How did we end up with 17-inch wheels for sportbikes?

Dear MOby,

And why didn’t anyone let me know that tire choices for the 18-inch wheels on my new 1987 Suzuki GSX-R750 were going to be severely limited? I guess it’s not a big deal, but it made me curious how we went from 18, 16, 16.5 and 17 inch tires not so long ago – to next to nothing other than 17-inch tires now on nearly every sportsbike and sport tourer sold today? Why only 17 inch tires on sports bikes?

With curiosity,

T.Rizz


Dear T,

It’s an interesting question with a fairly simple answer, but first a little history lesson or why not a long one, since it’s a slow news day? The first 1969 Honda CB750 “modern superbike” had a 19/18-inch front/rear tire combination, and the 1973 Kawasaki Z1 that usurped its title wore the exact same 3.25 x 19-inch front and rear tires. 4.00 x 18 inches. , on probably the same wire-spoke rims, and that was fine.

In 1980 we were beginning to suspect that we could never afford a Porsche 928, but we might one day yearn for a 1983 Suzuki GS1100E. OK, maybe a 550.

This GS was the new first “modern superbike” via its 16-valve Twin Swirl combustion chamber engine, but its 19- and 17-inch cast wheels were also quite high-tech. Wikipedia says the 1976 Yamaha RD400C was the first motorcycle from a major manufacturer to have cast wheels (18/18).

Enter the radial

On the occasion of the 25th anniversary of its first radial tires, in 2012, Michelin sent us this press release, which summarizes well:

Three years after its first use in competition, in 1984, Michelin decided to market its radial motorcycle tire. In 1987, the MICHELIN A59X and M59X marked the beginning of a revolutionary new era for high performance tires allowing riders to get the most out of the new motorcycles of the time. Today, all road, sport and supersport bikes are equipped with radial tires. Without the radial tire, racing bike engines would never have gotten this big since traditional cross-ply tires would not have been able to support today’s 1000cc engines. The radial tire has been the main driver for faster technical improvements for racing and production motorcycles in terms of torsional stiffness of cycle parts as well as engine power.

In 1983, thanks to the genius of Freddie Spencer, Michelin won the first Grand Prix on a 500cc motorcycle equipped with a radial tire (on the rear wheel only). The following year, Randy Mamola became the first rider to win a Grand Prix race (San Marino) on a motorcycle fitted with radial tires on the front and rear wheels. A radial tire undergoes less heating than a conventional tire. As a result, the rubber remains more flexible and offers better grip in turns.

Pirelli was there too, building bespoke MP7 radials for the crazy 1984 European-spec 150mph Honda VF1000R—a 120/80-16 front and 140/80-17 rear.

Bridgestone, too: When the next “first modern superbike” Suzuki GSX-R750 arrived in 1986, it rode Bridgestone Cyrox 18-inch radials.

Radial tires were here to stay by the time I arrived in California: the amazing 1988 FZR400 and FZR400R I cut my teeth on at the Rock Store ran on 110/70-17 and 140/60-18 radials. . The even more amazing FZR1000 a year later, and Suzuki’s new GSX-R1100, both have big radial tires on wide 17-inch wheels. Meanwhile, contemporary sport tourers like the GSX-F1100 Katana and Yamaha FJ1100 were a little behind on the 16-inch bias-ply tires.

I loved these things. The 1991 FJ1200 has a 120/70-17 radial up front to go with its 16-inch bias-ply rear.

Your now highly collectible Honda RC30 launched the world with an 18-inch rear and 17-front curved ball, and Mr. Baba decided to mix it up again with a 16-inch front tire on the world’s next first modern superbike, the 1992 CBR900RR.

Does anyone know the answer?

