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Speedo "retro-mod" quesions

parsons

New member
I'm sorry that I don't fully understand how mechanical speedo's work and the math behind the ratios--figured someone smart on here might be able to nudge me in the right direction. From my reading it appears that each and every bike that BMW produced seems to have slightly different speedos or at least speedo ratios. I'm guessing this may align to the actual gearing ratios of the bikes themselves, and correspondingly how the mechanical cable interacts to inform the speedo. I am curious if that means BMW hard-coded gears into each speedo accordingly, or are they adjustable somehow?

I have an American R60/6, but I hate the look of the gauges (well I like the look of the actual gauges, but hate the design and plasticy look of the gauges and lights in the cluster). I'm doing a pseudo "retro-mod" look to the rest of the bike (all reversible for anyone gasping), having replaced much of the stuff on it that reminds me of the '70s bikes in lieu of earlier looking pieces/parts. The gauges are kind of my last front I'm considering tackling, and have my eye on a /5 Speedo/Tach combo, which I find very appealing visually.

1). I presume the existing speedo / tach cables would connect ok (physically) to the /5 combine gauge...but please correct me if that assumption itself is wrong?
2). I presume that the ratio of the /5 gauge I bought wouldn't necessarily "mate" with the ratio on my bike, and the speed and/or tach would be off, readings-wise?

I'm guessing that because many of the aftermarket speedos are GPS-driven, it is, in fact intended to get around this challenge of mating particularly non-standard ratios?

Smart brains appreciated and thanked in advance. Mine is taxed on this subject.
 
A little help

You are correct airhead speedometers are matched according to the gearing. The final drive is stamped with the gear ratio. The bottom of the speedometer has a number and letter combination. W=?, This number gives an idea as to what the internal gearing of the Speedometer is and can be matched with a chart to determine what W number speedometer mates with what final drive gear ratio.

Contacting someone like Terry Vria's, terryvrla@hotmail.com or Rick, overseasspeedometer@gmail.com might put you on to what it would take to match the /5 combo to your bike. I won't bet on it but I would assume the /5 speedometers have the same W=number system or something similar.

A repair shop may also be able to re gear a /5 speedometer to match the /6 final drive if in fact there needs to be a change. Not knowing how speedometers are calibrated or adjusted for accuracy it may also be possible to just adjust out any speed difference incurred if any because of the change.

As for the mechanical tachometer, again, mating the /5 tach to the /6 depends on what the gears are involved in the gear drive on the cam as well as internal to the tach. Cables are cables, There won't be a problem (I don't think) with cables.

Sorry, I am not much better help, I can say I have dealt with Both Rick and Terry and find them to be very good guys who do great work for a reasonable price. St.
 
Snowbum has a page on gear ratios that show who rear drive ratios match the speedometer numbers.

https://bmwmotorcycletech.info/ringgears.htm

Another consideration on replacing the stock speedo unit is the need for the generator bulb circuit. The Gen light in the speedometer unit is required in order to provide the necessary current for the alternator to self charge and begin producing current to charge the battery. Without it, the battery will discharge.
 
Good point

Kurt makes a very good point. The /6 instrument cluster uses a different array of indicator bulbs.

Oh wait, I just thought of something even more important, kick me if Im wrong but isn't the /5 speedometer and tachometer built into the headlight housing? If this is the case, your problem may be a lot more than just changing the speedometer and tachometer.

The BMW main wiring harness feeds into the /6 headlight shell, as well as that of the /5. I am not an owner of a /5 so I don't know much about the internal wiring of this system but I imagine it is different from the /6.

In the /6 which I am familiar with, there is a color coded board with the two fuses in the back of the headlight shell. This is the main distribution block or center of the Main wiring harness as well as the various sub harnesses for turn signals and such. I don't know how much of a hassle it would be to wire the /6 harnesses into what ever system is found inside the /5 headlight. Someone with more knowledge of /5 bikes can clear up if the /5 headlight shell has the same kind of distribution board or something completely different.

Regardless, of the internal distribution system of either /5 or /6, you might find it to be a challenge to get all of your wiring system changed from the stock /6 to the /5. Then again, it may not be so bad having never looked into a /5 headlight, I am in the dark, LOL.

Ok, in regard to the charging system bulb. Kurt is 100% correct, this bulb needs to be in the circuit or bypassed. I do think the /5 has a charge indicator light. If I recall, there is a charge light, oil pressure light, neutral light and turn signal light.

There are people far more experienced with conversion bikes than I and maybe I am over reacting, making a mountain out of a mole hill. It will be interesting to hear what you do and how you make out. Cheers, St.
 
News

So, I no sooner got done writing about the difference between /6 and /5 instrument/headlight systems and lo and behold, a fellow doing a rebuild on a /5 has a good picture of the inside of the /5 headlight shell.

The picture confirms the big difference in the wiring between the two bikes. The /5 is much different than the /6.

5 head light inside.jpg

So, not to dissuade you from making the change if you choose to do so. I am giving you a heads up the job may be more complex than you thought.

