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Old 10-26-10, 01:51 PM   #1
chagzuki
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Thudbuster and Dahon geometry

The Thudbuster design has been bugging me for ages now and I've only just realized that the Dahon seat tube angle exacerbates the problem, unless the Dahon versions have been optimized to compensate for the steeper seat tube angle that Dahon's have. Does anyone know if this is the case?

The initial stage of travel is highly inneficient IMO, i.e. it's near-horizontal, so the more back-leaning the seat tube the better it suits the Thudbuster design, AFAICS.

The way to compensate for this with the LT would be to cut a few mm off one of the elastomers so that the default position is further into the arc of travel; that would likely make for a much more efficient motion, but the saddle would be set further back, perhaps too much so. And with the current versions the clamp is set at the back so there's limited scope for moving the saddle forward.
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Old 10-26-10, 02:02 PM   #2
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I have a four year old Dahon/Thudbuster combo. The real difference appears to be in the lever action on the elastomers - as seen by just leaning on the saddle, vs the newer design LT on our Fridays. The older one is stiffer, and uses the called for weight category elastomer color combo to get the same "action" that the newer LT's need the weight category higher (than we actually are) elastomers to achieve.

Both feel relatively the same. I don't have both bikes with me right now, but my little pic in the upper left-hand corner of this post shows them one behind the other - I think the seat tube angles are pretty much the same. Did find a shot of my Dahon next to one of our non-Thudbuster equipped Pocket 8's - seat tube angle looks about the same.

ADD: Found larger version of the little pic - looks like a bit of seat tube difference, but I replaced the Blue/Black elastomers on the Friday with Black/Black, so they now feel similar. (I weigh 205-207 dressed.)

Lou
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File Type: jpg IMGP1188 (Medium)..JPG (90.2 KB, 67 views)

Last edited by Foldable Two; 10-26-10 at 02:17 PM.
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Old 10-26-10, 02:17 PM   #3
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Quote:
The initial stage of travel is highly inneficient IMO, i.e. it's near-horizontal,
Are you asessing that with your body weight on the saddle? ie the response to a bump when riding, rather than the static deflection?
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Old 10-26-10, 02:35 PM   #4
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I am, yes, so long as you go by the recommended elastomers. If you use softer ones then obviously the compression is greater and the angle better. . but that leads to more pogoing. I did a bit of analysis in photoshop and figured out that for small-medium sized bumps, as the rear wheel is raised the saddle moves along a near-straight trajectory, i.e. it's an arc so wide as that the curvature is negligible. The angle of that motion is around 37 degrees. The thudbuster doesn't get near that until far into the arc. At 37 degrees it's true that there's a lot of horizontal as well as vertical movement occurring but there's still more vertical than horizontal and with firm elastomers the opposite is the case with the thudbuster. So it efficiently dampens front to back movement but not so much vertical. So I guess the aspect of the design that's made it so popular is the lack of sticktion rather than the efficiency of the motion.

I guess if your saddle has the right kind of give then that combined with the thudbuster motion could be very efficient.

Unless I've misjudged something, though I can't see what that could be.
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Old 10-26-10, 03:45 PM   #5
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you guys worry to much
it works

go riding

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Old 10-26-10, 04:08 PM   #6
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Hey, the technical/design side is interesting. Meaty and nutritious.
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Old 10-26-10, 09:02 PM   #7
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We like them - no over-analysis here.
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Old 10-27-10, 06:58 AM   #8
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I believe it's the same ol' Thudbuster, just on a seatpost compatible with Dahons.

Offhand I'm not convinced a Thudbuster would be of much benefit to a Dahon, since there is so much flex in the post to begin with. I'd imagine you would benefit far more from either lower-psi tires or some type of wheel / frame-based suspension.

Another option is a sprung saddle, since that won't have any horizontal travel.
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Old 10-27-10, 07:20 AM   #9
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Originally Posted by Bacciagalupe View Post
I believe it's the same ol' Thudbuster, just on a seatpost compatible with Dahons.

Offhand I'm not convinced a Thudbuster would be of much benefit to a Dahon, since there is so much flex in the post to begin with. I'd imagine you would benefit far more from either lower-psi tires or some type of wheel / frame-based suspension.

Another option is a sprung saddle, since that won't have any horizontal travel.
have you tried one ?

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Old 10-27-10, 07:26 AM   #10
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A sprung saddle may well be the best solution overall but there don't seem to be many on the market. Which is probably about aesthetics. . . they look low-tech, but actually the current range of elastomer comfort saddles owe almost zero of their comfort to the elastomers (which barely compress), they're just there for show. All the compression is in the foam. Springs offer plenty of stiction-free movement.

I'm going to demo an ST over the next few weeks and see how I get with it. I've tried it with the recommended elastomer so far and, having analyzed the motion, decided to give a softer elastomer a go in order to enage more (some?) of the vertical travel, I've got a feeling it ought to be as effective as the LT with the recommended elastomers. It does look less cumbersome than the LT when folded.

