Tyre Anomolly

[Gubbins]

Before I buy or do anything I have a browse through here because the regular posters seem to be knowledgeable and give good sound advice...
Having read about tyre types, pressures and all the rest I bought 2 puncture resistant hybrid tyres to replace my worn knobblies that came with my hard tail 29er MTB.
Did I expect too much? Having endured a summer of being bounced out of the saddle at every pothole with 70psi in them I honestly cant tell if they roll better, go downhill faster or give me more distance per charge, but that could be down to my, and the batteries general decline through age.
Well, winter is here, or will be soon, the off road bits I use are getting muddy, so its back on with the knobblies... First impressions are.. wow, they are only half the weight of the road tyres and seem to roll much better, and so far I can see a visible improvement in distance travelled per charge because I can keep it above the cut off much easier... Or so it seems!
Its also more of a pleasure to ride without having to dodge pot holes or lift of the saddle if you cant, and it doesn't squirm or slither about when you hit some loose stuff under braking.
I know I could buy a sprung saddle but I consider such things to be for the older or more infirm rider (no offence intended) and I am not yet ready to call myself an old man and will not go down that road without a fight!!
So I wonder if the benefits of a high pressure smoother tyre are offset by the extra weight they add to the bike?

 

[neptune]

Phill, I think a key question is, what percentage of your mileage is off road. Most of my mileage these days is on road, and unassisted. My regular road bike is HYBRID bike on relatively narrow tyres at about 60 PSI. Lately, I have done a few miles on a rigid mountain bike on knobblies.This bike seems harder work on the road, but is better to ride on unsurfaced paths. I guess it is a case of horses for courses as they say.

 

[Artstu]

It sounds like you just bought the wrong tyres, which ones were they?

 

[Gubbins]

It sounds like you just bought the wrong tyres, which ones were they?

Halo twin rail multi tyre...
http://www.halowheels.com/products/part/TYHAT92

 

[Artstu]

Clearly the wrong tyres then. Not that this will help you, I have just fitted two of these in 1.5" on a friends bike to replace some worn out Big apple tyres. Amazingly even with 90 psi in they are more comfortable than the big apples, and roll very nicely too, we keep thinking a tyre has gone flat, with the comfort being so good, and a good price too.

http://www.wiggle.co.uk/schwalbe-city-jet-mtb-tyre/

These could suit you down to a tee I would think http://www.wiggle.co.uk/schwalbe-land-cruiser-rigid-city-road-tyre/

 

[Blew it]

The correct pressure for a 2.2" section tyre is 40 psi for a 75 kg rider. For every kg rider weight above that, increase the pressure by 1%.

A large section tyre inflated to 70 psi cannot flex in the way it is designed to when ridden on a coarse surface such as hard-pack or coarse Tarmacadam. Each little projection in the surface will present a ramp which the tyre has to roll up and over. In each rotation of the wheel, hundreds of these little ramps add up to a fair bit of resistance. The same tyre at 40 psi will simply deform at each mini-ramp and roll smoothly, absorbing very little energy in doing so.

Narrow section road tyres at very high pressure absorb very little energy due to their relatively tiny footprint

 

[jackhandy]

I find Schwalbe Smart Sam +'s to be a good compromise for road & trail use on my 29er.
I run mine at 40 psi, or a tad less at times.

The proper off-road knobblies on both my bouncers are truly horrible on tarmac - Like wearing football boots

 

[Gubbins]

The correct pressure for a 2.2" section tyre is 40 psi for a 75 kg rider. For every kg rider weight above that, increase the pressure by 1%.

A large section tyre inflated to 70 psi cannot flex in the way it is designed to when ridden on a coarse surface such as hard-pack or coarse Tarmacadam. Each little projection in the surface will present a ramp which the tyre has to roll up and over. In each rotation of the wheel, hundreds of these little ramps add up to a fair bit of resistance. The same tyre at 40 psi will simply deform at each mini-ramp and roll smoothly, absorbing very little energy in doing so.

Narrow section road tyres at very high pressure absorb very little energy due to their relatively tiny footprint

I think they are 29x2.2 and on the tyre sidewall they are marked max for on road 85 psi, off road 55psi. The high pressure making it run on the 2 rails in the thread (hence the name " twin rail") the idea was to make the bike more free running making it easier to ride above the cut off... The discomfort could be tolerated if there were definite benefits, but now having changed to lightweight off roads running at 25-30 psi I find that those benefits were never actually there... Tis a bit of a conundrum......

 

[JohnCade]

I put some Specialized Nimbus road tyres on my MTB a couple of years ago and it ran much like my old road bikes on tarmac with plenty of air in the tyres. Vast improvement of the knobblies it came with for the road.

I'm using Marathon Plus tyres on my Kalkhoff Agattu and I find they roll well past the cut off speed with little resistance. I do put plenty of air in them though and run them at 80 psi.

 

[Blew it]

.. Tis a bit of a conundrum......

Yes it is, it's all about 'Rolling Resistance' and other such stuff.

There is some pretty weird science involved in designing a bicycle tyre which can proceed over very rough ground without slowing or needing additional pedal effort to maintain a given speed. If the tyre is grossly over-inflated, those sciences are immediately defeated.

I recall, way back in the mists of time when I swapped my car tyres from cross ply to the new-fangled radial ply type. On the way home I noticed the steering was extremely heavy at low speeds. (Very few cars or even lorries had power assisted steering in those days) On returning home I looked at the new tyres and thought "they haven't put enough wind in them". The fact is, those seemingly under-inflated radial ply tyres returned greatly improved mpg figures over their rigidly constructed cross ply predecessors.

Perhaps the almost universal use of radial ply tyres nowadays is the reason why all cars have power assisted steering.

 

[RobF]

If you said wider tyres roll better than narrow ones many cyclists would give you an argument.

Yet this is what Schwalbe say on the subject:


Why do wide tires roll better than narrow ones?
The answer to this question lies in tire deflection. Each tire is flattened a little under load. This creates a flat contact area.

At the same tire pressure, a wide and a narrow tire have the same contact area. A wide tire is flattened over its width whereas a narrow tire has a slimmer but longer contact area.

The flattened area can be considered as a counterweight to tire rotation. Because of the longer flattened area of the narrow tire, the wheel loses more of its roundness and produces more deformation during rotation. However, in the wide tire, the radial length of the flattened area is shorter, making the tire rounder and so it rolls better.

Rolling resistance:
At 2 bar a 60mm wide tire rolls as well as a 37 mm tire at 4 bar.


http://www.schwalbe.com/gb/rollwiderstand.html

 

[jackhandy]

.

Rolling resistance:
At 2 bar a 60mm wide tire rolls as well as a 37 mm tire at 4 bar.


http://www.schwalbe.com/gb/rollwiderstand.html

That's interesting.
Presumably assumes similar tread patten & depth?