1980 BMW R100T Fork Spring Preload Questions

[nevadaslim]

I purchased a used 1980 R100T off eBay. My first Airhead, so I'm not all that familiar with them or their idiosyncrasies.

Went through and rebuilt the forks. I purchased all new internal parts including a new set of Wirth springs. Can't find the
receipt but I believe them to be Model # 91079. The springs didn't come with any preload spacers, but after I finally
installed the springs I realized I need some kind of preload! Way to much initial play befor the spring actually engage.

I did a search on this site for "R100 fork spring preload spacers" and came up with nothing.

So my questions are:
* Does anyone manufacture metal preload spacers for Airheads? I've read PVC pipe is not the way to go.
* If no one makes-them, any suggestions what to use, and how long they should be?
* I understand the amount(length) is an arbitrary question, but a ballpark figure would be nice to start with.

Thanks for any help...

 

[20774]

The search feature inside vBulletin kinda bites...I rarely use it. Try going to google and entering this in the search box "site:http://bmwmoa.org R100 fork spring preload spacers". I got a few hits that might prove useful.

Not sure where you heard that PVC is not good for a spacer...I hear that all the time from Tom Cutter, etc. For a ball park figure, I seem to remember you want the bike to sag to about 1/3 of the total travel when you take the bike off the centerstand and sit on it. Off the top of my head, I'd say that's something like 2.5 to 3 inches.

Snowbum talks about fork sag here - http://bmwmotorcycletech.info/frontforks.htm - looks like he likes 2 inches.

 

[ccolwell]

PVC works well. Sag does not need to be precise on these unless you want to push them hard. Start by measuring the length of the original spring and spacer and then make a spacer such that it plus the new spring equal that length. If the sag is in the 1.5-2.5 inch range ride and see if it works for you.

 

[PAS]

My Haynes and Clymers list the spring free length as being 21.3779" to 21.850" I would make spacers to match these numbers as a starting point. I have used PVC spacers for many years and miles with no problems.

 

[nevadaslim]

The search feature inside vBulletin kinda bites...I rarely use it. Try going to google and entering this in the search box "site:http://bmwmoa.org R100 fork spring preload spacers". I got a few hits that might prove useful.

Not sure where you heard that PVC is not good for a spacer...I hear that all the time from Tom Cutter, etc. For a ball park figure, I seem to remember you want the bike to sag to about 1/3 of the total travel when you take the bike off the centerstand and sit on it. Off the top of my head, I'd say that's something like 2.5 to 3 inches.

Snowbum talks about fork sag here - http://bmwmotorcycletech.info/frontforks.htm - looks like he likes 2 inches.

Thanks for the replies!

Actually it was on Duane Ausherman's webpage he mentions the PVC spacers, http://w6rec.com/duane/bmw/fork_travel.htm.

"BMW used spacers made of aluminum, not PVC plastic. The plastic is reported to get brittle and disintegrate over some years. The risk is yours.

While most riders can lose 1/2" of travel and probably not notice, just about none of us can lose 2" and not notice. A spring that needs to be compressed with the use of spacers to get the desired tension is improperly designed.

A common spring replacement is made by a company called Progressive. BMW forks with Progressive springs can work for some riders. I suspect that the springs are of good quality, but they are too short. They include a spacer to make up for the short length. That just isn't a good idea. BMW finally did away with the spacer for the same reason, it can waste fork travel. In general, springs from Progressive weren't satisfactory for most riders as they were a bit hard.

Many would swap out the older sacked out springs and use the ones from Progressive. They would fail to do the job properly and discover that the forks didn't work properly. The springs got the blame, not the job of installing them. It seems simple, but is far from it.

BMW offers a heavy duty fork spring. It is actually about 3/4" shorter than the weaker, but original spring. In time, a spring becomes compressed or as we say, it is "sacked out". A sacked out spring will be much shorter than when new. Check the BMW specification for proper length."

Bottom-line, I bought a pair of brand-new German Wirth springs, made years after the last Airhead rolled-off the assembly line. One would think that by now they would have figured out the correct length/tension to manufacture Airhead springs and the discussion would be a mute point. But no, they haven't, and apparently neither has The Progressive Spring co.

