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Old 11-07-2005, 11:31 AM   #1
ducsingle OP
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R80ST crash rebuild: front end options

I've been reviewing front end options for rebuilding my R80ST and would appreciate any thoughts on the pros/cons of the following:

Option 1: stick with the R65 type fork I had on the bike originally. Pros are I have a spare in the garage and the wheel and fender will easily fit. Cons are the R65 fork is a little bendy, RaceTech doesn't make a cartridge emulator, and the stock brake setup isn't great.

Option 2: install an R100R front end. Cons are $$$ - - - the cost of the fork isn't too bad, but I would probably do a custom front wheel (R100GS/R100R front hub laced to tube-type rim). Plus the R100R fork is configured for an 18-inch front wheel, so I'm not sure how that would work with the 18-inch ST rear wheel. Pros are better suspension and brakes.

Option 3: install an R100GS front end. This seems to be a popular
conversion for the R80G/S in Europe. Cons are $$$ and suspension/brakes wouldn't be as good as Option 2. I also wonder
about frame geometry since the GS has a 17-inch rear wheel and the ST has an 18-inch rear wheel. Of course different aspect ratio tires have an effect on this too. And I would need to install a G/S type rear shock, but I need a new rear shock anyway.

There might be other options. For example, there are some posts on the Horizons Unlimited board about installing USD forks from an RM250. However, I wouldn't consider this unless I could talk to someone who had done it.
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Old 11-07-2005, 11:55 AM   #2
sharkey
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Quote:
Originally Posted by ducsingle
Option 1: stick with the R65 type fork
Option 2: install an R100R front end.
Option 3: install an R100GS front end.
The real question is: what do you want to do with the bike? What kind of bike do you want it to be?

If you want it to look stock, 1 is the best option.
If you want it to handle well on the tar, 2 is the best option.
If you want it to handle well off the tar, 3 is the best option.
(or a beefy set of off-road forks)

-----sharks
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Old 11-07-2005, 12:43 PM   #3
ducsingle OP
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I doubt the bike will see anything more severe than a fire road, which is doable with the stock or R100R forks. However, right now I'm leaning towards the GS front end. My R100GS of a few years ago handled pretty good on the street. Plus I'm putting a bunch of other adventure touring stuff on the bike (big tank, solo seat + rack, etc.), and the GS front end will make the bike more appealing to a buyer if I eventually decide to sell it.
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Old 11-07-2005, 12:52 PM   #4
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Well, there you go, your question answered. It's the option I'd be least likely to go for (may as well fit a Japanese dirt bike front end if you're going to bother) but it's *YOUR* bike!

You owe the Oracle: a bucket of prop wash ...

-----sharks
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Old 11-07-2005, 01:33 PM   #5
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There are a lot of unknowns going with a non-BMW front end. I would go that route if I could talk to someone who had done the same thing, but so far I've only seen second-hand posts about folks who have fitted RM250, KLR, etc. front ends.
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Old 11-07-2005, 02:28 PM   #6
Stephen
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I'd go with anything other than BMW forks. Well, almost. Some good road or dirt forks off a Big Four bike, or an old KTM. Any of'em will be plenty strong enough. Any will be long enough to make up for any tire/wheel sizes. Any will have far better damping, and far better brakes than what BMW supplies. Unlikely that any decent forks will be as small as those stock tubes -- what are they, 36mm? -- but maybe, and that would make a swap easy. Adapting triple clamps isn't a nightmare either, perhaps as simple as some adapter bushings for the bearings. Count on changing springs.

As for choosing wheels, start by seeing what tires are available in the different sizes. Old Guzzi twins (and Duc singles!!) ran 18 f and r, so street rubber is certainly available.

