Commuting - Knobbies or slicks

I currently have a Mountain bike and have to ride about 20 km's to work. All but 50 metres is on roads.
From postings in these forums I was under the impression that slicks would increase my speed but the guy at LBS told me that whaterver speed I picked up from slicks I would lose due to decrease in Diameter of the tyre.
Any opinions

Right. That's why professional racers ride those bikes with the 60-inch tires. Bigger tires are faster.

Seriously, that's nonsense. But you knew that, right?

Get the slicks. But maybe from a different shop, eh?

RichC

Originally posted by Ramon
the guy at LBS told me that whaterver speed I picked up from slicks I would lose due to decrease in Diameter of the tyre.
Any opinions
Eh?:confused:

Go slicks to go fast. The reduced drag by not having the knobbies will be more than overcome by any slight decrease in circumference. The old maxim is: If you can hear noise, it's costing you energy. I don't know of any knobbies that don't made a noise on tarmac.

If you want *some* tread but without the knobbies because you might go off-road on gravel at some time, Continental Town and Countries come well recommended (I can vouch for them having ridden in mud and slush -- they do a good job of not becoming clogged). The inverted tread means you are riding on the smooth crown of the tyre, while the tread on either side gives grip on gravel and mud and stuff. I think Continental also make another new model, the Contact, that is slick-smooth in the middle, and knobbied on the outsides. I've got them on a tandem, but haven't ridden them enough to give an opinion.

R

If you do slicks, get the slimmest, lightest ones that you can get away with, for low air drag and low rotational inertia. If you end up wrapping out your high gear with the slicks, due to the reduced rolling diameter coupled with the reduced air drag, then you might need a higher high gear in the form of a larger big chainring on your crankset, or a cassette with a smaller small cog. See how it goes.

Also, keep in mind that with small tires, your bike sits closer to the ground and is going to snag a pedal on the ground at a shallower bank angle than it did before. Be cautious about pedaling through corners.

Go with the slicks. They're much faster and a much more comfortable ride than knobbies. I also find that slicks can handle 90% of gravel roads.

Thanks for the replies.
I am impressed with the timely nature of advice offered in these forums

I should have looked at your profile before I replied. I imagine there aren't too many gravel roads to contend with up in Brisbane. I don't think I can recall seeing any last time I was up there.

The rolling resistance of a tyre is related to its pressure. Lower pressure = higher resistance. Rolling resistance affects cycling at all speeds. Modern MTB slick tyres can hold sufficient pressure (80-100psi) to be very efficient.
Aerodynamic drag is caused by the width of the tyre. Wider tyres have more air resistance, BUT air resistance increases with the velocity squared. If you double the speed, you increse the air resistance by 4. This type of resistance only comes into play at very high racing speeds. For most longer distance riding and commuter/utility use, it is not a significant factor.
Weight affects the acceleration, and a smaller slicker tyre is lighter.
Wheel diameter does affect rolling resistance, but some racers use a 26" tyre, its not worth using a fatter, heavier lower pressure tyre to bulk up the diameter.
Experience shows that a 1.5" slick tyre is efficient, yet comfortable and reliable on rough tracks. For really fast riding, you may want to go down to a 1" or 1.25", but most people stick with the 1.5".
You dont need knobbles or much tread to ride down flat rough tracks.

Originally posted by MichaelW
Wheel diameter does affect rolling resistance, but some racers use a 26" tyre, its not worth using a fatter, heavier lower pressure tyre to bulk up the diameter.


Do you have any data for this? I've never seen a cycling efficiency calculation where the output changes if the only variable is tire diameter.

I'm aware that on a gross level under real-world conditions -- a 700 wheel vs a small cart wheel, say -- the larger wheel will have many advantages (including reduced resistance) due to surface irregularities on the road.

But what would account for an effect on rolling resistance due solely to a difference of, say, an inch in bicycle tire diameters? (Not to rotational weight, or differences in the wheel, etc.?)

RichC

Its difficult to find a cycling-related ref. in which the various elements are analysed separately. Most just lump diameter, tyre diameter pressure weight etc into one discussion.

