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Page last modified 23:38, 19 Aug 2011 by internetscooter
Vespa Labs > Vespa 101 > Dynamics > Tyres
TyresFrom $1What are good tyres?I've read elsewhere the standard factory issue PX tyres are not the best. Should I consider replacing and if so any recommendations to increase safety? The tyres supplied with scooters are generally the lowest cost to meet the country standards. It does not make good business sense to do otherwise. It is very easy to improve the quality of tyre, either within the same brand or with a different brand. It is recommmended that the front and rear tyre be matched (Motorcycle Tyre Safety Information) New Vespa PX's come with Michelin S83's, these have poor grip and are only rated to a max speed of 100Km/hr. These tyres can be upgraded to Michelin S1's which provide better grip but are still only rated to 100Km/hr. For higher performance, Sava MC18/MC20 (and other tyres) are speed rated to 150Km/hr and are very high quality tyres. There are many tyres that are better performing than standard (and some worse). Below we discuss what to look for in the manufacturers tyre rating specification and how to match that to your riding requirements.
Tyre RatingsManufacturers state how their tyres perform in the tyre rating scale below:
What does the tyre speed rating mean?As the wheel rotates the tyre deflects as it hits the road, grips and releases, this is the thing that causes the most stress. Tyre speed ratings tells us how much stress a tyre can handle. 10 inch wheel have a big disadvantage because the tyre deflects more times per second than a bigger wheel. As an example, a Dunlop K627 15 inch motorcyle tyre is rated to 210km/h whereas the same Dunlop K627 10 inch tyre is only rated to 100km/h. Other things that influence the amount of deflection are load, being how much force is pushing down on the tyre, and tyre pressure, as a pumped up tyre deflects less than one that is under-inflated. The letter and number above translate to the maximum speed the tyre can be used at, along with the load on the tyre at the time. This is a measured result from safety testing and is what the manufacturer (legally?) stands by for a quality measure. So no mater what else they say on their advertising, the tyre rating is a fact you can rely on. e.g. "J" = Speed category 100 km/hr, "51" = Load index of 195 kg. A detailed example of the test procedure is found in Australian Design Rule 23/00. A brief summary is that the a "51J" rated tyre has to last 20 minutes at 93 km/hr, with correct pressure and a load of greater than 80% of maximum (i.e. ~160Kg). A "51P" rated tyre has to last 20 minutes at 143 Km/hr. "Last" means "After completion of the high speed test specified in Clause 23.3.5 no tyre shall have ‘Tread Separation', 'Ply Separation', 'Cord Separation', 'Belt Separation' or 'Bead Separation', 'Chunking' or 'Broken Cords'." So the test is for the limit of the tyre before it fails! Riding higher than this limit means the tyre may start to fail. At a guess, manufacturers though will probably use slightly lower speed rating to account for variations in their production quality (so all tyres coming out good and bad still meet the spec). Why you should be careful when considering "J" rated tyres for road useMany scooterists choose tyres by brand, X brand is better than Y brand. With a tuned scooter or one used for carrying loads/pillions, you need to understand tyre ratings rather than rely on just brand reputation. For example Michelin S1's are considered great tyres as Michelin has a good reputation. However let's look closely at why you should consider the tyre safety rating over brand. Many "good" tyres are only "J" rated (not just Michelin S1's) with an equally low load index, lets look closely at what this means for the perspective of a Vespa PX rider.
So at 100Km/hr you are riding at the very edge of the manufacturer's tyre limit! That is assuming that you have correct tyre pressure, if you don't you may be riding above the limit! And this assumes that you aren't ever going to carry luggage or a pillion. Michelin S1's were used in this example, this does not mean the are not good tyres. They are designed for a specific task, this "might" make them the best tyre for racing a light scooter round a short track but the same attributes that make them good for that, make them "bad" for uses they are not designed for. In short, if the manufacturer is telling you not to use something through their specification, don't! Buy the right tyres for the right application. Table of Vespa Tyres in order of High Speed/High LoadThe following lists tyres in order of best performing tyres down, first by maximum speed and then by load they can carry. Within ranges of tyres there are also sometimes hard and soft variants. Soft are more sticky but wear quicker and harder are more durable.
*Wide tyre kit required to fit to a 10" wheel. Not included in this table are race tyres (such as the Heidenau Slick) which are classified as NHS (Non Highway Service). See http://www.reifenwerk-heidenau.de/modules/reifenliste/view.php?point=3&rtyp=18&profil=117&pic=81.
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What this means is that when you hit a bump, instead of the force hitting a 10Kg wheel, and then that wheel displacing and the force then going into the rear shock (spring), it has to shift about 40Kg of wheel+engine. So the rubber takes a battering. On top of that most of the weight is at the rear.
What you can do is rotate front and rear tyres... or just state how long your front tyre lasts in the next conversation ;)
Also point out your spare and the fact that you can fix a repair yourself due to the split rims.
I had been living in Melbourne for about 5 years, for the dry lake racing I had to check tyre speed rating (that's what got me looking at the subject). I went out to the lab and looked at what my current tyres had. In Melbourne Sava's are available Michellin S1 were not, but my spare was a Michellin S1? How could this be after 5 years? Here's the reason...
1) I wear the Sava MC18 down till it needs a change.
2) Change with the spare S1
3) Put a new Sava on as spare.
4) Go for a long ride, S1 gets a flat
5) Put on spare Sava, new tube in S1 and that now becomes the spare.
6) Go back to step 1 (5 years later still the same S1)
Most of the flats I got were on the way to rallies while loaded up.
BTW I decided to add the comment because I saw the picture of tubeless rims with J rated tyres. For a lot less effort you can improve safety by buying higher performing tyres. Schwalbe actually have the best rating based on speed and load. So I'd go first higher rated tyre and then tubeless rims (but only if they are TUV approved)