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Additional Motorcycle Wheels?

  1. Dec 22, 2009 #1
    If we were to put two relatively small wheels on the side of a motorcycle would it decrease the performance of the motorcycle?
     
  2. jcsd
  3. Dec 22, 2009 #2

    mgb_phys

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    No, and I don't think you are allowed to join the hell's angles if you have stabilzers !
     
  4. Dec 22, 2009 #3
    Trikes are OK with Hells Angles. Four wheel's are a no-no except in the junior, under 12, leagues.
     
  5. Dec 22, 2009 #4

    mgb_phys

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  6. Dec 22, 2009 #5
    Well, if the supporting arms of those extra wheels do not flex much, there is a serious problem with higher speed turns. You will flip over!
    I know this because I was researching motorized tricycles a while ago and was warned about turning above certain speeds. Those "safe speeds" are much lower than for a 2 wheeled motorcycle.
     
  7. Dec 22, 2009 #6

    DaveC426913

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    I don't see how you could do this. Unlike 3- and 4-wheel vehicles, 2-wheel vehicles must roll when they turn. In fact, even going straight, they maintain their balance by adjustments of roll.

    Stabilizing wheels would be disastrous.

    I would bet money that, if you actually tried this experiment, you would not get above 20mph and 100 feet before you rolled the bike.
     
  8. Dec 23, 2009 #7

    Danger

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    Actually, the California Superbike School uses specially designed outrigger 'training wheels' to remove the fear of tipping over during cornering. :biggrin:
    That's not practical for the street, though. From a scientific standpoint, any addition such as extra wheels will increase aerodynamic drag.
     
  9. Dec 23, 2009 #8
    Actually if the stabilizers are far enough apart they could easily improve performace.

    For example a car generally has more grip in a curve than a motorbike has simply because its outside wheel is further out from the centre of mass than it is on a leaning bike. (if you took away the inside wheel on the car it would fall inward). In effect a car is always leaning into the curve, even when it's standing still. The same would be true for a 2 wheeled bike with wide enough stabilizers.
     
  10. Dec 23, 2009 #9

    DaveC426913

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    This is counterintuitive. Why do you say it is so?

    When cars flip out, they do so by flipping outward, not inward.
     
  11. Dec 23, 2009 #10

    rcgldr

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    The main reason a car has more grip is that the size of the contact patches are larger on the car. Also if by "generally" you're comparing street cars with a typcial sport motorcycle, the bike has more grip because it uses a softer compound tire, compensating for the smaller contact patch. If you mean racing cars versus racing motorcycle, then the racing cars have better grip.
     
  12. Dec 24, 2009 #11
    I agree with Dave.

    Maybe it's just me, but I don't understand what's so hard about this!

    Get on a regular motorcycle and go, say, just 1mph.
    Now, WITHOUT leaning, turn the handle bars slightly.
    You will turn.

    NOW. Do the same going 10mph(or whatever the minimum is for total weight).
    You will flip over!
    So, you MUST lean(tilt) the entire motorcylce in order to prevent flipping over.
    Right? If you don't believe it I'm not loaning you my motorcycle.

    With that in mind, non-flex stabilizer wheels PREVENT LEANING.

    Much like a kid's tricycle.
    Try going even 5mph on one of them and make a reasonable sharp turn. Forget it, you will flip over!

    If the stabilizers have flex(to allow leaning), that's a different story.
     
    Last edited: Dec 24, 2009
  13. Dec 24, 2009 #12
    Man up and ride a regular motorcycle. The only real reason I could see someone needed training wheels err "stabilizers" is if they are on too big of a bike to safely touch the ground with their toes. Again you shouldn't be on a bike that is too big for you to begin with.

    Now to the science thing, If you were to have training wheels, excuse me, stabilizers on your bike you wouldn't be using the bike to its full potential, since they are made to be dropped into turns. Even if the stabilizers were flexible and out far enough, they wouldn't allow the bike to follow its natural progression through the turn.
     
  14. Dec 27, 2009 #13
    sorry jeff, but I don't think that's true. I think the size of the contact patch on a motorbike is huge when taken in proportion to the weight of the vehicles. If tyre size was the only factor, bikes should have tremendous cornering grip when compared with cars. But the fact is that they don't.
    Well , (you contradict your first statement here btw), but I don't know where you get you're information Jeff but the fastest street legal motorbikes don't corner better than street legal sportscars. There's plenty of videos on the net that illustrate this fact. The bikes leave the porsches/ferraris in a straight line, (and maybe under braking too), but they always loose ground to the cars through the curves.

    I think that motorbikes just LOOK faster in a curve because they lean into it. Appearances can be deceptive.

    To DaveC426913, if you remove the wheels from the left side of a stationary car it falls to the left. If you did so on a car while it was going through a left hand corner it would still fall to the left.

    In other words (the more complicated part), the line drawn from the centre of mass of the car to the outside wheel(s) is always 'leaning closer' to the ground than the same line taken from the centre of mass of a motorbike taking the same curve at the same speed. That's always true. So the car is always 'leaning into the curve' more than the bike is.
    In fact it has to, otherwise it would flip over. ;_)
     
    Last edited: Dec 27, 2009
  15. Dec 27, 2009 #14

    DaveC426913

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    You are comparing apples to oranges.
    No, the car is leaning out of the curve. If it takes the curve too fast, it will start to flip; its centre of mass will rise, lifting its wheels and losing traction and skidding.

