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N/A | National Motorcycle chassis design in theory and practice

Discussion in 'Racing, Motorsports, and Track Days' started by kneedragon, Oct 15, 2016.

  1. #1 kneedragon, Oct 15, 2016
    Last edited by a moderator: Oct 16, 2016
    That title sounds strangely familiar, I don't quite know why...


    I am responding to this...

    N/A | National - MotoGP 2016

    Going back to the 1990s, Ducati had a young engineer who was good with chassis, and he was quite well grounded in all the ... folklore and general opinion of the 'experts' of that time, and then he had an accident and ended up in a wheelchair. But he came back to Ducati and kept working for them, and I rather think nobody was game to question him, or tell him to take a different direction, because of the wheelchair...

    Some aspects of the generally accepted wisdom of the time, had been challenged and proved wrong, like the idea that the ideal or perfect motorbike (fast roadbike or race bike) would have a chassis that was completely stiff and rigid. Experimenting with 500 grand prix bikes had showed that the ideal flex was a bit less than the typical roadbike of that era had, but if you made the thing too stiff, that didn't work either. For one thing, it had no 'feel.'

    Ducati used a 'trestle' chassis in all their bikes, and it had certain strengths and weaknesses. It was very well understood.

    Our young engineer wanted to make an entirely different chassis. He wanted to go back to a concept used in the past by others, including the original Vincent Rapides. Phil Irving had designed the engine for that thing, or at least took two cylinders that already existed and stuck then onto a common crank, and made a V twin. Then he wrote Tuning for Speed, and a small number of technical articles for magazines (about 10,ooo ~ 12,ooo) and then he got drafted by Jack Brabham, to design a cylinder head he could drop onto a (basically) production aluminium Buick V8, and go F1 racing. (That's another story...)

    So the Vincent had a pressed metal contraption, that bolted to the two cylinder heads, and extended forward and held the steering head. Everything then bolted to those parts. You had a triangular cantilever swing arm that was about 30 ~ 40 years ahead of its time, you had two shocks side by side, laid out like a later mono-shock, and you had this little lump of metal that held the whole front end on. And you had a few brackets and bolt holes and all the other bits and pieces bolted to the central assemble that way...

    Our engineer in the wheelchair at Ducati liked and admired this concept, and had the brainwave that using modern materials and techniques, you could build a much better bike. So he started to design a "frame" that mounted very solidly to the front and rear heads, and held the steering head bearings, and that's about all it did. It weighed about 3 kg or less, and it was about the size of a shoe-box.

    The problem with this thing is 1) it costs a motza (that's an Italian word, comes from the Catholic church and it's been used by Ferrari for years) and you can make bits thicker or thinner, you can change the orientation of the weave... but the major paths and directions of flex are dictated by the basic geometry of the object. If you have something along the lines of a conventional old fashioned bike frame, think dual full cradle, like a Norton Featherbed, you can make some bits stronger or weaker and you can dictate how much it flexes, and where, and in what plane, and... and the essential design and layout didn't come from the genius pen of any one man, it came from the pedal bicycle and that came from the Hobby Horse and that was just born of idle curiosity... The essential design and layout of a motorcycle we already have. Now if you try and replace the tubular motorbike frame, which came from the safety bicycle, (or two of them) with a high tech carbon fibre shoe-box, even if you can get it to flex by the right amount, you really can't change where and how and in which direction it flexes. At least not properly. And when you try to experiment with it, it takes six weeks and thousands of $ (lira?) worth of work and fabrication from the people who build fighter planes and F1 cars, to get a replacement. Ie, it's a very very slow (and expensive) concept to experiment with and do trial and error testing.
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  2. "Love your work mate, big fan" :happy: But you'll regret it.

    I know that Ducati from the steel trellis frame, the carbon monocoque and the earlier versions of the twin spar alloy where all focused on very heavily on being extremely rigid, rigid was fantastic for deep braking and control while braking. From the best i can understand the 'black art' in chassis design is trying to deliver and extremely rigid frame in the direction of braking force and at the same time offer linear amounts of flex proportional to lean angle.