So from what you've said, and what Duane has to say, I may just compromise and start with 1", and see what that gets me. Still need to find a good material.

Duane mentions "check the BMW specification for proper length". That sounds like a good place to start, does anyone know where I could find the correct fork spring length for a 1980 R100T?

Also, over the last couple of years that I've been slowly restoring this bike, I kinda remember seeing somewhere, some short preload springs that apparently went in on top of the main springs, ring-any-bells?

Thanks again...

 

[20774]

Also, over the last couple of years that I've been slowly restoring this bike, I kinda remember seeing somewhere, some short preload springs that apparently went in on top of the main springs, ring-any-bells?

I don't remember springs in the top, but rather springs in the bottom. Anti-bottoming springs were sold (maybe still are) and there are emulators (Race-Tech?) which may serve the same function.

 

[cycleman2]

Front end sag for most motorcycles is going to be in the area of 1 - 1.5 " and is a percentage of fork travel, say 20-25 %. Depends on how you like your bike to handle & ride. The initial sag gets the spring into its designed operating range. To measure your sag use a zip tie and place it on the chrome portion of the fork, tight against the fork lower portion. Weight off the front end. Get on the bike and sit with both wheels on the ground. The zip tie will move up the chrome portion of the fork and stop when the fork spring can't travel anymore. Put the bike back on its center stand or take the weight off the front end. Measure the distance between the bottom of the non travel portion of the fork and the zip tie. This will give you your initial sag. Most of the early BMW's where set up with very soft front springs, which you will see when you measure the sag on your bike.

There is a big difference between a progressive fork spring and a linear fork spring. Progressive springs are just that, they have an initial soft portion ( wider coils ) that collapses until the closer wound portion of the spring takes the load. With progressive springs you may or may not need a spacer. Progressive springs tend to get very hard nearing the end of their travel.

A linear fork spring on the other hand is a spring that has equal spaced coils throughout it's length. For example, if it takes 50 lbs to collapse it 1 " then the next 50 lbs will collapse it another 1" and so on until it uses up all its travel. So this spring doesn't have a soft portion and you adjust the preload and sag with spacers. Manufacturers of these springs include the spacer material and directions on how to calculate the length of spacer. The spacer material is a PVC type but not the thin wall stuff you buy at the local hardware store. The strength of the linear spring is calculated by the bikes weight and your weight, including a tank bag if you use one of them. You certainly could use aluminium spacer, but there is really no need as the PVC type of material in the spacer is very thick and sits between 2 washers so it has no direct contact with the spring ends.

For the best handling the linear spring is the way to go, and it allows you to tune the spring rate for your weight etc. Progressive on the other hand work for a large group of riders but are a compromise as you have to live with the spring rate the manufacture calculated for your bike.

I've used linear springs in my bikes and have even taken out the progressive spring and replaced it with a linear spring in my GL1500 Goldwing . That is a big heavy bike and the handling improved with the linear spring. Too much initial sag with the progressive spring. I also changed the fork springs to linear in my Vstrom. Much less dive under braking.

So the choice is yours. But check out linear fork springs you may like them

 

[nevadaslim]

Front end sag for most motorcycles is going to be in the area of 1 - 1.5 " and is a percentage of fork travel, say 20-25 %. Depends on how you like your bike to handle & ride. The initial sag gets the spring into its designed operating range. To measure your sag use a zip tie and place it on the chrome portion of the fork, tight against the fork lower portion. Weight off the front end. Get on the bike and sit with both wheels on the ground. The zip tie will move up the chrome portion of the fork and stop when the fork spring can't travel anymore. Put the bike back on its center stand or take the weight off the front end. Measure the distance between the bottom of the non travel portion of the fork and the zip tie. This will give you your initial sag. Most of the early BMW's where set up with very soft front springs, which you will see when you measure the sag on your bike.

There is a big difference between a progressive fork spring and a linear fork spring. Progressive springs are just that, they have an initial soft portion ( wider coils ) that collapses until the closer wound portion of the spring takes the load. With progressive springs you may or may not need a spacer. Progressive springs tend to get very hard nearing the end of their travel.

