Explain it to me like I'm five / lowering 78 R100RS front end

[hayden90]

So Im 27 and have every intention of turning my beautiful newly purchased 78 r100rs into a cafe racer. I have been bitten hard by the cafe bug so please don't try to talk me out of this project or lecture me on the beauty of the Italian wind tunnel designed fairing all you loyal old curmudgeons. I know it's a handsome bike but I want to make it my own piece of art not someone else's. I have no experience in working on motorcycles but thanks to being a plumber, I have a wealth of tools and know how to use them. I can handle the simple stuff like removing the fairing, moving the ignition to the headlight, and anything bolt on. I'm interested in giving it a more athletic look by lowering the front end. Nothing drastic, just an inch or a couple.

Is this something I can do in its bone stock form just by tightening something on the forks and if so how? Can you buy shorter springs or a kit? And most importantly, how safe is it to do this and how will it affect the rideability. Will it handle sharper or just totally out of wack. Again, you will have to explain it to me like I'm new because that's what I am! . I have a solid basic knowledge so I should be able to metaphorically "smell what you're steppin in" but any details and specifics will be solidly appreciated!

 

[20774]

I can't really help with how to lower the front end. You can't just slide the forks higher up into the top triple tree...it doesn't work that way.

But as for rideability, you will be changing the geometry of the bike. Specifically, the trail of the front end. The trail is the distance between the projection of the line down the steering stem to a point where it hits the ground. That point is in front of where another point is on the ground...this point is directly below the centerline of the axle. You want this number to be positive. The bigger it is the more stable it is however the heavier is the steering. Think of one of those raked out old choppers. If the trail becomes quite small, the stability of the handlebars decreases. Think of those wheels on shopping carts which are yawing back and forth as the cart is being pushed. Sure, with a small trail, the steering is quick. But if the trail is too small, the steering can get away from you resulting in an accident.

I don't know how much effect an inch or two will make. I tend to not futz with the geometry of the bike...engineers designed it that way.

 

[Anyname]

I'd actually expect that the best reason for not lowering a BMW would be those large cylinders poking out the sides. When riders race airheads they often raise the engine in the frame for more ground clearance.

 

[Friedle]

lowering front end r100RS

You mentioned you were a plumber and had plenty of tools. If you really can't leave well enough alone, a fresh blade in your hacksaw might be a good starting point to screw up a well balanced good handing bike.

Friedle

 

[69zeff65]

Forking by Frank

I think he is still in business. Google Forks by Frank and order a set of fork tubes for your bike but specify you want them 1.5 inches shorter than stock. Rebuild your front forks using the shorter fork tubes and you may consider a set of stock /5 front springs while your at it.

The good thing about lowering it this way is if you don't like the ride or the way it handles or you decide to sell the bike some time in the future you can install the original fork tubes and springs.

 

[ccolwell]

If I understand your goal correctly, the idea is to lower the front end and leave the shocks stock to get the ass up nose down look. If so, you should consider the easier solution of simply getting longer shocks. As everyone else notes, this will screw up the handling -- probably not disastrously if you don't go too far but disturbingly if you're used to the stock feel (I fiddled with the adjustable length shock on a Ducati 900SS enough to find that the stock position suited me best). Changing the shocks will get you past some of the problems noted above, viz., ground clearance for the cylinders (and the pegs!) and having the fender get too close to the engine or triple clamp. And it should be relatively easy to decide what length shock to get; you can cut some steel bar and drill holes for the shock mounts at various lengths, replace the shocks with that and see what it takes to get the look you want. I'd start with 1/2" -- you might be surprised what a little will do.

Lastly, I'd finish it off with a cool looking and very functional steering damper. Changing the steering geometry that way will make it more quicker and more unstable and a damper will help with that.

 

[RPGR90s]

So Im 27 and have every intention of turning my beautiful newly purchased 78 r100rs into a cafe racer. I have been bitten hard by the cafe bug so please don't try to talk me out of this project or lecture me on the beauty of the Italian wind tunnel designed fairing all you loyal old curmudgeons. I know it's a handsome bike but I want to make it my own piece of art not someone else's. I have no experience in working on motorcycles but thanks to being a plumber, I have a wealth of tools and know how to use them. I can handle the simple stuff like removing the fairing, moving the ignition to the headlight, and anything bolt on. I'm interested in giving it a more athletic look by lowering the front end. Nothing drastic, just an inch or a couple.

