F800GS - RXV Shiver'ed Fork Conversion

What year? What is the cartridge rod diam?

I pulled the HyperPro "Big Tank" progressives out and replaced with the RaceTech springs. Unfortunately the snow flew before I had enough time to get them really dialed in. But just changing the springs and nothing else was a huge improvement.


Float? Not sure what you're referring to.

What rate are tge race tech springs?
They are straight rate springs which is better. The valving is tunable and progressive so the springs don't need to be.

By float I'm sure he means air over oil. How much do you have? That can help tune in the suspension as well.

Float refers to the float in the mid valve shims, air over oil is called air chamber length.

I don't get the completely stupid mistery that seems to surround BMW fork springs, whether OEM or aftermarket - nobody actually tells you what rate their springs are. So you will have to hope that they are actually right for you, whether you are a 150 or 250 lbs rider.

The Marzocchi shiver springs come in 2 different stiffnesses. .45 or .5.
http://www.af1racing.com/store/Scripts/prodList.asp?idCategory=180

The forks I bought used already had the stiffer springs. I am NOT a fan of progressive springs. Prefer straight rate.

BMW stock spring rate available here:
http://racetech.com/ProductSearch/2/BMW/F 800 GS/2008-10

Says .44 which is why I wanted the stiffer springs.

BTW I don't think racetech's spring rate calculator for the BMW F800 is correct. It says at 185 lbs I should have 0.876 kg/mm spring. That would in my opinion be way too stiff. If you go to the G450X and check there for dirt riding at 185 lbs it says .48 spring. If you add some for the weight of the bike then .05-.55 is probably closer. That was my figuring anyway. The Marzocchi Shiver'd conversion I did siffened it up nicely and tuneability is great.

There spring rate calculator is off if you ride anything but motocross. Custom springs are needed for this bike, most bikes with this conversion need .54 to .62 dependant on the weight of the rider.
Lukas is correct about his float description.

What would be your suggested sag setting for the front and rear?

Bitubo springs are .60 kg and I believe you can buy them separately from their cartridge. Ohlins springs are .55kg and work fine with my Bitubo cartridge replacement.


I think the rev tech calculator is way off. Their replacement spring is S4047 without any weight given. If you do the weight calculator it recommends S4047/95 which is a .95kg spring.

Yeah the Race Tech calculator recommends whichever Race Tech springs that are closest to what you need. The problem is that they only have .95kg springs so for rider weight from 32lbs to 300lbs they recommend the .095kg springs. Luckily they happen to work for me @240lbs plus TT big tank etc.

As far as float goes...no idea. I'd never heard the term before it was posted here yesterday

Springs hold the bike up. If your springs are in the right SAG range then you are good to go and the rest is handled with the valving, oil, and adjustments.

If you are not in the right sag then you need stiffer or less stiff springs OR more or less preload.

Which is why I asked about the proper SAG settings?

Anyone got a line on some 45mm internals or complete forks? Shoot me a PM. Thanks!

Sent ya a PM. There are sets around.

These are the springrates aviable according to Shiver manual, http://slorider.com/Aprilia/manuals/Marzocchi_Shiver45.pdf, page 91.

The springs in my Aprilia RXV Shiver was definitaly 4,8 according to lengdth and wire diameter. What is a bit confusing is that the BMW OEM springs are exactly the same. Racetech is probably the only source that tells OEM springs to be 4,4, either we have different setup in Europe and USA or RT are wrong.

What about the shock? Is the springrate ok, or does it have to be stiffened too when upgrading the fork?

The rear shock is ok. The front was the problem. The rear seems to work a bit better now that it is not overwhelming the front froks.

That said I still plan to repalce it wtih an elka when $$ allow for it.

BTW that link is to the Factory Works forks. The Aprilia spring rates in the US are availble over on the AF1 website. They sell the replacement springs but htey are pretty expensive vs. other springs.

Well it looks like they upgraded their website and offer another spring.http://racetech.com/ProductSearch/2/BMW/F%20800%20GS/2008-10
Now .75kg and 95kg. Still seem heavy to me. Especially when compared for other springs offered for this bike. Ohlins .55kg, Bitubo 60.kg, Standard Hyperpro progressive .52-74kg.

A caparable bike that is heavier, especially in the front. Stock 950 is 4.5NM which converts to .49kg. Koonz racing offers a .62kg spring for the 800xc which is also heavier than a F800 in front.

i have found the marzocchi forks on my te 250 husky to be not nearly as good a fork as on my old honda cr 250,just wondering why you chose the marzocchi for your conversion?i know the new huskys went to kayabas.

Because the internals from the Marzocchi are a direct fit to the stock BMW F800GS fork tubes. That means you use the stock fork tubes, stock tripple clamp, stock wheel, brakes, etc. all stays the same.

If you were to use a CR 250 that would either:
a) use the internals in the BMW F800GS fork tubes IF they fit (i.e. similar size internals) but then have to machine the top cap to fit the stock tubes and bottom lugs to fit the CR 250 adjuster. [note: this actually was my original plan using some WR450F forks]
or
b) change over the entire front end and use the CR 250 forks complete and the CR 250 front wheel which would have only one front brake, and a host of other fitment issues.

Using the stock fork legs was easier for me and with the revalve and right set up by a good suspension guy the Marzocchis are a very good fork. The stock set up may not be as good but the design of the Marzocchi forks is pretty similar to other fork companies so by revalving the shim stack they have have good progressive performance. At least that is my own personal experience.

Whomever noted that it's pretty hard to find forks online wasn't wrong, and pardon me if this information was posted somewhere earlier in the thread and I didn't catch it, but do all RXV forks fit, and are they all Shivers? I've found a couple of sets on eBay (albeit, for closer to $300 in most cases; I can't even get ACCESS to CafeHusky.org to find the $50 bargains that were mentioned earlier) that say they're from 2006 Aprilias, but elsewhere online it lists the RXV front forks as being 48mm.

Am I missing something in the measurements? Am I getting circumferential and stroke measurements confused? The thread's getting so long now, it's somewhat hard to separate the good stuff from the bad.

You will find anything on ebay, you just need some patience There are lots of diffrent bikemodels, some sellers don`t even know for sure from which bike the parts belong. The only way is to ask the seller for the critical specs that you want before you buy.

I've had good luck finding them on the AF1 Aprillia forum under the RXV/SXV board.