newjazz

hello,

ok, let me explain, i would like to transform my hard tail long tail yuba mundo to rear suspension!
initially i was thinking of just cutting the chain stay away from the seat stay to form a simple swing arm but, before i attempt this i would like some advice. anything, i mean any ideas would be greatly appreciated!

drowling23

Umm, your bike is quite long. even if you manage to put in a suspension mechanism between the front part and the rear part of the bike, regardless of the length of suspension you choose, the actual amount of vertical suspension will be marginal due to the rather small angle you'll be making with the chain stay.

Also, it's entirely unclear where you would put the bottom pivot for the suspension. Apart from the location near the crank, there's no obvious position where this would be possible. You are looking at a fairly serious frame redesign.

Andrew R Stewart 

I'l add to the negatives and mention the changing loads and their effect on any suspension sag.


BTW why do you want suspension? If it's for comfort then consider a suspension post. If it's for control then you need to slow down. You have a truck not a Baha race rig. Andy

newjazz

true, i considered this so,
I am not looking for a huge amount of travel, 2 inches (4 cm) would be fine!......guys, i am already on my third back wheel and fourth tire as a result of pinch flats from the surprise pot holes here in Paris!
i know that loading would effect the how much actual usage but, i usually have the same constant load, a guitar amplifier! rarely, to i have someone riding on the rack bedsides, i could get an adjustable preload shock, no?

however, its the pivot spot that i am not sure about!
oh, i could post a pic of my bike but, dont have a website to link to.......

newjazz

GOOD POINT!........but, even at a slow pace i have damaged the tweeters in my amplifier just from the shock!..... this is paris!
given, some of the streets here are smooth as glass but, then there is also streets that are "pavot"........

unterhausen

I dont' quite understand how you would suspend the load. Would you attach the rack to the frame and decouple it from the wheel? I would find a suspended mountain bike rear triangle and figure out how to fit your current frame with the required pivots and shock mount points.

Does it have a steel frame? Can you post a picture?

Andrew R Stewart 

I think the problem lays with the speakers, not the bike. Are you running a portable PA/music system? We have a guy here in Rochester who does this. His rig is used for the City's "Slow Rides". As we gather this is a neat thing. But when we ride as a group and the music is loud enough to be heard over traffic and travel further then the few riders about the rig the sound level is really obnoxious. When we ran our Santa Ride I worked the intersections and got real tired of the noise as I rolled up and down the line of riders getting back in position for the next intersection I was responsible for. Andy

newjazz

Thanks, fit the advice but, I would like to add rear suspension! Here is pic... txt

fietsbob

Used to be a company offering a Hub with an elastomer doughnut surrounding the axle bearing assembly.. Yes that is Past Tense.

those are Aluminum frames ,right ?, if you had aluminum fabrication and welding experience you would not have needed to post here first, I suspect..


create a suspension scheme for the load, that cabinet, within the bike.. not expecting to re engineer the bike, itself....







...

CliffordK

What about hunting down an Extra Cycle Free Radical, and mounting it to a suspension MTB (perhaps with some mods).

https://www.xtracycle.com/free-radic...onversion-kit/

They show up from time to time on Craigslist as well as E-Bay.

You might need to beef up the suspension a bit.

Andrew R Stewart 

Clifford- Have you ridden a heavily loaded cargo bike? They are already a handful at times with the load "wagging the dog" to a degree. Add the hinges that pivots are and the leverage changes from what a "standard" suspension is designed to work with one might end up with a loosy, inch worming ride. besides if the load is still directly attached to the suspended wheel the shock to the load isn't much different then a hardtail with load.


For damping shock to the load it is the load that needs to be suspended. I don't off hand know of any cargo bike where the load is the suspended element. Andy

newjazz

the yuba mundo frame is not aluminium but, STEEL!.........like i said, more than often i dont put more 25 to 35 ibs. on the rear, given, the frame is rated to carry 200 kilo!
if i dont get any input on the design of the rear, i will simply cut off the chain stay, add a pivot and mount a DMN coil over shock!
last night i played a small gig on the opposite end of Paris and the new suspension fork worked fine carrying an instrument on my back, a small amp on the front, a small mixer and it DAM sure made the ride more comfortable!
I AM CONVINCED THAT MODDING THE REAR SUSPENSION WILL MAKE THIS BIKE THE ULTIMATE ELECTRIC LONGTAIL CITY BIKE!

come on, guys give me some ideas on how to get this done!

unterhausen

Andy's point is that a mountain bike suspension is designed for the loading and dimensions that it usually sees. It is a very highly evolved system, and it really isn't adaptable to other systems. The geometry is totally different than a cargo bike. You probably have to go with a suspension that is more like a car, with the dampers and springs pushing up on structure that isn't there yet. There are very few people in the world that can successfully design a suspension, and they aren't here.

