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Main
Date: 23 Sep 2007 01:30:56
From: Bill
Subject: 700x25 tire + 30mm aero wheel instability
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Surprising experience, bike has become unstable at higher sppe with wider
tires. I have a pair of Mavic Expert semi aero 30mm wheels that I have
ridden for years with 700x23 tires. They have always tracked well and
ridden very predictably. A few weeks ago I decided to add some comfort and
went to 700x25s. Same brand/model of tire, Michelin Pro Race. At higher
speeds the bike suddenly wanted to wander and veer from side to side. at
first I thought the carbon steerer might be damaged. I pulled the for to
double check. Certainly looks rock solid.
Turns out the problem is repeatable at 28 + mph. I believe the very round
profile of the larger 700x25 in conjunction with the aero rim is acting as a
wing. When the airflow is slightly off center at 28 mph and up it creates
lift that pushes the wheel on direction or the other. When it is brought
back across center the lift is transferred to the other side and forces
oversteer and instability. Anyone else experienced this problem with an
aero wheel and larger OD tire?
Bill
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Date: 27 Sep 2007 07:15:46
From: joseph.santaniello@gmail.com
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
On Sep 27, 3:01 am, Dan Becker <No...@address.invalid > wrote:
> In article <1190790537.536299.247...@g4g2000hsf.googlegroups.com>,
>
> <"joseph.santanie...@gmail.com"> wrote:
> > On Sep 26, 4:00 am, Dan Becker <No...@address.invalid> wrote:
> > > In article <1190705332.283202.31...@y42g2000hsy.googlegroups.com>,
> > > Wow. Using that chart, figuring total weight for bike and rider as
> > > Wayne indicated, pressures for me are about 88 psi front and 109 psi
> > > rear!
>
> > Yep! Give it a try.
>
> I did this afternoon. I have an open mind, but it really wasn't a fair
> test. I had the bike set up for TT/Tri (one of the interesting features
> of the Soloist Team), which was the first time I have ever ridden that
> geometry. Interesting; I can see the benefits to going fast with it.
> Also, since the bike is new, the shifter cables are stretching and the
> shifting quickly went south, so a lot of hunting around and never got a
> rhythm going. So there were too many variables at work to really get a
> good sense. But it wasn't a disaster feeling, so I'm going to continue
> to try it out for a bit.
With a TT setup you will probably have a differnt weight distro than
suggested on the chart. You might want some more air up front as a
result.
> > > My riding is strictly fast road for short duration...mostly 1 to 1.5
> > > hour rides, with some 2 to 3 hour spins on weekends. So I'm not looking
> > > for comfort, speed is my demon, so I like tires hard and fast.
>
> > Comfort is a relative term. My riding sounds similar to yours, so I
> > think I know what you're after. Comfort doesn't mean slow...
>
> Agreed. Just noting that a "vertically compliant" (man, I'm getting
> tired of that phrase) ride is not a major factor to me in my riding
> style and choice of machines or tires. But if this approach doesn't
> have a speed penalty, then I'm certainly not opposed to less shake,
> rattle, and roll.
Buzz is no good, and if the road is rough, not too much air might be
faster.
Joseph
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Date: 27 Sep 2007 07:02:29
From: Dan Becker
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
In article <1190877346.182206.4180@22g2000hsm.googlegroups.com >,
<"joseph.santaniello@gmail.com" > wrote:
> On Sep 27, 3:01 am, Dan Becker <No...@address.invalid> wrote:
> > In article <1190790537.536299.247...@g4g2000hsf.googlegroups.com>,
> With a TT setup you will probably have a differnt weight distro than
> suggested on the chart. You might want some more air up front as a
> result.
I took that into account and adjusted the pressures accordingly.
> > Agreed. Just noting that a "vertically compliant" (man, I'm getting
> > tired of that phrase) ride is not a major factor to me in my riding
> > style and choice of machines or tires. But if this approach doesn't
> > have a speed penalty, then I'm certainly not opposed to less shake,
> > rattle, and roll.
>
> Buzz is no good, and if the road is rough, not too much air might be
> faster.
That's what Wayne's post lead me to believe; I should have chosen my
words less pejoratively than saying "doesn't have a speed penalty."
What you guys are clearly saying is that it is rather a case of having
my cake and eating it too.
I'm appreciative to all for the replies. This is a fascinating,
counter-intuitive discussion for me.
Dan
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Date: 26 Sep 2007 21:14:05
From:
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
On Sep 25, 11:16 am, Wayne Pein <wp...@nc.rr.com > wrote:
> Dan Becker wrote:
> > In article <1190619362.457543.233...@y42g2000hsy.googlegroups.com>,
> > <"joseph.santanie...@gmail.com"> wrote:
>
> >>Not that I think it has anything to do with the problem, but 100psi in
> >>the Michelin 25's sounds like a lot to me, particularly if 105
> >>suffices in the 23's.
