Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > Track Head Angle - Suspension Setup to Suit?

[zhed44]

I've just reset the steering head angle to the track setting.

I know bike setup is a highly individual thing, but does anyone have any suggestions regarding complementary suspension settings?

The bike is a 2002 748R (full Ohlins). Currently on the standard settings. I'm about 14st and the bike is mainly used on the road, with the occasional trackday.

Thanks.

[748adam]

on this one i have no idea!! but i do have suspension envy!!! hahaha try giving reactive suspension a ring, dont have a number to hand but will have when i get back.

Adam

[Shazaam!]

http://www.ducatisportingclub.com/sh...ad.php?t=46605

[zhed44]

Originally Posted by Shazaam!

http://www.ducatisportingclub.com/sh...ad.php?t=46605

Thanks Shazzam.

I take on board the safety/potential tankslapper issues, but TBH, to me, subjectively at least, a bike that steers quickly inspires a lot more confidence and therefore feels a lot safer than one which feels reluctant to turn. I've run the steeper head angle on my previous 748BP and 996S without incident, but that is not to say I am complacent about the issue.

In short, as with so many aspects of life in general and motorcycling in particular, it's a matter of balancing the risks and I feel I am more likely to crash as a result of mis-judging a bend due to the standard set-up's sluggish intial turn-in (and thereby ending up target-fixated on the opposite kerb), than I am likely to bin it due to a tank-slapper. I hope I am correct in that judgement. Less analytically, I simply get far more enjoyment from riding a "flickable" bike.

[Shazaam!]

Good answer, but there are other ways to improve turn-in.

Running wide coming out of corners is often due to the rear of the bike being too low or the front too high relative to each other. This can result from a multitude of things, predominantly a too soft spring rate or too little preload on the rear spring.

Chassis Geometry - Rear Ride Height

Raising the ride height has a similar handling effect as making the steering head angle steeper. The head angle change does it in a different way by shortening the trail dimension instead of tipping the bike on its nose. The head angle should only be altered after all the other 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.

The handling is very sensitive to rear height changes. Small changes can drastically change the way the bike turns and holds a line. As a rule, the more rear ride height you add, the faster the bike will turn. The ride height should be set to make the bike turn quickly, not fall into a corner, or require rider input to hold a line. A high rear end and a low front effectively give the front forks a steeper angle. This results in a quicker (some say slightly nervous) steering, especially when braking hard. You may also feel a tendency of the bike to oversteer (the rear wheel looses traction and slides before the front.) There is also a tendency to stand up more while braking in corners.

The rear ride height adjustment sets the distance between the rear axle and the tail piece. The only time you should have to adjust this tie-rod is if you change the final drive ratio sprocket sizes and you have to compensate for a slightly too-long or too-short chain that places the axle outside the correct eccentric hub position. Alternatively, you can remove or add chain links to obtain this orientation.

If the final drive ratio has been previously changed. First, assure that the chain eccentric is set between the 6 and 9 o'clock position. Then check the static sag, make sure it's set to right value. Then adjust the ride-height by changing the length of the tie-rod to raise or lower the ride height.

If you haven't changed your sprockets then you're in luck. The standard setting is with the rod at its shortest, i.e. lowest ride height.

If you've changed your sprockets and didn't record your initial height setting then you need to have Ducati use the factory ride height tool. With the rear fully extended, measure from the top edge of the tool to the dead center of the axle. This should be 237 mm. Lengthen or shorten the linkage rod to get this number.

The tie-bar is adjusted using 17 mm and 19 mm wrenches. The bottom nut is a left hand thread and the top nut is standard. You turn both nuts the same way to loosen. After you loosen the nuts, just turn the rod in the reverse direction to raise the ride height.

In the future when you make changes, measure the distance between the two ends and record this length. Make small changes in height and record each one so that you can return to the best setting for you. Changes should be made in 5-10 mm increments.

Note

Your ride height adjuster is at it's shortest position when delivered. So, if you change to a larger sprocket that takes your eccentric from (say) the 4 - 5 o'clock position to the 6 o'clock position, you have no way to drop the ride height further. This means you'd need to remove two links and then reset your ride height.

Front Ride Height

Lowering the front ride height or raising the rear ride height are not equivalent adjustments.

If you raise the rear end using the ride height adjuster, or go to a taller rear tire, you raise the C.G. relative to it’s initial position.

In particular, the thought that lowering the front (raising the forks) to improve turn-in response is incorrect. This will give you a lower C.G.

Ducati Corse, in a 1996 memorandum*, recommended raising the front 10mm to increase “flickability" as in a chicane. 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 (per the Ducati race engineers).

* Ths memo was previous available via the search engine at the old Ducati.com web site but lost when they put up the new site and no longer available.

The same advice is currently given in the factory race bike setup manual according to Felix.

Take a look at 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 higher in the frame to do the same.

[chris.p]

Originally Posted by Shazaam!

If you've changed your sprockets and didn't record your initial height setting then you need to have Ducati use the factory ride height tool. With the rear fully extended, measure from the top edge of the tool to the dead center of the axle. This should be 237 mm. Lengthen or shorten the linkage rod to get this number.

Shazaam, are you saying that the rear of the bike must be "topped out" i.e. lifted so that there is no static sag????


Chris

[Shazaam!]

No, raising rear ride height using the adjustment rod has no effect on sag values.

[chris.p]

Originally Posted by Shazaam!

No, raising rear ride height using the adjustment rod has no effect on sag values.

Sorry, it appears that the last part of my post went AWOL???
Meant to say-:


Quote:
Originally Posted by Shazaam!
If you've changed your sprockets and didn't record your initial height setting then you need to have Ducati use the factory ride height tool. With the rear fully extended, measure from the top edge of the tool to the dead center of the axle. This should be 237 mm. Lengthen or shorten the linkage rod to get this number.



Shazaam, are you saying that the rear of the bike must be "topped out" i.e. lifted so that there is no static sag???? when you measure from the centre of the wheel nut to the top edge of the tool???


Chris

[zhed44]

Originally Posted by Shazaam!

Good answer, but there are other ways to improve turn-in.


Raising the ride height has a similar handling effect as making the steering head angle steeper..... etc

Yes, I've thought about jacking up the rear, but I'm only 5'8" and so I wouldn't really want to increase the seat height any further. Also, the 748/916 series bikes already lean over an awfully long way on a very flimsy sidestand mechanism, and living as I do in a hilly part of town with lots of strange cambers in the roads, I wouldn't want to push my luck or risk my fairings by putting any additional strain on that assembly.

Just out of interest, by how much would the rear need to be raised to replicate the effect of the steeper steering head angle?

I suppose the OE seat height could be maintained by making a corresponding change to the front ride height, but I have a feeling this would be opening up a world of setup issues due to the change in the CoG, not to mention the impact on ground clearance and the operation of the sidestand.

[Shazaam!]

Originally Posted by zhed44

Just out of interest, by how much would the rear need to be raised to replicate the effect of the steeper steering head angle?

I calculate it's about 16mm rear ride height, which reduces the trail by 6mm, which is the trail difference between 'road' and 'race' front settings. As I recall one turn on the adjuster rod corresponds to about 8mm ride height change, so that'd be about two turns.