacrifice corner feel, feedback and rideability for the 300/350ft of braking feel and feedback". Fontana is a track with a crazy amount of accelerating and braking so it is easy to get focused on that, but overall I may be better off to ignore the braking issue and just try to carry more speed into the relevant corners. That's another way to shorten my braking distance.

 

I'll play with rebound and see what it does; I get the point about how it could get too quick and make it bouncy, but there enough bumpy places on the track that I should quickly be able to identify if the rebound gets too quick.

 

Good feedback from all of you, thanks for the advice!

[csmith12]

For completeness, let's look at it one more way. I bring this up because having the same problem as you on the brakes, I always want to check the rider as well as the bike.

 

Are you charging the corner? (that was my main problem) Perhaps SR #7 is showing up as a wiggly rear wheel.

 

So you mention there are many new things going on. New people, new setup, pressure to perform, ect... ect... Any way to divide and conquer? How about this, can you ride the track with no brakes to find your entry speeds? After all, the brakes are nice and all, but the main point is to get your entry speed perfect.

[Hotfoot]

For completeness, let's look at it one more way. I bring this up because having the same problem as you on the brakes, I always want to check the rider as well as the bike.

 

Are you charging the corner? (that was my main problem) Perhaps SR #7 is showing up as a wiggly rear wheel.

 

So you mention there are many new things going on. New people, new setup, pressure to perform, ect... ect... Any way to divide and conquer? How about this, can you ride the track with no brakes to find your entry speeds? After all, the brakes are nice and all, but the main point is to get your entry speed perfect.

 

Good questions and there are indeed a lot of things going on, including a coach that puts some emphasis on being VERY aggressive. I was not charging the corners to begin with, but when we first made the change that affected my braking distance, then yes tons of SRs started firing off - I began braking at my prior markers and usual intensity, but the bike behaved very differently, I was overloading the front and lofting the rear so I had to back off the front brake and quickly ran out of stopping distance. So yes, the first few laps the eyes got wide and the arms got tense and my corner entries were a bit ragged, all the effects of charging. To handle that, I started braking much earlier and more gently, but my laptimes were 2 seconds slower as a result (there are multiple hard braking zones at Fontana), thus my concerns about trying to fix it.

 

After paying a LOT of attention to making sure I wasn't tense in my arms or target-fixed, my corner entries improved and the laptimes got a little better. In the last few laps I focused on finding new, appropriate brake markers and THEN my laptime improved again.

[csmith12]

Cool track, looks alot like Gateway in St. Louis.

 

Ok then, one last thing. Let's work the problem from the other end backward...

 

Quick turning, we both know that the the turn in point affects your brake marker. For those problem corners, can you adjust your turn in point via a quicker flick or track positioning to allow for a better brake marker and more compliant feel in the braking zone? While it might not agree with the "race line" perfectly but you know... each rider has their take on lines. Or will it kill an early, clean throttle roll? Alternate lines are useful tools, perhaps use the late brake line/turn in to guard/make the pass when you need it, use your qualifying type turn in and line for lap times and closing gaps, ie to up your corner speeds.

[Cobie Fair]

This might have been covered in what you meant about pressure off the arms, but are you using both legs/knees to help support you, as well as the core muscles?

 

CF

[khp]

Hotfoot,

 

Could you give us an update - did you find a solution, and in that case, what was it?

 

"Inquiring Minds Wants To Know"

[Hotfoot]

Thanks for asking. I have multiple solutions to try but the final competition round is not until Nov. 28th, so I haven't had a chance to try them out yet!

 

At the end of the last round I raised the front of the bike back up partway, hoping to find a balance that gives me the sharp handling but with reasonable stability under braking, but I haven't ridden it that way yet.

 

Also in chatting with Keith about it, he asked if I could get lower on the bike to get the COG lower, which was a really good point; I can definitely keep my upper body lower in the hard braking zones and that should help reduce the tendency for the rear wheel to lift. That's an easy thing to change so I'll definitely do that.

[khp]

Also in chatting with Keith about it, he asked if I could get lower on the bike to get the COG lower, which was a really good point; I can definitely keep my upper body lower in the hard braking zones and that should help reduce the tendency for the rear wheel to lift. That's an easy thing to change so I'll definitely do that.

 

I should know better than arguing with Keith, but if you lower your upper body to lower the CoG, you will also bring the CoG forward. I don't know which effect will have the biggest impact on the braking stability, but as you're pointing out, it's an easy thing to change and test out so by all means do it and see what it does. And please do report back here on your findings

[csmith12]

khp, unless you're double jointed in your back, keeping a lower CoG in the braking zone normally comes along with sitting farther back in the seat.

