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Dick Mann Lean angle

Discussion in 'Motorcycle Related Discussions' started by jseng1, Oct 23, 2019.

  1. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    My brother works on Vincents all the time, in his retirement. The other day, he said 'if there is a wrong way to do anything, they have done it on a Vincent'. There was guy in Melbourne in the 60s who was always bullshitting on about how good Vincents are. He tried to road race one, and after he had slid up the road on his back at 100 MPH in front of a big crowd, he fitted a sidecar to it and went racing safely. I find that photo of Surtees on the Vincent reassuring. It lets me know that he was actually human. 'Some things are so bad that they are good' ?
     
  2. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    When you are in a corner at an extreme angle, there is a balance which must be maintained between the power you apply and the grip you have with your rear tyre. If the angle of lean is less, you can apply more power. If the bike quickly becomes upright as you come around a corner, it does not matter if the rear wheel spins as you accelerate. With a bike such as a TZ750 Yamaha, you have to allow for sudden changes in the power delivery. With a Commando, you don't usually have that to worry about. With my bike, I always go under the other riders in corners. Most race bikes tend to run wide in corners. The steering geometry is critical.
    With that bike of Dick Mann, I think it is a 4 pipe CR750 Honda - every time it came on song, it probably would have given it's rider a kick in the bum. So if it was set up to oversteer, it would have been more difficult to ride well. If you have got a bike which is nasty, neutral steering is better.
    There is a video by Alan Cathcart about the Suzuki MotoGP bike of about 1993, which was set up to oversteer. It was underpowered, but won the championship that year. A current MotoGP bike is probably never set up that way. Cathcart's article on the Kocinsky RC45 Honda is also interesting. It could be powered through corners.
     
  3. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    I found out about bikes understeering when brakes are applied or drag, by dodging small trees at Phillip Island in 1969. I did not know why I could not get around any corner. When the front bake drags, the more you accelerate, the more the front goes down. I can laugh about it now, but at the time it was not funny.
    I might have this wrong, but I think that when you reduce the yoke offset, you increase the trail. When you increase the rake, you increase the trail. When you lower the yokes on the staunchions, you decrease the rake, so you decrease the trail. When you raise the rear suspension, you decrease the rake, so you decrease the trail. When you decrease the trail, you make the bike more stable. When you increase the trail, you make the bike less stable and more likely to oversteer.
     
    Last edited: Oct 25, 2019
  4. cehenard

    cehenard VIP MEMBER

    Joined:
    Sep 29, 2014
    When I grow up I want to be acrotrel. I'm always amazed by people who know EVERYTHING. I also like the picture of Surtees on a piece of crap Vincent, trail breaking through a curve. It lets me know I'm not totally stupid.
    Charlie
     
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  5. Snotzo

    Snotzo

    Joined:
    Mar 12, 2013
    Guys,
    do yourselves a favor and read ALL the posts, then you'd understand that the imbecile hanging off the Vincent is NOT John Surtees, but some Ape the Racer type, posing for a magazine picture shoot. Surtees was a very neat, tidy rider who knew the benefit of keeping as well tucked in as possible to minimise windage and drag. The tyres available in his day were even worse than those Dick Mann had, and they were pretty damn awful compared with what we have today.
     
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  6. o0norton0o

    o0norton0o VIP MEMBER

    Joined:
    Apr 27, 2015
    Alan, It's obvious you don't know the mechanics of rake and trail. If your front end dives under breaking, you momentarily get steeper rake and LESS trail. Ask yourself this, if Less trail is less stable, then how can the bike become more stable when braking compresses the front end and gives you LESS trail...

    I'm done correcting you on this forum. I wish one of the racers here would correct you but I'm sure you would just talk in circles like you usually do, and next time you post it will be the same mistaken physics and incessant babbling about "tightening lines"...
     
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  7. acotrel

    acotrel

    Joined:
    Jun 30, 2012

    Less trail makes the bike more stable, in fact if the trail is small enough the bike can stand up under brakes and turn the wrong way throwing you off-balance. ( Garden gate Nortons were like that). When you practice on a race bike, you usually start off fairly slow and work up to the corners on the circuit as you brake - you also practice getting on the gas earlier coming out. The objective is to reduce the rolling distance in the middle of the corner. As you get faster, you eventually reach a point where you go into the corner a bit too hot. The next thing is you find yourself trying to wash-off speed in the corner, so you brake slightly harder. Then as the front stays down, you tend to run wider with the edge of the bitumen coming towards you. You are often at an extreme angle of lean and near the limit of adhesion of the rear tyre. If you keep holding the brake, you continue on your outwards trajectory until you hit the grass and drop. If you get back on the gas earlier, the front comes up and the bike will usually steer out of your problem. It all usually happens at fairly high speed, but because you have been practising, you can usually cope.
    What I have just said applies to a bike with NEUTRAL steering. If the bike understeers, the situation is worse. If it oversteers when you gas it, you can almost power right through the corner after you have braked before it.
    .
     
    Last edited: Oct 26, 2019
  8. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    With a manx Norton which has 19 inch wheels and 24.5 degree rake, it is almost impossible to reduce the yoke offset and give it more trail. When you ride the bike, the most noticeable thing about it is that if you get a bit off-line, you just give it more stick and it will come back on line. The fork yokes off some rigid frame nortons look the same as those on the manx, but have much more offset. If you fit those by mistake, it is a recipe for disaster. The bike's handling is a combination of rake and trail. If you fit smaller wheels, the trail changes and the bike becomes heavier handling. Most modern manxes probably have 26 degree rake and 18 inch wheels, to get decent rubber. If you could reduce the yoke offset, it would not be necessary to change the rake on the after-market frames.
     
