Anyone know what the pros and cons of this? Any good links on frame geometry?
Thanks
bike geometry
Thu, 07/13/2006 - 3:57am
Thu, 07/13/2006 - 5:28am
#1
Sloping Top Tube: a.k.a. Compact Frames
"These can be good for a short rider who needs stand-over clearance. Or perhaps someone with a long torso and short legs. Other than that, compact frames are mostly an advantage for manufacturers who only have to make 3 or 4 frame sizes instead of 6 or 7.
Some will point out that the smaller frame is lighter and more rigid. But it requires a much longer seat post, and seat posts are heaver than seat tubes.
""Chainwheel""
"
Thu, 07/13/2006 - 6:03am
#2
"The advantage of sloping top tubes is that, for a subset of the cycling population who need it, it allows you to get the bars up high without compromising stand-over clearance. It basically can achieve ""French Fit"" without a high top tube. This assumes you buy a sufficiently large frame to do this.
The advantage of level top tubes is aesthetics. Sloping top tubes look like ass, after all.
Meaningful frame geometry is determined by the head tube and seat tube angles, the rake of the fork, and the length of the chainstays. Proper _handling_ is achieved by having a bike that fits your body and distributes your weight appropriately. Everything else is immaterial.
Searching here will get you some info on geometry, and Peter White's site has a good article on fitting. The Competitive Cyclist page has a reasonably decent spiel on the different types of fit -- tourer/randonneur/French, vs. classic race/Merckx, vs. modern race geometry and fit.
Cheers,
AC"
Thu, 07/13/2006 - 6:07am
#3
where does one...
"Go to have one's bike ""fit?"" professionally?"
Thu, 07/13/2006 - 6:33am
#4
Bike fitting
Virtually all truly great cycle shops will have professional bike fitters and fitting machines - I know SBR, Toga and Sids all do. I cannot recommend this strongly enough. make an appointment, bring your bike, and plan to spend 60-90 minutes being measured, spinning on your bike, having adjustments made, etc. You can be fitted on a current bike or be fit for a custom bike - whatever your budget allows. This is much more than raising or lowering the seat and can make a big difference. I know that Toga and SBR will do a fitting as part of a road bike purchase.
Thu, 07/13/2006 - 6:36am
#5
Thanks
Will do.
Thu, 07/13/2006 - 6:49am
#6
Not a simple answer
"Typically, TDF cyclists travel with an orthopedist and a team of chiropracters specialized in adjusting the riders' physiogomy to a UCI pre-approved frame set. (aka the ""procrustean"" method)
http://en.wikipedia.org/wiki/Procrustes
:)
----------------
Alternately, the modern concept of a ""fit kit"" was coined by Serotta (?) to market its system of measuring riders -- and interpreting those measurements into the dimensions for its custom-made bikes. This allowed the bikes to be sold from any location, obviating the need for the enduser to journey to upstate NY.
Also, besides enhancing its rep as *the* premiere custom bike builder, Serotta makes beau coup $$$ in training fees and selling the adjustable fit machines.
http://www.serotta.com/pages/size.html
There are those that deride the ""fit kit"" as a ""good starting point"" but I had mine done and have been satisfied with the orthodox interpretation.
NYCC had someone in from Serotta at a monthly meeting. Maybe there's an tape ... ?
One more point, the guy from Serotta mentioned that it was good for riders to spend 10% of their time in the ""drops"". (I typically spend 50-90% of my time there, depending on conditioning and ride length). It is my understanding that a ""flat"" top tube is more conducive to multi-positioning while a sloping tube is really designed to be ridden on the ""hoods"".
Interestingly, all of Serotta's current bikes have sloping tubes with two exceptions: their CXII TT bike and Ottrott CX cyclocross
http://www.serotta.com/pages/cxii.html
http://www.serotta.com/pages/ottrott_cx.html"
Thu, 07/13/2006 - 9:45am
#7
Fit Kit and Serotta
"Serotta's system is called the ""Size Cycle,"" which is distinct from the Fit Kit.
http://www.cyclemetrics.com/Pages/FitLinks/bike_fit_links.htm
The fitter from Serotta who said that riders spend (or should spend, a big difference, but I forget) 10% of their time in the drops was Paul Levine."
Thu, 07/13/2006 - 10:01am
#8
Fit and stuff
"""It is my understanding that a ""flat"" top tube is more conducive to multi-positioning while a sloping tube is really designed to be ridden on the ""hoods"".""
Not really. As long as the relative position of the saddle, pedals, and handlebars are the same (and that can usually be worked out), it shouldn't make much difference as far as fit is concerned whether the top tube slopes or not.
As for the various fit systems, the key thing is rider feedback, not just measuring body parts and plugging numbers into a formula. Most of us shouldn't be set up on the bike like a TdF racer. It sounds like you are set up pretty well if you're spending that much time in the drops. Many recreational riders almost never use the drops, which begs the question: Why use drop bars?
""Chainwheel"""
Thu, 07/13/2006 - 10:40am
#9
"Agree.
Though I should be said that the 6'0"" Tour sprinters who ride eeeeeetty-bitty bikes with 140mm headtubes do ride on the hoods 90% of the time, whereas ten years ago, they were riding bikes with 170mm headtubes (and more stack height) and riding the drops 90% of the time.
The concurrent timing of that change and the introduction of ""compact"" frames is probably the genesis of this myth, and, worse, probably the reason compact bikes with short headtubes and (aaaargh!) fat spacer stacks are so prevalent.
- AC
La vaca dice: If you have more than 10mm spacer under stem, bike no fit! If you have no 2mm spacer over stem, mechanic no fit!"
Thu, 07/13/2006 - 7:45am
#10
Paul Levine opened a shop in NYC recently. 64th and West End I think. Maybe 65th and West End. Anyway, getting your bike fit by anyone other than Paul seems silly when Paul is around.
