Steering feels heavy

[jimmyx]

I am in the process of building a K100 scrambler( see post in projects) took the bike for a spin around the block with no seat ( at the upholsterer ). I lowered the fork tubes in the triples to accommodate moto style bars. The front end feels heavy at slow speeds,as if it wants to turn on its own. I have never owned a street bike, is this just typical behavior for this style of bike at low speeds? Maybe the wider bars? Any info would be great .
Thank you.

[johnny]

changing the moto geometry can do that... did it feel heavy prior to lowering the front end... is your rear shock whack... did you do the center stand steering bearing test...

j o

[jimmyx]

Hey Jo, Yes, a bit heavy the first and second times the rode the bike but, it had all the fairings and body parts installed. Previously the fork tubes sat about an 3/4 inch above the top triple clamp, now they are flush. Not sure what stock is. Again, I have really only ridden dualsport bikes. This may be normal?

Shock may be whack....will investigate the steering bearing test. Bike has about 32k miles.

[johnny]

since you dont have a baseline its hard to figger out...

motobricks have heavy steering to begin with... folks thinks their steering bearings are either notched or gunked up with old lube or both... generally its because they do not have the skill to push lean whack... so they feel things that really aints there... its all in their head... like hearing things that really aints there...

so... on center stand with front tior off the ground as high as possible... the steering should go full lock to full lock effortlessly... with steering centered... move slightly right and see if it will go to full lock by gravity by its self... then do the same thing to the right... and feel for notches...

heavy steering on my motobricks has generally been the rear shock being whack or the sag isnt in the sweet spot... then its forks not having the right amount of juice... then its tiors... alignment... steering bearings...

moto geometry especially the relationship between front and rear ride height means everything... when you find the sweet spot you will find the yeeeeehaaaaa... until then you will may feel like you are gonna slide out or cartwheel off...

if i know my fork oil is right... i would be looking at the rear shock... it looks oem... aints no yeeehaaaa left in a 32k oem rear shock...

j o

[jimmyx]

Cool....Thanks Jo! Tons of great info here...I learned so much about this bike from this forum, good group of peeps . Have been doing all my own maintenance/repairs/customization . New fuel injectors( rebuilt ),new fuel pump and filter, cleaned black gunk out of tank, new rear brake res. and lines, electrical info for my lights/wiring. Tire size info.....the list goes on. Great site. Its  rewarding to immerse yourself in a bike. I did it with my XRR on advrider with the same results!
Thanks again

[pdg]

Seeing as you've dropped the forks through the yokes, you've effectively raised the front end. It might just be the angle of the pictures, but it now looks decidedly 'arse down'... What you've done is make a chopper - means that at slow speed the front wheel will try to 'flop' over one side or the other with even the tiniest amount of lean and it'll be heavier. :falldown:

If the tops of the forks were 3/4" proud of the yokes before (excluding the plastic caps if you have them, just to the top of the metal tube) it wouldn't surprise me if you have a short rear shock and the forks were pulled through to make the geometry 'closer', afaik the stock setting is flush... What length is the rear shock with the bike on the centrestand?

On my 75 (identical frame geometry) the oem rear shock died quite well so I got an aftermarket off ebay, which turned out to be a short one - I dropped the front nearly an inch to try and compensate and still had floppy yet heavy steering with little low speed precision. Since then I've done a few suspension related things:

Dropped the forks through as much as possible to raise the front.

Put rubber bushes in the tops of the forks to add some preload and get my sag a bit better.

Made a mount adaptor to lift the back end as high as it would go without the UJ in the shaft binding - I did this by supporting the shaft with a small jack (with no shock fitted) and kept lowering it until I could feel the UJ, then put it up a little and made the adaptor to suit. This adaptor is a 'prototype' for testing.....

After doing all that, it feels much lighter to steer at low speed and this is where I've got to - you should be able to see how much the top shock mount has moved, originally the top bolt was behind the end of the side panel:



I also have slightly wider handlebars too (originals are sat on top for comparison):

[ReneZ]

Your fork tubes are as they should be/normally are (practically flush with your top bracket). Are you sure the front tyre has sufficient air? I tested a bike the other day and had the same experience, there was barely any air in the tyre.

[jimmyx]

Hey pdg,
Cool... Thanks for the response, I was contemplating that exact modification..... I was thinking of welding on an extension tab, about one inch to raise the rear. I am glad this has been done already, I will follow your lead on this.....how much did you add to your 75? The ass-end is not as bad as it looks, no seat ,my rear shock is approximately 13.25 inches center to center.
Thanks!

