Hot answers tagged geometry
12
This is a common problem, but really not a big deal. I've usually heard it called "toe overlap". I have it on all my bikes.
Basically, it's a bit shocking the first time it happens, but you get used to it. It's no big deal. If you're simply aware that it can happen at slow speeds, you'll avoid it easily enough. Since it can only happen at slow speeds, it's ...
10
This might not be a very good place to start from when sizing a bicycle. Your inseam measurement is from the top of the crotch (top inseam point) to the BOTTOM SIDE OF THE ANKLE (lowest inseam point). Your feet go all the way to the floor.
Inseam is specifically to determine what pants you wear. I might point out that pants and bicycles are made and ...
9
I see frame geometry having 3 primary affects
Fitting the rider; which you're already addressing and I won't talk about here... But a lot of geometry stuff comes down to making the other stuff work with fitting riders on the bikes. It's very important.
Fitting stuff on the bike
Handling characteristics.
Since you asked, I'm talking about your basic ...
8
there's a good write-up about this here: http://www.calfeedesign.com/tech-papers/geometry-of-bike-handling/
In general the steeper the angle the more agile the steering. If you like steeper you might say "quicker, more response", if you didn't like steeper you might say "twitchier".
A 1/2 degree difference is probably not going to make that much difference ...
8
It sounds as though you are talking about what Sheldon Brown term "reach", which is
normally measured center-to-center along the direction of the extension
So this does not take into account the angle of the stem, which could reduce the length forward that the handlebars extend by a small amount if they are on a large angle up or down.
7
First off, understand that the geometry of the bike affects stability, especially the "marriage" between head angle and fork rake. Adjusting these parameters (which can really only be "adjusted" by the frame builder) has a very dramatic effect on stability.
Beyond that, the hand position has an effect in a couple of ways. First, if the hand position is ...
7
I think you answered your own question when you stated "I don't race." I know many in our club who enjoy the Roubaix. I personally prefer riding my steel Soma ES over my carbon race bike for most things, including fast club rides. Don't get me wrong, a twitchy race bike is great in a crit, but the other non-race bikes have had their design optimized for ...
7
There are several good systems. I'm a certified BG fitter, as well as certified with the retul system. You're familiar with the BG system, as you've already been through it.
Retul is a system which uses power measurement and body position sensors on a 3 dimensional wire frame (virtual) reproduction of your bike and body. It allows an experienced fit ...
6
I have a very similar setup (SKS Chromoplastics), and can say the following:
I installed a suspension forks and then the former length of the metal wires bacame too long for the setup. I BENT them in a sharp turn to run parallel to the mudguard (of course it can be bent in any suitable direction, just NOT point straight back like yours). Haven't had any ...
5
If there's one thing I've learned about bike fit over the years, it's that it's rather controversial. I was strictly "old school" since I started cycling seriously in the mid 70s.
Standard measurements for seat height, saddle fore-and-aft adjustment, knee-over-pedal adjustment, reach, etc. No high-tech goodies.
You used these "ball-park" measurements to ...
4
A local bike shop owner pointed out to me that getting the right frame is the most important thing on a bike. If it's not right, then any other money or effort you put in to the bike is wasted. So, good topic!
Grant Petersen wrote this article about geometry on Rivendell's site: http://www.rivbike.com/kb_results.asp?ID=34. It's not a complete treatment of ...
4
It's close enough for a very rough guess, but in most cases (especially if using a sizing formula) you'll want to measure the distance from the ground right up to your pubic bone. Unless your pants drag along the ground, you're inseam size will be a bit shorter: somewhere in the range of 1-3" (as a guess).
You can get this quickly measured at many road ...
4
Less fork offset on it's own means more trail. The fork length and wheel size will also affect this though, so you'd need to get all the numbers and maybe draw it out to work out the final difference in trail.
More (longer) trail makes the bike more stable (especially at speed) but less manoeuvrable. Touring and downhill bikes tend to have more trail, while ...
3
Since you are new to BMX I would find a good local shop that specializes in BMX. In my area the three largest conventional road/MTB shops don't carry BMX. We do have two very good shops that only sell BMX and skateboards. So don't be dismayed if the first shop you check has nothing you want. If you can't find one, stop by the local skate/bike park and see ...
3
Unfortunately my crummy draw tool won't let me place the lines very accurately, but this is the idea:
The radii describe right angles to the two chain lines. I'm pretty sure the two wrap angles on the two sprockets will add to 360 degrees. The upper quadrilateral has been divided into a rectangle (if my lines were square) and a right triangle. The ...
3
Changing from 50 to 65 (or the opposite) is definitely noticeable. And depending on your needs, switching may improve your riding.
Switching from 50 to 65 will mean more pressure on the front end. That means better cornering (the front end will not wash out easily) and more stability on the downhill. Some people also mention that it'll improve climbing on ...
2
Ask yourself a question...if you end up getting a Roubaix, for example, will you buy it and still be hankering after a carbon frame? If that's the case then perhaps it would be better to get the carbon frame now rather than to get a bike, be not entirely satisfied with it, and end up buying a carbon bike anyway in a year or so.
I just mention this ...
2
I suspect one of the reasons you feel unstable riding on the tops on your current bike is because your hands are to the inside of the drops, positioned so close to the stem it makes it hard to control the bike.
With a 'flat' bar your hands will be positioned much further apart (maybe even more so then when in the drops on your current bike), providing more ...
2
As mentioned in other answers, trail does affect how the bike rides. I don't necessarily agree that a higher trail number means more manoeuvrability. Most bikes have trail numbers between 60-66 these days. Much older bikes had low trail numbers between 35 and 50. There are a number of reasons for the change. One advocate of Low-Trail handling is Jan Heine, ...
2
In a perfect world, every bike would be assembled from a FRAMESET, which is a frame-fork pair designed for one another. With a frameset, very relevant parameters can be actually DESIGNED into the system, instead of derived from it. The main parameters which depend on fork-frame interaction are, in my perception, bottom-bracket height, seat-tube angle, ...
1
Flatland frames generally have shorter top tubes, steeper head tube angles, shorter rear ends, etc... The down tube in your picture is designed to give you more room for front wheel scuffing. I'm noticing more and more flatland frames are designed to look like a typical street/park frame, but the geometry is not the same. I believe there are hybrid frames in ...
1
I have Planet Bike Cascadia fenders and my shoes did clip the metal rods/wire fender supports after I had the fenders installed. This happens when I am making a tight turn while continuing to pedal. Simple solution for me was to cut the protruding rod/wires. Initially I tried to use a hacksaw but had little luck as the coating was hard and the saw just ...
1
Have a look on the second hand market for 'Giant Trail' mountain bikes from a few years ago. These had an unusual frame design with a lower top tube, wider, more stable bars and disc brakes. Giant Rincon Trail, Giant Boulder Trail were a couple of the affordable models I remember.
1
Lighter and stronger are the real gains. Also there is coolness factor. In a rare move I wish to cite for points 1 + 2:
Look, who has the longest unbroken history of carbon fiber frame making in pro road racing, uses the tapered fork steerer design to eliminate the narrow waist at the junction of the fork crown and steerer. This allows their all-carbon ...
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