TT frame sizing question

Quoted message said:

Hello, RBR

I'm planning on picking up a TT bike soon and am wondering if anyone
knows offhand what the differences in toptube length there should be
between road bike and TT bike in general. For instance I ride a 57.5
cm top tube currently and am happy with it. For the TT bike and it's
inherent aero bar position should my TT bike also have a similar-
length top tube? I remember hearing that a TT bike should have a
shorter top tube due to the aero bar but if that's so how much shorter
and why? Thanks and I'll take my answer off the air.

Take a look at the bars and stem you're planning on using to get the
right fit and try to size the bike frame appropriately. If you can
vary the stem length, use a shorter one and a longer top tube.
--
JT
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Most guys seem to be using TT frames that are a bit smaller than their
normal road frames. One reason is to be able to get sufficient drop
from the seat to the bars. If the seat tube is too tall, then you
have to use one of those funky negative rise stems to get the bars
low. So that generally means the top tube will be a bit shorter than
on the road.

Personally ... I got a new TT bike this year (Felt). I ride a 53cm (c-
c) seat tube on the road. The Felt is advertised as a 54, but it is
more like 48cm center-center. The top tube is I believe 54cm, which
is a bit shorter than my normal 55cm. BUT ... because the seat is
pushed more forward than on the road it effectively shortens the top
tube even more. I am using either a 90mm or 100mm stem (I think the
90) which is pretty short ... but this setup is working out pretty
well.

The next smaller size, 52, I think would have been too small for me
though.

I'd suggest getting a fit from someone who knows how to do a TT fit.
B

Okay thanks for your answer. Paraphrasing, go 1CM shorter but not much
more so you can lay out okay on it and then ride a shorter stem. Now
I'm wondering if that advice works when the seat is pitched forward in
the 78 deg. virtual seat angle config? Still learning ...

Thanks again,

-Rick

Quoted message said:

Okay thanks for your answer. Paraphrasing, go 1CM shorter but not much
more so you can lay out okay on it and then ride a shorter stem. Now
I'm wondering if that advice works when the seat is pitched forward in
the 78 deg. virtual seat angle config? Still learning ...

I'm not sure what my actual seat angle is, but I think it's in the
76-78 deg range. I've got the nose of the saddle in front of the
BB ... but I have short legs.

I don't know that I'd focus so much on top tube length. First I'd get
the seat tube length right, since that's going to determine whether
you can get the bars low enough. If on the edge ... a little small is
probably better than too big. If you are serious about it I'd go to a
shop or find someone who has done TT fits before getting a bike and
finding it's too small or big.

Here's a good article on tt / tri bike fitting:
http://www.slowtwitch.com/mainheadings/techctr/bikefit06.html

Quoted message said:

Okay thanks for your answer. Paraphrasing, go 1CM shorter but not much
more so you can lay out okay on it and then ride a shorter stem. Now
I'm wondering if that advice works when the seat is pitched forward in
the 78 deg. virtual seat angle config? Still learning ...

One more thing to add ... with my 54 TT frame, I have the bars as low
as I can get them without going to a different stem. So I'm right on
the border of going to the smaller frame.

Quoted message said:

Hello, RBR

I'm planning on picking up a TT bike soon and am wondering if anyone
knows offhand what the differences in toptube length there should be
between road bike and TT bike in general. For instance I ride a 57.5
cm top tube currently and am happy with it. For the TT bike and it's
inherent aero bar position should my TT bike also have a similar-
length top tube? I remember hearing that a TT bike should have a
shorter top tube due to the aero bar but if that's so how much shorter
and why? Thanks and I'll take my answer off the air.

Remember that the rules have changed for UCI compliant racing. This
forced the saddle BACK a bit in order to keep the hands behind the
front axle.

John offered you some good advice but I wouldn't take the other too
seriously. You should be able to feel if you can get flat enough or
not to use a very low position and unless you're a triathlete pushing
the saddle forward for a virtual steep seat tube angle simply isn't
going to work any better than retaining your normal leg/pedal angle.

