SS yolks on Monster?

[Bitza]

Hi all, OK has anyone out there any experience of using (or the equivalent of) yolks off a 1998 900ss on a 1994 Monster? Forget all the handlebar/headlight/instrument fixings ect. all I'm interested is the effect on the bike's geometry and consequently what it's like to ride. The basic difference being that the SS forks are set about 5mm further forward. I'm sure somebody out there must know such stuff, although I think I might have a vague idea, it would be nice to hear from somebody more knowledgeable. Thanks all Bitza.

[Bitza]

A bit more information after a bit of research, early Monsters have a 25mm offset, whereas 851/888 which uses the same frame has yolks with 30mm offset as does the ss and later Monsters. Apparently more offset gives less trail which in turn tends to give less stability & quicker turning. My current thinking is that by fitting ss yolks I should be able to maintain my current trail value while also reducing my current front end bias that has resulted from raising the rear end/dropping the front end, which in turn might help cure the lack of rear end grip that I have been troubled with (referred to in a previous thread) when using the original 93 yolks. If anyone could shred any further light on the subject, i.e. whether what I'm saying is in any way correct I would be obliged. Otherwise I'll just continue to talk to myself, all the best Bitza.

[chris.p]

A bit baffled as the yolks themselves don't effect the offset, unless of course they are adjustable, The offset as far as I am aware for monsters and SS's is down to the frame angles??.

[Flip]

Originally Posted by chris.p

A bit baffled as the yolks themselves don't effect the offset, unless of course they are adjustable, The offset as far as I am aware for monsters and SS's is down to the frame angles??.

I'm baffled too- I thought Yolks were only fitted to 'Scramblers' but there may have been some old obscure Italian manufacturer call Omletta?

[Bitza]

Thanks for that Flip, just the kind of deep insight that's needed to eggsplain the situation.

Offset is the distance between the steering stem center and the fork centers,meaning that SS yolks hold the forks 5mm further forward than early Monster ones.

[Flip]

Seriously though, can you post a link to your thread about rear end grip please?

I run my '97 Monster with the rear raised a fair bit (more so since fitting steering slowing Michelin Pilots after Pirelli's) and can't say I have ever suffered from a lack of rear grip other than a little wheel spin occasionally when pulling away with a bit of enthusiasm on slippery surfaces/railway crossings etc. but nothing particularly worrying.

[stopintime]

More offset will 'quicken steering' / 'reduce stability' in much the same way as raising the rear / lowering the front will.

[Mr Gazza]

I think offset refers to how you separate the whites?

Okay.. The trail is measured where a line through the centre of the steering head stem meets the ground, to a point plumb from the axle on the ground (the centre of the contact patch).
Several factors influence the trail.
1) The rake, The angle of the forks. This is primarily set by the angle of the steering head tube in the frame, but can be effected by pitch change due to changes in wheel size and how the front and rear ride height is set. (not to mention the dynamic changes when riding).
2) Offset of the fork tubes in relation to the steering head. (the YOKES)
3)Offset of the axle. This can be placed ahead or behind the fork leg, but in the case of Ducatis is on the centre line.

By using YOKES with more forward offset, the wheelbase is increased and the trail is reduced. the former improves stability very slightly (unnoticeably) and the latter removes stability and increases sensitivity to rider input.

Further reduction in trail is induced by raising the rear end, as this steepens the rake. As does dropping the bike on the forks.
If the front is raised by the same amount as the rear, rake and trail are maintained from the starting point.

Bitza, everything you are proposing will reduce the trail and stability (quite a lot!)

The lack of rear wheel grip is not really effected by these factors except for the fact that a bike with severely reduced trail will be more sensitive to all inputs.
However if you mean weight distribution, when you mention front bias. that does effect the grip, if the rear wheel has less weight over it.
Dropped bars move your upper torso forward. This can be compensated for to a degree, by shifting your bum back, but makes it uncomfortable and not easy to reach the bars if you're a shortie.
Under braking (say entering a corner) the weight is transferred to the front wheel and helps no end with grip for the braking force, (provided the forks have fully compressed and the contact patch has expanded).
The rear wheel will be correspondingly lighter and could be in the air. ( don't use the back brake in an emergency stop as the gyroscopic effect of the rotating wheel provides stability.)
It takes some time for the weight distribution to recover to the normal ratio after hard braking, while your body settles back, the forks rebound, the fuel sloshes back and so on. It's very easy to whack the power on before this is sorted out and the result is a bit of a fish tail.

