Service
SERVICE
Tire size confusion
I find myself unable to decide which tire size to buy for the front of my 1984 Nighthawk S. I replaced the rear 130/90-16 with the same size K391. Now I find that Dunlop does not produce a 110/90-16 for the front. What Dunlop has available comes only in 100/90, 120/90 and 120/80-16 sizes.
Would you please enlighten me, as well as others, as to the effects and characteristics of changing sizes of tires? 1 w ant to know' if bigger (wider) is always better. Also, what effect does profile have? Is it okay to mix 60/70/80/90-profile tires on the same bike? Alex Nall Ramona, California
Generalizing about tires can be somewhat chancy, as there seems to be an exception to every rule, but we'll try an yway.
Most bikes tend to work best with tires of approximate! y the same size, aspect ratio and profile for which they were designed. Racers may find they can turn faster lap times with oversize tires, but they're usually willing to sacrifice handling feel or ride qualit y for pure cornering power. Bigger tires, especially on the front, may well be more harmful than beneficial to handling feel. Larger front tires generally slow down steering response, and may increase an y tendency for a motorcycle to sit up when the front brake is applied while cornering. Wider tires ma y also make a motorcycle more sensitive to road imperfections, as bumps can hit further off the tire centerline, increasing their tendency to steer the front wheel.
Furthermore, when tire companies talk about 60, 70, 80 and 90-series tires, they're describing the lire's aspect ratio, not its profile. The aspect ratio is the height of the tire section divided by its width; the lower the aspect ratio for a given tire width, the lower the overall height of the tire. Tire profile is simply what it says it is: the overall profile, or shape, of the tire section.
Selection of aspect ratio may be decided by a motorcycle's manufacturer due to space constraints as much as it is to other tire characteristics. In other words, the tire has to fit the bike. If a tire is to be really wide without being so tall as to raise the rest of the motorcycle, that tire must either be based on a small-diameter wheel, atuse a low aspect ratio. Sport bikes, on which ride is less important than cornering capabilities, usually go the big wheel/low-aspect-ratio route. 7hat 's because low-aspect-ratio tires have short sidewalls and stiff 'carcasses, characteristics that favor cornering over ride. Bikes where load capacity and ride quality matter, such as tourers and cruisers, more often use smaller-diameter wheels with taller tires.
Aspect ratios may differ from front to rear tire, but usually not by much. And. almost needless to say, styling certainly enters into a manufacturer's choice of tire sizes.
As for your Nighthawk S. there's no need to delve too far into theory: For the front tire, Dunlop recommends the 120/80-16 K39L That should work well, but with some increase in steering effort.
What happened to the CX?
How come Honda doesn’t produce a longitudally positioned VTwin like the CX500 and CX650 Customs anymore? Were there too many problems with this engine configuration? Scott Watson Stuttgart, West Germany
/ he CX300 had some early teething problems with cam-chain tensioners; but once these problems were cured. there were no serious faults with the 500 or the CX650. Honda appears to have abandoned this engine configuration for marketing reasons; most motorcyclists seem to fnd a traditional VTwin (such as the Honda Shadow) more attractive.
Cold shifter
I bought a newr VF1000R and find the bike very enjoyable. However, I do have a question concerning the hydraulic clutch.
When the bike is cold or the outside temperature is low (30 to 40 degrees), it is quite difficult to shift. When the bike and temperature are warmer, the best shifting occurs w hen I barely touch the shifter and clutch, and maintain rpm. When I intentionally try to shift (pull in the clutch, drop rpm, and then shift), it is almost impossible to shift into fourth and fifth gears. So far. mv dealer tells me this is normal. Is he right? Chris V. Cipriani Raleigh. North Carolina
Your shifting difficulties result from a dragging clutch that isn't completely disengaging. That wasn't an unusual occurrence with VF750Fs and VF! 000s. but yours seems worse than normal. To begin with, cold engine and cold weather shifting can be improved by switching to a lower-viscosit y oil (10w40, or for really cold weather. 5w30, instead of 20w50 or 40or 50-weight). or by using a synthetic oil.
Improvements beyond that will require some clutch work. A first step would he to bleed the hidruialic st'sle,ii to ensure that full chile/i travel can be used. I/I/wi doesn I offer improve inc/its. it will he necessary to disassemble tile chile/i and check for out-of-tolerance clutch plates amid (011 1/)O/lelits; acceptable tolerances are ycn in Hoiida Ic service manual. But eveii at best. some elate/i drag mnai' re/na/n. making s/i/fling a hit clunki.
Single-purpose dual-purpose
I own a 1983 Yamaha XT550 and am presently considering converting it into a twisty-road Thumper. My main concern is whether I should replace the wheels or alter suspen sion in any way to improve handling on the road. I will use quality street tires and low bars among other alter ations for Street use. Please give me any ideas you might have regarding this project. G. Peel Los Angeles. California The ,,iain c/lange if iou want to use street tires will be to lace a I 9-iuic/i ri/n to i'ouir front ii'/ieel: on/i' dual-purpose tires and sonic /0w-per/or/i iaiice ribbed frouzi tires are ai'ailable in 1/ic 21-inch size. (Sou;ie of/lie latest dual-purpose tires are quite good. /iowei'er: Metzelei~ Continental and Pirelli all sell dualpurpose tires that stick len' well on pai'enient. hut not as hell aS sport con zpound. pu/re-st reel t irc~s.) T/ia t change alone would trans/or/li i'our XT i/ito a hackroad bullet. Addition a/fr. ,firming up tile front and rear spring rates slight/i' would keep the hike froni /liol'ing around ouu its 5t15/)elisiO/i 50 /1111(11 i/i corners.
