1989 k100rs

[gietl]

Forum looks sleepy, figured I would post. I have a 1989 K100RS SE, SE for special edition. Has the white and blue BMW colors. I've owned it abut 3 years. Looking at getting a F800ST now hence the reason I am here.

Here is a pic of it:

[Darren J]

Always liked the older K's. How many miles on it?

[gietl]

IT has about 45,500 miles. When I got it I believe it was around 38,000. Not a lot of riding over the last three years. I was sidelined numerous times for medical reasons.

Amazingly, I get a lot of comments on it, good and bad. I have had a number of people in cars pull up to me at stop lights to ask about it. Of course I always get comments about the fuel pump whine.

Drawbacks to these old bikes, they are heavy and they handle that way. Not very well balanced at low speeds, but the confidence is there as it ratchets up.

Overall good bikes that seem to hold their value pretty well even after 20 years. Of course a lot has changed in that time.

[Dave May]

Nice K. I recently bought a 1988 K100rs. I've had several K75's so thought I'd try the 100. Quite a bit more power but seems very heavy. The F800 is definitely a light weight in comparison to both Ks.

[Teep]

test rode my friends 89 K100rs and yeah, very heavy indeed... would not even imagine trying to do some of the stuff I do w/the F800 which slips in/out of the city for me so nicely...

I let the friend ride my S and he liked it, said it had a similar riding position but a bit more wind on the chest ;)

-tp

[pedantic_pete]

My first BMW was a K100RS. I subsequently had a K75S (the smoothest engine I've ever had - but gutless too!). These are pretty big and heavy bikes. The only spills I had on them were very low speed drops when manouevring them by hand. (Oh and the time a couple of weeks after buying the K100 when I rode off with the read wheel still chained!)

I enjoyed those bikes while I had them, but really performance-wise they are pretty old hat. The F800 makes more power than the K100 did (I think) but with considerably less flab. The seat height is quite high on them as well. (Perhaps not as high as my GS, but combined with the weight, that led to the ease of dropping at low speed.) After the K75 I progressed on to an R100RS, which had much better performance, then had an R1150RT (more power but also more weight) before buying a new F800GS.

I had one or two major problems with the shaftie bikes: final drive shaft broke on the K100RS and gearbox shaft broke on the R1100RS (was off the road for weeks while the dealer tried to track a replacement down - and ended up £900 poorer as a result). The gearboxes on all the old BMW shafties were notoriously agricultural. The F800 gearbox is much smoother.

I couldn't see myself going back to the old K series bikes. If money were no object (it is!) then I'd love one of the newer generations of K-bikes like the K1200S (or more likely the GT) or the K1300 series (not ridden the latter). But the F800 is really economical to ride as long as you don't run into serious mechanical problems which a few riders on this forum seem to have.

[pedantic_pete]

I meant an R1100RS btw, not the old R100

[Dave May]

The K100rs does put out a few more BHP than the F800s but is weighs 100lbs more. The Ks do exactly what they're made for - sitting on the motorway doing big miles, with a few twisty bits at either end. I didn't realise how underpowered the K75s was until I bought the K100rs, but I still love it.

[pedantic_pete]

Just checked on the power outputs of these bikes:

K75S ............... 70 bhp
K100RS ............ listed variously as 90 or 100 bhp, depending on where you look (year changes?)
F800 ............... 85 bhp

Hence I stand corrected on the F800 being more powerful than the K100. Of course, these would have been as new. Given wear on the piston rings and bores, valves and seats etc. the compression ratio of the older bikes would have gone down somewhat, affecting power output. But you're right Dave, the F800 isn't as powerful.

The kerb weight of the K100RS is quoted as 277 kg. The F800 series are as follows:
S ......... 182 kg
ST ....... 187 kg
GS ....... 185 kg
R ......... 177 kg (plus 2 bhp up on other F800 models)

Hence we're talking in the region of only 2/3 the weight of the K100RS, but producing at worst 85% of the power.

[Teep]

torque numbers please...

-tp

found some:
1986 K75 68 Nm @ 6750 rpm
1983 K100RS 86 Nm 63 ft lb @ 6000 rpm
2009 F800S 86 Nm @ 5,800 rpm


btw: I think after 85 they detuned the K100's which may explain the differing bhp's you found.

[pedantic_pete]

K75S ............... 67 Nm @ 6750 rpm
K100RS ............ 86 Nm @ 6000 rpm
F800S .............. 86 Nm @ 5800 rpm
F800ST ............ 86 Nm @ 5800 rpm
F800GS ............ 83 Nm @ 5750 rpm
F800 R ............. 86 Nm @ 6000 rpm

(Figures mainly derived from http://www.bikez.com/ )

So amazingly, the F800 series bikes are up there on torque with the larger capacity K100RS.

