Harley-Davidson EVO Sportster Rear Suspension Modifications

By Broc Luno

Okay, so a lot of us that have a few years under our belts and either couldn’t, or wouldn’t, afford a Harley are finally buying one. We’ve all played with endless dirt-bikes and UJM street bikes, the odd Limey bike and occasional Kraut Hammer. Now we have the overall experience to know what value and fun under our butts feels like and when the deal comes along, we have the resources to take advantage. In my case it was a barn find 1997 Sportster 1200C with about a quarter inch of bird droppings and barn dust covering it, but basically all there with about 24K on the odometer. It was parked due to a divorce fight and the price was right.

The bike started and ran with a jump (eventually), but was in need of some serious TLC. Many tens of hours with Blue Magic and shop rags (clean ones), soap and water, Windex and, okay, this looks more like a Harley and less like a tractor. Under the dirt and surface rust was a nice chrome motor and the rest of factory chrome was mostly still attached.

Some dime sized rust spots that I’ll touch up with Dremmel tool and silver paint and the chromed rear alloy rim that is beyond touch up. White creeping crud was pushing the chrome off everywhere. Oh well, a SS wire brush in the die grinder and a can of Hammer-tone Grey Metallic Rustoleum spray paint will get it back to adequately presentable enough. You really can’t see much of the wheel behind the bags, anyway.

Get the wife on the back and away we go. Second tank of fresh gas and it’s starting to clean up and run better. Pulls hard, shifts OK, stops well and still has the little nubs on the Metzlers front and rear. The story was that it was just serviced before it was parked. It seems to be true. The battery holds a charge and everything I see is in the right place and well adjusted.

However, as we ride around the country lanes and back-roads, I seem to notice that we bottom the suspension too often. Click the springs to #4 on the collar and it helps when riding double, but it hits harder than I like riding solo. No shock tool (no tools at all, but I’m not complaining), so quickie roadside adjustments are not real convenient. Besides, the chromed factory Showa’s only seem to have rebound dampening, no compression dampening at all. OK, so I call some of my bud’s that have Sportys and ask about their rear shocks? I test ride a local’s 1200C and it’s worse than mine.

I’ve built too many dirt bikes to not to know a thing or two about suspension. An inch and half of shock travel is not enough, even with inclined mounting that gives somewhere between 1.5 and 2X the shock travel to the axle and wheel. (Harley knew about alternate rear suspension geometry on the old Iron-head before Maico and Husky brought it to most of the dirt crowd.) Hell, we have bumps bigger than that around here.

Read the web talk and it’s obvious that folks either don’t know much about suspension, believe the wrong info, or never built a dirt bike. I give them the benefit of the doubt, but I see real questionable statements here and there. Obviously, I need more info and I can’t trust the web, so I’ll have to do it myself, just like the old days.

I see that Evo XL’s have shocks that run the gamut from real short (Low-Riders) to pretty long (Euro export Sport models). The range seems to be 10.5” center to center on the mounting eyes (not counting aftermarket “slammer” shocks), to 13.5”. There are some applications where they are fitting 15” shocks for off-road desert sledding. (Fitting 15” shocks requires some sophisticated mods to the belt drive clearances and you can’t run the stock exhaust or even dual straight pipes. You need an upswept 2:1 header to allow the axle/wheel full travel.)

For the street, the best of the best all around daily use seems to be Legends Air Shocks with onboard compressor for adjustment on the fly at $1500 a pair. That’s a very large piece of the total price I paid for the bike! The best non-air shocks seem to be Ohlins or Wilbers at about $1200 a pair (still ouch), down to serviceable used take-off’s for about $40 a pair on e-Bay.

I have H-D OEM Showa’s at 11.5 inches as the bike came and I want to know if the steering geometry will go to hell if I jack up the back end a bit for more travel, so I get a used pair of 13.375” take-off’s (H-D Showa’s) from eBay and bolt them up. Go out and blast some corners hard enough to be marking the edges of the tread on the Metzlers, not quite dragging the pegs, and everything seems okay.

Steering is not quite as relaxed as it was. Stock, you could ride the OEM configuration with hands-off the bars down-grade for miles, just leaning with body weight to handle sweepers and it was rock solid. Now, it’s not quite that lazy. You need to keep one hand on it, or at least ready to touch the bars. However, it’s not nervous or anything. It still tracks straight over bumps and such. Real nice solo, but still too soft two-up. Still bottoms too much with both of us on board, even preloaded all the way. However, now we know that at least a 1200C with a 21” front wheel will handle 13.375”shocks without a speed wobble.

