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Discussion in 'Hacks' started by Get Back, May 25, 2009.
I've been pondering leading links for a while and have come up with the below sketch regarding the braking dive characteristics using a freely rotating calliper mount with tie rod back to the fork tube. I've ignored the mechanical anti-dive through the angle of the lower link in relation to overall centre of gravity. That will need another sketch.
OK so I went ahead and did a sketch for mechanical anti-dive through the angle of the lower link in relation to overall centre of gravity (COG). The larger the value of "Y" the larger the moment arm the COG has to act on the suspension during braking.
Larger "Y" = more brake dive.
Smaller "Y" = less brake dive.
And BMW effectively accomplished that with the Telelever..........
Yeah the BMW solution works on geometry too. Sometimes it doesn't work so well as you may have seen recently. It does have the advantage of maintaining geometry regardless of steering angle compared to leading link fork. Not all of us want to ride BMWs though
That is not how it works, according to:- Tony Foale, Motorcycle Chassis Design: The Theory and Practice. Check it out on line!
Is it available free online or a recommended book to purchase?
What in particular are you referring to Phyllis?
Anti-dive....and how it is worked out, and why!
" One often sees comments to the effect that Parallelogram designs remove all braking effects from the suspension, we can see that this is clearly not true."
This is a direct quote from Tony Foale.
How can you guys just make shit up? Tony Foale is an EXPERT in the field of motor cycle design and construction. Study his work and learn something!!!
(smiley face) Phyllis
Ah okay gotcha. I may be guilty in stating some of the things related to anti dive. It is true that floating calipers make a big difference in that area as opposed to a fixed caliper. However, nothing is a total absolute even though the overall effect is true. I apologise if I am the guilty one and will have to figure a better way to state the truths associated with floating calipers..........Yes, Tony Faole is one of very few true experts in a field full of so many that simply repeat what they have heard and he is highly respected . ..........................................................................Years ago he went to work with Sedgeway. He contacted us to build a roll cage prototype from some prints that were provided. In looking at the prints I had to turn down the project as they were very detailed and had a tolerance of like .0.10. I contated Tony and told him about this . His basic response was " You are kidding !! (I thought he was going to be dissapointed with us) ...Then he wet on to say " Send those prints back I am going to have a talk with drafting as there is no way anyone could expect to be able to hold that kind of tolerance. I mentioned it to them before but obviously they did not listen!" He was a little amazed and went on to talk about real world realities vs drafting room dreams. LOL. Quite a guy and, yes, highly respected by many for many years.
What, no technological leaps forward since January? Let's get on it, everyone.
Perhaps you would like to provide some force vector diagrams to point out where I have gone wrong?
Or do you just prefer to blindly follow any old text written down in a book regardless of how fictional it may be. Like the Bible.
Oh, this is going to be good.
IF the caliper is fixed to the swingarm such as with a Unit leading link the suspension and braking tend to be at war. it creates what some brag to be anti dive. IT also makes the front wheel lock up pretty easily which is not and advantage. With a floating caliper this does not happen depending on the angle of the link holding the caliper vs the swingarm angle. Note that we prefer the axle to be higher than the swingarm pivot point to free up the action more.
I'm faced with a bit of a conundrum. So a few general tech questions if those more experienced can assist please
I want to finish my light-weight hack for the CRF1000 AT. But I am a bit stumped on the front end. Don't have the money to start experimenting so need to commit to a solution by doing as much research as possible.
My requirements are:
light-weight hack to carry fuel, fridge, spares etc- but capable to carry a person weight wise- so not a passenger module, but with a seat
decided to build a leaner that can be chocked to a fixed unit when required.
tough - need to be able to cover heavy corrugated roads at a reasonable speed comfortably, maybe 80km/h
plenty of suspension travel to soak up the ruts, potholes and rocks
will be incorporating a drive system for the sidecar wheel for assistance in sand/mud etc.
It seems everyone goes for the leading link suspension getup. I can understand the advantages for road work and stability at speed, but it just doesn't look like it would word that well off-road. I'm sort-of thinking of tele-lever front-end of the GS BMW's- really great on-road, but not so good off-road and dropped for bikes like the HP2.
So the guys that have some experience in this, because I except its all compromise, which delivers the better off-road ability, performance, suspension travel and shock-absorbsion please? (i.e. leading link or conventional forks?)
Motocross sidecars all use LL front forks, they seem to handle off road pretty well.
Just my 2c worth but I think you are discounting Links too easily. I've used links for years and I've gone over some of the roughest tracks imaginable including corrugations that seem to go on forever and I've never had a problem with my links.
If they are well made with the right springs on them you will find they are more than adequate.
They will easily handle corrugations at much higher speeds that 80kph.
You don't want to over think it too much. Use what people have been using for years. Me personally, the less technical anything is the less things can go wrong.
I dare say you know the sidecar boys in WA. Have a look at their outfits. They have been to even rougher places than me and they use links as well.
Again just my 2c worth.
Just back from 900km of Victorian high country, mainly gravel roads and tracks........some no track.
Standard suspension soaks up anything you throw at it. A weapon on the dirt with the exception of too much dive.
Steering input on dirt is ‘fine to ever so slightly heavy’ compared to my Ural. Input required on tight twisties such as the sealed “Omeo Highway” is a good upper body workput.
I have made the decision to go LL but will keep it supple but maybe with less travel.
......my camping box as above, also takes a comfy seat and screen for wifi....
Oh, don’t go too light weight because you will just have to add weight.
Empty, mine is a handfull of danger and much slower. If I was not well experienced I possibly would not be here now......but that is another two stories.