  9. o0norton0o

    o0norton0o VIP MEMBER

    Joined:
    Apr 27, 2015
    Here ya go. Perhaps you can correct the rest of the planet starting with this wikipedia page...
     
  10. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    With my bike, there is never any feeling of resistance as I turn into corners. If you can feel that happening, your steering is probably more towards neutral that that of my bike. If you have to reverse steer, your bike is a pig,.
     
  11. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Depends on the weight of the motor. Some Harleys use rakes of 31 degrees. Doesn't increasing the rake increase the trail ? The problem is there is a presumption that more trail increases stability. It also depends on whether you are braking or accelerating. Less trail as you brake causes the bike to be more stable, but as you accelerate the bike tends to run wide. If you give it more trail, the effect is a shift in the handling profile, towards less stable as you brake and more self-steering as you accelerate. With most road bikes, as you accelerate out of corners they tend to run wide. A TZ350 Yamaha is designed to stay neutral as you accelerate, so nothing nasty happens. It has 26 degree rake very short yoke offset and 18 inch wheels. My bike has 18 inch wheels, about the same wheel-base and I use TZ350 fork yokes with 27 degree rake. It does not handle like a TZ350 Yamaha - it is much more active when I accelerate out of corners. It makes a very big difference to the way you ride the bike. I have never been so heavy-handed in my life. With most bikes, you need to be very careful in corners. With this one you simply flash in under brakes and get straight back onto the gas.
     
  12. Seeley920

    Seeley920

    Joined:
    Jan 6, 2009
    when you've only got 25 hp you can do that o_O
     
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  13. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Commandos are not very powerful. And you need to what you can with what you have got. My bike gives me a bit of apprehension. I once led a field full of Z900 and H2 Kawasakis for almost a full lap of Winton, with my 500cc Triton - when I lowered the gearing and softened the suspension. The Seeley 850 is much faster than that. With bikes when things are going really well - that is when you are likely to have your biggest crash, because you get complacent. I suspect the bike is waiting to bite me - if it has another hidden handling defect, it will probably reveal itself when the bike is going extremely fast. So far I have done about 200 reasonably fast laps on it, but time will tell.
    The last time I raced was about 6 years ago, and I don't know when I can get on Winton again. But I am starting to get over my grief thing- so in while, I might have another ride.
    Two of my friends have died and both were associated with my racing activities at Winton. For about three years I went to the historic meeting there, got to the gate, then turned car around and went home . For the last two years, I have actually gone inside and watched the bike practice sessions.
     
    Last edited: Oct 26, 2019
  14. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Al, sometimes I like to pull your leg a bit mate...

    Not this time, I’m being serious for once...

    You haven’t raced for a long time. That means that really, to be safe, your bike pretty much needs pulling apart and ‘going through’ before racing it again. So, whichever way you look at it, it’s gonna be time and cash consuming.

    But worse, you used to race at a certain level, but now you’re out of practice and with older / slower reflexes. You face a real danger of thinking you’re the same rider that you used to be as soon as the ‘red mist’ comes... and coming a cropper.

    And worse still, you clearly have a lot of apprehension / anxiety in your about venturing back on the track, which as you know, is a sure fire way to increase your chances of crashing.

    All in all mate, what I’m saying is, is it really worth it ?
     
    Last edited: Oct 27, 2019
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  15. Danno

    Danno

    Joined:
    Feb 7, 2010
    My Harley-riding buddy who used to have an H2 750 3-banger still thinks it was the fastest bike ever to hit the streets. I offered him a ride on the back of my ZX-14, but he declined.

    The world changes every day and if you don't change with it, you're left in the dust.
    I was a re-entry rider after a 15-year layoff and basically had to learn everything all over again. I can imagine how tough that would be for a re-entry racer.
     
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  16. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Nigel. - Here is a simple straight forward question : Modern Ducati racers have adjustable rake which is effected by bushes in the steering head. If the bike is running wide as you accelerate out of corners, which way would you move the rake to stop it from doing that ? - would you increase the rake or would you decrease it ?

    The last time I raced was about 6 years ago. The competition were all the fast guys in period 4 historic on methanol-fuelled 1100cc CB750 Hondas. In the first two races, I was well up in the lead bunch. In the last, I rode under the three leaders and was passing the front guy when the fuel line popped off. These days it takes me about 5 laps of Winton to get up to 90% of race speed. The last 10% comes from a couple of race rides. So please don't bullshit me about making comebacks. In the past I have raced when I've had influenza - nothing can be worse than that. These days I'm very unfit, but if I had more money I would still race.
     
    Last edited: Oct 30, 2019
  17. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Joined:
    Dec 3, 2012
    I would be looking at the other end first.
     
  18. acotrel

    acotrel

    Joined:
    Jun 30, 2012

    Which way did Mike Edwards move the rear suspension and did it work ? If you raise the rear suspension, you decrease the rake. There are about three of his videos which show the same thing :

     
  19. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Joined:
    Dec 3, 2012
    Swing arm angle and anti squat have an effect on exit behaviour as does weight transfer on entry under braking.
    I prefer to just enjoy the ride, wave to the cows.
     
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  20. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    There have been Honda race bikes which have had low centres of gravity. Because the bike does not rock backwards and forwards so much, they did not handle very well. The Kocinsky RC45 Honda did not have adjustable rake, so the handling was changed by altering yoke offsets and the suspension. In the same year. the Aaron Slight bike was different to suit his point and squirt style, which was slower than Kocinsky's technique of powering through corners.
     

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