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Old 10-05-2012, 11:12 AM   #1
PenultimateMan OP
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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!).

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?

Help!
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Old 10-05-2012, 12:14 PM   #2
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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.
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Old 10-05-2012, 12:51 PM   #3
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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.
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Old 10-05-2012, 12:59 PM   #4
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Quote:
Originally Posted by PenultimateMan View Post
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.
Yes.


Quote:
Originally Posted by PenultimateMan View Post
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.
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Old 10-05-2012, 01:24 PM   #5
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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.
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Old 10-07-2012, 03:03 PM   #6
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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.
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Old 11-08-2012, 03:08 PM   #7
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Quote:
Originally Posted by Ducksbane View Post
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.
I can partially answer this question. Im 40, 120kg all kitted up, and the stock 45s (2009)were crap. I had springs and oil done and they were much better, but not GREAT.

Just traded on a 2013. The 43mm are better, to me, than the stock 45mm. Less dive, more plush...but not as good as my improved 45's, and sstill not GREAT.

I havnt had the new ones apart. I am working ona cunning plan with Lukas. Pics in about a month I reckon.
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Old 10-07-2012, 03:13 PM   #8
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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.
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Old 10-07-2012, 04:20 PM   #9
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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 these.....me 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?
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Old 10-07-2012, 07:15 PM   #10
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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.
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Old 10-07-2012, 07:28 PM   #11
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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.
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Old 10-07-2012, 08:13 PM   #12
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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.
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Old 10-07-2012, 08:25 PM   #13
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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


Rant over, GL with the new bike
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Old 10-07-2012, 09:10 PM   #14
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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


Rant over, GL with the new bike
A'hem.....I HAVE a 09 F8GS...I HAVE ridden a 2013 F8GS, and I am going to either keep my improved 45mm front end, or do an upgrade to the 2013 43mm. nuff said.

On the posts about the F8 not being a dirt bike?....I used to think like that..:)..but just spent 10 days on the dirt, in the hills, on gravel roads, on single track, up hills, through creeks........this thing suprised the hell out of me. The longer the trip went, the smaller the bike felt.
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Old 11-22-2012, 06:10 AM   #15
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Cool2 Best logic yet...

Quote:
Originally Posted by RandomZ View Post
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


Rant over, GL with the new bike
This is the best piece of logic I've seen. It could potentially save $$$$. Thank you for stating the obvious.

I'm in talks with my dealer to trade my R12GSA & g450x for a new F8GS. I believe the F8 will be better suited for the riding I do most often and enjoy the most.

So, it's not completely clear to me...the forks in the 2013 model have changed? I have seen mention that they are now [better?] 43mm WP whereas before they were [crap] 45mm Marzocchi. Is that correct? If this is the case, I'm certainly going to buy the bike and ride it before replacing the suspension.
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