Steering angle

[NBs996]

Yes I know this has been discussed recently, but I just took the leap of faith and changed mine to the steeper angle, so here's my thoughts on the mod...

It's a dead easy job to do even if you think you're mechanically incompetent, but if you know what a spanner looks like then this is a job you can easily do, and here's how...

I found it easier, for access to turning the castle nut, to take the top yoke off.
1) First lift the front of the bike to take weight off the the front wheel (Abba stand and jack), this relieves the pressure at the top of the forks so that they're not trying to bend in the bottom yoke, and also lets the top yoke slide off/on with ease
2) Unbolt steering damper from frame
3) Loosen the three 10mm clamp bolts that secure the top yoke, and pull the yoke off (damper can stay attached to it)
4) Remove the circlips from the recesses at the top and bottom of the steering head tube and loosen the 2 clamp bolts (6mm hex)
5) Remove the retaining pin at the top of the steering head tube (6mm hex on the left side of the tube)
6) Turn the castle nut 180 degrees
WARNING: Don't be tempted to bash it round with a screwdriver - the posts on the castle nut are soft, you'll destroy them! Use a C-spanner and tap it round with a hammer - try pulling the C-spanner round only if you don't mind ripping skin off your knuckles!
7) Re-assemble in reverse, using the forward frame mount for the damper.

It took me about 45 minutes to do the the job without a manual, and this included a trip to Halfords for a 6mm hex socket.

The result:
I can't believe what a difference it's made! If you think your steering is slow, this apparently minor tweek will make you really happy :D

I put two more clicks on the steering damper to counter the theory of messing up front end stability, and it's no different to what it was before.

I'm pleased I did this, it should really come into it's own on the track - Just wish I'd done it sooner!

BEWARE: The steering hits the lock stops A LOT sooner than before, so watch out for this when turning at low speed on full lock - this nearly caught me out. I said NEARLY caught me out! Just get used to the new turning circle with your feet down before trying the feet up low speed U-turns, that's sort of "back to basics" but we all know what happens when you've got more lean than lock :o

happy spannering :D

nb

[dickieducati]

cheers for that, mines getting done this saturday, getting it done at dealers as im crap at spannering. glad you could notice the difference. hopefully i will too. im on track the following weeekend so will give it a good comparison then.

[baylissboy]

NBs996

As discussed recently,both my bikes are modied in this way,i'm very happy with them that way,glad you are too!!!

When we were talking about doing the job i may have made it sound a little harder than it is,it's very difficult to guage how difficult a task is when you don't know somebodies technical ability!! Anyway,glad you managed it without any fuss!!:D

[psychlist]

Like I've said to you before I've been wanting to try it ever since I got the bike, just not had the nouse nor the capability to do it. If your very kind offer of assistance still stands I'd like to take you up on it, whenever it's convenient for you sir :eureka:

[NBs996]

I'll bring my hammer round at weekend paul. :devil:

Oh, and maybe some spanners and a torque wrench too!

nb

[psychlist]

Originally posted by NBs996
I'll bring my hammer round at weekend paul. :devil:


Ooh! Sailor :o Make sure it's a big one not a puny little peening hammer :P

[Loz]

Is there anything in the world that cannot be fixed with a good heavy hammer and a pair of mullgrips? (And maybe an impact driver, too)
:bouncy:

[Garibaldi]

I've already jacked up the rear ride height and that also made a big improvement to the slow steering. Its also very much quicker to do. Just remember that one of the nuts on the ride height adjuster is a left handed thread. Sorry, cant remember which one and I don't have access to my bike or manual just now. Two turns is enough.

Has anyone tried both jacking up the ride height and adjusting steering angle. If so, was it better again or worse?

[psychlist]

Already got my rear ride height jacked up so I'll let you know :o

[Nigel C]

Originally posted by Loz
Is there anything in the world that cannot be fixed with a good heavy hammer and a pair of mullgrips? (And maybe an impact driver, too)
:bouncy:


Yeah just ask Rattler he's an expert with big hammers :D

[RickyX]

Originally posted by Garibaldi

Has anyone tried both jacking up the ride height and adjusting steering angle. If so, was it better again or worse?

