Ask the Geek: CBR Forks, Engine Damage and Race Tires

Your Abnormal Guide To Things Abnormal

In the thick of it
I have a problem with my 2006 Honda CBR1000RR. Recently I noticed some oil dripping down one of the tubes on my forks. Being a mechanic, I didn't think much of it, dropped the forks, and replaced the seals. I had some 15-weight fork oil on the shelf, so I used that to refill to factory level. Before that, everything was gravy. I had fine tuned the suspension a few weeks ago. However, when I reassembled everything and went for a test ride, after the tires were warm I pushed it around a little bit. The bike now understeers like one of those cheesy Smart cars. I have the preload topped out on the front (I'm a big guy, topped out is exactly factory sag) compression is at about 80 percent of max, and rebound 45 percent (the rebound damping on this bike is very overpowering I've noticed, even more with the 15-weight). I'm using Pilot Power 2CT tires. The only other change I've made is raising the forks a negligible amount. They used to be 4mm from the top, and now they're topped out. Turning down the damping for the 15-weight oil isn't helping much. If you tip the bike in the corner, it washes pretty well, but throw in some throttle and you can get into a hellacious drift. What in the world is causing this?
Eric Beebe
San Gabriel, CA

The 15-weight fork oil you used is way too heavy for your CBR. Showa cartridge forks such as the one on your bike typically call for 5-weight oil. By using a much thicker oil your front suspension can't react quickly enough when you go over bumps or apply the throttle, leading to the drifting effect you are feeling. The change in fork height may be making the situation even worse, but I'd suspect the oil is most of the problem. Even changing the damping adjusters won't account for that much of a change in viscosity, so you'll have to drain the oil and start over with something lighter.

Are they supposed to run like that?
After a minor crash, my bike lay on its side running for three to four minutes before I could get to it and switch it off. I was wondering if running while lying on its side could have done any damage to the engine? The bike seems to run fine and does not make any unusual noises. Is there anything to worry about?
Mark B. Beberman
Macon, GA

That is a long time for a bike to be running on its side. It's difficult to say if there is any damage to the engine or not, as each motorcycle and situation is different. The biggest worry, of course, is that the engine starved for oil for those few minutes. If your bike ran for that long and doesn't make any noises or burn excess oil now, that's a good sign that oil was still circulating while it was on its side. You can also pop the valve cover off and check the camshafts for abnormal wear, as they are the usually the first item to suffer from lack of oil. Also take a peek inside your airbox and make sure oil didn't come up through the breather tube-that could cause problems later. Newer bikes have a tipover switch to kill the engine in cases like this, if your bike has one you should check or replace it in case the same thing happens again.

In Alaska?
I recently visited a local sales/service shop to have the rear tire replaced on my 2006 Suzuki GSX-R1000. The only tire they had in the correct size was an Avon Viper AV62. Being in a bit of a hurry (first mistake) to make an afternoon ride with some friends, I agreed to the installation. Noticing the near complete lack of siping on the tire, I figured it to be pretty sporty, but neglected to ask whether or not it was a DOT race tire. (second mistake) Sure enough, after a little research, I found "recommended for track use" just about everywhere. My question is: Do these tires have a finite number of heat cycles before they're "cooked"? The literature says they come up to speed quickly, but a good majority of my riding is stop-and-go commuting and putting around town, with spirited weekend trips of 300 to 400 miles. Here in Alaska, this late in the season ambient temperatures may start out in the mid-30s, low-40s, and rise to maybe 60 degrees in the afternoons. Can I trust this tire to stick further down the road with the relatively low speeds/temps it'll see? I realize mileage will be nothing spectacular, but what are the long-term effects of repeated heat cycling on a tire such as this?
Jorge Reyes
Anchorage, AK

Our good friends at Avon recommend that you replace the AV62 with either the VP2 Sport or Storm tire. For starters, the AV62 is a 55-series tire, not the 50-series your GSX-R was originally fitted with, and it's better suited for track use. You'll have a tough time getting the tire up to its correct operating temperature and keeping it there. "Being in Alaska is definitely not the place for a racetrack tire in the fall," says Sukoshi Fahey, Avon's North American Sales Manager. "It is a street-legal tire but only barely, and only for somewhere like California where there are lots of twisties and hot temperatures would I suggest this tire for road use. I wouldn't be so concerned with the number of heat cycles but rather the fact that I don't think it's going to give him the grip he would like." Ms. Fahey also points out that while the VP2 and Storm tires have a road hazard warranty, the AV62 does not. Also, be careful of mixing front and rear brands and models. Ideally, you'd replace both tires as a set to keep your GSX-R handling its best.

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