Tune Your Tires!

With wide tires, you can tune the ride of your bike to the terrain and to your personal preferences. This gives you options that simply did not exist in the past.

Gone are the days when we inflated our narrow tires to the maximum pressure and rode on rock-hard rubber. Even with narrow tires, you can lower the pressure a bit to get a (slightly) more comfortable ride. Of course, there is only so much you can do – the feel of the bike won’t really change. There is simply too little air, and you’ll get pinch flats if you reduce the pressure enough to make a real difference. The only way to transform the feel of a racing bike is to get different tires – that’s why professional racers have always run hand-made tubulars with supple casings (well, at least since the 1930s).

With wide tires, supple casings also make a huge difference. In addition, you can choose your tire pressure over a wide range: The 54 mm-wide Rene Herse Rat Trap Pass tires that Hahn is running in the photo above work great at pressures between 20 and 55 psi. That means you can cut the pressure to almost a third of the maximum, if you want. (For comparison, this is like running narrow 120 psi racing tires at 45 psi. Don’t try this with 25 mm tires!)

With wide tires, you can tune the feel of your bike by adjusting the tire pressure. The same tire will feel completely different depending on how hard you inflate it. This is something that you really start to notice with tires that are wider than 40 mm.

At 55 psi, my Firefly with its Rat Trap Pass tires feels firm and buzzy like a road bike on narrow tires. There is no noticeable flex in the tires, no matter how hard you corner, or how fast you sprint. You’ll feel every detail of the road surface almost unfiltered. The extra air does take off some of the harshness, and the extra rubber gives you more grip, but the feel is similar to a bike with narrow, high-pressure tires.

Why doesn’t the 54 mm Rat Trap Pass feel wallowy like a 25 mm tire at 55 psi? If you think of the tire as an air spring – a piston in a cylinder – then pressure is only one factor. The other is the diameter of the air cylinder. To compress a 54 mm tire takes more force than to compress a 25 mm tire, even if both are inflated to the same pressure.

Even with wide tires, you can get the feel of narrow tires, if you inflate them to (relatively) high pressure. But you also have options to tune your bike by letting out some air.

At first, not much is happening – 55 psi is far more than most riders will ever want to use in these tires. At 30 psi, you still get the firm feel of a ‘road bike,’ but more shock absorption and even better traction. This is the pressure I ride on very smooth roads.

At 25 psi, the tire has a lot more compliance. Now it really feels like an ultra-wide tire. It still corners great, but you can go over bumpy roads and really feel the suspension. This is the pressure I use on most paved roads.

On rough gravel, I let out even more air. At 20 psi, the tire really floats over the gravel. This is how I imagine a rally car with ultra-expensive shock absorbers feels: ‘breathing with the surface,’ gently going up and down over bigger undulations, but insulating you from the smaller bumps and vibrations. It’s an amazing feeling, and, without the bike bucking under you, you can put down power at all times. It’s fun to ride at ‘road’ speeds on rough gravel.

And even at this low pressure, there is enough air to prevent the tires from bottoming out. Even with tubes, I don’t get pinch flats – unless the terrain is really rough and rocky and speeds are ultra-fast.

When you’re descending at very high speeds on very rough terrain, you’ll have to increase the tire pressure a bit to avoid bottoming out too often. Even if you run your tires tubeless, you risk cutting your tires and damaging your rims if you bottom out too often and too hard.

When you return to pavement, 20 psi isn’t enough. The tire starts to squirm and run wide in corners. When you rise out of the saddle, it feels wallowy as it compresses under the thrust of your pedal strokes. And if you really push the limit, the tire can collapse in mid-corner.

Back on pavement, I inflate the tires back to 25-30 psi. If my ride includes both pavement and gravel sectors in quick succession, I often just keep the pressure around 25 psi, so I don’t have to mess with it.