I have done both...can get a bit lively if one encounters a bump while cranked over...however it certainly improves the steering response.

[Steve]

How do you jack up the rear ride height?

[Shazaam!]

I have done both ... can get a bit lively if one encounters a bump while cranked over ... however it certainly improves the steering response.


http://home.san.rr.com/shazaam/HeadAngleTrail.jpg

Chassis Geometry - Fork Angle & Trail

Stability and Steering Angle

The central issue with making this change is stability. A motorcycle is designed to return to its straight-ahead condition after hitting an object or bump in the road that causes the front wheel to deflect slightly to the right or left. In other words, it has to remain stabile for a variety of road conditions, and motorcycle stability is foremost a safety issue.

The way dynamic stability is assured is to design a bike with enough distance between the point where the front wheel touches the road and the intersection point between the steering axis and the road. This is called the trail dimension.

A longer trail dimension increases the motorcycle's stability on straights, but will also negatively affect the motorcycle's turning effort, i.e. more rider's strength is required in corners and transitions. However, the more trail the greater the ability of the bike to self-correct it's steering. It's a longer trail dimension, for example, that allows you to easily ride with no hands on some bicycles but not others.

A shorter trail dimension, on the other hand, produces a lower opposing force to steering inputs. It's kind of like power steering. So the steering requires less rider strength, but larger handlebar displacements from bumps in the road and corners are fed back to the rider. Said another way, the shorter the trail, the more rider input that is needed to hold a line and the more responsive the bike feels since it is more sensitive to steering inputs.

The two superbike steering angle positions, 23°30' and 24°30' produce trail dimensions of 91mm and 97mm respectively. The wheelbase, also an important factor in stability, remains unaffected when you change it. As a comparison, the Monster steering angle is fixed at 24° and the trail dimension is 94mm. Adjusting the trail dimension on most manufacturer's bikes is not an option.

As an aside, when you change to the steeper 23°30' position you loose a significant amount of steering lock making low speed U-turns more difficult. Also, the ignition steering head lock doesn’t engage in the steeper position.

Now, here's Ducati's warning: "Trail should only be altered after all the other (geometry and suspension) changes have been made and you are comfortable on the bike. If the bike displays any instability problems they need to be sorted out first, as this steering head angle change will magnify these characteristics."

(One reason, for example, is that part of its effect mimics changing the rear ride height.)

The Haynes Service manual goes on to say "Warning: The steering head angle must be set to the road position (longer trail) whenever the bike is used on the road. If the steering angle is set to the race position (shorter trail) ... the handling of the machine could become unpredictable on uneven road surfaces."

So, shortening the trail is considered unwise for street riding (unlike tracks) where bumps in corners, potholes and other road hazards repeatedly challenge your bikes steering stability. Here's a case where inexperienced or uninformed riders who set-up their street bike chassis geometry as racebikes are just looking for trouble.

Trying to mimic factory race bike set-ups can get you into trouble. It's central to racing that race bikes often need to sacrifice high-speed stability to handling. Riders may initially run the steeper steering head angle but often, as they get faster, they realize they want more stability, not less.

To get more stability there are two things that Ducati typically changes on their racebikes: the triple clamps and the swingarm. They use triple clamps with less offset, typically 27mm instead of the stock 36mm, and use a 25mm longer swingarm to increase the wheelbase. These changes to the triple clamps or the swingarm have the effect of moving the center of gravity forward which is the typical starting geometry of the Corsa race bikes. Remember, changing the steering head angle does not, by itself, change the wheelbase or alter the center of gravity.