    I do remember Stoners frustrations with the steel frame where in its flex department its was all braking, he described it as imprecise and abrupt. Stoner is the type of guy that likes to push the bikes to its limit and little passed it so that he knew where the limit was so that he knew how hard he could push it. Where he struggled with the steel frame was its flex wasn't something he could rely on and often caused him to push past its limit and crash. I remember an interview with one of the bike engineers explaining that his 2007 win was slightly attributed to the fact he was using the Bridgestone tyres, from memory they had a better front but the rear lacked the grip of the Michellin. The GP7 Ducati had its engine placed further back in the frame than many of the other bikes, this weight distribution was something that they didn't plan and stumbled upon by pure arse. The weight of the engine further pack in the frame helped load up the rear tyre a little more than the other bikes which allowed the Bridgestone to hook up and work giving it awesome drive out of corners. The engine in the GP7 was powerful, but this wasn't really an advatange like many people think, manly because its powercurve was to brutal and unusable in anything other than a straight line, electronics where not as good then.

    Stoner had great finese with his throttle control, he could brake deep, turn the bike fast and save it for crashing (with its poor frame feel) with his lighting fast reflexes a bit like Marc Marquez does, he would stand it up as soon as he could to make use of the brutal power the bike had to catapult it out of the corners. I know he used to drag the rear brake on the GP7 while he was getting on the gas to try and control it because the electronics couldn't do the job in those days. His team mate Caparossi's results where actually getting worse on the GP7 compared to previous years. From memory i remember Rossi having Carmello broker a deal so that he could run on the Bridgestone tyre the following year.

    The steel frame it had wasn't really the reason it had success in 2007, I know how stubborn Italians can be and can only imagine what was said at the behind closed door meetings in 2008 when an engineer suggested they bin the steel frame that they developed since 2003 and finally just won a world championship on the year before .... and change to a carbon frame. I'm sure it didn't go down well so I can only attribute that they must have been pretty certain that they where going in the wrong direction with it before they switched to the carbon monocouque they carbon frame didn't really give them better results, worse if anything but its paved the way for their alloy/magnesium or whatever it is monocouque chassis now used on the panigale.

    My eyes are sore, your turn
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  3. #3 kneedragon, Oct 16, 2016
    Last edited: Oct 16, 2016
    You know this story at least as well as I do.

    I was intensely curious, while Rossi was at Ducati, and then when they admitted defeat and went to a 'normal' aluminium 'deltabox' type frame. Now the new 'conventional' frame they have, seems to be getting better, but it's still not on quite the level of the Honda or the Yamaha. I think purely in terms of chassis at the moment, the Yamaha is in front. Honda know what they're doing, but they have a rider in M&M who is a demon braker and he asks for a bike that doesn't wheelstand or stoppie, so they're back to making it long and low, like an NSR500. Pedrosa is a slightly different kettle of fish, because he's so small and light, and what they have to make for him is quite specialised.

    I'm trying to remember who built that Al frame originally for Ducati. It was Kalex or Speed-Up or someone, a Moto2 company anyway. I think they did good work but I'm not sure it was great. And Ducati insist on keeping the 90 degree V4 layout, tipped well forward, which mirrors the layout of their twin cylinder road bikes. Now as you mentioned, there are some good things about that, and some bad. It does result in a natural weight distribution that's quite low and rearward. That does have the effect of getting power down early and helping you get off corners. And it does have the effect of allowing very heavy braking (at least as long as you don't lock the front wheel) and the bike resists doing a stoppie. The heavy bits are low down and well back. Now I got laughed at a bit the last time I talked about what this does, but...

    Ride a few 4 cyl universal Jap 4s. Get used to them, learn the balance. Now, go find an old 2 stroke trailbike. I have in mind a DT125, DT175 or DT250. The engine is very small and light, and the weight distribution is a bit like a V twin, like a Ducati or an twin cyl Aprilia. It's a WHOLE DIFFERENT FEEL. The entire dynamic is similar, but not the same. Now go jump on a Vespa. The heavy bits are right at the back. The geometry is a bit different and you have tiny wheels but... the Vespa sort of continues the same trend. It's lighter at the front and there's nothing up front with any weight or structural strength to it. You can't do a stoppie on one (I know, I've tried) but they do mono very easily. And if you power on out of a slow (slippery) corner, the rear isn't going to slip - you'll unweight the front and it will wash...
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  4. I cant remember who did the Ducati frame for Rossi either, I do remember they had to bring someone in to do it for them rather than have Ducati design it. I agree its frame isn't quite there yet and I'm very curious about how it does with its winglets removed. They seem to use them heavily and I often wonder how they will do next year where they lose the advantage it gives them. The Yamaha is a pretty well balanced bike, I know this year Honda have struggled with out their bespoke electronics.

