Thudbuster and Dahon geometry
#1
Senior Member
Thread Starter
Join Date: Jul 2008
Posts: 1,984
Bikes: Brompton, Dahon Vitesse D5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
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.
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.
#2
Senior Member
Join Date: Aug 2005
Location: Vancouver, Washington and Ocean Shores, Washington, USA
Posts: 1,319
Bikes: 2 - 2007 Custom Bike Fridays, 2 - 2009 Bike Friday Pocket 8's, Gravity 29'er SS, 2 - 8-spd Windsor City Bikes, 1973 Raleigh 20 & a 1964 Schwinn Tiger
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
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
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
Last edited by Foldable Two; 10-26-10 at 02:17 PM.
#3
Senior Member
Join Date: Jun 2010
Location: Tarago, New South Wales, Australia
Posts: 68
Bikes: Birdy, self-built recumbent suspension trikes
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
The initial stage of travel is highly inneficient IMO, i.e. it's near-horizontal,
#4
Senior Member
Thread Starter
Join Date: Jul 2008
Posts: 1,984
Bikes: Brompton, Dahon Vitesse D5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
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.
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.
#5
New usename ThorUSA
Join Date: Nov 2004
Location: Southern Illinois USA
Posts: 2,469
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
you guys worry to much
it works
go riding
thor
it works
go riding
thor
#7
Senior Member
Join Date: Aug 2005
Location: Vancouver, Washington and Ocean Shores, Washington, USA
Posts: 1,319
Bikes: 2 - 2007 Custom Bike Fridays, 2 - 2009 Bike Friday Pocket 8's, Gravity 29'er SS, 2 - 8-spd Windsor City Bikes, 1973 Raleigh 20 & a 1964 Schwinn Tiger
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
We like them - no over-analysis here.
#8
Professional Fuss-Budget
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.
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.
#9
New usename ThorUSA
Join Date: Nov 2004
Location: Southern Illinois USA
Posts: 2,469
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
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.
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.
thor
#10
Senior Member
Thread Starter
Join Date: Jul 2008
Posts: 1,984
Bikes: Brompton, Dahon Vitesse D5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
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.
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.
#11
Senior Member
Join Date: May 2005
Location: Albany, WA
Posts: 7,393
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Likes: 0
Liked 7 Times
in
6 Posts
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.
#13
Professional Fuss-Budget
https://store.velo-orange.com/index.p...g-touring.html
https://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....
#14
Senior Member
Join Date: Sep 2006
Location: NW England/Aveiro
Posts: 638
Bikes: Joey Sport; Mezzo D9;Curve D3; Surly LHT self build cargoesque
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 15 Post(s)
Likes: 0
Liked 2 Times
in
2 Posts
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.
"I'm Thor"
"Should've uthed a thprung thaddle thilly"
Now I will do penance by getting back to work and off this forum.
#15
Senior Member
Thread Starter
Join Date: Jul 2008
Posts: 1,984
Bikes: Brompton, Dahon Vitesse D5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
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.
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.
#16
Newbie
Join Date: Aug 2017
Posts: 3
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Folding bike touring gearing
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)
#17
Banned
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..
there is a preload bolt running thru the LT version , but not on the ST
Or the new eeSilk , a lighter one for the gravel grinder set ..
(own 1 LT, 1 ST)
...
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..
there is a preload bolt running thru the LT version , but not on the ST
Or the new eeSilk , a lighter one for the gravel grinder set ..
(own 1 LT, 1 ST)
...
Last edited by fietsbob; 05-29-19 at 11:55 AM.
#18
Senior Member
Join Date: Sep 2004
Location: Chicago area
Posts: 2,541
Bikes: Airborne "Carpe Diem", Motobecane "Mirage", Trek 6000, Strida 2, Dahon "Helios XL", Dahon "Mu XL", Tern "Verge S11i"
Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 978 Post(s)
Liked 574 Times
in
395 Posts
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
#19
Senior Member
Join Date: May 2005
Location: Albany, WA
Posts: 7,393
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 321 Post(s)
Likes: 0
Liked 7 Times
in
6 Posts
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.
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.
#20
Senior Member
Join Date: Sep 2004
Location: Chicago area
Posts: 2,541
Bikes: Airborne "Carpe Diem", Motobecane "Mirage", Trek 6000, Strida 2, Dahon "Helios XL", Dahon "Mu XL", Tern "Verge S11i"
Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 978 Post(s)
Liked 574 Times
in
395 Posts
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
These images were taken on the train after I got to the station standing up.
Steve
#21
Senior Member
Join Date: Jan 2017
Posts: 1,064
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 350 Post(s)
Likes: 0
Liked 122 Times
in
90 Posts
The top head of my thudbuster st started to rotate around the lower seat post. But it was still under the warranty period so they exchanged the whole unit. I didn't look closely at the old unit, but the new unit they sent me had a pin which passed through both the seat post and the head. I asked if this pin was holding the 2 parts in place, but they said it was a butted join and weren't sure what the pin was for. I assumed they meant that the head was pressed into the post. If in the future the head starts rotating again, I might drill a pair of holes and press in pins.
Regarding the travel Arc of the ST, it feels like the vertical movement is less than the horizontal movement. My back is sensitive to the change in position, so I decided to use the middle elastomer, which seems to move 1cm to the rear when I sit lightly on it. The soft one travels really far so I won't use it. The hard one dampens very little for me so I won't use that either.
I assume that Dahon seat tubes have slightly steeper angle since the seat tube passes behind the BB. This would shift the thudbuster movement slightly more horizontal than vertical. But the thudbuster is still very effective in absorbing shock even from cobblestone roads.
On another note, the clamp screw and nut stripped out and getting replacements is a pain because they're not standard fasteners. I have to wait a few days for the parts to arrive before I can ride again. The manual says 6.8Nm, but strangely the text printed on the clamp says 5 Nm. I hand tighten with a short wench so I assume I made it 6 Nm. But next time I'll check with a torque wrench. The problem is that I've been testing several saddles and have been readjusting the screw which wasn't turning smoothly. Maybe the washer isn't sitting level on the bearing surface. I wonder if I should grease the threads.
Having 2 screws on the clamp really helps with precise saddle adjustments.
Regarding the travel Arc of the ST, it feels like the vertical movement is less than the horizontal movement. My back is sensitive to the change in position, so I decided to use the middle elastomer, which seems to move 1cm to the rear when I sit lightly on it. The soft one travels really far so I won't use it. The hard one dampens very little for me so I won't use that either.
I assume that Dahon seat tubes have slightly steeper angle since the seat tube passes behind the BB. This would shift the thudbuster movement slightly more horizontal than vertical. But the thudbuster is still very effective in absorbing shock even from cobblestone roads.
On another note, the clamp screw and nut stripped out and getting replacements is a pain because they're not standard fasteners. I have to wait a few days for the parts to arrive before I can ride again. The manual says 6.8Nm, but strangely the text printed on the clamp says 5 Nm. I hand tighten with a short wench so I assume I made it 6 Nm. But next time I'll check with a torque wrench. The problem is that I've been testing several saddles and have been readjusting the screw which wasn't turning smoothly. Maybe the washer isn't sitting level on the bearing surface. I wonder if I should grease the threads.
Having 2 screws on the clamp really helps with precise saddle adjustments.
#22
Senior Member
Thread
Thread Starter
Forum
Replies
Last Post
Derailed
Folding Bikes
21
09-16-16 01:41 PM