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Message started by FunTimes54 on 03/30/20 at 19:24:13

Title: Hard tail struts, safe?
Post by FunTimes54 on 03/30/20 at 19:24:13

hello. I ride a 2005 s40 boulevard. Over winter I have put it through quite a bit of changes including building some hard tail struts. I went ahead and welded in an additional pipe 1” diameter 10 or 12 gauge between the swing arm and the frame for extra support. My question is how strong are the bolts that held the bottom of the shocks on. I used the stock bolts but fear them shearing off when riding. I do not think this is likely but thought I would see if anyone else has any experience here. I have added some photos of how I have the struts set up. Thank you in advance for any help. I know I have seen some info on this and it may have been covered somewhere so if I am repeating something I apologize in advance.

Title: Re: Hard tail struts, safe?
Post by Job on 03/30/20 at 20:09:33

Fun Times, I think that with your extra support you should be ok. The struts take much more impact than the shocks ever would, but hard tail frames aren't any heavier built. I would like to see pictures of the whole bike. What I can see has my curiosity going. Jeff

Title: Re: Hard tail struts, safe?
Post by FunTimes54 on 03/30/20 at 20:37:01

No problem. I have a picture attached. Thank you for the info!

Title: Re: Hard tail struts, safe?
Post by srinath on 03/31/20 at 06:07:04

I had a Vulcan 750 that was "strutted" out. It started to bend the lower shock peg. I put shocks back on it.
The shocks dissipate impact energy over their travel. The longer the travel larger the denominator of force/distance is and hence the lighter the loads on all related parts are. With a solid rod you're looking at near 0 distance - its not true 0 because steel has a Young's modulus - stress/strain - so it travels - but its of the order of microns not inches.
I would think it would beat itself up. Now the seat has springs, so you've taken a part of the loading from being unsprung to sprung. I however still don't think it would stand up to hard use. But most of the time these are light use show bikes, for that it would be fine.
Cool.
Srinath.

Title: Re: Hard tail struts, safe?
Post by FunTimes54 on 03/31/20 at 06:27:38

Srinath, thank you for the info. Did you have any additional bracing on your Vulcan to keep the swing arm from moving? This is why I added the additional pipe between swing arm and frame so that the bike wouldn’t be able to fold up and would take a lot of the impact off the bolts, and in theory absorb it in the frame tubing. Just wondering if that extra will keep the bolts from bending.

Title: Re: Hard tail struts, safe?
Post by srinath on 03/31/20 at 08:15:16

76455E64595D55430504300 wrote:

More rigid isn't the answer. You've got more structural pieces so if one starts to crack you have a couple others as backup to get home. Savage is lighter than a Vulcan, your seat is sprung, mine wasn't, and I beat on my bikes relentlessly. You likely are a lot gentler. That paint job and all the fabbed parts tell me you aren't a "ride hard and put away wet" guy. I am. So you would be not running into any problems like mine I'm sure, lots of people strut these bikes out. Only a complete Idjit would do that to a Vulcan - that too one that was all stock otherwise LOL. I got it that way, and put shocks I had lying around from an eliminator (same shock) with a blown motor.

Cool.
Srinath.

Title: Re: Hard tail struts, safe?
Post by srinath on 03/31/20 at 10:00:21

Please tell me that passenger seat (hard to see) is just for looks. That would vastly improve your tendency to break - if the seat is just for looks. Don't be putting on a 300lb passenger on there and running down a bumpy road.
Cool.
Srinath.

Title: Re: Hard tail struts, safe?
Post by FunTimes54 on 03/31/20 at 16:01:26

I ended up building a rounded piece out of 3/8 solid round and bending it to fit under the fender. I lathed out some round fittings and tapped them so I could run bolts through to the underside of the fender. I had to drill some new holes and welded in some nuts. After doing this I built the seat to fit the stock fender and then built the tail light mount, in retrospect would have been easier to just get a new trailer fender or something like others have and modded it. All this being said the point was to stiffen the fender and put support under the seat so someone could sit there if necessary. I don't have passengers too often and if I do it is just to get from a to b not any serious riding. That seat is STIFF and has minimal cushion so it is out of necessity not practicality. I was going for the 60's cut down triumph kind of look. I thought it would be cool with the bike having the single so I wanted that fender seat and the high sitting springer.

Title: Re: Hard tail struts, safe?
Post by srinath on 03/31/20 at 17:25:34

Again - rigid is your enemy. If you dissipate a bump's energy over 1", that's cool for all the thin stuff you have bolted to the "shock". Dissipate it over 1/1000th of that and you can see why the loads will be 1000X as much.

Energy = force X distance. Since energy loss from hitting a bump is the same, you dissipate it over 1" like the stock shock does, all the parts get 1/1000th of where you try to dissipate it over 1 thou.

