IanS

I was directed to this article on tyre pressure and speed which basically says that in terms of rolling resistance, lower pressures are faster in all but very exceptional conditions (perfectly smooth roads):

https://www.huntbikewheels.com/blogs...ich-is-fastest

Apparently this isn't that new a concept, but for various reasons, most riders still use higher pressures, self included.

I would like to experiment with lower pressures, but feel we are a little compromised on a tandem due to mass. We couldn't run a 25 mm tyre at 60 PSI for example. In fact, I don't think we could run a 25 mm on anything less than around 95 PSI (our mass including bike is around 425 lbs). We could however, go wider though. We are running 32 mm Marathon Plus on a couple of my bike for training which seem to be bomb proof, but have stiff walls which defeat the object of using lower pressures according to the article. Apparently you need a supple tyre wall to benefit.

So I was wondering whether anyone had any experience using lower pressures in wider tyres, the tyres they used, and the kind of pressure people have managed to run safely (ie. tyre not coming off the rim in high speed bends for example).

If it helps, based on my understanding of the interviews, you need less energy to go the same speed using lower pressure supple tyres. So far they've gone as wide as 54 mmm tyres and are still seeing this benefit. Obviously there is going to be some kind of compromise when aerodynamics are also considered, but according to the interview, top time trialers are running 25 mm tyres at low pressures (didn't say what) these days.

dabac

There's an article somewhere on how to inflate by ride height rather than pressure.
Makes sense.
Rolling resistance is pretty much driven by the amount of deformation in the tire. Amount of deformationfor a given rim/tire combo is set by pressure and load.
Pressure is easier to measure, but ignores the influence of load.
So basically you check the sag, how much closer to the ground the rim becomes when you get on the bike, and adjust pressure until you reach a recommended percentage of sag.


Don't remember which though, sorry.

Road Fan

Google "Frank Berto Tire Pressure Bicycling Quarterly" and you'll get the article. The article is about setting pressure based on the weight each wheel is supporting and the actual tire width. The chart calculations are BASED on wheel sag, but it's a really inconvenient procedure at the gas station. Much better to calculate your total bike + riders + gear, estimate 45% front and 55% rear, and check the chart.

If it says, for example, that your 25 mm tires need 160 psi, you might think about getting wider tires and checking the pressure capability as you shop.

For example, for me on a single, a 28 mm tire set needs about 80 in the front and 95 in the rear. For another of my bikes with 42 mm tires (a 650b), I need about 50 psi front and 60 psi rear. I haven't done the evaluation yet for my tandem because, well, it's still under construction.

I find the lower pressures are comfortable and don't really feel slow. Higher pressures do FEEL faster, but the theory is that they feel faster because you feel more vibe and shake from the road surface. I bet the subjective aspect will be different for say, carbon versus aluminum, but I haven't seen any research on that, and I also think it's rather inconsequential anyway.

I can't say if the softer tire is actually faster - too many variables for a test that I could do that would convince me. But the comfort is nice.

waynesulak

Much discussed topic. I suggest searching the forum using the built in search tool or better yet google. There is a lot of good info buried in the posts if you want to spend the time to sift thru them.

for example:
" "pressure" site:https://www.bikeforums.net/tandem-cycling "

Note the first and last quotation marks are to force the forum to display the url without converting it to the forum web site name and should not be included.

FBinNY 

The real takeaway is not to start by worrying about ideal pressure. Instead, start by selecting the right tire width for the payload. If you look at the automotive world, you'll note that tire width is proportional to payload.

On bikes wider is often better, but that doesn't mean widest is best. Find a tire that has enough width to support the load, yet isn't much heavier, and (obviously) has adequate clearance in the frame. Then experiment with pressures. You'll find that, within reason, higher pressures roll faster on smooth pavements, but will cost you speed on bumps, and can also cost you traction.

So, use judgement guided by these limiting factors. Too much pressure causes lost traction, and rough handling and higher resistance on bumps. Not enough pressure will slow you down, feel sluggish, and can cause rim dents or snake bite punctures. If there's no happy median between these two, then you need wider tires.

pdlpsher

The best tire pressure and rolling resistance data is found here: https://silca.cc/blogs/journal

oldacura

So - a lot of people have studied this in great detail and have written lengthy articles on it.

Can anyone bottom-line this data & recommend an ideal pressure for a team + bike weight = 330# on 25mm tires?