If someone who has retrofitted the /5 system onto the /6, reads this, I hope they write something to help. St.
 
Or you consider an example of implementations I've done on a couple /5 and /6 builds.

/5 headlight shell with a Speedhut digital speedo/tach and added a 3 position standard ignition key. Leaves plenty of room inside the shell for neat wiring. Also added an LED headlight bulb.
 

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Or you consider an example of implementations I've done on a couple /5 and /6 builds.

/5 headlight shell with a Speedhut digital speedo/tach and added a 3 position standard ignition key. Leaves plenty of room inside the shell for neat wiring. Also added an LED headlight bulb.

Very nice work.
 
Very nice

I figured someone who has done a restomod would be better help than I would. All I am good for is making parsons aware of what he might be getting into.

Greg, that is a beautiful job. My friend Glenn has done similar rewire jobs when restomoding /2 bikes. My brain just went blank, what is the term for swapping out the /2 engine for a /5 or newer? He has also done a scrambler bike. Like you, he does proper rewiring and high quality materials. As a shop owner, he doesn't want the customer to come back with problems.

LOL, one of the other threads in the airhead forum mentioned the changes in the 84 and newer bikes. One of the best things BMW did to make life easier is they moved the jumping snakes out of the headlight shell on under the gas tank. St.
 
Wow, thank you...

Team--

First off, I'm overwhelmed with how many of you responded so quickly. Outstanding forum for a newbee, so thanks so much for that to everyone. Also, the super helpful tone from everyone is genuinely very appreciated and all offered great info and thoughts. I'm going to take some time to read through all of the stuff in detail, follow the links thoroughly, etc.

I realize this whole endeavor was NOT going to be an easy thing (especially as I'm trying to be mindful of making everything reversible). I know that the /5 speedo/tach combo sits in the light bucket and had considered doing that as part of the project, but in looking at the cost of a chewed up /5 bucket and then looking at the inside of my own light bucket at the wiring, I've somewhat hesitant to mess with that route, even though I think it would be super cool. With the refurbed speedo and used /5 bucket I'd already be $1k in without having done anything. And to go through all that only to find the readings were going to be off by 10-20% definitely didn't make sense. Hence my post to see if the idea of the /5 speedo could even make sense functionally first (I will read more before I totally rule it out!).

As an alternative idea to the /5 light bucket, and/or a way to use my existing gauges, I have previously used a local industrial designer/builder to build a keg washer for our brewery, and I was blown away by his skills and the resulting machine. I am considering reaching out to him to discuss building me an improved "cluster" somewhat similar to a Triumph one that either bolts onto the tree, or have him integrate a new triple tree into the cluster itself. My idea would be to essentially either leverage a new Katdash as the brain, or perhaps even use my replaced original controller as the brain (or another used one), and with the right exposure on the back, the existing wiring harness could be used unmolested. Now, I'm sure I'll be hitting +$1K costs with this route as well, but once cadded up it could perhaps be duplicated and sold, as I'm sure there are other /6 owners who might not love the plasticy look of the current /6 cluster. Anyone seen that done previously? I'm a little surprised someone hasn't designed, milled, built and marketed what would essentially be a better /6 enclosure.

Anyway, I'm sure I will have more questions, but thanks again for all the responses.
 
Greg, that looks awesome.

Or you consider an example of implementations I've done on a couple /5 and /6 builds.

/5 headlight shell with a Speedhut digital speedo/tach and added a 3 position standard ignition key. Leaves plenty of room inside the shell for neat wiring. Also added an LED headlight bulb.


That looks amazing. Did you find any wiring downsides elsewhere over time? I have a local mechanic who himself rides a /6 (I think his is a /6?) that he has done a lot of work to, and he warned me that hacking up the wiring may not be in my best interest from a reliability perspective (hence part of my interest in limiting my changes to using the current harness and not messing with wiring "upstream").

This is my first bike in 25 years and consequently I don't want to get too over my head on this first one...serious amateur here.!
 
Mods

Hey Parsons,
I can see you have your head on right and are aware of what it may take to get what you want.

Rewiring a bike can be a nightmare if someone doesn't know what they are doing, has no electrical skills, (for example can't read a schematic), or is a sloppy person, (does hack work or uses poor quality parts).

I have seen some rewired bikes and they are terrific a sight to behold. I have also seen and worked on bikes where the owner had done such a crummy job everything had to be redone. If you have the skills and patience needed to do the job right, the /6 wiring is not all that complex. Far less complex than a bike with computer controls and fuel injections and all the new stuff on newer bikes.

Perhaps, you can private message one of the other people who posted in this thread about their experience and start a more meaningful dialogue.

Unlike 20 years ago, there is now a growing number of people and shops building custom bikes. The internet makes it so much easier to find them and contact them regarding parts, and techniques. You are a smart man for taking advantage of this.