Tire pressure is not just about shock absorption – it also affects the power transfer of your bike. A frame that is too stiff for the rider’s power output and pedaling style is harder to pedal – a little compliance smoothes out the power strokes and allows the rider to put out more power. We call this ‘planing,’ but it’s hardly a revolutionary idea.

Usually, that compliance comes from the frame. That is why high-end, superlight bikes perform so well, even on flat roads where the weight doesn’t matter. The lighter frames use less material, which makes them more flexible. Conversely, ultra-stiff bikes can feel ‘dead’ and hard to pedal to many riders.

With wide tires, that compliance can come from the tires, too. When we tested the Jones (above), we found it to perform wonderfully with its tires at ‘gravel pressure.’ When we aired up the tires for a fast road ride, the bike suddenly felt sluggish. This is the opposite of what conventional wisdom might tell you, but when we lowered the tire pressure again, the wonderful performance of the Jones was back. This has nothing to do with rolling resistance – it’s all about how much power we could put out thanks to the added compliance in the system. The Jones ‘planed’ best with its tires at relatively low pressure. This means that you can use tire pressure to adjust how much ‘give’ you have in your bike’s power transmission. I’ve found this a useful tool to get the most out of many Bicycle Quarterly test bikes.

Speaking of rolling resistance – don’t tires roll slower when you let out air? At least with supple tires, tire pressure makes no discernible difference, not even on smooth roads. As long as you have enough pressure that the bike is rideable, your tires roll as fast as they do at higher pressures. And on rough roads, lower pressures will be faster, both because the suspension losses are reduced and because you can put out more power.

Tuning your tires is fun. It optimizes your bike for your preferences and for the terrain you ride. Of course, tire pressure first and foremost depends on your weight – the numbers in this post assume a bike-and-rider weight of about 80 kg (175 lb).

Tire pressure also depends greatly on the casing of your tires. The values in this post are for Rene Herse Extralight tires. With Standard or Endurance casings, you can run about 10% less pressure. With a stiffer casing, you run even less air, all the way to airless tires that run at zero pressure. As your tires get stiffer, you lose the ability to tune your ride, because air pressure plays a smaller role in supporting the bike-and-rider’s weight. The beauty of supple tires is that air pressure is the main component that holds up the weight of bike and rider. This makes it easy to tune your tires.

Rather than inflate your tires to a set number, experiment with tire pressures to see how this changes the feel of your bike. Also remember that the gauges on pumps aren’t always accurate – use them only to replicate a setting that you’ve found useful in the past, rather than try to inflate your tires to an exact pressure. Once you’ve found values that work, you can quickly change the feel of your bike based on where you’ll ride and how you want your bike to feel. This makes cycling even more fun!

Further information:

About Jan Heine

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Rene Herse Cycles, that turns our research into the high-performance components we need for our adventures.
This entry was posted in Testing and Tech, Tires. Bookmark the permalink.

29 Responses to Tune Your Tires!

  1. dhdaines says:

    This is fantastic timing as I just put a pair of Rat Trap Pass on my 26″ wheel touring bike, which now appears to have been specifically designed for them! My first instinct was to do as I do with other tires: inflate them to about 75% of the maximum, or 40 psi / 3 bar. They feel like really good road bike tires at this pressure, and are capable enough on trails but they do seem to bounce too much. Good to know that I can go considerably lower, even on the road.

    Are these recommended pressures okay with tubes? I would be a little wary of going down to 20 psi because of pinch flats…

    • Jan Heine says:

      I run my Rat Traps with tubes. 20 psi at my rider-plus-bike weight is no problem, even on relatively rough terrain. Of course, it all depends on your weight and riding style.

    • Derek says:

      I bought Rat Traps as soon as they were available and they work great on my touring bike, with the same pressures that Jan talked about.

      • Derek says:

        Being able to run 25psi on a road ride is so different. Sometimes I catch myself still weaving around trying to find the smoothest part of the road/path like I used to with narrow tires. Then I remember what I’m riding, shrug, and go straight over stuff that used to make me cringe. Cool.

