Front brake tuning!

You might be able to fit a zip tie but it would finicky to check afterward (but possible)
Sag is to do with spring rate and preload of the spring.
Static sag is the amount the bike sags (travel used) under it own weight at standstill unladen.
Loaded sag is with the rider on board.
Internal preloading of the spring will change it but their is a relationship between the two that determines if the spring poundage is in a range suitable for the weight of the rider.
A spring that suited a heavy rider would give less sag for a light rider,the fork (in this case ) would ride high in the stroke and most likely top out (worse with the stock clunky fork) giving a non optimum ride or feedback.
The range of springs for a Commando is limited unlike modern machines.

I see no reason why a Commando with Lansdowne inserts and decent rear shock absorbers could not handle as well (most likely better) than modern 'retro motorcycles with a bit of fiddling.

Not the best but an idea of the concept.

http://www.motorcyclenews.com/mcn/produ ... nsion-sag/

Same as old twin shocks that you rotated the spring collar to compress the spring when you loaded the bike or had a passenger.
The spring poundage was not effected but the extra preload on the spring reduced the sag to minimise bottoming out with the extra weight.

Here is a unit I made for one of my bikes when nothing else was available.

Time Warp said:

I see no reason why a Commando with Lansdowne inserts and decent rear shock absorbers could not handle as well (most likely better) than modern 'retro motorcycles with a bit of fiddling.

Click to expand...

Maybe mis-alignment of the steering head, swing-arm axis, wheels, frame centre line....

Sag is the suspension compressing a little under weight so it can rebound for a depression in the road or trail.

If your riding style requires you to brake that heavily, you'd be dead already with the original front brake. It couldn't stop a wet fart. Seriously, having to brake hard enough to have the kind of problems you describe suggests you should change your driving style so you don't have to use the brakes so hard.

I did about 40,000 miles on the prototypes with the original wimpy Italian front brakes and never got close to gwetting my ass wiped out.

Frank if only we always had the leisure to hardly need brakes but regardless how good braking is, its usually the weakest element of cycle controls and pilot skills. It may seem silly to work up braking so hard it tests stability as we hardly ever should need too, but if we continue in this sane safety 1st vane then anyone who rides is in denial. Heck everyone and their sister can drag race and run around turns pretty dang well but not everyone can bring themselves to practice to braking maximums. Obviously some folks just like to see what they can get away with seeking thrills so takes some nerve wracking practice to know what you and your cycle are capable of. I say start on dry level grass, then grassy slope, then wet conditions to get sense enough for Gravel practice, more similar to pavement, all seems just fine> SPLAT. At least on the grass its always same lack of grip instead of building to of point of no return>SPLAT. Peel has only one mystery to me, not so much what causes it but What is the significance of lower fork/axle becoming blurred to vision in some turns [when I'm brave enough to get a peek in conditions of onset]. Does it distract from traction or assist it? I watch Peels front tire when riding it locked for some bike lenghts but fork flutter of blurring didn't stand out to take note of, just inability not matter what to get a stoppie, which pleases me no end as means all braking goes into linear slowing not tipping over on nose like my modern cripple will at less G pull down. If Peel's basically factory Roadholders can take those loads then so should Lansdowns so suspect something else.

Totally agree with Hobot's advice on practicing braking. It's not good having to perform an emergency stop when you can't remember the last time you did one. Too little or too much braking can both lead to a collision.

Thanks guys, this to me is the really important part. I have had a couple of close shaves recently mainly due to being distracted by something, a rattle something in a field or generally enjoying myself only to find out the the guy in front does a full ABS stop so he can turn left or right before missing a junction. The other reason is that here in Germany the road speed is high and you need to keep up to stop people trying to nip past in silly places - a serious problem. Most small cars here are very quick and have amasing brakes, anything like a BMW of which there are a lot, can out accelerate me and waste me into his rear by slamming on the brakes. I really don't drive that quick. Sure, I like to get a move on and enjoy a bit of motion but most importantly, I do like to "feel" my machine and hopefully be in control.

