Raising the suspension - Harley Davidson Street Forum - Street 500 and 750
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post #1 of 16 Old 11-04-2017, 04:09 AM Thread Starter
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Raising the suspension

Looking for a softer longer-throw suspension, a touring setup for comfy commuting.

How about the Progressive 412 shocks?

13.5" is a half inch longer than the stock of 13", that would give 5" rear travel instead of stock 4.5, sounds great, but if the spring is stronger it won't help, just give a harsher ride.

Anyone know if that shock will give a softer ride on the rear?

I am tempted to just buy them to find out.

If I could find a 14" that fits a Street 750 that would be better but I haven't found anything.
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post #2 of 16 Old 11-09-2017, 05:46 PM Thread Starter
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I guess this is the beginning of a build thread for improving the rear suspension on a Street 750.

I apologize for the incorrect number in the previous post, I had the suspension travel confused for the two bikes:

Rod = 4.5" rear travel
750 = 3.5" rear travel - I know I will want more for my commuting needs.

Take off 1.5" for SAG and the 750 is pretty limited.

All of those numbers are suspect in my opinion, I am going to measure it myself once I get everything off.

I had a long thread over at the hdforum where they taught me about shocks, more than I ever wanted to know, but here we go:

I ordered the progressive 12 series (which is a 412 with user installable springs).

The Progressive 412 (and 12) is available in a few sizes, the one I am interested in is the 13.5" size, 1/2" longer than stock,which should add almost an inch of travel, and also jack up the rear almost as much. You need to do those together, or the wheel will contact the fender before the shock bottoms out.

The spring rates they offer are:

Light - 70/120 - for riders below 160 lbs (with gear, cases, etc).
STD - 90/130 - for riders 160 to 250 lbs
HD - 105/150 - for riders 250 and up.

The 412 is only available with STD and HD (heavy duty) spring rates.

Note that they are all progressive springs (not to be confused with the brand name Progressive), which means they start at a lower compression rate and increase to the higher rate as they are compressed. Our OEM shock is also known to be progressive, as a result it is really hard to bottom out, that's pretty good for an OEM shock.

The thing with spring rates is to use longer travel you need a lighter spring rate than you would normally use, so those rider weight ranges change quite a bit. Adding travel won't help if the spring is strong enough to prevent bottoming out with a smaller travel. I am a lighter rider so am already at the lowest preload setting for STD springs.

So I ordered the 12 series in a 13.5" with a set of both std and light springs to try. And $50 for the spring compression tool, "user-installed" is stretching it a bit (pun there).

At any rate that should get me a usable 3/4"+ of travel, and a softer ride as a result.

I'll be installing them this weekend if everything arrives and I can get those bolts off myself.

I'll post with pics once I get it on and adjusted. Living with the new suspension may take a bit longer to see how I like it, so I might do a long-term review later.

And I ordered them in black, everything else on the bike is black, the chrome springs don't really belong.
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Last edited by Kurt; 11-09-2017 at 05:51 PM.
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post #3 of 16 Old 11-09-2017, 11:55 PM Thread Starter
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The shocks and springs arrived today.

Here are the parts: the open boxes are the Progressive 12 series 13.5" shocks and the light (70/120) springs, and the other box has the std weight springs (90/130).

I measured the shocks, they are 13.5" fully extended, center hole to center hole, exactly as advertised.

Without springs I was able to compress the shock by hand to measure it's travel. The 4.1" travel claim is slightly exaggerated, it actually has 3.75" travel and the rubber stop is apparently expected expected to compress a bit more than 1/4" to yield the total 4.1" claimed travel.

The stock shock has only about 2 1/8" travel before the stop, although the stop is thicker and softer than the Progressive one, maybe can compress up to 1/2". That means this upgrade will be an even bigger (and even more desperately necessary) improvement.

Keep in mind that because the shocks are mounted at an angle, 1" of shock travel produces about 1.25" of wheel travel.

The numbers add up, about 2.75" of total OEM shock travel adds up to the claimed 3.5" of wheel travel.

And 4.1" of new shock travel adds up to 5.1" of wheel travel!!!! Now that's more like it, that's more than my adv bike.

The progressive instructions say to mount the shocks first without springs, and verify that fully compressed there is an inch of clearance, half of that inch will be used by the rubber stop when it compresses.

