01 January 2010

On Geometry

Recently, I've made two changes to the bike's geometry. The 1999 Monster is a member of the 1993-2001 Monster Frame series, which shares many features with the 851/888 bikes. The main differences are an additional brace near the steering stem was removed to accommodate the Monster's air box and the rear section of the frame is welded on, rather than being a subframe (subframes ARE used on all 'new' Monsters, a la 696/1100 and generally all other Ducatis, including the Hypermotard and the Superbikes).

A distinguishing feature of the 851/888/Monster's frame from the newer 2002-2009 ST based Monster frames is the hooped swingarm suspension. The swingarm connects to a hoop or arch that connects to a pivot or lever arm, which in turn is connected to the top of the shock. The hoop is originally made of steel and comes the color of the bike's frame. Thus, mine was antique gold. Until I changed it. For several years, I've been running a lighter and stiffer billet swingarm hoop. It left the geometry essentially the same, but gave a slight amount more feedback while looking really good. It came to my attention that DMF Member sweir1171 was making a ride-height adjustment kit. The kit features two machined, threaded risers that will raise the tail of the bike a few cm. They work fantastically and went right on.

Such a modification will change the wheelbase of the motorcycle and quicken steering.

While I quite liked the quicker steering and change in feel, I was also interested in improving the feel of the front end. The forks have been reworked with a basic respring, revalve and re-oil using RaceTech components, but aside from the slightly stiffer and lighter CycleCat top triple and clipon handlebars, not much else had changed. This is when I contacted IMA SrL. These guys are fantastic to work with.

There are a few differences in the pre-02 Monster frames and the newer Monster (02-09) frames beyond the rear suspension assembly. The older frame Monsters, along with all Supersports, utilize a narrow steering stem and are equipped from the factory with tapered roller bearings. The offset (the distance between the centerline of the forks and the steering stem) is 25mm. To put this into perspective, superbikes frequently leave the factory with 36mm offsets, and aftermarket triples may change this down to 32 or even 30mm. Several vendors sell triples with offsets as low as 27mm (Ducshop).

Newer Monsters (02+) have a bigger 30mm offset from the factory, use a much larger diameter steering stem and do not come with roller bearings from the factory (though one could upgrade to SpeedyMoto's set if they like). The rake change from old style monsters to new style monsters is a small but perceivable 23 or 23.5 (depending on the source you read) to 24 degrees. IMA produces beefy billet aluminum triple sets (upper and lower, including steering stem) for older Monsters and Supersports that increase the offset to 30mm, same as the new Monsters, and even allow for the use of a Monster-esque bar on a Supersport (if one was so inclined). They provided me with a black anodized set for my Monster.

Installation involves suspending the front end of the motorcycle, removing the wheel, gauges, controls and anything touching the triples. Once that's all taken care of, the triples are loosened and removed from the bike. The inner races must be knocked out of the steering stem before the new races may be inserted. Then a new tapered bearing that has been well greased is driven on to the IMA triple's stem. The factory uses SKF bearings, and that's what I replaced the set with (obtained from CA-Cycleworks in SpeedyMoto's convenient packaging). Then its all put back together, titanium bolts all around, and you get:

From a bit of a distance:

Update - 3/29/2010
The finished product has a trail of approximately 90.5mm, and started closer to 96mm. original wheelbase was 1430mm, and the final result is minimally smaller. The feel is fantastic on the street, though I've only put about 1,000mi on since the original writeup. I've yet to find really great roads outside of DFW like I had nearby in Middle Tennessee. Looks like its time to start taking off bling so I can track this bike. Or perhaps its time to invest in a 2nd bike for track only.