CliffordK

Yes, I have ridden one with 100+ pounds on the rack, but I didn't like the feeling of a high load, and for other reasons, I much prefer the load on a trailer. Most trailers don't have suspension, but I have seen a couple with suspension including pet trailers.

I did end up with a flex problem with my home built cargo bike, perhaps due to a weak front frame, and an alignment issue, then when pushed by a heavy trailer downhill, it can cause handling to be a bit difficult. I haven't had a heavy load on the rack for some time, but I don't think the flex was as big of an issue with the bike alone.

Putting suspension under the rider, and the load unsuspended over the tire might not handle too bad, if one got the spring right. Or, like you say, it could give an odd springing sensation. However, reading back, that wouldn't provide the benefit the OP wanted, protecting the load.

Looking at the photo of the Yuba:


I'm not quite sure where I'd cut it. It appears to be designed with an integral strong mixte style rear triangle.

One could cut at the bottom bracket and behind the seat post, and build a setup similar to the Free Radical on a suspended MTB, but it would do nothing for the load, and give the potential issues Andrew mentioned.

I do think suspension could be built, but would probably require some major reconstruction to work effectively. I.E. building a new bike or rear-end.

I'd probably elongate a frame similar to the Yuba frame, and build a yoke type suspension. Two generally rigid pivots, and a single spring element.

SuspendedCargo.jpg

If one put in two springs for independent suspension, one would risk side by side wobble., and perhaps also damaging one's hub axle and quick release. The rear end would have to be as rigid as possible, thus a pivot and single suspension element.

Pivot could be forward or rearward, depending on how one wished to do it.

An alternative might be similar to vintage stingray bikes where the frame was rigid, but the load (seat) was suspended.



However, care would have to be used to prevent inducing a wobble.

Of course, the simplest option might be just adding more padding to the rack, so the load would be bouncing on foam rather than on a hard surface.

Tire pressure? Perhaps trying the largest rear tire that would fit, at the lowest pressure that doesn't bottom out.

taras0000

You make it sound like the people here have something to lose if they don't give you a solution, as if your giving them the chance to help you will be to their benefit.

What do you plan on doing if you "simply cut off the chain stay, add a pivot and mount a DMN coil over shock!"? Do you have the equipment and knowledge to do this sort of thing? If so, then why are you asking for input, and if you don't, then why the hell would you go ahead and trash your bike?

You need a custom builder to start from scratch to give you what you want. In the meantime, slow down, pay attention to what's in front of you, or find a more suitable means of transporting your fragile equipment.

squirtdad

Just to note...early reference to pinch flats: these normally occur be cause of lack of tire inflation...ie tire not properly inflated. A suspension won't help that

CliffordK

Yes and no.

Having a little give in the system so the wheel can bump up without fully lifting the load (and rider) might help reduce pressure on the tire and wheels, and thus reducing pinch flats. Also a reason why cyclists often stand up when they see a bump coming.

Andrew R Stewart 

I always considered suspension's (of the wheels, not the rider) main benefit to be that of control, not comfort or pinch flat prevention. When the road is rough lifting off the saddle helps the rider to stay centered and in control. A rider bucking up from an impact isn't the way to steer and balance. Andy

fietsbob

What kind of machine shop do you own?

newjazz

i dont own a machine shop but, i did have a lathe and milling machine that is still in new orleans (i now live in France!)
i do have some experience stick and mig welding as a hobbyist! listen, i may not be an engineer but, i am far from ignorant on modding!
i have rebuilt two triumph motorcycle engines a few years ago and did a engine swap in a honda prelude without help!........however, i prefere to play jazz to make my daily bread!

unterhausen

That bike looks like it would be really hard to get a suspension on. I think I would try to suspend the load after beefing it up a little. And I would put the biggest tires possible on it. The good news is that Paris is relatively flat.

CliffordK

Yes, low pressure large tires.... air ride.

fietsbob

AFAIK, TIG, is what the Bicycle industries have used for a long time ..

Mig may be adequate for heavier steels on Motorcycle frames , or farm tractors...

Have you MIG welded Aluminum before?








..

CliffordK

The Yuba should have an all steel frame.

I have tried MIG welding a frame. It made a bit of a mess, but so far has held together.

TIG, however, gives much cleaner welds.