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Sachs Rear shock issue - Breva 11

Discussion in 'BNS12 Chat & Tech' started by GrahamNZ, Feb 24, 2010.

  1. GrahamNZ

    GrahamNZ High Miler

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    (Split from the Monoshock removal thread. - Todd)

    Re; OEM Sachs unit: The NZ suspension Guru has come across several Sachs units on Aprilias (and our Guzzis are effectively Aprilias) where the damping piston had been fitted the wrong way around. As You know, a unit with bad compression response can easily give the effect of spring bottoming. BTW at the "Standard" preload setting my Breva has 10mm unladen sag, (7% of axle range) which does not indicate that the spring is too light for the bike's weight. Maybe with a large rider, pillion and luggage it may be of course.

    On the other hand the front unladen sag is 30mm (25% of axle range) which is a bit more than ideal.

    Measurement starting points were taken with helpers lifting the weight off the suspension but with the wheels still on the ground. That method ensures that the topout springs don't produce false readings. Sag figures were taken after the suspension had been depressed and allowed to settle back naturally. Without fuel would have been even better but the bike had about 16 litres aboard at the time.

    Update:
    Interim report from the NZ suspension Guru. Basically the message is that the OEM Sachs shock is poorly matched to the bike. The spring is too light and to try to compensate has too much initial preload. A more powerful, non-progressive Ohlins spring with less initial preload will be fitted to correct this. The damping characteristics are also woeful but can be altered to correct that.

    In short, I'm not imagining that the rear suspension unit isn't up to snuff and my arthritic back isn't totally responsibe for the pain it feels.

    My advice is to go for a better quality Penske suspension unit, as Todd is offering, if you can afford it. Fitting a different spring will help, but not cure the damping inadequacies, in fact it may make the inadequacies more apparent.

    Seat of the pants judgements are one thing, but no equivalent to what a suspension dyno will reveal.

    I dread to think what the local Guru will say when he attacks the front forks. At the moment the plan is to fit Race Tech cartridge emulators and non-progressive Ohlins springs of a suitable strength and initial preload.

    More later.
     
  2. GrahamNZ

    GrahamNZ High Miler

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    Upgrading the rear unit is now completed.

    A more powerful Ohlins spring has been fitted with 10mm initial preload - that's the preload not controlled by the adjuster. The original Sachs spring was too light for the bike and had a massive 20mm of initial preload in order to give a reasonable unladen sag figure, but was then riding too far into its stroke, making it prone to bottoming and robbing ride height and consequently ground clearance and steering response. The stock spring is never likely to be satisfactory, even on smooth roads. IMHO getting the springing matched to the bike's own weight is fundamantal and not to get that right is unforgivable for any manufacturer.

    Now for the damping. IF the springing had been appropriate, the damping MAY have been OK on smooth roads but not for anywhere where abrupt bumps or corrugations are present. NZ backroads in particular can be pretty gnarly and for our conditions the damping is woeful. A lot of reworking of the damping has been done to suit our roads, and the new spring, and according to the suspension guru, few if any bikes have stock damping which can cope anyway.

    More later after suitable testing, but IMHO NZ owners at least should seriously consider upgrading the suspension. These bikes deserve it and our roads demand it. Ditto the front suspension. Unfortunately it will be later this month before the forks can be upgraded as well.
     
  3. GrahamNZ

    GrahamNZ High Miler

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    My upgrade was under $NZ600. With the exchange rate around $US0.68 at the moment getting one of your Penske units here would cost a lot more. Like, unit cost, shipping to NZ - which is a lot, GST of 12.5% in $NZ. I considered a Penske but the $ put me off. Also our suspension Guru can modify the unit if required and he's a genius in whom I have total confidence. For cost conscious NZ owners my recommendation is to have Robert Taylor tayler your suspension to suit your riding mode and weight.

    For ANYONE else, my recommendation is to go for the most sophisticated Penske unit offered by Todd you can afford. As these are usually long-term ownership bikes, you will forget the cost but never fail to marvel at the improved ride quality.

    Oh, and do the front end mods he suggests too, cartridge emulators but with a constant rate spring. To quote our Guru, "There may be a place for a well designed rising rate spring, but what most bikes need is a diminishing rate spring, if such a thing was possible." Imagine how any damping system could cope with a spring of variable strength - of course it can't.
     
  4. Zapa

    Zapa Cruisin' Guzzisti

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    I went with rising rate springs for the front without the cartridge emulators... :/

    Shock is still unchanged. We'll see.
     
  5. GrahamNZ

    GrahamNZ High Miler

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    Zapa

    The damping rod forks on the Breva are about 30 year old technology when fitting rising rate springs and playing with oil viscosity and volume were all that could be done to upgrade them. But technology has moved on and the cartridge emulators effectively turn the forks into tunable modern forks. Who would want 30 year old tyre technology now, so why accept 30 year old suspension technology?

    Opinions vary on most things, including rising rate springs. My opinion is to avoid them, because Ohlins don't favour them and nor does the NZ suspension Guru. Ohlins are generally considered the ultimate suspension components, as shown by the bikes and racers using them. My 1997 Triumph Trophy was transformed by fitting Ohlins suspension. A bit like comparing midnight in a coal mine during a power cut with the blazing light of the NZ sun on 22 Dec. Our air here is extremely clear by the way, and everything tends to look excessively sharp!

    Fitting rising rate springs alone may be better than doing nothing but that's all that can be said for it. IMHO of course!

    Then again, if the roads ridden are perfectly surfaced then the stock suspension may be OK. Heck, even a rigid bike might be OK. But here and in many other places I suspect, roads are far from perfect and the best upgrade that can be made is to improve the suspension. Fankly I'm ashamed that I've put up with the stock suspension for so long. My worsening arthritic back and my Buell's vastly superior suspension made me realise that and do something about it.
     