And this from a cow who doesn't really believe in bike fits... The cow believes you should get a proper bike, set the seat height appropriately, set the saddle with the scoop in-line with the seat tube and go ride 500 miles. Then adjust for setback, and start worrying about reach and drop (or not, really, since once the seat height and setback is is right, it doesn't even really matter all that much.)
The cow wants a 55cm Ridley Damocles or Time VXRS ULTEAM with a 140mm stem. He won't be able to ride it further than 80 miles, but it'll handle *sharp*!
The cow is very opinonated today.
AC
Thu, 07/13/2006 - 9:19am
#11
set back
How exactly does one adjust for setback?
If you don't believe in fit, is it by feel or soomething else?
Thu, 07/13/2006 - 10:33am
#12
"I put the nose of my saddle somewhere around 7cm behind my bottom bracket center line (depending on which saddle). This puts the scoop in the saddle about aligned with a 72 seat tube, or 5mm behind (72.5 st) or 10mm behind (73 st). For every 10mm back and forth, I go up or down 3mm. Then I ride my bike around and see what feels good. On my Rambouillet, which is a bike I ride primarily seated when climbing, I've pushed my saddle back another 5mm, so the nose is about 75mm behind the bottom bracket. On my Pegoretti, I like it at about 70mm behind the bottom bracket.
The goal is to arrive at a good compromise between weight on your butt (lots of setback), the ability to climb strongly seated (lots of setback), and the ability to spin comfortably on the flats (less setback). KOPS is a bunch of BS, but it's true that this ends up for most people to be KOPS or 10-20mm behind KOPS. Certainly, if you're in front of KOPS, you have some explainin' to do.
How did I arrive at 70mm, initially? I aligned the saddle scoop with the seat tube and checked that I was within a few cm of KOPS. That's a good enough starting point.
And I suppose I should clarify; it's not that I don't believe in ""fit,"" it's that I don't think professional fittings are strictly necessary for production bikes. With a bit of experience, you can figure out what setback you need and what stem length works and gives proper handling.
Fitting on a custom bike is different. There, the frame designer is trying to build a bike with the right weight distribution for you and so on. Though most of those guys should probably stick with the C.O.N.I manual, too.
And FWIW, I would never trust a shop guy to ""fit"" me to a custom bike. That's what the frame builder should do.
- AC, 1st Cow"
Thu, 07/13/2006 - 9:31am
#13
It will handle sharp?
"Anonymous Cow wrote: ""The cow wants a 55cm Ridley Damocles or Time VXRS ULTEAM with a 140mm stem. He won't be able to ride it further than 80 miles, but it'll handle *sharp*!""
No, the opposite of sharp, it will be obtuse.
And what's this speaking of yourself in the third person? Please don't act like a jerk.
Mordecai ""insert smiley"" Silver"
Thu, 07/13/2006 - 10:20am
#14
That's acute joke, atmo.
Thu, 07/13/2006 - 2:08pm
#15
Paul Levine
>>getting your bike fit by anyone other than Paul seems silly when Paul is around.<<
Spending the $375 that Paul charges for a fitting seems silly when the guys at Toga, Sids, et al all charge one-fifth of that...and, by your own implicit admission, do as good a job. (I'm presuming that anyone who believes a professional fitting for a production bike is unnecessary will agree that they are all equally unnecessary regardless of retail price.)
Fri, 07/14/2006 - 7:28am
#16
No, I didn't imply that at all.
Here's what I believe:
Most bike shop employees are not very good fitters. (Yes, I know there are exceptions, but Toga? Come on.) In fact, most seem to know a heck of a lot less than I do about fitting people on bikes, and you don't see me hawking my bike fitting services.
So, if a person is not going to educate himself sufficiently to do a bike fit on their own, they ought to go get a fit by someone who actually knows what they're doing. Paul Levine seems to meet that criteria, according to those who've had him fit bikes.
- Christian
Thu, 07/13/2006 - 3:50pm
#17
One disadvantage of sloping top tube
One disadvantage of the compact frame/ upward sloping tob tube is that when you make turns, your foot can actually bump into the wheel if your pedal is forward (i.e. roughly the 3-o'clock position) on the turning side. I was told this before (and forgot), and only found out again for myself when I started riding my new upward-sloping frame. I've basically had to learn to always keep my feet in the 12-o'clock/6-o'clock positions if I'm turning my handlebars more than 20-25 degrees to the left or right, so that my foot doesn't kick the tire. Note that it's not because I have bigger-than-normal feet - I'm a 9 1/2, which is small for my height.
It's slightly annoying, but not necessarily a deal breaker.
Fri, 07/14/2006 - 7:32am
#18
This concept is called toe-overlap. And it has nothing to do with whether your top tube slopes or not. It just has to do with the front-center distance of the bicycle, and the size of the front wheel.
It's a design issue.
Fri, 07/14/2006 - 8:23am
#19
Toe overlap is endemic to small frames, particularly w/fenders.
All my bikes have it.
Scary the first time if you're not expecting it, otherwise no biggie.
Fri, 07/14/2006 - 8:51am
#20
Bad on fixed gears, tandems, and loaded tourers. Otherwise ok.
BTW, it's only endemic on badly designed small bikes. Properly designed small bikes don't use 700c wheels. :)
Fri, 07/14/2006 - 2:08pm
#21
My regular, flat-top tube frame has toe overlap. My compact, sloping-top tube frame doesn't. Both bikes handle wonderfully. I didn't even realize the new bike is sans toe overlap for two to three months.
In regard to the concept of riding in the drops, most club riders don't do it enough. The drops are vastly more stable. You have much more leverage on the brakes, and you are far less likely to go endo if you hit a pothole.