Santana Tandems have a decent discussion of the 700c/26" choice at
http://www.precisiontandems.com/artbillwheelsize.htm

There are very fat slick MTB tyres for road use, the idea being to increase the outer diameter of the tyre. I question the wisdom of lugging all that extra rubber around for some small theoretical increase in RR with diameter.
I really dont want to add to the accumulated cycling voodoo, so if anyone else knows of a good ref, fire away. In the meantime. I stand by the empirical advice that a nice slick 1.5" tyre is fast, efficient and comfy.

Thanks for the citation. If they're right (and I still think there are too many variables), then the larger diameter tire has less rolling resistance:

"If they both corner at the same speed, is either wheel size more efficient? Yes. Because of its smaller diameter, the 26" tire is forced to deform more to apply its equal-area-yet-fatter contact patch to the ground. When we put the same weight on both bikes it's easy to observe more "bulge" in the sidewall where the 26" tires meet the ground. Greater tire deformation (sidewall flex and tread squirm) equals greater internal tire friction; the leading cause of rolling resistance."


Originally posted by MichaelW
I really dont want to add to the accumulated cycling voodoo, so if anyone else knows of a good ref, fire away. In the meantime. I stand by the empirical advice that a nice slick 1.5" tyre is fast, efficient and comfy.

Yup. And while I don't have data, Ramon's LBS guy's contention is simply ludicrous.

RichC

Originally posted by MichaelW
The rolling resistance of a tyre is related to its pressure. Lower pressure = higher resistance.

True, but only for tires of the same construction on a hard road. a 200 psi knobby will almost certainly have higher rolling resistance than a 60 psi slick.

The Continental Town & Countries are a good tyre but the sidewalls will crack after time. They only come in large sizes 26x1.9 and 26x2.1 and can only be pumped to 65psi. They are also hard to get on and off rims.
I now use Michelin Wild Grip City's and they are a softer compound and at 26x1.5 very narrow. They take 80psi, and are easy to mount. Also available in 26x1.25.

CHEERS.

Mark

Originally posted by Rich Clark
Yup. And while I don't have data, Ramon's LBS guy's contention is simply ludicrous.In one sense, yes. The reduction in rolling diameter only means that the rider has to pick a slightly higher cadence or else a higher gear.

In another sense, however... what if you don't HAVE any higher gears? ;) I commute on a mountain bike with a 2.35" rear tire and a 46 x 11 high gear, and I can wrap it out when I'm inbound on downtown, since I'm going downgrade in general. Even on level ground, I reach cruise speed on my 46 x 11 unless the winds are against me or I'm tired.

So if I were to put on a pair of 26 x 1.1" Ritchey slicks or something...? That's right, I'd be wanting a 50-tooth chainring, or else I might actually end up going slower for want of a high-enough gear (I don't spin well, not with 180mm cranks and a low, off-roadable seat position).

If this is what Ramon's LBS was trying to convey, they might have a valid point. Most mountain bikes these days have either a 42 x 11 or 44 x 11 high gear that's easily spun out on a moderate downgrade, even with a full-sized drive tire. Does that make sense?

I guess my advice goes on the assumption that the rider will be going 15mph/25kph where the air drag starts to make a difference.

Originally posted by Dutchy
The Continental Town & Countries are a good tyre but the sidewalls will crack after time.

The set I tried a couple of years ago only lasted about 3,000km or so before the sidewalls went. I can get 10,000km out of a pair of cheap slicks, sometimes more.

I've found Vredestein Spiders good for commuting - 1.95" with a slick centre and recessed knobs on the shoulders. Fast rolling on tarmac, highly puncture resistant (3700 miles on the front so far). The knobs don't touch the ground unless cornering hard or on very soft surfaces, I wouldn't use them in real mud but they're not bad off road and silent on road. Disadvantage wise, the puncture resistant strip makes them a little heavier and less flexible than average, and they're a little tricky to seat.

They're a good compromise tyre though for mainly road work and occasional off roading.

