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Thread: 1984 R100RT - auxiliary light and rear tire size

  1. #1
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    1984 R100RT - auxiliary light and rear tire size

    Hi Folks... Nice to be a new MOA member here ;-)

    I have two questions re my 1984 R100RT... I am think of mounting a pair of auxiliary lights -- either Denali or Clearwater -- but am unsure what mounting option I should use. Have you any experience mounting lights onto this particular RT model? What mount do you use? Can you post some pics?

    Second, someone told me that I can use up to a 120mm width tire for the rear (stock is 4.00H18). Does anyone here use anything wider than 4.00 tires on the rear?

    Thanks for the help,
    Wai

  2. #2
    If you have crash bars, top of crash bar mount is good.

    The bike was intended for inch sized tires. 3.25x19 front and 4.00x18 rear is what the bike is designed for. The 120 tire is metric sized and is a 90 profile vs. the original which is a 100 profile. The 120 is also difficult to get on and off because of clearance at the final drive. 110 is the widest "wrong" rear tire that I would use.

    Wider is not better. Bikes are designed from the tires up. When you change the size of the tires, you become the bike designer because a number of handling related dimensions are changed with tire size.
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  3. #3
    Liaison 20774's Avatar
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    Welcome to the forum!
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
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    Quote Originally Posted by beemerphile View Post
    If you have crash bars, top of crash bar mount is good.
    Beemerphile - thanks. I should have added that I prefer not to add a crash bar -- it is my understanding (could be wrong) that installing a crash bar means cutting into the fairing, which I prefer not to do.

    Does anyone else know of a mounting solution that doesn't involve a crash bar?


    The bike was intended for inch sized tires. 3.25x19 front and 4.00x18 rear is what the bike is designed for. The 120 tire is metric sized and is a 90 profile vs. the original which is a 100 profile. The 120 is also difficult to get on and off because of clearance at the final drive. 110 is the widest "wrong" rear tire that I would use.

    Wider is not better. Bikes are designed from the tires up. When you change the size of the tires, you become the bike designer because a number of handling related dimensions are changed with tire size.
    I agree with you... I was asking out of precaution after hearing that suggestion. Thanks again.

  5. #5
    Registered User PAS's Avatar
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    Quote Originally Posted by waishiunyc View Post
    Beemerphile - thanks. I should have added that I prefer not to add a crash bar -- it is my understanding (could be wrong) that installing a crash bar means cutting into the fairing, which I prefer not to do.

    Does anyone else know of a mounting solution that doesn't involve a crash bar?
    I mounted my "generic" lights under the lip of the fairing. It depends on the size of the lights and base if they will fit.
    1981 R100RT
    rt fog lights.jpg

  6. #6
    Liaison 20774's Avatar
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    PAS -

    Did you slip a thin piece of metal between the upper and lower parts of the fairing, and then had a hole drilled in the exposed plate to mount the lights? Seems like a decent way to go.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  7. #7
    Registered User STEVENRANKIN's Avatar
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    light mount

    I had seen lights mounted under the fairing lip on a metal bracket a couple of years ago in the Airhead's club forum. I thought it was a great idea as I would not have to cut holes in the lowers and mount tip over bars.

    When I asked if a member could send me a template of the mounting bars they used or, a better picture of the bars used so I could get a better idea as to how the lights were mounted, I got a smart assed reply from the jackass moderator. I should invite my buddies over for beer and the lights might get mounted.

    Needles to say, I never got a picture or answer from that forum.

    I am still interested in seeing a picture of the bar and material used as well as mounting points. Perhaps a template and type of material used.

    I find this forum has courteous members, at least the moderators are better so far than the Airhead forum.

  8. #8
    Liaison 20774's Avatar
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    A couple of older posts with a few more pictures for ideas...no templates though:

    https://forums.bmwmoa.org/showthread...Light-Mounting

    https://forums.bmwmoa.org/showthread...light-on-my-RS
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  9. #9
    John D'oh
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    120 / 90 - 18 is fine. They fit with a good shove, have a variety of interesting useful tread designs/load ranges and provide a larger contact patch. No issues with clearance with /6, /7 swing arms including the large tube swing arms of the early 80's as I have them mounted to two airheads in my garage, a 77 and an 83 - right now. If you don't fully inflate them prior to installing the wheel they do slip between the swing arm and final drive splines/brakes much easier.

  10. #10
    Liaison 20774's Avatar
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    I will never put a 120 on my /7 again. Way too much effort to put and take off. Note that all 120 tires don't have the same width...so while one might work OK, another might not. As has been said, wider doesn't really help with handling.

    Plus the metric tires lowered the bike so much that it made my sidestand unuseable.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  11. #11
    Registered User beemeruss's Avatar
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    Just to add to Kurt's sage advice, as much effort as it takes to remove an oversize tire there will be even more when reinstalling it. I once came within a blond one of collapsing my main stand as I struggled to push the wheel forward into place.
    Russ

  12. #12
    Registered User PAS's Avatar
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    Quote Originally Posted by 20774 View Post
    PAS -

    Did you slip a thin piece of metal between the upper and lower parts of the fairing, and then had a hole drilled in the exposed plate to mount the lights? Seems like a decent way to go.
    No plate, they are mounted to the fairing itself. The base of these cheap lights fit under there perfectly.

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