You can also measure how much travel you use on daily rides by pushing the rubber stop down the post, and see how far it gets pushed back up by your usage, fantastic way to dial in a shock.

I admit I am worried if the 13.5" is long enough to fit properly to prevent wheel well contact given the huge increase in wheel travel, but Progressive claims it fits.

To be safe, I ordered a pro-action 14" shock, with 4" claimed travel, they said progressive springs will fit in it. So one way or the other I should be able to find a match, since I have two spring rates and two shock lengths to choose from. The pro-action has much fancier damping, and a much higher price tag. We'll see which is the winner after this build completes.

Tomorrow the spring compressors should arrive...

Edit: I measured the distance from the wheel to the wheelwell with the stock 13" shocks fully extended, about 6". So the stock 3.5" travel leaves 2.5" of clearance. The 13.5" setup will allow the wheel to go 3/4" deeper into the well if the calculations are correct. I guess am worried about ground clearance over bumps, but that's a pretty small change, so likely ok. The 13.5" shock splits the difference, raises rear by 3/4" and allows 3/4" deeper into the well. The 14" shock would add all of it to the height of the wheel and not go any deeper into the well. Choices choices, I am probably going to try to make the 13.5" one work though.
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Last edited by Kurt; 11-10-2017 at 01:10 AM.
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post #4 of 16 Old 11-10-2017, 09:38 PM
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Great stuff. Written like an engineer (that's my guess). I'm hoping you have plans to sort out the front as well. Just for the needed data point, what's your riding payload, rider and gear?
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post #5 of 16 Old 11-10-2017, 10:32 PM Thread Starter
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Engineer, yes, guilty.

Me + stuff = ~160 lbs total.

Don't know how to deal with the front end yet, or if I need to, I know little about front suspension. What I do know is it has 5.5" travel which is fine. AFAIK the main worry will be if they become unbalanced as a result of softening the rear springs.

What little I know is you have to cut PVC pipe to adjust pre-load on these forks. Not sure I want to go there. But it's a possibility I suppose.

But you got me to start reading on front fork springs. The can-o-worms is now open... :-)
Looks like a similar deal, pick spring-rate and pre-load.
Edit: improving damping with valve upgrades also seems possible, the rear is definitely easier to deal with.

Last edited by Kurt; 11-11-2017 at 12:24 AM.
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post #6 of 16 Old 11-10-2017, 11:42 PM Thread Starter
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Here are the assembled shocks, a bit scary.

Here are the assembled shocks, with the 70/120 springs, set to the third pre-load setting, ready to put on. I think it looks better without the progressive plastic cowl, and the black is nice. Let me know what you think about the cowl, yay or nay.

FYI, even with the spring compressors installing the springs made me nervous (see the pic). If a spring launched it could cause serious injury. Definitely don't try this at home unless you are very mechanically inclined. I did it on a bed surrounded by pillows to catch it if it launched. No issues, but I was very slow careful and thought it through. Notice the part close to the body, I did not use the same position on the coil, because each side pulled the spring over a bit to get better purchase, that was my main trick. The pic is bad, shows before I figured that out.

The Progressive shocks are well designed, idiot-proof actually, you can't put the springs on wrong, I really appreciate that. :-)

They did have a few burrs left over from the manufacturing process. I had to scrape them off with a sharpening stone, these aren't $700 shocks and it shows.
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post #7 of 16 Old 11-11-2017, 01:19 AM
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Takes one to know one... I've not noticed damping issues with the front forks. Pre-load/spring rate seems to be the big problem. I think any damping change needed when the springs are right can be handled by oil viscosity. The front spring rate seems about right so my first attempt will be with pre-load. My forks have substantial sticktion, so this winter I'm going to disassemble the front end and make sure the stanchions are parallel. Stiction could be as simple as tightening the front axle bolts in the wrong order.
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post #8 of 16 Old 11-12-2017, 05:53 PM Thread Starter
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Quote:
Originally Posted by ButterSmooth View Post
Takes one to know one... I've not noticed damping issues with the front forks. Pre-load/spring rate seems to be the big problem. I think any damping change needed when the springs are right can be handled by oil viscosity. The front spring rate seems about right so my first attempt will be with pre-load. My forks have substantial sticktion, so this winter I'm going to disassemble the front end and make sure the stanchions are parallel. Stiction could be as simple as tightening the front axle bolts in the wrong order.
Keep us posted on the front pre-load, I find the front forks a bit bouncy, I feel every tiny pebble, I would like it a bit cushier if there is a way to get there. Maybe I have the same sticktion problem, don't know yet, I suppose I can just grab the bars and push to find out.

