[MileCruncher]

Couple of weeks back I went on a weekend overnight ride with some experienced riders one of whom is also nation level racer currently racing super bikes but has raced in rallies in the past. We had some interesting conversation regarding tyre pressure, tyre footprint, traction and terrain.

I have experience of only 2 Big ADVs - Tiger 800 and GS1300. Both bikes have manufacture recommended tyre pressure of 36PSI in front and 42PSI at rear.

Crux of the conversation with racer gentleman and other experienced riders is as follows:

• The manufacturer pressure recommendations are quite high and suitable only for 2-UP riding on tarred roads.
• With single rider even on tarred road, this pressure is very high and will make the bike bouncy. Plus the contact patch on the road will be minimum.
• As per him for tarmac there is no single correct tyre pressure but depends on bike + load. But still it would in the 30-35PSI range.
• The racer mentioned his tyre pressure for superbike on track is more like 30-32PSI, never more.
• Offroad trails / sand, this pressure will be in the range of 18-20PSI.
• As per him, for gravel, the pressure should be lower than 30PSI to maintain good contact patch and traction

I would like to hear from all about their take on the above and what do they follow. Hoping to learn from you all!

[praful]

Originally Posted by MileCruncher

I have experience of only 2 Big ADVs - Tiger 800 and GS1300. Both bikes have manufacture recommended tyre pressure of 36PSI in front and 42PSI at rear.
…
I would like to hear from all about their take on the above and what do they follow. Hoping to learn from you all!

First things first, always follow tyre and bike manufacturer recommendations as they have done the necessary R&D to arrive at the said numbers.

That being said, the 36 and 42 PSI seems very high.

I know this is not the same tyre or motorcycle, but here's a screenshot of what the service manual for my Aprilia Tuareg with Pirelli Rally STR stock tyre states.



As you can see the recommended pressures are much lower 29 for a solo ride and 29 + 32 for rider & pillion (or luggage).

While they have recommended same pressure for off-road, whenever I am going off-road especially in muddy and slushy conditions, I am usually running 20-22 PSI for better traction and also allowing more of the tyres to grip.

I would run the recommended 29 PSI only if I knew I was riding in hard rocky conditions to avoid any rim bending situations due to lower pressures. When I finish my off-road riding section and I know I am going to be exclusively riding on road now, I fill in the recommended 29PSI using my portable compressor.


Here is an interesting video that shows the difference tyre pressure makes offroad, granted this is for 4x4 but it applies to the two wheeled world as well.

https://youtube.com/watch?v=skCAWeSO...RvPq_H1AdDxNbq

[Rehaan]

Shooting from the hip, but I assume auto & tyre manufacturers come to the "ideal" tyre pressure based on optimizing for various factors:

• Traction
• Braking
• Cornering stability
• Fuel efficiency
• Ride comfort

Then, adjusting further for:

• Variance for load
• Variance for each specific model of tyre
• Variance for ambient temperature range

Depending on what you are optimizing for, you could adjust the pressure up or down.

The one factor here that I think is probably not the ideal optimization (for end users) might be "Fuel efficiency" -- where a higher tyre pressure would be more beneficial from a testing & therefore marketing standpoint... Though I'm not well versed with what the SOP is for FE testing (though I'd assume the manufacturer recommended tyre pressure is used).

[MileCruncher]

Originally Posted by praful

First things first, always follow tyre and bike manufacturer recommendations as they have done the necessary R&D to arrive at the said numbers.

I have always believed in this.

Originally Posted by praful

That being said, the 36 and 42 PSI seems very high.

But I also feel that this is high.


Not only that, the manual says ( I read it somewhere but unable to find) that in case of pillion and load, the pressure should be F-42 / R-46

Obviously this is for tarmac but am not sure really!

[siddhant]

I believe the manufacturer's recommendations are provided for the average driver. For different usecases, will these recommendations change a little bit? For ex, driving in city vs driving long distances on highways vs driving in hilly roads at high altitudes.

[GutsyGibbon]

Originally Posted by MileCruncher

I have experience of only 2 Big ADVs - Tiger 800 and GS1300. Both bikes have manufacture recommended tyre pressure of 36PSI in front and 42PSI at rear.

I ride with people from BMW motorcycle owners club of America, any deviation from manufacturer recommendations is really frowned upon. It’s 36-42 pretty much all the time.

I did ride with Dusty Wessels of MotoTrek, he allowed people to drop 2psi for rocky off road and back to 36-42 immediately. He insisted that the risk of hitting a rock outweighed traction gains on soft dirt.

Dropping 10psi for off roads is way off from manufacturer recommendations, it’s all ok till it’s not.

