why light wheels make your bike turn easier

Hi 'shrapnel,

Accelerating through and out of the turn loads the rear wheel, if a tyre is going to break traction it's easier to control if it's the rear rather than the front.

When a bike is cornering the forces are trying to push the tyre outward, imagine what would happen on a slippy surface for example. So loading the tyre due to braking when leaned over will cause the front to lose grip earlier. So your analogy regarding dragging wheels is irrelevant as the load due to gravity is acting vertically, not at an angle.

The suspension front and rear compresses anyway when cornering due to centrifugal force so you don't want to load it even more by braking. There's also static sag of the suspension to consider due to the weight of bike and rider.

The U.K police, and I guess many other police forces, are some of the best trained/skilled riders in the world. They can probably out ride the vast majority of riders on the road given comparable bikes. Many police race too.

Al,
Years ago when I was a little boy we used to practice at Calder Raceway near Melbourne on Fridays. The Victoria Police would often be there riding their BSA Gold Flash superbikes. We used to pass them so fast going into corners that we'd almost suck them off their bikes. We used to find it extremely amusing when they complained. They were the reason most of us started road racing in the first place. Essentially, they are all 'DUDS' ! - I can only think of one policeman who was ever any good, he was an A Grade road racer but never a motorcycle cop. Thank God for that !
Our Australian police are full of bullshit when it comes to road safety. The popular slogan is 'Speed Kills' - should be 'Speed Plus Incompetence Kills' however advanced driver training is all too difficult. Collecting speeding fines from idiots is much easier.

This has got a bit off topic but it's interesting.

I trail brake on short circuits, especially when the heat is on. No-one taught me, I just discovered I was doing it. I guess it would be a difficult skill to learn or to teach, and I would only advise it to someone who was willing to take instruction on a track first. There is no doubt that it works and it reaps dividends on short circuits. You need a decent, progressive disc brake and not some grabby drum. The tyre bites on initial turn in, the front suspension compresses and aids turn in, and you are progressively letting off the brake until you are at or near the apex. You never begin to apply the front brake when in the turn, all you are doing is very gently letting off the pressure on the brake lever that you began to apply before the corner.

This is to get round corners fast on a track, but there is another approach. If you watch some of the fast guys with drum brakes, they will get all their braking done in a straight line and then snap the bike into the turn much more quickly than an average rider would be comfortable with. And they probably have light wheels!

It seems to me that good, fast road riding involves gentle braking and slowish entry into blind corners especially, so perhaps there's not so much opportunity or need for trail braking on the road. But I would not discourage it if people have learned the skill. Did you post this link some time ago, Dances? http://thebellypan.com/?p=252

Dave

Dang just throw some dry sand or pebbles over the sections you want to practice then all the physics and inter acting dynamics become very obvious, then sand blast the same section to crystalline new edges and take it on heated tires faster and harsher till its feels like dry sand and pebbles - then see whose campsite or clinic you end up in. The only two surfaces that act about identical to throttle, braking, leaning and turning, is hard base groomed Gravel and nice smooth pavement, just one takes rather finer brake lean fork and throttle touch to negotiate successfully. Wet is in between but more like dry pavement than dry Gravel. The only reason racers can get some advantage from trail braking is because their cycles can hardly take much leaned side loads any way so the trail braking is kept in similar zone of corner G force loads threshold. If they go in much faster then bikes tends to leave the surface and lose control - as they are not very neutral balanced so don't hold same angle in the air that they left the surface at and don't land to just carry on, unfortunately. The more power to weight ya got the more ya'll tend to ease into turns as ya can blast out so well. The less power the more ya tend to barge right in gritting teeth hardly getting off throttle like the 125's, which can be surpassed by modern bigger bikes for last couple decades the whole way in and out. Now if a capable powerful modern could barge right in like a light 125 then you'd have some lasting thrills.

