Author Topic: Fork and suspension Lowering 1990 K 75S Questions (Read 28991 times)

mejetski2000 · « **on:** August 21, 2015, 09:16:31 AM »

Would like to lower my K75S about an inch or so. I know many shock companies can build shorter shocks but I'm wondering how to do the front forks. Can I cut the fork spring spacer, or spring AND spacer or do I need to get custom stations ? I have Progressive springs in there now. The suspension travel and current height looks like a 1" drop won't be detrimental.

TIA Pete

johnny · « **Reply #1 on:** August 21, 2015, 09:27:14 AM »

greetings...

id just drop the triple tree down 1" on each fork tube...

a 1" drop can be detrimental to your foots if you getts lazy and donts keep the balls of the foots on the pegs when canyon racing...

j o

mejetski2000 · « **Reply #2 on:** August 21, 2015, 09:58:11 AM »

Hey Johnny thanks for suggestion ! That's my final option but I'd like to maintain the appearance of stock setup if possible. I really don't carve hard on this bike since it's a husband/wife thingy lol. (Luckily I have other bikes for that)

Pete

MonkeyMcBean · « **Reply #3 on:** August 21, 2015, 10:38:31 AM »

Quote from: mejetski2000 on August 21, 2015, 09:58:11 AM

(Luckily I have other bikes for that)

Pete

Quite the list of other bikes. How big is your garage?

K75RT Keith · « **Reply #4 on:** August 21, 2015, 10:38:46 AM »

Alternatively, you could just put 70 series tires on her front and back. You'll lower the bike but not mess up the geometry.

TimTyler · « **Reply #5 on:** August 21, 2015, 11:01:38 AM »

It's not possible to raise the fork tubes by lowering the triple-tree with S-handlebars. The S-bars are in the way.

mejetski2000 · « **Reply #6 on:** August 21, 2015, 11:13:30 AM »

Tim's correct, even a half inch would be tight. I'm going to get with Ted at Beemer for the shock and additional info I think. I imagine I'm not the first short KB rider who's done this LOL. I have $900 budgeted which should get me set up.

mejetski2000 · « **Reply #7 on:** August 21, 2015, 11:15:39 AM »

Quote from: MonkeyMcBean on August 21, 2015, 10:38:31 AM

Quote from: mejetski2000 on August 21, 2015, 09:58:11 AM
(Luckily I have other bikes for that)

Pete

Quite the list of other bikes. How big is your garage?

Actually have 4 right now, but the K13 is up for sale. Bought a KTM 390 Duke in May.

TimTyler · « **Reply #8 on:** August 21, 2015, 12:11:25 PM »

You could cut the PVC spacers down a little.

mejetski2000 · « **Reply #9 on:** August 21, 2015, 12:15:28 PM »

My thoughts exactly : )

johnny · « **Reply #10 on:** August 21, 2015, 07:36:29 PM »

flip the bars over...

mejetski2000 · « **Reply #11 on:** August 22, 2015, 05:02:13 PM »

I got an e-mail from Beemershop and was advised against lowering the bike, which I don't understand since several companies are selling shorter than stock height shocks. Anybody running a 1" short shock that can give some feedback ?

johnny · « **Reply #12 on:** August 22, 2015, 05:22:37 PM »

greetings...

the reason is it changes the moto geometry and can cause whack... the beemershop wants no liability with regards to whack caused by something they suggested...

some folks here have lowered their motobricks... they will speak up when they see this thread...

j o

The Mighty Gryphon · « **Reply #13 on:** August 23, 2015, 11:49:50 AM »

Funny I should notice this thread this morning.

I lowered the front end about 1/2" when I first got my 75RT last year. Today I was riding with no hands to check alignment. At about 40mph the front end started to oscillate. Did it three times. Scary.

Looks like there is not enough trail to stabilize the front end with the forks lowered. Not noticeable when holding the grips even up to 110mph, but let go and things get a little loose.

Will be checking fork alignment and raising the front end this evening. My advice: don't drop the front end.

mejetski2000 · « **Reply #14 on:** August 23, 2015, 12:39:29 PM »

Gryphon Thanks for posting your experience. Did you shorten the spacers and are you running factory or progressive springs ? I believe the RT has substantially different geometry than the S model, ie travel and fork length specifically. Are you running a standard length shock or shorter ?

