OBRA: OBRA Chat: Questions about 650cc TT BI...

thomas morgan

2003-03-12

There is a segment in High-Tech Cycling by Ed Burke, on the effects of

different wheel sizes on time trial bikes. Basically my understanding was

that on a perfectly flat course running 2 700c wheels will be marginally

faster than 2 650s. But we are talking just barely, it works out that the

700c wheels going at I believe 30mph will give you an advantage of around 4

feet per mile so over 40k you would gain about 100ft compared to a 650c

bike. Which should be around a 4 to 5 second advantage over 40k. However,

if you start to throw in any hills the 650c has a climbing advantage so it

looks to be pretty much a wash on most courses, which have atleast some

rollers.

From: Mark Greenwood <mgree-@tqs.com>

Reply-To: mgree-@tqs.com

To: ob-@topica.com

Subject: RE: [OBRA Chat] Questions about 650cc TT BIKE????????????????????

Date: Wed, 12 Mar 2003 15:25:42 +0000

The only "fact" I've been able to uncover is: one has smaller wheels

than the other. ;-)

Seriously, I've heard lots of opinions, none of which are conclusive

arguments, and some border on the ridiculously hair-splitting. 650s

present a smaller aerodynamic profile, weigh less, have less rotational

inertia, yada, yada, yada... The less weight argument is patently bogus

(at least for flat TTs) because the weight of bike/rider only comes into

play during acceleration, not in the ability to maintain steady-state

speed on flat terrain (hill climbing is another matter). And as far as

rotational inertia is concerned, again it's an acceleration question;

once you've established rotational inertia, it should work FOR you, not

against... right?

I'm also interested in a TT bike and would be interested in hearing any

facts (or opinions!) as well. My own opinion is, unless you need the

650 wheels for fit reasons (e.g., you're very short, < 5'4", or perhaps

you can only achieve a steep tri geometry with 650s - if that's what you

want), it probably doesn't make a discernable difference which you use.

Absent any distinct advantage to the smaller wheels, I would prefer 700

for the eminently practical reason that I could use the same wheelsets

that I use on my RR bike.

Can anybody give me a convincing argument why I'd be faster on 650

wheels? Am I missing something?

Mark Greenwood

zach winter wrote:

Does anyone have any facts about the difference between a 650 cc TT bike

compared to 700.

I know the basics, such as more rolling resistance for 650, but an

increased

acceleration.

I have a 650 TT bike, and want to know if it is even worth racing in a

TT if

its just going to be slower than my 700 road bike.

If anyone has any knowledge on this matter and wants to share it with

me,

simply reply. Thanks ZW

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Erik Long

2003-03-12

<html><div style='background-color:'><DIV>

<P>Zach,</P>

<P>You will be able to TT faster on this bike than your road bike, especially if you get your aero position dialed. One thing to consider, though: The smaller wheel diameter automatically shrinks your gears and will require you to compensate with much higher gearing. For example, a 53x11 on a 700c wheel is a much higher gear than a 53x11 on a 650c (going two or three teeth bigger on each chainring should resolve the issue). This is why many many TT specialists in the grand tours used TT bikes with a 700c rear (for higher gearing and a 650c front (for lower aero profile) until they were banned by the UCI, and also a reason that most of them now prefer two 700c's over two 650c's.<BR></P></DIV>

<DIV></DIV>

<DIV></DIV>

<DIV></DIV>

<DIV></DIV>

<DIV>-Erik J. Long</DIV>

<DIV></DIV>

<DIV> </DIV>

<DIV></DIV>

<DIV></DIV>

<DIV> </DIV>

<DIV></DIV>

<DIV> </DIV>> Does anyone have any facts about the difference between a 650 cc TT bike

<DIV></DIV>>

<DIV></DIV>> compared to 700.

<DIV></DIV>>

<DIV></DIV>> I know the basics, such as more rolling resistance for 650, but an

<DIV></DIV>> increased

<DIV></DIV>> acceleration.

<DIV></DIV>>

<DIV></DIV>> I have a 650 TT bike, and want to know if it is even worth racing in a

<DIV></DIV>> TT if

<DIV></DIV>> its just going to be slower than my 700 road bike.