Last edited by chagzuki; 10-27-10 at 07:30 AM.
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Old 10-27-10, 01:51 PM   #11
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A TB makes quite a difference. If you haven't tried one then you wouldn't know. Once you get used to the 'squishiness' the huge bump-absorbing stuff really works.
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Old 10-28-10, 06:32 PM   #12
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Brooks B-66 + Thudbuster ST = Happy cheeks. I ride this on MTB trails!
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Old 10-28-10, 08:58 PM   #13
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Quote:
Originally Posted by chagzuki View Post
A sprung saddle may well be the best solution overall but there don't seem to be many on the market.
http://www.wallbike.com/catalog/saddles/sprung-saddles
http://store.velo-orange.com/index.p...g-touring.html
http://store.velo-orange.com/index.p...e-model-8.html

There's also the Topeak Allay saddles, which allow you to dial in the amount of give.

And Wallbike, unlike some, let you return a Brooks saddle....
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Old 11-02-10, 07:22 AM   #14
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Forgive me forgive me forgive me but I have to reprise/rewrite this old joke

"I'm Thor"

"Should've uthed a thprung thaddle thilly"

Now I will do penance by getting back to work and off this forum.
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Old 11-03-10, 04:34 PM   #15
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Erm.

Yeah, so having been riding a ST with softer-than-recommended elastomer for a week and a half I'm inclined to think my thesis was correct; it functions as well as the LT with recommended elastomer (well, I'm tempted to think it ought to function better but I can't really tell just yet). Overall it seems a better package, lighter and neater when folded. The only niggle is that it rattles when wheeled not under load.
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Old 08-11-17, 06:25 AM   #16
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Folding bike touring gearing

Quote:
Originally Posted by jur View Post
A TB makes quite a difference. If you haven't tried one then you wouldn't know. Once you get used to the 'squishiness' the huge bump-absorbing stuff really works.


Jur =- am busy reading your blog with interest.
I have 3 dahon folders (20") that I am wanting to equip for touring. Am wondering about a front derailliuer to add on a 39 chainring. (currently 52 on front and 11 - 32 on my bike and 11-30 on my family's bikes).


The 39 on the front will give me an easiest ration of 1.16, however I have no idea how easy that would be.
Can calc gear inches but seeing you're on a 20" as well....


Your thoughts please.
Thanks
Derrick (Brisbane)
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Old 08-11-17, 08:19 AM   #17
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NB: the telescoping type seat post passes behind the BB of the frame, Bike Friday as an alternate design example,
uses a folding seat mast, so the seat post centerline intersects the BB center..


Brompton has rear suspension in it's design , put people seem to want to stiffen it, apparently..






...

Last edited by fietsbob; 08-11-17 at 08:25 AM.
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Old 08-11-17, 08:23 AM   #18
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Quote:
Originally Posted by jur View Post
A TB makes quite a difference. If you haven't tried one then you wouldn't know. Once you get used to the 'squishiness' the huge bump-absorbing stuff really works.
I agree. I have 2 Dahons with ThudBusters, and can attest to the effectiveness. These are "long-travel" designs made (I think) as a special order for Dahon because there are some differences in construction, but they work the same.

One word of caution: you should inspect the joint between the seatpost and the suspension unit periodically for cracks. One of mine broke off at that joint, causing me to have to ride the last mile of my commute standing up. Luckily I had a few seconds of warning, so no soft tissue injuries were incurred.
This may have been a result of riding the bike in the winter... there's a lot of salt on the roads.
Steve
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Old 08-11-17, 03:23 PM   #19
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Hi Derrick,

I have struggled to get front derailers on my folding bikes and have used other solutions, a Shlumpf Speed Drive, but more generally a wide gear ratio. Typically 300%. The one Dahon we toured with had the extra chain ring used with long climbs. No derailer, we just shifted by hand on the few occasions it was needed. That was great since we would stop to rest at the top and manually shift up again. When touring you're not winning races so manual is just fine.

A bigger problem with that case was the chain dropping because of lack of chain guard. There are more solutions available these days to mount front derailers so it is a lot easier. Gear range from the mid 20s to 90 or higher would work great. Your fitness will dominate.
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Old 08-11-17, 07:29 PM   #20
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Pursuant to #18, here are images of the ThudBuster that broke. I have another one which I am comfortable using, but I'm inspecting it more carefully.
These images were taken on the train after I got to the station standing up.
Steve
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File Type: jpg ThudBuster broken off side view.jpg (90.9 KB, 14 views)
File Type: jpg ThudBuster broken off oblique view.jpg (91.3 KB, 14 views)
File Type: jpg ThudBuster broken off bottom view.jpg (88.9 KB, 14 views)
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