Tyre sizes

[jbond]

I'm in the middle of trying to understand tyre sizes and choices and exactly why I, people and the bike shops should choose one size over another. I had the experience yesterday of getting several completely conflicting bits of advice from various bike shops...

First some ground rules. I ride mostly on the road, but do stray onto bridlepaths, footpaths and tow paths. I try and avoid mud and really soft ground but will struggle through it if I have to. I also don't care much about comfort but do care about rolling resistance. My Ridgeback hybrid has Michelin City tyres in 32-622 at 80-90 psi. They're terrible off road, but are manageable as long as you don't get too ambitious. Off road tracks are ways of getting to interesting places, not things to be attacked as if you were on a motocross bike.

It seems to me that even though Pedelecs are heavy they're not that different from a big heavy person on a light bike. I'm only 70Kg, so all up weight is about 100Kg. That's the same as a 90Kg person on a lightweight 10Kg bike. However, Pedelecs and especially one's with rack mounted batteries are very rear biased. Which makes me think there's a good case for asymmetrical sizes. The one bit in this I'm not sure about is the effect on rolling resistance of tyre width. Received wisdom is that narrower tyres run faster. I'm not completely convinced but let's go with that. So really (for speed) you should run the narrowest tyres at the highest pressures you can get away with.

So now we switch to what Schwalbe actually sell. I think you could get away with the narrowest 26" tyre they do in the Marathon and Marathon plus which is a 35-559 rated for max 6.5 bar (95psi). There might be some justification for using the next size up on the rear. So that's the 40-559 6.0 Bar (87psi).

Meanwhile, the pedelec manufacturers are actually shipping 47-559 or even bigger and expecting people to run pressures more like 4.0bar (60psi). They seem to be choosing comfort over speed. But when mileage and efficiency are so important this feels like the wrong compromise to me.

Does that all seem sensible? Am I making a mistake trying to carry all that weight on relatively skinny tyres?

Then there's price. Marathon Plus are not exactly cheap. But as SWMBO said, why the hell are you worrying about 10 quid extra on a grand's worth of pedelec?

 

[NRG]

Everything you need to know about bike tyres:

http://www.schwalbe.co.uk/shopdata/files/TechInfo2-GB.pdf

 

[flecc]

I've used the Marathon Plus in two different and narrower sizes on an e-bike with a rear hub motor, the 28 mm on the front and 35 mm on the rear. The original tyres were 1.95" (50 mm) Kendas. Here's the original Kenda 1.95 with the 35 mm MP alongside:



The problem with narrow Marathon Plus is that they are too rigid, the ratio of the dimensions to the inner liner thickness making them much more uncomfortable than expected. The tiny gain in lower rolling resistance was almost undetectable and frankly not worth it, I would have been better advised to use MPs of 38 mm or more width and benefited from the improved "give".

As you'll see if you read that Schwalbe technical document, they insist that tyre width makes no difference to rolling resistance, so you might as well use tyres of adequate width and fine tune with the tyre pressures used.
.

 

[FatMog]

Everything you need to know about bike tyres:

http://www.schwalbe.co.uk/shopdata/files/TechInfo2-GB.pdf

Thanks for the link, v.interesting.

I want to put some wider tyres on my (non-electric) batavus bike; it currently has 37-622 tyres on it. Unfortunately I cannot find any indication on the rims themselves as to sizing, so I'm going by the link which suggests it would have a 19c rim. As I understand the document I can stick more or less anything I like on it up to 62mm wide, subject to frame and mudguard clearance.

Does this sound right? Seems unusually accommodating to me!

 

[Caph]

They seem to be choosing comfort over speed. But when mileage and efficiency are so important this feels like the wrong compromise to me.

This way of thinking always seems odd to me. I think that if you're going to add a motor and a big battery to a bike then little things like tyre widths are not really much of a concern in comparison. I run 2.25" knobbly tyres at a low pressure and I much prefer the added comfort. I just let the motor take any extra strain, but then that's what I bought it for in the first place!

 

[jbond]

Everything you need to know about bike tyres:
http://www.schwalbe.co.uk/shopdata/files/TechInfo2-GB.pdf

Wow. Talk about myths being dispelled. I found the comparison of width vs pressure vs rolling resistance eye-opening.

This year has been a bit of a sea change in my bicycling. For years and years I had a steel frame Peugeot racer converted into a hybrid and reduced to 5 gears. My son managed to get it stolen so that got replaced with a Ridgeback ally frame hybrid. Gosh, gears are useful, V-Brakes work, Shimano speedshift levers are neat. Now, it's an Aurora!

When I was a kid I did a bit of amateur racing. So I've always had this belief that you should run the skinniest tyres at the highest pressures and sod the comfort. On the hybrid (32–622), I can definitely feel the extra effort required when the pressure drops from the normal 80 psi to 60. The other interesting side of that graph is that above 5bar the graph has flattened with both sizes of tyre and there are only small gains to be made from over-pressuring it. But the fat tyre is still more efficient.

As for comfort vs efficiency. I use the bike for exploring the countryside and getting a bit of exercise. It's strictly for fun. I've got a tendency to go a bit too far and I hate that feeling of being 10 miles from home, 2 big hills in the way and pretty tired. At the start of the journey, the hills are just irritating and no fun. At the end they're seriously no fun. So I thought electric-assist would take some of the pain out of the process, add some fun and let me go a bit further on a sunday afternoon. So the compromise for me is all about range rather than comfort as I can get adequate comfort with good grips and seat regardless of how rigid the tyres are.

 

[allen-uk]

I want to put some wider tyres on my (non-electric) batavus bike;

Different ball game, mog, and dodgier.

As flecc points out, widths and rolling resistance on electric bikes have minimal effect; on non-electric bikes they have enormous implications.

I used to ride a standard 'hybrid' with big fat tractor tyres, until my local bike shop asked "Do a lot of off-road, then?" To which the answer was no, never. He changed them for an ordinary set of Schwalbes, and the difference was immediate and vast. I would guess that it took me 20% LESS effort to ride, particularly up hills, than with the tractors.

So, do you do a lot of off-road, then?


Allen.

 

[jbond]

As flecc points out, widths and rolling resistance on electric bikes have minimal effect; on non-electric bikes they have enormous implications.

I used to ride a standard 'hybrid' with big fat tractor tyres, until my local bike shop asked "Do a lot of off-road, then?" To which the answer was no, never. He changed them for an ordinary set of Schwalbes, and the difference was immediate and vast. I would guess that it took me 20% LESS effort to ride, particularly up hills, than with the tractors.

I wonder how much was the tread pattern and how much the width. And what pressures did you use on your tractor tyres?

I'm not sure about this idea that rolling resistance matters less on electric assist. Because it still affects range, speed and what the bike feels like when you're *not* using the assist or only minimally. ISTM that to get the ranges the manufacturers claim, you must put some effort in yourself.

 

[flecc]

I would guess that it took me 20% LESS effort to ride, particularly up hills, than with the tractors.

With the wrong tread that's very true Allen, but a fat tyre with a well designed tread needn't have high drag. Many use Schwalbe's Big Apple tyres which in the largest size are huge and very comfortable balloon tyres, but they suffer hardly any more drag than with average tyres.

Look on the link below at the Big Apple, then at the two "knobblies" below which will be high drag, then at the reviews below on the Big Apples:

Big Apple webpage
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[allen-uk]

Interesting flecc, thanks for the correction.

I shall investigate further for my next set of tyres for my ordinary bike.


Allen.

 

[theskip1]

you also have to take into account braking power. some of these e bikes are getting near small scooter and moped weights and need tyres to suit the wider the better, in wet conditions even more so.