MTB Tyre rolling resistance

[weeksy]

For those that haven't seen it, Enduro Mag just release a huge test of tires focused on RR and puncture resistance. It's an app-only publication, so I figured I'd post the results here from lowest RR to highest. Testing was done on a drum at constant speed and pressure and they said also verified by climbing a set rout maintaining a set power output, but it seems they're only sharing the drum test results. Not perfect, but interesting nontheless.

[Count Steer]

Speaking of which (but a different cycling genre) - on the TdF yesterday one rider informed another that he'd got a rear puncture. The bloke hadn't noticed. The commentator said it happens a lot because they run such low pressures.

I was v surprised because my memory of road racing bike tyres was that they were high pressure (needed a better pump!) to reduce rolling resistance.

Wossat all about?

[weeksy]

Speaking of which (but a different cycling genre) - on the TdF yesterday one rider informed another that he'd got a rear puncture. The bloke hadn't noticed. The commentator said it happens a lot because they run such low pressures.

I was v surprised because my memory of road racing bike tyres was that they were high pressure (needed a better pump!) to reduce rolling resistance.

Wossat all about?

The world has moved on. Now super narrow and super high pressure isn't a thing. people are running 30mm wide roadie tyres in races where 19mm used to be the thing.

https://www.cyclingweekly.com/news/prod ... ure-270668

Zipp (SRAM) has a very detailed calculator that enables you to plug in a range of data in order to get your starting points, Vittoria likewise.

Tommaso has some simple advice to get started on your ideal tyre journey, “if you used to ride 116-130 psi (8-9bar) on a 23mm tyre you might want to drop the pressure in a 25mm tyre by 1bar (14 psi), dropping another bar for 28mm and going down to around 72psi (5bar) for a 30mm tyre.”

Tubeless?

One of the oft-touted advantages of going tubeless is the ability to run lower pressures.

Indeed this can be the case. Add to the fact that a tubeless system offers a lower Crr when run at the same pressure as a tubed tyre, thanks to the elimination of the friction between tyre and tube.

However, the pressure differences might not be as marked as you might think. Zipp recommends just 1.5 psi lower for a tubeless setup over inner tubes with a hooked tubeless rim. This does change when using a hookless tubeless rim when pressures can be reduced by nearly 6psi.

Running lower tyre pressures can mean that you’re more susceptible to pinch flats. Tubeless technology was designed to eliminate this issue - and with regards to pinched inner tubes, it did so. However, the hard leading edge of a carbon rim can still cause the same to happen to the sidewall of the tyre if the impact is severe enough. Likewise, tubeless tyres can ‘burp’ air. Here, excessive compression causes the seal to break and the tyre loses some air.

Tire inserts or liners were created to eliminate both issues while at the same time helping to protect the rim from strike damage. Proponents of inserts also say they add some comfort and shock absorbance. However, those less in favour of the technology will point to the added grams and ask, why spend a fortune on lightweight, aerodynamically enhanced rims if only to add rotational weight?

Another point worth making when it comes to tubeless tyres is the added care required to keep your tyres at their optimal pressure. Compared with tyres fitted with inner tubes, tubeless set-ups tend to lose air far more quickly. While you may go a few rides without checking your pressure if you use the former, the latter is best checked before each ride

[Count Steer]

Intriguing. You'd think that a) increasing the size of the contact patch and b) introducing more flex due to tyre size and lower pressure would increase losses in energy transfer. ie be less efficient.

Are modern bike tyres ultra stiff?

(Cars seem to be going the other way in the quest for mpg. Lots of cars running narrower tyres around, particularly hybrids and full electric).

[weeksy]

Intriguing. You'd think that a) increasing the size of the contact patch and b) introducing more flex due to tyre size and lower pressure would increase losses in energy transfer. ie be less efficient.

Are modern bike tyres ultra stiff?

(Cars seem to be going the other way in the quest for mpg. Lots of cars running narrower tyres around, particularly hybrids and full electric).

I dunno mate in truth, i only know the high level details, not the exact how/why. One of our old posters Crosshair was very much a pioneer in forum land of lower pressures not mattering. But i only really pay attention to the full details on MTBs.
They're a whole different world though with the Radials giving a VERY weird contact patch compared to standard tyres, but apparently still giving amazing traction and rolling resistance too.

Obviously all the above is MTB related and yeah for sure on the gravity based options in general the sidewalls are stiff and thicker than they used to be. But they're also more compliant at the right usage. How... heck i dunno. Maybe @mboy will know more as he's a tyre god.

[Count Steer]

Be interesting to know, just out of sheer



Obvs the downhill/MTBs generally focus is more on grip in assorted conditions and, looking at some of the tarmac interfaces on the TdF, grip is waaaay down the priority list. A number of times riders just seem to lose the bike from under them on a little corner - like they're riding on ice (and they must absolutely dread damp roads).

Also, just checked and velodrome tyres are 120-200psi 'to reduce rolling resistance and allow for high speeds and centrifugal forces' so they're more like the old road racing tyres.

