Why are nobbly tyres less efficient?

[daz3210]

I've been thinking about this for a while.

Race cars use slicks to give extra grip, and the surface area touching the road is increased (on a size for size comparison) over treaded tyres.

On a MTB nobbly tyres reduce the amount of rubber on the road (as far as I can see), so why are they less efficient?

[Gizmoish]

A) because each time a nobble comes down the front of the tyre towards the ground, you have to 'climb over' the edge - its tiny but it adds up

B) because the blocks themselves flex which reduces the efficiency of power transfer from pedal to road.

[Engineer1]

They aren't if you are off road, try slicks or semi slicks on a trail, but put your MTB on a road and it will be hard rolling, so it's a case of choosing the bike or the tyre to suit your riding.

[daz3210]

Situation is I have a mtb that rarely leaves tarmac, and when it does its either cinder type canal towpaths, or occasionally grass/hard mud.

But, this year I am thinking of keeping it in use through the winter and may encounter ice and snow.

I was thinking of switching to semi slicks, but with winter fast approaching was thinking should I stick with the nobbly tyres until springtime.

I have a roadbike too, so have the best of both worlds I guess.

[robpearson]

racing car slicks are very wide, and have a correspondingly wide contact patch, road tyres at racing pressure only have a tiny width in contact with the road.

[Some Gump]

get a cheap set of extra wheels off the bay. job jobbed!

[GBDG]

A road bike tyre is about 1/4 as wide and pumped up to 120psi. When under load a nobbly tyre will compress and the area in contact with the road will be much larger than you would think. This effect is minimized because road bike tyres are at such high pressure.

[daz3210]

GBDG said:

A road bike tyre is about 1/4 as wide and pumped up to 120psi. When under load a nobbly tyre will compress and the area in contact with the road will be much larger than you would think. This effect is minimized because road bike tyres are at such high pressure.

But when you compare like for like sizes of MTB tyre,the slick ones are faster/easier are they not?

[gary71]

daz3210 said:

GBDG said:

A road bike tyre is about 1/4 as wide and pumped up to 120psi. When under load a nobbly tyre will compress and the area in contact with the road will be much larger than you would think. This effect is minimized because road bike tyres are at such high pressure.

But when you compare like for like sizes of MTB tyre,the slick ones are faster/easier are they not?

Yes, much! Rolling resistance is the key.

I use these Conti tyres for winter road riding. www.chainreactioncycles.com/Models.aspx?ModelID=78...

[McFsC]

Road bike tyre = one contact with the road.

MTB tyres = several contacts with road.

One larger contact with the road is less friction than several smaller contacts with the road.