<DIV></DIV>>

<DIV></DIV>> If anyone has any knowledge on this matter and wants to share it with

<DIV></DIV>> me,

<DIV></DIV>> simply reply. Thanks ZW

<DIV></DIV>>

<DIV></DIV>>

<DIV></DIV>>

<DIV></DIV>>

<DIV></DIV>> _________________________________________________________________

<DIV></DIV>> Tired of spam? Get advanced junk mail protection with MSN 8.

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<DIV></DIV>>

<DIV></DIV>>

<DIV></DIV>>

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Scott & Hilary

2003-03-12

I've raced on three different 650c TT bikes, and also TT'd on a couple of

different 700c bikes. I'll give my opinion, but it's really only anecdotal.

I'm an average sized guy (5'10" and thin), so according to the experts on

such matters I could ride 650 or 700 - I don't fit into the small or large

rider category.

- 650c wheels go uphill way better than 700c (assuming equal frame

stiffness)

- 700c wheels go downhill way better than 700c (especially if there is any

cornering involved. It just feels like you lose some rotational speed.

Again -this is anectodal).

- In a short (under 40k) TT, unless there is a climb, I think it's a toss-up

as to what size wheels go better. In that case, I always go with the more

aero wheels (in my case, that means I generally ride a 700c)

- In longer (40k to 180k) TTs, I've found it easier to keep the 650c wheels

rolling. Granted, this has a lot to do with the geometry - our 650c size TT

bikes are made for going long distances in an aero position. For instance,

I've raced one particular 1/2 ironman race on a 650c TT bike and a 700c OCLV

(w/modifications to the seat & seatpost to increase the angle). The time

difference between the two bikes was negligible. . . BUT, I can say I was

WAY more comfortable on the 650 bike - because of the geometry.

For what it's worth,

Scott Powell

Team O

From: Mark Greenwood <mgree-@tqs.com>

Reply-To: mgree-@tqs.com

To: ob-@topica.com

Subject: RE: [OBRA Chat] Questions about 650cc TT BIKE????????????????????

Date: Wed, 12 Mar 2003 15:25:42 +0000

The only "fact" I've been able to uncover is: one has smaller wheels

than the other. ;-)

Seriously, I've heard lots of opinions, none of which are conclusive

arguments, and some border on the ridiculously hair-splitting. 650s

present a smaller aerodynamic profile, weigh less, have less rotational

inertia, yada, yada, yada... The less weight argument is patently bogus

(at least for flat TTs) because the weight of bike/rider only comes into

play during acceleration, not in the ability to maintain steady-state

speed on flat terrain (hill climbing is another matter). And as far as

rotational inertia is concerned, again it's an acceleration question;

once you've established rotational inertia, it should work FOR you, not

against... right?

I'm also interested in a TT bike and would be interested in hearing any

facts (or opinions!) as well. My own opinion is, unless you need the

650 wheels for fit reasons (e.g., you're very short, < 5'4", or perhaps

you can only achieve a steep tri geometry with 650s - if that's what you

want), it probably doesn't make a discernable difference which you use.

Absent any distinct advantage to the smaller wheels, I would prefer 700

for the eminently practical reason that I could use the same wheelsets

that I use on my RR bike.

Can anybody give me a convincing argument why I'd be faster on 650

wheels? Am I missing something?

Mark Greenwood

zach winter wrote:

Does anyone have any facts about the difference between a 650 cc TT bike

compared to 700.

I know the basics, such as more rolling resistance for 650, but an

increased

acceleration.

I have a 650 TT bike, and want to know if it is even worth racing in a

TT if

its just going to be slower than my 700 road bike.

If anyone has any knowledge on this matter and wants to share it with

me,

simply reply. Thanks ZW

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Eric Kytola

2003-03-12

FWIW

from what i understand, the grand tours allow either 650c or 700c wheels in

the time trials, the only thing is that both wheels must be the same size.

last person i remember riding 650c wheels on both ends was Simoni in the

Giro. must be a reason for all the 700c choices...

