GrahamNZ
High Miler
(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.
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.