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Old 02-06-08, 06:50 PM   #1
jur
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Thudbuster vs rear suspension

Not long ago I installed Thudbusters on my wife's Yeah <Helios> and my Raleigh 20. After settling for the right elastomers, we were very impressed by the ability for bumps and shock to be smoothed over.

It really make a massive difference in some cases, eg on my wife's favourite ride, the Warburton rail trail, there is a very long bridge with rough transverse slats (did I say rough?) which makes for a very harsh jarring bumpy ride. On a narrow tyred bike you typically have to get off and walk. Not so with the Thudbusters. I ceases to be an issue. What also works well is pedalling with high cadence - there is not much of an issue with bouncing in the saddle.

Then I got the Downtube Mini with built-in rear suspension. I thought that because there is less sprung mass, it ought to work even better. Well, the first thing that became very obvious with my first ride on the Mini was the bounciness - I really had to concentrate very hard not to bounce a lot. So the first thing I did was to investigate the mechanism with a view to tightening the suspension screw which Yan mentioned once. But that did not change the spring constant - all it did was to move the end stop. So that didn't work. So I next implemented BruceMetras' solution of replacing the spring with an elastomer. Once I got the right elastomer in there, bounciness was much improved.

Unfortunately, much of the suspension's ability to absorb bumps was also lost. It still takes the edge off bumps but nevertheless is now is a harder ride than the Raleigh 20. And the other thing that has come out, while bounciness is much better, it is not gone. I still have to pedal at a lower cadence than my optimum to avoid pogoing on the saddle. Not so with the Thudbuster. I can pedal as fast as I want with no bouncing. Plus it is much smoother.

So apologies for this lengthy post, but now I wonder if this bounciness would be a problem with all bikes with rear suspension? If so, then for the sort of riding I do, a Thudbuster is a better option despite the sprung mass being much higher.
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Old 02-06-08, 07:58 PM   #2
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The built in spring in Downtubes is a huge weakness and Yan should just go with a cheap suspension seat post. Better folders like the Birdy and Moulton have better built in built in frame suspension but then again, you do pay a price. I happen to like the Brompton built in rear suspension but you do feel the bike go slightly slugglish at start up.

As for the Thudbuster, they are the standard by which all suspension seat posts are judged. Another alternative is the Brooks Champion Flyer. I could not believe how comfortable this saddle is because it feels hard upon inspection. But once on the street, it's obvious you can ride for miles with this saddle.

Yan and Dahon should have the Flyer on all their 16' inch wheel folders.
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Old 02-07-08, 03:47 PM   #3
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Which model Thudbuster did you use?
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Old 02-07-08, 03:57 PM   #4
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The long travel one.
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Old 02-07-08, 04:17 PM   #5
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So apologies for this lengthy post, but now I wonder if this bounciness would be a problem with all bikes with rear suspension?
"Bounciness" can be adjusted with the right spring/damper in almost any suspension setup. Unfortunately highly adjustable spring/dampers are not readily available in all sizes and are usually rather expensive.
In case of the Thudbuster your legs (and to some extend your arms) are part of the spring/damper system, in most suspension bikes they are not.
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Old 02-07-08, 08:06 PM   #6
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I've said it before, if the bike manfacturer is not going to invest in a costly frame suspension system, then they shouldn't even bother. I would rather buy a Thudbuster for a nonsuspended frame than one that's cheaply built into the bike.

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Old 02-07-08, 08:20 PM   #7
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I tested a Thudbuster on my Dahon Boardwalk S1, and also used it on my Boardwalk D7. I worked great with the stock seat, so I ordered our new Bike Fridays (my NWT and wife's Crusoe) with Thudbusters.

My wife, who had never ridden on one before, really likes it, too. I did have to change the elastomers on the new seat posts up one combination from the prescribed set-up - otherwise both of our seat posts were too spongy for our liking (based upon my experience with the Dahon specific Thudbuster).

My wife's Blue/Blue went to Blue/Black and normal Blue/Black for me (which is comfortable on my Dahon) has gone to Black/Black even though I weigh "only" 200 lbs. Both of my Thudbusters feel similar now. (I think my BF has the newer Thudbuster version.)

Bottom line: It works great. (The pictures below show the BF's BEFORE I changed the elastomers.)
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Old 02-07-08, 08:51 PM   #8
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Well I just went for a quick ride on a workmate's dually. I tied both almost lockout and fully active rear suspension setting, and there was very little bobbing going on even at crazy cadences.

I can't do that on my Mini.

I would conclude that damping is everything. maybe geometry has some influence as well. And maybe the seatpost flexing is another culprit.

* goes away, thinking about how to increase Downtube Mini's damping... *
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Old 02-08-08, 12:33 PM   #9
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I've said it before, if the bike manfacturer is not going to invest in a costly frame suspension system, then they shouldn't even bother. I would rather have buy a Thudbuster for a nonsuspended frame than one that's cheaply built into the bike.
I've never ridden the Mini but would definitely agree with this statement (based on all the comments regarding the bobbing which seems to plague many full suspension designs). It seems the Mini would be better as a rigid frame that's spec'd with Big Apple tires and a sprung saddle. This should hold the price point, and if enthusiasts wanted to, they could spring (pun intended) for a Thudbuster.
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Old 02-08-08, 12:58 PM   #10
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Well I just went for a quick ride on a workmate's dually. I tied both almost lockout and fully active rear suspension setting, and there was very little bobbing going on even at crazy cadences.
How did you like the dually compared to the thudbuster?
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Old 02-10-08, 01:13 AM   #11
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How did you like the dually compared to the thudbuster?
The dually won out. But you can't stand up to pedal *at all* unless you lock the suspension out. There the ThB wins out.
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Old 02-11-08, 12:24 PM   #12
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My Dahon Speed TR came with the Thudbuster Long Travel, and I think its by far surpasses most bike suspensions. It readily soaks up all irregulars in the road. I mounted a Brooks B-17 to it (note a cushy seat by any measure) and have really enjoyed riding dirt trails and gravel bikeways. I'm in the process of building out a Surly LHT and I'll be mounting a Thudbuster, though the Short Travel, to it.