-----Original Message-----

From: Mark Greenwood [mailto:mgree-@tqs.com]

Sent: Wednesday, March 12, 2003 7:26 AM

To: ob-@topica.com

Subject: RE: [OBRA Chat] Questions about 650cc TT

BIKE????????????????????

The only "fact" I've been able to uncover is: one has smaller wheels

than the other. ;-)

Seriously, I've heard lots of opinions, none of which are conclusive

arguments, and some border on the ridiculously hair-splitting. 650s

present a smaller aerodynamic profile, weigh less, have less rotational

inertia, yada, yada, yada... The less weight argument is patently bogus

(at least for flat TTs) because the weight of bike/rider only comes into

play during acceleration, not in the ability to maintain steady-state

speed on flat terrain (hill climbing is another matter). And as far as

rotational inertia is concerned, again it's an acceleration question;

once you've established rotational inertia, it should work FOR you, not

against... right?

I'm also interested in a TT bike and would be interested in hearing any

facts (or opinions!) as well. My own opinion is, unless you need the

650 wheels for fit reasons (e.g., you're very short, < 5'4", or perhaps

you can only achieve a steep tri geometry with 650s - if that's what you

want), it probably doesn't make a discernable difference which you use.

Absent any distinct advantage to the smaller wheels, I would prefer 700

for the eminently practical reason that I could use the same wheelsets

that I use on my RR bike.

Can anybody give me a convincing argument why I'd be faster on 650

wheels? Am I missing something?

Mark Greenwood

zach winter wrote:

Does anyone have any facts about the difference between a 650 cc TT bike

compared to 700.

I know the basics, such as more rolling resistance for 650, but an

increased

acceleration.

I have a 650 TT bike, and want to know if it is even worth racing in a

TT if

its just going to be slower than my 700 road bike.

If anyone has any knowledge on this matter and wants to share it with

me,

simply reply. Thanks ZW

_________________________________________________________________

Tired of spam? Get advanced junk mail protection with MSN 8.

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To respond to the whole group send to ob-@topica.com.

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Mark Greenwood

2003-03-12

The only "fact" I've been able to uncover is: one has smaller wheels

than the other. ;-)

Seriously, I've heard lots of opinions, none of which are conclusive

arguments, and some border on the ridiculously hair-splitting. 650s

present a smaller aerodynamic profile, weigh less, have less rotational

inertia, yada, yada, yada... The less weight argument is patently bogus

(at least for flat TTs) because the weight of bike/rider only comes into

play during acceleration, not in the ability to maintain steady-state

speed on flat terrain (hill climbing is another matter). And as far as

rotational inertia is concerned, again it's an acceleration question;

once you've established rotational inertia, it should work FOR you, not

against... right?

I'm also interested in a TT bike and would be interested in hearing any

facts (or opinions!) as well. My own opinion is, unless you need the

650 wheels for fit reasons (e.g., you're very short, < 5'4", or perhaps

you can only achieve a steep tri geometry with 650s - if that's what you

want), it probably doesn't make a discernable difference which you use.

Absent any distinct advantage to the smaller wheels, I would prefer 700

for the eminently practical reason that I could use the same wheelsets

that I use on my RR bike.

Can anybody give me a convincing argument why I'd be faster on 650

wheels? Am I missing something?

Mark Greenwood

zach winter wrote:

Does anyone have any facts about the difference between a 650 cc TT bike

compared to 700.

I know the basics, such as more rolling resistance for 650, but an

increased

acceleration.

I have a 650 TT bike, and want to know if it is even worth racing in a

TT if

its just going to be slower than my 700 road bike.

If anyone has any knowledge on this matter and wants to share it with

me,

simply reply. Thanks ZW

_________________________________________________________________

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zach winter

2003-03-11

Does anyone have any facts about the difference between a 650 cc TT bike

compared to 700.

I know the basics, such as more rolling resistance for 650, but an increased

acceleration.

I have a 650 TT bike, and want to know if it is even worth racing in a TT if

its just going to be slower than my 700 road bike.

If anyone has any knowledge on this matter and wants to share it with me,

simply reply. Thanks ZW

_________________________________________________________________

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