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Check ur tires

July 7, 2011
This tire is seriously worn

Click on the image for a full-size look

The picture on the left was sent to me by friend Jack in Spokane. It was the rear tire on his wife’s Vespa GT.

He’d filled it with air to the recommended pressure, but as she attempted to enter a freeway the tire deflated. It had worn down to the fabric in the ride from home to the freeway ramp.

As you might imagine, the consequences would’ve been disastrous had this happened at freeway speed.

Jack said he was waiting for the wear indicators to become visible. Unfortunately, Jack found out the hard way that scooter tires don’t have wear indicators.

Tires for cars and light trucks sold in the U.S. and Canada are required by law to have wear indicators in their tread. The indicator takes the form of a raised area in the tread groove that’s about 2/32″ shallower than the rest of the tread.

When the tread wears down sufficiently, the indicators form a strip across the tire tread, making it easy to spot a tire about to wear out.

There is, however, no such requirement for scooter tires.

Pirelli GTS

The tire in question was a Pirelli GTS25 (right), which is fitted as original equipment on Vespa’s GTS and GTV models. The slightly smaller GTS23 is used on the front wheel, but has the same tread pattern.

You’ll notice a squiggly central groove that runs the circumference of the tire. That had worn completely away in this case.

And that’s not to say anything was wrong. Scooter and motorcycle tires have a rounded tread profile because, unlike a car or truck, the bike leans into corners. The tread must extend up the sidewall so as to continue to direct water away from the tire’s contact patch.

But unless you’re doing a lot of canyon road carving, the center of the tread is going to wear out long before the upper edges of the sidewalls. You mostly ride straight and upright. Right?

Therefore, your tire’s central tread groove (or groove crossing the center of the tread) must be your guide as to when to replace the tire.

Scooters’ and motorcycles’ rear tires wear much more quickly than the fronts. They’re carrying most of the weight, and providing traction to move the bike. So it stands to reason they’ll wear out faster. Your old-skool Vespa or Stella has the same size wheels and tires on both ends, so you can rotate them and distribute the wear somewhat more equally. No such luck on modern Vespas, which have slightly larger tires on the rear wheel and seem to go through rear tires about every 4000 miles.

I see lots of scooters of all kinds with squishy rear tires. It’s not so hard to understand—modern scooters are (usually) so reliable it’s easy to get out of the habit of performing a pre-flight check. I have been guilty of this myself.

Keeping your tires at the recommended pressure is easy: a good tire-pressure gauge and a bicycle pump can be had at your local big-box store for less than 20 bucks, total. The old “penny test” applies here, too. Put a penny upside down into the tread groove. If the top of Lincoln’s head is visible, it’s time to replace the tire. Ditto if the center of the tread is bald.

So, the central grooves in some scooter tires do serve a purpose. They’re your wear indicators. Favicon

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4 Comments
  1. July 7, 2011 1:20 pm

    Orin – Excellent and timely advice. My mechanic at Tri-Sports in Topsham, Maine, Steve, recommended at new rear tire on my GTS 250. I balked, having just 3400 miles on the scooter. But he explained clearly the reasons scooters run through rear tires, and I’m bow the proud – and safer – owner of a new tire.
    Tom Keene Scooter by the Sea

  2. Jack Monaghan permalink
    July 7, 2011 7:38 pm

    Orin, Thanks for posting this I hope it prevents someone from having a worse outcome than we did. For the record the tires/bike had 6480 miles on it. I know some people say that you should just change tires after a certain mileage. 3400 for Savas’, and I’ve heard 5000 for Pirellis’ It didn’t make sense to me if the tires still had “life” left. Seems ironic doesn’t it? Won’t try THAT again!

  3. July 7, 2011 9:44 pm

    I got more than 17,000km on the first stock Kenda rear tire on the People 250, and replaced it with same. Now, it was probably overdue when I replaced it… no, it was overdue. But not by that much, really.

    The front now has a Pirelli GTS23, but IIRC, it’s a 110/70-16, and I got it from an Amazon dealer who was closing it out, for about $30, delivered. Hard to beat that. So far, that one’s looking really good, whereas at ~26,000km, the Kenda rear is looking about 70% done.

  4. Jack Riepe permalink
    July 8, 2011 2:08 pm

    Dear Orin:

    I am shocked at the low mileage figures cited by these scooter riders. (While other mileages cited — 17,000km and 23,000km — sound far beyond optimum.) I managed to get 12,000 miles out of a pair of Metzlers, and 13,000 out of a pair of Avons, before they really had to go. But I have since learned the value of reading the tire codes, to make sure I am not enticed into buying a discounted tire, that has been drying out on the rack for three or four years. I have no idea what scooter tires cost… I see one figure above that quotes $30. The tires for my K75 (BMW motorcycle) run about $120 on average, and $50 to mount and balance. I was under the impression that scooter tires ran about the same, and that changing the one on the back was a real pain in the ass. (Is that true?)

    I have discovered problems with tires that extend beyond the security of the wear indicator. These include fine cracks, cupping, or pieces of rubber gauged out of the tread. I usually discovered these in the garage, when I was fooling around with something else.

    On the BMW K75, it is easy to check the front tire when the bike is on the centerstand, as the wheel is off the ground and spins easily. The back is a bit more difficult. But I have gotten into the habit of checking my tires once or twice a month. When it comes to tires and brakes, the best surprise is no surprise.

    Fondest regards,
    Jack/Reep
    Twisted Roads

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