ADVrider (
-   Parallel Universe (
-   -   F800GS "Drop-In" Fork Replacement? (

PenultimateMan 10-05-2012 11:12 AM

F800GS "Drop-In" Fork Replacement?
After literal days (I have a lot of downtime right now) of searching for solutions to the problem posed by the supposedly poor front forks on the F8, I'm well and truly stumped about what to do when I pick mine up (in about 90-days' time): for quite some time, I had planned to get a second set of Shiver 45s from an Aprilia and follow Gangplank's "tutorial" for that mod to provide adjustable, quality suspension up front.

Then those tricky Krauts changed the size of the front forks (and made them SMALLER at that!). :becca

So I looked at and inquired about both the Bitubo and Traxxion cartridge mods, seeing whether they would be made to fit the new, smaller fork inner diameter. Answers were vague, and at $200-$700 more for the fix than what Gangplank managed to eke out with his conversion, the fix is outside of my original budget (but not out of the question; the suspension matters to me).

I know that there are loads of people in the forums who know a great deal more about suspension than I do, and I'm hoping they can help. My question is this: Is there a way to simply take a full set of fully adjustable donor forks off of another bike and use those? I realise that there'll likely be some machining involved with the feet in order to accommodate mounting the wheel and brakes, but surely there must be an easier way to fix this problem than with all of the aftermarket mods to the cartridges and caps that seem to only produce marginal results. Are there other forks that will fit in the F8's triples?


LukasM 10-05-2012 12:14 PM

WP43mm forks from a KTM should "drop in" the stock triples, but there is no right side axle clamp (fork bottom) with caliper mount available for them. If you want dual discs you'd have to go with 950/990 forks with 48mm slider diameter, but those will require some custom triples. Doable, but not cheap.

If somebody would tell me the diameter and thread pitch of the 2013 BMW fork cap I can check whether the cap (this houses the rebound adjuster knob and on some models also the preload adjuster) from an adjustable KTM WP 43mm fork - which houses the rebound adjuster knob and on some models also the preload adjuster - would fit.

Then the next question is if the BMW feet can be bored out to accept the adjustable compression holder, but I don't think this will be a problem.

After that it's only a matter of modifying the cartridge for the right length and stroke and fitting the right spring.

PenultimateMan 10-05-2012 12:51 PM

So, Lukas, if the caps fit and the feet can be machined, I'd just need the internals and the caps and the rest of the stock forks could be kept in place?

Also, and please pardon my ignorance, what would need to be done to simply adapt the KTM triples to the BMW? Are they mounted to the bike completely differently? Isn't it just a set of bearings and such that attach the triples to the front of the frame? I'm sure the whole process must be more complex, but I'm not privy to the complexities of it.

LukasM 10-05-2012 12:59 PM


Originally Posted by PenultimateMan (Post 19755662)
So, Lukas, if the caps fit and the feet can be machined, I'd just need the internals and the caps and the rest of the stock forks could be kept in place.



Originally Posted by PenultimateMan (Post 19755662)
Also, and please pardon my ignorance, what would need to be done to simply adapt the KTM triples to the BMW? Are they mounted to the bike completely differently? Isn't it just a set of bearings and such that attach the triples to the front of the frame? I'm sure the whole process must be more complex, but I'm not privy to the complexities of it.

First you need to find or have made triples with the right geometry, stock 950/990 have too much offset. Then you need to figure out the stem / bearings, steerings stops, clearances, etc.

PenultimateMan 10-05-2012 01:24 PM

This is why I love this site. Thanks for the consult, Lukas!

I keep hoping that someone who's already taken delivery of a 2013 F8 will take off their fork caps and provide the measurement, but so far no one has been forthcoming. I'm tempted to see if the parts folks at the nearest Beemer dealership will ante up with the info.

If no one's come up with the data by the time I pick up my bike, I'll take the caps off and measure them. Since it seems that the Shiver mod is now out of the question (and BMW can't/won't be prevailed upon to fix the problem themselves), the ball needs to be started rolling on coming up with a new solution.

Ducksbane 10-07-2012 03:03 PM

Has anyone ridden one of the new 800's to see if the WP's aren't better than the old Marzocchi's ?

Has anyone taken the forks apart to see if they are rebuildable ?

I think you need a bit more information before you start redoing the forks on a bike you don't have yet.

