I am building a BMW K 100 with an old  Hedingham Sports chair. (Pics to follow shortly)
I finally got all the plastic bits back from the painters (apart from a couple of vents in the fairing…Grrrr……..) And the bike is all back together apart from a few little bits of plastic which will take 20 minutes to fit.

I think I’m going to need a stronger rear shock because it sags a little (like me). Some people have suggested using a K1100 shock because it’s a bit longer. Can anyone confirm that is the way to go?
I have 15 inch Wasp wheels and subframe and LL forks because I bought the whole shooting match.

I’m gradually connecting everything and at least now it’s on three wheels and upright. I know I will have to adjust, adjust, adjust, adjust, because every time you change one angle of the dangle, something else moves.

I am okay with regard lean out and lead and toe out (or is it toe in? LOL) but I do have a rather simplistic question.

The whole thing and in particular the chair frame seems very low to the ground. I have about 5 ½ inches ground clearance between the steel cross straps which the Hedingham chair body rests on and the ground. All the proportions look okay although I haven’t done the final adjustments yet.

I’m sure it will aid the handling (LOL) but it just seems very low.

What ground clearance should I be looking for?

Suggestions please.
Kind regards

James

In the past I have fitted a long Paralever (100-16v) rear shock to give the xtra height.  It worked OK.  Currently I have a Koni(not an iKon) rear shock with screw adjustable preload, with that I can keep screwing the preload up till I'm happy. It's not saggy anymore and I'm finally happy with it.

I guess the right answer is to get a heavier spring to begin with.

Re the ground clearance, mine is running around 7.5" at its lowest point. I think I'd survive at 5.75 most of the time though.

Al

Hello!
Assuming you have a K100 2V Monolever you should be carefull using a shock with the wrong hight, this will change the angle and that isn't good for the drive shaft!
eBay will offer a good choice, the best price and good quality is YSS.
More expensive and good is ikon, wilberts etc.

YSS for K100 2V Monolever
http://www.ebay.co.uk/itm/FEDERBEIN-MONO-YSS-BMW-K-100RS-ABS-100-K589-NEU-/331654282004?hash=item4d3822bb14:g:AKsAAOSwyvBV9fMQ

For your other question I've got no answer :-)

Cheers

Espresso wrote:Hello!
Assuming you have a K100 2V Monolever you should be carefull using a shock with the wrong hight, this will change the angle and that isn't good for the drive shaft!
eBay will offer a good choice, the best price and good quality is YSS.
More expensive and good is ikon, wilberts etc.

YSS for K100 2V Monolever
http://www.ebay.co.uk/itm/FEDERBEIN-MONO-YSS-BMW-K-100RS-ABS-100-K589-NEU-/331654282004?hash=item4d3822bb14:g:AKsAAOSwyvBV9fMQ

For your other question I've got no answer :-)

Cheers

By extra height I mean that with the extra weight added by the sidecar is made up for by the longer shock absorber.  It still runs at the about the same height as a stock length shock fitted on a solo bike.

The YSS would also be a good answer, it has continuous threaded preload adjustment similar to the Koni I am using.

Al

I was also working on the premise that a longer shock would sag more and in effect have more preload before levelling out.
What I don't want to do is keep spending 150 quid a time, only then to have to try something else. That's why I was asking about experience.
The angle of the driveshaft had occurred to me but unless it is running at an obscene angle, I am prepared to risk that in the short term at least.

James, I go to the other extreme as I have a Spax rear damper that I have shortened, it's 13¼" between centres.

With my shorter than standard front dampers on my Wasp forks, I have just about 5" clearance between the sump of the engine and the ground. (I would imagine that the terrain that Al uses would probably need a bit more clearance.) 

That's my set-up that suits me and has done for years. I don't like the rear suspension to move very much, but I sometimes use my spare shortened Spax with a standard RS spring and a lot of pre-load which is softer but makes the handling a bit jellyish. 

