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fitting new Falcon alloy rear shocks

Discussion in 'Norton Commando Motorcycles (Classic)' started by SteveBorland, Mar 22, 2019.

  1. Fullauto

    Fullauto VIP MEMBER

    Joined:
    Apr 13, 2009
    I've got about 50,000 miles on a pair on basic Ikons with absolutely no issues. In fact, I don't even think about the rear end at all so, they must be doing well.
     
  2. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Al you may have a point about the damping, I’d not thought about that but it does sound logical / possible.

    And whilst I agree that it is very often the case that ‘front end issues are caused by the rear’ it wasn’t the case this time. The front wheel was visibly bouncing up and down. It only happened around Gerard’s which is a LONG sweeper (technically it’s taken as two bends). So in this case, I know I had issues at both ends, and each end was possibly also effecting the other!

    It occurred to me that as I only do few track days these days, I could waste the next 3-4 seasons on incremental trial and error problem solving... or I could bite the bullet and do it right (Maxton) and given I’m putting the 920 motor in, I wanted it to be right !

    Glen, they’re not cheap, I’ve forgotten exactly but shocks were nearly £500 and forks nearly £1000 by the time I’d done opting for the adjustability and having fancy plastic bushes made and blah, blah. The more basic ones are cheaper, and would probably be perfectly fine if I’m honest with myself!

    I think it’s important to note that my bike handled fine on the road, the shortcomings only showed up on the track, when pressing on a bit.
     
  3. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Unfortunately, you can usually only get a bike set up right by racing it. Even if you attend practice days, you often don't find all the bugs. When I was racing regularly, my bike was usually pretty good. These days, I cannot even ride at a practice day without finding major problems. When you are actually racing, your mindset is usually different from what it is on a practice day. On a practice day, I am never so determined, so the bike does not get stressed to the limit. For me, after 4 race meetings in a year, my bike and I are usually spot-on. But these days, you would have to be a millionaire. If I go to a practice day, after 5 laps I am usually up to about 90% of race speed, but that last 10% never happens.
    Public roads are often smoother than race tracks and in any case there are laws against riding your bike there at a level which would approach it's design limits. To me, I cannot understand why anyone would ever buy a Ducati sports bike and ride it on public roads - it is a shocking waste of something which is really beautiful. Some of the kids in Victoria love to ride their road bikes at Phillip Island, I suspect they really do not know what they are doing. If you don't race regularly, that can be very dangerous. On some of those smooth high speed bends, you only need to twitch to go wrong.
     
  4. Chris

    Chris VIP MEMBER

    Joined:
    Jan 21, 2008
    Springs fully compressed.
    Bike running wide exiting bends.
    Backside passing buttons!
    Picture tells the story.
    Maxtons were too short for a MK2.
    Chris 8083662332_b2a6993b80_b.jpg
     
  5. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    And springs too soft Chris?

    I think that bright red paint is too heavy.

    That’s why folk have bare frames innit ?

    BTW you’ve got some loo roll stuck on your back...
     
  6. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    But being serious for a mo’...

    Pics like that shows the value of track side photographers... big time.

    You can see from your pic that those shocks being too short and / or too soft have totally screwed up the design intent of the geometry of the chassis!

    Without the pic you might have been chasing your tail trying to figure out what was wrong for a whole season. Or more!
     
  7. Chris

    Chris VIP MEMBER

    Joined:
    Jan 21, 2008
    Hi Nige

    Correct on all points. When I saw the photographs I was thrilled. The bend leads on to the back straight, the camber goes away from you & being a car track it has big rumble strips & a trench the other side! I could not keep the bike off the rumble strip.
    Soft springs, shocks an inch to short? Driving hard compressing the back end & the bike walking, not evil just not not holding its line. I believed the rear tyre might have been on it's way, but the photo says it all.
    I don't think about the handling now, she wears an old pair of Koni's. The Maxtons are on the MK4 that uses a shorter shock, with the springs one up on adjustment.
    Chris
    Ps duct tape repair to gravel rash. Loo paper elsewhere!!,
     
  8. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    That frame looks to have less rake than 27 degrees. If it is one degree less, might make it tend to run wide coming out of corners. The Manx Featherbed frame has a rake of 24.5 degrees and extremely short yoke offset, and they tend to not run wide as you power out of corners, but come back on line as you give the motor more stick. Your yoke offset looks very similar to mine. I think the after-market featherbeds use 26 degree rake and 18 inch wheels and steer very neutral. Changing from 19 inch to 18 inch wheels on a Manx featherbed, makes the bike tend to run wide.
    Does your bike tend to understeer as you brake, or get hard to tip in ? If it does, it will probably tend to run wide when powering out of corners. Mine stays neutral as I brake and tends to tighten it's line as I power out. The problem might be, that I suspect that one day, my bike is going to high-side me as it wheel-spins coming out of corners. It feels really great, but that is often a bad sign.
     