PenultimateMan 10-07-2012 03:13 PM

No one's ponied up the information on the new forks. I suspect that's because there are simply so few out there yet, and the dissatisfaction hasn't set in with the front suspension that the Zokes had time to foster (five model years with the same kind of crappy fork). I'm not going to rebuild mine without riding them first, but I am going to at least take the caps off and measure the thread pitch and diameter for Lukas if no one else has done it by then. To tell you the truth, it's the lack of re-buildability that bothers me most on principle. I do believe that BMW engineers amazingly durable bikes, and their engines and systems seem second-to-none. That's why the second-party mediocre forks are all the more intolerable to me. Everything else on the bike can be made to suit the rider to some extent, and fairly easily repaired in the case of failure. The forks can't even be adjusted, let alone rebuilt when they fail. That's almost insulting with the price of the bike as a whole, and the par that BMW has set with the rest of the bike.

Hamish71 10-07-2012 04:20 PM

Hi Lukas/Penultimate Guy,

I have been asking Lukas similar questions on a different thread....was about to suggest we take it off line to discuss further, but hey, lets do it here.

My situation is that I HAVE a 2009 F800GS, and I am about to trade it for a 2013GS. My forks have been revalved, and better springs, and I am pretty happy with them, but I want them to be adjustable. I want to be able to run 17/21 in the dirt, and 17/19 with tubeless road tyres on the bitumen. I want to keep the BMW twin calipers, and I want to keep abs. I do not mind if I have to use a custom or ktm wheel, but, Id prefer to keep bmw wheel. I do not mind spending money to solve this....not ludicrous amounts, but some is ok.

The way I see it, my options are as follows:

1. Trade and get 43mm WPs....wait whilst the industry works out what can be done with no likey this approach. ALternatively, drop in a 43mm KTM fork.....what KTM runs 43mm??...I cant think of anything in the last 10 yrs?
2. Trade, but keep my 45mm forks and triples, do the RXV Shiver conversion. Whoever gets my 2009 will have 43mm on their bike......I dont really like the idea of going "down" in fork size, but I honestly do not know if these are better or worse than the 45mm zokes. I weigh 115kg, and I bottomed the 43mm on my test ride....but I would do the same on a stock 45mm.

3. Fully adjustable 48mm WPs. This is what I want to do, and it is here I am ready to pick Lukas' Brain.

Id be happy to get custom triples. My thoughts are that emig racing has already jigged the top clamp, and would just need to do the bottom?...that would mean the spacing is right? Given the bmw axle is 20mm, and the ktm 30mm the issue then becomes which foot to use, and thus what axle size will work...correct? I'm assuming that using the BMW spacing, but KTM feet, and using a ktm wheel, it would be too much to expect that the twin disks would line up beautifully with the BMW calipers?.....

Which I think means you need to either custom make new "BMW" feet and use a bmw wheel, or, use a ktm triple clamp, and a ktm wheel, and shim the bmw calipers to fit?

Am I on the right track?

Snowy 10-07-2012 07:15 PM

I started measuring different brands of USD forks to see if something would come close. The main issues were lack of right side caliper bracket on all the off road forks.

The next issue was all the modern internals are all bigger than the F8s.

The next issue is that the triples are too weak to go boring them out to accommodate larger forks.

The next issue is that any proper off road front end is about 10~13mm narrower from fork centre to fork centre across the triples.

You can start machining internals and stuff, but then you have to machine replacements when they wear out. I'd rather opt for an off the shelf deal.

I have the parts to fit a motocross front end, I just lost interest in the F800 along the way. It's actually frustrated me so much I went away for the long weekend in my car.

I'll see if I can get my bike mojo back and finish it. At the moment I can't be bothered riding it anywhere. Everytime I think of somewhere to ride it, I figure it'll only disappoint me. It'll pass.

PenultimateMan 10-07-2012 07:28 PM

For my own part, I don't plan to be using this thing like a dirt bike (it's not one; just too big and heavy), but as a true Adventure bike. I want it to be able to go over some very rough stuff without jarring me out of the saddle and also let me retain some feel on the road/trail. I'm not going to be doing days on end of single track. That being the case, I want the ability to dial in the suspension to fit me (96 kilos in-gear), and be able to rebuild the suspension when needs dictate. From a road-use standpoint, it'd also be nice to just eliminate the brake dive.

The full-motocross conversion is likely a bit too rich for my blood, but I'd love to be able to find a way to upgrade the stock forks enough to handle all of the stuff I want to do without the forks or me taking damage.

Snowy 10-07-2012 08:13 PM

Yeah, I know what you're saying. I did MX fork conversions with DR650s and inmates in the forum screeched and threw feces from the tree tops.

Comments in PMs like "A fork from a 250 can't possibly cope with the weight of a 650" gave me a reference point for assessing the knowledge of the contributor. Some people are clueless. I actually got abusive PMs for suggesting the swap could be done. I deleted the "how to" thread contents. If they want to be ungrateful they can go without.