Carbonfiberboy 

Nothing makes you slower than a pinch flat, so that's really the pressure governor on a tandem. And that's going to depend on your roads and ability to avoid things, so a good lower pressure will vary for everyone. Our sweet spot is running 23mm outside width rims with 28mm Conti 4000 IIs tires at 90 lbs. with an all-up weight of ~335 lbs. Those Contis measure ~31mm on our rims at that pressure after they're stretched out. We don't pinch flat with that combo, even on small potholes.

I use a simple formula to transfer pressure from one tire width to another. For instance in this case 31*90=2790. To get equivalent pressure for a tire which really measures 25mm, I'd go 2790/25=111psi. For a 23mm tire, 2790/23=121psi. That gibes with my experience. The wider tires are a heckuva lot more comfortable for the same pinch flat resistance.

Are wider tires faster? I think it depends on the tire and road surface. For smooth asphalt roads, my experience is that narrow high pressure tires are faster, the opposite being true on chip seal. Our Contis are just plain fast on any surface, very little to nothing to gain by going narrower.

mtseymour

Our experience is similar. We've tried various 28mm tires (Schwalbe One, Hutchinson Secteur) and 85-95 psi works well for our team weight of ~ 310 lbs. We've never had a pinch flat and have a good mix of comfort and rolling resistance. I'm surprised that some teams use 25mm or 23mm tires when more single bikes are moving to 25mm tires.

GCN has a short video on how pro riders choose tire width and pressure. It's notable that more pros use 25mm tires even when racing on fairly smooth roads.

https://www.globalcyclingnetwork.com...o-ditalia-2014

reburns

We use the same tires on the same width rims, and our total weight is close at probably ~350. We've been having good luck with 80F/90R psi. On narrower rims I kept pressures above 100 because lower started to feel a little sloppy, but not true on the wider rims.

OneIsAllYouNeed

15% tire drop gets you this:
330lb w/ 25mm (measured width): 143psi front and rear <--ugh. that's which our stokers need suspension seatposts and why tires only last 1000 miles.
330lb w/ 27mm (measured width): 127psi front and rear
330lb w/ 29mm (measured width): 114psi front and rear
330lb w/ 32mm (measured width): 98psi front and rear <-- probably the absolute fastest option for paved roads
330lb w/ 39mm (measured width): 72psi front and rear <-- really nice on poorly paved roads
330lb w/ 45mm (measured width): 58psi front and rear <-- suitable for off-pavement

twocicle

This raises a critical point not underscored above... AIR VOLUME is the key. You can talk about tire widths and air pressure, but it is air volume that will make or break (ie: pinch flat) your day. Less volume requires higher pressure to carry a given load. Conversely, more air volume allows you to use less pressure to carry the same load.

Do take into account both the tire width + rim width and the rim well (inside depth and area). Not all rims are created equal. Bottom line, generally wider rims (ie: inner width of >19mm) will provide room for more air volume which will allow for lower air pressure and a much nicer ride quality, while providing a stable tire profile equal to (or better than) a skinnier tire at higher pressure.

Dean V

According to Mavic going from 17mm to 19mm rim with a 25mm tyre increases air volume by 2.2%.
Not a lot really.

Leisesturm

I don't know how she does it but my stoker (blind) can tell when I've topped up the tires on any of our 3 tandems. She notices that we are easily, faster with higher pressures in our tires. She notices that we are faster on 1-1/4 tires than 2.0 tires, and faster still on 28mm (110psi) tires. I'm not sure she would care what Frank Berto, or any authority, might have to say about it. Her perceptions are all the validation on best practice that she (i.e. we) needs.

twocicle

Rim width is just one factor in the mix. Not looking at the entire picture is usually a biased outcome. Assume you are in part referencing this info from Mavic...

THE RIGHT TYRE WIDTH ON THE RIGHT RIM WIDTH - Engineerstalk : Engineerstalk
"A 2mm increase of the tyre width alone has a much higher impact (+15%) than a 2mm increase of the rim width alone (+2.2%). And of course, the combination leads to both air volume increases, which is even better."

^^^ still ignores rim well depth, perhaps to simplify their statements, or perhaps the math doesn't result in something favorable to their designs.

Dean V

Wouldn't increasing air volume from rim well depth make a tyre more prone to pinch flats?
As the tyre compresses from hitting a bump the internal pressure wouldn't rise as quickly due to the extra volume in the rim well, making it easier to bottom out.

Chancy

I agree Dean.
Extra air volume in the rim well (below the rim sidewall) would minimize the increase in pressure as the tire compresses from the impact. Thus a rim with a deeper well, and all else being the same, would bottom out with less impact than a rim with a shallower well.


Tailwinds,
Charlie

vrooom3440

I disagree with the notion of the importance of air volume.

