An Unholy Union V: DRZ forks on an Airhead

Discussion in 'Airheads' started by Ras Thurlo, Jun 28, 2014.

  1. Phreaky Phil

    Phreaky Phil Long timer

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    a Harley ! Talk about an Unholy union ! ! yes twin discs has crossed my mind. I guess the standard size rotors would be ok. The single 320mm I used to have on my Beemer with the WP forks was superb but it had a supermoto 4 piston calliper. Did you bore one of the left side axle holes to accept the larger part of the axle ?
    #61
  2. Prutser

    Prutser Long timer

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    The left side axle clamp was drilled out to fit the fat end of the axle. The material above and under the axle was a bit to thin for comfort so I welded plates on the clamp. Now it looks like it's stock.
    #62
  3. Prutser

    Prutser Long timer

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    The last few years I have seen a lot of airheads with forks transplants. A lot of those forks were put trough the triples to match the rear a bit better. Most of the right side up forks had fork protectors on them.
    So I made a few pictures to show what can happen when you put those forks trough the triples.

    This is how long a protector is when its fully compressed. When compressed it becomes a rubber tube about 10cm long.
    Which can reduce fork travel a lot!!!!! On some forks people mount those protectors on the top of the bottom slider.
    Than the compressed protector has no were to go !!!
    So some people think they have 210 mm fork travel but with a protector mounted wrong they only have 110mm travel left to use :rofl

    [​IMG]

    That compressed length is the reason the protectors are mounted that low on stock DRZ forks(half way on the slider)
    Mounted that low they wil be compressed OVER the slider and won't get stuck between the bottom triple and the top of the slider.
    That way they won't reduce fork travel.

    With forks pitched trough the triple there needs to be enough room under the bottom triple for the full fork travel plus the clamp that holds the fork protector on the top.

    This picture shows the length of the cartridge which is the full length of the fork. Next to it is a fully compressed DRZ fork.
    [​IMG]

    The chrome length you can see is all the room there is to mount the triples and the top of the fork protector.
    It depends on the type and shape of the triples how much room you have left to put those tubes trough the triples.
    After measuring lots of DRZ forks there are a few different ones out there although they should be the same.
    I have measured ones that had 270 mm of travel and found a few of the same forks that had 285 mm travel.

    [​IMG]

    On this picture it shows that two of the forks are longer and have more travel than the DRZ forks. So fork the hardcore off-road riders :freaky those longer ones might be the better ones if you like more travel. ( and if you don't mind a tall bike)

    [​IMG]
    #63
  4. Phreaky Phil

    Phreaky Phil Long timer

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    Ive just been doing some calculating of the difference between caliper size of GS and DRZ. The GS has a single 38mm piston and the DRZ has dual 27mm pistons. So the area of the GS piston is 1134mm. The two DRZ pistons is 1145. So in theory, much the same. May be worth a try ?
    Wonder what others have found on other GS fork conversions using twin piston calipers.
    Does that mean the GS master cylinder is to big ? at 13mm
    #64
  5. hardwaregrrl

    hardwaregrrl Can't shoot straight Supporter

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    :lurk
    #65
  6. Screaming Chicken

    Screaming Chicken Long timer

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    Might. Sort of. Given that the stock GS brake is rather crap to begin with, it's not a high bar...

    I've got a Brembo 4 pot on at the moment. That's 32/34mm, which then makes... 1712mm? That one works really nicely with that same 13mm master and it's quite a big difference in area with the DRZ caliper.
    #66
  7. Screaming Chicken

    Screaming Chicken Long timer

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    Thinking along the lines of what to do with the front brake. The stock DRZ stuff is obviously a bit weedy so it'll need a 320 at least. I'd prefer to not mess too much with the stuff on the handlebar, so that's a problem. What to do...

    And then something went click in my head:

    "I'll bet those Pretech guys mentioned by Rob Farmer in the other thread could do a nice little six pot number for a DRZ fork and a 13mm master..."
    "Yeah, but clearance with the spokes will be a bastard for any double-sided caliper and I don't really want to stick the cross-spoke boat anchor back in..."
    "I'd have to get one of those Prutser sets then for the extra width..."
    "Wouldn't that be nice?"

    This is how all those crazy builds start, isn't it? Just daydreaming away... My bank account hates my head. :lol3
    #67
  8. Phreaky Phil

    Phreaky Phil Long timer

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    Had a bit of a look to see how hard it would be to mount another caliper.
    [​IMG]
    It would be a fairly easy job to make a mounting plate for this caliper although I would get a road going version as this is a racing one and only has one seal, no dust/ dirt seal.
    #68
  9. Ras Thurlo

    Ras Thurlo Desert Lion

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    a brief trip to ebay resulted in plenty 320 DRZ kits for the supermoto crowd.

