Optimum tyre width for 26" rim?

[blackdog]

Hi there,
Apologies if this question's already been asked but I've had a search to no avail.

What's considered the optimum width for everyday riding with a mix of loose surfaces but predominantly road. No specific MTB use 'though as for that I'd fit knobblies.

There seems to be some debate regarding tyre pressures, rolling resistance, rotational mass etc. I'm contemplating buying some road biased tyres and currently find myself flip flopping anywhere between 1.5" and 2.0".

By the way, do MTB rims designed for tyres typically running fairly low pressures, have a psi/bar limit or is just the tyres?

Thanks.

[Brucey]

you'll get answers from 1.25" to 2" for this one, depending on riding preference and surfaces etc.

I used Specialized Nimbus for a few years and these were about 1.5" (even though they were marked as 1.4"). They were fine, but on rough ground I wanted them wider and on smooth roads I could have had them narrower... I've used 1.6" ones and they were good too.

You don't need to worry about the rims, pressure-wise. But do note that the tyre width alters the rim loading from pressure. To a first approximation a 1" tyre at 100psi exerts the same load on the rim as a 2" tyre at 50psi. Weird, isn't it?

hth

cheers

[gentlegreen]

I have over-engineered rims - Mavix EX721 that specify a minimum tyre width of 2 inches, but I love my Conti Country-plus tyres - 1 3/4 inches in old money.
Pumped up to 4 bar / 60PSI, I doubt they're the limiting factor when I do a 50 mile group ride. Solid as rock, never visited by the p* fairy, very secure on fast downhills on rough roads carrying an 18 stone rider with luggage.

When I ride on snow or dust I can see a very narrow actual contact ridge.

That said, a local guy I know who sees off roadies on his MTB has altogether narrower rims and tyres - probably about 1 1/4 - the width I used to have on my old 27 inch 10 speeds.

[meic]

I choose between the Panaracer Paselas, either 1.25" or 1.5"
Which are two different tyres rather than identical except for size.

or this for a more rugged yet still fast tyre

http://www.spacycles.co.uk/products.php ... 0s121p1682

depending on current prices and how I feel.

All three of these are much faster than any MTB tyre.

[Erudin]

I've got a rigid titanium mtb with virtually slick Michelin City 26 x 1.4" tyres on, and a front suspension mtb with semi-slick Continental Double Fighter II 26x1.9" tyres.

I've done the same 20 mile ride by road on both bikes out to Roadford Lake and 5 miles round the off-road bike trails there.

The 1.4 tyres feel like they have a lot less rolling resistance and corner better on the road than wider mtb tyres, on the bike trail in the dry they grip the loose chipping surface better than I expected but the ride was a bit harsh.

The 1.9 tyres roll well on the road, though climbing the hills felt harder work compared to the 1.4's or road bike tyres. Off road they perform great, plenty of grip on the trail, able to corner and descend faster than the 1.4's, soaked up the bumps on rough sections nicely.

If speed/road riding is a priority the 1.4's win, though my average speed was only 1mph faster on the 1.4's compared to the 1.9 semi-slicks. But the 1.9 semi slicks work much better off-road whilst still rolling well enough on the road.

[steeleagle]

The width of the rim is a very important factor to consider.

[WrightsW5]

I've got a bike with panaracer ribmo 1.25 on the front and michelin xc road 1.4 on the rear. I got a narrower rim for the front.

[uphillbothways]

Relevant data, courtesy of Schwalbe:




The data is unequivocal - at normal pressures, wider tyres roll better. Only two groups of riders will benefit from narrower tyres; Unusually lightweight riders, and riders who travel at high speeds in an aerodynamic position on smooth roads. The vast majority of riders would be better served with tyres much wider than is currently the norm.

[meic]

You say at normal pressures but that data is at the same pressure.

In reality most of us run thinner tyres at higher pressures. I tried running my 1.75" at 90psi and they did certainly fly along in a rather concrete sort of way.... until the rim "unzipped" along the spoke holes due to the enormous force of 90psi in a 1.75" tyre.

A lot of us are unconvinced and not out of some idealogical objection but because the promised gains turn out to be losses when we gave it a try. Possibly it is just the extra weight of fatter tyres and their inner tubes which outweigh the gains of the rolling resistance.

[squeaker]

Vittoria Rubino Pro Slicks (40 x 559) on 19mm rims at 45psi front / 55psi rear for me: but I wouldn't take them anywhere near damp grass

[uphillbothways]

You say at normal pressures but that data is at the same pressure.

The data clearly shows that wider tyres roll better even at substantially lower pressures. The most striking example being that a 32c Durano rolls better at 6.5 bar than a 23c Durano at 8 bar.

Most people's experience is of comparing wide heavy touring tyres with narrow racing slicks, which alters the most important variable - sidewall stiffness. Within practical limits, casing construction is much more important than either width or pressure. The Tour Magazin tests showed that the worst 23c clinchers had nearly double the rolling resistance of the best. Heavier tyres will feel slower due to the increased rotating mass, but that only affects acceleration, which is essentially irrelevant in a touring bike.

