Bike set up and geometries

[duke63]

Are there published figures of race bike geometries and set ups? I know Blade has looked and experimented with this.

Been doing a bit of reading as i want to experiment with my 748. Its one of the few bikes that has plenty of set up info out there but i just wondered how a well set up roadbike compares to a racebike.

Rake and trail and ride heights is all very interesting stuff and i want to learn a bit more about it and especially how it could make my bike better to ride.

Any recommended reading i much appreciated.

This website is the starting point of my 748 set up though. I don't believe the rear ride height on mine is set up even close to this one but i am going to have a better look this weekend.

http://web.archive.org/web/200411191934 ... ension.htm" onclick="window.open(this.href);return false;

[Blade]

There probably is but there will be more than one as its so individual and personal.

IMO there is one golden rule in setup. There is no perfect set up, its always a compromise and unique to the individual.

Improving turn in will reduce stability etc... Its all a compromise unless you have the new semi active stuff of course.

Best way to learn and find the best set up for you is to experiment. Can't remember the book you recommended to me a few years back on the subject but that's a good starting point .

[Blade]

Tbh there is a lot of bullsh1t on the net. Learn and understand the basics as theory and then experiment with your knowledge is the best you cab do IMO.

We learn more from our mistakes so experimenting is good. Don't be afraid to try something different as you can always go back. And when you get the front right and then make changes to the rear they will effect the front again so could need adjusting again. It really is a case of understanding the basics and playing with ideas of directions you want to go in to find your desired improvements.

Everyone wants some figures of the net which will magically transform the bike but they don't exist regardless of what people say.

OEM suspension in some cases has very little change for large adjustments as the manufacturers don't want you to screw up there bikes beyond what THEY preserve to be the best compromuse in set up for their version of Mr average weight and ability.

[Blade]

If you do have a play and have any questions I could help with you have my mobile number so don't hesitate to give me ring, always glad to help.

[Monty]

I've found the physics is very simple to understand, but applying it is fecking Voodoo!

[duke63]

Cheers. Blade.

I appreciate there is no right answer for everyone but no harm in trying to make a good bike even better.

I love the stability of my bike but it does take some effort to turn particularly at speed. I know that the two things are to some extent different ends of the set up scale but there should be a point somewhere in the middle where the bike feels as good as possible to me.

My first step will be to drop the forks through the yokes one more ring. Its suggested in that weblink and i was chatting to someone a few weeks back and he has his 916 set up the same.

The beauty of the 748/916 series is that the bike has a rear ride height adjuster ( and also a steering for angle aduster though its only recommended for track use).

This was quite an interesting piece i found the other day.

The central issue with making changes to steering angle 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 stable 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.

According to an earlier post by Jeff Koch, for superbikes, for every 1mm decrease in fork offset:

Trail increases 1.1mm
Wheelbase decreases 0.9mm
Height of the bike’s center of gravity increases 0.2mm
Percent of the bike’s weight on the front wheel increases 0.05 percent

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.

Again quoting Jeff, for every 1mm increase in rear ride height:

Trail decreases 0.4mm
Wheelbase decreases 0.2mm
Height of the bike’s center of gravity increases 0.8mm
Percent of the bike’s weight on the front wheel increases 0.03 percent

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/cedwa...pper_tt99.mpeg" onclick="window.open(this.href);return false;

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

One more thing.

Keep in mind that lowering the front ride height, or raising the rear ride height, are not equivalent adjustments. Lowering the front serves to lower the bike's center of gravity. With a higher front, raising the rear, raises the C.G.

Again, according to Jeff, for every 1mm that you raise the forks in the triple clamps (lowering the front end):

Trail decreases 0.2mm
Wheelbase decreases 0.5mm
Height of the bike’s center of gravity decreases 0.4mm
Percent of the bike’s weight on the front wheel increases 0.06 percent

Ducati Corse, in a 1996 memorandum that was posted on the old Ducati.com web site, recommended raising the front 10mm to increase "flickability" in turns. Yes, I said raise, not lower. Raising the front end raises C.G., and a higher C.G. makes the bike go to the tire edge quicker according to the memo. I was told that the same advice is given in the factory race bike setup manual.

Familiar with the Mille SP? It has the capability to raise the engine in the frame to increase C.G. to improve flickability. Same effect. Even the Mille R has the engine mounted higher in the frame to do the same thing.

From a chassis design point-of-view you generally you want the C.G. to be a distance equal to half the wheelbase above the line connecting the axles. Raising the C.G. above this point makes the bike easier to turn.

Once in a turn, a higher C.G. biases the weight more to the inside of the corner which helps the bike turn.

[Blade]

Don't push the forks through the yokes if you have a ride height adjuster. Lifting the rear will have the sane effect as lowering the front but without the reduction in ground clearance.

[Blade]

Your right there is no right answer for everyone but there is a right answer for you. Remember although you think the 748 is a good handling bike this is lmited to what you currently know / have experience off, there is a better set up if you look for it and sounds like you what to improve turn in. Don't forget front tyre profile will also influence this and a worm rear tyre will have reduced rear ride height. There are so may variables you have to consider but its very interesting, frustrating and rewarding experimenting with set up.

Make sure everything from bearings, to tyres, to linkages, to chain tension, to damper and fork condition are all in goof working order before starting and always set the static and dymanic sag first.