Also, Rene, I will check the psi on the front tire. It seemed fine, but it sat out covered for a whole season, have not checked it. Thanks for your input.

[pdg]

My original rear shock is 13.75" eye centre-eye centre...

Measuring on the frame now, there is about 14.75" between the original mounts. The 'new' top mount location is a shade forward too, but that really shouldn't make much, if any, difference.

I chose to make the adaptor bolt-on because it's still 'under test', and if the paralever pans out I'm going to have to change it again anyway.

In any case, if you are going to be altering the suspension geometry I'd recommend the same test I did before welding - have the bike on the centre stand (or as in my case supported on a bar), remove the rear shock with the FD supported by a jack, then slowly lower the FD toward the ground while turning the rear wheel/disc. It's kinda hard to explain, but you'll feel when the UJ starts to bind - this is something to avoid. When you are happy that you have maximum distance between the mount points, measure and then you can extrapolate how much to 'move' the mount.

I may have been able to gain another 1/8" or so at the wheel, but opted to play a shade on the safe side.

If any of that is hard to follow, feel free to shout.

[jimmyx]

Sprayed copious amounts of WD-40 on the steering head area.....aired up the tires a bit.....steering feels better. I will apply "spray grease" as a stop-gap until I can re-pack the bearings. Quick question on tires, I recently purchased new dualsport tires for this project, 3.50 x 18 TKC80 front and 130/80/17 kenda big Block rear. There is a 10% difference in Aspect Ratio,from  90% to 80% . The current street tire(Metzler with a huge sidewall) measures about 26" in diameter installed and the Big Block measures just over 24" uninstalled...seems puny in comparison. Will this effect the handling? Will my rear shock mount extension help with this?

[jimmyx]

New tires....rear sidewall photo....front tire....new supertrapp

[pdg]

Sprayed copious amounts of WD-40 on the steering head area.....aired up the tires a bit.....steering feels better. I will apply "spray grease" as a stop-gap until I can re-pack the bearings. Quick question on tires, I recently purchased new dualsport tires for this project, 3.50 x 18 TKC80 front and 130/80/17 kenda big Block rear. There is a 10% difference in Aspect Ratio,from  90% to 80% . The current street tire(Metzler with a huge sidewall) measures about 26" in diameter installed and the Big Block measures just over 24" uninstalled...seems puny in comparison. Will this effect the handling? Will my rear shock mount extension help with this?

With the change in aspect ratio, I would have expected less of a difference in diameter of tyre to be honest.

Not sure whether this information is new to anyone or not, but hey... The size of the tyre is about the carcass, the tread is 'supposed' to be irrelevant. A 130/90 should be 117mm 'tall', while a 130/80 should be 104mm (the aspect is a percentage of width). Doubling the difference, there should be a 26mm change in diameter between the two carcass sizes.

With the lower profile tyre being knobbly, I would have thought the outer diameter including tread would have been very close to the 'street' tyre you have/had originally. It is entirely possible that once it's fitted and inflated it'll be much closer to the original size - the shape of a tyre can change a fair bit depending on how it's stored and for how long...

As for handling/geometry - if the tyre diameter doesn't change much when fitted, your proposed modification to the rear shock mounts will put the bike pretty much where it was. A much bigger change in handling will come from the difference in behaviour between a street tread and a d/s tread - you will probably find that on tarmac the bike will feel more 'squirelly' (for want of a better word) and that because of the stiff bias construction of the kenda coupled with the lower profile you might feel more surface irregularities too.

Not sure on the 100, but on the 75 the engine is smooth enough that I can feel the tread blocks 'slapping' the road as a sort-of bum-hum  :hehehe

[jimmyx]

Thanks for your wealth of information PDG! I have ridden DS bikes with Dunlop d606's and Michelin t63's, kind of used to the "bum-hum" I may end up choosing a more street oriented tire(tyre?) at some point.

[pdg]

No probs - if I know something I'm happy to share :2thumbup: Not like it's exactly 'trade secrets' ;)

To be fair - the knobbly tyre hum is less actual vibration than most singles and twins (and 'normal' triples and fours) will produce from the engine, it's just a different frequency.

Around here, it's rare there's enough length of road smooth enough to really notice it anyway... But, I will say the Pirelli MT90 I had on before was brilliant on tarmac - wet or dry. It was just very slightly 'lacking' in mud and loose gravel. That's more like 80:20 dirt/street as opposed to the 20:80 of the Mitas though...