I don't know the spring rate of my rear spring, but the wire diameter is 11mm; for comparison, the K75 spring is 9mm, KRS 9.86mm and I have an extra strong spring at 11.8 mm.

Paul.

sidecar paul wrote:James, I go to the other extreme as I have a Spax rear damper that I have shortened, it's 13¼" between centres.

With my shorter than standard front dampers on my Wasp forks, I have just about 5" clearance between the sump of the engine and the ground. (I would imagine that the terrain that Al uses would probably need a bit more clearance.) 

That's my set-up that suits me and has done for years. I don't like the rear suspension to move very much, but I sometimes use my spare shortened Spax with a standard RS spring and a lot of pre-load which is softer but makes the handling a bit jellyish. 

I don't know the spring rate of my rear spring, but the wire diameter is 11mm; for comparison, the K75 spring is 9mm, KRS 9.86mm and I have an extra strong spring at 11.8 mm.

Paul.

Thanks Paul.
That is really useful. I have limited experience of outfits but on my solos I prefer firm at the rear also. (My GF has a very firm rear! LOL)
I never even thought of measuring the wire diameter which makes good sense.
I will measure the clearance under the sump and the subframe at the rear because it does seem lower at the rear than the front. If I were to put a spirit level aligned with the lines on the rocker cover or sump, I think they would slope down towards the rear.
It looked okay when it had the telescopic forks on but since I fitted the Wasp ones, the front seems higher.
All that apart though, the rear spring is much to soft for my liking even without the chair on.

The wire diameter is only one indication of spring firmness, you also have to factor in the amount of coils: Less coils is firmer, more coils is softer.  But if the amount of coils is the same then thicker wire does indicate a higher spring rate.

Al

AL-58 wrote:The wire diameter is only one indication of spring firmness, you also have to factor in the amount of coils: Less coils is firmer, more coils is softer.  But if the amount of coils is the same then thicker wire does indicate a higher spring rate.

Al

I exchanged emails with a friend of mine who bought a new shock from Hagon. He has just told me that they said they supplied him with the spring which wasn’t to his taste, they would exchange it for a heavier or lighter one.
That can’t be all bad.
My problem of course is that it’s not just the firmness but the length and of course the initial cost outlay which is going to be a mega-part of my very limited budget.

I’m getting closer.
Using this table from on here

k100v4/k1100lt/rs	385mm	15.16"
k75rt/s/k100rt/lt/rs	360mm	14.17"
k75/k100	345mm	13.58"

 
And this wire calculator
http://www.reliablespring.co.uk/calculator.htm
I have come to the conclusion that the existing spring is about 230 lb/in and I should have a 14 in shock
as the bike weighs 623 lb that would seem a little low
I also looked on the Ohlins spreadsheets I found on Google and the recommended spring rate for trackwork but for a K1100 is 286. They don’t list anything for a K 100.
So I’m thinking of starting at 300 and see how I get on.
I’m also going to do a little test on the actual spring which I have, this evening, with a set of scales and a hydraulic press.
I have spoken to Hagon, Realm/RAM, AVO and Protech. The only difference between them all seems to be knowledge of spring rates. I have used the latter products before and they have been brilliant although it has been on kit cars. The latter 2 know all about spring rates for cars but not for bikes. I know all the guys who have fitted AVO shocks on bikes and have been very impressed BUT don’t kow what spring rates they used L
As you might imagine, Hagon and RAM are tightlipped on spring rates.

Watch this space

G'day Touch , don't know if this will help you , two years ago I had an OHLINS BM137 custom built , the standard eye to eye length is 355mm , the spring that I opted for is a 48 Newton one ( you can do the conversion from metric yourself ) . I was advised that when this shock was 1st on the market in the 80's they shipped with a 52 Newton spring but many riders came back looking for a more compliant ride , most settled for 50 Newton springs . I went a little lighter because I don't do 2 up or carry much luggage , my shock was perfect right out of box , I only had to back off the compression / rebound damping a little

John Re