This has probably been posted before but couldn’t find it.

I’ve just read this but it still doesn’t make sense to me. I know when i’ve had much lower pressure in the rear (around 22) it has felt very draggy. I normally run a 1.90 rear tyre for most of my riding.

http://www.schwalbetires.com/wider_faster_page

full report: the truth about rolling resistance PDF

Not sure why it makes no sense to you? The article explains the reasons. On the road a harder tyre rolls more easily, but off-road lower pressures mean the tyre is more easily able to conform to the texture of the ground – hence less resistance. Since lower pressures also afford more grip it is a win-win.

I don’t think it’s quite as intuitive as you make out, glenp – or maybe i’m just dumb. On the road a lot of the rolling resistance is due to the deformation of the tire as it rotates. Lowering the pressure means the tire deforms more, hence increases rolling resistance (willing to be corrected if wrong!). The same thing must happen off-road, so if I hadn’t read the article I would have also thought less pressure = more grip + more rolling resistance.

There must be some point in “roughness of the terrain where it changes – and also with “muddyness”

At sits I am convinced the narrow hard tyres I used were quicker rolling than wide soft ones

I didn’t say it was intuitive – I said the article is very clear and easy to understand. The additional force needed to deform a larger softer tyre is taken into account in the feature, and is easily countered by the other benefits.

Very interesting (although I had seen it before).

That all kind of explains why my hemisphere on the back works.

makes no note of the tire weight? how many watts are used up dragging a 800g 2.4 tire up a hill compared to a 400g 1.7?

although it does vindicate my 2.35 high roller front and 2.4 holyroller rear setup with 25-30psi! (as invariably in this country 30-50% of the miles are road the inverted tread rear makes a lot of sense).

It does take account of weight. F=ma so it only matters when accelerating.

yes, and the test course was uphill (no ones contesting that bigger is better downhill).

Thus there is a power requirement to lift the extra 800g (400 at each end) from the bottom of the hill to the top.

Say his 500m test hill was a gaining 80m in height. And he’s completeing the course in 189 seconds at 9.5kn/h.

it takes 627J to lift the tires to the top of the hill, so a power of arround 3.3W. Thats for a completely smooth road test, as he points out, the continual bouncing up and down will increace this power off road.

And that is a great example of science by press release whereby you release results to the press/public before its published in a scientific journal. A bit like that “missing link” fossil in germany last month. Theres more money to be made from the public press than they would ever get in research grants resulting from scientific publication.

What about suspension reducining the lateral movement of the tire. No info was given on the bike used.Or the effect of conditions eg mud Would like to see the full paper before i buy some fatter tires

also i strongly suspect that the idea of bouncing up and down on the knobbles (ohh err missus) is a missconception. More likely to be the knobbels bending foreward/backwards s they load and unload? Hence why the big ramps on high rollers would help by preading the load over a bigger area of tire, but still maintaining a sharp edge.

Anyone want to do some FEA, or play arroudn with a stobeoscope and a bike on a treadmill? (will it takeoff?)

Basically a lower pressure provides less rolling resistance off road because with a higher pressure, the air is harder to pressurize further, so when you go over, say a root, instead of the tyre deforming as the air is pressurized, more of the bike is lifted upwards, turning your forward momentum into up momentum. With a lower pressure the air is easier to pressurize, so when the tyre makes contact with the root, the air pressure increases and the tyre deforms, meaning you keep more of your forward momentum.

Sounds like someone getting all too scientific & glossing other vital factors to me, but if all the top teams are riding squigy fat tyres at this years mountain mayhem, then I’ll stand corrected….

Im not convinced at all by this paper.

Firstly, it isnt even a proper scientific report (i’ve just written a engineering thesis myself at Oxford so i know what they look like) No real theory in there, just a few under defined empirical conclusions.

Plus it appears to be sponsored by Schwalbe, who sell larger than average tyres.

How about if the ground is soft and you are cutting thru the mud? We know narrower / harder tyres are faster on road. How rough does the track have to be for this effect to occur?

thin tires are neeeded in mud for clearance issues, ive been running big mud tires all winter, becasue theres cearance for 2.5’s out back normaly, 2.1 mud tires fit fine. Feel much nicer and grippier in corners than the narrow ones i used to run.

tj narrower tyres are not nec faster on roads in fact they have a marginally higher rolling resistance than wider tyres (all other things being equal).

They will usually be a little lighter and more aerodynamic.

Non peer reviewed rubbish. Ignore!!

Could be the most nerdy thread I have seen here yet.

Al – how come?

tyre surface in contact with the ground is more curved and so has to deform more.

For slick tyres on the road I heard that for the same pressure, a wide tyre rolls better than a narrow tyre, but narrow tyres are typically able to be pumped up to higher pressures which makes more difference overall. Think it was in Continental’s tyre literature.

Hmmmmmmmmmmmmmmmmm

Well, I checked Conti’s literature and couldn’t find it, so that’s wholly unfounded then. I swear I saw it though, honest…

Most of it looks rubbish to me and is clearly marketing hype.Don’t suppose that Schwalbe making fattish tyres has anything to do with it?? Have a look at the power figures quoted on grass/meadow early and later in the report. A bit different don’t you think?
Also look at the difference between power used through gravel and meadow-don’t think so
There is no reference to traction. The basis is that all of the power is used to overcome rolling resistance.This therefore assumes that there is no loss through loss of traction.
The analysis doesn’t work on the limit either. Do you really think that 1 psi is better than 30?

I’ve run UST for several years and often run them at around 25 psi and its amazing how you don’t feel any extra drag. I would say that in even in mud the lower pressure works as there is better grip, all else being equal. My only experience of wider tyres was a set of 2.3s (not very wide I know but I am a jey) and they felt slower to me, esp climbing on rough fire roads and tracks. Much grippier but the extra rsistence relative to my usual 2.1s could be felt.

I would have though that wider tyres were worth it for trail and all mountain riding and heavy riders but when pure xc speed is needed then 1.8 -2.1 will be ideal, depending on terrain and rider weight.

Alternatively it doesn’t work at the other extreme either – running tyres at 60 psi rather than 30.

Mind you I’ve always been confused as tyre manufacturers seem to reccommend running tyres at much higher pressures than people do in the real world.

As an example Conti advise running Mountain Kings at 50 psi – don’t know anyone who does.

Here

http://www.conti-tyres.co.uk/conticycle/ti%20mountainking.shtml

See above hh45 running 25psi, bet manufacturer recommends much higher.