Is this something I can do in its bone stock form just by tightening something on the forks and if so how? Can you buy shorter springs or a kit? And most importantly, how safe is it to do this and how will it affect the rideability. Will it handle sharper or just totally out of wack. Again, you will have to explain it to me like I'm new because that's what I am! . I have a solid basic knowledge so I should be able to metaphorically "smell what you're steppin in" but any details and specifics will be solidly appreciated!

One thing I've learned over the years is that old curmudgeon's are typically guys with experience.

If you want to alter the bike, go for it, but the beauty of older Airhead BMW's is their total balance of comfort, handling, power, reliability. Best to save the parts you're removing, as you may find that you'll grow tired of the "look" of the bike and have the urge to put it back to stock, so you can enjoy its full capabilities.

 

[mika]

I don’t have a quick answer for you because I haven’t played with an airhead in some time. In other applications the quick hack to lower the front end was change where the forks were mounted in the triple clamps. The long version was adapting other parts and front ends. BMW parts are incredibly interchangeable so spend some time in a part fiche like Max BMW’s.

Before you spend money on parts I suggest you spend some on Tony Foale's book along with spending some time at his website.
http://www.tonyfoale.com/
His book, Motorcycle Handling and Chassis Design, the art and science, is a must have if you are heading down this road. The garage of hard knocks has shown me you can have a great looking cafe bike that rides like.... if you don’t do your homework before you open your toolbox and wallet.

Good luck with your project!

P.S.: Old forum saying...this thread is worthless without pictures.

 

[robsryder]

Making changes to a motorcycle's handling by raising or lowering front or rear suspension can have dramatic effects not immediately obvious when viewing a static bike. Alas, the analysis of motorcycle handling dynamics can be complicated to evaluate. A few places to start gaining information are linked below -

https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

http://www.tonyfoale.com Note: Tony Foale sells software that will allow for complex analysis of changes to motorcycle suspension and other parameters. He also has a number of technical papers and documents available for download. At one time he offered seminars in the dynamic analysis of motorcycles - I found the seminar to be interesting.

The book "Motorcycle Dynamics 2nd ed." by Vittore Cossalter is quite thorough, but not really simple.
https://www.amazon.com/Motorcycle-D...=sr_1_1?s=books&ie=UTF8&qid=1491008535&sr=1-1


My suggestion is to leave the suspension alone. If you really wish to make changes, make very small incremental changes and test the handling under "controlled" circumstances, ideally at a track or at least roadway with little traffic. Handling could get "squirrelly" in a hurry. Tony Foale told some stories about professional race teams that discovered the hard way the negative consequences of making suspension changes without thorough analysis.

 

[khittner]

The OP, Hayden90, is the fellow who recently stumbled into ownership of a fairly virgin '78 R100RS Motorsport, and was seeking counsel (See the string dated 3/7/17, entitled: "Is This What I Think It Is?") on how to chop it into a cool cafe bike. I thought we had him talked down off of that ledge, but it seems that he's only slightly scaled back his misguided plans.

Hayden: You're beginning to appear unworthy of your motorcycle. Respect your elders' advice, or sell the bike to someone who will treat it as it was meant to be. Go find yourself a clapped out old Honda, Yamaha, or Triumph, and do what you will. And, no, you can't add a "master suite" or a "man cave" to a Frank Lloyd Wright house, if you somehow inherit one of those.

 

[hayden90]

I appreciate all the advise you guys have given and i now have a wealth of sources to look into but it sounds like it's just generally a bad idea. I think I'll leave it as it is and just be happy with clip-ons.

Mr khittner1, I will be posting the bike to the marketplace this weekend and if it doesn't sell for a profit of any kind by the end of summer I will be doing with it what I please. It is mine after all. But I do look forward to your reasonable offer to my posting and, once it's yours, you may do with it what you please. But if it doesn't sell, I'll post pictures when the project is complete and I hope I am not shamed from the forum for it. It may take years but if it doesn't sell I plan to create a "motorsport cafe racer". Same white with red/blue pinstripes paint scheme and red outline around the headlight on a Ducati style fairing with a more aggressive, sporty vibe. I totally understand if you don't see my vision but, I am a perfectionist and will do it in the most tastefull, respectful way and I think some members of the MOA will be impressed.