    The cycle, on the other hand, is leaning into the curve, which is why it will not flip over; what it will do is lose traction, begin to slide outward and its centre of mass will drop.

    But I still don't know why you think a car leans into a curve. It most definitely does not.
     
  16. Dec 27, 2009 #15
    Sorry for any confusion dave, but maybe you didn't quite understand what I was trying to say. My fault for not being more explicit, or more articulate.

    I mean the car is 'leaning into the curve' because almost all of the grip from a car pushed hard through a corner is generated from its 2 outside tyres. The car is now a 'motorcycle', pretty much balancing all its weight on those 2 outside tyres. OK? It's one of the reasons that motor racing is something of an art, the dynamics of the car are constantly changing depending on the situation, and keeping the car on the road takes a lot of skill.

    That's one of the reasons I don't agree with Jeff when he says a car has more grip than a bike in a curve because it has 4 tyres etc.. Fact is, in a curve at around 1G, the car is only really using 2 wheels. Apart from that this was probably way off topic

    Hope I explained myself properly this time.. (maybe ..).
     
  17. Dec 31, 2009 #16
    There are three components to "performance":

    1. acceleration
    2. cornering
    3. braking

    When you compare a sport-bike to a sports-car, the bike will only win #1 due to its superior weight-to-power ratio. The car wins in #2 and #3 as documented by numerous motorycle magazine comparisons in the past several decades. Around various racetracks in the country, this duel has been repeated time after time and the top bikes always loses to the top cars.

    This doesn't even consider the relatively closer configuration of a sports-bike to its all-out race relative. A top sportscar is much, much further away from a true racecar; yet it can still beat a bike in 2 out of 3 performance areas.

    As to T.O.E. Dream's question, what is meant by "performance" and how are these two additional wheels configured?
     
  18. Dec 31, 2009 #17
    Um, isn't that why curves in racing(not all racing, of course) are "banked"? To keep all 4 wheels on the ground and in functional use?!!
     
  19. Dec 31, 2009 #18

    rcgldr

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    In some cases, bikes can also out brake cars due to softer compound tires. At Willow Springs 2.5 mile race track, the fast guys can run around 1:28 on stock bikes (like GSXR 1000) with DOT tires. There are few stock sports cars that can match that time. The top race bikes run around 1:20->1:21, back in 2000 when AMA superbike was 1000cc, 1:19.029. Since AMA superbike is now back up to 1000cc again, I assume lap record will drop back down to the low 1:19's again.

    Motocycle lap times and records on page 11:
    http://my.wsmcracing.com/ul/file/Newsletters/WSMCNews1109.pdf

    Race car records:
    http://www.willowspringsraceway.com/trackinformation/records.asp [Broken]

    Because of the round profile, the contact patch on a motorcycle is small compared to a sports car with 250 to 325mm treadwidth, perhaps the overall contact patch area of the 2 tires on a bike is 1/6th or less than that of the 4 tires on a sports car. The bikes generally run softer compound tires than all but the lightest of cars. The Caterham CSR, at < 1400 lbs, is one of the lightest street legal cars, and is a somewhat popular track car in the UK and Europe.
     
    Last edited by a moderator: May 4, 2017
  20. Dec 31, 2009 #19
    Total contact area has to do with tyre-pressure. Autos typically use about 40psi hot on the track. Take the case of a 3200lb sportscar, 3200lbs/lbs/sq.in. = 80 sq.in contact patch. Motorcycles typically use 50-55psi hot and end up with more weight per sq.in. on the ground.

    Coefficient of friction for rubber changes with vertical loading in a non-linear fashion. I'll try to find a chart of CoF versus vertical loading. I think it was in one of Carroll Smith's "To Win... " series.

    And the big track at Willows is a power-track. So the motorcycles will obviously do well. Although a previous-gen. Corvette Z06 will do 1:29 on street tyres. Add DOT-R tyres and you can shave 3-4 seconds off. Here's the results from the http://web.archive.org/web/20030924233239/www.opentrackchallenge.com/trackrecords/willow.htm. Street cars aren't too far off the AMA SuperBikes times. If we really wanted to compare cornering and braking of cars vs. bikes, we'd us the Streets course or Laguna Seca.
     
    Last edited by a moderator: Apr 24, 2017
  21. Dec 31, 2009 #20
    Jeff, you seem to forget that a car can't use all 4 tyres in a curve. That would be against the laws of physics as I'm sure you're aware. In corners at 1G and above the car's only really using the 2 wheels on the outside. So it's just a very heavy motorbike really. A porsche 911 for example weighs around 5 or 6 times that of a sport motorbike, and all of that weight is is on 2 tyres when its pulling 1G or more.

    If bikes have to resort to using softer, grippier tye compounds to keep pace with the cars through the curves then you're agreeing with my statement that with all else being equal, the car will have more grip in the curve than the bike. In other words the bikes have to 'cheat' to keep up. QED...

    Btw, the Caterham is only popular with people who can't drive rear or mid-engined cars. Real sports cars have most their weight on the rear end to keep the vehicle more agile. [You can argue that it's more complicated than that, but agility is what it boils down to] This has nothing to do with bikes v cars though, I just don't think of caterhams as real sports cars....
     
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