Even if somebody has done exactly what you want to do, you're still gonna hafta think and work. If you don't want to spend much time on this, then you should go stock. R100R uses Kbike fork; lots better for this app than the R100GS marzocchis. But you're still gonna hafta do some things to fit'em.
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Old 11-07-2005, 03:41 PM   #7
Frank Warner
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You could also fit a bm K series fork - they are much stronger than the R series forks. The K11s came with cartidge forks. Same head stems and bearings too.
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Old 11-07-2005, 04:34 PM   #8
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Yeah, BMW used essentially the same forks on the 4-valve K-bikes and R100R models. These aren't bad, and RaceTech offers a cartridge emulator kit for them. Plus these forks accomodate the later Brembo calipers, which are a huge improvement over the stock ST, G/S, and GS brake setup. I just got an e-mail from a guy on the ST list who went this route with an 18-inch R100R front wheel (with the stock ST 18-inch rear wheel) and he says the setup works well.

Installing a really nice front end probably isn't worthwhile as the frame and rear suspension will still be a limiting factor.
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Old 11-07-2005, 06:40 PM   #9
ozadvntr
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Why don't you wreck that old ST and sell me the 32/10 diff, you'll be far better off.

TIC

PLEASE
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Old 11-07-2005, 07:18 PM   #10
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Go Option 1


Option 1: stick with the R65 type fork I had on the bike originally. Pros are I have a spare in the garage and the wheel and fender will easily fit. Cons are the R65 fork is a little bendy, RaceTech doesn't make a cartridge emulator, and the stock brake setup isn't great.

I have rebuilt my R80G/S. Running R100RS 70HP motor Rebuilt
Rechromed Forks with Gold Valves fitted. You 'CAN' fit gold Valves to them. Try to get a 80G/S fork Brace. Voila great Front end!!!
Other Details of my R80G/S Dakar


Completely Rebuilt Gearbox

HPN 1st gear (5% Lower)

HPN 5th gear (5% Taller)

New 32:10 Final Drive 5% Taller than Stock (Swiss R80ST)

New Brakes 310mm floating disc & 4 Piston (K1100) Brembo


Made my own mounting bracket - 15mm Master Cylinder




2,200 k’s Since completed.

Fuel range 530-550 k’s - 6 litres per 100 k’s On trip to Phillip Island

New Silver Paint, the bike is running a R100GS PD front guard in Sliver with a Black Thumbnail. Chrome Handlebars, engine bars and pannier Racks and carry rack.

Pezz :)
R80G/S Dakar
KTM 640 Rallye - For Sale
KTM 660 Rallye
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Old 11-07-2005, 07:24 PM   #11
Pezz_gs
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Quote:
Originally Posted by ozadvntr
Why don't you wreck that old ST and sell me the 32/10 diff, you'll be far better off.

TIC

PLEASE
Just buy a new one Michael . . . .

Pezz :)
R80G/S Dakar
KTM 640 Rallye - For sale
KTM 660 Rallye
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Old 11-07-2005, 09:10 PM   #12
ozadvntr
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I have, it's on the way at the moment.

I have 2 G/S's.
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Old 11-07-2005, 10:11 PM   #13
sidetrack
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I fitted a USD 1992 YZ250 front end into my R80G/S. Steering head bearing sizes are identical. This is obviously critical if you are going to have a straight forward conversion. Bottom yoke goes straight in, top yoke slightly higher so made a spacer to suit. Gives slightly higher handlebars but this is OK. Forks in and now comes the part when you need the experts. I wanted to use the original BMW wheel so took forks to our very clever local engineer who loves working on motorcycles.He made a new axle and appropriate spacers.
Now the bike handles off road situations really well and still looks stock.
YZ forks may not be what you want on your ST though .
Perhaps you can find a more roady front end with the same steering head bearing sizes. Check the length of the forks. They should ideally be the same but at least similar to maintain the original steering angles.
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Old 11-08-2005, 02:40 PM   #14
ducsingle OP
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Great to hear from someone who has actually fitted a non-BMW front end on a G/S. I might make a trip to one of the local dealers this weekend to check out late model front end options.

Why did you go to such great lengths to keep the BMW front wheel?
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Old 11-08-2005, 03:57 PM   #15
sidetrack
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I went for about a 500km trip with the YZ250 front wheel, disc and brake caliper. Wasn't happy with the braking or the look. Thats the reason I chose to use the original wheel. Also was a good time to have a 4 pot caliper fitted.

This has made an immense difference to the braking. Still has heaps of feel. Very necessary as I enjoy my gravel roads, but heaps of retardation if if you haul it on on the seal.
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