How To Fit Larger Race Tires on the 848 Superbike
TThe 848 is a brilliant street bike, but an even better track/race bike. However, as time has marched on, one glaring limitation of the 848 has reared it head. Rear tire fitments. This isn’t an issue if your 848 lives on the street as a canyon carver or state-street queen. But if your 848 lives on closed circuits, this is becoming more and more of an issue.
In the world of race tires, the 848s 5.5-inch back wheel is totally up to snuff, but the space available at the front of the swingarm limits tires to a true 180/55-17. The problem is race tires do not really come in those sizes any longer. Dunlop makes two rear tire’s a 190/55 and a massive 200/55. Pirelli on the other hand still makes a 180/55, but they are getting harder and harder to come by, where the 180/60 is very common while still being a tire designed for the 5.5-inch rear wheel. This isn’t even getting into the fact that race tires aren’t anywhere near the sizes marked on the sidewall, in many cases race tires are much larger than what they are labeled as.
This poses little problem for the conventional swinging arm crowd, like CBR600RR’s and the like. These tires are still built to fit properly on 5.5 or 6.0 inch wheels and on a conventional swingarm, there typically is plenty of room to accomodate the additional tire height. However the 848’s single-sided-swingarm is a problem. In most cases, you can fit a 180/60 or even a 190/55 without a problem. The problem is there is no more room left over to get the tire-warmer on. And for those who run race tires, that is a very big problem indeed.
You can try and source a “kit” swingarm from Ducati - the swingarms they use for WSBK/BSB and AMA racing, but you’re looking at upwards of $3,500 smackers just for the swinging arm. Or you could source the hub and wheel from a 1098/1198 which would put you on a 6.0-inch rear wheel, but again, you’ll be looking at around $1,000 for a wheel, hub and all other parts, even if you were able to find quality used parts.
There is a much more affordable way to fit larger race-tires on the 848 however. Although, it does mean that you have to run specific gearing.
On the 848, if you run a 15-tooth front and a 42-tooth rear, adding one link to the chain length you can make it work. You also have to “notch” the rear brake bracket to allow the swingarm eccentric full rotation. Here’s how it’s done.
First, when we decided it was time to make these changes, we figured we may as well switch to a 520 chain in the process. We choose AFAM because they have a reasonably priced, high-quality quick-change rear sprocket carrier that, while expensive, subsequent sprockets become quite affordable.
It goes just like any other sprocket change. Start by removing all the old bits, but before installing the new bits, we have to pull the rear hub apart. You’ll need a quality set of spring clip/retaining clip pliers.
Remove the rear wheel, then remove the nut on the sprocket side as well.
Remove the rear caliper and speed sensor.
At this point the rear disk and center hub will slide out on the left side of the bike.
Once removed, use the spring-clip pliers to remove the giant spring-clip on the right side of the hub. This holds the brake caliper bracket in place, yet once removed the bracket comes off and can now be modified. We need to widen the slot so that the pin (attached to the swingarm) will allow the eccentric to rotate just a little bit more.
We slipped the bracket into a mill and proceeded to remove about 1/4” of an inch of material from the slot. However, this could also be accomplished with some patience and a file. Not a great deal of material needs to be removed.
Once the slot has been widened, we can reinstall the rear hub. Now is also a great time to inspect, replace or re-pack the rear wheel needle bearings.
Reinstall the sprocket and the chain, but be sure you measure twice before cutting and riveting the chain. We need to rivet the chain with the swingarm at the latter half of it’s adjustment. And in case you are in need, we love our Motion Pro Jumbo Chain Tool. It's lasted us nearly a decade now.
With the larger sprocket, slightly longer chain, notched brake caliper bracket, and once the new chain is installed and adjusted correctly, you should still have 3/4 to 1-inch of remaining chain adjustment. Which should be more than adequate to deal with the subsequent chain stretch.
But now, the 848 can run modern race tires and tire warmers. But just to be sure, we used a flap wheel and removed just a little bit of the weld and aluminum from the front of the swingarm where the tire was rubbing.
And that's it. You can now run modern race tires on your vintage 848 Superbike!