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Old 02-11-08, 03:12 PM   #13
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Well I just went for a quick ride on a workmate's dually. I tied both almost lockout and fully active rear suspension setting, and there was very little bobbing going on even at crazy cadences.

I can't do that on my Mini.

I would conclude that damping is everything. maybe geometry has some influence as well. And maybe the seatpost flexing is another culprit.

* goes away, thinking about how to increase Downtube Mini's damping... *
The geometry of the rear suspension is huge. The higher the pivot point (real or virtual) of the suspension, the more 'anti-squat' (due to pedaling) the suspension will have in it. Of course, as it get higher and higher, the path of the wheel gets less and less vertical which causes other issues.

Damping can help significantly, but it has it's downside. Damping takes mechanical energy (i.e. your spinning legs) and converts it to heat (instead of pushing you forward). I'd rather take that mechanical energy from my legs and turn it into kinetic energy of me and the bike going forward.

A lot of the problem comes from the spring selection. When pedaling at a good cadence (90 rpm, 180 leg strokes), you'll be supplying a 3 Hz input. To have a suspension with such a short amount of travel, Yan has had to stuff a pretty stiff spring in the suspension (or risk a bunch of bottoming out). Well, I'm going to bet the natural frequency of the system is around 3 Hz. So a normal pedaling cadence excites the rear suspension and you bounce up and down.

The Thudbuster has more travel and so it can use a softer spring (elastomer). This means the natural frequency might be more like 1.5-2 Hz. Well, when you're pedaling at a 45-60 rpm cadence, you generally aren't pedaling hard. You don't put much energy in the system and it doesn't get too excited (bouncy).

It would be interesting to see if a softer elastomer eliminates a lot of the pedal bob you get on the Mini. My guess is that it would, but that over small bumps you'd now have to deal with the suspension bottoming out harshly. Out of the saddle, most full suspension bikes bob a lot. Big inputs and low cadences really move things around.
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Old 02-11-08, 04:05 PM   #14
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A lot of the problem comes from the spring selection. When pedaling at a good cadence (90 rpm, 180 leg strokes), you'll be supplying a 3 Hz input. To have a suspension with such a short amount of travel, Yan has had to stuff a pretty stiff spring in the suspension (or risk a bunch of bottoming out). Well, I'm going to bet the natural frequency of the system is around 3 Hz.
Your bet would pay off. It is smack where I want to pedal, also with the current elastomer.

I'll put in the softer elastomer again and keep it in there for a while to really get to know it's response. All I did before was stick it in, go for a very short ride, and reject it again.

I wonder if elastomers with more lossy material is available? I keep thinking of the dually and how well it worked. If I can't improve matters well enough, I may just lock out the suspension and see if I can cobble a ThB on the seat post. Or maybe I should get the Big Apples first since I am stil using the original tyres which are pretty harsh.
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Old 02-11-08, 08:55 PM   #15
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get the big apples first ,.... to get a good baseline ... than look outside the box....

the elastomers for example.... like a too hard one and a too soft one ... they could be cut in half and both used ....voila ... now you have a progressive elastomer... thats what I think the bike needs to make the suspension work better

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Old 02-11-08, 09:17 PM   #16
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get the big apples first ,.... to get a good baseline ... than look outside the box....

the elastomers for example.... like a too hard one and a too soft one ... they could be cut in half and both used ....voila ... now you have a progressive elastomer... thats what I think the bike needs to make the suspension work better

thor
Combining 2 elastomers is a good suggestion - I haven't thought of that before (despite it being in use on my ThB!) And I will order some BAs soon, next week...
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Old 02-11-08, 11:44 PM   #17
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If you're running a Thudbuster, then make the suspension rigid as a baseline. An aluminum block or very stiff polyurethane (Shore 90 hardness) would work. You'll probably find that the Thud doesn't need any help from the rest of the bike.

As far as the Big Apples go, money is never wasted on good tires.
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Old 02-15-08, 05:30 AM   #18
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Jur who did you buy your Thudbuster from? Was it an Australian source?

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Old 02-15-08, 06:40 AM   #19
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JensonUSA. Aussie marketplace - gouges. Ouch. (And postage was 'free', part of a huge group buy of Prolink Gold which I organised )
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Old 02-15-08, 11:15 PM   #20
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Well, I put the soft elastomer back in and went for a short ride. I ignored initial bounciness and just rode. Had hardly gone around the corner on a bumpy singletrack when suddenly *click* huh? waddat??

It felt OK and I rode on for a few meters, in fact it felt great. I stopped to make sure nothing broke and then saw the elastomer had actually broken and escaped the joint, bulging the concertina sleeve out to one side looking like it's about to give birth. (I sorta expected this result.)

Walked back home (dang it takes long to walk) and put in the hardest elastomer, went for another ride. It felt the same as the medium one so I'll keep that in for some time to get the feel for it.
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