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1Back to top Go down   Dirtying up a K75S - just a little Empty Dirtying up a K75S - just a little on Mon Mar 25, 2019 8:01 pm

Rockman

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I have a 91 K75S. Nice bike, runs well etc, but I find the front suspension lacking on some of the crappy roads around here (dirt and sealed), and the handle bars are too low for comfort on longer trips. I was thinking all I need to do is fix the front suspension and fit higher/wider bars.

Looking at an exploded view of the forks it appears that the K75S has shortened "sport" suspension, with the main difference being 2 short springs and a spacer instead of the 1 longer spring used in the standard forks. If this is the case then I should be able to simply get standard length springs and swap the bits over. Can anyone confirm this is the case? Any recommendations on fork oil weight and amount?

As for the bars, Ideally I'd fit GS style bars but retain the fairing etc, obviously with longer cables and brake lines. Any comments on this? Alternatives?

    

2Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Mon Mar 25, 2019 8:10 pm

Two Wheels Better

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It's not as easy as swapping the guts since the 'S' forks are rebound one side and damping the other. It would be easier to locate some good tubes with guts from a K100 standard, RS or RT of a similar vintage. Their plusher, longer travel might be ideal for a K75S you're trying to ride more relaxed on. I use 5W in my S forks, but many swear by 10W. Some more relaxed ProTaper fatbars with 28mm centres (and the adapters) go easily onto the 22mm saddles of your K75 triple clamps. I have ATV low bars on Big Block.


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1977 R75/7-R100 grey, '87 K100RS red, '93 K11-K12 aka 'Big Block' black, '96 K1100RS black, '98 K1200RS red, '09 K1300GT red, & 2013 R1200RT-Polizia black & white.

    

3Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Mon Mar 25, 2019 11:58 pm

MartinW

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Initially when I first got my 75s it used to trap my thumbs against the tank on full lock. Over the years the bars have been rotated up and back and eventually modified to go up and back with bar back spacers. I have replaced the front brake hose with the same length as the OEM one. The bars are now comfortable and I haven't had to lengthen any hoses or cables. I did have to lengthen the crash pad brackets with a bit of flat bar in order to get it to fit by 3/4". Before you start doing major modifications try adjusting your bars and perches. Also try changing the weight and amount of your fork oil slightly. More oil than standard makes the forks firmer less oil makes them softer don't reduce them too much or add too much.
Regards Martin.


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K75s Hybrid
    

4Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Tue Mar 26, 2019 7:14 pm

Rockman

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@Two Wheels Better wrote:It's not as easy as swapping the guts since the 'S' forks are rebound one side and damping the other. It would be easier to locate some good tubes with guts from a K100 standard, RS or RT of a similar vintage. Their plusher, longer travel might be ideal for a K75S you're trying to ride more relaxed on. I use 5W in my S forks, but many swear by 10W. Some more relaxed ProTaper fatbars with 28mm centres (and the adapters) go easily onto the 22mm saddles of your K75 triple clamps. I have ATV low bars on Big Block.
Probably a dumb question, but if I am just substituting a single long spring for 2 short springs and a spacer, wouldnt the damping stay untouched?

    

5Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Tue Mar 26, 2019 9:59 pm

Laitch

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@Rockman wrote:Probably a dumb question, but if I am just substituting a single long spring for 2 short springs and a spacer, wouldnt the damping stay untouched?
Probably, but what do you believe would be achieved by having just the one long spring, aside from having less parts to misplace during future disassembly? Smile

Exactly how is your moto's front suspension lacking? As MartinW has suggested, much can be accomplished simply by changing the weight of fork oil, and I'll add that cleaning the internal components, tube walls and replacing worn components might improve matters, too. A rear shock in good condition is also essential for optimal handling results regardless of what changes are made in front.


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1995 K75 73,000 miles
Dirtying up a K75S - just a little Usa-lo10
    

6Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Tue Mar 26, 2019 11:00 pm

Rockman

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@Laitch wrote:
@Rockman wrote:Probably a dumb question, but if I am just substituting a single long spring for 2 short springs and a spacer, wouldnt the damping stay untouched?
Probably, but what do you believe would be achieved by having just the one long spring, aside from having less parts to misplace during future disassembly?  Smile

Exactly how is your moto's front suspension lacking? As MartinW has suggested, much can be accomplished simply by changing the weight of fork oil, and I'll add that cleaning the internal components, tube walls and replacing worn components might improve matters, too. A rear shock in good condition is also essential for optimal handling results regardless of what changes are made in front.
I am after a little more suspension travel mainly. The shorter, stiffer sports suspension just knocks me around on poorly paved roads, especially with the lean forward riding position. I dont remember having the same problem with my previous K100's (5 of them).