By the way, rubber weighs more than Aluminum so to put more heat absorbing/spreading rubber surface down its more beneficial to fit a larger/wider alloy rim than a bigger fatter tire on narrower rim plus shorter side walls this way adds some stiffness stability to tires. Alas I've gone sour on wide tires as don't care for patch shape on very edges so more in 125 camp, till the tires melt. If ya fit bigger tire on wider rim then ya nullify the above advantage, but do increase the security sense factor up till loads its feeling like snot piling up on tire edges ...

I have sworn and declared to never race with a drum brake ever again. I still have a dislocated chromo-clavicular joint from the last time I was chucked over the handlebars . If you ride a bike with a peaky top end motor, drum brakes are the last thing you need. Discs are reliable, rarely drag or lock on, so if you can ride reasonably well you usually stay upright. These days I can still ride a motorcycle fast, however I go nowhere near crashing. - Twin discs with Lockheed calipers on the front, and single cast iron disc with Honda caliper on the back and a gentle torquey commando motor- lovely stuff ?
If you are in a corner going fast, you cannot afford to do anything jerky. Having a drum brake lock even momentarily can spell disaster, and if the front drum drags you are off into the bush when the bike suddenly becomes very stable.

Al-otment said:

Hi 'shrapnel,

Accelerating through and out of the turn loads the rear wheel, if a tyre is going to break traction it's easier to control if it's the rear rather than the front.

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Well we clearly do not see things the same here. Accelerating through a turn indicates entering and apexing at less than top speed. Unless you have experienced the benefits of feather breaking then it is clearly not for you. If your UK Police Recommendation citation has merit, then I cannot reconcile how so many people who race have got this feather braking all wrong.

Your UK Police recommendation citation does make sense for the beginning rider; that would be my recommendation for the beginning rider.

@daveh: No I did not post the article but good reading. I enjoyed the bit about "The confused “safety experts” in this country would have everyone believe that speed and safety are mutually exclusive"

@acotrel: A little harsh on those who serve and protect but I see your point.

Dances, I don't have much time for the car racing fraternity, however I see merit in people joining car clubs. In Australia racing drivers are dismissed as 'petrol heads'. The sad truth is that most of our motorists have never experienced their car swap ends at high speed. 'Practice makes perfect' and 'racing improves the breed'. Of course that doesn't balance the budgets of the state governments. These days our cars are so good that any lose is a really big one. In any case since the police concentrated on harassing drink drivers our road toll has fallen dramatically. I suggest the residual is due to extreme incompetence amongst drivers. It is very incompetent to speed on our country roads at dusk, we have very big grasshoppers here.

To quote the most famous motorcyclist ever (Marlon Brando) - 'I don't like cops' - (unless they are doing something to save me) !

acotrel said:

Al,
Years ago when I was a little boy we used to practice at Calder Raceway near Melbourne on Fridays. The Victoria Police would often be there riding their BSA Gold Flash superbikes. We used to pass them so fast going into corners that we'd almost suck them off their bikes. We used to find it extremely amusing when they complained. They were the reason most of us started road racing in the first place. Essentially, they are all 'DUDS' ! - I can only think of one policeman who was ever any good, he was an A Grade road racer but never a motorcycle cop. Thank God for that !
Our Australian police are full of bullshit when it comes to road safety. The popular slogan is 'Speed Kills' - should be 'Speed Plus Incompetence Kills' however advanced driver training is all too difficult. Collecting speeding fines from idiots is much easier.

Click to expand...

Wel it's obvious that, in the UK at least, the police riding standards are way above the ability of the Melbourne police from 'years ago' on BSA A10's that you overtook as 'a little boy'. So what bike where you on? BSA Bantam with lowered suspension so your feet could touch the ground?

Have a look on You Tube ref. Police Motorcycle Competition. Keeping on topic, lighter wheels will definitely be helping to make those full dress bikes turn quicker.

Police will not be hired if they have too hi of IQ's, like the majority of us, so any poor riding they demo is mostly the bikes they are stuck on or having to follow some department rules-policy as plenty of Police could qualify as stunt riders after spending so much time on them.