My SS was a sod for this! Answer… Get a Monster..

[Mr Gazza]

I am assuming that you propose using the yokes in their proper pairs and not using an SS top yoke with a Monster bottom...Of course you wouldn't!

That wouldn't work, obviously, but the trail can be manipulated with different offsets on top and bottom yokes. (Provided the angles in the bores are correctly machined).
Norton did this with the late 850 Commandos, although I'm not sure which way they went.

Interestingly, if the forks are made steeper by pushing the top forwards, it increases the trail and vice versa.

[Darkness]

It’s my recollection that the head angle is steeper on an 888 compared with a monster, with the option of going steeper again for track use.

There are some interesting comments in Shazzam’s Post here:

https://www.ducati.ms/forums/80-hall...wheelbase.html

There’s also a useful thumbnail sketch attached which shows the geometry.

If you move the forks forwards relative to the steering stem you will reduce trail: something you’ve already done by raising the tail and steepening the fork angle.

I would be tempted to draw out the standard geometry at normal ride height and both extremes of suspension movement, then do the same for your modified geometry to see what changes you get, before trying it out for real.

[Dukedesmo]

Originally Posted by Mr Gazza

That wouldn't work, obviously, but the trail can be manipulated with different offsets on top and bottom yokes. (Provided the angles in the bores are correctly machined).
Norton did this with the late 850 Commandos, although I'm not sure which way they went.

Ducati also made bikes with adjustable steering head and offset: 916 models have an adjustable headstock where the bearings are in an eccentric carrier, having 2 positions; IIRC 24.5 degrees in the 'road' position and 23.5 in the 'race', however not many run the race settings (even in racing) as it upsets the bikes rock solid stability.

Similarly they offered adjustable offset yokes on some race homologation models (748R IIRC) but I think the general consensus with both adjustments was that they were normally only done in conjunction with longer swingarms etc. and not for road use.

Of course none of this relates to a Monster (unless you use a 916 type frame to build it from, or are big into customising?) as the parts are not interchangeable.

AFAIK Ducati saw no need to offer this adjustability on more recent (and more capable) models, having done all the messing about/adjusting etc. at great cost only to discover that one setting was generally better for all uses.

That said my Monster's steering is certainly more 'lively' than the 916, especially at high speeds where it can get a bit twitchy under circumstances where the 916 is as stable as you like, as such I wouldn't be looking to do anything to quicken it up...

[Darkness]

Some interesting stuff on bike frame geometry here too:

http://bienvillestudios.com/index.php/chassis-dynamics/

[Luddite]

An excellent explanation from Mr Gazza (worthy of Tony Foale, I'd say!).

Just to help illustrate the point, I found this gif on ducatiforum.co.uk, which nicely demonstrates the result of changing the fork offset. (Apologies for the K*M logo!)

Originally Posted by Mr Gazza

...but the trail can be manipulated with different offsets on top and bottom yokes. (Provided the angles in the bores are correctly machined).
Norton did this with the late 850 Commandos, although I'm not sure which way they went.

I think the Diavel uses this trick to allow it to run a lazy 28° rake but still have reasonably quick steering.

[utopia]

Presumably your thinking is that you can quicken the steering by fitting the yokes with increased offset but then lower the rear (or raise the front) until this restores the steering speed to its former level .. in the hope that this results in better rear end grip.
I'm afraid that my knowledge goes no further than yours on this, but I agree that it all sounds logical.
On the other hand, I am not aware of this being a commonly used method of achieving your desired result (but that may just be down to my personal lack of experience).
It might be worth a try but I think I would be more inclined to look at the operation of the rear suspension first, to deal with rear grip issues .. but again my knowledge is more theoretical than from practical experience.

As Flip said, a link to your "lack of rear grip" thread would be useful.

Its interesting to learn that the SS yokes have greater offset though.
I might even be curious enough to get hold of a pair to experiment with, just for the sake of furthering my chassis knowledge.

[Darren69]

What he and others have said, really. I think the risers are a popular mod for those bikes and it seems like a drastic mod you're proposing but I've not heard anyone else having those issues. I have an S4 and I know its a different frame with different geometry but I never heard of anyone else having these isssues with either frame and I did a similar mod on mine for the same reasons with a longer tie bar and it is much better and I've not had any rear grip issues. Sorry I can't offer any more advice.