>
> > I just bought a Cervelo Team Soloist that arrived with Vittoria 25s,
> > don't remember the exact model. It is the first time I have ridden
> > anything bigger than 23s. They are big round donut things, no real
> > apparent sidewall, in cross-section just a treadless smooth circle of
> > tire compound.
>
> > The sidewall says inflate to minimum 140 psi, max 160 psi. The Vittoria
> > rim tape says max 145 psi (yep, a slow leak puncture flat on the second
> > ride, so I'm not too impressed with the casing on these things).
>
> > I'm curious about your 100 psi "sounding like a lot." Is that a blanket
> > statement, or particular to Michelin tires?
>
> > I'm 6-2, 195 lbs, so not a lightweight but not quite a Clydesdale.
>
> > I'd welcome insight on pressure for these tires, given your experience.
>
> The optimum combination of comfort, cornering ability, and low rolling
> resistance comes from a tire drop of about 15% of tire width. A total
> weight of 195 plus 20 lb bike (215 lbs) with a 25C tire shows an ideal
> inflation pressure of 95 lbs from an old graph I have.
>
> This doesn't account for differing loads on the front and rear tires.
> The rear has greater load, so the front and rear tires should have
> slightly different pressures. A recent article in Bicycle Quarterly did
> address it though, but I've lent it to a friend so can't relate the info
> to you.
>
> Wayne- Hide quoted text -
>
> - Show quoted text -
Frank Berto wrote an article promoting the 15% drop that is available
for a small fee if you are a member at www.roadbikerider.com. It's
about six printed pages long.
Smokey
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Date: 26 Sep 2007 07:08:57
From: joseph.santaniello@gmail.com
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
On Sep 26, 4:00 am, Dan Becker <No...@address.invalid > wrote:
> In article <1190705332.283202.31...@y42g2000hsy.googlegroups.com>,
>
> <"joseph.santanie...@gmail.com"> wrote:
> > On Sep 25, 3:23 am, Dan Becker <No...@address.invalid> wrote:
> > > In article <1190619362.457543.233...@y42g2000hsy.googlegroups.com>,
>
> > > Vittoria 25s,
> > > don't remember the exact model. They are big round donut things, no real
> > > apparent sidewall, in cross-section just a treadless smooth circle of
> > > tire compound.
>
> > Mmm. Sounds comfy! What model? Sounds like a tire I'd like. 25 and no
> > tread. The Michelins are too big for my frame so leaves and junk get
> > jammed.
>
> Diamonte Pro Light, 25-622, 700x25C. I misspoke below...the pressure
> range on the sidewall is 130 psi (9 bar) to 160 psi (11 bar).
>
>
>
> > > The sidewall says inflate to minimum 140 psi, max 160 psi.
>
> > > I'm 6-2, 195 lbs, so not a lightweight but not quite a Clydesdale.
>
> > It was a qualified blank statement. I figured that if 105 was the
> > "proper" inflation for you with 23's, then 100 for the 25's was too
> > much. But now seeing your weight, I think perhaps the 100 is a bit
> > high and the 105 a bit low. The Michelin 25's are extra big so they
> > almost count as 28's.
>
> > I'm 6'3" 215-230 (dependent upon many factors WAY outside the scope of
> > this post!) and I use around 90-95psi with the Michelin 25's, but with
> > narrower tires like Veloflex Pave 22's I need to go as high as 130 or
> > so. For the most part now I use Vittoria Pave 24's which I pump up to
> > about 110 when I care, but when I'm just going for a ride, as long as
> > they are hard I just ride.
>
> > Here's a handy chart that shows various casing sizes and load weights
> > (per wheel) for figuring tire pressure:
>
> >http://tinyurl.com/yukgw3
>
> Wow. Using that chart, figuring total weight for bike and rider as
> Wayne indicated, pressures for me are about 88 psi front and 109 psi
> rear!
Yep! Give it a try.
> My riding is strictly fast road for short duration...mostly 1 to 1.5
> hour rides, with some 2 to 3 hour spins on weekends. So I'm not looking
> for comfort, speed is my demon, so I like tires hard and fast.
Comfort is a relative term. My riding sounds similar to yours, so I
think I know what you're after. Comfort doesn't mean slow...
> These numbers are so far below the range imprinted on the tire casing.
> What am I missing here? Seems like such a soft tire would put the rims
> at risk of damage on road hazard impact.
The range printed is I think more to attest to the strength of the
casing. While the risk of pinch flats is greater, the 15% droop should
be enough to protect the wheel.
Joseph
Joseph
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| | |
Date: 26 Sep 2007 21:01:13
From: Dan Becker
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
In article <1190790537.536299.247230@g4g2000hsf.googlegroups.com >,
<"joseph.santaniello@gmail.com" > wrote:
> On Sep 26, 4:00 am, Dan Becker <No...@address.invalid> wrote:
> > In article <1190705332.283202.31...@y42g2000hsy.googlegroups.com>,
> > Wow. Using that chart, figuring total weight for bike and rider as
> > Wayne indicated, pressures for me are about 88 psi front and 109 psi
> > rear!
