CB650R Tyre pressures and preload.

[Hornet76]

Here’s a cool explanation about tyre pressure

 

[JZA]

Here’s a cool explanation about tyre pressure

This is ridiculous. Who is going to go and test with 5 different pressures, in 1psi steps, allowing the tyres to cool down to "cold" temps between each run. And who the hell can tell the difference between 39 and 40 PSI? Maybe if you could get off one bike and straight onto another identical bike with different tyre pressures but the reality is that if you did these tests it would be different days for each test, different temps and you wouldn't be able to remember exactly how the last test felt let alone the 3 tests before that. Yes, you should play with tyre pressures, but he should have talked about different feelings and what that might mean and how to deal with it.

E.g.
If you find that the tyre feels slippery and skittish when cold, lower pressures 2 PSI to encourage faster warm-up and more grip at the expensive of longevity. Test and reduce more if needed.

If you Find that the tyre feels sloppy and wallows around in the corners, then try adding 2 PSI. This will stiffen up the tyre carcass but also reduce comfort and potentially reduce grip. Test and adjust again if needed.

If you tend to ride very fast and hard then try removing 2-4 PSI (or -6 if you are riding fast on a track) since your tyres will get a lot hotter than someone who is just dawdling along. This will mean that when your tyres get hot, they won't be over pressurised, but it also means that if you do a short ride, like going to the shops or a short commute to work then your tyre will be underpressurised and may wear faster.

You should not be scared to play with tyre pressures but just stay within 30-36 front and 36-42 rear unless you know what you are doing. Our bike recommends 36/42 F/R and there's nothing wrong with staying with that pressure but if you want to ride hard and get the tyres hot you should lower your pressures a bit since the pressure will rise as the tyres get hotter. If you want more comfort at the expense of longevity then lower your pressures. If you want better fuel economy then run them at stock 36/42 PSI or even a little bit higher but don't go too high because you will compromise grip. If you have a pillion or bags on the back of your bike then put more pressure in because it will squish more but don't go over the max pressure on the sidewall of the tyre.

Basically 36/42 if you are a beginner and not riding too hard and don't want to think about tyres. 32/38 if you ride hard and don't mind wearing out your tyres a bit quicker. 34/40 if you are somewhere in between. 30/36 if you ride fast at a track (proper fast). Maybe add 1 PSI to the rear if you are heavy like 90+kg. Also keep in mind that most pumps with gauges are inaccurate and probably only get your tyres to within +/- 2 PSI of what you set it to so I wouldn't stress too much about it but if you DO want accurate tyre pressures, buy a good quality digital tyre pressure gauge like the Topeak SmartGauge D2.

Disclaimer: I am not a motorcycle mechanic, I'm just a dude who likes motorbikes and mountain bikes. I have played with tyre pressures a bit and have a decent understanding. I am also a structural engineer, so I have strong logical and rational reasoning skills. If anyone has any other thoughts on this topic and/or wants to correct me on anything, feel free to join in the discussion!

 

[JZA]

I decided to try talking to ChatGPT about this topic and asked it to create a summary explaining how changes in tyre pressure affect the bike, tyres, wear, grip etc and give advice on tyre setup for different riding styles and conditions. Below is copy-pasted from ChatGPT:

Effects of Tire Pressure Adjustments​

1. Increasing Tire Pressure:
   • Reduced Rolling Resistance: Higher pressure results in a smaller contact patch, reducing friction and improving fuel efficiency.
   • Longevity: Tires tend to wear more evenly at recommended or slightly higher pressures, which helps maximize their lifespan.
   • Stability at Higher Speeds: A firmer tire provides stability during fast, straight-line riding, as well as under heavy loads, which is useful on highways or with luggage.
   • Trade-Off: Increased pressure can reduce grip, especially in corners or on wet roads, and can make the ride feel harsher on rough surfaces.
2. Decreasing Tire Pressure:
   • Improved Grip: Lower pressure allows a larger contact patch, increasing traction, especially in corners or on slick surfaces. This can boost handling and confidence on twisty roads.
   • Enhanced Comfort: The tires absorb more road imperfections, creating a softer, smoother ride.
   • Trade-Off: Too-low pressure can lead to excessive heat buildup and increased wear, especially if you’re riding aggressively or at higher speeds. This can also affect stability, particularly on long, straight stretches.

Selecting the Right Tire Pressure​

• For Everyday Riding and Longevity: Stick close to the manufacturer’s recommended pressure, often around 36 psi front and 42 psi rear. This balance provides stable handling, good tire life, and a comfortable ride for daily commuting or touring.
• For Spirited, Intermediate-Level Riding: A slight drop, such as 1-2 psi, in both front and rear pressures, can increase grip and handling without a major hit to tire longevity. This setup works well for intermediate riders looking for improved feedback and comfort on winding roads.
• For Track Days or High-Performance Riding: Lower pressures (by 3-4 psi) may be optimal for maximum grip, but they can significantly increase tire wear. This approach suits advanced riders or those pushing the bike hard on a closed course.