    Last edited: Mar 24, 2019
  9. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    With a road bike, it is supposed to become stable as you brake and the rake steepens, and stay neutral as you accelerate out of corners and the rake becomes shallower. The problem is you just cannot ride that sort of bike very quickly through corners, because you cannot get back on the gas early enough. That is probably why when you watch an on-board video, most guys are forced to back-off when halfway around corners. When I was racing years ago, I never thought about such things - I simply adjusted to the bike. With the Seeley, I just found out by accident, and scaring myself.
    If you think about it - if you are running wide, it is not natural to gas the bike harder. The usual response is to brake or at least back-off, then the bike becomes more difficult to turn.
     
  10. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    If your shocks are too short, you have probably shifted the mid-point of the steering geometry. The steering would be too unstable, both going in and coming out. You want the shocks shorter as you come out of corners, not going into corners. Going in, you want the bike to rock forward and steepen the rake until the bike becomes neutral steering. Then rock backwards and oversteer as you power out. With my Seeley, I had the experience where the bike did not stay neutral as I braked - as I braked it tended to stand up. Then when I braked hard going into a corner during a race, it actually stood up and turned the wrong way, throwing me off balance. I turned it on again to get it to the grass and drop it, and it came back under control. Then I dramatically reduced the yoke offset and all became lovely. So you figure it out. You need to be conscious of what your bike is doing as you brake and accelerate in corners. What I have been saying is obviously not what most guys believe happens.
     
    Last edited: Mar 24, 2019
  11. Chris

    Chris VIP MEMBER

    Joined:
    Jan 21, 2008
    Bike handles like a dream. Look at where you want to go & it goes there. Drive it through the bends as hard as you like. Brake as hard as you like. Standard set up as per the way Colin Seeley made it. Just a bit orange.
    When I ran my Rob North for the first time it handled well but ran wider on the bends, it didnt just go where you wanted like the Seeley. However once I got it up to speed & gave it the berries, it was spot on. You just had to run it as it was intended to be used.
    Chris
     
  12. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Colin Seeley's bikes and the Featherbeds were obviously developed over many racing miles. When I bought my Mk3 Seeley, it had been used to house a heavy 750SFC Laverda motor and had Ducati 450 fork yokes which had about 70mm of offset. After I had the problem, I fitted TZ350 Yamaha yokes which have about 30mm of offset.
    I have a magnetic base protractor which I stick to the fork stanchion. But I can never replicate the conditions at the front of the bike which occur when I am actually riding it. My suspension travel is about 2 inch, front and rear, and the wheelbase is about 54 inch. So the difference between the two rake angles (and consequently the trail) when braking and accelerating is 3/5 ths of bugger all - but it is critical.
    My other project is a 600cc two stroke - a modified H1 Kawasaki motor in an Egli replica frame. I use RGV250 Suzuki wheels and front forks. The early RG250 had an 18 inch rear wheel and 17 inch front, but I use the later RGV set-up with two 17 inch wheels. Between the two arrangements, Suzuki specify half a degree difference in rake . If I get it wrong, it can really stuff me. That half a degree can be extremely dangerous.
    Before I had the Seeley, I would simply adjust to whatever bike I rode. Now I think differently. I never previously rode a bike which gave me such confidence. When it self-steers in the right direction as I power out of corners, I can give it so much stick and so early, that it is obscene. It is not me, it is the bike - it never runs wide as long as I keep accelerating. On high speed bends, it is just bloody rude. You simply brake slightly before them then give it everything right through the bend. When I ride it, I sometimes think 'I should not be doing this', it feels wrong- but it is quick.
     
  13. SteveBorland

    SteveBorland

    Joined:
    Nov 15, 2010
    I'll be (hopefully) taking photos on Thursday evening partly to help me decide how to get around this problem.

    So far, I've had the following thoughts:
    1. dump the chainguard
    2. cut a hole in the existing guard
    3. make up a simple guard from folded sheet metal of glass fiber
    4. move the top shock mount outboard by 7mm
    5. find an existing guard and modify
     
  14. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Number 1 sounds simplest Steve !
     
  15. SteveBorland

    SteveBorland

    Joined:
    Nov 15, 2010
    Simple is good :)
    First step though is removing the standard guard to see how much space there is. I notice that you were using the steel body shocks, which are rather smaller in diameter, that makes a big difference.
     
  16. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    My Falcons were alloy bodies Steve.

    Maybe you’ve got a posher version with more adjustability or something?
     
  17. SteveBorland

    SteveBorland

    Joined:
    Nov 15, 2010
    No, you're perfectly correct, same ones as I have. I was confused (blinded??) by the Maxtons, which do seem slimmer in that area :)
     
  18. peter12

    peter12

    Joined:
    Jun 18, 2013
    Surely not old tyres Chris?!
     
  19. Chris

    Chris VIP MEMBER

    Joined:
    Jan 21, 2008
    Hi Peter
    Just brought a set of scrubs, just to be told they are ancient lol
    Speak soon
    Chris
    Are you about in April?
     
  20. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Many old tyres return to giving grip after being used a bit. These days, the young guys are very tyre dependent, so rain becomes a leveller. I use Battlaxe tyres, and when I first got them, they meant nothing to me because I was riding so far within their safe limits. My riding style has been conditioned by pain. In the old days you only had to have the slightest change in mental state and you were down.
     

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