>
> Yep! Give it a try.
I did this afternoon. I have an open mind, but it really wasn't a fair
test. I had the bike set up for TT/Tri (one of the interesting features
of the Soloist Team), which was the first time I have ever ridden that
geometry. Interesting; I can see the benefits to going fast with it.
Also, since the bike is new, the shifter cables are stretching and the
shifting quickly went south, so a lot of hunting around and never got a
rhythm going. So there were too many variables at work to really get a
good sense. But it wasn't a disaster feeling, so I'm going to continue
to try it out for a bit.
> > My riding is strictly fast road for short duration...mostly 1 to 1.5
> > hour rides, with some 2 to 3 hour spins on weekends. So I'm not looking
> > for comfort, speed is my demon, so I like tires hard and fast.
>
> Comfort is a relative term. My riding sounds similar to yours, so I
> think I know what you're after. Comfort doesn't mean slow...
Agreed. Just noting that a "vertically compliant" (man, I'm getting
tired of that phrase) ride is not a major factor to me in my riding
style and choice of machines or tires. But if this approach doesn't
have a speed penalty, then I'm certainly not opposed to less shake,
rattle, and roll.
Dan
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Date: 26 Sep 2007 07:05:12
From: joseph.santaniello@gmail.com
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
On Sep 26, 5:11 am, Paul Myron Hobson <phob...@gatech.edu > wrote:
> > <"joseph.santanie...@gmail.com"> wrote:
> >> Here's a handy chart that shows various casing sizes and load weights
> >> (per wheel) for figuring tire pressure:
>
> >>http://tinyurl.com/yukgw3
> Dan Becker wrote:
> > Wow. Using that chart, figuring total weight for bike and rider as
> > Wayne indicated, pressures for me are about 88 psi front and 109 psi
> > rear!
>
> > My riding is strictly fast road for short duration...mostly 1 to 1.5
> > hour rides, with some 2 to 3 hour spins on weekends. So I'm not looking
> > for comfort, speed is my demon, so I like tires hard and fast.
>
> > These numbers are so far below the range imprinted on the tire casing.
> > What am I missing here? Seems like such a soft tire would put the rims
> > at risk of damage on road hazard impact.
>
> That chart is shooting for 15% vertical deflection of the tire sidewall,
> which is not a whole lot. That should optimize your contact patch,
> therefore your rolling resistance should be optimized as well, IIRC (I
> probably don't).
>
> \\paul
Yes, and too hard particularly on less than perfect surfaces will
perhaps actually increase rolling resistance, and probably reduce
traction.
Joseph
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Date: 26 Sep 2007 11:43:21
From: Wayne Pein
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
joseph.santaniello@gmail.com wrote:
>
>
> Yes, and too hard particularly on less than perfect surfaces will
> perhaps actually increase rolling resistance, and probably reduce
> traction.
>
This is what the testing in Vintage Bicycle Quarterly (now Bicycle
Quarterly) showed. If the tire is supple and the inflation pressure
lower, the tire absorbs the imperfections rather than the bicycle and
rider and thus rolls faster. With a stiff casing and hard pressure, the
bike and rider bounce vertically and are slower.
Wayne
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Date: 25 Sep 2007 00:28:52
From: joseph.santaniello@gmail.com
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
On Sep 25, 3:23 am, Dan Becker <No...@address.invalid > wrote:
> In article <1190619362.457543.233...@y42g2000hsy.googlegroups.com>,
>
> <"joseph.santanie...@gmail.com"> wrote:
> > Not that I think it has anything to do with the problem, but 100psi in
> > the Michelin 25's sounds like a lot to me, particularly if 105
> > suffices in the 23's.
>
> I just bought a Cervelo Team Soloist that arrived with Vittoria 25s,
> don't remember the exact model. It is the first time I have ridden
> anything bigger than 23s. They are big round donut things, no real
> apparent sidewall, in cross-section just a treadless smooth circle of
> tire compound.
Mmm. Sounds comfy! What model? Sounds like a tire I'd like. 25 and no
tread. The Michelins are too big for my frame so leaves and junk get
jammed.
> The sidewall says inflate to minimum 140 psi, max 160 psi. The Vittoria
> rim tape says max 145 psi (yep, a slow leak puncture flat on the second
> ride, so I'm not too impressed with the casing on these things).
> I'm curious about your 100 psi "sounding like a lot." Is that a blanket
> statement, or particular to Michelin tires?
>
> I'm 6-2, 195 lbs, so not a lightweight but not quite a Clydesdale.
>
> I'd welcome insight on pressure for these tires, given your experience.
