I wondered how folks have been getting on experimenting with different rear shock absorber lengths for 2002 to 2007 swing arm conversion on Evo models?

I've been re-reading a couple of threads about this conversion, e.g. dresser-rear-suspension-thump and evo-dresser-swingarm-upgrade. I am not sure whether this post should be in Evo or Touring section.

I've stuck a 2007 swing arm on an Evo Road King and am mocking it up at present. I discovered my old air shocks had leaked out a lot of their dampening out and sizing up the swing arm and shock absorber mounts, realized that it's a lot longer.

• What lengths of shock absorbers are people putting on them ... and how do they sit and handle if standard length shocks are used?

I understand the later models used longer shocks but it looks like the older bikes need even longer ones as the top mount for the later models looks like it is further back too. I'd say it has to be around 13.5" to get the right angle on the swing arm, i.e. slightly below horizontal, but could even be longer.

And matching sag to the front is a whole other question.

At the same time, I would also like to share my bike with the 'old man' and he has short legs now and again. If swopping short shocks on and off allows me to do so, then I'd be happy with that ... the increased distance and angle would work like a rear suspension lowering kit.

I wonder what people's experiences were.

I see Bitchin Baggers offer a rebuild and shortening service and I wonder how good such shocks rode at the end of the day. Air shocks such as Legend would probably fix the problem of two different riders, but they are out of my budget, and I understand don't ride as well as sprung and damped ones.

I could afford two good traditional set for the price of one adjustable air ones.

Thanks.

 

Hello old chap and welcome to HDF! My Ohlins are nominally 13" (actually a similar metric length that I don't recall, 330mm?), so very close to stock. My bike being an early Evo, my original swingarm was actually shorter than the 2007 one I now have. I haven't compared the two arms closely, to see if the lower mounting points are in the same location, but after long touring trips abroad I can confirm that all is well.

As for air shocks, do yourself a favour and throw them in the bin! If you can't afford decent replacements at present, but can use the ones you have for a while, save yourself the time and money modifying them. The damping system inside them is just not up to the job IMHO, especially if you ride 2-up.

 

I wonder if our frames are similar?

Did that make your swing arm basically horizontal or parallel to the ground at rest?

My thought with the originals is just to use them as a cheap short shock which lowered the bike a little, as an alternative for the old man to use. Not me.

He's not going to push the bike (literally or metaphorically ... he's well into his 70s!).

The alternative was just to have them rebuilt short, or buy a cheap alternative new set, like the cheaper Hagons or Progressives. It'll screw with the handling a little, I know that but better than nothing and him not being able to reach the floor.

 

Well I've just been out to the garage to answer that one! Static the s/a is slightly higher at the trans end, although probably roughly level while riding. I have the cheaper Hagons on my Sporty, which are OK, but not much to write home about, although better than stock. I would buy their Nitros next time. My Sporty was new when I bought it, but those air shocks of yours aren't!

 

It always used to be good form for the swing arm to be angle down at the rear at rest. From memory, about 12 degrees I think.

On a lowered bike it is going to be pointing upwards at the end. All wrong from a frame design point of view. Under load, the chain/belt is going to be becoming looser, and the frame geometry folding down in the middle and kicking the fork angle out further.

Incidentally, back in the real world, I just discovered today that some production bikes now have adjustable swingarm pivot points to allow for adjustment in this area.

The other area when H-D suffer slightly from, is the distance between the center point of the small pulley, and the pivot point of the swing arm.

330mm is going to tiny fraction less than 13". I'm thinking 340mm, or even longer would be acceptable. Hagon have a wide selections of lengths and 'make to order' in a few days.

Sure, both their budget range and solid struts are probably going to be better than a pair of 96 shocks!

You've done some work on your front forks adjusting squat there ... did you spend any time measuring squat at the rear?

Note, the bike's rear end, not your own.

 

The swingarm should be roughly horizontal while riding, meaning that the wheel and swingarm axles should be level. That way the chain or belt varies in length the least as the suspension moves up and down. The further away from horizontal the swingarm gets the more variation in length there is for the chain or belt to span.

 

I wont argue against that ... changes in frame geometry at the front end under acceleration and braking also come into play.

I went and measured up my old air shocks, and they were 12.5".

The new swing arm is longer and the shock mounting placed further back. I am sorry but I should have measured up the old swing arm before I sold it to make a more accurate assessment of the size required.

Did you keep yours?

However, I am thinking that the 1/2" ... to 13" or 330mm ... is not actually long enough and I could go longer.

Hagons ... and I suspect others ... make rods in 10mm steps, therefore the next size ups are 340 (13.38") or 350mm (13.77"). A slightly longer shock would very slightly shorter the trail at the front end and increase ground clearance, would not it?

Speaking to them, there are many factors to take into consideration that I will have to measure, e.g. fender clearance and total travel I think for the dampener length.

Rear end sag, except of my own and women of my age, is not something I have actually gotten around to considering at present.

They say matching rear end sag with front end sag at the Race Tech end is a key to good handling, although on one's woman it's best to have none at either end, I think, but it requires picking up a far more recent and expensive model.

 

What I did with my bike, when doing my current reworking of it, was simply to take the shocks off, then jack the rear wheel up into the rear fender until the distance from top shock mount to swingarm shock mount corresponded to the fully compressed length of my shocks (around ten inches as I recall).

I had stacks of clearance, well over an inch, in fact so much I didn't give it another thought. A ball of plasticine on the tyre, or some other squashable stuff, should help confirm the actual clearance. So if you use shocks around 13" long with around 3" total travel you will have no clearance problems. Doesn't matter what the difference in length of old and new s/a is! I did the above with my '07 s/a in place.

My Ohlins are infinitely adjustable, so I have been able to achieve the correct 1/3rd static sag. The standard range of Hagons doesn't have that degree of adjustability (nor do most brands). Their Nitros may be, I'm not sure. As for the front end, sag is 'simply' a matter of adjusting spring packing to get it right, again 1/3rd of total travel, which IIRC corresponds to about 1.5". Quality of damping and hence ride I'll leave for another day!

Hope that helps!

 

Is three inches of travel as much as we get? Jeez, no wonder ...

I appreciate that there is more than adequate clearance, I was just wondering about calculating the length more accurately from a geometrical point of view, and being an H-D nerd. I think I'll treat myself and tend towards the longer rather than short limit.

As for what the "opposition" is up to ... this is the what the Bitchinbagger guys are do. 12.75" shocks reduced to 10.25"!

At $175.00, it's a little bit more expensive than a solid strut and a flat tyre but I cannot image it giving much better performance. That's 0.75" of travel. They're selling pre-modified shocks (cores included) at $315.00!

Previous, my bike had a 1" lower kit at the rear and I would hit speed bumps and scrap footplates daily.

Ta.

 

Some brands of shock give 4" of travel, but that is as good as it gets. In considering Ohlins and talking through the various options with Howard at Motorcycle Metal, he recommended separated gas/oil shocks with 3" travel over emulsion 4", because they have superior damping. Mrs B and I have never bottomed out with our Ohlins, despite 'only' having 3". What am I saying.......

As for any air shocks, pass by, there's a good chap, that money is best spent elsewhere.