Understanding spring rates and shock rebuilds RD04 AT Honda
 

Advise needed ….


I’ve decided to have my Honda AT RD04 rear shock rebuilt before going away. It seems the best precaution, bearing in mind the bike is ‘92.

So the standard spec states a maximum weight of 194kgs, I think with extra fuel and luggage for 2, I’ll be over this and possibly up-to +/- 225 kgs. My question is how do you decide on a replacement spring ? just max carry weight, however I think there is more to it, bounce back spring rating etc…. so what should I be looking for ? It will mostly be road use, however gravel roads often have the shock killing ruts in them.

Btw the wife prefers a soft ride on the back :-)
Has anyone used Falcon Shock Absorbers , so far they’ve offered excellent service…..


many thanks

Matt

Hi
I am thinking of changing my original Showa shock.I was looking at the Ohlins unit 46HRCS.Its very expensive compared to other makes but its re-buildable and Ohlins have a good reputation.If you change the rear shock you could change the front fork spring to a harder Wirth spring and some thicker oil.
You could try asking at the Honda trail bike forum at Honda Trail Bike Forums .They are very helpful and some of the people posting on the site are very knowledgable about Afica Twins.
Good luck.


EDIT....I see you have already been there!!!

Thanks for the reply, from what I remember the Olhins shock is way out of budget, I recon with my own rebuilt and uprated spring, should cost €300.

many thanks Matt

Matt,

I don't know a lot about bounce back spring rating, but that has to be controlled by the damping, so I guess it is important to match the spring to damping, or have the adjustability to match the damping.

I would start with the spring you have at the moment and have it measured, 13 years old it may be a bit tired. Springs are measured by the amount of force used to deflect it by a linear amount for instance 20Kg per 1 cm or some times 2 kg per mm. If you give the shock builder the amount of sag you currently have when fully loaded (or a know amount of weight) he should be able to make a judgment on the spring you need. You will have to tell him how much spring pre load you are using.

If you don’t have one you may consider remote preload adjustment.

Steve

Spring rate = is selected simply by weight of rider, bike, passenger fuel etc. A shock expert/pro should be able to help you determine the right spring for your load and bike. It will be MUCH heavier than stock. It's very important to get the loaded sag right, and that's where an expert that will work with you comes in.

THEN you set the oil bit of the job - compression and rebound damping rates. They are determined by the oil weight, and the valving in the shock. Again, the expert can adjust those as needed. FIRST guess might not be quite right, so be prepared for some tweaking time.


No idea about Falcon! Ohlins gets a bad rap for our kind of travel - many bad reports.

Technoflex, Works Performance, and a few others work well. BUT are expensive, certainly much more than a shock rebuild - but can work out cheaper after your fourth standard shock shipped in to Timbuctoo.

Matt,
There are some other factors to consider when going so far over the AT's
spec'd gross weight limit. No matter how stiff you go on suspension and no matter how perfectly the bike's suspension is dialed in, you can have other negative affects resulting in ill handling from an overloaded bike.

The AT is an early 80's design that came along before the current beefy forks and triple clamps seen on "modern" dual sport/adventure bikes today. Additionally, the AT lacks the massive swingarms and stiff, strong frames that are lighter and stronger than the AT or other 80's generation bikes.

It is here modern bikes like the BMW GS, Vstrom and KTM 990 really have an advantage. They can be over loaded and still ride fine, especially the BMW
and Vstrom.

In handling you may find paved twisty roads have the bike flexing quite a bit with vague steering with a sort of delayed reaction to where you feel like you're pulling a trailer or like the bike has a hinge in the middle. Granted, suspension up grades will help but it can't totally cure a flexy frame, wimpy fork tubes and a spagetti swing arm with 225 kgs and a passenger on board.

What to do?
A fork brace will help but the best thing is to lighten the load or literally, pull a cargo trailer. YES! you can do this and it works!!

Another negative from overweight will be possible cracked frame, subframe, luggage racks, bent/broken wheels, early death for bearings and so on.

As far as suspension goes, first find the stock spring rates on the
AT's shock spring and front springs. As a rough guide, I would go about 20%
stiffer on rear spring and about 20% stiffer up front.

Damping too will need to be increased quite a bit. A shock expert needs to do this. The Showa is a fine shock if re-built completely/correctly. Or look at Wilbur's (German) too, a quality item that is rebuildable and cheaper than Ohlins. Re-valving the front forks with emulators and heavier oil/oil level will help. Bit of trial and error needed on the front forks to get this right. Once again, an expert can help here.