>
> Thanks,
> Dan
It was a qualified blank statement. I figured that if 105 was the
"proper" inflation for you with 23's, then 100 for the 25's was too
much. But now seeing your weight, I think perhaps the 100 is a bit
high and the 105 a bit low. The Michelin 25's are extra big so they
almost count as 28's.
I'm 6'3" 215-230 (dependent upon many factors WAY outside the scope of
this post!) and I use around 90-95psi with the Michelin 25's, but with
narrower tires like Veloflex Pave 22's I need to go as high as 130 or
so. For the most part now I use Vittoria Pave 24's which I pump up to
about 110 when I care, but when I'm just going for a ride, as long as
they are hard I just ride.
Here's a handy chart that shows various casing sizes and load weights
(per wheel) for figuring tire pressure:
http://tinyurl.com/yukgw3
Joseph
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Date: 25 Sep 2007 22:00:40
From: Dan Becker
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
In article <1190705332.283202.31080@y42g2000hsy.googlegroups.com >,
<"joseph.santaniello@gmail.com" > wrote:
> On Sep 25, 3:23 am, Dan Becker <No...@address.invalid> wrote:
> > In article <1190619362.457543.233...@y42g2000hsy.googlegroups.com>,
> >
> > Vittoria 25s,
> > don't remember the exact model. They are big round donut things, no real
> > apparent sidewall, in cross-section just a treadless smooth circle of
> > tire compound.
>
> Mmm. Sounds comfy! What model? Sounds like a tire I'd like. 25 and no
> tread. The Michelins are too big for my frame so leaves and junk get
> jammed.
Diamonte Pro Light, 25-622, 700x25C. I misspoke below...the pressure
range on the sidewall is 130 psi (9 bar) to 160 psi (11 bar).
> > The sidewall says inflate to minimum 140 psi, max 160 psi.
> >
> > I'm 6-2, 195 lbs, so not a lightweight but not quite a Clydesdale.
>
> It was a qualified blank statement. I figured that if 105 was the
> "proper" inflation for you with 23's, then 100 for the 25's was too
> much. But now seeing your weight, I think perhaps the 100 is a bit
> high and the 105 a bit low. The Michelin 25's are extra big so they
> almost count as 28's.
>
> I'm 6'3" 215-230 (dependent upon many factors WAY outside the scope of
> this post!) and I use around 90-95psi with the Michelin 25's, but with
> narrower tires like Veloflex Pave 22's I need to go as high as 130 or
> so. For the most part now I use Vittoria Pave 24's which I pump up to
> about 110 when I care, but when I'm just going for a ride, as long as
> they are hard I just ride.
>
> Here's a handy chart that shows various casing sizes and load weights
> (per wheel) for figuring tire pressure:
>
> http://tinyurl.com/yukgw3
Wow. Using that chart, figuring total weight for bike and rider as
Wayne indicated, pressures for me are about 88 psi front and 109 psi
rear!
My riding is strictly fast road for short duration...mostly 1 to 1.5
hour rides, with some 2 to 3 hour spins on weekends. So I'm not looking
for comfort, speed is my demon, so I like tires hard and fast.
These numbers are so far below the range imprinted on the tire casing.
What am I missing here? Seems like such a soft tire would put the rims
at risk of damage on road hazard impact.
Dan
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Date: 26 Sep 2007 11:47:48
From: Wayne Pein
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
Dan Becker wrote:
> These numbers are so far below the range imprinted on the tire casing.
> What am I missing here? Seems like such a soft tire would put the rims
> at risk of damage on road hazard impact.
>
My guess is their range is really their maximum. Most tires show a
single max (not a range) far below those Diamontes.
Wayne
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| | | |
Date: 25 Sep 2007 23:11:55
From: Paul Myron Hobson
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
> <"joseph.santaniello@gmail.com"> wrote:
>> Here's a handy chart that shows various casing sizes and load weights
>> (per wheel) for figuring tire pressure:
>>
>> http://tinyurl.com/yukgw3
Dan Becker wrote:
> Wow. Using that chart, figuring total weight for bike and rider as
> Wayne indicated, pressures for me are about 88 psi front and 109 psi
> rear!
>
> My riding is strictly fast road for short duration...mostly 1 to 1.5
> hour rides, with some 2 to 3 hour spins on weekends. So I'm not looking
> for comfort, speed is my demon, so I like tires hard and fast.
>
> These numbers are so far below the range imprinted on the tire casing.
> What am I missing here? Seems like such a soft tire would put the rims
> at risk of damage on road hazard impact.
That chart is shooting for 15% vertical deflection of the tire sidewall,
which is not a whole lot. That should optimize your contact patch,
therefore your rolling resistance should be optimized as well, IIRC (I
probably don't).
\\paul
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| |
Date: 24 Sep 2007 00:36:02
From: joseph.santaniello@gmail.com
Subject: Re: 700x25 tire + 30mm aero wheel instability
|
On Sep 24, 12:16 am, "Bill" <b...@example.invalid > wrote:
> "Kinky Cowboy" <u...@domain.com> wrote in message
>
> news:pgccf31u79lp29tdhc8hv903o9mmraluch@4ax.com...