 

If you have watched the twist 2 dvd, there a scene where the rider is hard on the brakes. Sitting up straight, unlocked from the bike and stiff armed... the bike stoppies. Locked on and loose arms is smoother and in control. What is NOT "said" in the video is, the rider is sitting farther back in the saddle AND has a lower CoG. I have watched many scenes in slow motion, things get real interesting at 1/4 speed.

[khp]

@csmith12 Hotfoot is already sitting fully back so she cannot sit further back - see her first post. So lowering her upper body should also bring her CoG forward a bit, right? I could be missing something vital here though

[csmith12]

I don't think you're missing anything. I just didn't take her post as meaning 100% back in the seat, just back far enough to get a good lock on the bike and then maybe a bit farther. I dunno, I am sure she is not sitting so far back she becomes disconnected. So maybe there is some room to play with, maybe there isn't, but yea... any mass moved forward will move the CoG.

[Hotfoot]

I have to say, it's fun having you guys discussing my riding and kicking around ideas. I am often in the position of having to guess at what another rider is doing, when trying to help them on the forum, and in THIS case I can actually TELL you what the rider is doing.

 

I AM sitting somewhat back in the seat, but there is more room to go. I can't sit ALL the way back, though, because I am too short for that and it becomes difficult to steer the bike because I can't comfortably reach the bars.

 

Yes, if I get lower on the bike I will automatically be able to scoot back in the seat a bit more. More importantly, though, it will put my arms more parallel to the ground, which will help reduce any downward pressure on the bars. (I do my best to lock in and keep my arms relaxed, but when braking as hard as possible on the S1000rr it is extremely difficult to be 100% off the bars, especially at the end of the day when I start to get tired.)

 

Sitting too upright under hard braking is one of the most common things we see contributing to stoppies when doing the braking drills on the brake rig. However, that sitting upright is almost always paired with stiff arms and stiff upper body and back, so it is not just a COG issue, it is an issue of loading a lot of additional weight on the handlebars, as the upper body is thrown forward from braking forces and that weight is transmitted directly to the bars. I am sure I was sitting up more than normal and definitely I was more tense as my SRs were firing off when the bike surprised me by NOT stopping as quickly as it had before.

 

The very first thing I am going to do on Saturday - which is our final round - is go get better reference points for braking. I made an adjustment to the bike and put the front end halfway between the high and low settings I tried last time, and I will go ride it like that and get some visual reference points. Those reference points should help reduce the SRs that contributed to my braking issues: (1) tensing up my body thinking I was running out of braking room (2) sitting up too much - if I have good enough reference points I can get lower on the bike and not feel like I have to sit up to see better (3) tensing up due to thinking I am running out of room and (4) braking too hard/too late for the setup of the bike - we changed the bike setup but I tried to use the SAME brake points and they didn't work anymore. A better plan on when to start my braking will allow a less abrupt application AND release of the brake.

 

I am VERY appreciative of all the ideas presented here, and I'm excited to get out there and start trying things. Looking at my laptimes and my improvement, I think I have a decent shot in the competition... but I do still have a little more work to do in the social media area. This week is the last week for voting - you all have been a huge help, thanks again and I'll let you know what happens!!!

 

Here's the link to the voting:

https://fastrackriders.info/academy-voting/

 

I'd love to have your vote, but I won't hold it against you if you vote for Mario.

[rchase]

Despite Mario being one heck of a rider my votes will always be for you Hotfoot.

 

Nothing useful to add but an amusing observation. It's interesting to see sometimes the different challenges we deal with for ergonomics on bikes. I can't get far enough back in the seat. While sitting on the passengers pillion would not be much better the though has crossed my mind.

[khp]

Hotfoot, great to have you to inject some knowledge in this exchange of guesses

 

My personal experience with braking is that stiff arms are much more harmful than sitting upright. I should know, because at 6'6" I can sit with an almost vertical back and still have bent arms. Of course, having the forks to bottom out is a very effective way of ensuring a stoppie (DAMHIK). But that shouldn't be your problem. It's the braking force vs rake/trail/CoG that's making the problem for you.

 

In my 6 years as an instructor at a MSF-like course, I've worked on braking with more students than I can count and letting your arms loosen up worked for all, regardless of bike types (from Harleys to Ducatis) and rider body size.

[Hotfoot]

Riding today. The geometry change seems to be a good compromise, handling is pretty good and braking is more predictable. Sitting lower and farther back is helping. Got better brake markers.

 

Only in the second session but I got another 1.5 seconds faster.

[khp]

Great to hear Hotfoot!

1,5sec faster in just the second session is pretty awesome. Just how much time have you shaved off on this particular track since starting the program? Did you know the track (layout) from before?

[Hotfoot]

Yes I had ridden there before, but on my Moriwaki 250, not the BMW. I dropped about six seconds in three rounds.