Rishi
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Posts posted by Rishi
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I've recently been in a "discussion" with some friends about what actually happens to the rear under acceleration. It started like this:
A discussion about trail braking included this line:
On shaft-drive bikes it's particularly usefull as the arse-end of shafties rise on acceleration, rather than squatting.So I replied, as per the advice in the Twist DVD:
Chain drive bikes also rise on acceleration, the same as shaft drive.Well, that created a furore. Here were some of the responses:
Only some do. Most don't. It depends on the angle of the chain pullStill believing that the world is flat Rishi?Stand beside a chain-drive bike.Imagine a triangle formed by three points- the top of both sprockets , and the swingarm-pivot.
As you apply power, the top line (the chain) tries to shorten by pulling the top of the rear sprocket towards the top of the front sprocket.
Most of this results in the wheel turning, but some will shorten that line causing the swingarm to go up, and the back of the bike to squat.
All chain-drive bikes with suspension will do this.
Trailbikes try to minimize it by running the chain close (it not on) the swingarm.
BMW/Husky try to minimize it with their weird co-axial swingarm-pivot/counter-shaft.
But it is always there.
Like much of what is taught in Code's stuff, it is simplistic. And not necessarily correct.The issue of rear squat has been explained by a number of people, including Tony Foale. Chain pull is just one of the factors. The location of the COG of the bike also comes into it, as does the position of the rider and his impact on the COG. Suspension settings also come into play.
Much of it has to do not only with chain pull, but also the correlation between the rear contact patch and the swingarm pivot, and how that relates to the COG. Therefore wheelbase and swingarm length also play a factor. As does rider weight.
Watch a video of a bike on a dyno (any bike) and the rear will rise under acceleration. That is because it is a static test and some of the real world forces, such as weight transference and rider position are not at play. Put the same bike on the road and it will most likely squat.
There is a reason Ohlins invented the Rebound Separator Valve, and it was to reduce the impact of rebound damping when driving out of a corner, or in other words, to help stop the rear squatting under power, which makes the bike run wide as the front end geometry is lengthened. They would not have invented it if it wasn't necessary.
Terry Hay fitted the valve to the rear shock of my TRX when he overhauled the suspension to help limit the squat under power. If you want to argue with one of the best known suspension experts in the country, then go right ahead.
If you look at bike racers, they will get their weight as far forward as possible under power when exiting a corner. This is not just to reduce the bike's want to lift the front wheel, but to try and compress the front (and stop the rear squatting) so the bike still turns well and holds its line.
Using any sort of static test for this situation is meaningless.
I know Code has done a video that supports his assertion, but my point is simply that rider position and suspension setup have a major influence, so the assertion that all bikes will rise at the rear under power is simply wrong. Some will, but most chain driven bikes will squat, and not necessarily simply because they are chain driven.For example, my Aprilia hardly squatted at the rear at all under power. In fact if it did, it wasn't even noticeable. It was even hard to wheelie as it had so much weight over the front. Consequently the weight transfer under power was minimised and the rear didn't really squat that much. This was all due in unequal parts to the suspension setup, my body position on the bike and the geometry of the bike. The TRX squatted considerably, but much less so after Terry Hay installed the Rebound Separator Valve. The new Ninja1000 squats more than all of them. Respringing the rear end will help it, but it is a bike that will always squat, even with a new shock, purely due to its weight distribution and the riding position which limits where I can place my weight.
Truth be told, I've never ridden a chain drive bike that noticeably raised its rear end under power, and I've ridden a LOT of bikes in the last 20-plus years. Some of that will be to do with my weight, which is higher than the average rider, and the effect it has on the bikes COG (namely raising it and moving it rearwards).
Suspension engineers in race teams spend a lot of time working with rebound settings to limit the bike wanting to run wide under power, and it does this because the rear end is squatting. If Code is right in all cases, then they are all obviously wrong?
It is beyond my knowledge to refute or judge any of these claims. And with a wealth of mis-information on the web I won't be using Google to answer the question. Can any of the coaches or engineers comment on the claims above?
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Vision skills are near useless if its a blind 90 degree corner intersection. esp when someone rushes out without warning or looking when you have right of way.
I would argue your vision skills are the only thing that will help you in that situation. Your vision skills will tell you how much space you actually have and therefore how fast you should be travelling and also where you should be positioned. Again, the number written on a sign on the side of the road does nothing for you. Except perhaps give a false sense of safety.
If the speed limit is 50 BUT my sampled reflex buffer is much less, i wont ride at 50 ; i'll ride slighty below my sampled safe speed (ie 35-40)
And if the limit is 50 but you feel you can safely go much quicker?
PS> i am in no way saying vision skills are useless in other situations; in fact the skill have saved my bacon multiple times on public roads when there are no/little blind spots.
Problem is i live i an urban built up area with lots of blind spots due to crappy public infrastructure planning, hence much more exceptions come in.
It would be far better then to never look at your speedo and instead always be aware of these potential hazards. Again, knowing your speed in numbers is of no benefit.
Does this count as some sort of 10$ rule subset/ mode?