If you look at the TT positions of some of the people riding the
fastest you'll see they're all over the place. Low and flat is good
but most people can't maintain long term power output crunched down
like that.

Many Pros are now using a "moderately low and flat" position with the
aerobars slanted upwards to pull their elbows forward and open up
their lungs and to close up the gap between arms and chest which
causes a great deal of drag. This doesn't look aero but for most
people who aren't as flexible as Greg LeMond it works better.

In most cases you should be working on maximum power output over the
length of time of the TT and not try to optimize aerodynamics which is
a losing proposition for anyone without access to a wind tunnel.

Quoted message said:

Quoted message said:

Hello, RBR

Quoted message said:

I'm planning on picking up a TT bike soon and am wondering if anyone
knows offhand what the differences in toptube length there should be
between road bike and TT bike in general. For instance I ride a 57.5
cm top tube currently and am happy with it. For the TT bike and it's
inherent aero bar position should my TT bike also have a similar-
length top tube? I remember hearing that a TT bike should have a
shorter top tube due to the aero bar but if that's so how much shorter
and why? Thanks and I'll take my answer off the air.

Remember that the rules have changed for UCI compliant racing. This
forced the saddle BACK a bit in order to keep the hands behind the
front axle.

???

Quoted message said:

Remember that the rules have changed for UCI compliant racing. This
forced the saddle BACK a bit in order to keep the hands behind the
front axle.

There are several measures that must be met to make the position UCI
legal. Saddle wrt BB is only one, and it has nothing really to do
with where the hands are. There is also a requirement that the bar
extensions do not extend farther than 'x' mm (750?) from the center of
the BB (not saddle).

My saddle is in front of the BB yet the position is legal because my
knee doesn't go in front of the pedal spindle. I was measured at
nationals. No way could I ride with my seat in my road position. The
nose of the saddle would be up my ... well you get the picture.

Quoted message said:

In most cases you should be working on maximum power output over the
length of time of the TT and not try to optimize aerodynamics which is
a losing proposition for anyone without access to a wind tunnel.

If you are serious about TT'ing then you want to get as aero as you
can comfortably maintain. You don't need a wind tunnel to do that.
I'm not particularly flexible, and don't think my bars are all that
low. In fact I feel pretty comfortable. The article on Slowtwitch
isn't recommending anything that radical either.

If you don't doubt that the better TT'ers try to get aero ... go look
at some pics from the US nationals. Sure you will find some fast guys
that don't look too aero. But I think you'll find that for the most
part find the fastest guys/girls are pretty aero.

check out these pages:
http://cu.7springs.com/pages/gallery.php?gallery=296830&offset=0

Also note Kristen Armstrong in there on the last page, with a nice-
looking position.

Since the poster is buying a dedicated TT bike, one would assume he's
serious about it.

B.

Quoted post said:

My saddle is in front of the BB yet the position is legal because my
knee doesn't go in front of the pedal spindle.

The furthest forward the saddle can be under the "morphological
exception" is inline with the BB. The nose of the saddle cannot be in
front of the vertical plane of the BB.

from the UCI rulebook :

1.3.013 The peak of the saddle shall be a minimum of 5 cm to the rear
of a vertical plane passing through the bottom bracket spindle (1).
This restriction shall not be applied to the bicycle ridden by a rider
in track sprint event, keirin, 500 metres or 1 kilometre time trials;
however, in no circumstances
shall the peak of the saddle extend in front of a vertical line
passing through the bottom bracket spindle.

On Aug 16, 4:21 pm, "[email hidden]" <[email hidden]>

Quoted message said:

The furthest forward the saddle can be under the "morphological
exception" is inline with the BB. The nose of the saddle cannot be in
front of the vertical plane of the BB.

Hadn't noticed that. Neither had the USCF officials apparently.
Their measurement jig I think is set up to see if the seat is 5mm
behind the BB. Then if not, you can ask for the exception at which
point you get on the bike and they drop a plumb bob to see where your
knee is.