In order to have the bike handle OK unloaded you may want a rear spring that, when fully loaded, two up, has you cranking in some preload to make the race sag number correct. (Between 2 and 3 inches sag on that bike I'm guessing)

Or, if you don't care about unloaded solo riding, then go stiffer on the rear spring and try to have the correct sag with almost NO preload dialed in.
This will give the BEST ride when fully loaded. The bike will be a bit taller but should ride well even in roughest situations, but it will be wallowy from flex
mentioned above. But it's all you can do really without changing bikes.
:scooter:

Anyone know the url for technoflex ? I thought they we're based in Holland ... I only find their agent in the states...

Many thanks
Matt

That would be the all up weight of the bike? Changing the shocks will not change the max weight of the vehicle .. that would be set by looking at the strength of the frame, swingarm, spokes, rims, etc etc .. not just the shocks.

Sorry .. but you need to know.

Good shocks, correctly set up will reduce the impact damage to the suspended parts of the bike .. but not the rims, spokes etc (the unsuspended bits).

Cargo trailers on the back of bike on dirt roads don't work too well .. well that has been my observation. Might be better to reduce the weight, send some things onwards to hotels and leave luxury items out. Take less parts, use newer ones on the bike before you go.

I imagine these cats have some different ideas on trailers! I've been in conversation with the owner of this Canadian outfit. Their web site is being rebuilt but I've seen pics of the things in some nasty, technical single track....pulling a trailer. Here are some pics in more mild conditions.

The company is called Trail Tail.

Patrick

http://patricksphotos.smugmug.com/ph...38542633-M.jpg

http://patricksphotos.smugmug.com/ph...38542615-M.jpg

http://patricksphotos.smugmug.com/ph...38542636-M.jpg

http://patricksphotos.smugmug.com/ph...38542623-M.jpg

Im no expert in springs or damping, but I agree what Mollydog said about the Africa Twins shortcomings. It is a very old construction, and gets bad when loaded to the limit. I remember doing a tour in the Italian Alps with 3 bags and all other stuff you can imagine, plus a pillion, it was just terrible to ride.

Newer bikes, like the Vstrom, seem much more tolerable to even slightly overload them. I dont think that only suspension tweakings will make the AT like them (though surely it might make it better than it was).

Yea, my web search has come up with the same agent in the States + another in Oz:-

Technoflex Suspension Specialists - Motohansa BMW

at the bottom of that page there is a url for technoflex in the NL (Technoflex.nl - technoflex Resources and Information. This website is for sale!) - worth a go?

Cheers,

Off topic: I like the look of those pics of bike trailers - it's the first one I have seen with a swinging arm, which is a great idea compared with a direct axle.

Trail Tail info
 

You can't see it well in these pics but these trailers also have a rising rate rear mc type rear shock on there....its at the back of the trailer. They claim they handle very well....the pics of nasty single track are impressive.

Cost is about $800 US. More with Top cover. Fully street legal.

Here is a comment from the owner answering some of my questions:

Take a look at the AfricanQueens - Spezialteile für Enduros und Reiseenduros. for alternative spring rates for the xrv. For travelling 2 up go stiffer back and front. Remember the week wheelbearing in the back wheel (left side), bring 1/2 extra, and change before you leave. Good luck with your travell, and watch your weight carefully. Try not to overload.


Mollydog: Have you ever tried an XRV or even seen one?

Talking about spagetti sving arm? XRV has an massive aluminium one, more than up to the jobb.

thin forks: actually the samme dimension as the road rocket suzuki you talk about, of course with more travel, and it comes with a brace. Do trawel bikes need 50 mm forks?

soft frame: I would say the xrv frame is pretty solid, with a good sub frame. RD04 was/is the choice for rally conversions. And i would say is is more solid than the old GS units, i dont know with the new 1200.

soft wheels? I have never heard of people having trouble with them so i suspect they are as good as anny.


Maybee know something about the actuall bike before you say it is a peace of shit?

I do aggree about not overloading the bike.

Mvh Frode

Have I missed something?
 

I don't see these expressions, or anything remotely like them in this thread! :rolleyes2:

(but Mollydog is well able to speak for himself :thumbup1:)

Still :offtopic: - maybe this should go into a new thread?


Mollydog,
Ta for the extra information; those trailers are well thought out and designed it seems to me. I assumed that there is a shock with the swing arm; any idea how they deal with steering in slow, tight turns at, say road junctions from a standing start - do they have a ball joint behind the attachment to the bikes' swinging arm for instance?

Not everyones cup of tea to pull one of course - the light weight bikes shown in the pics are obvious candidates and I guess they could find their limits easily enough in either deep sand or mud.

The price is competitive with the cost of hard bags and racks at the current exchange rates, so maybe someone should be importing these into Europe??!

Kelowna; nice place from memory. Toured through there a few years ago, unfortunately on 4 wheels at the time.
(I guess the pics are BC and not, as I assumed, good old USA!)