At the end of the day, stock standard the MX forks work far better than revalved and resprung standard forks on something like the DR. Respringing them made them handle on the DR just like a 450 handles. They work exactly like they do on the smaller bikes. Quite literally you can ride the big bike just like a small bike. Over rocky fire trails average speeds according to my GPS went from 45kph to 60, then 70. Sections I had to pick my way through became sections where I point and twist. To the point where you have to start learning how to handle a large bike when in the air for extended periods.

I have a set of RM250 conventional dual chamber forks on one DR and I'd happily swap those onto the BMW. with a 0.55kg/mm spring rate and 300mm travel and 48mm legs they are far stronger, and far better at taking the abuse with the weight than the standard BMW forks. They were set up for a DR in full heavy touring set up with a 30 litre tank and gear. Heavier than a standard BMW.

I've actually given the idea a lot of thought. A motard disc on aftermarket wheel for an RMZ with a billet hub and super heavy spokes, fit the ABS ring, 4 Piston caliper. WooHoo. Every component is far stronger than the original BMW equivalent.

Properly built there's no reason at all I couldn't ride the F800 like I do my DR. It's a better balanced bike. Weight isn't the issue people think it is once the bike has suspension that is set up properly for the task. The DRs proved that to me.

The OD of the BMW steering head bearings is the same as the OD of almost every single Suzuki dirt bike steering head bearing from the last 20 years. The triples for the RM and DRZ conventionals are far stronger than the standard BMW ones.

It's a thought. Realistically, even the standard front end of a DR650 with Gold valves and heavy springs would be far superior to the BMW USD front end. Less travel than a pure off road MX front end, more travel than standard BMW, and a fork closer to the length of the standard BMW ones. Win/win. ABS sensor is easily set up on a DR front wheel.

Got a friend with a DR? Buy him an RMZ front end for $400 and swap. He'll love you for it.

Think outside the box.

RandomZ 10-07-2012 08:25 PM

Good grief, haven't even got the bike and already trying to change what you "think" is a lousy component? Wait till you get the bike, ride it, and then decide. It blows my mind when working with customers who are looking at a new bike who say "well if i buy the bike i'll need to get a taller windshield" or "i'll need to change the stock tires." People give the interwebs too much credit, just ride the bike and see. For 2013 the F800GS is vastly improved over it's predecessor. Buy it, ride it, and then tweak as needed :evil

Rant over, GL with the new bike :lol3

PenultimateMan 10-07-2012 08:34 PM

So is it reasonable to think that a USD upgrade that would fit a Suzuki would also fit the F8?

Snowy 10-07-2012 08:43 PM


I use a spring rate of 0.55kg/mm in my Suzukis. I use 0.55kg/mm in my BMW.

Overall length of the USD Showa is within 40mm of the standard BMW. with my Ohlins rear shock being higher than standard, it'd work fine with the forks raised maybe 20~30mm in the triples.

The standard F8 forks are shit. Pure shit. The one reason I don't like riding it off road.

Steering stem height is the same, bearing ODs are the same. there's no reason it can't be done. Brakes is the only significant hurdle, because of the abs, even that is do-able with the right approach.

All that remains is to do it.

Valving wouldn't even need to be changed. Put a set of 0.55kg/mm springs in a set of Showas, use billet triples and fit it all up.

I prefer the Showa dual chamber conventionals for Adventure bike applications, purely because they hold far more oil and are not prone to spewing it all out when the seals wear. yeah, they leak, but you can live with it for months. Not like USDs when they do start leaking.

With the Showas, there's spares out the wahzoo. Common as brown dogs.

PenultimateMan 10-07-2012 08:53 PM

"Good grief, haven't even got the bike and already trying to change what you "think" is a lousy component?"

I understand whatyou're saying, and as I said, this is more just me finding ways to occupy idle time than anything serious yet. I will ride the bike before I do anything, and I'm not simply taking it as read that the suspension sucks on the 2013s as well.

That being said, the sheer physics of them reducing the size of the fork doesn't bode well. Neither does the fact that, with all of the other changes that were made and widely-lauded by BMW's marketing department, the suspension swap wasn't amongst them. In fact, it was so surreptitious as to be unknown to a number of the dealers, it seems. If they had actually improved the suspension, would they be so hushed-up about it?

At the end of the day, I'm mostly miffed about having a long-standing plan in the form of the Shiver swap pulled out from under me. I'd actually ridden on those forks, and knew that at least the brake dive would have to be remedied. Consider the research into my options should these forks prove to be as soft as my way of assuaging anxiety.

At any rate, thanks for the call to sanity. It's just that I haven't actually gone crazy just yet.

Times are GMT -7.   It's 12:30 PM.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2015