What to do now? Write Progressive an email and give them our weights, the bike model and year, how much we pack in the bags, etc. Wait for a reply with recommended shocks and springs. For dirt bikes, I used to do this with S&W or Koni. However, the big Harley supplier, either their own label, Drag Specialties, or Bikers Choice, seems to be Progressive. I suspect that this firm bought up the S&W tooling, because there are a lot of similarities between the older MFG and what’s going on now. (That is just my speculation.) Anyway, they seem to be the market leader in volume of sales, if you trust the posts on the web. (Never a wise idea. -Editor.)

Meanwhile, I spot a pair of used “Piggy-Back” 13.5 inch Sportster OEM shocks as used on a lot of the Sport models and as exported to Europe. They were on eBay for slightly over a C-note and they look to be in decent shape. I think they have adjustable dampening via external knob. If the seals are not blown (and there is no evidence in the photos), they should be serviceable. Grabbed them with a BIN and we’ll see what the next level is about. If they don’t work out, Progressive will have my info soon, so I can always go there.

The XR1200X rear shocks are probably the best OEM take-off option, but don’t come up that often. Since it’s from a 2010 model bike, it will be 13.5 inches long also. They retail for $410 each at your Harley dealer. For that kind of money, you can almost move into brand new Progressive 970’s, which are reputed to be very good shocks. The downside is the preload screw collar. Great for tuning on track days and such, but a bummer if you have to tweak it quickly, because your wife has decided to go along. For family riding, stepped preload collars are usually the handiest.

There have been comments on the ‘Net about belt tension changes with long shocks. However, as long as we stay within what the Motor Company builds for various models on the same basic frame, we won’t likely get into any belt issues.

It comes down to what sort of ride you want and what ride height with which you are comfortable. I have a 33 inch inseam and I can flat-foot-it on both sides of a 1200C with 13.375 inchers on. So as long as you can easily get it off the side stand and keep it upright at a stop light, it seems you are good to go up to this rear shock length, at least.

What we have not spent any time discussing yet is spring rate, the part that actually supports the load and maintains the ride height. I suspect that is a whole paper by itself. There are single and dual rate spring packs and progressively wound springs. Springs are usually about $80 a pair, so if you need a higher rate, it’s just a matter of swapping. Most of the better shocks are inertia sensitive, so they will compensate for the higher rebound speeds of stiffer springs accordingly. Adjustable shocks can be dialed-in for a range of spring rates.

There is a phenomenon that is related to spring rates and dampening called "pogoing." This is when the bike is in a corner, it wants to oscillate up and down in the rear. This is driven somewhat by inadequate springs (too soft) and mismatched dampening. Stiffen the dampening and it will go away. Stiffen the springs and it will also vanish. However, to do it with springs, they have to be overly stiff. Thus, it’s much better to attack this problem with dampening.

Our first 13.375 inch test OEM Showa’s exhibited pogoing riding double. In addition, we are bottoming on big bumps with the shocks fully preloaded. Therefore, we know that weak rebound dampening and no effective compression dampening, plus spring rates that are less than needed are problems.

For the number two test pair, I suspect that the springs will be significantly stiffer and I should be able to dial in the dampening. Pogo gone, or so we hope. That’s the only vice the longer first test shocks have shown. Solo riding, they are major improvement in ride comfort and bump handling and with a moderate load (solo), no pogoing at all. We are close to the end goal.

I’ve had the number two test pair on for a couple of days and the ride is nice. Zero pre-load on the springs and both the compression and rebound dampening set at 4 clicks from the softest position. The compression dampening is a dial on the remote reservoir. The rebound dampening is dial hidden in the bottom shock eye that turns a rod inside the shock shaft, very sneaky. They work well for solo riding. I’ll get the wife to help with an afternoon ride in the next few days and see where we are two-up.

You may wonder how I can tell they are an improvement. It’s pretty easy and somewhat intuitive. If you are riding down the road and you smack a big bump, ask yourself, which end of the bike bothered you on that hit? If it’s the back end, that’s where you start working first. As of today, it’s now the front end that I notice more. That means the rear end is better, maybe good enough.

Well, not quite. Absolutely dynamite solo. Just dial the ride you want. Pre-load one notch for me (I weigh 220 pounds) and set the dampening as desired. At 6 clicks on both, a very nice ride no matter how spirited I get. However, with the wife on board and the preload full, we still bottom now and then on square-edged bumps. If your total load is less than about 350 pounds, these shocks should work just fine.

The bottom line for us (I weigh 220 and she’s 170 pounds) is going to be diet (we’re doing that) and some slightly stiffer springs. I still have tons of dampening adjustment left (8 more clicks on both). We just need another 15 to 20 pounds per inch on spring rate and we are golden. Or, air shocks. Given our weight and gear, it might be air shocks in the end, probably Arnott/Bilstien. However, if I get lucky and score some slightly heavier springs, we can still save a buck or two and ride on.

Now, to find a source of heavier springs that will fit. The saga continues.

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