Image source: extreme angled close up of the author’s rear Pirelli Diablo Rosso Corsa tyre after a track day at Philip Island

This article is © 2020 arc@arcnineohnine.com  and may not be reproduced without written consent.

This article looks into the factors affecting motorcycle tyre wear and what can be done to increase tyre lifespan. With sets of unfitted tyres generally costing around AU$500 for a supersport litre bike, this is often the most regular maintenance event which can add up to a considerable amount financially over the lifetime of your precious steed. The author concludes that road-based tyre wear is mostly caused by riding style and road surface with mechanical issues able to significantly and negatively affect wear.

Arc is hard on tyres. Always has been, probably always will be.

Yes, I’m hard on tyres (or tires for the others). Typically, I get no more than 6,000 km from a set of supersport tyres. Some sets I’ve had to replace at 3,000 km and this is on the public road, not the track! With “touring” tyres I’ve scant got past 8,000 km, and with some I haven’t even got close to that. And this is despite hearing from some fellow riders about their +15,000 km old hoops.

 

1.0 What’s this thing called “grip”?

No article on tyre wear would be complete without introducing the concept of “grip”.

For a complete, exhaustive, incredibly detailed and very professional tome see this article which with over 96 pages of text, images and graphics covers seemingly everything that there is to know about tyres and grip, from the School of Engineering at the University of Pisa, Italy and created by the Société de Technologie Michelin.

At a very high-level summary, grip is generated in one of two ways: through indentation and through molecular adhesion.

  • Indentation happens at the millimetre scale and is caused by deformation of the tyre surface with respect to the road surface; and
  • Molecular adhesion occurs at the micron scale as evidenced by tyre being left behind on the road surface and is caused by molecules in the tyre stretching and forming and unforming bonds

Molecular adhesion is the mechanism behind tyre wear, resulting in rubber deposits or marbles…

The scientific reasons why are extensive, just trust me on this. I’d also argue that viciously sharp grit impregnated in road surfaces will carve rubber off tyres too, see the below section titled “The road surface”.

2.0 The contact patch

Surely we’ve all heard about just how much (or little depending on your perspective) of your tyre is actually touching the ground? It’s variously cited as something like the palm of your hand and we’re not talking about giant-sized hands. Go on. Take a look. Do it right now. Open your hand up and take a good, long hard look at the size of your palm (sniggers from the back row are to be dutifully ignored at this juncture). It’s not much and that’s how little of your rear tyre is likely making contact with the road surface. Sure, different bikes will have different contact patch sizes, but the point is that it’s not much. Not much at all. Not much at all that’s keeping you stuck to the road surface itself and moving in the direction which you’re piloting.

Image source: author playing Call of Duty® WWII

3.0 Replace tyres as a set?

Pirelli Diablo Rosso Corsa II, one of my most favourite tyre choices!

Three to six thousand kilometres to a set? Yes, really, only that many kilometres from a set and I do replace them in sets. Some may claim that you can typically get 1.5 fronts to a rear but to me it’s a false economy, especially when this investment is the one keeping you connected to the road. Why replacement in sets? My thinking on this extends on the “false” economy of not changing tyres as a set. It gets down to wear. Sure, your rear might be at the wear bars when you have a few mm left on the front. But how about what both tyres, taken as a set, have gone through in their lifetime? Umpteen heat cycles which will have taken away oils and compounds within the tyre itself. How about grip? It stands to reason that as a tyre wears it provides less overall grip; the handling will change as the tyre wears too and there will be an impact on wet grip as well. Think about what you’re asking of your worn front tyre in terms of grip if combined with a new rear. What would it be like to have less grip on your front tyre, the one that is charged with up to 80% of your braking force? Do you really want to go there?

Sure, go ahead and save a few bucks and replace tyres separately but I change mine as a set. I wear them as a set and see no scientifically backed reason why you wouldn’t want to replace them as a set; one of the simplest investments you can make is in “sticky rubber” and I like my rubber as sticky as I can get it, within reason, more on that in a moment.

4.0 The role of suspension on tyre wear

How will your suspension affect your tyre lifespan? If you’re thinking this then you’ve never looked into the near art form that is setting up your suspension “properly”. Properly for your weight, your bike’s weight, your bike’s geometry, your riding style and the surface on which you are riding. Spend any time doing track days or researching them and you’ll see examples of gross and hideously deformed tyres. The preload (how much your suspension is loaded up when at rest), high and low-speed compression (how your suspension compresses and the rate at which it does this) and rebound damping (how your suspension extends back to “neutral”); how quickly, slowly and under what characteristics. Spring rate. No, not how much accom will cost pre-summer. Spring rate, as it pertains to suspension, is the weight that is needed to compress a spring by a specific amount and if that rate is linear or not (sometimes you can overhear huddled cognoscenti in deep, druidic like conversation weighing this up). Your suspension oil height and type, air gap, shimming and suspension internal characteristics; all these will apply, as too does the rate of weight transfer during acceleration and under braking. All of this, in terms of your suspension, will affect your tyre lifespan; your tyres are an extension of your suspension. How your tyres flex, deform and rebound forms an active part of your bike’s suspension, just how active depends on your set up and how you ride.