Richard

Originally posted by Chris L
The set I tried a couple of years ago only lasted about 3,000km or so before the sidewalls went. I can get 10,000km out of a pair of cheap slicks, sometimes more.
Odd about the feedback on these. I've had no problems with T&Cs in use, although my MTB has now sat idle for around 20 months. They got a lot of use in commuting, on MTB trails and touring on gravel roads. One of my most exciting moments was doing 78km/h fully loaded downhill on a 12% loose gravel road. I gave passing thought to the idea the T&Cs might blow out, but they didn't. The same T&Cs are still being ridden after I gave them to a work colleague to put on her bike. They did about 5,000km before I passed them on, and they still had OK sidewalls.

The original versions were made in Europe and were very beefy with a hard tread compound. A friend had a set that he did more than 15,000km of touring on, and the tread was still like new. Then Continental switched to having them made in Thailand (IIRC). The tread was not as thick, and on some tyres the mouldings were such that they did not cover the threads.

I could still run them at 80psi. I'm told they are very good in snow because the inverted tread doesn't get clogged up so quickly.

R

Originally posted by mechBgon

If this is what Ramon's LBS was trying to convey, they might have a valid point. Most mountain bikes these days have either a 42 x 11 or 44 x 11 high gear that's easily spun out on a moderate downgrade, even with a full-sized drive tire. Does that make sense?


Using the extreme example of a 26x2.35 vs a 26x1.0, Sheldon Brown's gear calculator says that at a cadence of 100rpm, with 175mm cranks, a 44t chainring and an 11t cog, a rider would achieve 31.4mph with the bigger tire and 28.5 with the smaller.

This of course doesn't factor the increased resistance of the larger, fatter, squirmier tire and how much more effort it would take to maintain that cadence.

So yes, you're right, you could spin out with a smaller diameter tire at lower speeds than with a larger. How likely is that? If it doesn't come close to happening with the larger tire, I don't think it's likely to happen with the smaller. And even if it does, I don't think most commuters spend all that much time in high-speed descents. And even if your commute is all downhill in one direction, whatever you lose on the descent from having a slightly smaller tire I expect you'd make up during the climb in the other direction.


Even on level ground, I reach cruise speed on my 46 x 11 unless the winds are against me or I'm tired.

If you're cruising anywhere near 30mph on the flats on a MTB, my hat's off to you.

RichC

I'll just say this: if I had a 26 x 1.1" drive tire or a 42 x 11 high gear, I would be very frustrated :)

I guessing the LBS guy didn't have any slicks in stock. What a butt head telling you that load of crap. I'd find a new LBS to deal with.

Dave
who is partial to Tioga City Slickers in either 1.25 or 1.5 width

The only problem I have with the 2.1 Town and Countrys is the weight. They are heavy, heavy tires. But I have never had a flat... I can't see much of a reason to ride knobbies unless you have a significant amount of loose terrain on your commute. I run out of gear several places on my commute even with the larger diameter tire, so if you are going to go with a 1.5 or smaller, get a larger chainring to go with it. I'm about to make that switch myself and get rid of the P.O.S. biopace ring that I have...

I have Michelin Wildgripper City's, they are a brilliant commuting tyre.

Schwalbe make decent semi-slick tires for commuting as well. Currently I'm running Schwalbe Marathon's. Cannot remember the specks off the top of my head.

--J

I'm using IRC 80 / 20's on my mtb to commute. They are heavy, but they hold up well, and the 80% smooth patch beats the daylights out of the knobbies I took off!

there are a lot of sizes.. I personally like the 1.15 ones.. But if you have gravel paths, you might want the 1.38 slicks.

Originally posted by Juha
Schwalbe make decent semi-slick tires for commuting as well. Currently I'm running Schwalbe Marathon's. Cannot remember the specks off the top of my head.

Schwalbe's newest full slick is the Stelvio. If I remember correctly, it's a narrow 1.1", 125 psi, 26-inch tire. It's of dual compound construction (different rubber on tread surface and sidewalls) and has a puncture-resistant liner and Kevlar bead. Supposedly a very, very fast tire.

