I'm having trouble getting my head around this and I know that all HD Forum members go to bed at night and solve these "questions-of-the-universe" as they sleep. Please let me know if you have FACTUAL info on this stuff!!! Links to sites-of-knowledge would be greatly appreciated.

Let's say we have a bike with a single vertical shocky. At maximum height the travel distance measures say 4 inches. When it bottoms out it measures 0 inches. We put a big dude and his missus on the back, bike hits big pothole and shocky bottoms out. OUCH!!!

Now we lower the bike 2 inches. The ride is a fair bit firmer (I assume). Dude and wife hit same pothole at same speed.

Does the shocky botttom out???

Does it bottom out on even lesser a pothole??? Or does it need a bigger pothole???

In the first instance, the bike is already on the way down when it gets to the 2 inch point so already has some downward momentum.

Thanks in advance for your very educated and well-thought out responses!!!

cheers

kiteman

 

 

 

Dear Kiteman,

You have not provided enough information to solve the problem.
One would need to know the following:
- have you changed the springs?
- have you changed the pre-load?
- have you changed the shocks?
- what have you done to the damping?

Essentially, the energy of the bump is counteracted by spring force over the distance traveled plus any force that comes from compression damping inside the shock.

A simple example: Let's say that the average spring force is F and the distance traveled is D, then the energy absorbed is F x D = FD. If you reduce the distance traveled by half (4" - 2" = 2") then to get the same energy, the average force needs to be doubled (2F x D/2 = FD, the same). Therefore, with half the travel and twice the force, for any given increase in load (e.g. a pothole) the suspension would compress half as much, and your bum would feel that the ride was much harder. On average.

However, there are ways of fiddling with the suspension (pre-load, spring rate, rising rate geometry, compression damping adjustments) that will modify the result a bit. IN GENERAL, however, if you want a good ride, you want the MOST suspension travel you can get, so that you can smooth out the bumps with as little extra force as possible. So, if you lower your bike AND reduce the suspension travel (which is what many do), the chances are that you'll get a harder ride and the bike will "buck" more on bumps. Why do dirt bikes have long travel suspension? - they go over big bumps, and don't want to destroy the rider's spine.

Hope that helps.

Gonzo

I just knew there would be someone out there with the knowledge of "gonzo" !! Thanks heaps for the response mate. I should have said originally that, for the 2nd test, the spring is compressed from 4"down to 2" by some imaginary means before starting but nothing else changed.

Let's say you have a bike with shockies that have less maximum travel than normal, like a Rocker as compared with other Softails, then how would you go about selecting the best possible shockies for it? There seem to be so many possibilities and they can't  all be as good as each other. The original HD shockies are just fine at standard height. When lowered an inch it is pretty good when 2-up but bloody hard when 1-up (mostly at high speed). I could possibly do more experimenting with pre-load adjustment but it would be so good to be able to measure it with a "perfect-ride" gauge!!! So far, the air shocks by Arnotts are looking the best possibility with on-board compressor and switch-as-you-ride. I know lots of guys have their favourite brands of shockies but the best advice is from those riders who have tried several brands and have run them lower than standard height. I have also heard that air shocks have been known to leak which would leave me with a Hardtail RockerC !!!

I mention Arnotts as they have a shock made specifically for the Rocker.

All suggestions welcomed and appreciated. Especially gonzo's!!!

      

 

I have the Arnotts Air Ride system on my FLHRC and have had it for over a year now.The ride is extremely firm initially ,but becomes softer after a short time.With the onboard compresssor,it only allows you to adjust the ride height with the bike stationary and NOT on the fly.Another thing to be wary with when you fit height adjustable rear shocks is to make sure that you calculate the minimum or collapsed length of the shock and make sure that you have clearance from the top of the tyre,or if you have done like I have,and fitted bigger diameter rims and wider rims and tyres,also make sure that you have clearance to the wiring loom under the rear guard.Apart from these things to watch for,the Arnotts system is quite good.

 

nobody

Thanks for the bouquets, but I don't deserve them. The problem is theoretically simple, but for the average guy-in-the-street (including me) it's really difficult in practice. The reason is that without a lot of work, or experienced mates, you don't have enough data to make your decision.

Two items to consider:

1) When you change the pre-load, in general all you change is the ride height (unless increasing the pre-load actually causes the suspension to top out). You don't change the spring rate, i.e how much extra the spring compresses for an extra, say, 50kg. This applies also to air suspension. So, pre-load only adjusts how much of the shock's maximum travel you're going to be able to use.

2) Assuming you adjust the pre-load to get somewhere close to maximum travel, you will then find that a) the shock bottoms - meaning you need a higher spring rate, b) the shock does not bottom but gives a hard ride - meaning you need a lower spring rate, or c) all is fine - you're lucky.

All shocks (even HD ones) provide pre-load adjustment. Not all shocks can have their springs replaced. I think the best solution is to buy a shock that can have its spring replaced and that has alternative springs available.

None of this touches on damping adjustment, which can have a significant effect. However, in my book, damping adjustment will never fix bad springing. Get the springs right first.

I bought $2000 Progressive AirTails for my Road King. The springing did not work for me, and I had to increase the capacity of the air chambers to reduce the spring rate (it's an air spring). Drilling holes in my $2K shocks was a nail-biting experience, but it worked.

My 2c worth.

Gonzo.

Thanks for that, noboby. I was looking at:

http://hdforums.com/forum/touring-models/182586-anyone-using-arnott-air-ride-yet-2.html

but I notice that Arnott's website states clearly that adjustment should be when stationary.

Luckily, with the Rocker I won't have the tyre and wiring clearance problem........just a very hard ass if the air gets dumped!

Kiteman,the only time you have problems with the touring models is if you go to larger diameter and wider width rims anyway.So stock wheels is ok.The good thing with the Arnotts systemis that the compressor is manufactured to be fitted in a specific place,so that unlike some other systems,you don't have to mount compressors in saddlebags etc.

 

nobody

Hey Nobody (am I talking to myself?)

When you set your pressure for the Arnotts shocks, do you do it with the bike loaded (i.e. with you, pillion, etc on board)? Also, how do you actually decide on the pressure? I set mine so that I get about 10-20mm deflection when loaded. For me this means 24psi for me solo, and 32 psi for me-and-the-missus. I set both with the bike unloaded so that the shocks are fully extended. Then when we get on, the shocks compress a bit.

What do you do?

Gonzo

The latest edition of Heavy Duty magazine (issue 104) has an interesting article on suspensions on page 132. They are talking about putting Progressive Suspension 440's on a bagger.

Yeah, I saw that on the cover and then tried to find it in the index. After I worked out the cryptic "Shocking Truth" I jumped to page 132 with great expectations. However, I thought the article was pretty superficial. Essentially it was "buy then install" without much analysis.

Maybe someone can elaborate: what IS "Inertia Active System". It's obviously state-of-the-art, but what is it? I have it on my Progressive Airtail units, but I don't know what it is. Progressive's website is useless.

My 2c.

Gonzo

Gonzo

I never bothered to put a guage inline with my rear shocks and compressor,even though one is available.I just know how high to set the suspension for when I am solo and for when I am 2 up.My shocks are shorter at 12" than the standard.When set at its full height I have never had the suspension bottom out 2 up.

 

nobody