    I got a 320 disk and relocation bracket from uk ebay and it was not that expensive. The disk feels great, the relocation bracket needed a minor amount of shimming to fit, which is counter intuitive for a "kit" but was not a big issue.

    http://www.ebay.co.uk/itm/171136928750?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649



    now on my ex-city 100GS with Prutser's triples and DRZ forks and calliper, and a stock paralever swing-arm :evil

    btw. the steering lock on these triples is great, felt better than OEM steering lock

    [​IMG][/URL][/IMG]
    #69
  10. Screaming Chicken

    Screaming Chicken Long timer

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    Nice bike. :D I'd seen it already in nearly-done state last week. Turned out well. Even had a little sit/stand on it to try those footpegs. :lol3

    The 320 disc won't be a problem, plenty of options for that indeed. I'm a bit worried about the DRZ caliper vs late GS master cylinder combination. I see you've got the early controls, do those have a different master cylinder?
    #70
  11. Phreaky Phil

    Phreaky Phil Long timer

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    looking good. Are you an official triple clamp tester. When are they ready for public consumption ?
    #71
  12. Screaming Chicken

    Screaming Chicken Long timer

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    Huh.

    The MC that came with my DRZ fork is marked 1/2, so presumably 1/2" or 12.7mm. That's very nearly the 13mm of the GS MC. Caliper pistons are 2x 27mm as expected.

    [​IMG]

    Meaning it should work reasonably well as is with the GS MC and/or the DRZ (S/E unknown, it's a 2006) this lot came off had crap brakes from the factory.

    MC:caliper ratios:
    DRZ: 1:9.2
    GS w stock caliper: 1:8.6
    GS w DRZ caliper: 1:8.6
    GS w 1100 caliper: 1:12.9

    Anyway. Looks like it'll just about do to start with, getting a 320 on there will make it at least slightly better than the stock GS brake.

    Comparing some measurements of stock GS forks and DRZ forks, widest point across the top clamp is actually slightly narrower on the DRZ, so that looks promising for getting it into the PD fairing. Biggest problem will be the distance between the top of the steering head and the fairing below the clocks. As far as I could measure it (crudely, without taking things apart) it might just fit with the DRZ legs flush with the top clamp and taking a bit off that fairing edge as shown by Phil on page 3...

    Prutser, just for curiosity's sake, how thick is your top clamp? It looks fairly thick, is it thinner than a DRZ top clamp plus spacer? (3.5 cm + 1 cm spacer?)
    #72
  13. Prutser

    Prutser Long timer

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    For this bike I made a stem my self because the metal ones still didn't come in :ddog
    When those metal stems are ready I can start shipping the triples.

    But as soon as they come in I will mount two sets to check everything on a stock G/S frame with the small tank so we can make some steering stops for those.

    Ras isn't the "official" tester although his bike is the first to ride with the triples.
    #73
  14. Phreaky Phil

    Phreaky Phil Long timer

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    Thanks Bas. They look great on the bike. Looks like Ras has got a stock GS master cylinder so will be interesting to see how well the brake works with that setup.
    Are his forks still stock length or shortened ?
    Better send him out for some " testing " anyway. And a few more pics of the bike. :D
    #74
  15. Ras Thurlo

    Ras Thurlo Desert Lion

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    Unfortunately not, am just a regular member of the public, but with an exceptional taste in bikes :D
    #75
  16. Phreaky Phil

    Phreaky Phil Long timer

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    That looks like it might be the same as the DR 650 m/c which shares the same caliper as DRZ. The Different DRZ 's must come with different m/c's :huh
    #76
  17. Screaming Chicken

    Screaming Chicken Long timer

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    In that case...

    I've done a couple thousand miles on a rental DR650 in NZ and never noticed anything wrong or bad about the brake on that.

    Gives a person hope. :lol3
    #77
  18. Screaming Chicken

    Screaming Chicken Long timer

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    Just for completeness sake...

    MC:caliper ratios:
    DRZ w 1/2" MC: 1:9.2
    DRZ w 11mm MC: 1:12.2
    GS w stock caliper: 1:8.6
    GS w DRZ caliper: 1:8.6
    GS w 1100 caliper: 1:12.9
    #78
  19. Prutser

    Prutser Long timer

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    I mounted a 12mm mc on the bike. It feels firm but still with a good response and feedback from whats happening down there.
    I'm sure 98% of the people would be real happy with a brake like that.
    But if you would be able to find an even smaller mc the brake would still be really firm but with a little, little bit more lever travel and a bit less force needed to pull the lever.

    I thought this fork was shortend 4cm but it has an 18" rear wheel and a longer shock. It can just stand on the centerstand with both wheels on the ground. Its really a great set-up all together.
    #79
  20. Prutser

    Prutser Long timer

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    But now the footpegs are even 2cm lower :D
    #80