Back to speed handling mysteries, there is another factor I've run into on braking or not for turns and when to get on throttle to turn harshly, the speed alone factor. I could not use much throttle on P!! till over 60 mph or just spun, similar on THE Gravel - any power, brake or fork turn is supper dicey traction wise at low speeds but becomes less so the faster ya go on it. So if I enter at fast enough rate there is more grip to power and lean on but of course the centrifugal forces go up too so still dicey not to slip out but done right its a breath taking way around the corner cripples. The faster around ya go the lower ya need to lean to counter the fling up hi side forces, yet also reduces and changes the tire patch shape, which is what turned me so sour on wide tires compared to narrower. The elite's tires have improved last decade and so has their digi controls but I still see these elites wiggle tails on over powering exits which Peel did not even if tire spun some, the chassis twisted nicely to take it up w/o the swishshash of rebounds. Worked out that if I took it fast low enough [to some degree] on Peel she'd pull a freaking sideways wheelie off peg scrapping leans! Ya just can't get that low sharp and fast if counter steering as front washes out before the rear can load it on. Above this fun as hell phenomena on Peel she still had more traction but the speeds-centrifugal forces get so high she lifts whole bike off surface to hi side, which is even funner=faster but stops the forward acceleration so only useful in very tight spots to land already aimed well to power into the next switch back.

Tire profile matters as much or more than tire compound I found out the hard way doing this on real race tires so sticky even cold cig butts filters stick to it when parked. So would too light a wheel spin out too soon compared to heaver one dampening down the torque spin hits?





I tend to brake on the bias but don't aim at apex but on full throttle straight through it. I do not use the lines of motorcyclers but more like the rally drift car point and shoot w/o the delays of drifting sliding flat tracker load relieving. A motorcycle can take extremely high turn changing loads for an instant but not for very long.

What's not clear from my diagram is that the braking zone when braking on a bias is not much shorter then when trail braking -- but it is a little shorter. This is because you are essentially braking in a straight line and as a result you can brake harder for the whole braking zone. The net result is that there is some savings in braking distance compared to trail braking. The trick is to wind up at the apex just at the desired speed for the apex, but have saved 10-20 feet prior to the braking zone.

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more > on car type lines which are more like Peels lines than motorcycle lines.
http://forums.pelicanparts.com/1536088-post23.html

Naw that's not how I do it in a hurry so does not apply to Ms Peel, which I brake early enough to be slow enough I can aim over in slight leaning curve going well past apex under high power [almost straight past] to start loading suspension to take out slack then shoot almost to far edge to hook over a very sharp tire straining jerk around that aims bike into next longest straight line to the next apex or just out into a long stretch to relax and catch breath while topping out. It allows the shortest braking and most time on hi throttle I know of with least tire let go instants of acceleration hesitation. This is where wheel lightness gyro effects matter to me as can get so high ya jerk on forks and nothing happens in time, or becomes more like front's inertial resistance stability is wagging the tail behind in response more than steer as expected. So got in habit of mostly letting forks go as rear chirps out a step or so to pivot on more planted front, which hooks up rear more suddenly for rather more sudden exciting G force hopefully in the right direction in nick of time. That held on to far over leaning steady technique gives me Post Traumatic Stress Syndrome flashbacks. Only thing worse to me is applying brakes is that condition.

Oh yeah don't take that much braking to just lean over a wee bit so can get going fast enough at the real hook em over point the rear tire grip is surprisingly high, for an instant. Front is freaking useless just then but to get out the way of the Rear Ruling the Roost. If the front is being loaded then ya sure ain't accelerating very much.

Years ago a friend of mine had a long stroke manx as a road bike. Mr Policeman chased him up a winding country road when he was going to visit his friends. He knew the cop was there, however simply blew him to the weeds. After he finished his bit of business, he was returning towards home and found the cop picking himself up off the road, so he stopped to help him. The cop threatened him with everything he could muster. My friend said to him 'don't be bloody stupid, you did it to yourself'.
My friend got his later, when going to a race meeting, and they pulled the short stroke manx off the trailer when they were miles from anywhere . He rounded a bend when really flying, and blundered into a small town. He shut off and idled through it. The police utility truck coming the other way did a screaming U turn, and they booked him for the lot. It was a big number back in those days.