Image source: author-supplied, ideal racetrack tyre temperature pattern

Right, having not even remotely done justice to the black art of suspension and seriously glossed over a complex subject, suffice to say that incorrectly or badly set up suspension will seriously affect your tyre wear and will leave behind visible wear characteristics from which you can perform a post mortem. The venerable Dave Moss has stacks of info on this and there’s also a great guide with photos of the most common types of tyre wear from over/under inflation, too cold or too hot a tyre and several shots of what incorrectly set up suspension will do to your bike’s tyres.

If you’re interested in learning more about some of the black arts of riding, see this post on this site and for a suspension bible you simply can’t go past Sportbike Suspension Tuning by Andrew Trevitt and for those keen to DIY see Race Tech’s Motorcycle Suspension Bible (Motorbooks Workshop) by Paul Thede and Lee Parks, I have both of these books and highly recommend them.

5.0 Causes of tyre wear

Getting back to tyre wear. Your suspension will affect your tyre wear, more so on the track and far less visibly on the public road. Off the track I’ve most often seen scalloping of the leading or trailing edge of tyres on the sides and often with different directions on the front and rear tyres. What causes this and why is left as an exercise for the reader (see Trevitt). While this scalloping will affect lifespan I’ve never, ever, worn out the edges of a tyre through public road use. It’s always the rear tyre’s centre strip that goes first. Why’s this? Simply put, it’s typically caused by power. Applying a lot of power without regard to mercy. Rolling on like you mean it. Twisting your right wrist. Laying on the power. Dialling it on. WOT (whole open throttle). Throttling the chicken, spanking the monkey (oops, sorry, that’s from a different post). Seriously, power. That and actually riding your beast. Actual riding will always affect tyre lifespan. Think about how much time your bike gets ridden upright getting to the “fun” roads, think about the proportion of time which will likely be biased to freeway type commutes to get to the fun bits and this is where so much of our rubber gets lost. To the freeway. To the unexciting roads, in the traffic. What can we do about that? Not much to be honest. I have seen and heard of people trailering their bike to places like Jindabyne (seriously) and sure if that works for you, go for it.

So, given that wear is inevitable what’s at play with wear? Where can we help reduce it? Start with understanding what it is and why it happens. The scientific community will likely add in the word “entropy” about now: the tendency for systems to naturally transition from a state of order to disorder; how things age and decay.

 

5.1 Riding style

How you ride will arguably be a significant, if not the most significant factor affecting your tyre wear. This varies from “ride it like you stole it” through to “only ridden to/from religious services on Sunday” and while a weekend fang may be your definition of a religious event, an aggressive riding style will wear your tyres more so than a sedentary one. How you decelerate with either or a combination of engine and both brake controls, how fast you enter corners, how you accelerate, when and where, will all affect wear. How smooth your inputs are with the controls will also affect your tyre wear characteristics, this includes not just throttle and brakes but also steering, weight transfer and body positioning.

5.2 Torque

With great power comes great responsibility

How much torque you can lay down on the road surface through your engine’s native characteristics, your choice of front and rear sprocket sizing and your internal gearing set up, these will play a role in rear tyre lifespan. I’ve tried various combinations of sprockets including -1/+1, -1/+2, -1/+3 and -2/+3. The site gearingcommander.com will be your friend here for sorting through what length chain you’ll need for various combinations and what the maximum km/h will be with each combination together with the expected RPM at various speeds and gears and importantly what the shift change graph will be for each combination. Across all these combinations I’ve not seen a major or significant impact on rear tyre wear – remember this is for a street setting though. What I have seen is an increase in fuel consumption with extreme sprocket setups like -2/+3 and wanting an extra highway gear to shift up into. Sure, it takes the sometimes perceived snatchiness away from first gear and ostensibly as you’ll be in second gear more than first that is true, but learning to use first as she came out of the factory is a skill too. I remember watching an onboard video of Qatar laps being cut on a ZX-10R gen 4 and being surprised how much of that track, which isn’t a slow one, was being navigated in first gear.

A bike pushing 200 brake horsepower even with a 190 or 200 sized rear tyre is going to chew through tyres more than a similarly equipped bike with a quarter of the available power.