    

7Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Tue Mar 26, 2019 11:04 pm

MartinW

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Handle bars can be adjusted so you don't lean forward.
Regards Martin.


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K75s Hybrid
    

8Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Tue Mar 26, 2019 11:08 pm

Two Wheels Better

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I agree that you get pummeled on rough Aussie roads using S forks. I fit them to my RS years ago and when I ride a 'regular' suspended K I can't believe how plush and waggy they feel. I prefer the S fork for their precision and that's why I choose to use 5W at the spec level because they seem to react more quickly and yet feel supple on staccato bitumen surfaces. I'm about 90-odd kilos suited up so this works for me.

I do have 25mm risers and 50mm extenders ('bar width) with aluminium straps riveted on to hold the dash pad in place.


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1977 R75/7-R100 grey, '87 K100RS red, '93 K11-K12 aka 'Big Block' black, '96 K1100RS black, '98 K1200RS red, '09 K1300GT red, & 2013 R1200RT-Polizia black & white.

    

9Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Tue Mar 26, 2019 11:23 pm

TacKler

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You could replace the S/RS bars with K75C bars.  You will require longer cables and brake lines.  The 75C also has the RT style of dashpad.  

There was an article years ago on a BMWK bike website which I cannot find.  This is the closest though  https://www.webbikeworld.com/bmw-k-bike-handlebar-conversion/  As it is written by a 'Merican it is really dumbed down and they expect you to have no common sense or mechanical skills.  Think of the recent media article of BA flying to Scotland instead of Spain - Navigation for Dummies.

One of my 75s already has this conversion but is currently unregistered.  The 75C style of bars really do make a difference though.  However, if you look at it closely, aesthetically it looks a bit odd.  

Another option is fitting RT bars.  

I hope this helps.


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10Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Tue Mar 26, 2019 11:58 pm

Rockman

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Ok, I'm going to try bar raisers that lift up and back an inch or so first, together with 5wt oil in the forks before I resort to anything more radical.

    

11Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Wed Mar 27, 2019 1:41 am

Gaz

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Phil, I went the whole hog on the wider bars with my K75 Project and fitted R80G/S bars and I like it - of course no fairing bodywork on it.

That bike is fitted with the S forks, I believe it was an option on the 1990 K75 (factory naked version). I found the fork internals not arranged as per factory when I opened them but thanks to Inge I got that info and initially set them up with 5wt oil as per TWBs preference. It rode well and tracked well even on Dungog type roads but too harsh for my liking so after about 20,000km I went to 7.5 wt oil and they were noticeably better for me. I am no suspension guru but I felt that it might be the fork rebound that was giving me the harsh feeling and a heavier oil might help with that.

So next fork oil change I am going to go with 10wt and see what happens.
By the way, I use the standard 280ml per leg as per factory specs for those forks.

Cheers


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Gaz
1990 K75 6427509; 1987 R80G/S PD 6292136; 2010 G650GS ZW13381; 95 K1100LT 0232224
    

12Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Wed Mar 27, 2019 3:57 am

MartinW

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I've just finished a fork fluid change and brake fluid change. While I was in there I noted what was done in lifting my bars. All I did was get another set of fork caps and stick them on reversed on top of the fitted clamps followed by the original caps using longer bolts, and the bars were rotated up. If it helps I'm just under 6' at 5'7'' and average arm length for my height. And as stated previously the only other mod was to extend the pad brackets by 20mm. My 92 75s is fitted with Showa forks which are supposed to be better and running 400cc of 7.5W Motul synthetic oil. Pictures are available if needed.
Regards Martin.


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13Back to top Go down   Dirtying up a K75S - just a little Empty Re: Dirtying up a K75S - just a little on Wed Mar 27, 2019 6:45 pm

Rockman

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Thanks fellas. I'll try 7.5 wt oil as per Gaz's recommendation for starters. I was also eyeing off some R series high lift bars on the Motobins site for a R80 project I'm working on. These are 70cm wide with a 15 cm lift. I'll probably get a set for the R80 and just try them on the K75 to see how they fit.

    

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