The K491 at 12,400 miles - still going strong!
Being unhappy with the cost of frequent tire replacements on the PC (I ride about 20K miles/year), today I mounted a true distance tire, the Dunlop K491 in 140/90x15 on the back. Others have reported using this tire successfully on the PC and I've had great service from 491s on other motorcycles. It WILL fit with about 1cm of clearance at the yoke of the swing arm. The tire is of course somewhat taller than the 80 series OEM... looks like about 1/2" larger radius which should translate to roughly a 5% reduction in RPMs in top gear. There's lots more tread on the 491 than on a 555 or 177, it has two glass belts (the K177 has one; the K555, none) and a load capacity of 739lbs versus 677lbs for the 177.
Handling is as yet an unknown; it's raining tonight so I couldn't test it. By Monday I should be able to provide some relative observations on the impact on the PCs behavior. BTW, I'm running an almost new K555 (120/80) on the front - there is no 491 in right size for the 17" front wheel.
Jim Randall
From:
Jim Randall [SMTP:jrandall@tricon.net]Well that certainly generated lots of discussion. Let's see if I can answer all the questions in one message.
Consider this a long term test; I'll report again at a later date. BTW my mileage on rear mounted K177s has ranged from a high of 17K miles to a low of 7K miles. Frankly I don't think I rode that differently with the two extremes and I'm pretty consistent with air pressure maintenance. Beats me why there was so much difference.
Jim Randall
From:
Jim Randall [SMTP:jrandall@tricon.net]I reported last week that I had mounted a Dunlop K491 on the rear of my PC but until this weekend I hadn't had a chance to ride on it much. This is the completion of my previous post. If you're late tuning in to this, the Dunlop K491 is a high mileage touring tire and is sold only in a tall 90% sidewall/tread with size. BTW, this relationship is called the aspect ratio of the tire.
The K491 on my bike is a 140/90x15. The OEM K555 is a 140/80x15. This means the K491 is theoretically 14mm larger in radius than the K555/K177. Based on total measured radius of 305mm, the higher profile tire is 4.6% larger and should reduce engine revs by that amount in top gear.
Some list members expressed concern about the handling changes which might result from this exchange and in fact, one member reported a bad experience with the K491. However, at least two others however wrote to say they were already using a K491 without mishap.
My observations...
The tire clears all the PC components ('95 model) without a problem - the closest point is at the yoke of the swing arm where there's less than a 1cm of clearance.
Engine rpms are reduced by at least 5% - remember I'm going from a worn-out K177 to a new K491 so the difference in radius is the sidewall height + tread depth. With the old tire my speedo indicated 58mph at 4K rpm. With the K491, the speedo shows 62mph at 4K - that's closer to 7% than 5%. I was surprised at how noticeable this is. I found myself shifting down more often in curves and running more in 4th gear in the sweepers. However, overall I like the effect. The PC engine has plenty of torque so it handles this with aplomb and the reduction in rpms makes the bike feel just a bit more relaxed at speed.
Handling...
My first 50 miles or so on the new tire were all about town so I really didn't get to push the tire until Saturday. Nancy and I enjoyed a great day of riding in mountains of eastern TN, western NC and southwestern VA with "Jim" Davies (evil twin to Tim Davies) and Stan (a.k.a. Rocky Rocheux) and Caroline Rockland. I led these brave participants in the second annual East Coasters May Day ride over my favorite stretch of asphalt - US 421 from Bristol, TN to Mountain City, TN. During this time I was able to explore more of the outer limits of the K491. I was pretty cautious at first since I didn't know what to expect but I continued to push harder until the toes of my size twelves scraped the tarmac. When my toes touch, the pegs are just a few milliseconds behind so I couldn't have gone much faster without the pegs beginning to fold. My take - there is a slight difference in the feel of the bike. It's not noticeable at all at touring speeds but at the extreme, it may take a bit more pressure on the bars to push the bike over. However, the tire grips all the way to "toe-down". Handling is still crisp and the bike still transitions beautifully over center - very smooth and predictable. When riding hard with the old K177 on the rear, I always found my self scooting up on the seat and leaning over the handlebars a bit more to put more weight on the front wheel. This seemed to make the bike track better. With the K491, the bike felt stable and solid with my butt against the passenger seat (where I normally ride) and with a more upright sitting position. It felt to me like cornering on a Gold Wing looks - i.e. a centered, up-right rider with the bike leaned over until parts begin to touch. Could I corner faster on the K177? Maybe, I don't really know; but, I do know that K491 is stable within the range of cornering lean angles I'm willing to ride. When we stopped to regroup, I examined the wear patterns on the tire. The only surface untouched was the last 1/8" of tread. With the K177/K555, I think there would have been more like 3/8" of unexplored territory so I suspect there is more potential cornering capability with the OEM tires "at the limit".
Conclusions...
I'm satisfied with the K491. I like the reduction in engine speed and I don't find any serious handling limitations for the kind of riding I do. I guess we'll just have to see if I get better tire life than on the other models; more in about 6 months...
Your mileage may vary,
Jim Randall
jrandall@tricon.net
http://jinux/
The K491 at 12,400 miles - still going strong!