      • Alan Rutherford says:

        Today I tried this on my weekly Lief Erickson Trail ride — I dropped my Rat Trap Passes from 28 to 20 psi for the 11 mile gravel portion. I couldn’t believe how better it was!

  2. Pk says:

    If you want to see actual proof that a flexible frame is fast, go to the 9:00 mark of this video and watch Sean Kelly and his noodle Vitus get shot out of a cannon. Perhaps the strongest rider on the least stiff bike ever.

  3. Harald says:

    So is the next step a system where you can change the tire pressure while riding? Looks like this has already been invented for MTBs (but surely could use some refinement): http://adaptrac.com/

    I’m usually too lazy to adjust tire pressure during a ride (at least when it involves pumping up the tire rather than just letting air out).

    • Jan Heine says:

      We’ve thought about this, but the complexity (and weight) outweigh the advantages.

    • Mitch says:

      I found my reluctance to adjust tire pressure during a ride was mitigated by the low pressure tires themselves (assuming you choose a hand pump you like). When I ride narrow tires at high pressure, any pumping out on the road with hand pump requires that tense fight to get the last 10 psi up to 100psi, and even getting to 90psi was a pain I avoided on the road if possible. Any tire pressure below 60psi I find so easy to adjust that I sometimes don’t even bother with the floor pump before a ride, even if I think I may need to add air, because it’s so easy and quick to hop off and put a few psi into tire at low pressures.

  4. Stephen Poole says:

    What (portable) tyre pressure gauges have people found to be both accurate and reliable, for touring? Thanks. 🙂

    • Jan Heine says:

      Any gauge will do, since accuracy is not required. All you try to do is get back to the value that you found to work in the past. It doesn’t matter whether that is 25 or 35 psi, as long as it works for you and you can replicate it. With experience, you also know how much to let out for ‘gravel’ and how many pump strokes it takes to get back to ‘pavement’ that you can dispense with the gauge altogether.

      The values mentioned in the post were established using the gauge on a floor pump that has proven to be reasonably accurate.

      • Stephen Poole says:

        Okay, repeatability is good enough, understood; that’s how I use my old Silca track pump at home. How about reliable, and preferably available in Europe, where I am until September? (So not a US-made product.) The Schwalbe gauge I have at home was DOA. 😦

  5. Allen Potter says:

    I really appreciate all of the thought that has gone into this! And of course I’m incredibly grateful for the tires that you’re making. I doubt I’ll ever go back. A general question: I’m using 32mm Stampede Pass tires w standard casing (and tubes). I understand your ultimate conclusion is to test it for yourself, but I wonder what your pressure would be for the high and low end with these tires, knowing that I ride some gravel, but nothing too crazy that the tires just aren’t wide enough for. My weight is close to the assumed weight in the post. What would you feel comfortable deflating these tires to?

  6. mrgiff says:

    Pump recommendations for these plump tyres? The little ones take an age!

    • Jan Heine says:

      Full-size frame pumps are great, but hard to find and even harder to mount on most bikes. The longer models from Lezyne work well, too – just make sure you don’t get the ones where the hose threads into plastic (which inevitably strips).

  7. Rick Thompson says:

    Very useful info, as usual. Two questions on low pressure limit:
    1) Does tubeless at low pressure do any damage to the sidewalls? My Snoqualmie Pass EL weep sealant through the sidewalls, it seems to be more weeping if I ride low pressure (< 25 psi).
    2) Is there a low limit for cornering safety on the bigger tires? If the tires don't bottom on the rims are they safe to keep the bead seal when cornering hard?

    • Jan Heine says:

      Riding at very low pressures flexes the tire sidewalls more. This increases the wear. For me, it’s acceptable if I get ‘only’ 3000 miles out of a set of tires before the sidewalls become too porous for tubeless – I still can run them with tubes afterward.