Good luck, with what ever way you chose to go to get what you want. Drop some pictures of your progress if can. St.
 
thanks again...please keep posting ideas if you have them

In full disclosure, I'm first going to lower the headlight on the forks (with aftermarket headlight brackets) and mod up a new cluster mounting bracket to simply lower the existing gauge pod as well, hopefully more in line with the bars. If cosmetically that gets me past my design anxiety, I am likely to "stop" there on this bike (for now!). My sidecar handlebars are (hopefully) en route and the whole front end will hopefully have "bolt on" mods that will get it closer to my cosmetic goals for not a lot more money (relatively speaking of course!).

BTW, I am in love with this bike. It's super fun to ride, seems super reliable (especially for a bike that is almost 50 years old), and is a pleasure to look at while it's just sitting in the garage. It's a luxury to be able to sit and think about how I can make it look even cooler and not be thinking about what $ I need to spend to keep it starting and running. A nice place to be--thank you BMW and this forum! That privilege is definitely not lost on me.
 
In the Airhead era, the only gearing difference between Airhead models in a given production year is with final drive ratios. All transmissions are the same.

(Yes there was a "race" transmission but you're as likely to find one of those as you might find a bike with factory installed 336 cam--it's essentially irrelevant.)

So, the speedos are geared to match the installed rear gears. A 1000 with more power will have a higher ratio than a 500 with hardly any. Not rocket science.
 
that makes sense...thx

I see the W value marked on my speedo. Assume those align to the final drive ratios their intended to match.
 
I have seen some rewired bikes and they are terrific a sight to behold. I have also seen and worked on bikes where the owner had done such a crummy job everything had to be redone.

I have a /7-based scrambler in the shop now - finally about to leave - that was halfway switched over to M-gadget. What a wiring mess that was. I pulled out all kinds of cut-off wires, standardized things, re-wrapped, etc. I ended up using the headlight circuit board a lot more than the original builder did, just so that the bike could be repaired in the future without cutting wires.

In retrospect I should have built an all-new wiring harness, but that wasn't in the original work list. "Re-wrap those exposed wires" turned into days of work because there was so much wiring going through the handlebar.

I realize this is no longer a consideration for the O.P., but the connection board in the headlight bucket is central to how the wiring is structured in the /6 through '84 twinshocks (not R65), and you will need to recreate that functionality somehow if you want to use the switches and so forth as they are. The OEM wires are fat... connecting them becomes bulky. You can use much thinner wires with LED lights, but if you go too far they become fragile, like the M-gadget stuff can be. The wires from their bar-end turn signals and instrument are like thread.
 
A good caution

Anton, I have seen bikes hacked up like you write about and unfortunately more than I should. I don't own a shop but hang out at one and he gets a lot of bikes coming in with the plea "please make this work". A solid quarter of the time the reason for a bike not working is because of a hack Job by either a previous owner, or an owner who didn't know what he was doing. LOL, I fall into the second category myself sometimes.

There are people out there who can rewire properly. My guy has stocked up on proper gauge and color wire to match BMW. He uses properly neatly soldered and shrink wrapped connections with if needed quality plugs and connectors. This is what someone who is going to build a cafe or scrambler should always do.

Just out of curiosity, you just did a bike with an M unit, my memory prickles with a thought of a fellow writing into the Vintage BMW club forum trying hard to get a bike's electrical system working properly. After a lot of back and forth a bunch of us kind of told him we hadn't a clue what his problem was, and he would have to deal with the company making the M unit. There has never been a followup as if he solved his problems. To be honest, his problem was not knowing what he was doing ie, no concept of a circuit, an inability to read a schematic and perhaps a misunderstanding of what he was trying to accomplish.

To be honest, it is a pain in the butt just replacing the stock wiring harnesses with stock replacements talk about jumping snakes in a small basket but, I can't fathom trying to wire in alien technology! St.
 
I enjoy electrical work but I still come away from every major job with immediate self-feedback about how I would do it differently if I had it to do over again. This particular bike came to me with a lot of the main harness wires cut off but not removed back to the circuit board and existing new wiring not colored properly. The wires for the neutral, oil and brake switches are sort of on their own and were still intact, so I kept those but ran a lo of smaller wires up to the bucket. The M-unit was under the tank but the instrument was wired to the bucket so the indicator lights and so forth needed to get to the bucket. Bar-end signals and three pushbuttons on each side all ran through the handlebar and down through the stem. If there had been a good way to share a ground I could have eliminated three wires but disassembling that system in the future (like for handlebar replacement) could have been a nightmare. I should have ditched the through-the-stem part and ... should have, should have.

Most of the harness (everything on the input side to the M-unit and the LED outputs) could have been re-done with .35mm^2 wire with small connectors. I have plenty of terminals including some with very small pins for the K5x cop bikes but the housings are still relatively large.

Again, rewiring was not in the scope. I just had to deal with the stuff I ran across, though. Forked terminals jammed into other connections, bad crimps, etc. The bike itself is really pretty; it's just that the builders need a technical guy on staff. The bike came here for a brake upgrade and some other mechanical and technical improvements, but not electrical trouble.
 
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