 

[khittner]

Hayden---I'll leave it to the real aficionados to pipe up here, but BMW actually did that to a very few Motorsports back in '78. It was the uber-rare R100SRS Motorsport. Same bike with the S-type bubble fairing. Google it.

Oh, wait---here's some good news: The BMWBPRC (BMW Busybody Peer Review Committee), meeting in a rare late night session, has indicated that it would conditionally approve removal of your bike's RS fairing and related accoutrements if there's a timely replacement made with a properly pinstriped S-fairing and the associated handlebars and hardware, new, or of the same vintage, and the original RS fairing, handlebar, and hardware are retained in reasonable condition for the benefit of future generations.

 

[pglaves]

He seems to have a very nice '78 Motorsport RS. Folks should be lining up to buy it from him. If I read the other thread correctly he got it at a reasonably low price. Making a bit of a profit for his trouble ought to be easy. Maybe somebody, even, has a decent /6 to trade him.

 

[swall]

Lowering the front end can really screw up the rake and trail relationship on an Airhead. Not good. Airheads already do not have a lot of trail--trail is essential for high speed stability. Even putting on a low profile front tire can upset this to the point where you can have a high speed wobble.

 

[hayden90]

It's listed in the marketplace now. Check it out and don't hesitate to make an offer. She's gotta go sooner rather than later so I'm flexible.

 

[112190]

Thank goodness the Motorsport is going to survive intact.

Paul's right. This young man needs a good /6 to play around with.

 

[khittner]

Hayden, it's more bike than my CFO will let me afford, and an RS, even as nice as that one, isn't a bike I find comfortable to ride. It certainly looks like a new owner would have no particular problem riding that bike from mid-Ohio to home. But, if it would help facilitate the sales transaction to a new owner who will keep that bike as-is, I'm willing to use my pick-up truck and loading ramp to get the bike from your place in Delaware, OH, to anywhere in Ohio, Michigan, Indiana, or Illinois, for the cost of gas from Delaware to wherever it needs to go. I've carried my quite nice '84 R100RT Last Edition a bunch of times in my truck's bed from mid-Michigan to Chicago, and I know how to strap a faired BMW down without damaging the bodywork or suspension in transit. If the new owner understandably wants to ride with me, that'd be fine, but isn't necessary from my standpoint. If the buyer wants to do it themselves, that's also perfectly understandable, or if they also want a bonded, insured carrier, that's not me---I'm just a middle-aged airhead owner willing to lend my equipment and experience to help get the bike, as it is, where it needs to go, with the same caution and prudence that I use with my own bike. Call it airhead mutual aid.

 

[cycleman2]

I appreciate all the advise you guys have given and i now have a wealth of sources to look into but it sounds like it's just generally a bad idea. I think I'll leave it as it is and just be happy with clip-ons.

Mr khittner1, I will be posting the bike to the marketplace this weekend and if it doesn't sell for a profit of any kind by the end of summer I will be doing with it what I please. It is mine after all. But I do look forward to your reasonable offer to my posting and, once it's yours, you may do with it what you please. But if it doesn't sell, I'll post pictures when the project is complete and I hope I am not shamed from the forum for it. It may take years but if it doesn't sell I plan to create a "motorsport cafe racer". Same white with red/blue pinstripes paint scheme and red outline around the headlight on a Ducati style fairing with a more aggressive, sporty vibe. I totally understand if you don't see my vision but, I am a perfectionist and will do it in the most tastefull, respectful way and I think some members of the MOA will be impressed.

It is your bike do with it what you want. I restored a non stock basket case R75/6 and made it into more of a café type bike, because the bike had no real value as a clean R75/6 which it was not. ( The frame and serial number were out of a R50/5, the engine out or a R75/6 - 75 vintage ) so it goes on from there.

In your search for the café look. One idea you might want to consider is to go to slightly longer shocks in the rear ( my current R1100s ) has two different length torque arms you can use that will raise the rear end of the bike up 1 ". The higher height was used for the racing bikes. ( More clearance for the cylinders & they put a bigger back tire on.) Then do something with the back fender & seat to make it more clean and give it a look like the current minimalist bike. Also with the front you could go with a linear fork spring and then play with the spacer length. The linear fork springs can be order in various different strengths so that will not affect the final front end handling. Most of the airheads where softly sprung and had a lot of initial front sag.

Then again if the bike is a bit of a rare one, sell it and by a basket case and put it back on the road. Good luck in your quest.