Generally a tuff issue. In truth, people are going to pull out on me, I am going to day dream and wild pig (seriously) could run out on me. In this mode I will probably panic. Most of the bikes I have I can't lock the front brake when I grab a handful on a dry road and to be honest, I would probably de-tune a brake if it did. I like using the brakes especially into the corners (if I need to) and feathering off as I start to apply gas again, not racing around but driving quickly, well within the limits of me and the machine. This is why and I totally agree, that training for braking hard is so important. The other night I felt rather ruff (sick) for a couple of hours after bouncing and shaking me and the bikes to bits for 30 mins on a good "test" road. Must be off my trolley but anyway,I feel a lot better about the bike now and seriously hope I never have to do an all up emergency stop. The exercise has definitely been worth it!

Fork twist?

Sorry if I missed it but on my scan of this thread, I see no discussion of the need for a fork brace.

Under hard braking, a single disc front end WILL twist AND that causes binding within the two forks' tubes/bushings as they twist against each other.
The parts are no longer in parallel. Period.

No amount of futzing with damping or spring can fix the binding caused by that twisting.

I know that some on this forum think that fork braces are over rated, citing racers and their race bikes that didn't have them. I disagree.
That argument is also an argument against electronic ignition, flat slide/smoothbore carburetors, fuel injection, 4 valve heads, and foot shifters.
Lots of winning racers didn't use those things either.

And, the shift to upside down forks was the next step in the evolution of the telescopic fork AFTER all the OEMs were sticking integrated fork braces on all of their latest non-upside down forks. That is, the OEM engineers recognized the problem of twist and combatted it first with braces and then with upside down forks.

Another aspect - axle diameter. Our dinky single sided axle clamp is also a part of the problem.
Notice how modern designs use large diameter hollow axles that are clamped on both sides - also to defeat twist, even on twin disc set ups.
And, the axles often are clamped with four bolts, two on each side, not just one on one side.

Nigeldtr - BTW - wish I had your forks and brake on my bike - well done.

I respectfully disagree that one side brake rotor drags forks out of line or twists them as the drag force from road grip is from tire centered in forks. The reason for dual brakes is mainly spreading hi heat loads against fade and to even out the gravity imbalance pull on one side of forks to bias which way they go when hands off. What does twist up forks on harsh braking is road texture uneveness on tire chirp skips twicthing forks and the mass of pilot rider bearing down slightly off center this way and that, so identical issue to tame braking with single or dual rotors.

Again I mention my horror-disappointment on my loosey goosey factory Trixie Combat lack of current brake security both in loss of tire grip and antics of forks snatch down fighting when I took list advice to try a smaller 100 front tire. UGH. Again I mention Peel could ride her 110 front tire squealing to lift rear off ground some for 6-10 bike lengths and not loose control by lack of fork stability with brace installed. Staying in saddle was main thing that limited Peel, rather harsher pull downs than Ninja or SV650 can dream about as they flip head over tea kettle.

Nigeldtr I too get some queasiness and brain fog fatigue after rough rides and close calls braking making me grit teeth to my shoulders which squashes - jars pressure on brain stem with rather less trying distances than your 30 mile tester. Someday I fear enough of this sense will sink in to get over this motorcycle hobby. On predicable sudden hard braking I tend to jab rear brake an instant before front brake to squat bike then maintain some constant rear drag while squeezing front - as best way to slow w/o having to counter balance and fight the rear passing by my hip first.

I had one event on SuVee holding way back from mc traffic down steep twisty so could blast around the sharps w/o runing into them, to come around 10 mph marked blind to see school bus broken down and bikes all stopped like a dozen lengths ahead at 40's mph leaned so forced into trail braking that then hit winter ice sand layer which then tripped bike down but resisted innate temptation to stomp R foot on ground to hold up like a flat tracker as already learned that'd just snatch tarmac gripping boot sole under falling bike, so let go of front same time as stomped an instant on rear brake which hi sided bike back up right and aimed us at diagonal into wrong lane & car grill approaching few dozen yd away, to stay pure upright nailing front in terror to slow enough I could release an instant to whip back in my lane then again squeal heated race only 120 tire to stop about one bike length away form bowling down a handful of bikers. I can't claim I did this with practiced skill to brag about but by golly I've never seen stunt riders or road racers pull a stop off like that. Never again please, Yet its the type of handling antics I crave to do on Ms Peel once past the sluggish counter steering corner rates and no brakes needed nor better forks desired. Trail braking sucks and is only good for corner cripples that have to be already slow enough they can put extra strain on leaned stressed fork front patch. UGH>