Absolutely. How much of a distraction is it to have to know how fast you're travelling at every point regardless of the conditions just to avoid getting fined for a non-event that is exceeding a politically chosen value. How much more relaxed would you be knowing you could ride any road using only visual skills and not having to remember the limit/note changes in the limit/worry about getting fined? More attention for other key elements of riding and less general stress? Sounds safer to me.
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I dont like to speed for safety and financial reasons ; Im a law abiding citizen when possible
It's interesting that you think there are safety reasons for adhering to arbitrary speed limits. There are financial ones though, absolutely.
for some roads , esp straights with intersections, i think its a good idea , the reaction time buffer for unexpected incidents is pretty ok of you are in the legal limit.
for some corners, nah...
Knowing how many km/h you're travelling is not useful information. That buffer you're talking about is a vision skill that needs to be learnt. Simply travelling at the number shown on the sign tells you nothing.
This false sense of security is one of the fatal flaws with speed limits in general.
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I dont like to speed for safety and financial reasons ; Im a law abiding citizen when possible
It's interesting that you think there are safety reasons for adhering to arbitrary speed limits. There are financial ones though, absolutely.
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CSS covers trail braking in Level 3 and also in CodeRace. Here is a thread with a great post from Keith about it:
That's interesting, as I've done Level 3 and there was no mention of trail braking. All five CSS days I've done have been "brake-free" unless we felt like using them in later sessions; even then there was no specific drill on braking.
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I've run off twice (Eastern Creek Turn 1, Wakefield Park Turn 2) and have been able to work out at least a couple of things that went wrong. I'm practising lots to iron such things out of my game!
The crash in which my leg got snapped however was due to other riders crashing into each other and then sliding down the track into me, so there isn't much to be learned from that other than sometimes the completely unexpected actually does happen
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Quick/Pivot steering slows the bike down. A lot.
This fact finally *really* dawned on my at my last (5th) CSS course a few weeks ago and allowed me to get through the day in 4th gear with no brakes (bar a couple of stuff-ups) even at the two hairpins at Eastern Creek. By reminding myself that steering quickly would wipe lots of speed off most of my entry speed panic simply vanished. Now I have this with me on every corner everywhere I ride.
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Mea culpa. I didn't think that through properly. Of course a gentle throttle off will have a different impact than chopping the throttle. I now agree (and disagree with former me) that a nice, controlled throttle roll-off with some body hook technique will help, so too then rolling on the throttle back on after sorting out your line and speed.
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I'd say 2 years at least. Even Lorenzo only came 4th (?) in his first year. MM will be competitive and maybe snag a win or two in 2013, but I think a championship against the calibre of rider currently in MotoGP is beyond a rookie, even one as obviously gifted as him.
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Hello all,
I'm a Sydney-sider who is very interested in most things motorcycling, especially riding faster. Well faster *and* making it through to the next turn. I've done Levels 1-4 and 4 again, and will almost certainly head out for more school time in 2013. Current ride is a VFR800 - one of the good ol' ones with gear driven cams.
I started racing a Hyosung GT650 locally this year, only to suffer a pretty badly broken leg in a race. Before the break I was inquiring about the process for becoming an instructor with CSS. Now I'm focussing on getting back onto the bike and track successfully, and taking my bike-craft seriously enough to start that process again! I should be racing again in November at the final round of the season.
Part of that process will be reading and where appropriate (!) taking part in the conversations on here. Be sure to let me know if I'm saying something patently wrong at any point!
Rishi
PS Hi there Mugget! Any other 2wf folk posting in there that you know about?
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At the start of the year I'd just completed L4 and spoke to my coach (hi Jason!) about potentially becoming an instructor. Then I broke my leg pretty badly in a race. So my goal is to spend the next 12 months (or how ever long it takes) to get back to that level and well beyond to legitimately start the process for becoming an instructor with CSS here in Australia.
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Are you sure about that? Rolling off the throttle will initially make the bike run wide, right?
I believe a slight roll off of the throttle would result in a slight weight transfer forward, which is effectively the same thing you are achieving with the hook turn technique, shifting weight forward, compressing the fork's which results in a shorter wheelbase, netting you a tighter turning radius or line.
now completely chopping the throttle will probably not get you the same results
Eventually. But that is after some other undesirable things might happen, including running wide. As someone else pointed out it violates Rule #1 of throttle control and isn't in the list of exceptions. Check out Twist II the DVD - it gives the science behind why you'll initially run wide if you close the throttle mid-turn, and also why eventually your line will tighten. Despite the shortening of the wheelbase there is initially a change in the contact patch of the front tyre and an unintentionally induced countersteer the wrong way. Eventually the bike slows down etc. and your line will tighten.
But the DVD explains it a lot better than my few sentences do!
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You can definitely use the hook turn on a decreasing radius turn; your line will tighten up. A slight roll off of the throttle also works, say from 1/2 throttle to 1/3 throttle.
Are you sure about that? Rolling off the throttle will initially make the bike run wide, right?
Arguments For "the Rear Squats Under Acceleration"
in Cornering and Techniques
Posted
Thanks Hotfoot! I will give your ideas a go on my local forum and see what response it gets.