47c vs 35c tyres - differences in speed?
 

I've been reading up about the move towards wider road tyres to reduce rolling resistance, increase comfort and, potentially, speed. It seems that for racers, there is a sweet spot around the 28/30mm mark beyond which the benefits of the counterintuitively smaller contact patch of a wider tyre begins to be outweighed by the loss of aerodynamics...

There's loads of info about this for this size bracket of tyre, but less so for wider, touring tyres.

I have a hybrid framed tourer and have had 47c 1.75in Conti Contact tyres on it for years. Really comfy and have served me well touring in places like Morocco and Jordan where the tarmac can be poor in out of the way places.

I'm just about to do the Lon Las Cymru, Wales end-to-end and have on a whim bought some 35c Schwalbe Marathon Classics on the off chance that they might roll faster than the 47cs on the good tarmac expected on this route. They are also about 250g lighter each than the Contis.

Am I right, though? According to Bicycle Rolling Resistance the marathons have much less rolling resistance and less weight, but what about internal friction, contact patch sizes, etc etc? The marathons have noticeably stiffer casing and obviously higher pressures...

Sorry, probably just getting myself all confused for not much difference and should've saved the £55!

I have toured on 40mm wide Marathons (with Greenguard) and found them to roll well and provide good flat protection, have not used the Continentals that you cited. I suspect only lab tests could tell you which rolls better.

Last year I bought a Jamis Renegade that came with 40mm Donnelly gravel tires. I was definitely slower on pavement than on my road bike with 32 tires - very noticeable. For a 3 day tour I did across Florida, I put on some 35mm Schwalbe Marathon's I had laying around (Marathon Plus, I think). They definitely rolled faster than the 40 MM but gravel tread was surely a factor, too.

Just for grins,before getting rid of a old, old hybrid bike bike I took off the new 38MM Schwalbes Marathons (whatever Marathon type is rated a bit better on gravel, a bit worse on road) and put those on the Jamison and did a number of packed dirt, crushed limestone rides and a few well groomed gravel stretches, which are mostly what I do when not on paved roads. Those were a good compromise compared to the 35s.

Unless you are averaging well above15mph/25kph aero effects from the tires are in the noise.

So, depends on the type of riding you do but for paved roads with bad stretches as you describe, Schwalbe Marathons have been working great for me for years.

I ride various tires, 28, 35, 38, 45 and while different tires ride differently, regular marathon 35s which I have on one bike, ride well enough.
im not familiar with your contis, but I strongly suspect you'll appreciate and notice the bike is quicker, less effort for same speed with the 35s vs 47s.
the 35s also do a good job on rough tarmac, of which we have a lot of here in Montreal.

sounds like a great ride, never got to ride in Wales when I had family living there.

I would guess that at lower speeds, say, less than 25 km/h, and on rough terrain or soft surfaces, the wider tire will be smoother and faster.

At higher speeds and on smooth tarmac, the lighter and narrower tire will probably have the advantage. Don’t underestimate the difference in aerodynamic drag from a wider front tire.

This is, of course, assuming the tires are different widths but otherwise identical. If one of the tires is a heavy OEM tire with a thick flat resistant layer and the other is a supple casing lightweight tire like a compass Grand Bois or something, then there is no reasonable comparison to be made based on widths.

I bought my Renegade in 2018 and it came with 36 mm version of these tires (X’Plor MSO) - some 30 TPI variety which seem to not be listed for sale anywhere (only 60 and 120 TPI), I guess it is a cheaper OEM version. These tires feel significantly slower and definitely produce much harsher ride compared to both Conti GP5000 32 mm and Vittoria Voyager Hyper 37 mm (which measure 39 mm on my rims). They are also noticeably more noisy on smooth roads. GP5000 and Voyager Hyper despite their huge size difference were actually much closer to each other in comfort and ride feel, so I'd say gravel thread and general hard construction of the gravel tires is the main factor by far, they just can't be compared with road tires. Narrower GP5000 indeed feel faster and, especially, snappier - bike turns, accelerates and climbs much more eagerly with them, it just feels very different, much more agile. Still, for me over long rides (e.g. 50+ miles) average speed seem to be very close, within 1 mph on all of these 3 tires. :)

Expensive 'fast' wider tires are the niche market https://www.renehersecycles.com/ is claiming to supply..

I gotta try some of those tires, just as soon as I wear out the Schwalbe Marathons I've been running for six years. They may not be very supple or fast, but they last for thousands of miles.

On my Trek 520 I've tried up to a 42 mm Conti Top Contact tires. They we're very stable and flat resistant, but heavy and clunky. I went next to Schwalbe Marathons in 700x35. I immediately noticed a considerable improvement in rolling resistance and agility, but they were a little less stable & a bit more "squirrelly" at high speeds down the big hills that I ride down, most of which have less than ideal surfaces. I also had a few snake bite flats with them, so I next replaced them with the same tire in a 700x38. They're a little heavier but not by much & they have proven to be robust enough for what I ride on. So since they've served me so well for 3 years now, I'd have to say that for my riding, the 38s seem to be an optimal choice. Of course, YMMV.

I do something a little different. On my Lynskey Backroad I have a set of Conti GP4000 S2 700x28 on some lightweight rims for everyday riding. They indeed feel light and lively. When I go out to CO each summer I switch over to Marathon Green Guard 700X32 on some heavy rims. They are better for some of the hard pack gravel roads. I train on them for about a month before I go out. The switch creates an appreciable amount of extra effort.

I certainly notice the same thing. Today i rode my 45mm tyred bike for the first time in a while, nearly always riding my lighter bike with 28s just because it's faster for less effort. It is interesting the change of effort from my 28 bike to 35 to 45, although the bike weights certainly are a factor. It is pretty cool though with the 45s going over bumpy and loose surfaces and the Cadillac Mercedes feel, and for sure wider is faster over rough roads and our bodies save energy from the cushy ride.

It's interesting to experiment with tires. I recently put Schwalbe G-One Speed 40-584 tires on a gravel/touring bike that came with Schwalbe Smart Sam 54-584 knobbies. I don't actually ride much off-road...the G-One's are faster but still surprisingly comfy. 3 years ago I switched another bike from heavy (model?) 38mm Marathons to 50mm but lighter/more supple Marathon Supremes---speed about the same but Supremes more comfy & handled better.