Thanks, Pete

TimTyler · « **Reply #15 on:** August 23, 2015, 12:50:36 PM »

Quote from: mejetski2000 on August 23, 2015, 12:39:29 PM

I believe the RT has substantially different geometry than the S model...

I don't. the RT has a larger radiator and a lot more fiberglass.

mejetski2000 · « **Reply #16 on:** August 23, 2015, 01:15:17 PM »

Hey Tim, what I've seen so far is that the S forks have less travel and a different fork oil volume than a later RT. Every manufacturer I've checked also have different part numbers for their spring kits and rear shocks also. I agree that the RT likely has more front end weight than a S model for sure. Not sure how relevant the RT suspension is compared to the S.

TimTyler · « **Reply #17 on:** August 23, 2015, 01:19:26 PM »

I thought you meant frame geometry. Angles and such.

mejetski2000 · « **Reply #18 on:** August 23, 2015, 01:49:18 PM »

Nope, sorry should have been more specific on my end.

The Mighty Gryphon · « **Reply #19 on:** August 23, 2015, 02:10:22 PM »

As far as I can tell, the front forks are standard "94 RT. I recently installed and balanced a new front tire. Fork oil has about 12,000 miles and front end damping is good. No leaks/good seals. Besides the lowered front end, the only other notable factor is that there is a very slight, barely perceptible play in the steering bearings.

In any event, I am raising the front end and retightening the axle clamp screws forthwith.

mejetski2000 · « **Reply #20 on:** August 23, 2015, 03:10:22 PM »

I installed Progressive Suspension springs in mine about 20 years ago. I'd like to replace them with fresh springs when I add the new shock. I have new Honda 10wt to go in as well. I'm hoping Progressive can advise how much to shorten the spacers.

Nine80seven · « **Reply #21 on:** November 02, 2015, 12:26:46 PM »

Generally, are all forks for two valve bricks, '85-'89' the same? Or, as the mark aged were forks upgraded internally? Have never read a synopsis of the development of these forks through the series.

I know forks stamped S are different. Are later forks better than early forks? I got early forks, '85, progressive with bottoming springs, seem to work for me, just wondering. Reason I ask is got a pair of '87s laying around and maybe a switch out would be cool with the integral aero brace and fender. This is on a early '85 KRS.

lmiklosy · « **Reply #22 on:** December 18, 2017, 06:38:06 PM »

Gryphon: There should be zero slop in the steering head bearing. The R models will oscillate violently with any slop there, to prevent it I pre-load the steering stem on the R. The K is different. On the K tighten the steering stem bearing shell lightly by hand till it stops - don't force it further. Then tighten the Fitting bolt to 33 ft-lbs followed by the Hexnut to 33 ft-lbs (pg 374 Chpt 10 Figure 58 Clymer). The fitting and nut is used together to prevent preloading the shell bearing during assembly. Take a test ride and check for oscillations.

I'm a fan of lowering these K75s, dropped my steering crown as far the handlebars would allow. Next step is to grind a LITTLE on the handlebars to allow more clearance, maybe cut the shock strut after that. I find no adverse handling issues when riding the lowered frame, think the shorter wheelbase is a plus. For taller riders the extra knee bend might mean trouble, I'm 5'-10" with no discomfort. Cutting the spacers changes the fork dynamic, it removes preload in the fork spring that in turn changes the ability of the fork to isolate the chassis and rider from road vibration.

Would have started a new topic but discovered this old thread.

tweather · « **Reply #23 on:** March 01, 2025, 08:33:41 PM »

So to lower a K75 RT, with fairings removed, sounds like springs in the back and a fork adjustment would do the trick. Combine that with a lowered seat setup and maybe shaving the seat a bit… would y’all say that’s the best way to lower the bike without sacrificing the handling? And running lower profile tires?

frankenduck · « **Reply #24 on:** March 01, 2025, 09:17:30 PM »

Running lower profile tires gets you about 1/4".

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Author Topic: Fork and suspension Lowering 1990 K 75S Questions (Read 28991 times)