Well, I just don't have enough grey cells to figure the fork brace bit out. When I look at a caliper slung under the fork leg I can't help thinking it's going to twist the leg upwards and forwards when braking hard. Then again, the wheel will be trying to push the caliper through the fork leg so surely with a single disc they must twist and pull to right , hmm or perhaps left ?(disk on RHS). Logic tells me I should have 2 discs on the front loading the legs the same and the tyre working in the centre of all these forces :?: As I say not enough grey cells for this one. To me the brace may help but only 2 discs will fix :?: I think a Yam XS 650 front end fits?

xbacksideslider said:

Fork twist?

Sorry if I missed it but on my scan of this thread, I see no discussion of the need for a fork brace.

Under hard braking, a single disc front end WILL twist AND that causes binding within the two forks' tubes/bushings as they twist against each other.
The parts are no longer in parallel. Period.

No amount of futzing with damping or spring can fix the binding caused by that twisting.

I know that some on this forum think that fork braces are over rated, citing racers and their race bikes that didn't have them. I disagree.
That argument is also an argument against electronic ignition, flat slide/smoothbore carburetors, fuel injection, 4 valve heads, and foot shifters.
Lots of winning racers didn't use those things either.

And, the shift to upside down forks was the next step in the evolution of the telescopic fork AFTER all the OEMs were sticking integrated fork braces on all of their latest non-upside down forks. That is, the OEM engineers recognized the problem of twist and combatted it first with braces and then with upside down forks.

Another aspect - axle diameter. Our dinky single sided axle clamp is also a part of the problem.
Notice how modern designs use large diameter hollow axles that are clamped on both sides - also to defeat twist, even on twin disc set ups.
And, the axles often are clamped with four bolts, two on each side, not just one on one side.

Nigeldtr - BTW - wish I had your forks and brake on my bike - well done.

Click to expand...

I would happily try a fork brace if I could get one that looked man enough to do the job. I did see one with eccentric rings for fine adjustment of the centre distance but can't remember who made it :?:

hobot said:

I
Nigeldtr I too get some queasiness and brain fog fatigue after rough rides and close calls braking making me grit teeth to my shoulders which squashes - jars pressure on brain stem with rather less trying distances than your 30 mile tester. Someday I fear enough of this sense will sink in to get over this motorcycle hobby. On predicable sudden hard braking I tend to jab rear brake an instant before front brake to squat bike then maintain some constant rear drag while squeezing front - as best way to slow w/o having to counter balance and fight the rear passing by my hip first. >

Click to expand...

Hi Hobot, once upon a time I used, go shooting into people's front gardens or disappearing up someone's drive as an escape route or going into motor cross mode over fields and ditches. Not my thing anymore, I love the hobby but it's tuff out there, everything happens a lot faster now, well from my perception, which does worry me if I think too long :!:

Well, my opinion is that forks twist under hard braking unless they are braced/axle clamped or that twist is otherwise designed out, as with upside down forks.

Your symptoms seem to be consistent with forks that are binding under brake induced twist.

OMG! I've experience what fork bind feels like and didn't consider that possible in Lansdownes but it don't take much to really be disconcerting fighting back oppositely from road texture twitches and pilots to delayed reactions, ugh. Braking is such serious business especially to those few who do brake till scared, so keep mentioning how shocked displease I was with similar hopping and skipping straining forks on factory Trixie I didn't get with one size bigger tire. Got to figure it out or slow down the thrills and 'safety' beyond reason. Much as I brag on Peels handling and involuntary saves on plain '72 and my SuVee650 its braking ability-bravery sense I test and rate myself rider skills on so don't really think I've got that down even on Peel that could take more whoa than I could hold on to and still be on back side of brake lever to actually squeeze it. What else is left but hobot desparte pointers to try?