The critical factor is the area of the contact patch. The contact patch does not care about volume nor rim depth. Really the contact patch is a function of load and pressure: given a load and pressure the tire will deform (ie: flatten) until the Pressure X Area == Load. Yes the width of the tire will change the shape of the contact patch but NOT the area. Area will be constant for a given pressure and load.

Back in the day some of us messed around with removing the springs from motorcycle forks and using air pressure instead. One of the parameters was to change the volume of air by adding/removing damping oil from the fork. This did not change ride height, that was only changed by air pressure. What it did change was the compression ratio or how quickly pressure (and thus stiffness) built up. Higher compression ratio meant that there would be less deflection over the same bump.

That said, I suspect compression ratio is irrelevant here due to the volume of the entire tire being much higher than the volume of the small area of deflection.

WRT width... for a given width a perfect circle contact patch is:
23mm == 415sq mm (0.64 sq in -- supports 64 lbs at 100 PSI)
25mm == 490sq mm (0.76 sq in -- supports 76 lbs at 100 PSI)
28mm == 615sq mm (0.95 sq in -- supports 95 lbs at 100 PSI)

YMMV but if we figure 200 lbs of rider/bike on a pair of those 23mm tires at 100 PSI, we have a 1 sq in contact patch (1.5x our example above). Running a 28mm tire would only need 70 PSI for the same deflection at that load.

StephenH

It is rather informative when two or three people strike out, and the one bragging about his super fast tires is also the one that has a couple of flats on a 200k, and so the people with slow tires wind up waiting on the guy with fast tires. Moral being, you need to strike a compromise there, too, as the ones tabulating speed of tires don't bother tabulating in any extra flats from using those tires.

Stick69

Our tandem came with 25mm Continental GP 4000. At 390 lbs we run them at 120 psi. One of the bridges we cross has expansion joints that look like pinch flat test obstacles. So far so good and the Stoker is happy without any other shock absorption. We may go to 28mm rear at some point but 28mm front would be hard to slip through the front brakes and we remove the front wheel when we transport the bike. We are new to all of this but what we are doing now seems to be working​ OK.

IanS

Re contact area and pressure, I think this is the point, although clearly pressure is related to the volume of air contained in the tube. For a wider tyre, if the contact area remains the same, you need less pressure in the tyre. Based on my understanding, the theory then goes that if the tyre is supple, and does not have stiff side walls, it deflects more which in turn reduces rolling resistance and as a side effect, also improves comfort.

Unfortunately I don't think this is going to be that helpful in terms of performance on a tandem though because I'm not sure there is a suitable tyre / rim combination which would enable us to run low pressures aerodynamically. But in terms of comfort, maybe.

Anyone got any suggestions on wide supple tyres which don't have stiff side walls?

chojn1

The last time I recommended some tires to a friend he had an absolutely terrible experience with them, so I am a little leery about any tire recommendations. But, we have been very happy with the Schwalbe G-One we are currently using. We do ride in any on-road and off-road conditions with them. They're rock solid and very comfortable. YMMV

Alternatively, Compass tires has been selling wide supple road tires for years. We had an extralight pair once. They were light, fast and comfortable. But, they were not durable in the conditions we like to ride.

CJ

waynesulak

You make an important note about recommendations. Different teams put widely different demands on tires and wheels. Often teams do not appreciate this and are disappointed with recommended products, so test it for yourself is the best advice.

Not only team weight and roads but riding style can have a big impact on tire durability. For instance when the bikes with skinny tires & expensive carbon wheels slow for rough roads and railroad tracks, we like to hold on to our hard gained momentum and bomb through.

We ride compass and have found the super light ones flat easily in wet weather on the tandem but do OK on singles. On the tandem we like the Compass tires with the standard casing. We have used 700c / 30mm wide and 650B / 38mm and 42mm.

OneIsAllYouNeed

Everything in the Compass Cycles catalog - 26", 650b, and 700c in lots of widths
Soma Supple Vitesse 700c x 33, 38, 42
Soma Grand Randonneur 650b x 42
Vittoria Voyager Hyper 700c x 32,35*,04
Panaracer Pari Moto 650b x 38,42*

Most of the tires are available with extralight or standard casings, or longer wearing tread. I'd recommend choosing for the heavier of those two options for tandem use. There's some anecdotal evidence that the extralight Compass tires, in particular, are too delicate for tandems.

*I'm currently using these on my tandem.

metrotyres01

Tyre pressure and has a direct connection with speed. It is pressure that not only determines speed but also fuel consumption and proper balance.