Well-controlled tire pressure experiment

[Jeremy McCreary]

Excellent controlled experiment on the effect of tire pressure and quality on rolling resistance on simulated tarmac and cobbles using a very impressive test rig:

The cobble data has direct application to gravel riding.

Thinking on tire widths, pressures, and rolling resistances has been evolving in recent years. The pros are increasingly going to wider tires at lower pressures on all surfaces, as clearly demonstrated in the 2024 Tour de France.

This trend was already well underway when the 4th edition of Bicycling Science came out in 2020. Excellent discussion of the physics and supporting data there.

As the book points out, an overlooked effect of excessive vibration is excessive rider fatigue. You've no doubt felt this yourself, and you can see it quite clearly in the GCN test rider's body language every time he got off the bike after a cobble run. The higher the tire pressure, the greater the vibration, and the more wasted he looked at the end.

Any vibration reaching the rider is dissipated in the rider's body. Reflexive bracing against the vibration takes up precious rider energy. That's why long rough rides are so exhausting.

So cushier tires aren't just more comfortable. To a point, they're also more rider-efficient on rough surfaces.

My coming Vado SL 5 EQ will come with tubed 700x38 Nimbus tires rated for 50-80 psi. My first mod after deciding to keep it will be to replace them with tubeless tires allowing lower pressures.

 

[fooferdoggie]

I did this long ago when I had a long wheelbase recumbent with a windscreen. I rolled down the same hill every day and I was able to test it with far less wind effect. but now tires are made that don't need as high of psi. I have seen 8 extra commute mikes and 3mph faster with the same wattage output going from the stock trek 2.4 tires and 2" fast supple lower psi tires.

 

[Mr. Coffee]

The cobble data has direct application to gravel riding.

Cycling unpaved roads presents a pretty complex universe of surface types and difficulties and I do not think you can reduce it to some kind of 1-dimensional state. On the average, you'll probably work harder riding off pavement than on, and again on the average you'll probably want a lower tire pressure than on pavement. Beyond such broad generalizations you can't say a lot.

"Gravel" hereabouts can vary between fist-sized boulders to semi-solid glutinous swamp muck. Even when you are talking about literal "gravel" that came out of the back of a dump truck that can vary between spiky asymmetric chunks that pack nicely (though tough on your tires) to rocky ball bearings that can be bottomless and give you no traction and control and make for very frustrating miles. Locally the very best "gravel" riding is usually on packed fines, which can be wicked fast and smooth if they are a little bit damp but can be insanely slippery and uncontrollable if they are frozen.

Some unpaved trails in coastal areas can be surfaced with crushed seashells, which can be a nice surface though murderous to your tires.

Don't even get me started about washboards and potholes.

 

[Sparky731]

I am a fan of tubeless running on the low end of the recommended psi.

BUT, after a catastrophic blowout I have learned the benefit of ebike rated sidewalls.

 

[DaveMatthews]

I am a fan of tubeless running on the low end of the recommended psi.

BUT, after a catastrophic blowout I have learned the benefit of ebike rated sidewalls.

What tire was it that blew out?

 

[gromike]

Excellent controlled experiment on the effect of tire pressure and quality on rolling resistance on simulated tarmac and cobbles using a very impressive test rig:

Thanks for that rabbit hole Jeremy.
Though I will never ride on a 4 inch fatty, even at 1/2 bar!

 

[Stefan Mikes]

My coming Vado SL 5 EQ will come with tubed 700x38 Nimbus tires rated for 50-80 psi. My first mod after deciding to keep it will be to replace them with tubeless tires allowing lower pressures.

I recommend checking the

Tire Pressure Calculator

Finally a tire pressure calculator based on real-road rolling resistance measurements. On real roads—rather than on a steel drum in the lab—supple high-performance tires work best at considerably lower pressures than most cyclists are used to. Lower pressures roll as fast or faster, while...

www.renehersecycles.com

choosing the Soft setting and comparing the result to the minimum pressure moulded on the tyre sidewall. There is a good theory and research behind the calculator.

Tubeless certainly allows riding close to the inflation lower limit. An example:

I might weigh up to 103 kg (227 lb) in the full cycling clothing. My slimmed down Vado SL with Range Extender is 17 kg (37.5 lb). The pannier might weigh even 6 kg (13 lb) at the beginning of the trip. All making 126 kg (278 lbs). Tyre size is 42 mm.

The calculator reads: "Use 3.3 bar (48 psi) for Soft". I actually use 3 bar (45 psi) tubeless for regular riding or 2.8 bar (40 psi) for mixed terrain. The lower inflation limit for these tyres is 35 psi. The shock absorption capability of the Tracer Pro tyres I use is as good I could recently replace a suspension seat-post with a dropper...

I'm sure Jeremy you could ride 38 Pathfinders tubeless even at 45-50 psi, (depending on your body + e-bike + cargo weight) pretty safely. It gives a lot of compliance.

 

[6zfshdb]

Interesting experiment, but I can see where this would be more important for conventionals, rather than e-bikes. The motor compensates for the higher rolling resistance. Sure, you may loose some range but how many of us end a ride with a fully exhausted battery? If in doubt, carry a spare.

Weight is also less of a concern on an e-bike. The extra few #'s of front/full suspension, suspension seatpost and shock stop stem aren't really noticed and compensate for any improved ride you might get from tire type or altered pressure.