>
> > On Sun, 23 Sep 2007 01:49:31 -0700, "joseph.santanie...@gmail.com"
> > <joseph.santanie...@gmail.com> wrote:
>
> > >On Sep 23, 3:30 am, "Bill" <b...@example.invalid> wrote:
> > >> Surprising experience, bike has become unstable at higher sppe with
> wider
> > >> tires. I have a pair of Mavic Expert semi aero 30mm wheels that I have
> > >> ridden for years with 700x23 tires. They have always tracked well and
> > >> ridden very predictably. A few weeks ago I decided to add some comfort
> and
> > >> went to 700x25s. Same brand/model of tire, Michelin Pro Race. At higher
> > >> speeds the bike suddenly wanted to wander and veer from side to side.
> at
> > >> first I thought the carbon steerer might be damaged. I pulled the for
> to
> > >> double check. Certainly looks rock solid.
>
> > >> Turns out the problem is repeatable at 28 + mph. I believe the very
> round
> > >> profile of the larger 700x25 in conjunction with the aero rim is acting
> as a
> > >> wing. When the airflow is slightly off center at 28 mph and up it
> creates
> > >> lift that pushes the wheel on direction or the other. When it is
> brought
> > >> back across center the lift is transferred to the other side and forces
> > >> oversteer and instability. Anyone else experienced this problem with
> an
> > >> aero wheel and larger OD tire?
> > >> Bill
>
> > >Strange. I've used Michelin Pro Race 25's on Velocity Deep-V's and
> > >narrower tires as well and have not noticed what you have found. When
> > >it is windy, both types of tires exhibit some instability, but very
> > >minor and only at speeds well above 28mph.
>
> > >Here's a theory: The larger wheel diameter is changing you trail and a
> > >combination of things is making this 28mph threshold show this
> > >behavior.
>
> > >Another idea is that the tire isn't round as mounted. I've had
> > >problems getting the beads to seat properly with the 25 Pro Races.
>
> > What about tyre pressure? Getting a 25 for extra comfort implies lower
> > pressure, which combined the wide tyre/narrow base which inherently
> > reduces tyre stability is all going in the same direction. Also, the
> > tyre mass is increased, which increases moment of inertia about the
> > steering axis.
>
> > Bigger tyres actually increase trail, which might also lower the onset
> > speed of 'shimmy', if that's what you're experiencing.
>
> > FWIW, I used to run 700x37 tyres on a narrow Shimano R500 semi-aero
> > wheel and never had any problems up to the highest recorded speed of
> > 47mph, but I bet a straight guage steel Kona Project2 fork is stiffer
> > than any carbon road fork.
>
> > Kinky Cowboy*
>
> > *Batteries not included
> > May contain traces of nuts
> > Your milage may vary
>
> Tires appear round and properly mounted, Tire pressure is 100 psi, I run 105
> in the 23s. I'll put the front one on an Open 4cd Monday or Tuesday post
> what I find. These same wheels on this bike have been over 50 mph numerous
> times and never exhibited any undesirable traits.The bike is a Serotta CSI
> that has always been well behaved. Unlike its predecessor, a Serotta CRL,
> that was a whippy shimmying noodle. One note, the front end feels like it is
> being pushed to one side and when corrected, pushed to the opposite side. It
> is not a oscillation. If I let it go it would just corner -until I ran off
> the road- in the direction it started in.
> Bill
> Bill
Not that I think it has anything to do with the problem, but 100psi in
the Michelin 25's sounds like a lot to me, particularly if 105
suffices in the 23's.
Joseph
|
| | |
Date: 24 Sep 2007 21:23:56
From: Dan Becker
Subject: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
In article <1190619362.457543.233080@y42g2000hsy.googlegroups.com >,
<"joseph.santaniello@gmail.com" > wrote:
> Not that I think it has anything to do with the problem, but 100psi in
> the Michelin 25's sounds like a lot to me, particularly if 105
> suffices in the 23's.
I just bought a Cervelo Team Soloist that arrived with Vittoria 25s,
don't remember the exact model. It is the first time I have ridden
anything bigger than 23s. They are big round donut things, no real
apparent sidewall, in cross-section just a treadless smooth circle of
tire compound.
The sidewall says inflate to minimum 140 psi, max 160 psi. The Vittoria
rim tape says max 145 psi (yep, a slow leak puncture flat on the second
ride, so I'm not too impressed with the casing on these things).
I'm curious about your 100 psi "sounding like a lot." Is that a blanket
statement, or particular to Michelin tires?
I'm 6-2, 195 lbs, so not a lightweight but not quite a Clydesdale.
I'd welcome insight on pressure for these tires, given your experience.