[abhi_tjet]

Originally Posted by MileCruncher

Obviously this is for tarmac but am not sure really!

Multistrada also has same tyre size and air pressure recommendation is also similar. Irrespective of single rider or with pillion, front is around 35 psi. Rear is recommended as 36 psi - if only rider, 42 psi is recommended with pillion.

It’s mentioned to increase air pressure if road conditions are bad to protect from rim damage and puncture.
For tarmac with loose gravel or just slush, reducing pressure might work. However, for places with sharp stones, I will be comfortable with oem recommendations.

[Torq-D]

These tyre pressures are recommended for maximum load (rider+pillion). Owner’s manual also mentions ideal weight of rider and pillion for such recommended tyre pressures.

When it comes to superbikes on track or street, tyre pressures should always be in range of 28-34 psi taking so many factors into consideration. for example rider’s weight, temperature of track, extent of lean angles and ease of tipping your bike into corners.

When bikes are run with such recommended tyre pressures it’s quite easy to tip your bike into corners due to more rounded profile with high pressures. But at same time, in straights one looses out on contact patch (again due to much more rounded profile) and which in turn effects braking performance.

[t3rm1n80r]

Originally Posted by MileCruncher

I would like to hear from all about their take on the above and what do they follow. Hoping to learn from you all!

Thanks for starting this thread. I've always wondered about the correct interpretation of tyre pressures that the manufacturers mention in the user manual. The way I see it:

• Tyre pressure varies quite a lot during the day (a period of 24 hours) depending on the tyre temperature. For example: 30PSI filled at morning 7:00 am in rainy weather would increase by a few PSIs in the afternoon when there is no rain and the road is dry. But 30PSI filled at night 1:00 am in summers would increase by a lot at 2:00 pm scorching heat. A more intuitive way to explain it would be by the Ideal Gas equation: PV=nRT. Assuming volume of the tyre remains constant, and there is almost negligible to no air leakage, Pressure is directly proportional to Temperature.

• Manufacturers cannot control the tyre temperature as it depends on a lot of parameters like ambient temperature, road surface, driving style, tyre rotating speed, wear, etc. But can come up with a tyre pressure value that is good enough for all conditions, considering different tradeoffs(comfort, fuel economy, service intervals due to increased load on engine, etc).

• Therefore, I think the pressures mentioned in the manual are tyre pressures under average operating conditions rather than stationary tyre pressures. These are good to be used as starting points for fine tuning the pressures that work specifically for the user.

I've played a lot with my motorcycle's tyre pressures over the period of two years to validate my hypothesis (mostly by feel, not very scientific or formal). And now I've gotten a decent understanding of what tyre pressures to set at the start of the ride depending on the conditions I'm going to ride in so that the feel from the tyres remains almost consistent to my liking.

Edit:

Originally Posted by Rehaan

Shooting from the hip, but I assume auto & tyre manufacturers come to the "ideal" tyre pressure based on optimizing for various factors:

I agree.

[shyamg28]

Originally Posted by t3rm1n80r

...Therefore, I think the pressures mentioned in the manual are tyre pressures under average operating conditions rather than stationary tyre pressures. These are good to be used as starting points for fine tuning the pressures that work specifically for the user.

I believe that's partially incorrect. Only partially, because I agree with the rest of what you mentioned.

Because tyres warm up when on the move, all manufacturers only recommend cold tyre pressures, i.e., stationary, before every ride.

I know that still leaves room for debate on what the stationary temperature in each location is, itself.
But that it's cold temperatures we need to check & fill per recommendations is non-debatable.

Excerpts from the V Strom manual -





Personally, I follow manufacturers recommendation to the T, when riding with pillion especially.
When riding alone, I have benefitted from drop in pressure, especially when going off road. How much of a drop, again, no empirical or scientific evidence backing here.

However, I have categorically never gone ABOVE manufacturer recommendation.

[100Kmphormore]

On my Himalayan ( I say this as a function of weight - with panniers and crash guards, comes close to 210 kg ), the OEM recommendation, added with a mandatory cold condition, was always the best configuration, especially when 2 up in all conditions. It reduced the rate of punctures too - during my ownership I only had one, apart from a blowout, but that was due to tyre wear.

I test rode a VStrom 650, which weighed a little more than that and the pressure was off by around 3 psi - it really impacted low speed ride and steering feel almost immediately. The correct recommedations had the desired effect. Would never recommend to change pressures irrespective of conditions unless the OEM gives it in writing or you see them carrying out changes at offroad events - these will be the guidelines from technical team as its a make or break difference as a selling point for the brand.