 

[Stefan Mikes]

Interesting experiment, but I can see where this would be more important for conventionals, rather than e-bikes. The motor compensates for the higher rolling resistance.

I beg to differ.

Jeremy intends to ride a Vado SL, which is a low power e-bike (the rated 240 W mechanical power is only the maximum. A typical assist could be as low as even 50 W). With a lightweight low power e-bike the factors such as tyre pressure or brand/model take tangible effect on the ride. A heavy, stiff or improperly inflated tyre will make a Vado SL ride slower and with greater effort. (Even the riding position takes an effect there). The range might not be important when your battery is 500, 600 or 700 Wh but certainly the 320 Wh one needs to be spared.

Sure, you may loose some range but how many of us end a ride with a fully exhausted battery? If in doubt, carry a spare.

Some $500 extra.

Weight is also less of a concern on an e-bike. The extra few #'s of front/full suspension, suspension seatpost and shock stop stem aren't really noticed and compensate for any improved ride you might get from tire type or altered pressure.

Vado SL 5.0 EQ has the rated weight of 36 lb (without pedals). Oh yes, you do not want to spoil the benefits of such a lightweight e-bike with impropriate or wrongly inflated tyres.

 

[PCeBiker]

The motor compensates for the higher rolling resistance.

My motor does all the work.
It compensates for my complete lack of input.

Sure, you may loose some range but how many of us end a ride with a fully exhausted battery?

I used to exhaust my battery on every trip.
I was always worried about making it home.

If in doubt, carry a spare.

I finally managed to get a second battery securly installed after it broke the rear rack off my e-bike,..

It looks like trash, but I can finally ride without any range anxiety or speed wobble.

I went on a 100 km ride two days ago in complete comfort.

My ass held out for over 4 hours.

Weight is also less of a concern on an e-bike. The extra few #'s of front/full suspension, suspension seatpost and shock stop stem aren't really noticed and compensate for any improved ride you might get from tire type or altered pressure.

I just weighed my e-bike on two bathroom scales and got ~82 pounds and I weigh ~170 pounds ready to ride, so 252 pounds total.

I used to weigh 255 pounds so I weigh -3 pounds when I'm riding now.

I better not lose any more weight or I might float away??

 

[Jeremy McCreary]

I recommend checking the

Tire Pressure Calculator

Finally a tire pressure calculator based on real-road rolling resistance measurements. On real roads—rather than on a steel drum in the lab—supple high-performance tires work best at considerably lower pressures than most cyclists are used to. Lower pressures roll as fast or faster, while...

www.renehersecycles.com

choosing the Soft setting and comparing the result to the minimum pressure moulded on the tyre sidewall. There is a good theory and research behind the calculator.

Tubeless certainly allows riding close to the inflation lower limit. An example:

I might weigh up to 103 kg (227 lb) in the full cycling clothing. My slimmed down Vado SL with Range Extender is 17 kg (37.5 lb). The pannier might weigh even 6 kg (13 lb) at the beginning of the trip. All making 126 kg (278 lbs). Tyre size is 42 mm.

The calculator reads: "Use 3.3 bar (48 psi) for Soft". I actually use 3 bar (45 psi) tubeless for regular riding or 2.8 bar (40 psi) for mixed terrain. The lower inflation limit for these tyres is 35 psi. The shock absorption capability of the Tracer Pro tyres I use is as good I could recently replace a suspension seat-post with a dropper...

I'm sure Jeremy you could ride 38 Pathfinders tubeless even at 45-50 psi, (depending on your body + e-bike + cargo weight) pretty safely. It gives a lot of compliance.

Thanks! The tire pressure calculator says 46-56 psi for 38 mm and my expected gross weight of 195 + 40 = 235 lb.

Found one seemingly knowledgeable long-term Pathfinder reviewer who claims to have gotten away with 36 psi on some 1,700 mi of mixed surfaces with excellent results. But he never stated his gross weight.

The Pathfinder's braking performance in sand worries me a little — even at low pressure. Very thin see-through veneers of sand are common here — on coastal roads on windy days, and on nearly every hard-packed trail.

Problem is, steep descents are common here, too. That slick center tread isn't exactly confidence-inspiring.

 

[Chargeride]

Fatigue yes, but absoutely everywhere else in the real world skinnies are best.
The eco plus setting on my fattie pretty well just turns it into an ordinary bike.

 

[PCeBiker]

Fatigue yes, but absoutely everywhere else in the real world skinnies are best.
The eco plus setting on my fattie pretty well just turns it into an ordinary bike.

Big skinny wheels have always been the most efficient and effective.

 

[Stefan Mikes]

Thanks! The tire pressure calculator says 46-56 psi for 38 mm and my expected gross weight of 195 + 40 = 235 lb.

Trust me, 45 psi on tubeless 38 mm tyres is an excellent figure!

The Pathfinder's braking performance in sand worries me a little

I was imprecise; i didn’t mean the braking capability. You simply would not be able to ride a sandy road such as this one:



On the other hand, I might try riding it carefully with Tracers, especially with the seat dropped half way

 

[Sparky731]

What tire was it that blew out?

Rear tire. I was riding at low torque <10mph but must have twisted the tire just enough to blow out. Quite a mess as it spewed sealant all over. <800 miles on PanaRacer GravelKing tire. I have ridden these tires for >3k miles with no problem. Always liked the tires. Earlier in the day I had ridden very rough trail and my guess is I had a bead leak and didn’t realize it. My gross weight is 145 + 60.