  6. Zapa

    Zapa Cruisin' Guzzisti

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    Well, the fork should be being dismantled as I type, so I'll let them tweak the suspension with the Hyperpro springs and 15W oil I brought to them and see what I get. I won't make less than 10K Km with that setup, and by then I can decide to install the emulators over those springs if i'm not happy.
    Fortunately for me we have quite good roads around here, and I can always ride slower in the bad ones ;)

    Of course I'm assuming the 12S and Breva forks are identical apart from their different tuning screws...
     
  7. rturo

    rturo Cruisin' Guzzisti GT Contributor

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    Graham
    With the front I was unhappy with the amount of dive from the off. I’m sure the cartridge option you have gone to is best upgrade without chucking the legs and couple of suspension guys here in the UK recommended such. What I settled for was getting a suspension specialist (that's all he works on) to strip it down and rebuild the forks. He fitted better quality springs (non-progressive) and top quality oil. Great improvement and I put most of it down to optimizing the springs to suit only one set of parameters (ok weight), and the fact that the guy selecting the springs and filling the legs was selecting from experience, then testing, the best oil weight to match the springs … fancy that

    I always work on the law of diminishing return … if $$ gets me 80% of the possible improvement is it worth the same amount again to get the last 20% .. especially if I don't ride hard enough to use the last 20%... horses for courses.

    I haven’t found the rear unit on my B11 to cause me any worries. That doesn't mean I disagree with your/Todd’s findings. Perhaps it’s just a combination of my extra weight/Additional Seat Suspension that masks the weakness, or that I ride too slow to worry it – I’ve never even grounded the stand... you are both making me think about it though.

    Art
     
  8. GrahamNZ

    GrahamNZ High Miler

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    Art

    You're lucky to have a suspension Guru to call on. Our Robert Taylor is exactly that and works only with suspension. Fitting decent constant rate front springs - the stock are progressive - and appropriate oil is certainly a step in the right direction. Where the emuators earn their keep is that they improve the damping and are tunable.

    There is only one word for the rear suspension unit - shocking. It's undersprung and has woeful damping characteristics for all but the smoothest roads. On the way home with the new bike over our "racer road" mountain range I had to stop and wind the rear preload to max because the stand was grounding so badly. My normal riding weight is 90kg plus 10kg of luggage, so I'm not a big chap. Even with the stand modified with a grinder, it still grounds a lot. It'll be interesting to see how the reworked rear end alters that.
     
  9. rturo

    rturo Cruisin' Guzzisti GT Contributor

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    I managed to find a suspention guy who was only 100 miles away ... the roads between are good bike roads so the improvement was easy to feel ... the downside was that I had to leave the bike a few days so he could try more than one spring/oil combo if necessary ... and so I ended up with a "Car/Train/Taxi/Work/Taxi /Train/Bus" journey from hell to pick it up..... need a trailer if need him again!
     
  10. kiwi dave

    kiwi dave GT Reference

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    Graham, it's interesting that you're finding the spring rate inadequate, compensated with greater preload and compression dampening. Knowing that preload adjustment does not change the spring rate, the "harshness" of the ride must be the result of the compression dampening. I await your back report with interest.

    Of course, this scenario has already been experienced with the early Norge (including mine) which shares that same rear shock and spring as the Breva. It is only 15 kg heavier, so when riding two-up with luggage, I soon found the limitations of the setup and replaced the spring with a beefier unit. But I don't think I've ever bottomed out the suspension on the Breva or the Norge, the main frustration was scraping the centre stand when it was being forced lower because of the muffler spacer necessary to accommodate those horrible Aprilia pannier bags. Perhaps I just don't ride hard enough, although I have bottomed out earlier (pre-EV) California suspensions (both front and rear).

    I guess the main problem is that spring rate has to be matched to the load, and this requirement can change significantly when changing from solo to adding a pillion and luggage. I don't think any manufacturer has the answer for this, although I was curious about gas suspension on some Harley models.

    Keep up the good work and the reports.
     
  11. GrahamNZ

    GrahamNZ High Miler

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    Hello Dave

    The "development work" continues, which is why I haven't posted results yet. Robert is very busy just now with his race bike work so I'm awaiting return of the unit after further damping recalibration. I can now remove the shock by myself in 10 minutes and refit it in 12!

    What is clear already though is that the impact damping in particular isn't up to our gnarly road surfaces. The new spring is much better at coping with loading weights but the damping is being increased to match it better.
     
  12. kiwi dave

    kiwi dave GT Reference

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    Hmmm, I would have thought that a beefier spring and increased dampening would be less able to absorb those smaller bumps that you described was getting to your back.

    I guess the proof is in the pudding.

    BTW, I don't think our Kiwi roads are that bad. The surface chip seems hard on the tyres, especially in the South Island, but for "bumpiness", they compare favourably to what I experience in the USA (West Coast).
     
  13. GrahamNZ

    GrahamNZ High Miler

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    Hello Dave

    The new spring does support the load better, as witnessed by better sag figures, so it's probably just fine. What seems to be needed now is more rebound damping because during testing I found greatest compliance when using maximum rebound adjustment. What I probably need to do next is to have someone without a back problem evaluate the ride. Friend Brian, whom you've met, is the victim I have in mind. He likes Guzzis and I've left mine to him in my will!

    Faith and hope!
     
  14. GrahamNZ

    GrahamNZ High Miler

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    Damping tuning now revised. Result, bliss at the rear. Now the sharp bumps which matter are being noticed at the handlebars instead of the seat. Winning! Now for the forks......
     

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