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14

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 ...


13

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 ...


12

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.


12

I thought this was an interesting question, so first of all, +1. First off, the sloping tube (your second image) is known in cycling parlance as a compact frame. I found an article on the Giant web site about the advantages of a compact frame. When I say "advantages" - this is Giant's word not mine! The full article is here, but to summarise it: the ...


11

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 ...


11

Much of this is due to UCI regulations. They specify what shape and size of frame can be used. It is not allowed to add extra parts just for improving aerodynamics. See the UCI document Technical Regulations For Bicycles - A Practical Guide To Implementation (PDF) which covers most of this. As it says for Article 1.3.020, the frame elements must be ...


11

Where should pedals be located (relative to the rider)? Wherever its most comfortable for you. It's a matter of personal preference (*). What works for person A won't necessarily work for person B, even if they have the same measurements and/or similar bikes. Your riding position relative to the pedals will change depending on the type of bike, terrain, ...


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

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 ...


9

The S shape allows for: stronger head tube and bottom bracket welds without the need for gussetting. You'll find this on more trail focused bikes (such as AM, FR and DH). wheel clearance for long travel forks wheel clearance for the front wheel (ie. 29er's) Still allows for room for a water bottle within the front triangle


8

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 ...


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

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 ...


6

All else being equal, longer chainstays equate to a longer wheelbase, and the rear wheel trailing further behind you. You are correct in your assertion that as wheel size increases so too does chainstay length, though many manufacturers have put considerable effort into minimizing this and as such the increased chainstay length is not directly proportional ...


6

in my experience. BB height affects stability of your ride, but mostly while standing on the pedals since you weight is then directly on the BB. but raising it 7mm may or may not make a difference in your ride. however, raising it ABOVE the axle height will make a dramatic difference in stability. BMX bikes are incredibly nimble (aka unstable) due to them ...


5

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 ...


5

A lot of people commute on cross bikes just fine (and even prefer them to conventional road bikes). He's full of it - the amount you'd need to forget to have issues is roughly being confused enough to think you're an onion (and if you're this confused, well, you're screwed anyway!), especially at commuting speeds. There are different bicycles for different ...


5

As others have said, just because the bike shop says it's a good fit, doesn't make it so. Their incentive is to sell a bike off the floor so they'll find the one that fits best and sell it to you. I got a custom fit and I have longer thighs than most people. This meant that to get the seat position right, I had to have my saddle further back from the pedals ...


5

As for sheer maneuverability, seat tube angle may in some (rather extreme) cases affect wheelbase, which affects stability at variety of speeds. Also seat tube angle will have some minor effect on the position of rider's centre of gravity making it slightly easier to descend with smaller seat tube angle... I guess it would be an unnoticeable difference ...


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

When the head angle is steeper, the bike becomes more nimble and twitchy. The bike reacts faster to steering input making it prone to oversteer. Road bikes tend to have "steep" head angles in the 72 to 74 degree range. A half degree is more noticeable on bikes with steeper head angles, especially at higher speeds. However, if you're a casual rider than a ...


4

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 ...


4

Most 120mm forks have a similar axle to crown height and it's more or less 40mm higher than the axle to crown height of typical 80mm fork. There are of course differences between models, but not really enough to matter. Typically hard tail frames are designed around a range of fork sizes. 120mm would be long for an XC frame that came with an 80mm fork. I ...


4

The trend towards compact frames goes back to the early 90s and an Englishmen named Mike Burrows. Burrows helped design several time trial frames which featured a radically lowered (but not sloping) top tube and a very long seat post. During this time most time trial bikes had top tubes that sloped from the seat DOWN to the head tube (the opposite of what ...


4

I had the same problem on a regular non-suspension bike on the road, if the slope is steep enough. The main cause is technique, and its exacerbated by your suspensions. As you push down on the leading pedal the bike wants to rotate the other way, like you're lifting the handlebars and pulling a wheelie. Your suspension is probably acting as an amplifier ...


4

What would be some good examples of test cases to assess the impact of these parameters? Build a testbed bike that has adjustable parts covering the different parameters you care about. Instrument it appropriately and measure the changes to the factors you care about as you vary the parameters. This is necessarily vague because there are upwards of 10 ...


4

As indicated by out by Criggie in the comments to our original post (OP) your question is also about bike fit as bicycle geometry and fit are interwoven issues. I will do my best to disentangle the different aspects of fit and geometry as well as answer the intent of the question. Geometry and Fit Geometry is the angles and lengths of tubes that make up ...


4

Here's some images to help see the relative differences. Note they assume your stem starts at the same point, so if you're thinking of raising it, print the top one out on paper and then draw your riser in, and how the other stem sizes would work. If you're feeling unsure, wimp out and buy/borrow an adjustable stem. They're heavy and complex, but you ...


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 ...



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