Thanks,
Dan
|
| | | |
Date: 25 Sep 2007 12:16:59
From: Wayne Pein
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
Dan Becker wrote:
> In article <1190619362.457543.233080@y42g2000hsy.googlegroups.com>,
> <"joseph.santaniello@gmail.com"> wrote:
>
>
>>Not that I think it has anything to do with the problem, but 100psi in
>>the Michelin 25's sounds like a lot to me, particularly if 105
>>suffices in the 23's.
>
>
> I just bought a Cervelo Team Soloist that arrived with Vittoria 25s,
> don't remember the exact model. It is the first time I have ridden
> anything bigger than 23s. They are big round donut things, no real
> apparent sidewall, in cross-section just a treadless smooth circle of
> tire compound.
>
> The sidewall says inflate to minimum 140 psi, max 160 psi. The Vittoria
> rim tape says max 145 psi (yep, a slow leak puncture flat on the second
> ride, so I'm not too impressed with the casing on these things).
>
> I'm curious about your 100 psi "sounding like a lot." Is that a blanket
> statement, or particular to Michelin tires?
>
> I'm 6-2, 195 lbs, so not a lightweight but not quite a Clydesdale.
>
> I'd welcome insight on pressure for these tires, given your experience.
>
The optimum combination of comfort, cornering ability, and low rolling
resistance comes from a tire drop of about 15% of tire width. A total
weight of 195 plus 20 lb bike (215 lbs) with a 25C tire shows an ideal
inflation pressure of 95 lbs from an old graph I have.
This doesn't account for differing loads on the front and rear tires.
The rear has greater load, so the front and rear tires should have
slightly different pressures. A recent article in Bicycle Quarterly did
address it though, but I've lent it to a friend so can't relate the info
to you.
Wayne
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Date: 25 Sep 2007 07:54:15
From: Lou Holtman
Subject: Re: Inflation pressure [was: 700x25 tire + 30mm aero wheel instability]
|
Dan Becker wrote:
> In article <1190619362.457543.233080@y42g2000hsy.googlegroups.com>,
> <"joseph.santaniello@gmail.com"> wrote:
>
>> Not that I think it has anything to do with the problem, but 100psi in
>> the Michelin 25's sounds like a lot to me, particularly if 105
>> suffices in the 23's.
>
> I just bought a Cervelo Team Soloist that arrived with Vittoria 25s,
> don't remember the exact model. It is the first time I have ridden
> anything bigger than 23s. They are big round donut things, no real
> apparent sidewall, in cross-section just a treadless smooth circle of
> tire compound.
>
> The sidewall says inflate to minimum 140 psi, max 160 psi. The Vittoria
> rim tape says max 145 psi (yep, a slow leak puncture flat on the second
> ride, so I'm not too impressed with the casing on these things).
>
> I'm curious about your 100 psi "sounding like a lot." Is that a blanket
> statement, or particular to Michelin tires?
>
> I'm 6-2, 195 lbs, so not a lightweight but not quite a Clydesdale.
>
> I'd welcome insight on pressure for these tires, given your experience.
>
> Thanks,
> Dan
I would say experiment a bit, starting at 6.5 bar and up. My guess is
around 7 bar is OK for your weight.
Lou
--
Posted by news://news.nb.nu (http://www.nb.nu)
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Date: 23 Sep 2007 01:49:31
From: joseph.santaniello@gmail.com
Subject: Re: 700x25 tire + 30mm aero wheel instability
|
On Sep 23, 3:30 am, "Bill" <b...@example.invalid > wrote:
> Surprising experience, bike has become unstable at higher sppe with wider
> tires. I have a pair of Mavic Expert semi aero 30mm wheels that I have
> ridden for years with 700x23 tires. They have always tracked well and
> ridden very predictably. A few weeks ago I decided to add some comfort and
> went to 700x25s. Same brand/model of tire, Michelin Pro Race. At higher
> speeds the bike suddenly wanted to wander and veer from side to side. at
> first I thought the carbon steerer might be damaged. I pulled the for to
> double check. Certainly looks rock solid.
>
> Turns out the problem is repeatable at 28 + mph. I believe the very round
> profile of the larger 700x25 in conjunction with the aero rim is acting as a
> wing. When the airflow is slightly off center at 28 mph and up it creates
> lift that pushes the wheel on direction or the other. When it is brought
> back across center the lift is transferred to the other side and forces
> oversteer and instability. Anyone else experienced this problem with an
> aero wheel and larger OD tire?
> Bill
Strange. I've used Michelin Pro Race 25's on Velocity Deep-V's and
narrower tires as well and have not noticed what you have found. When
it is windy, both types of tires exhibit some instability, but very
minor and only at speeds well above 28mph.
Here's a theory: The larger wheel diameter is changing you trail and a
combination of things is making this 28mph threshold show this
behavior.
Another idea is that the tire isn't round as mounted. I've had
problems getting the beads to seat properly with the 25 Pro Races.
