BMW K bikes (Bricks)

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1Back to top Go down   Minimum fork travel K100 Empty Minimum fork travel K100 on Mon Jul 01, 2019 10:03 am

George_Pap

George_Pap
Silver member
Silver member
Hello all, I would like to ask what is the minimum "safe" travel that I have to maintain in my front forks without the fear of bottoming? I mean what the minimum height distance between lets say fork seals and lower triple tee ( yoke ) 
By default it was set to 180mm but I want to lower the front to 120mm
I have WP springs installed and SAE15 fork oil. Do you think its gonna be dangerous in sudden braking under load?
Thank you


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K100RT (Early 1985 -nonABS)
    

2Back to top Go down   Minimum fork travel K100 Empty Re: Minimum fork travel K100 on Wed Jul 03, 2019 6:54 am

stevenh

stevenh
active member
active member
@George_Pap wrote:Hello all, I would like to ask what is the minimum "safe" travel that I have to maintain in my front forks without the fear of bottoming? I mean what the minimum height distance between lets say fork seals and lower triple tee ( yoke ) 
By default it was set to 180mm but I want to lower the front to 120mm
I have WP springs installed and SAE15 fork oil. Do you think its gonna be dangerous in sudden braking under load?
Thank you

This is quite a loaded question. From my racing days this first things to set correctly, were your suspension and get a the best set of tyres you can afford. What exactly are you trying to achieve ?

The manual says SAE5 fork oil, 410cc of oil in each leg (which sounds like a lot to me) and 135 mm of travel.

So your SAE 15 will make the forks a little stiffer, if you want to lower the front end you should NOT change the distance between the lower tripple clamp and the seals. But raise the forks up through the top tripple clamp. But 60mm you are suggesting is quite extreme and it will severely change the geometry of the bike and the (handling) the bike will oversteer and turn into corners much quicker, even dangerously so. Usually if you lower the front end you have to lower the back as well 

Check your oil levels are exactly the same in each fork. take the weight off the front wheel, remove the fork caps. make a dipstick to check levels
Put a zip tie around the fork stanchion push it down the fork to the seal, go for a ride try some hard braking. The zip tie movement will tell you how much travel you are using.
Push the forks trough the top tripple clamp at small increments 5 - 10mm (max) test ride, feel the difference. Try another 5mm  etc

Take care when experimenting. You can make your bike very unstable.

    

3Back to top Go down   Minimum fork travel K100 Empty Re: Minimum fork travel K100 on Wed Jul 03, 2019 8:30 am

duck

duck
Life time member
Life time member


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Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
http://www.ClassicKBikes.com
    

4Back to top Go down   Minimum fork travel K100 Empty Re: Minimum fork travel K100 on Wed Jul 10, 2019 2:51 am

jbt

jbt
Silver member
Silver member
Of course it will be dangerous. Minimum fork travel is your maximum fork travel. The spring rate and the oil viscosity must be adapted to the weight of your bike and you. Adapted doesn't mean that it wears a shiny commercial emblem on the box. It's a number before kg/mm. And SAE 15 grade is too much , but there's a large difference between commercial viscosity and real viscosity, varying much with the temperature.
Nothing is designed to cope with a reduced fork travel in your fork, spring nor hydraulics. Even the back suspension needs to be adjusted to the front one.
And the question you shold ask is "how will my bike be rideable if I lower my front fork?"
Answer: very badly. Reduced trail gives unstability and shimmy, if you ad this to a stiffer front suspension, the front wheel won't spend much time on the tarmac.
Modern bikes have all a very reduced fork travel, even so-called trail bikes have a shorter travel than your K.
But the internal hydraulics are very different and, overall, they nedd this short-travel forks because the extra wide tyre they show (for commercial reasons only) forces to have a narrow fork angle to preserve manoeuvrability. Your K has a very reasonable tyre width and can enjoy a normal fork angle with a normal fork travel that will preserve comfort on any road.
If you're short legged, choose a lowered seat instead.

    

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