Incidentally, I just made a quick trip down to the office on my mountain bike, and this time I strapped my cheap digital watch to my handlebar to gauge my cadence. Even with a 46 x 11 x 2.35", I'm hitting 85-100+ rpm on the way in.

I actually try to stay near the 30mph speed limit on the steepest section of the descent by feel (in my younger days, I hit 55mph/90kph on this section with my road bike), but even then I'm nearly wrapped out simply keeping up with traffic, which I guess is doing around 33mph there.

FWIW I went from knobbies to slick on my MTB-turned-commuter and I was
whizzing along doing 20-22 mph on the way into work and with knobbies
that thing always wanted to go 17-19 mph. YMMV.

I ride continental top touring 2000, 26 X 1.75, they roll nicely, flat little and last around 5000 miles. They also carry loaded panniers well at 45 psi. I also use them on my touring bike 700 X 32C, they too roll well and ride great loaded.

I'm in Brisbane too, Ramon. Which bike shop was this? Perhaps I can recommend a better one.

I've been using Geax (made by Vittorio) slicks recently. They can be run at high pressure (100psi +) and have a thick enough tread that they're reasonably puncture resistant. I found that even going from the T & Cs to a thinner, slicker tyre added a few kms to my normal cruising speed. I also agree about the sidewall issue on the T & Cs.

Knobbies on the road? I'd rather have gum surgery.

Originally posted by Allister
Knobbies on the road? I'd rather have gum surgery.

:roflmao: :roflmao:
I was talking about my last ride on the road with a knobbie-equipped MTB (from home to Fern Tree and the start of the Pipeline Track just before last Xmas). Wish I had that line -- it's the perfect description of how it felt!

Hi,
this is what Thorn bicycles Co. has to say..l...
"Why 26" wheels?
We believe that apart from very specific uses (time trialling, road racing, track racing and possibly some
Audax riding / very fast touring), the 26” (MTB) wheel is the most desirable wheel to specify for your new cycle. There is so much variety now on offer, in both tyres and rims, that the perfect combination for any solo application is possible. We have, at one extreme, a rear wheel built with a lightweight 28 hole Shimano XTR hub, DT revolution spokes (with alloy nipples) and Mavic X517 rim weighing in at 862g! Marry this with a 1.5" folding Panaracer Hi Road tyre and latex tube and you have a very fast, comfortable, reliable and ultralight combination that makes 700 x 28 feel sluggish, heavy and bone jarringly uncomfortable. At the other extreme we have 48 hole Shimano XT tandem hubs (spaced for solo use), DT 2.0mm plain gauge spokes (brass nipples) and Sun Rhyno rims which, when mounted with Schwalbe Marathon XR 1.95" tyres, and heavy duty Michelin butyl tubes, are the strongest, most durable and most reliable combination available today ... perfect for full-on expedition use on metalled or unmetalled roads or no roads at all! Between these two extremes there are many diverse combinations and beyond these extremes there are skinny (uncomfortable) 23mm racing tyres and, we understand, there are also tyres with big knobbly treads designed for off-road racing! All these tyre combinations fit the same size rim!
Tyres for this size wheel are available in every country in the world.
After conducting many experiments we have found that the rolling resistance of many of the tyres we recommend to be lower than that of narrow 700C sizes. This causes surprise to many, as skinny 700Cs have been one of cycling’s holy cows. Skinny 700C tyres are more aerodynamic, so they are still the best choice for use at higher (racing?) speeds. But we are convinced of the superiority of the 26" wheel over the 700C sized wheel. Obviously the heavier the rider, the heavier the load, and the more extreme the terrain, the more noticeable the advantages are.
We believe any open minded person will agree with our findings; and remember, we offer our 7 day money back guarantee to back this up (14 day with XTC Classic SWB & XTC 2002). "

They don't seem to mention it on this page; but they prefer the 1.4 inch size, as do I. Btw, you are gonna love it.