Paved surface, Slicks vs Fat MTB Tires: 15% diff?



P

(PeteCresswell)

Guest
Been riding with my son-in-law on-and-off for about a year now - so I'm pretty
sure of his comfortable cruising speed on the FS bike with WTB Mutano Raptors
@35 psi I let him use: it's right around 12 mph with no wind and no grade.

Last weekend, we did a 3-hour ride with one change: I put 1.25" slicks on the
bike an pumped them up to 90 psi.

His comfort-zone cruising speed seemed to go up to almost exactly 14 mph...maybe
even 14.3 or 14.5. I always let him set the pace - mostly following a little
behind and to one side, so there wasn't any 'pushing' involved.

On a few lunchtime rides during the week, I tried doing 10-miles for time on
each type of tire. Only got four rides in (2 each set of tires). My average
on the slicks was 17.4 mph. On the WTB's it was 15.6.

Overall that sounds to me like a 12-16% advantage on a paved surface for slicks
at 90 psi vs high-volume MTB tires at 35 psi.

Do those numbers hold up in anybody else's experience?
--
PeteCresswell
 
M

Matt O'Toole

Guest
(PeteCresswell) wrote:

> Been riding with my son-in-law on-and-off for about a year now - so
> I'm pretty sure of his comfortable cruising speed on the FS bike with
> WTB Mutano Raptors @35 psi I let him use: it's right around 12 mph
> with no wind and no grade.
>
> Last weekend, we did a 3-hour ride with one change: I put 1.25"
> slicks on the bike an pumped them up to 90 psi.
>
> His comfort-zone cruising speed seemed to go up to almost exactly 14
> mph...maybe even 14.3 or 14.5. I always let him set the pace -
> mostly following a little behind and to one side, so there wasn't any
> 'pushing' involved.
>
> On a few lunchtime rides during the week, I tried doing 10-miles for
> time on each type of tire. Only got four rides in (2 each set of
> tires). My average on the slicks was 17.4 mph. On the WTB's it
> was 15.6.
>
> Overall that sounds to me like a 12-16% advantage on a paved surface
> for slicks at 90 psi vs high-volume MTB tires at 35 psi.
>
> Do those numbers hold up in anybody else's experience?


I've had similar experiences. There's definately a huge difference in RR but I
think the actual speed difference is also due to psychological factors -- the
lower RR of the slicks encourages you to push harder.

There's a big difference among available MTB slicks too. Some are hardly better
than semi-slicks, but others, like the Conti Avenue, are as fast as skinny road
tires. One season when the trails were very hard-packed I left the Avenues on
for my MTB rides. My average ride times went down considerably, even though I
had to ride carefully and slowly through the more difficult dirt sections.

Matt O.
 
On Wed, 11 May 2005 19:20:34 -0700, "(PeteCresswell)"
<[email protected]> wrote:

>Been riding with my son-in-law on-and-off for about a year now - so I'm pretty
>sure of his comfortable cruising speed on the FS bike with WTB Mutano Raptors
>@35 psi I let him use: it's right around 12 mph with no wind and no grade.
>
>Last weekend, we did a 3-hour ride with one change: I put 1.25" slicks on the
>bike an pumped them up to 90 psi.
>
>His comfort-zone cruising speed seemed to go up to almost exactly 14 mph...maybe
>even 14.3 or 14.5. I always let him set the pace - mostly following a little
>behind and to one side, so there wasn't any 'pushing' involved.
>
>On a few lunchtime rides during the week, I tried doing 10-miles for time on
>each type of tire. Only got four rides in (2 each set of tires). My average
>on the slicks was 17.4 mph. On the WTB's it was 15.6.
>
>Overall that sounds to me like a 12-16% advantage on a paved surface for slicks
>at 90 psi vs high-volume MTB tires at 35 psi.
>
>Do those numbers hold up in anybody else's experience?


Dear Pete,

It sounds quite reasonable.

When I replaced the Fury Roadmaster's ferocious knobbies
with state-of-the-art $10 slicks at the same 60 psi
pressure, I set a new record on the first ride, faster than
any of the previous 250 4-mile runs (shorter and probably
flatter than your rides). I was so excited that I couldn't
do simple arithmetic:

The Fury easily set a new record on its first try,
11:52 and 20.53 mph, about 9% faster than normal--and that
was its second ride of the day.

A less excited and less innumerate poster would have divided
the right numbers (61/773) and come up with only a 7.9%
improvement.

http://groups.google.co.uk/group/rec.bicycles.tech/msg/c0f9b42fa475bd5f?hl=en

Raising your tire pressures from 35 psi to 90 psi would
improve things even more.

Carl Fogel
 
C

chalo colina

Guest
(PeteCresswell) wrote:
>
> Overall that sounds to me like a 12-16% advantage on a paved surface

for slicks
> at 90 psi vs high-volume MTB tires at 35 psi.


What is the % difference between the two tires' diameters? Did you use
the same speedometer setting for both?

That could account for part of the difference.

I know that fat knobbies _feel_ at least 15% slower than high pressure
slicks. But I'm not sure that impression would stand up to objective
scrutiny.

Chalo Colina
 
M

Mike Quin

Guest
In article <[email protected]>, (PeteCresswell) wrote:

> Overall that sounds to me like a 12-16% advantage on a paved surface for slicks
> at 90 psi vs high-volume MTB tires at 35 psi.
>
> Do those numbers hold up in anybody else's experience?