Basically, everything was in motion. The radial tire revolution opened the door to the horsepower revolution and the chassis revolution, and all the engineers were actively trying to find what worked best as the appetite for sportier sportbikes grew. . It was a great excuse for factories to race. Former PR Dunlop and Cycle Magazine guy Ken Vreeke got this from Eddie Lawson, who won the 1988 500 GP championship on a Yamaha before doing the same on a Honda in 1989:

When Kenny and I went in 1983, we tested the 16 and 17 with the 500 GP bike. The bike didn’t spin on the 16 because it was wider. The 17 turned much better—the geometry on this bike worked with the 17. Later on through the year we only ran 17s on the Yamaha.

When I went to Honda, they wanted me to try a 16. I knew I wouldn’t like that. But then I tested it and it worked great and we won races on the 16. Later the Honda geometry changed and the 17 worked great. So I was able to experiment with both sizes, and it really all depended on the geometry of the bike at the time.

Which is perfectly logical. Honda said the purpose of the 16 in front on the 900RR was to reduce weight and provide more contact patch, but many testers felt the RR was twitchy up front and labeled the bike Experts Only.

OG CBR900RR came with a 130/70ZR16 front end, which was supposed to offer more grip and less weight. (photo JB)

What we’ve learned since is that more front grip isn’t a good thing at all if it upsets the front-rear balance. Serious roadracers regularly drift both ends of the bike, especially now with traction control, and regardless of tire size, we’ve always known that maintaining the rear will come off before the front is key. We also learned the value of the standard steering damper.

SPECIFICATIONS

And while Honda was battling Yamaha was battling Suzuki in the golden age of 500 GP racing, Michelin was battling Bridgestone and, in America at least, Dunlop. All tire manufacturers were also looking for an edge, which meant building tires to fit whatever wheel the customer was convinced was the winning hand that week – 16, 16.5 or 17 inches.

Neill Rampton, at Dunlop, was there:

“In GP and WSBK, rims weren’t defined by regulations in the late 90s and early 2000s. That’s how we came to the R420 (16.5”). There were also many different rim widths used (even within the same team). I think with most series going to spec tires, everyone realized how much money they were wasting on carbon rims and 17-inchers. the regulations made sense. Especially for SBK, where the OEM fitments were all 17-inches to start with.

Our favorite sick friend, Kaming Ko, recently asked Pirelli to produce a set of 16.5 inch tires for his old Ducati MotoGP bike.

World Superbike tire competition was the same, but on a slightly smaller scale and on production machines. For 2004 the decision was made to make the WSBK a specific tire series, with Pirelli stepping in to supply 16.5” tires to all teams.

Following the success of this experiment*, the tire war also stopped at the Stylema in MotoGP when, in 2009, it too became a series of specific tires, with Bridgestone as the sole supplier of 16.5-inch rubber. The move both leveled the playing field – or at least gave riders something they couldn’t blame for poor results – and cut costs in the wake of the previous economic crisis.

Four years later, in 2013, World Superbike made the change from 16.5 inches to 17 inches Pirellis. The Italian tire giant is contracted to be WSBK’s tire supplier, for all classes, until 2023 – a 19-year run.

The final coup de grace for any non-17-inch sportbike tire came in 2016, when Michelin took over from Bridgestone as MotoGP’s sole tire supplier, and proclaimed it would be 17-inches for all of you in the future. Like Eddie said, you can make a 16 or a 16.5 or a 17 or 16.25 or a lot of other sizes work just fine once you adjust the geometry of the bike to it, but why spend all the money? money and effort to produce so many sizes, and do the dealers stock them, etc., when 17″ front and rear seems to have made everyone happy? Now all you care about is the width. And atmospheric pressure. And made up. And?

——————————————-

* Pirelli issued a press release after that first WSBK season which said, in part: So what has changed with Pirelli and the specific tire rule? Almost everything. Last year, 218 points separated the top three drivers at the end of the season (103 points between the two official drivers, 115 points between second and third place). This year, there were less than 100 points between the top five runners. Neil Hodgson has won every race up to Laguna Seca last year, while this year’s championship has been called “one of the most exciting and hard-fought” in the series’ 17-year history. It was the last weekend.

Related Reading:

Staying the course: the FZR400 and FZR1000

Suzuki GSX-R750: old versus new


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