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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 |
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#2
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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! |
#3
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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 |
#4
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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. |
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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 |
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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. |
#7
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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 |
#8
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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 |
#9
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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 |
#10
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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 |
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