Sounds about right - my commute went from 20 minutes to 15 when I
switched from hybrid tyres (knobblies with a centre ridge) to
semi-slicks (Specialized Nimbus EX). I also found that the bike was
much easier to handle.

--
Mike Quin <[email protected]>
 
V

Victor Kan

Guest
(PeteCresswell) wrote:
> Also, there's the "aerodyne effect" that somebody else observed - wind
> resistance of the knobs. Kind of makes me want to take a disk sander to a
> couple of my old WTB casings, pump 'em up all the way, and try some more
> runs....


I vaguely recall someone's tire rolling resistance tests where the
lowest RR came from a Nokian knobby tire that had the knobs ground off.

I can't seem to find a reference, but other tables I have found on
google indicated that the Nokian City Runner tire was very low RR, but
that might have been overinflated--not sure.

--
I do not accept unsolicited commercial e-mail. Remove NO_UCE for
legitimate replies.
 
P

(PeteCresswell)

Guest
Per chalo colina:
>What is the % difference between the two tires' diameters? Did you use
>the same speedometer setting for both?
>
>That could account for part of the difference.


Beeeg diff, but speedos were calibrated so that each bike showed the same speed
when we were riding neck-and-neck.


>I know that fat knobbies _feel_ at least 15% slower than high pressure
>slicks. But I'm not sure that impression would stand up to objective
>scrutiny.


Now that somebody has introduced the idea of pumping up the knobbies, I'm still
not either.

Also, there's the "aerodyne effect" that somebody else observed - wind
resistance of the knobs. Kind of makes me want to take a disk sander to a
couple of my old WTB casings, pump 'em up all the way, and try some more
runs....
--
PeteCresswell
 
D

Dave Larrington

Guest
Victor Kan wrote:

> I vaguely recall someone's tire rolling resistance tests where the
> lowest RR came from a Nokian knobby tire that had the knobs ground
> off.


Possibly Ian Sims' tests of (mainly) small diameter tyres:

URL:http://www.legslarry.beerdrinkers.co.uk/tech/GS.htm

Back in the Old Days, HPV racers would often use BMX racing tyres with the
knobs ground off, coz decent small diameter road-stylee tyres simply didn't
exist.
--
Dave Larrington - <http://www.legslarry.beerdrinkers.co.uk/>
Pepperoni and green peppers, mushrooms, olives, chives!
 
On Fri, 20 May 2005 19:25:53 -0700, "(PeteCresswell)"
<[email protected]> wrote:

>Per Dave Larrington:
>>URL:http://www.legslarry.beerdrinkers.co.uk/tech/GS.htm

>
>What I got out of that was: on a hard surface, for all tires tested, the higher
>the pressure the lower the rolling resistance.


Dear Pete,

For pure rolling resistance, this is true when measured on a
smooth steel drum (Jobst Brandt's approach):

"Rolling resistance tests are relatively simple, once a
rolling test stand is built. In such a test, the drum on
which the loaded wheel rolls is brought to a desired speed
and allowed to coast down to a lower speed while counting
the number of revolutions and fractional revolutions. This
is a standard coast-down test that has been widely used."

http://www.terrymorse.com/bike/rrdiscuss.html

Or when measured at less-than-aerodynamic speeds on a flat
surface (Dave Larrington's approach):

"The tyre testing procedure involves rolling the tyre/wheel
combination along a flat surface and so represents the real
case of using the tyre on the road. The tyre is also loaded
with a representative weight and rolled at a controlled
speed. The speed of rolling is slow so that aerodynamic
forces do not come into play."

http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm

Both methods give a very good idea of the relative rolling
resistance of tires under pure test conditions, which is
useful.

But on real pavement, which is quite hard, the surprise is
that higher unsuspended bicycle tire pressures soon lead to
greater rolling resistance not seen in pure tests.

The reason is that the highly inflated tires start bouncing
the rider and bike higher and higher on ordinary hard
surface irregularities that lower pressures smoothed out
with less effort.

So higher pressures pay off on smoother surfaces--wooden
tracks are smoother, though not as hard as pavement, so
track bikes can benefit from impressively inflated tires.

Lennard Zinn explains this idea, points out that we often
confuse a "livelier" ride on harder tires with a faster
ride, and mentions that the fastest real road tire pressures
are usually closer to 100 psi than to 170:

http://www.ottawabicycleclub.ca/phpBB2/viewtopic.php?t=137&

Carl Fogel
 
K

Ken

Guest
"(PeteCresswell)" <[email protected]> wrote in message
news:[email protected]
> Per Dave Larrington:
>>URL:http://www.legslarry.beerdrinkers.co.uk/tech/GS.htm

>
> What I got out of that was: on a hard surface, for all tires tested, the
> higher
> the pressure the lower the rolling resistance.
> --
> PeteCresswell


What I got out of this thread was yes higher pressures do lower rolling
resistance on smoother surfaces.

Seems to me from my own experiences that this is true. I have tried
experiments with actual tires on actual bikes on actual roads, and found, in
my opinion that under most conditions higher pressures to lower the
resistance.

Ken
 
P

(PeteCresswell)

Guest
Per [email protected]:
>But on real pavement, which is quite hard, the surprise is...



I've kept this taped to my workstation ever
since I saw it in somebody's sig:
-----------------------------------------
"The important things are usually simple.
The simple things are usually hard.
The easy path is always mined."
-----------------------------------------
(Anonymous)

--
PeteCresswell
 

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