    In 2015 at Sepang when they where using the best ever electronics version and software package they even then said that the bike was faster at Sepang because the high air temp and humidity caused the engine to make less power and the power to come on less abruptly, this allowed the electronics to to work better than it did at other places at controlling it out of corners and keep it smooth and not bounce around. I attribute some of the difficulty they have had this year down to not being able to optimise drive out of corners through tuning like they used to in the year previous. I know the 2015 bike was 'faster on paper' by design, but just didn't suit Macs wild and loose style of riding. He needed a bike to be more forgiving rather than a less forgiving more correct engineering design that may give an extra few 10th's if you do everything spot on perfect every lap like Jorge does.

    I think Jorge will be great for Ducati in developing the bike in the right direction. I am a huge fan of the Suzuki Chassis, i think its a brilliant design, its like 7 bolts per side to change the carbon engine mount and give the bike a completely different character to its flex. I know their approach has been handling first before power, to the point they wont introduce extra power to the bike if the handling suffers so i think they are going at it with the right attitude. Ducati focused heavily on the power. I remember them at Phillip Island just walking past everyone down the straight almost effortlessly. It was also not bad under brakes, If they had a frame that could turn like the Yamaha it would be unstopable.
  5. So, Ducati have built a MotoGP bike that rides rather like a Vespa, or a DT 125. It's very good on the brakes, at least while it's still upright, and it's very good on the power from mid-corner, as you start to power-down. It has Horsepower. It has Desmo valves and this is perhaps the case where those really do make perfect sense. The weakness(es) of the Ducati, it doesn't quite have the perfect weight distribution for best mid corner grip or speed, it works rather better with a big wide sweeping line and lots of lean angle, but that's mostly to cover other weaknesses. It's not a bike you can be brutal with, on the front end, because it will wash out. But once you get to the apex and start to open the throttle, it rocks back and puts weight on the back wheel, and you can get a massive amount of forward drive. The danger here is that you can un-weight the front wheel while you're still leaned over enough to need it, and the bike will power-understeer. (Remember that term? People used to say the Ducati "understeers?") Get on something slippery, on a Vespa, and do a sharp turn, then nail it as you pick up. It will push the front, or understeer...
  6. I know Honda have never battered and eyelids when changing from 500cc 2T to 9904T, then to 8004T, then back to 990T, Fuel restrictions, tyre manufacturer changes, forced to lease full spec bikes, nothing phased them, until they threatened to take their electronics away .. first response was "this is ridiculous, thats it we will pull out of the series all together".

    Just reading between the lines but it sure seems the bespoke electronics where pretty important to them.
  7. Never really thought about that with the Ducati but your right, the rearward weight bias when juicing it up will defiantly not help it steer any better. May be a case of they change its weight distribution it can turn better but lose out on rear drive. Probably a choice that helps better exploit the power the engine makes.

    I thinks its great how they used the demo valves over pneumatic. I remember when they where entering the sport in 2003 they announced it would be a V4 rather than a twin, but to keep in with its heritage it would fire the cylinders in a 1/3 - 2/4 arrangement to make it work like a doubled up twin. Don't know if they still do that or not but thought is was pretty cool at the time.
  8. Well, they have become important. They didn't have that stuff on the 500s and they didn't have it on the early V5 RC211V. With that, they had a rider who was good, a crew chief who was good, a fair bit of power, and a chassis that was just RIGHT. (They roped in the man who'd just designed the 919 Firblade, with the concepts of mass centralisation, and going faster by being manageable, not just brutally powerful. He didn't start by asking what you wanted to go fast - he started by asking what made certain smaller (cheaper) bikes so easy to ride, and why the big beasts were so hard. With the 'Blade, he built a (nearly) litre class bike on the scale of a 600, and tried to make it handle like a 600. That's why the first one had a 16" front wheel. This was the man who built the original 4 stroke 5 cylinder Honda GP bike. It's a completely different mindset to the one Honda normally uses. Partly the bike was good because it had Rossi on it, but partly it was just a very easy bike to ride and handle. That was the first and primary objective.
  9. #9 kneedragon, Oct 16, 2016
    Last edited: Oct 16, 2016
    "...the rearward weight bias when juicing it up will defiantly not help it steer any better. "