They didn't check to see how far in front of the 5mm limit my seat
was. (I think it's maybe 1-2mm).

B.

Quoted post said:

On Aug 16, 4:21 pm, "[email hidden]" <[email hidden]>

Quoted message said:

The furthest forward the saddle can be under the "morphological
exception" is inline with the BB. The nose of the saddle cannot be in
front of the vertical plane of the BB.

Hadn't noticed that. Neither had the USCF officials apparently.
Their measurement jig I think is set up to see if the seat is 5mm
behind the BB. Then if not, you can ask for the exception at which
point you get on the bike and they drop a plumb bob to see where your
knee is.

They didn't check to see how far in front of the 5mm limit my seat
was. (I think it's maybe 1-2mm).

B.

If you're not a pro this is WAY down on the officials list of things
to worry about, especially with the new rollout rules.
Bill C

Bill C said:

If you're not a pro this is WAY down on the officials list of things
to worry about, especially with the new rollout rules.

Not a pro ... but this was Nationals. The evening before, they were
checking anyone who wanted to be checked, and then writing down who
got an exception. There were plenty of officials and plenty of time.
I think maybe it was a bit new to them too.

Before your start time the next day, you had to get your bike checked
again then go straight to the staging area (so you couldn't go and
change it). So they were certainly concerned with doing it right.

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

If you are serious about TT'ing then you want to get as aero as you
can comfortably maintain.

I agree with you here but the problem is that you can't FEEL how aero you
are. What feels aero may have more drag than other positions with don't look
so aero.

Quoted message said:

If you don't doubt that the better TT'ers try to get aero ... go look
at some pics from the US nationals. Sure you will find some fast guys
that don't look too aero. But I think you'll find that for the most
part find the fastest guys/girls are pretty aero.

The fastest guys are _usually_ but not always the most aero looking. That
doesn't mean they are. LeMond finally leaked the information that he was
essentially as aero with and without the bars.

In article <[email hidden]>,

Quoted post said:

Bill C said:

If you're not a pro this is WAY down on the officials list of things
to worry about, especially with the new rollout rules.

Not a pro ... but this was Nationals. The evening before, they were
checking anyone who wanted to be checked, and then writing down who
got an exception. There were plenty of officials and plenty of time.
I think maybe it was a bit new to them too.

Before your start time the next day, you had to get your bike checked
again then go straight to the staging area (so you couldn't go and
change it). So they were certainly concerned with doing it right.

It's worth noting that many pro riders are trimming their saddles so they can have
them fairly far forward and still be in compliance with the seat setback rules:

http://tinyurl.com/2xcpql

--
tanx,
Howard

Never take a tenant with a monkey.

remove YOUR SHOES to reply, ok?

Tom Kunich' cyclintom@yahoo. com said:

I agree with you here but the problem is that you can't FEEL how aero you
are. What feels aero may have more drag than other positions with don't look
so aero.

I suppose that is true at some level. But there is a lot that you can
determine without a wind tunnel, and you can also make use of someone
who has experience with doing TT bike fits, and make use of the
experience of people who have done work in the wind tunnel (kraig
Willett, John Cobb, etc.) and write about it. Sure you're not going
to fine tune it as much as someone who goes to the wind tunnel
though.

If I'm on the TT bike, and I'm riding at a given level of effort, and
I take my hands off the aero bars and sit up higher, then my speed
drops. That is obvious. So there is some level that you can determine
without a wind tunnel. Otherwise we'd be riding road bikes with our
regular road bars.

I know one guy who paid for wind tunnel testing ... and he ended up
lowering his bars even more (and having to get one of those funky
stems). Also brought his arms closer together, and it made a
difference to consciously keep his head and shoulders low. Whether
that is specific to his particular body, I don't know. I believe
Kraig Willett writes that in his experience the single easiest thing
he's found is keeping your head low.

Quoted message said:

LeMond finally leaked the information that he was
essentially as aero with and without the bars.

