Service

SERVICE

Paul Dean

A belt in the back

I want to raise the gearing on my stock 1992 Harley-Davidson Fat Boy for an upcoming cross-country trip to Sturgis. Stock gearing uses a 71-tooth rear pulley and a 131-tooth drive belt. To avoid the considerable hassle of purchasing and installing Harley’s International Sprocket/Belt Kit, can I simply bolt on a stock 1995 rear pulley, which has 65 teeth, without having to replace my stock belt with the 129-tooth belt from a ’95 model? In other words, can my ’92 model’s rear-wheel adjusters take up the slack in my stock belt, which is two teeth longer than the belt normally used with the smaller pulley? Alan Pelton

Pittsburgh, Pennsylvania

Sorry, Alan, but if you change to the '95 rear pulley, you must also use the 129-tooth belt. The Fat Boy’s wheel adjusters do not have enough range to compensate for the 131-tooth belt's extra length.

Changing to a 65-tooth rear pulley while retaining the stock, 32-tooth front pulley would net an S.47-percent reduction in overall gearing. In real-world terms, this translates to your Fat Boy being able to go just under 70 mph at 3000 rpm in top gear with the taller gearing, whereas it would only do about 64.5 mph with stock gearing. You could, however, keep your stock belt and rear pulley by replacing the front pulley with a 34-tooth unit available from Andrews. That would yield a 5.85-percent reduction in gearing, meaning that the bike would go just over 68 mph at 3000 rpm in top gear. The Andrews pulley is expensive, though—about $150, compared to around $45 for a stock front pulley.

Either way, you 'll have to disassemble the primary drive to remove the continuous belt. And while you re in there, you should replace your front pulley either with the Andrews unit, or with the improved stock pulley and mounting hardware used on 1994 and later Harleys. Pre94 front pulleys tend to come loose on their shafts, so the later belt drives use a slightly redesigned pulley, spacer, seal and nut retainer that eliminate the problem.

Tires and tribulations

I have a ’94 Yamaha FZR600 and, as you know, the stock tires are really skinny. 1 would like to put a bigger footprint on the road without going to the great expense of buying a new set of rims, and I’ve been given a lot of different advice regarding wider tire sizes. Some say I will get better grip by going to wider tires, and some say I will get less grip by putting wider tires on my stock rims. Some recommend I use a 150/70-18 on the rear, and others say 1 should instead go to a 150/60-18.

I need a straight answer. I will be moving out of the country soon and am planning to take my bike with me. Therefore, I will need to take some tires with me, too. Please give me your advice. Calvin CheunQ

Yorba Linda, California

As a general rule of thumb, Calvin, putting wider-than-stock tires on any bike tends to do more harm than good when used on that particular bike ’s stock rims. In most cases, the stock rims are narrower than recommended for the wider tires, so the sidewalls get pinched in just enough to reduce their rigidity under high cornering loads. That same pinching also causes the tread to be pulled into a tighter radius, resulting in a slightly smaller footprint. There are exceptions, but if a manufacturer thought that putting wider tires on any given sportbike’s rims would enhance that bike ’s cornering ability, those tires would be standard equipment.

Having said that, / can also tell you that for the type and level of cornering that is possible on the street, you could bump up to the next-wider tire size on the rear of your FZR600 with no adverse results. The stock rear tire is a 140/60VRI8, so stay with the 60percent profile ratio and use a 150/60 F R18. Don’t go any wider than that, and don't use the 150/70-profile tire, either; its taller sidewalls tend to flex a bit more under any heavy-loading circumstances, a trait made worse by the slight pinching mandated by the narrow rims. The 70-series tire also is larger in diameter, which would effectively raise your gearing and reduce peak acceleration.

As for the front, I suggest you stay with the stock, 110/70ZR17 size. If you go up to a 120/70 front, it will make the FZR s light, neutral steering-one of its most admirable attributes-noticeably heavier, and cause the bike to sit up more when braking while leaned over.

Been there, done that

It’s been done. Like everything supposedly socially and technologically innovative about the ’90s, it’s really something we got bored with back in the ’60s. I’m referring to Chad Trent’s letter, “Reversal of Four-tune,” in your June Service column. In this case, the symmetrical arrangements of headbolts and camshafts in the Triumph 650 Twin facilitated reversing the head. Locating the carbs in front and pipes in back was considered showbike-trick chic a generation ago. It was just as technically impractical as Paul Dean’s elucidation made clear.

No matter how avant-garde an idea you think you thought, the Limeys probably thunk it first, usually long, long ago. Who was it who said that those who don’t learn from history won’t learn much from back issues, either. If you want a real techno eyeopener, tour the infield museum at the Indianapolis Motor Speedway. Double overhead cams, intercooled superchargers, fuel injection—all this was high-tech in the ’20s. The final reality check occurs when you come nose-to-bevel-gear with a single-overhead-cam four-banger from 1903.

Kommandant Springfield, Missouri

Astute observation. But that noseto-bevel-gear stuff sounds painful.