How about using a quickshifter? It’s arguable that this could lend itself to increased wear through being able to lay down more power over a shorter duration but then again could reduce wear through smoother power transitions without causing the rear tyre to grab the road surface with a cutch-based gear shift. My feeling is that the correct use of a quickshifter with clutchless shifting at high RPMs will reduce overall rear tyre wear vs using a clutch lever instead. It’s a feeling, not scientific and I’d love to get paid to undertake the research to back this up 🙂

5.3 The road surface

The west is the best
The west is the best
Get here and we’ll do the rest
The blue bus is calling us
The blue bus is calling us
Driver, where you taking us?

The Doors, 1967. The End. Hollywood, California: Elektra Records. Available at: <https://youtu.be/BXqPNlng6uI> [Accessed 4 July, 2010]

The actual road surface will likely have the most significant impact. Anyone who’s ridden a motorcycle in Tasmania will know how abrasive the road surfaces are in the southwest. If you’ve not ridden Tasmania, put it on your bucket list right now. Some of the very best roads in the world and if taken at the right time, late summer but avoiding school holidays, will leave you with lasting memories of deserted roads heading off to deserted dams with great camber filled with deserted high-speed sweepers and deserted tight twisty bits. Highly abrasive road surfaces though. Did I say deserted enough times? It really is almost deserted except in peak season when caravans and camper vans seemingly flood the roads, flooded by Tasmanian standards 🙂

Image source: author-supplied, road surface near Heemskirk and Corinna Roads, western Tasmania – crazy hard and very rough,  as rough as a rough thing (pineapple?)

Image source: author-supplied, road surface adjacent to Lake Plimsoll, western Tasmania – a very sharp gravel surface impregnated into the bitumen

The road surface around Trapyard gap is some form of quartz compound but only go here over summer as the road is closed over winter due to the ~1,500 m altitude and often serious snowfall. Trapyard Gap is a great route west though from the amazingly awesome Blue Duck Duck ride (see the BDDR link for 41 minutes of film shot on the recently sealed and outstandingly awesome Omeo to Mitta Mitta Road). Researching this article and according to the Mohs hardness scale, quartz ranks at number seven on a scale of one to ten, with a “ten” being diamond! No wonder it eats tyres. I suspect that the middle section of the Eildon-Jamieson road is similarly composed of a highly abrasive material – the EJ road literally eats tyres, you can spot the wear difference from just one 57 km lap!

Image source: author-supplied, Trapyard Gap, south of Falls Creek, Victorian high country – skippy and brumby country.

Image source: author-supplied close-up of lose, fine, sharp, quartz gravel mostly pressed into the bitumen at  Trapyard Gap

How about gravel roads? Yep, that’s likely to eat tyres too. Why? Because the surface is loose and acts like a rasp or file, tearing away at your precious tyre surface. Sometimes I’ve felt for my tyres, felt for the necessary pain I’m inflicting upon them in their service of the master, a master who’s traversed many an unsealed road to get to the other side, the best bits, the bits hidden from those unwilling to wear the surface, to bear the sacrifice.

Image source: author-supplied, taken looking northwest from the south end of the Jamieson road 13.7 km north of Licola – here’s hoping that one day this will be sealed and create a magical route through to Licola avoiding the tedious, straight and very flat transit from Moe through to Glen Maggie.

Image source: author-supplied, taken at Thomson Dam

5.4 Traction control

To achieve the most speed through a corner, some slippage of the rear wheel is necessary. If you have traction control then this will affect wear, especially if set to the least intrusive mode providing some rear wheel slippage. I’ve been surprised noticing how often my traction control dash indicator has come on after reviewing dash cam film when I’ve been riding on the most intrusive setting. I can mostly tell by the retardation of the engine note but often at the most intrusive level this can go unnoticed. Slipping the rear wheel certainly causes tyre wear. Below is a slow motion clip of TC engaging on my first litre bike, the TC graph is in the middle bottom of the LCD display, recorded in 2011 during a Preston Motorcycle Club recreational ride day at the Victorian State Motorcycle Sports Complex, Broadford.

5.5 Air Pressure

Per the many articles on racetrack-based tyre wear, your choice of tyre pressure will have an effect, more significantly if you really deviate from your manufacturer-recommended pressures. Overinflation will likely create strange handling characteristics and a very hard ride with an almost wooden feeling. Underinflation will wear the centre of your rear tyre faster on the public road through the increased heat generated as it flexes more with less air pressure in the tyre. I’ve yet to find benefit in using anything other than stock air pressures on the road. At the track, that’s totally different and the public road is not the racetrack.

 

5.6 Speed

I almost used the word “velocity”; the word “speed” gets such a bad rap these days. Speed doesn’t kill, it’s the sudden stop that may do that. I have zero statistical data to back up the assertion that increased speed equates to reduced tyre lifespan, nor do I have any scientific or even quasi-scientific data to the contrary. I suspect that as most supersport and even touring tyres are often “(##W)” rated – they have been designed for sustained use at 270+ km/h – then speed isn’t likely to be a big contributor to wear at street speeds for such rated tyres (Pirelli Diablo Rosso Corsa II and the Metzler Roadtech 01 for example). This is just an assertion though and as per the quickshifter section, I’d love to get data and a sponsor to prove/disprove this.