      We haven’t had any problems with tires coming off the rims even at low pressures, but the sidewalls can collapse under the cornering forces, or the tire can ‘burp.’ Please use caution when running extremely low pressures, especially on surfaces with a lot of traction, where the forces on the tires are greater. On loose gravel, the tire slides before it will burp or collapse, but on pavement or semi-dry mud, you can run into problems.

    • Jan Heine says:

      We don’t list a low pressure limit for our tires, because this depends completely on the weight of the rider-and-bike. A 50 kg (110 lb) rider can run very low pressures safely, while the same pressure will not work for a significantly heavier rider.

  8. mtbvfr says:

    Hi Jan,

    What pressures would you suggest as a “safe” starting point for the Naches Pass Extralight tyres with a bike of around 10-11 kgs with a rear rack that can support 30 kgs and a Front rack that can support 20 kgs and a rider weight between 60 & 70kgs etc? How much would you increase the pressure for each additional kg?

    Assuming a possible weight distribution of 40/60%, would 40/50 psi be a good starting point?

    Thanks, MTB.

  9. Daryl says:

    Could we tempt Rene Herse to make a supple 16″/349 tire please?

  10. DaveS says:

    On the first photo of this blog, there is a clear cap on the water bottle that is mounted on the underside of the down tube. Where can I acquire one of these caps? Seems like a good idea on keeping the mouth piece of the water bottle clean!

    • Jan Heine says:

      The ‘cap’ is the bottom of a PET bottle (orange juice, bottled water, etc.) that I cut off and inverted. The photo was taken in Mexico, and we were traveling through areas with lots of livestock, so I made the cap the night before the ride…

  11. Jo Ooms says:

    Hello Jan,
    First of all I love the content and the way you bring it (Understandable and in a polite way. The latter seems to be a rarity these days).
    I understand that wider tires need less pressure for the same comfort level as a narrower tire because of the tension on the casing.

    What are your thoughts on the approach of Jarno Biermann of BicycleRollingResistance on comparing tire sizes for comfort? (Ignoring the fast fact that he tests on smooth drums that do not take suspension losses into account).

    Basically he claims that 2 tires of different sizes wil have the same comfort if they have the same tire drop in mm for a given rider + bike weight.
    Do you agree on this?
    -or should the tire drop be expressed in % rather than mm?
    -would the increase in tire volume play a significant role in the comfort level?

    If Jarno is correct on the comfort side of things the procedure would be as follows (for road bikes)
    -drop the tire pressure in you tires until the road buzz goes away
    -if your tire does not bottom out you are fine
    -if the tire does bottom out: go a size up and reduce the pressure a bit more

    I weigh 60 kgs and can get away with 60 PSI on 25 mm supple tires on 622-21 rims (width becomes almost 28 mm).
    Do I have anything to gain from going to 28 mm with a lower pressure to attain the same comfort level?

    • Jan Heine says:

      I haven’t looked too much into Jarno’s ideas, so I can’t comment directly. The idea to look at tire drop like you do at suspension travel – as a value in millimeters – is interesting, but there is a lot going on that defies simple formulas. If you like what you ride currently, I’d say continue to ride it. You may want to try other bikes if you have the opportunity, to see whether you don’t like something like 42 mm tires at 30 psi even more…

  12. Frank Bar. says:

    Would it be much of a hassle to also list pressures in a non-imperial unit? It doesn’t have to be Pa, the SI-unit, but “bar” would be nice for many of your international readers. All the best
    — Frank

    • Jan Heine says:

      I apologize to our international readers. I always struggle with the units. Bicycle Quarterly has adopted the metric system, so we list all measures in metric, with Imperial units in parenthesis. English-language blogs seem to have standardized on Imperial units, so that is what most readers expect. Sometimes, I put the metric units in parentheses, but this makes the text much less readable. I’ll probably go back to that.

      In the mean time, you can get to bar by dividing the psi by 15. So 30 psi is 2 bar…

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