Last edited by Kurt; 11-12-2017 at 10:29 PM.
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post #9 of 16 Old 11-12-2017, 05:55 PM Thread Starter
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Here is the final theorycraft in summary form:

To sum up so far, now that we have accurate measurements for the Harley Davidson Street 750 and the relatively economical Progressive 412/12 13.5" shocks:

Summary: The plan is to change wheel travel from 3.5" to 5.1" and use cushier springs.
Will raise the rear by 3/4", which affects kick-stand and center stand.

Here are the accurate numbers:

OEM shock:
13" length, 2.75" shock travel, fixed-rate springs (rumors of progressive springs are false, obvious once I had them off), unknown spring weight, guess around 120.
2" bump travel, based on 3.5" wheel travel, minus 1.5" sag
6" wheel well clearance shock fully extended
2.5" clearance fully compressed.

Progressive 412 and 12 (only the 12 is available with the light spring).:
13.5" length, 4.1" shock travel, available spring weights: 70/120 (light), 80/130 (std), 105/150 (heavy duty).
3.6" bump travel based on 5.1" wheel travel, minus 1.5" sag
raises wheel 3/4"
6.75" wheel well clearance shock fully extended.
1.6" clearance fully compressed (1" is minimum recommended).

The plan is to try the 70/120 spring initially and see if that can be dialed in for a 160 lb rider. Also have 90/120 and 112 (from Pro-Action) springs to try.

So that's it for the theorycrafting, next post is how it worked in practice.

Last edited by Kurt; 11-12-2017 at 10:36 PM.
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post #10 of 16 Old 11-12-2017, 06:29 PM Thread Starter
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Declaring Victory - Although I had hoped for more.

Now for the real-world stuff.

Surprise discovery (minor):
- rear swing-arm is limited how far the wheel can extend, about 1/8" less than the 13.5" shocks want to go, I had to use the spring compressors to get them on, ok, no problem. Slightly less travel than I hoped for but still in the ballpark of much better. Also means a 14" shock will not fit this bike. You can't raise the rear much over stock, maybe 1/2" tops, but that's a half inch, glad to have it.

The amount of travel and other theory-craft numbers seem to be accurate, fantastic.

So it went on, see the pic, I put the collars on, but they are likely going to come off, right now one has a collar, and one doesn't.

The ride reports:

First ride (40 mi round-trip to work, my commute route, has some nasty bumps at 70 mph):
- 70/120 springs maximum preload - The numbers I had been given by Progressive support lead me to believe this was about the right place to start. This was a very harsh ride, my back was not thanking me. I had to stand up on bumps, same as my adv bike, but worse, much worse. The bike is otherwise nice, bigger engine than I am used to, love the SE pipes, etc., but I'll stay on subject here.

Second ride (same 40 mi trip):
- 70/120 springs, minimum preload (1/4" more SAG than recommended, this is not a problem). Ride was much better, still harsher than the adv bike, but my back could tolerate it nicely, until I hit a big bump on the freeway at 70mph, ouch, big ouch. I suspect I bottomed it out, but don't know for sure.

Third ride (short neighborhood jaunt over nasty bumps), also minimum pre-load:
- to test the theory I had bottomed the suspension, I did the trick of moving the rubber stop down the post until it contacts the body. It will be pushed up only as far as the maximum suspension travel used on the ride, rode around over some big bumps at 30-45 mph (my local streets leave a bit to be desired, useful for the test).

I used all but 1" of travel, this is perfect, looks like this is the sweet spot for me, I may not have bottomed out after all.

Conclusion

At this point I am declaring victory, I get a noticably softer ride than the stock or the 412 std spring. Most or all of the suspension travel is being used. The downside is this bike still has a harsh ride by my aging back's standards, but I made it a lot better.

So, if you are in the 160ish or lower range (with gear), the Progressive 12 series 13.5" shock with the 70/120 springs is an economical way to soften the ride a bit.
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Last edited by Kurt; 11-12-2017 at 10:49 PM.
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