Harder and more rigid will let it run longer before it shatters when you it
that mondo bump. Softer and more flexible will let it wallow and wiggle over the same bump and feel like you're riding a bowl of jello for a few seconds and keep going like nothing happened.

Cool.
Srinath.

Title: Re: Hard tail struts, safe?
Post by justin_o_guy2 on 04/02/20 at 07:04:24

The sway of tall buildings is designed In, because rigidity is fatal.

Title: Re: Hard tail struts, safe?
Post by Gary_in_NJ on 04/02/20 at 10:46:15

The lack of compliance in the swingarm may result in failures in the frame. After all, the frame has been designed with tubing and welds that assume a functioning suspension. Somethings got to give.

Title: Re: Hard tail struts, safe?
Post by srinath on 04/02/20 at 11:10:53

True. But, springing the seat, big balloon tires, lightening of the rear like that heavy A$$ fender and sissy bar elimination plus the fact a passenger wont be on it all alleviate the problem a lot in case of the savage.
My Vulcan didn't have any of those working for it. The fool just removed the rear shocks and put steel rods. I bought it in the darkness, the bent shock mount was actually visibly crooked.
Any case, it is a theoretical concern for sure, on a lightened single seat bobber that is more show than go would never have a problem.

Engineering is about compromise. But the fact is, energy is dissipated by the countering forces in the shock over the travel distance. 1/2 the travel and the force doubles. You're dealing with 1/10 or less travel, accordingly you need to lessen the energy (lightning etc) or strengthen to take 10X the force - or some combination of both.

Cool.
Srinath.

Title: Re: Hard tail struts, safe?
Post by FunTimes54 on 04/02/20 at 11:26:29

Thank you all for the input. I found another post on here about struts from years ago and one member added that the top member of the frame on the left side where the strut or shock bolts in actually cracked, the bolting member on the bottom never bent but the frame cracked on top. With this being said do you think that the lower shock mounting bolts are stronger than the frame itself? This would be ideal in my situation because all I fear is shearing a bolt and dumping the back into a sudden death crash. If something would bend or crack in the frame to give me warning and I could limp home I have no fears of wrecking. Also, being as I have welded the support in would most if not all the pressure be going into the frame since the swing arm is now unable to move up or down taking all the pressure off the mounting bolts? I called around to some shops before strutting and most seemed to say this would be no problem. One shop claimed those shock mounting bolts are built for air craft? I don't ride extremely hard or far. I may do 50-100 miles a week in summer. All highway or back road travel 70 max most of the time. I like the way it rides the hard tail doesn't bother me I just want to ride in peace knowing I wont be splattered on the road at any second which takes all the fun out of riding in the first place. It seems since they sell these struts for sportsters and what not they must have been tested? But then again I could be wrong.

Title: Re: Hard tail struts, safe?
Post by Gary_in_NJ on 04/02/20 at 11:48:04

I'm sure the struts would look fine after the crash, but the broken frame will lead the investigating team to the likely failed component.

I've never built a hardtail, and quite frankly have little interest in ever riding one, but if I was going to undertake such a conversion, I would learn all I could about how the upper and lower mounting points are designed and built, and I would look for a fastener that could handle the calculated amount of sheer. You have calculated that figure, right? I wouldn't want to guess at that figure.

Title: Re: Hard tail struts, safe?
Post by srinath on 04/02/20 at 11:55:08

182B300A37333B2D6B6A5E0 wrote:

Yea that part is wide wide off the frame to clear the pulley. That's my first danger spot. And near impossible to brace/fix IMHO without it looking like a piece of CCCrap.
Cool.
Srinath.

Title: Re: Hard tail struts, safe?
Post by Dave on 04/03/20 at 04:18:03

Makes sense the upper left side would be the failure point. It sticks out farther from the frame than the other 3 fastening points.

I am not sure what rear tire pressure you should run.....maybe not as much as stock. The only suspension you have is the seat and the rear tire.

When my bike was stock I hit a pothole and bottomed out the suspension, and I got that jingly electric shock feeling in my spine and neck.....the shock that happens when your spine is compressed. If that can happen with 1.5" of shock travel - how bad would it have been with no shocks?
:o

I realize this is a look that helps create the Bobber - but those of us who ride and put lots of miles on the bike tend to install longer shocks with a bit more travel......it is a comfort thing!

Title: Re: Hard tail struts, safe?
Post by srinath on 04/03/20 at 05:49:20

Tie pressure is dictated by the tire. Maybe you could look for a lower pressure tire, but if a tire recommends say 34-42 psi - you really cant drop under 34 without losing some aspect of the tire.

I bobbed mine, and still had shocks. But ofcourse that's just 1 bobbed look - there is several others. I got rid of passenger seat, the sissy bars, ground out the spot welds and trimmed the fender to finish 4" behind the rider seat and mounted taillight and plate to sort of be a fender.

Cool.
Srinath.