Cycle design / fashion - sloping top tubes, high seat-post etc 26" etc
 

Anyone care to suggest why modern bikes tend to have sloping top-tubes ?
I more-or-less understand the engineering merit of butted tubes, and perhaps
conical tubes, but I can't understand the merit of a sloping top-tube. Isn't
this effectively, just a smaller frame, with a great long seat tube.
Couldn't you build a lighter and stronger bike by having the biggest frame
possible - using the strength inherhent in the geometry rather than the
materials. The less seat tube poking out, the weaker and lighter this part
needs to be and the less force there is on the bit on the frame it goes in ?
I'm not saying it's wrong, just I don't see why

Also, why 26" wheels rather than 700c ? According to the Thorn website
there's less rolling resistance, but more air resistance. I don't doubt it,
but why less rolling resistance ?

I have a Thorn bike with both these features and I'm very happy with it -
and it seems easier to pedal than my old 700c / 27" bike though that was old
and lower-quality, albeit not much heavier, and OK for what it was.

Any thoughts ?

Hywel

Cycle design / fashion - sloping top tubes, high seat-post etc26" etc
 

Hywel & Ros wrote:
Anyone care to suggest why modern bikes tend to have sloping top-tubes ?
I more-or-less understand the engineering merit of butted tubes, and perhaps
conical tubes, but I can't understand the merit of a sloping top-tube. Isn't
this effectively, just a smaller frame, with a great long seat tube.
Couldn't you build a lighter and stronger bike by having the biggest frame
possible - using the strength inherhent in the geometry rather than the
materials. The less seat tube poking out, the weaker and lighter this part
needs to be and the less force there is on the bit on the frame it goes in ?
I'm not saying it's wrong, just I don't see why

Also, why 26" wheels rather than 700c ? According to the Thorn website
there's less rolling resistance, but more air resistance. I don't doubt it,
but why less rolling resistance ?

I have a Thorn bike with both these features and I'm very happy with it -
and it seems easier to pedal than my old 700c / 27" bike though that was old
and lower-quality, albeit not much heavier, and OK for what it was.

I have a Thorn Nomad and from experience, I doubt the rolling resistance
claims even with narrow slicks fitted. The best-rolling bike I have has
the old size 27" (633mm) wheels. Thorn wheels are very strong though.

The sloping top tube was originally for more standover clearance, but it
does give a stiffer rear triangle. The longer seatpost has a very
slight shock-absorbing effect because it's canted backwards. On a road
bike it's partly a case of selling the things to MTBers who believe the
sloping top tube looks modern. It really cocks up all the bike sizing
equations!

Cycle design / fashion - sloping top tubes, high seat-post etc 26" etc
 

Hywel & Ros wrote:
Anyone care to suggest why modern bikes tend to have sloping

Giant claim they need to make only three frame sizes and adjust the stem and
seat pin to suit the rider. Keeps production costs down. Makes the bikes
look like Grifters

Cycle design / fashion - sloping top tubes, high seat-post etc 26" etc
 

snip snip
The sloping top tube was originally for more standover clearance, but it
does give a stiffer rear triangle. The longer seatpost has a very
slight shock-absorbing effect because it's canted backwards. On a road
bike it's partly a case of selling the things to MTBers who believe the
sloping top tube looks modern. It really cocks up all the bike sizing
equations!

Does it really give a stiffer rear triangle? I sometimes ride my
brother's hardtail (just for a change). They're different bikes so
obviously it's difficult comparing apples and oranges but his has a
sloping top tube + "shallower" rear triangle. It makes the ride a lot
less stiffer.

Another reason for sloping top tubes perhaps is that a lot of bikes
sold nowadays are catered for jumping/downhill/trials/etc. A sloping
top tube helps to protect the jewels somewhat more than a horizontal
one. However a lot of mountainbikers buy their bikes without knowing
what purpose the bike was designed for so you see a lot of them
around. The long (5inch +) travel seen on a lot of DH/FR/etc bikes
also probably mean that it's "easier" to design bikes with a sloping
top tube and make them look cool at the same time.

Cycle design / fashion - sloping top tubes, high seat-post etc 26" etc
 

"Hywel & Ros" writes:

Anyone care to suggest why modern bikes tend to have sloping top-tubes ?
I more-or-less understand the engineering merit of butted tubes, and perhaps
conical tubes, but I can't understand the merit of a sloping
top-tube.

Better stand-over height.

Isn't
this effectively, just a smaller frame, with a great long seat tube.

When I was a lad we were advised not to have our saddles up too far
because of flex in the seatpost, and, consequently, to get the biggest
sized frames we could manage. Seatposts are obviously stronger these
days.

In an emergency stop, falling off your saddle on to the top tube is
**sore**.

Also, why 26" wheels rather than 700c ? According to the Thorn website
there's less rolling resistance, but more air resistance. I don't doubt it,
but why less rolling resistance ?