Tailoring to Conditions​

• Cold Weather or Wet Roads: Slightly lower pressures can improve traction by creating a larger contact area and generating more heat through tire flex. This helps tires reach their ideal temperature more quickly in colder conditions. However, avoid dropping the pressure too much, as excessive flex can lead to instability, rapid wear, and, on dry roads, even overheating.
• Long-Distance or Fully Loaded Riding: Higher pressures help maintain stability under load and improve fuel efficiency on long rides, especially on highways.

Final Tip​

Start with the manufacturer’s recommendation, and then adjust incrementally by 1 psi at a time based on feel and tire wear. Small tweaks can make a noticeable difference, helping you find the ideal balance between grip, comfort, and longevity for your unique riding style and conditions.

 

[John Jive]

Set tyre pressure as per manufacturer's recommendation.
Get your suspension set up by a professional.

 

[JZA]

Set tyre pressure as per manufacturer's recommendation.
Get your suspension set up by a professional.

While setting the tyre to the manufacturers recommendations might seem like the obvious choice, it does get a bit blurry when you fit tyres that are not OEM. Different tyres have different carcasses and therefore require different pressures. The manufacturers recommend pressure is a good starting point but not necessarily ideal for your tyres, riding style or conditions. Even a brand new set of tyres may have a different ideal pressure compared to a worn set of tyres just because the rubber is thinner on a worn set and therefore the carcass is more flexible.

 

[John Jive]

Manufacturer being the people who make the tyres (not Honda)

There's so much snobbery and psychology around tyres. Get what you can afford and look after them.

 

[Redrocket]

....and don't forget, if you have a slow puncture pump up your tyre before setting off on a long journey....🤓 Modern tyres are immeasurably better than the stuff around when I started riding 55+ years ago. I used to follow the manufacturers' recommended pressures back then and I do now. I always use the same gauge at home and know that the pressure varies a little according to ambient temperature anyway (I believe quoted pressures are at a defined temperature). A little variance either way is unlikely to make a modern bike a disaster to ride like BMW airheads could be if other than Metzelers were fitted. Modern suspension and tyres are vastly superior and I for one know that they perform way better on the road than my skill level will ever reach. Track riding is different altogether.

 

[JZA]

I've done about 3,750km on my Metzeler Roadtec 02's. I've been running 33/39 F/R (36/42 is Honda's recommendation). The traction has been fantastic and it makes the ride a bit smoother due to the tyre soaking up some of the smaller bumps BUT I have noticed that the rear is flattening off a bit in the middle. I'm already down to about 2.5mm at the lowest point in the middle of the tyre and still about 4mm at the deepest point of the tread about half way between the middle and edge of the tyre. I am going to try increasing the pressure back to Honda's recommendation of 36/42 and see if that slows the wear in the middle.

Note that I don't ride on motorways and I don't do burnouts. I live in Wanaka, New Zealand which is a town in the mountains so whenever I go on the open road it's twisting roads. I do ride quite quickly, cruising at like 130km/h on the straighter sections of road and I go pretty quickly through the twisty stuff. The roads around here are all chip seal as well so that's a bit rougher on the tyres. I sometimes take my GF on the back of the bike but I always put the pressure up to 42 on the rear when she is coming with me. I feel like a sport touring tyre should last longer but I think I will be lucky to get 6,000km out of this rear tyre. Hopefully increasing the pressure to 36/42 will improve longevity without affecting handling. I already noticed it feels bumpier with the tyres at 36/42 but I guess it's a trade-off for longevity and to save $$.

 

[John Jive]

I've done about 3,750km on my Metzeler Roadtec 02's. I've been running 33/39 F/R (36/42 is Honda's recommendation). The traction has been fantastic and it makes the ride a bit smoother due to the tyre soaking up some of the smaller bumps BUT I have noticed that the rear is flattening off a bit in the middle. I'm already down to about 2.5mm at the lowest point in the middle of the tyre and still about 4mm at the deepest point of the tread about half way between the middle and edge of the tyre. I am going to try increasing the pressure back to Honda's recommendation of 36/42 and see if that slows the wear in the middle.

Note that I don't ride on motorways and I don't do burnouts. I live in Wanaka, New Zealand which is a town in the mountains so whenever I go on the open road it's twisting roads. I do ride quite quickly, cruising at like 130km/h on the straighter sections of road and I go pretty quickly through the twisty stuff. The roads around here are all chip seal as well so that's a bit rougher on the tyres. I sometimes take my GF on the back of the bike but I always put the pressure up to 42 on the rear when she is coming with me. I feel like a sport touring tyre should last longer but I think I will be lucky to get 6,000km out of this rear tyre. Hopefully increasing the pressure to 36/42 will improve longevity without affecting handling. I already noticed it feels bumpier with the tyres at 36/42 but I guess it's a trade-off for longevity and to save $$.

Love to see some pics of the area you live and ride.
Ride safe 👍