Ohlins - weird sag figures?

[sproggy]

I realise that the subject of adjustment on Ohlins shocks has been discussed many times, so apologies for bringing it up again but having searched through past threads I can't find an answer.

I've just fitted a second hand rear Ohlins to my 1150, retaining the standard front which has the preload on the second 'notch'. I've set the Ohlins up with rebound 12 clicks off max and preload initially on 3 turns off minimum. However even setting it anywhere from minimum to maximum, I don't seem able to get the sag figures right - the preload setting makes only a couple of mm difference.

Sag without me on the bike is 25mm, compared to the recommended 5-10mm. Sag with me on the bike is 53mm which would be OK if not for the previous reading. Help!

Riding the bike is inconclusive because the roads are damp and very cold, but I slid the rear several times and it felt a bit like riding with an under-inflated rear tyre. The tyre pressures are correct and there is no kink in the preload tube.

I am about 73kg (160lb?) plus kit and I was told that the spring is standard although I can't see the number now it's fitted. I have just noticed when I went to check, though, that there is oil visible on the pushrod which doesn't strike me as very healthy. Perhaps I need it rebuilding? Not news I want to hear when I've only just bought it, but you take those chances....

Can anyone suggest what the problem might be? Otherwise it looks as if I might have to pay a visit to Harris and/or revert for the moment to the standard shock.

 

[sproggy]

Actually, forget all that - the unit is shot and badly in need of a rebuild - it's leaking oil all over the place.

Kind of explains why I couldn't get the preload adjusted right if there's not much oil left in it......

 

[garyfzs]

They need rebuilding about every 12000 miles, hope you didn't pay too much
Gaz

 

[sproggy]

...hope you didn't pay too much
Gaz

Well having found that it's unusable without a rebuild yes, I did.

But even with the cost of a rebuild it still comes out costing significantly less overall than a new one and once Harris have worked their magic it'll be good as new and a known quantity so I guess it could be worse.

Had it not been re-buildable it would have been a different matter!

 

[Mzokk]

Sag isn't going to be affected by the banjaxed hydraulics. The 5-10 mill static sag referred to in the Ohlins Manual is really for sports bikes where suspension travel is about 120mm. The BM has 190 mil of suspension travel. On a sports bike you have the right sort of spring rate if with static sag set at 5-10mm you get 25-40 mm of laden sag ¼ -1/3 of the suspension travel. So for the BM you’d be looking for about 20-25mm of static sag and 45-65mm of laden sag for the same effect. My only experience with ohlins is on my GSXR600. Great bit of kit but came standard with way too much rebound damping so much so the shock couldn’t react to a series of bumps and pumped down. Lots of adjustment to sort it mind. Haven't a clue how you would measure front sag on the bm with the telelever front (easy to do with conventional forks using a cable tie) But set it up with similar laden sag at each end and so that it boings down and up at the same rate either end when you compress the suspension.

 

[Mzokk]

Clarence Bell

Northern Office 9 Cardy Road

Greyabbey

Newtowards

County Down

BT22 2LS

N. Ireland

Telephone 0044 (0)28 4278 8854

FAX 0044 (0)28 4278 8841


This chap is the Ireland Ohlins importer and charges £80 to rebuild re oil and regass shocks. Haven't a clue what you'll be charged over there mind!!

 

[sproggy]

Sag isn't going to be affected by the banjaxed hydraulics.

It is. The hydraulic preload adjustment is knackered (leaking oil) which means it's not possible to increase the preload above that which results from the static mechanical compression of the spring. Since increasing preload is the means by which you reduce sag, the sag is very much affected.

I take your point about the GS being able to cope with more static sag because of the increased travel compared to a sports bike, although one 'informed' guide I read claimed that this (unloaded) figure applies to the GS as well - the loaded sag is greater than a sports bike, though.

Ian

 

[cookie]

sag will be affected if the shock has lost it's nitrogen charge.

 

[Mzokk]

True Sorry

 

[Mzokk]

Just measured the Static sag on my 12,000 mile standard gs from a marked point on the pannier rail to a mark in the center of the bevel box. Unleaden 522mm bike balanced both wheels on the ground 487. This means 37mm static sag. This is on the standard shock at the std position with standard rebound damping 1/2 a turn out from fully in. I find this setting fine maybe a bit soft for going really hard. On my GSXR I set the static sag at 8-10mm for track days with a bit of added compression damping to reduce squat out of corners. On the road this is backed off to 15-20mm static sag and the compression damping added for the track is removed for added comfort. For your suspension to work properly it must go down when you hit a bump and up when you go over a depression. Most of the guys I know who road race set the suspension as soft as they can get away with without the bike wallowing or bottoming out.......which is usually pretty firm, but if its too firm traction is poor and the bike chews its tyres. Get your shock rebuilt with the correct spring for your weight (or a compromise if you carry a regular passenger!) Start with softish settings say the standard amount of static sag and add preload and rebound damping until you get the sort of suspension control that suits you and your riding style on the roads you use. Only adjust one thing at a time and keep notes. For example for my Ohlins shock the rebound damping recommended as a base setting was 14 clicks out from fully in with 48 clicks of adjustment. I backed this off to 25 clicks after a test ride as the ride was hard and the traction poor. 25 clicks was a bit wallowy in fast bends but fine (for me) everywhere else. Settled on 22 clicks out EIGHT away from the Ohlins recommendation as a base setting.

For your bike trust the seat of your pants

 

[sproggy]

Thanks for the figures - they'll be useful once I've had the shock rebuilt. I think the spring is OK for my weight - perhaps slightly too stiff but then I ride a lot with a pillion so, as you say, a reasonable compromise. I had 25mm static sag (unloaded) with the leaking Ohlins but I haven't checked with the standard unit. Any other riding observations are pointless at this stage - it was awful!

For your bike trust the seat of your pants

The seat of my pants told me it was scary! Incidentally the rebound damping was almost on full on the standard unit and I had a very harsh ride. Reduced it now but have yet to test it - anyone know what's the standard setting?

The only advantage of the weekend's experience was that I've got changing the rear shock down to a fine art!