I think that must be bollox [tm]. Rolling resistance is a function of
the size of the contact patch which is a function of the pressure in
the tyres. The air resistance thing is much more complex, but the
difference between a 26" and a 27" tyre really can't be much. Bigger
wheels cope better with irregular surfaces, and it's notable that some
mountain bike designers are now experimenting with 28" wheels,
which, interestingly, is exactly what I had on my very first bike.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

do not sail on uphill water
- Bill Lee

Cycle design / fashion - sloping top tubes, high seat-post etc26" etc
 

ouch wrote:

Does it really give a stiffer rear triangle? I sometimes ride my
brother's hardtail (just for a change). They're different bikes so
obviously it's difficult comparing apples and oranges but his has a
sloping top tube + "shallower" rear triangle. It makes the ride a lot
less stiffer.

Yes - it's a lot smaller and when you're out of the saddle a flexy
seatpost is neither here nor there.

Cycle design / fashion - sloping top tubes, high seat-post etc 26" etc
 

Simon Brooke wrote:

Anyone care to suggest why modern bikes tend to have sloping
top-tubes ?
I more-or-less understand the engineering merit of butted tubes, and
perhaps conical tubes, but I can't understand the merit of a sloping
top-tube.

Better stand-over height.

And less need to make more frame sizes.

Weight is another agument, but a longer seatpost can make up for that.

Isn't
this effectively, just a smaller frame, with a great long seat tube.

When I was a lad we were advised not to have our saddles up too far
because of flex in the seatpost, and, consequently, to get the biggest
sized frames we could manage. Seatposts are obviously stronger these
days.

I don't think so. Ideas and commerciality is different these days. (I
think I just made that word up?).

In an emergency stop, falling off your saddle on to the top tube is
**sore**.

It is but you can still fall on a low top tube if feet come off pedals and
legs buckle. Don't need much clearance on a road bike normally (many road
bikes have sloping top tubes as well as MTBs).

Also, why 26" wheels rather than 700c ? According to the Thorn
website there's less rolling resistance, but more air resistance. I
don't doubt it, but why less rolling resistance ?

I think that must be bollox [tm]. Rolling resistance is a function of
the size of the contact patch which is a function of the pressure in
the tyres.

Suppleness of tyre is also a big factor - not that diameter affects it,
AFAIK.

~PB

Cycle design / fashion - sloping top tubes, high seat-post etc 26" etc
 

In article , Simon Brooke
wrote:
and it's notable that some mountain bike designers are now experimenting
with 28" wheels, which, interestingly, is exactly what I had on my very
first bike.

Were you a policeman?

--
A T (Sandy) Morton
on the Bicycle Island
In the Global Village
http://www.sandymillport.fsnet.co.uk

Cycle design / fashion - sloping top tubes, high seat-post etc 26" etc
 

Sandy Morton writes:

In article , Simon Brooke
wrote:
and it's notable that some mountain bike designers are now experimenting
with 28" wheels, which, interestingly, is exactly what I had on my very
first bike.

Were you a policeman?

No. The family spent all its money on boats (I had my own boat long
before I had my own bike) and it was an ex-army job which my dad
picked up in a junk shop for fifty pence. I rode it for about four
years between when I was about twelve and when I was sixteen, and
actually did a lot of miles (and had a lot of fun) on it. It left me
with an abiding hatred for Sturmey Archer gears.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

do not sail on uphill water
- Bill Lee

Cycle design / fashion - sloping top tubes, high seat-post etc 26" etc
 

Hywel & Ros wrote:

Anyone care to suggest why modern bikes tend to have sloping top-tubes ?
I more-or-less understand the engineering merit of butted tubes, and
perhaps conical tubes, but I can't understand the merit of a sloping
top-tube. Isn't this effectively, just a smaller frame, with a great long
seat tube.

Not really, because the steering tube isn't shortened. The smaller rear
triangle is meant to be stiffer and the sloped top tube is a bit shorter
and therefore lighter. But the longer seat tube will cancel at least part
of these effects, so I think in these respects any differences between
designs will be negligible.

Higher standover clearance is more noticeable, and I find it a definite
advantage.

But significantly to manufacturers, the compact frame design allows for more
flexibility in seat post length and so they seized the opportunity to save
money by reducing the number of available frame sizes.

And as a boon to marketing departments, introducing the "modern" sloped
design put replacement pressure on owners of "outdated" traditional bikes.


I'm not saying it's wrong, just I don't see why

Also, why 26" wheels rather than 700c ? According to the Thorn website
there's less rolling resistance, but more air resistance.

I would have thought it's the other way around. But anyway, any effects due
to a rather small difference in wheel size are negligible compared to
factors like tyre width, pressure, and tread pattern.


I have a Thorn bike with both these features and I'm very happy with it -
and it seems easier to pedal than my old 700c / 27" bike though that was
old and lower-quality, albeit not much heavier, and OK for what it was.

All kinds of things other than wheel size could explain that better: higher
tyre pressure, better seating position, lower handlebars (and therefore
less drag), a cleaner chain, ... .

Andy