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For bikes like these, why aren't the rear shocks (the shocks are directly above the pedal) vertical like those of a motorcycle? I don't see how the bike can take shocks when the shock absorber is at such a low angle.

A friend said the mud-guard is so high because there's no other way to attach it to the cycle at a lower height. Is that really the reason why the mud-guard is so high?

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This counts as a BSO, not exactely a bike... –  heltonbiker Jun 26 '12 at 20:11
    
Don't all MTBs? :) –  Stephen Touset Jun 26 '12 at 23:14
    
BSO = en.wikipedia.org/wiki/Bicycle_Shaped_Object :) I'm amused, but intrigued as well. Never knew. Could you share a few pics of proper bikes and how does one recognize them? –  Nav Jun 27 '12 at 2:55
    
@heltonbiker My thoughts exactly. After a little Googling, I found they sold these bikes in India for about 6600 INR, or about 125 $US. I read once, that one problem with all low priced bikes with shocks, is that they usually have bad designed shocks, because all the good designs were patented, and you can't produce a low priced bike while paying for the licensing costs of a patent. So they have to find out how to put shocks on a bike in a way that works, but doesn't infringe on any of the existing patents. Because of this, you end up with some really interesting suspension configurations. –  Kibbee Jun 27 '12 at 12:29
    
@NAV: symptoms of BSOs are: components that resemble hi-end gear (disk brakes, shocks) but have a very poor finish; "fancy" frame "design" choices with no structural or functional purpose; Excessive, visually polluted proliferation of accessories; Low price; Not being sold in bike shops (for example, department stores or supermarkets); Being given as a prize; Appearing on some wannabe "eco-friendly" car advertisement. –  heltonbiker Jun 27 '12 at 17:31
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From my understanding, one of the major features for bicycle suspension is vertical travel. This is to increase pedal efficiency and rear wheel feel. This is why you see engineers jump through hoops when designing rear suspension for bicycles. For example, take a look at the Pivot Mach 429. If I count correctly, this bike has 5 points of rotation to accomplish beter pedal efficiency as well as offering more rear-wheel travel. Some motorcycles do have non-vertical mounted suspension as well; the first to come to mind is the Kawasaki Ninja 650.

As for the "mud-guard", that is often referred to as a filth prophylactic. This isn't intended to do much more than keep mud off your shirt and backside. Full fenders can be quite difficult to mount to a full-suspension bike (everything keeps moving, man!) so filth prophylactics are common "good enough" equipment. They also tend to have very little in frame requirements (full fenders require braze-ons for mounting them), so they fit on most any bike.

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The rear wheel is attached to stays that connect to a pivot point. As long as when the rear wheel moves upwards, the wheel and stays all rotate around the pivot to compress (or stretch, depending on shock type) the shock, then the rear suspension should work fine.

Take a look at this bike, the shock is vertical. But, unlike the picture you showed, there are a number of pivot points. The bike you showed has a single pivot near the crank and pedal area. http://www.dirtragmag.com/sites/default/files/blogarific/wp-content/uploads/2007/06/trek-fuel-ex-full.jpg

The mudguard is high so that the wheel doesn't hit it and to ensure there is plenty of mud clearance. Most mountain bikers I know don't bother with mudguards, because the faff of them is annoying (it's not because of lack of mud, I'm in the UK and it can get pretty muddy at times). So, they're usually not fitted to mountain bikes as standards. That means, this one has to be fitted to the seat tube, and it doesn't move with the wheel as it takes up shocks.

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The fender or "mud guard" is so high because if it was much lower the tire would be banging into it whenever the shock compressed.

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Sorry, should've added more info. I asked the question about fenders because I've seen it on bikes without shock absorbers too: unnoonnygroup.com/image/cache/data/CYCLES/Adults/… –  Nav Jun 27 '12 at 7:29
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There are two possible reasosns: 1) That bicycle is cheap and was built by someone who didn't really know what they were doing. 2) That type of rear fender has a pivot point in it to allow proper positioning. Sometimes, if the pivot is loose, the fender tends to fall as the bike hits bumps. It may be that the fender was installed like that to keep it from lowering onto the tire as the rider bike moves along. It's more likely the first one though. –  jimirings Jun 27 '12 at 12:03
    
There's a simpler explanation. It's a cheap plastic part with no pivot, and it's easier to make a bunch that are all identical than to make one for each bike with a different seat tube angle. –  Stephen Touset Jun 27 '12 at 12:42
    
@StephenTouset That's definitely a possibility. I've just never seen one without a pivot. Making it fit any bike regardless of seat tube angle is why they usually have one. But I shouldn't be surprised to find out there's an even cheaper one. –  jimirings Jun 27 '12 at 16:14
    
@jimirings: I'd go for 1. The bicycle was built by someone who didn't really know what they were doing. –  Nav Jun 29 '12 at 3:17
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What's above the rear wheel for vertical shocks to mount to?

It's pretty clear from the provided picture that the fulcrum for the rear wheel is near the bottom bracket. An upward force against the rear wheel will cause it to lift, reducing the distance between it and the mount point of the shock, allowing the shock to resist that movement.

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Ok, so in ordinary English, it means that the point of rotation of the black bars is near the pedals. So a shock to the rear wheel pushes the rear shocks in exactly the angle that it is at. What about the mud-guard? –  Nav Jun 26 '12 at 15:09
    
We've already shown that the wheel will move upward when an upward force is applied to it. I think you can work out the answer to that question from here. :) –  Stephen Touset Jun 26 '12 at 18:01
    
Ok, so how about this bike? unnoonnygroup.com/image/cache/data/CYCLES/Adults/… There's no wheel movement upward and downward. –  Nav Jun 27 '12 at 7:27
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What counts is where a tangent from the rear wheel meets the rearmost point of the mudguard. As long as that line clears the rider they will get reasonable protection from the worst of the filth. The idea is to carve out a rider-shaped hole in the stream of muck thrown up by the rear wheel. Those guards are not about keeping the rider dry, they're about making the rider less dirty. –  Kohi Jun 28 '12 at 23:12
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