Daveh and Dances are correct.

They are talking about going fast, not discussing how Mr. Magoo is supposed to ride, or how police administrators can best reduce motor officer disability claims.

Another thing about trail or feather braking is it extends the range of locations for THE braking point; it reduces its importance, it broadens and opens options within the corner; late, early, matters less; you can be late and recover, or early and tighten your line for an earlier "stand it up and gas it" exit.

The Victoria Police have got a good record with high performance cars. Years ago when they got the Interceptor Fords, they took one off into the bush within about 5 minutes. Recently they got a few Subaru WRXs, and did a big job on one of those too, when they found it's limitations. Generally speaking their training seems to be good. I've had one with me when driving my car, and he continued to act as observer. However I don't believe many of them would get anywhere near an experienced racing driver who was actually trying. The simple fact of life is that you cannot beat the radio and the road block, so few people make a run for it these days. The other thing is that there is strong public opinion about police chases which cause the deaths of innocents, so it rarely happens now.

'tighten your line for an earlier "stand it up and gas it" exit.'

You are talking about 'point and squirt' technique. It is difficult to beat a good rider on a bike which has optimum handling which allows good steady hard on the gas while cranked over coming out of corners. The earlier you get on the gas coming out of a corner the quicker you are towards the end of the straights. If you gas it too hard you have a high-side, so smoothness is a key requirement. A lot of bikes have a tendency to run wide, so you cannot gas them early in corners. That is when you stand them up and give them everything in a straight line, however it is slower doing it that way. Bikes with peaky motors are safer when you do that, however I suggest commando motors are not usually like that.
Have a look at the Agostini video clip, you will notice that nothing is ever jerky, always strong deliberate power delivery, and smooth back-off. It is difficult to ride a two stroke that way. There is another clip which shows Ago at the Nurburgring racing against a field of two strokes. I have it and got it off free-to-air TV. Unfortunately when I uploaded it Duke Video claimed ownership of it , so it was terminated. It is really worth watching, if you want to know how to race successfully.

xbacksideslider said:

Daveh and Dances are correct.

They are talking about going fast, not discussing how Mr. Magoo is supposed to ride, or how police administrators can best reduce motor officer disability claims.

Another thing about trail or feather braking is it extends the range of locations for THE braking point; it reduces its importance, it broadens and opens options within the corner; late, early, matters less; you can be late and recover, or early and tighten your line for an earlier "stand it up and gas it" exit.

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I only live for corners. But your advocating keeping the brake on to go faster right? I can see a problem there.

I don't think I use the trailing brake technique. Perhaps it has something to do with steering geometry ?

xbackslider, I like your theory about a 'range of options' in corners. With my bike I anticipate where it will come out of the corner and hope it will be there when it gets there. If I put my mind to being anywhere when I'm actually in the corner, it is there instantly. It is very quick steering and you don't need to lose concentration. You learn to be super-smooth and positive.

Al-otment said:

I only live for corners. But your advocating keeping the brake on to go faster right? I can see a problem there.

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Al - what we were talking about above was more race craft than road riding. Trail braking on the track allows you to reach the apex of the bend faster than you otherwise would, when you are already slowing down, if you see what we meant. It is not something you do on every corner.

After the apex, you can stand it up and gas it or use the more classic technique, depending on the bike, the rider's style and the shape of the corner.

Re police riding, a few years back I was in the south of France, and we met up with three off-duty motorcycle gendarmes who came for a spin with us in the mountains, on their own sports bikes. As you would expect, they were well-disciplined and maintained a good, fast rhythm. I have no doubt they would be very competent riding in all weather conditions and performing all the tasks that would be demanded of them a lot better than the average Joe. Put them on a track, and they would need to knuckle down and learn race craft just like anyone else.

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