[JamJar]

Intriguing. You'd think that a) increasing the size of the contact patch and b) introducing more flex due to tyre size and lower pressure would increase losses in energy transfer. ie be less efficient.

Are modern bike tyres ultra stiff?

(Cars seem to be going the other way in the quest for mpg. Lots of cars running narrower tyres around, particularly hybrids and full electric).

The lower pressure and wider tyre actually gives more traction as the tyre absorbs the bumps and imperfections in the road maintaining contact and drive. The older narrow high pressure tyres wre losing contact with the road over all the imperfections in the road.

[Count Steer]

Intriguing. You'd think that a) increasing the size of the contact patch and b) introducing more flex due to tyre size and lower pressure would increase losses in energy transfer. ie be less efficient.

Are modern bike tyres ultra stiff?

(Cars seem to be going the other way in the quest for mpg. Lots of cars running narrower tyres around, particularly hybrids and full electric).

The lower pressure and wider tyre actually gives more traction as the tyre absorbs the bumps and imperfections in the road maintaining contact and drive. The older narrow high pressure tyres wre losing contact with the road over all the imperfections in the road.

Well, I guess they've done the sums and found it makes sense in terms of efficiency but I find it surprising that a fatter, heavier, lower pressure tyre is more efficient overall. Especially if they're running such low pressure they need someone to tell them they've punctured!

Explains why velodrome tyres are old skool though. The surface is considerably better than the road. (Definitely the case here. ).

[Mussels]

Not very scientific but I found the same commuting on my ebike years ago, narrow high pressure tyres didn't improve my commute time at all but did make bike parts fail more often through harder shocks from the road.

[JamJar]

Intriguing. You'd think that a) increasing the size of the contact patch and b) introducing more flex due to tyre size and lower pressure would increase losses in energy transfer. ie be less efficient.

Are modern bike tyres ultra stiff?

(Cars seem to be going the other way in the quest for mpg. Lots of cars running narrower tyres around, particularly hybrids and full electric).

The lower pressure and wider tyre actually gives more traction as the tyre absorbs the bumps and imperfections in the road maintaining contact and drive. The older narrow high pressure tyres wre losing contact with the road over all the imperfections in the road.

Well, I guess they've done the sums and found it makes sense in terms of efficiency but I find it surprising that a fatter, heavier, lower pressure tyre is more efficient overall. Especially if they're running such low pressure they need someone to tell them they've punctured!

Explains why velodrome tyres are old skool though. The surface is considerably better than the road. (Definitely the case here. ).

I suspect that his tyre had not gone down completely or he had tyre inserts.

[MingtheMerciless]

Paging @mboy !!

Also when are the XC radials coming out?, need one for the back of the Curtis, more than willing to be a demo rider

[mboy]

Intriguing. You'd think that a) increasing the size of the contact patch and b) introducing more flex due to tyre size and lower pressure would increase losses in energy transfer. ie be less efficient.

Are modern bike tyres ultra stiff?

(Cars seem to be going the other way in the quest for mpg. Lots of cars running narrower tyres around, particularly hybrids and full electric).

Some (many) bike tyres are quite stiff these days yes, often to make them more durable/reliable for a given application. Sometimes this can increase rolling resistance, but not always.

Car tyres work in a very different way to a bicycle tyre. Car tyres are subjected to much higher speeds, and rely on a "radial" construction (I'll come onto why radial MTB tyre construction is different in a moment) to stop the tyre tread from growing... These are usually steel belts, sometimes kevlar, but either way, their job is to keep the tyre radius/diameter stable at changing speeds...

With a stiff tread area, it is more typical these days for car tyres to find their compliance from their sidewall construction (amusing you might think, given how so many modern cars have such big rims with low profile tyres fitted!) as the tread area has to be relatively stiff to maintain its shape at speed (you absolutely DO NOT want tyre growth at speed on a family car!). If you haven't handled a modern car tyre off a rim at all recently, you might be quite surprised just how supple the sidewalls are (often less stiff than a Gravity focussed MTB tyre!) considering the job that they do...

Tyre science is really quite complicated though, and doesn't always follow linear rules though. My understanding of it is greater than most (I talk about the things for a living), but it is not at the level of the tyre designers whose job it is to make a product that works for a given application, despite all the complexities and constraints imposed upon them. My job is more of a middle man to help explain the science in terms that people might relate to, and to explain the potential benefits or pitfalls they might experience.

@weeksy that's a useful chart, and hasn't thrown up any surprises for me based on my own knowledge of tyres within that test group... What is the puncture % rating with regard to though? And the rolling resistance, I guess they're measuring in watts (and for a single tyre? At what pressure, what speed etc.?)...

[weeksy]

Testing was done on a drum at constant speed and pressure and they said also verified by climbing a set rout maintaining a set power output, but it seems they're only sharing the drum test results. Not perfect, but interesting nontheless.

Enduro used: 1.5 bar, 50kg load, 20 kph

[Mr Moofo]

My MM Gravity ultra soft was pretty good in the dust of Morzine - saved me a few time
And the Michelin Wild enduro work well on the back end - but it was loose and dusty

I, however was a glorified mobile chicane …