Some here have suggested that you can get the same effect (reduction in trail) with a finer adjustment by increasing the rear ride height instead. However, you'll need to raise rear ride height 16mm to get an equal amount of trail reduction, and in doing so you'll also end up increasing the height of the bike's CG by about 12mm that (among other things) will increase loading to the front tire, so when hard on the brakes, the rear tire gets/feels very loose.

One improvement with the steeper angle that’s been observed is in trailbraking - The bike stands up less on the brakes, which can be a benefit on backroads where you never quite know what might be coming up around the next bend. Also, some feel that the steering is more neutral at large lean angles.

The area of major concern is tankslappers. Reducing trail by reducing the force that centers the front wheel will give you more headshake, especially when accelerating (less weight on the front wheel) out of bumpy corners.

You won't get a tankslapper out of most corners if you change to the steeper steering head angle, but you will make them more likely, and more violent, when they do occur. Some will say to crank-up an adjustable steering damper to settle the steering, but dampers will only resist changes in steering direction and don't provide a restoring force to re-center the wheel like trail does. The higher damping rates also spoil your quick steering and cause weave instability problems when cranked-up too high.

For those of you who haven’t experienced this phenomena, see one here:

http://www.randtclub.com/Video/cedwards/tankslapper_tt99.mpeg

I’ll choose more stability over quicker steering any day.


[Edited on 6-18-2004 by Shazaam!]

[NBs996]

OK, so questioning an expert like Shazaam is putting me on pretty shakey ground so I'm ready to be corrected/beaten up, but it's that last paragraph that I'd like to take up.... and it's not a disagreement as much as a lack of understanding!

A tank slapper occurs when the front end shakes left/right/left/etc until it finds its resonant frequency, causing it to become violent. Adding a damping force to this shake will interfere with that resonation and help prevent the build-up to the optimum frequency for the violent shake to occur. So whilst the damper doesn't do anything to re-centre the wheel, it does help prevent it happening, so if you want to increase the tendancy to shake (i.e. steepen the steering angle), then you should also increase the resistance to this by turning up the damper. Right?

I don't see how winding up the turning resistance on the damper can have any noticable impact on change of direction, as this is determined by the geometry of the bike and not the force needed to turn the handlebars. Just a small movement on the bars is enough to get the bike from one side to another, and once the initial force is applied then the damper gives no further restance in keeping the bars turned. The only effort required on the riders part is to resist the bikes natural desire to bring the front wheel in line with the back, and therefore bring the bike upright, so surely an increase in the steering damper would only assist the rider in holding the bars in the turned position?

Go on Shazaam..... tell me what I'm getting wrong!!

I do agree that it's better to have the stability on the road in favour of quick turning, but so far I don't find any noticable reduction in stability... and maybe I won't, because my road use is very limited and nearly always slow and sensible (honest!). If I was a fast road rider then I probably wouldn't have gone for this mod, but the track is what I bought the 996 for so the track setup needs to used - can't wait for Cadwell again!

[Garibaldi]

As I ride on the road quite a bit, I think I'll stick with just the tail up and leave the steering angle as it was. To be honest, I haven't noticed a reluctance to turn on track days anyway.

I also noticed that the tendency to sit up whilst breaking into a corner is now virtually non existent after jacking up the ride height. Note that I also made some suspension adjustments as per Performance Bike recommendations.

[bradders]

mine sits up immediately if you touch the brakes...and that was before I lowered the rear...now I'm confused:puzzled: could be another argument for countersteering???

[dickieducati]

Originally posted by NBs996

I don't see how winding up the turning resistance on the damper can have any noticable impact on change of direction, as this is determined by the geometry of the bike and not the force needed to turn the handlebars. Just a small movement on the bars is enough to get the bike from one side to another

no expert but i think it will: its not just down to geometry force plays a part too. dont know if you've done the CSS but one of the ways they help you to understand the force required to quick turn is by getting you to try to turn the bars with you fingers pointing down on top of the bars (ie being unable to exert hardly any force) then with your fingers horizontal to bars (clearly far easier) if the damper is wound right up it will require more force to turn it.