Image source: 1954 animated adaptation of George Orwell’s classic novella Animal Farm

5.7 Season

Like on your steak? No, the climatic season; winter, summer etc. That will affect wear too. This is tricky as it comes interrelated with your choice of tyre pressure and compound. At a gross level on a 30+ degree Celsius day, it wouldn’t be unusual to see a road surface temperature far in excess of that, FTR bitumen apparently melts at around 60C and I’ve ridden several roads over high summer in Victoria in the high 30s where the road surface was a wet sheen of semi-melted bitumen. How does that relate to wear? My thinking, not backed through experimentation, is that the hotter the road surface then the more likely it is for micro components of the tyre compound to remain in the fine surface of the bitumen and more easily tear away from your tyre. This isn’t a scientifically backed assertion but anecdotally I feel that my tyres wear less over winter, how much is hard to say as I wear different tyres over the summer and in the winter.

5.8 Front vs rear wear

I’m assuming that rear wear is mainly caused by acceleration with 175+ BHP of power, through cornering, by “backing it in” and how soon you get on the gas while cornering. With the front tyre, it’s likely caused through both load change under braking and similarly to the rear tyre through cornering forces shearing away the surface bonds. Why so much less wear vs the rear? I’ll put this down to weight too as well as the influence of acceleration tending to lift the front and squat the rear.

5.9 Wheel alignment

An incorrect wheel alignment will likely cause unnecessary tyre wear: this is the alignment of your rear wheel to your front wheel. How do align your wheels? There are a couple of methods from the time consuming but exact “old school” string method through to hi-tech (and cost) laser alignment and the author’s favourite by using an alignment bar. The alignment bar fits into the swingarm pivot point and the rear wheel axle and allows you to confirm that the distance is the same on both sides of your bike, this does, of course, presuppose that your chassis is straight. How about the adjuster blocks on your swingarm or using expensive but very bling Lighech adjusters which include integrated pick-up spools? Sure you can use these but a great many pundits on the ‘net have proclaimed the swing arm stampings to be variously inaccurate through to wildly so – if that’s the case with yours, it will affect any aftermarket adjusters hence the author’s preference for a swing arm based measurement bar. An incorrect wheel alignment will also affect handling and cornering with odd steering and the bike tending to veer to one side likely also causing undue and premature wear on both your chain and sprockets.

5.10 Unbalanced tyres

An unbalanced tyre means that it won’t roll straight and will be felt through increased vibration at the front end with wobbly steering. An unbalanced rear wheel is much harder to detect. Incorrectly balanced wheels will affect bearing wear and certainly cause undue tyre wear, the increased vibration could also lead to various nuts unfastening themselves. Typically, your tyres are balanced at fitting by your favourite friendly (or surly, depends on how you roll) tyre mechanic. Wheel weights are fitted to ensure that the wheel rotates evenly and it’s not just the tyre that may be out of balance, your rims straight from the factory may not be perfectly balanced natively too. You can add small glass beads to the inside of your tyres to act as balancing instead of the more usual weights taped to your wheel rims, but these stop working at high speed, precisely when you’ll most likely want, nay need correctly balanced wheels.

 

6.0 Tradeoffs

Tyre choice is a trade-off between grip and longevity with handling and “feel” thrown in to complicate matters and let’s not forget the use case or intended purpose, track days or freeway commuting and our bike set up. Easy, get the stickiest rubber. OK, but how do you rate and measure that when you throw in intangible value judgements like feel? What about less than optimal conditions, say a cold damp road with some fine gravel, leaf litter or bark? How will a slick track tyre grip on that surface? Not as well as a treaded tyre, it may not grip at all as it simply wasn’t designed for that use case. So, with this in mind, where to from here?

Simply put, the grippiest and stickiest tyres simply won’t last as long as the longest-lasting touring tyres, they’ll have different grip characteristics too in the rain and in hot and cold weather.

 

A subsequent article will look at the author’s experiences around what footwear is available for a modern, fashion conscious supersport sportsbike and coming back to the start of this article: I am hard on tyres. I think this is primarily caused by the roads I ride, often well off the beaten track, my bike’s power delivery and how and when I roll on the throttle, especially on corner exit. Through your riding style you do have some control over how and at what rate your tyres wear. This style is often judged in terms of how “smooth” you are. Correctly set up, tuned and well maintained suspension including correct wheel alignment, tyre pressure etc will affect tyre lifespan too. Choice of road surface is to a degree a variable, but I’ll willingly sacrifice any set of tyres to Western Tasmania’s wilderness on any day!

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