    Right, right. Point is, you can't fix one without giving away the other. Imagine 2 dirt-bikes, playing around on a gravel carpark. One is a DT250 and one is a Kawasaki KLX650 single. The big kwak is going to have lots of weight on the front, and it's going to be loose at the back. The DT is going to have radically different power delivery, that's nowhere near as good, but it's got no weight and it's got lots of power, and the weight distribution gets power down. The big 4 stroke SHOULD drive forward much much better, and it has a front end you can trust, but once you start to see those two bikes playing, your opinion of dirty old 2-strokes will step up a bit...

    But if you try to ride the DT250 fast along a twisty tar road, suddenly the weight dist and slow thump-thump power of the big Kwak will work. It's a question of what's the right tool for the JOB. Now on the tar, MOST of the time, I'd take the KLX. I am just used to that heavy-at-the-front type dynamic. You can take it a bit too far, the ZX14 was maybe a bit too far, but the Aprilia was too light in the front.

    You go back a few years, and I really thought the balance of a 900 Bol d'or was just about perfect. I thought the current ZX10R was bluddy good, too. I have a few issues with that bike, but the chassis and the handling suit me beautifully.
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  10. #10 AJV80, Oct 16, 2016
    Last edited: Oct 16, 2016
    There is a couple brief Honda videos on the design of the RCV211 and RCV212 and how they came about the bikes and what focus they had, subtitled unfortunately. They say the 212 struggled on power compared to the competition, but the 211 was defiantly the best bike of the 990 generation. Rossi had to pull a rabbit out of his ass to win on the Yamaha for the first couple years. They kept the V4 in the 213 though rather than revert to the V5, I think it was lighter than the 211's engine and helped handling. The benefit of the V5 was you could orientate the motor with 3 cylinders forward or 3 back to optimise the weight distribution more so than the V4 could.

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  11. I have a soft spot for the 2T's use to love my YZ125's, I learned to ride on a YZ250, but the light weight of the bike and myself meant I would lap faster on the 125. power is great but you need the weight to use it, I used to have to sit on the back of the mudguard to try and get the power down from a race start on a 250 and even then it wasn't enough.
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  12. #12 kneedragon, Oct 16, 2016
    Last edited: Oct 16, 2016
    Yeah, the 5 cylinders gave several advantages. It gave better weight dist, it gave an odd design that put Honda on the front page, it gave a nice noise, and it gave 20% more valve area / circumference, which helps top end power. Most of all, when they first dreamed up the formula, they 'corrected' for the weight and the number of cylinders, and you really had a disadvantage if you built a 6, huge disadvantage if you built an 8. But the min weight for a 5 was only slightly more than a 4, because they didn't think anybody would do it. Honda did the maths and jumped on it. It was perfect for them.

    Wandering off for a visit to the land of Nod. I need to do a service inspection on the inside of my eyelids. You've got to stay on top of this maintenance sh1t....
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  13. I know that part of the reason they didn't use the V5 on the 213 was additional friction losses that could be overcome with the V4 config, I know they have struggled this year smooth power delivery without their electronics, but there are strong rumours they will run the V4 next year with a big bang firing order like the Yamaha's. No-one has spoken about it officially though but the rumour has been talked about enough in the paddock to give it some validity.

    Of all the bikes i heard at Phillip Island I found the Ducati engine sounded the most, evil. It sounded like a possessed demon. Well Stoners did anyway, Hayden's had the TC setting up to about 11 i think, he was having a shit of a time on the GP9 running up the back of the pack in almost last position. Stoner was smoking everyone up from on his White Knight Ducati. You could hear the difference in Stoners and Hayden's engine and how severe the TC was on Hayden's, no doubt it was slowing him down.