[Shazaam!]

Good question.

The distinction here is that the damping force is velocity dependent, the trail force is not. That is, when you apply more force to the bars as you try to turn faster, the larger the resisting force supplied by the damper. For slow steering corrections there's little effect as you point out. As you crank up the damper, you get a larger resisting-force from the damper for a given rate of angular rotation of the handle bars. So in fast side-to-side transitions, increased damping slows the rider's handlebar input. The faster the transition or amount of damping you dial-in, the greater the effect. Indeed, that's why you have a steering damper, to resist fast-acting tank-slappers. Adjustable dampers allow you to strike a compromise between instability and sluggish steering.

Dynamic stability is a complicated issue. Flight vehicles can be described analytically in terms of stability derivitives but motorcycles are just too difficult to simulate on a computer. So you do testing on new designs instead. Somewhere along the way, Ducati engineers and test riders found a need for a steering damper and the need to warn you to use the steep steering angle with caution. You may never encounter the riding condition that they did, but I suggest that you be ready to deal with it.

BTW, I studied aerospace dynamics at university and worked for decades in the field of structural dynamics, so stability analysis is my field of expertise. When I suggest caution here, I do so simply because it’s a true safety issue.

[Edited on 6-18-2004 by Shazaam!]

[NBs996]

What I'm suggesting here is that after you've initially pushed the bar to initiate the bikes change of direction, the rotated position of the bars does not change during the turn, therefor during the transition from full left to full right lean the bars are pretty much static, and unaffected by the damper. Also I don't think the damper has any significant resistance compared to the force fed back from the road - Lift your front wheel clear of the floor and see how little effort it takes to turn the bars, even with the damper wound up, this doesn't change when the bike is in motion does it?

What I'm trying to achieve is less effort in turning the bike from side to side, which proved to be hard work at Silverstone through those 5 consecutive changes starting at Maggots, and I'm still convinced that the stiffness of the damper has very little effect on turning speed. Yes, the handlebar input has more resistance, but the duration of rotation is so brief that I consider it irrelevant. Also, any resistance given by the damper is only a small percentage of that given by the bikes own natural desire to straighten itself - especially at speed. So when you consider the reduced effort you need as a result of the geometry change it's LESS effort overall.

Although I'm nowhere near your level of expertise shazaam, I too studied aerodynamics, and now teach it at grass root level to Air Cadets, so I don't need any convincing that caution needs to be exercised here! I never meant to suggest otherwise, only that it's not noticable to me with the way I ride on the road. I do look forward to taking it to the track where the change should be much more noticable.

Roll on Cadwell/Rockingham/Lydd/etc.... :D

[Jon]

I was told that the Ohlins damper only needs to be set low. I don't know the correct wording for it, but the damper starts off soft with increasing stiffness with each stroke. So if the bars do wobble a tad while cranked over, don't adjust it out as it just might be that the damper will take care of it all by its self. I have mine set at 4. It does shake its head over 70 mph if hitting a bump or other, but never gets out of hand.

[skidlids]

Just thought I would point out that the RRW/X model Fireblade having the tank slapper at the TT has nothing to do with increased ride height, in 2002 we took Weeksy old Fireblade (same model) to the TT fitted with a Ohlins rear shock, every practice session we added more rear ride height until we finally ran out of adjustment. Bike was perfectly stabe aided by the Ohlins steering damper and after starting in 89th place on the road finished 29th in Bronze Replica time with DJ wining on a GSXR1000. The Blade lapped at around 115mph.
There is far more to bike setup than meets the eye, tyre profile and construction for starters and Trail as mentioned by Shazaam is a major contributor.

[Shazaam!]

You're right, the damper force IS significantly smaller than the road forces generated by the trail dimension moment arm. It's particularly interesting that when this restoring moment drops (as you reduce the downward force on the front wheel - accelerating out of a corner, for example) is when a tankslapper usually starts. It can take you by surprise, it sure did for me.