A linear fork spring on the other hand is a spring that has equal spaced coils throughout it's length. For example, if it takes 50 lbs to collapse it 1 " then the next 50 lbs will collapse it another 1" and so on until it uses up all its travel. So this spring doesn't have a soft portion and you adjust the preload and sag with spacers. Manufacturers of these springs include the spacer material and directions on how to calculate the length of spacer. The spacer material is a PVC type but not the thin wall stuff you buy at the local hardware store. The strength of the linear spring is calculated by the bikes weight and your weight, including a tank bag if you use one of them. You certainly could use aluminium spacer, but there is really no need as the PVC type of material in the spacer is very thick and sits between 2 washers so it has no direct contact with the spring ends.

For the best handling the linear spring is the way to go, and it allows you to tune the spring rate for your weight etc. Progressive on the other hand work for a large group of riders but are a compromise as you have to live with the spring rate the manufacture calculated for your bike.

I've used linear springs in my bikes and have even taken out the progressive spring and replaced it with a linear spring in my GL1500 Goldwing . That is a big heavy bike and the handling improved with the linear spring. Too much initial sag with the progressive spring. I also changed the fork springs to linear in my Vstrom. Much less dive under braking.

So the choice is yours. But check out linear fork springs you may like them

Thanks for the comprehensive reply, it was very informative.

You may have touched on something w/o knowing. To my best knowledge I've never ridden on a bike with progressive springs. And perhaps that in it's self is the problem. They just seem way to soft initially, which maybe perfect for the highway cruiser-type, but I'm more into tight, responsive handling. I'm not knocking the "cruiser-types", just not my style.

That said I may try 1" of preload, and if that don't help, I'll try switching back to linear springs. I like the idea of them being more predicable.

Now my only problem is finding linear springs. It seems progressive is the new norm. Perhaps a new set of BMW OEM springs would work? When I checked MAXBMW they sell one pair for my bike, they're described as:
* 31 42 1 232 017 COMPRESSION SPRING REINFORCED (to 09/80) $45.99 The price is cheap, it's the swap-out time that pains me. It's still 100° in my garage here in Vegas.

Having never ridden on a new set of OEM BMW springs, these might be perfect. Any comments? Any suggestions on other sources for linear springs?

 

[nevadaslim]

I don't remember springs in the top, but rather springs in the bottom. Anti-bottoming springs were sold (maybe still are) and there are emulators (Race-Tech?) which may serve the same function.

Ahh, perhaps you're right, they went in the bottom! Only seen them once for sale, and never again.

 

[PAS]

Thanks for the comprehensive reply, it was very informative.

You may have touched on something w/o knowing. To my best knowledge I've never ridden on a bike with progressive springs. And perhaps that in it's self is the problem. They just seem way to soft initially, which maybe perfect for the highway cruiser-type, but I'm more into tight, responsive handling. I'm not knocking the "cruiser-types", just not my style.

That said I may try 1" of preload, and if that don't help, I'll try switching back to linear springs. I like the idea of them being more predicable.

Now my only problem is finding linear springs. It seems progressive is the new norm. Perhaps a new set of BMW OEM springs would work? When I checked MAXBMW they sell one pair for my bike, they're described as:
* 31 42 1 232 017 COMPRESSION SPRING REINFORCED (to 09/80) $45.99 The price is cheap, it's the swap-out time that pains me. It's still 100° in my garage here in Vegas.

Having never ridden on a new set of OEM BMW springs, these might be perfect. Any comments? Any suggestions on other sources for linear springs?

Yes they are available BUT! The price appears to me to be $45.99 EACH!

 

[nevadaslim]

Yes they are available BUT! The price appears to me to be $45.99 EACH!

Yes, that's $92, small price to pay if it solves my problem and I can move on to my next problem. You can't imagine how much time I've wasted researching this problem.

Thanks for the reply...

 

[ccolwell]

The Progressive spring company will be surprised to find that their springs didn't work for 'most' riders; they seem to have sold a ton of them. My R75 had them; they worked well on the road and at Watkins Glen in one of Reg Pridmore's Class schools. I think they are a good option for someone who wants to ride at less than a fast sport pace.