Joseph
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Date: 23 Sep 2007 10:42:30
From: Kinky Cowboy
Subject: Re: 700x25 tire + 30mm aero wheel instability
|
On Sun, 23 Sep 2007 01:49:31 -0700, "joseph.santaniello@gmail.com"
<joseph.santaniello@gmail.com > wrote:
>On Sep 23, 3:30 am, "Bill" <b...@example.invalid> wrote:
>> Surprising experience, bike has become unstable at higher sppe with wider
>> tires. I have a pair of Mavic Expert semi aero 30mm wheels that I have
>> ridden for years with 700x23 tires. They have always tracked well and
>> ridden very predictably. A few weeks ago I decided to add some comfort and
>> went to 700x25s. Same brand/model of tire, Michelin Pro Race. At higher
>> speeds the bike suddenly wanted to wander and veer from side to side. at
>> first I thought the carbon steerer might be damaged. I pulled the for to
>> double check. Certainly looks rock solid.
>>
>> Turns out the problem is repeatable at 28 + mph. I believe the very round
>> profile of the larger 700x25 in conjunction with the aero rim is acting as a
>> wing. When the airflow is slightly off center at 28 mph and up it creates
>> lift that pushes the wheel on direction or the other. When it is brought
>> back across center the lift is transferred to the other side and forces
>> oversteer and instability. Anyone else experienced this problem with an
>> aero wheel and larger OD tire?
>> Bill
>
>Strange. I've used Michelin Pro Race 25's on Velocity Deep-V's and
>narrower tires as well and have not noticed what you have found. When
>it is windy, both types of tires exhibit some instability, but very
>minor and only at speeds well above 28mph.
>
>Here's a theory: The larger wheel diameter is changing you trail and a
>combination of things is making this 28mph threshold show this
>behavior.
>
>Another idea is that the tire isn't round as mounted. I've had
>problems getting the beads to seat properly with the 25 Pro Races.
>
What about tyre pressure? Getting a 25 for extra comfort implies lower
pressure, which combined the wide tyre/narrow base which inherently
reduces tyre stability is all going in the same direction. Also, the
tyre mass is increased, which increases moment of inertia about the
steering axis.
Bigger tyres actually increase trail, which might also lower the onset
speed of 'shimmy', if that's what you're experiencing.
FWIW, I used to run 700x37 tyres on a narrow Shimano R500 semi-aero
wheel and never had any problems up to the highest recorded speed of
47mph, but I bet a straight guage steel Kona Project2 fork is stiffer
than any carbon road fork.
Kinky Cowboy*
*Batteries not included
May contain traces of nuts
Your milage may vary
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| | | |
Date: 23 Sep 2007 22:16:55
From: Bill
Subject: Re: 700x25 tire + 30mm aero wheel instability
|
"Kinky Cowboy" <user@domain.com > wrote in message
news:pgccf31u79lp29tdhc8hv903o9mmraluch@4ax.com...
> On Sun, 23 Sep 2007 01:49:31 -0700, "joseph.santaniello@gmail.com"
> <joseph.santaniello@gmail.com> wrote:
>
> >On Sep 23, 3:30 am, "Bill" <b...@example.invalid> wrote:
> >> Surprising experience, bike has become unstable at higher sppe with
wider
> >> tires. I have a pair of Mavic Expert semi aero 30mm wheels that I have
> >> ridden for years with 700x23 tires. They have always tracked well and
> >> ridden very predictably. A few weeks ago I decided to add some comfort
and
> >> went to 700x25s. Same brand/model of tire, Michelin Pro Race. At higher
> >> speeds the bike suddenly wanted to wander and veer from side to side.
at
> >> first I thought the carbon steerer might be damaged. I pulled the for
to
> >> double check. Certainly looks rock solid.
> >>
> >> Turns out the problem is repeatable at 28 + mph. I believe the very
round
> >> profile of the larger 700x25 in conjunction with the aero rim is acting
as a
> >> wing. When the airflow is slightly off center at 28 mph and up it
creates
> >> lift that pushes the wheel on direction or the other. When it is
brought
> >> back across center the lift is transferred to the other side and forces
> >> oversteer and instability. Anyone else experienced this problem with
an
> >> aero wheel and larger OD tire?
> >> Bill
> >
> >Strange. I've used Michelin Pro Race 25's on Velocity Deep-V's and
> >narrower tires as well and have not noticed what you have found. When
> >it is windy, both types of tires exhibit some instability, but very
> >minor and only at speeds well above 28mph.
> >
> >Here's a theory: The larger wheel diameter is changing you trail and a
> >combination of things is making this 28mph threshold show this
> >behavior.
> >
> >Another idea is that the tire isn't round as mounted. I've had
> >problems getting the beads to seat properly with the 25 Pro Races.