I think this is yet another case where intuitive experience is just dead wrong, one of those longstanding myths that refuses to die. It's the same sort of voodoo that causes bike journalists to describe frames as "plush" or "harsh", or describe wheels as "uncomfortably stiff".

[meic]

That is not how I interpret that data.

The first three tyres are all at the same pressure, which I would say is the correct pressure for the 25mm and the 23mm is under inflated and the 28mm is over inflated.
The under inflation causing the 23mm to absorb energy and the over inflation causing the 28mm to absorb less energy.

Likewise the highest performing 32mm tyre is over inflated at 6.5bar for its size.

This all fits nicely with my intuitive experience that the highest pressure a tyre can take means less rolling resistance.

[Brucey]

my two penny's worth;

Whilst I don't disagree wildly with the results of these tests, I do feel that they should be put into context.

1) Yes you might save 3W with fat tyres over skinny ones in rolling resistance, but at (say) 15-20mph you will have to find another 10W or more from somewhere to push the blessed things through the air. Go any faster and it gets worse, much worse.

2) Wider tyres at the same pressure put more stress on a carcass of a given construction. This means that in many cases you must run at lower pressures with wider tyres.

3) Weight; wider tyres of the same construction get (roughly) pro-rata heavier with width. If they also take the same pressure they get heavier again.

4) if you are determined to run low pressures with wide tyres, think about having reasonably wide rims. Narrow rims with wide low pressure tyres (basically where the tyre is about double the rim width) can yield handling that varies between 'interesting' and 'alarming'.

5) The rolling resistance tests reported in the link above appeared to use a smooth metal roller. The curvature of the roller may have favoured a wider tyre over a narrower one, since the contact patch shape would be less distorted by such a curved roller with a wide tyre.

6) The rolling resistance data may have been skewed by the smoothness of the test roller. Real-world roads are not smooth, and tread rubber scuffs and squirms within the contact patch. Both these things absorb energy and neither is likely to be correctly represented in a test on a smooth metal roller.

7) The smooth roller wasn't 'bumpy' ; wider tyres absorb small bumps better. As a rule of thimb, any road that is rough enough to be jiggling you around in the saddle is absorbing energy.

So overall, with fat tyres, I draw the following conclusions;

'More comfortable' ; yes, of course.

'Lower rolling resistance'; sometimes, certainly.

'More efficient'; yes, at low speeds on bumpy surfaces, not necessarily elsewhere.

'Faster'; No.

Re 'Faster' If you have enough energy to do 10mph and you fit fatter tyres with lower rolling resistance you might do 10.2mph or something. But on smooth roads, at any much higher speed (say 15mph +) fitting fatter tyres will slow you down because of the aerodynamic drag, the weight, etc.

cheers

[blackdog]

Just caught up with this after a couple of days. Thanks very much for your answers. I'll have a proper read when I have a little more time. Cheers.

[reohn2]

You say at normal pressures but that data is at the same pressure.

The data clearly shows that wider tyres roll better even at substantially lower pressures. The most striking example being that a 32c Durano rolls better at 6.5 bar than a 23c Durano at 8 bar.

Most people's experience is of comparing wide heavy touring tyres with narrow racing slicks, which alters the most important variable - sidewall stiffness. Within practical limits, casing construction is much more important than either width or pressure. The Tour Magazin tests showed that the worst 23c clinchers had nearly double the rolling resistance of the best. Heavier tyres will feel slower due to the increased rotating mass, but that only affects acceleration, which is essentially irrelevant in a touring bike.

I think this is yet another case where intuitive experience is just dead wrong, one of those longstanding myths that refuses to die. It's the same sort of voodoo that causes bike journalists to describe frames as "plush" or "harsh", or describe wheels as "uncomfortably stiff".

I completely agree.
I am a total convert to wide tyres for comfort with no appreciable loss of speed other than acceleration as you rightly say,which isn't that significant for the majority of riders and even for the most of the remainder it's in the mind.
A light 700x35 tyre such as Schwalbe Kojaks,or similar, are an absolute joy to ride and at 345g can't be described as a heavy tyre,obviously a big inner tube is needed(@ 150g for a Schwalbe one) as is a wide touring type rim(DRC ST19 @580g) which adds upto a peripheral combined weight of 1075g compared with say a narrow general purpose though not ultra lightweight 700c rim @ say 500g and a narrow "training tyre" @ say 290g,narrower tube @ 120g = 910g a saving of 165g(5.8oz)*.That may mean a lot to some but isn't worth a hill of beans to me who rides rough pothole strewn tarmac.
The comfort difference of the bigger tyre for my old wisen arthritic body is amazing
If anyone is concerned about tyre roll when cornering I can't say I've noticed any difference and whilst I'm no Billy Whizz I'm not overly cautious either.One area where the bigger tyre is in its element is when decending,at over 40mph on rough tarmac they are superbe!

*If we take things to the extreme for everyday use with a 450g rim a 230g tyre and save a further 20g(?) on a lightweight tube 450+230+100g= 780g gives a weight saving of a further 200g but we're getting toward very lightweight stuff with all the vulnerability that goes with it on the UK's rough and pothole strewn roads.
PS,I normal cruise at about 17to19MPH to give an idea of my ability.