When you’ve only got two points of contact between you and the tarmac, then it should come as no surprise that making sure you’ve got your tyres set at the correct pressure is very important.
Running your tyres are the correct pressure will ensure optimum handling and safety, while also giving you better mileage.
In their previous issue, the team at Fast Bikes Magazine put the team at Michelin ‘under pressure’ to find out more…
In a pneumatic tyre, the air pressure carries the load – that’s you, your bike, and a pillion and luggage if you have any.
The overall load, in combination with the force put through the tyre and the pressure, will define how much a tyre deflects – in other words, how much it flattens out when in contact with the road surface.
The more load you add, or the lower the pressure, the larger the contact patch becomes. A contact patch that is too large or too small will see an uneven distribution of pressure, causing irregular wear and giving you less grip.
Underinflation also places additional stress on the carcass of the tyre, and this can lead to sudden failure.
The right pressure offers the best grip, feel and wear.
Michelin recommend checking your pressures every couple of weeks, but more often if you clock up high mileages.
If you spot uneven wear during your pre-ride checks, it is worth getting some advice from a local dealer before your tyre is ruined. You probably won’t reverse it, but could stop it getting worse.
The bike manufacturer recommended pressures in your handbook are usually always the best to use, but a one size fits all approach won’t always suit every single rider.
Bike and tyre manufacturers do their best to ensure that it doesn’t matter which brand of tyre you fit, but sometimes you may need a slight tweak to suit you and your riding.
Remember that just because another rider doesn’t have an issue with running a different pressure, it doesn’t mean they are actually getting the very best from their tyres. They may be constantly on the limit of their over-stressed rubber, whereas using the correct pressure would give them with a proper safety net.
A track tyre doesn’t really get much rest, and as such both the tyres and the pressures they run at are very specialised to get the best performance possible.
Unlike road tyres, track tyre pressures should be checked when hot – after 1 hour in tyre warmers, they should be set to the correct hot pressure recommended by the tyre maker. They should then be re-checked straight after a first session of at least four quick laps.
Any difference in the reading pre and post-session indicate the tyres are cooling down or heating up on track. Heating up is less of an issue in the UK, but cooling down isn’t good, and both can lead to a drastic reduction in grip along with increases in wear.
Assuming your bike and suspension are set up properly for track use, then pressure should be the first thing you check if the tyre doesn’t appear perfect or perform properly.
Advice on pressure will change from one tyre maker to the next, but with Michelin an increase in pressure will cause the tyre to run hotter.
As such, by upping the pressure on a cold morning, you make a smaller contact patch which works the rubber harder to achieve a higher temperature. This then transfers the heat through the tyre to achieve the correct operating temperature and deliver the best performance.
Some other brands respond better by dropping the pressure to increase casing flex, which then generates the required heat.
Tyre makers work with the bike manufacturers either as an original equipment supplier, or because they want to make a suitable aftermarket option.
Both bike and tyre makers work within guidelines from the ETRTO to try and provide a degree of consistency to riders.
The idea behind this is that a rider should be able to consult their bike handbook for recommended pressures, and whatever replacement tyre they choose will work well at those pressures.
You should find a sticker under your seat or on the swing arm with recommended pressures. These are based on expected load and weight distribution, along with the type of bike and the intended use.
Check your pressures when the tyre is cold for road use, and hot when on the track.
Road tyres run at lower temperatures and are much less sensitive to changes in conditions. They also warm up faster, and are intended to work in a wider range of conditions. Even modern sports tyres are quite forgiving to big changes in temperature, so checking them when cold is the most consistent way to do it.
With a track tyre, you tend to have a very narrow window of acceptable operating temperature. The cold pressure is pretty much irrelevant when you’re only running the tyres hot.
Air expands with heat, so a tyre that is set at 36 PSI at circa 15°C may increase to 39 PSI after a fast run when it has fully warmed up.
After a short run, the tread may feel just as hot, but the pressure could be just 37 PSI. That’s simply because the tread has fully warmed up, but the carcass and the air inside the tyre has not.
With no way of measuring the air temperature inside the tyre, you can’t make an informed decision as to what that 37 PSI means. Does the tyre need more air, or more time to heat up?
That’s why you measure pressure when the tyre is cold.
An over-inflated tyre will give a firm rider that can feel harsh. Most likely, you’ll feel all the small changes in road surface.
The bike may also feel skittish, affected by tiny steering inputs and small changes in body position.
Under-inflation is slightly harder to spot.
Your wheel and tyre assembly will lose pressure very gradually over time anyway, and you’re unlikely to notice the very slight degradation on each ride as a result.
Eventually you may notice the handling becomes less responsive, and feedback becomes vague. Wet weather performance may also begin to suffer as the tread grooves become more squashed together in the contact patch.
The way a road tyre gains grip is very different to that of an off-road tyre.
Road tyres generate grip in part by the indentation of the road surface into the tyre, and also on a molecular level as the rubber interacts with the road.
For off-road rubber, grip on loose surfaces comes from the knobbles digging in to the terrain.
On harder, more uneven terrain the tyre moulds itself around the surface and generates grip in a similar fashion to a road tyre. At this point, it becomes key to get as many of those tread blocks in contact with the ground as possible, so a flexible carcass and lower pressure helps with this.
An enduro bike may run the rear pressure at 12 to 15 PSI, but on power off road bikes this could spin the tyre on the rim, hence the use of a rim lock.
These sorts of pressures would quickly cause a tyre to overheat on a big adventure motorcycle, but on a lightweight enduro machine of 100 to 120kg it is no issue.
Dakar riders tend to run a more robust tyre at a higher pressure, as their average speeds are much higher and the tyre has to take a lot of knocks which it needs to absorb.
A big adventure bike is really seeking to do the impossible – they need higher tyre pressures just to carry the weight of the bike and rider. That’s why Michelin’s Anakee Wild is designed to work on and off-road at the same pressure.
No on Michelin tyres, although other brands may differ.
Only the Michelin Power Performance range uses various compounds, but they have a very specific operating window – the rear tyre needs to be at 135° so they are only made available to the most demanding of riders. If you don’t race for a living, the commercially available range will be more than suitable for your needs.
If you increase the load significantly, then you’d need to increase the pressure for a tyre to perform in the same way on both a lighter and then significantly heavier bike.
Modern road tyres have to be very adaptable as there’s broad spectrum of bikes and riders out there.
If you can’t find the information you need then bike dealers, tyre dealers and the tyre manufacturers should all be able to help.
Looking at bikes of a similar weight, running the same type and size of tyre would be a good way to get an indication of the suitable pressure. Slight over-inflation is always preferable to under-inflation, so play it safe if in doubt.
Tyre makers are used to receiving unique enquiries, so if you can find the right person to talk to it can help a lot.
- Good handling
- Feel
- Responsiveness
- Stability
- Good grip
- Comfort
- Good MPG
- Good mileage
- Safer ride
