This may seem like a stupid question, but I've got fairly thick tyres on(WTB Prowler MX) and it seems like I cant carry any momentum. Would changing to thinner/lighter tyres make alot of difference? also, would the other tyres affect the comfort of the ride cos these seem to soak up the bumps?

apparently, off road, wider tyres roll easier

you sink even deeper into the mud (snow in winter).

hmm i have 2.25 on front and a 2.1 hi roller on back of my 5 and it was good in the claggy autumn and spring mud but have just fitted 2.35 front and back hi rollers to my altitude 50 so ill let you know but going from big rear to small rear i did notice a difference but how much of that is a placebo effect i dont know.

Cheers, I was thinking along the lines of more friction=slower, makes sense to sink deeper though.

I saw some measurements last autumn and it was something like 20W difference in rolling resistance between thin and fat tyres (fat less)

totally depends on conditions… to take an extreme, a thin tyre on road will roll much better than a 3.5" wide surly snow tyre… but the surly will work a load better on snow.

in really claggy mud i find my 1.9 front and 1.5 rear combo works better than a pair of 2.25s.

I think it was this work by [or on behalf of] Schwalbe that SFB is referring to

Having a decent light pliable carcass/tread speeds things up also.

Yes, try something like the 2.4 Nobby Nic's (600-660g) – my fav trail centre and Peaks/Lakes tyre.

Or the 2.1 version for Enduro's (500g).

Gutted, was hoping a thinner tyre would give me more momentum, turns out I'm just slow!

A thinner tyre will probably be ligher and easier to accelerate though….

A thinner tyre will probably be ligher and easier to accelerate though….

yes, if you don't mind the persistent drag

Thinner is snappier (although this might be due to less weight), more mud clearance and if it is swampy your tires will cut through and hold less mud therefore not be as heavy! However since swapping have noticed being a little bit more cautious on really rocky downhills.

Thinner usually ends up with me having to get new rims, as I weigh a bit 😯

What that Schwalbe report shows is that obviously terrain makes the biggest difference to rolling resistance.

On rough terrain the type of tyre makes a big difference and efficiency savings can be made by choosing the correct tyre and pressure.

However on gravel the differences seem to be smaller. In this case surely the differences in the weight of the of the tyre will may be more important. (which Schwalbe say is 4.2W for 500g difference between both tyres.)

Also it would be better if they had
1. taken into account even larger tyres at some point this have to stop paying dividends.
2. taken into account rider/bike weight which has to affect the size of tyre needed

It would be interesting to see if a typical race course in the UK say a gorrick was more similar to the meadow or gravel track tested.

And as mentioned there does not appear to be a mud test!

from that report:
"To accelerate a pair of tyres with extra weight of 500g from 0 to 25kph in 4 seconds requires and extra 4.2W. On the other hand the wider tyre on a grassy surface saves you 15.5W"

simonfbarnes – Member

A thinner tyre will probably be ligher and easier to accelerate though….

yes, if you don't mind the persistent drag

It will be lighter and easier to accelerate whether or not he minds the drag.

Also don't under-estimate the difference between tubes (and weight) and tubeless.

Big volume run tubeless and low pressure, well low compared to most. On sunday at afan i started at 30psi, then dropped to 25psi – loads of grip!

It will be lighter and easier to accelerate whether or not he minds the drag.

thanks for clarifying that Al

Heh. Don't like you own pedantry eh?

lighter thinner tyres will make you go faster xc over a distance A to B, i.e a race or an event

Bigger tyres will be quicker where the need for grip is more important, i.e a downhill race/event.

bugger science, this is why peaty races with big squidgy tyres, where grip is more important and xc race boys race with thin fast tyres like racing ralphs.
The lower the pressure then although you are getting more grip you are losing energy, a bit like a full susser where when you stand up to pedal the suspension takes up some of the forward energy thus you dont accelerate as quickly as say a hardtail where little energy is lost and more forward energy happens

Don't like you own pedantry eh?

I think you'll find that was yours…

bugger science…The lower the pressure then although you are getting more grip you are losing energy

well, obviously we should ignore measurements and go with radoggair's assertions

It's really complicated. On flat hard ground (e.g. tarmac) a narrow hard compound tyre will be quickest. On flat soft ground the quickest tyre will be the one whose pressure hits the sweet-spot where losses due to the tyre sinking into the surface plus losses due to the tyre's flexure an adhesion with the surface reach a minimum and the softer the ground the lower this pressure will be. The lower this pressure is then the wider the tyre should be to minimise losses through optimum contact patch shape. On hard but bumpy ground the quickest tyre will be the one whose inherent suspension characteristics absorb these bumps with minimum loss of energy without driving up losses due to flexure and adhesion to too great a degree. Whilst when the ground is really soft and wet the adhesion between the contact patch and the mud will start to cause greater losses than the losses due to sinking into the ground, hence the narrow mud tyres thing.

As soon as you start pedalling the softer the tyre, the more the losses but conversely on softer ground a softer tyre could reduce these losses due to minimising sinking into the surface. And as soon as you go round a bend or brake or accelerate hard then grip matters more than the rolling resistance, so the most efficient tyre is the one that lets you brake the least.

The only constant is that a more flexible tyre will always be more efficient and have more grip. But optimum width, tread and pressure depends on the terrain, the bike, the rider and the riding style.

For hard surfaces…

1. On a hard surface, comparing two tyres pumped up to the same pressure, a wider tyre will have less rolling resistance.

2. Thinner tyres will usually be inflated to a higher pressure, which can be more significant however (esp. for a smooth surface).

3. Thinner tyres can result in less aerodynamic drag for roadies, although I have no idea how significant this is.

bugger science…The lower the pressure then although you are getting more grip you are losing energy

well, obviously we should ignore measurements and go with radoggair's assertions

Thanks Mr Barnes, i've been trying for ages to tell everyone that when it comes to science, ask me 😉

I tried CX Pros 1.35's and they just dug in so deep it was silly. I had to walk a gentle hill because they dug so much, and when I looked back I could see a 2" deep groove where I had been and gentle dimples where everyone else had ridden.
RRs all year round now.

That piece of research is interesting but it does not cover many circumstances – higher speeds for example or wet / soft ground – I think it is a far more complex situation than that bit of research shows and in some circumstances even offroad thinner tyres are quicker / take less effort. I have no evidence to back that up however