[Dave May]

Guys, you getting far too technical for me!!! The different outputs for the K100rs are probably the difference between the 8 valve or 16 valve

[pedantic_pete]

Dave, just by way of explanation, the power figures tell you how much performance you can get if you wring the neck out of your bike at high revs. Effectively, power is torque x engine speed. Situations where you might want to use the big power numbers are for instance, on a track day. In the real world, however, I agree with Teep, it's torque you want, and preferably the lower down the rev range the better. That means that on the road you are more likely to be able to just open the throttle to accelerate away, without having to drop down too many gears.

[Dave May]

I very rarely get my rev counter anywhere near the red. Both the Ks will pull away from under 2k revs, not quickly but smoothly. The F800 will pull from 2.5k. I guess that's the torque.

[pedantic_pete]

Yes and no. Torque also depends on engine revs, depending upon the tuning of the engine. Some engines will produce a very flat torque curve (relationship of torque to revs), so you have quite a lot of torque at low revs (like the very smooth old K series bikes) which only increases slightly as you increase revs, whereas others are tuned to give more performance higher up the rev range (typical for racing bikes), so may not produce any usable torque below even 4-5000 revs. The R-series BMW flat twins are fairly torquey, but don't produce much to speak of below about 3000 revs.

I've been trying to find a torque and power curve for the F800 to illustrate this, but haven't found one on-line. Here's one I found for the K100RS. Not very clear I'm afraid, but the line which peaks somewhere in the middle of the display is the torque and the one that peaks higher is the power curve. Sadly neither shows the response below 3000 revs.

[Dave May]

Pete, this is information overload!!! I know I'm being lazy but as long as the bike works the way I like it to I'm happy. The Ks are definitely the bike to use in heavy traffic, I can just stick it in 5th and leave it there. The F800 takes a little more work but is much more rewarding once the roads open up.

[gietl]

The HP differences in the K100's should be between the 8v and 16v motors. The K is smooth as glass whereas the F800 is a torque monster.

The K could really use a 6th gear for my commute, but it revs fairly high. Just lose a bit of efficiency when you get 70 + MPH.

I have leaned the K over pretty far, you'd be surprised, but it is a little freaky in twisties throwing it side to side. One thing you will always get with a K, a totally solid feel. The bike will never feel "light" and I think think that helps with rider confidence.

Other than a little clutch hand fatigue on the F800 my heavy traffic experiences haven't really been different between it and the K.

[pedantic_pete]

Sorry Dave. But as you say, it's how the bike feels that matters. The technical stuff comes in useful if you want to compare different bikes before going for a test ride. Also, it's not often you get to ride lots of different bikes back-to-back to compare them.

[pedantic_pete]

Originally Posted by gietl

The HP differences in the K100's should be between the 8v and 16v motors. The K is smooth as glass whereas the F800 is a torque monster.

The K could really use a 6th gear for my commute, but it revs fairly high. Just lose a bit of efficiency when you get 70 + MPH.

I have leaned the K over pretty far, you'd be surprised, but it is a little freaky in twisties throwing it side to side. One thing you will always get with a K, a totally solid feel. The bike will never feel "light" and I think think that helps with rider confidence.

Other than a little clutch hand fatigue on the F800 my heavy traffic experiences haven't really been different between it and the K.

I agree. The K has remarkably narrow handlebars, so isn't easy to flick. Counter-steering is essential. And it's very stable at speed. The F800GS has much wider bars. I can also attest to how far you can lean it over, having first test-ridden one on a track day.

[gietl]

Tomorrow I should be saying goodbye to this bike It is bittersweet.

[windy]

To bad. I owned a '85 K100 EML sidecar as well as a '85 K100RS,I rode the RS so seldomly that I sold it. It felt and handeld heavy,not so with the EML. I owned it from '85 to '97 and logged over 106,000 miles on it. The last time I saw it ,at the MOA rally in Johnson City it had logged almost 170,000 miles. For what these old K's are selling for(not much) I'd keep it and get the f800. I have a '04 K1200GT with over 50,000 miles and have no plans of selling,but it handles alot better than the old K. Also known as the "Flying Brick" or "Wisper Jet".

[gietl]

It is too bad. I was trying to sell it earlier this year and a prospective buyer dropped it causing extensive cosmetic damage. After estimates and trying for a resolution I had to make a claim against my own policy.

The bike has gone to live in Arkansas with another BMW enthusiast who had been looking high and low for an SE like mine. He will fix it up and make it his own. It's tough though. Was a great bike, but it was hard enough playing tetris trying to park 2 bikes and two cars in the garage.