I don't ever remember reading that but I guess it's possible. I know
there's no way I can go as fast in my road position as I can on the TT
bike. In a 40km TT we're talking 2.5 mph at least.

B.

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Quoted message said:

LeMond finally leaked the information that he was
essentially as aero with and without the bars.

I don't ever remember reading that but I guess it's possible. I know
there's no way I can go as fast in my road position as I can on the TT
bike. In a 40km TT we're talking 2.5 mph at least.

I don't remember where I saw the numbers but LeMond once stated the numbers
and it was something like only one percent difference with and without the
aero bars. What this implies is that the reason that he beat Fignon is
PROBABLY because he could hold his aero position easier with the elbow pads.

Tom Kunich' cyclintom@yahoo. com said:

If you are at the level of TTing in which you don't know that being low on
the bike and sitting upright aren't the same thing then perhaps you are
talking about something entirely difference from what I am.

the point was that you can obviously determine that some things make
you more aero without going into a wind tunnel.

if we can't do anything with confidence to improve aerodynamics
without going into a wind tunnel, then why do we bother with TT bikes
and aero bars?

B.
ps. i've gone sub 54:00 for 40km on the TT bike ... no way can I do
that on my road bike.

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Tom Kunich' cyclintom@yahoo. com said:

If you are at the level of TTing in which you don't know that being low
on
the bike and sitting upright aren't the same thing then perhaps you are
talking about something entirely difference from what I am.

the point was that you can obviously determine that some things make
you more aero without going into a wind tunnel.

You can tell major things that any butt-head could tell you. But when you
get to the level of using a TT bike you've already done the major things and
any "improvement" is impossible to pull out of the noise without wind tunnel
testing.

I'm not disagreeing with you on your major point, I'm just saying that
people who are setting up TT bikes already know the major things they have
to do and you can't tell whether they'll get an improvement by dropping
their bars or raising them without a wind tunnel test or a GREAT deal of
patience testing on a closed course.

Quoted message said:

if we can't do anything with confidence to improve aerodynamics
without going into a wind tunnel, then why do we bother with TT bikes
and aero bars?

Because you THINK it improves you. Remember that every ride is more
experience and possibly a more relaxed position and a better psychological
form.

Quoted message said:

ps. i've gone sub 54:00 for 40km on the TT bike ... no way can I do
that on my road bike.

We're back to identifying that being on a road bike in the drops is more
aero than riding a mountain bike with knobbies.

Tom Kunich' cyclintom@yahoo. com said:

I'm not disagreeing with you on your major point, I'm just saying that
people who are setting up TT bikes already know the major things they have
to do and you can't tell whether they'll get an improvement by dropping
their bars or raising them without a wind tunnel test or a GREAT deal of
patience testing on a closed course.

yes, I don't think we're at odds here. I just don't know where's the
line at what you can and can't tell without getting tested in a wind
tunnel. Riding on the hoods is not as aero as in the drops. Riding a
TT bike with aero bars is generally more aero than a road bike in the
drops. (but look at some triathletes and that is not true, so it does
make a difference in how you set it up). Beyond that?

I think if you're serious about doing TT's you're probably going to be
willing to be patient and do some testing on a known course.

When I got this latest bike, there was a free fitting. I think the
guy had done mostly age-group triathletes. I didn't "feel" as though
the position was very aero (I didn't feel any more aero than on my
road bike, and looking at my speed for a given level of effort
confirmed that). I know how fast I can go on my road bike in a solo
effort in a race, and I wasn't much faster than that on the TT bike.

So then I went to a guy who's done a lot of road and TT fits, who does
the FIST and also Wobble Naught methods. He'd set up a good number of
TT fits, and had a sense for what worked and didn't.

I was noticeably faster after that fit. Did he make me more aero? Or
more efficient? I guess I couldn't tell you for sure. I think he did
make me more aero -- my arms are a bit closer and he dropped the bars
(but not so much that it's uncomfortable). The first guy had me
sitting up probably as high as I am on my road bike riding on the
hoods. I would find it hard to believe that I'm not more aero now.