That said, I do agree that progressive springs are not good for a sport bike. My Speed Triple had them and the transition from soft to hard in strenuous braking before a corner was not confidence inspiring. A switch to straight wound springs was a vast improvement. I put RaceTech straight wound springs in my R90S (along with Gold Valve emulators) but I was looking for a sporty ride. I got it and was very happy. It's worth thinking a bit about how you will actually ride the bike.

 

[cycleman2]

If you are looking for linear springs, just query them on Google. Racetech & Sonic come to mind.

Not knocking Progressive Springs, just depends on what you want in the handling department. As with most things bike related, its your bike, do what you wish.

 

[chasmrider]

I would call Racetech, http://www.racetech.com/, that's what I did for my PD. I replaced the progressive springs, and added 2 gold valves. the difference was amazing.

 

[nevadaslim]

I would call Racetech, http://www.racetech.com/, that's what I did for my PD. I replaced the progressive springs, and added 2 gold valves. the difference was amazing.

Yeah, I did some searches and also came up with Racetech, and that was about it, other than replacing my springs with brand new stock BMW springs(COMPRESSION SPRINGS REINFORCED), whatever that means.

Racetech's site/webpage was confusing as heck. All kinds of options, including drilling holes, and sending your forks in for machining. After reading for 15 min. my eyes were rolling in the back of my head.

I quess my riding style is somewhere between the average highway cruiser, and the full-on race geek. I just want tight, predictable handling, that I can p-u-s-h with confidence every once and a while. After-all, it's a 35 y.o. motorcycle with only 64HP, no need to go crazy on a race suspension.

That's why I'm wondering if anyone has tried a new set of OEM BMW linear Airhead springs? The term they use is, "COMPRESSION SPRINGS REINFORCED". Sounds like they may be improved.

 

[cycleman2]

I would doubt if they are linear. Airheads from my experience with my R75/6 had a lot of sag.

 

[PAS]

Yeah, I did some searches and also came up with Racetech, and that was about it, other than replacing my springs with brand new stock BMW springs(COMPRESSION SPRINGS REINFORCED), whatever that means.

Racetech's site/webpage was confusing as heck. All kinds of options, including drilling holes, and sending your forks in for machining. After reading for 15 min. my eyes were rolling in the back of my head.

I quess my riding style is somewhere between the average highway cruiser, and the full-on race geek. I just want tight, predictable handling, that I can p-u-s-h with confidence every once and a while. After-all, it's a 35 y.o. motorcycle with only 64HP, no need to go crazy on a race suspension.

That's why I'm wondering if anyone has tried a new set of OEM BMW linear Airhead springs? The term they use is, "COMPRESSION SPRINGS REINFORCED". Sounds like they may be improved.

I thought of going the Racetech route a few years back for my 81 RT but found that it was a lot of hit or miss approaches and some that have done so on my type of forks were not at all happy.

 

[PGlaves]

Insert spring in tube. Measure from top of spring to top of tube. Subtract the distance from the bottom of the plug to the top of the tube. That is the shortfall in the height of the spring.

Cut a spacer that shortfall distance plus 3/4 inch. PVC is OK. Insert springs. Insert spacers.

Fill with the specified amount of 7.5wt or 10wt fork oil. Then add 20cc additional fork oil in each fork.

Ride happy.

 

[jagarra]

On my old 74 R90 it had a sagging problem. I bought the BMW extra heavy duty springs that are listed on the OEM fiche which seemed to make it ride a bit higher. I use 7.5 wt oil, made the mistake of using too high a viscosity oil (15 wt) and the front end just didn't work and wouldn't rebound. As far as spacers, using PVC is a quick and inexpensive way to determine what length spacer you need. Be sure to put a large fender washer between the spring and spacer. If you want to follow Duane's advise then you could cut some from a metal tube later.

 

[happy wanderer]

Insert spring in tube. Measure from top of spring to top of tube. Subtract the distance from the bottom of the plug to the top of the tube. That is the shortfall in the height of the spring.

Cut a spacer that shortfall distance plus 3/4 inch. PVC is OK. Insert springs. Insert spacers.

Fill with the specified amount of 7.5wt or 10wt fork oil. Then add 20cc additional fork oil in each fork.

Ride happy.

Just curious why the additional 20cc?