wouldnt car suspension bushes or exhaust hangers be useful for the rubber spring

Here are 2 suspension bushes made from doorstops in action:

bush made from 1 doorstop plus 1 10mm thick piece from another doorstop cemented on it, sanded down for smoothness:
http://i160.photobucket.com/albums/t...i/IMG_0294.jpg
Installed with me seated normally: Note how much it bulges out. Installed with mudguard washer.
http://i160.photobucket.com/albums/t...inirubber1.jpg

Bush made from 2 shortened doorstops cemented end-to-end:
http://i160.photobucket.com/albums/t...i/IMG_0295.jpg

Installed with me seated normally: Note how much less it bulges out compared to the other one. It has a recess at each end, so no mudguard washer is needed.
http://i160.photobucket.com/albums/t...inirubber2.jpg

I cannot explain why the 1st one bulges out more than the other. I guess I have to hand back my suspensionology PhD. The only attempt at an explanation is that the 2nd one is captured/constrained more due to the recess allowing it to go deeper into the frame socket.

The 1st one is noticably softer due to this effect. The 2nd one used to be 2 separate pieces, and it was stiffer then. It would be stiffer still if a mudguard washer was placed in between the pieces. You could tune it for rider weight this way.

Hi Dr Jur,

I wonder whether the position of the lamination and associated rigidity from the glue may explain this effect?

Edd

:)

The glue is rubber cement, ie real rubber dissolved in a solvent, same stuff for patching tubes, so that can't be it, methinks.

Dr Jur,

I was thinking of other laminated materials that are stronger/stiffer than the original material of the same thickness, although the effect is probably with material that has grain or fibres running in different directions e.g. gulan beams. The only other thing I can think of is that the rubber is manufactured in such away that it is not homogenous through out its length.

Edd

Dr. Jur:

I got the rubber doorstops that you kindly mailed to us and am contemplating installation of your Nirvana suspension technology. After reading carefully through this thread, I have one remaining question for you.

I'm a little heavier than you at 86kgs (all muscle, you understand ;)). So I'm thinking I need a little stiffer setup than the one you found to be perfect. Therefore, I'm thinking that I don't cement the two doorstops together and have them compress independently. Does that make sense to you?

Thanks in advance.

What I would suggest as a 1st experiment is to use 1 doorstop with as big a washer you can find. I lately found that mine was softer perhaps not due to the length increased due to glueing, but due to a smaller washer which I had used. The doorstop therefore had less of its bulk to compress resulting in softer behaviour. With the bigger washer it was stiffer again. The stiffest I got was with 2 stops end-end.

So try the single stop with big washer first as a reference point.

I'm well over 240 lbs, and my IXFS (the 20" 9 speed bike) seems fine for me. I've got a Mini on the way as well, but I may just lock the suspension out on that and put Big Apples on when I'm done putting it out for review.

Like to see your Mini sometime when you get it SB if you are ever in London.

I'm in London all the time (it's those trips that got me into folders, both 20's and Downtubes), and I'll be more than happy to arrange to meet and let you have a butchers and a ride. You can bring your Brommie and we can swap experiences! (actually, I think I'm over the Brompton max weight)

Hi Sammyboy,
I'll be interested in how the Mini works out for you. You are also fairly tall, yes? My weight and height are what have kept me from getting a Mini.
Juan

Hey Doc Jur:

I did it! I installed your Nirvana suspension mod! The procedure went very smoothly as I had nice detailed pictures to consult.

I haven't taken it for a long ride yet, just down the street. But initial results are very encouraging. It has basically reduced pogo-ing to a negligible amount. There is an incline section leading up to my house where all the frequencies line up in a harmonic orgasm and the Mini pogos every time. Tried it a couple of times tonight and voila, the pogo-ing, she is gone (95% anyway).

I just installed one doorstop, per your suggestion. I'll see how it goes on a longer ride to see if it warrants any more tweaking. Hopefully, this configuration will hold up.

Thanks again Doc for your detailed investigations and sharing it with us!

:beer:

Congrats on your suspension upgrade. Will you also change out the components that cause the swingarm to fishtail?

I'm not planning to. I checked my Mini, and it doesn't appear to be a problem (keeping fingers crossed).

I did the Antipodal Suspension Upgrade too. I was in a rush, so didn't photograph anything; and I was away from my computer, so I didn't consult the excellent directions provided above. I used about one-and-a-half doorstops (the leftover bit is 25 mm). I didn't glue the two pieces together. The exposed part of the rubber is now 40 mm unloaded, and it compresses to 34 mm when I sit on the saddle.

I've ridden 28 miles on it so far, 18 of them in the last two hours. Comments? Well, for the first time, I'd have to say I didn't think about the suspension once! Never bottomed out, never pogo'd, didn't have any creaking noise.... Draw the conclusion of your choice; it seems I noticed nothng at all. Presumably I was, like Jur, in Suspension Nirvana.

Note, at one point, heading up West Side Hwy at about 17 mph, I hear the distinctive sound of a tire blowing out. It sounded like my rear wheel. I pulled over, anticipating that harsh bumping of rim on pavement. But I soon saw that both tires were (and are still) fully inflated. Bizarre; what could that sound have been? Never found out; must have been a passing car.

One more word to Jur and Pine Cone: Thanks!

Did you try to find something here in the U.S. that would have worked?

I went to the hardware store, but found only the standard American doorstops, not the rubber kind that Jur sent. So I signed up for the Bike Forums International Parts Exchange program once again :).

Congrats to you too. It's a really a nice modification. Yan should really take note of it and change the specs of the bike to this. It's much better ride and should be cheaper too.

On the "bang" noise - I wonder if the doorstop/elastomer was not fully seated at first, then popped fully in while you were riding. It's that, or you had too many beans for lunch! :D

Jur,
Could you help? Just acquired a used downtube mini capreo 9 and wanted to change the spring mechanism into the one
you created with the door stops. What is the company name you acquired them from? I will try emailing them to see if they would send some
to Canada.

Thanks
Gregory Szabo
gszabo@ess.ca

I doubt that you would have any joy from contacting them - it is a franchise chain store that sells all sorts of rubber products. I could send you some doorstops myself, if that store still keeps them. I'll check.

Hello,

Sorry for the reply to an old post. But did you make the replacement bushings?

Thank you
Mirfi

Yes, on a lathe that I had access to at the time.