> >
>
> What about tyre pressure? Getting a 25 for extra comfort implies lower
> pressure, which combined the wide tyre/narrow base which inherently
> reduces tyre stability is all going in the same direction. Also, the
> tyre mass is increased, which increases moment of inertia about the
> steering axis.
>
> Bigger tyres actually increase trail, which might also lower the onset
> speed of 'shimmy', if that's what you're experiencing.
>
> FWIW, I used to run 700x37 tyres on a narrow Shimano R500 semi-aero
> wheel and never had any problems up to the highest recorded speed of
> 47mph, but I bet a straight guage steel Kona Project2 fork is stiffer
> than any carbon road fork.
>
> Kinky Cowboy*
>
> *Batteries not included
> May contain traces of nuts
> Your milage may vary
>
Tires appear round and properly mounted, Tire pressure is 100 psi, I run 105
in the 23s. I'll put the front one on an Open 4cd Monday or Tuesday post
what I find. These same wheels on this bike have been over 50 mph numerous
times and never exhibited any undesirable traits.The bike is a Serotta CSI
that has always been well behaved. Unlike its predecessor, a Serotta CRL,
that was a whippy shimmying noodle. One note, the front end feels like it is
being pushed to one side and when corrected, pushed to the opposite side. It
is not a oscillation. If I let it go it would just corner -until I ran off
the road- in the direction it started in.
Bill
Bill
|
| | | | |
Date: 23 Sep 2007 19:15:54
From: Tim McNamara
Subject: Re: 700x25 tire + 30mm aero wheel instability
|
In article <rBBJi.128058$ax1.62279@bgtnsc05-news.ops.worldnet.att.net >,
"Bill" <bill@example.invalid > wrote:
> One note, the front end feels like it is being pushed to one side and
> when corrected, pushed to the opposite side. It is not a oscillation.
> If I let it go it would just corner -until I ran off the road- in the
> direction it started in.
Headset adjustment?
|
| | | | | |
Date: 24 Sep 2007 00:48:02
From: Bill
Subject: Re: 700x25 tire + 30mm aero wheel instability
|
"Tim McNamara" <timmcn@bitstream.net > wrote in message
news:timmcn-C100DA.19155423092007@news.iphouse.com...
> In article <rBBJi.128058$ax1.62279@bgtnsc05-news.ops.worldnet.att.net>,
> "Bill" <bill@example.invalid> wrote:
>
> > One note, the front end feels like it is being pushed to one side and
> > when corrected, pushed to the opposite side. It is not a oscillation.
> > If I let it go it would just corner -until I ran off the road- in the
> > direction it started in.
>
> Headset adjustment?
Chris King, smooth and firm.
|
| | | | | | |
Date: 23 Sep 2007 20:17:40
From: Tim McNamara
Subject: Re: 700x25 tire + 30mm aero wheel instability
|
In article <6PDJi.128489$ax1.37462@bgtnsc05-news.ops.worldnet.att.net >,
"Bill" <bill@example.invalid > wrote:
> "Tim McNamara" <timmcn@bitstream.net> wrote in message
> news:timmcn-C100DA.19155423092007@news.iphouse.com...
> > In article <rBBJi.128058$ax1.62279@bgtnsc05-news.ops.worldnet.att.net>,
> > "Bill" <bill@example.invalid> wrote:
> >
> > > One note, the front end feels like it is being pushed to one side and
> > > when corrected, pushed to the opposite side. It is not a oscillation.
> > > If I let it go it would just corner -until I ran off the road- in the
> > > direction it started in.
> >
> > Headset adjustment?
>
> Chris King, smooth and firm.
Too firm? This description really points to something north of the fork
crown.
|
| |
Date: 22 Sep 2007 21:37:37
From: Tim McNamara
Subject: Re: 700x25 tire + 30mm aero wheel instability
|
In article <kljJi.124386$ax1.96992@bgtnsc05-news.ops.worldnet.att.net >,
"Bill" <bill@example.invalid > wrote:
> Surprising experience, bike has become unstable at higher sppe with
> wider tires. I have a pair of Mavic Expert semi aero 30mm wheels that
> I have ridden for years with 700x23 tires. They have always tracked
> well and ridden very predictably. A few weeks ago I decided to add
> some comfort and went to 700x25s. Same brand/model of tire, Michelin
> Pro Race. At higher speeds the bike suddenly wanted to wander and
> veer from side to side. at first I thought the carbon steerer might
> be damaged. I pulled the for to double check. Certainly looks rock
> solid.
>
> Turns out the problem is repeatable at 28 + mph. I believe the very
> round profile of the larger 700x25 in conjunction with the aero rim
> is acting as a wing. When the airflow is slightly off center at 28
> mph and up it creates lift that pushes the wheel on direction or the
> other. When it is brought back across center the lift is transferred
> to the other side and forces oversteer and instability. Anyone else
> experienced this problem with an aero wheel and larger OD tire?
I doubt it's a "wing" effect. Try the same tire with a non-aero rim.
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