[djamgils]

I made a graph with the aid of Linkage containing the percentage of anti rise for 3 different types of linkages.


What amount of anti rise would be the optimum? And are there more aspects when you consider braking performance?

With 100% anti rise you would have no attitude(is this the correct word for staying levelled) change while braking, this seems to be a very good thing but are there any negative effects to this?

 

[illflip]

i could of made the same graph in mspaint

 

[jonKranked]

I know a sure fire way to acheive 100% anti-rise:












seeing your fat, elderly neighbors naked.

 

[demo 9]

I know a sure fire way to acheive 100% anti-rise:












seeing your fat, elderly neighbors naked.

must spread(i cant)

 

[klunky]

What?

 

[sonnythe]

On a more serious note. What is anti-rise or rise for that matter in?

 

[djamgils]

when you apply the brakes there will be a deceleration of the total mass. This results in weight transfer and a forward pitch movement. It is possible to influence the amount of pitch with pivot placement. And 100% anti rise would have the bike levelled when only applying the rear brakes.

Something I was also wondering about, if you would have the same anti rise curve with a different mechanical layout would it then still react the same under braking?

 

[jonKranked]

What?

OH MAN!!!!

+rep

 

[illflip]

when you apply the brakes there will be a deceleration of the total mass. This results in weight transfer and a forward pitch movement. It is possible to influence the amount of pitch with pivot placement. And 100% anti rise would have the bike levelled when only applying the rear brakes.

Something I was also wondering about, if you would have the same anti rise curve with a different mechanical layout would it then still react the same under braking?

brake dive?

and honestly...i think your asking the wrong forum.

 

[General Lee]

What?

Alfred Kinsey: What happens when you 'do it'?

 

[no skid marks]

Having ridden a few bikes(single pivot)of similar design with and without floating brakes. I generally prefer to have the squat of no floater. There are pros and cons to both. Without the floater(squatting when braking)the geo stays more consistent, and I use less low speed comp to hold the front up when to avoid diving when braking into corners. I find I can feel and control the rear tyres traction better with the rear brake, but there's probably a lot less of it.
With a floater(zero-small amount of squat), the bike absorbs bumps a lot better as the rear end remains more active when braking, beneficial through braking bumps. The bike doesn't brake traction as easy and I find is a lot safer when panicking because you've hit something wrong or are a bit out of shape.
Ideally I think a small amount of squat would be ideal. I'm a bit of a hack, and I think squatting(suspension stiffening) is no big deal for smoother riders.

 

[djamgils]

brake dive?

and honestly...i think your asking the wrong forum.

Brake dive is the front end diving, rise is the rear end rising.
Do you have another forum where I could get a bit more serious answer?
I was under the impression that RM was the place to ask for in depth tech stuff.

 

[djamgils]

Having ridden a few bikes(single pivot)of similar design with and without floating brakes. I generally prefer to have the squat of no floater. There are pros and cons to both. Without the floater(squatting when braking)the geo stays more consistent, and I use less low speed comp to hold the front up when to avoid diving when braking into corners. I find I can feel and control the rear tyres traction better with the rear brake, but there's probably a lot less of it.
With a floater(zero-small amount of squat), the bike absorbs bumps a lot better as the rear end remains more active when braking, beneficial through braking bumps. The bike doesn't brake traction as easy and I find is a lot safer when panicking because you've hit something wrong or are a bit out of shape.
Ideally I think a small amount of squat would be ideal. I'm a bit of a hack, and I think squatting(suspension stiffening) is no big deal for smoother riders.

I have ridden a session 77 with floating brake and that was really bad. When sagged you will have pro-rise and thus as soon as you hit the brakes it actively pitches you forward.

 

[djamgils]

Maybe if I also show what curve belongs to which frame it will be more interesting for some people.


By djamgils

As stated by DW and Socket the Session 88 has a similar curve as FSR.
You can also see the pro rise effect of a parallel floating brake (so parallel to the line trough the rear axle and the pivot point)
And you can also see that the vpp used on the socom is al over the place, like stated in the DW patent.

the reason why I am looking into this is because I am looking for a new frame. And I wanted to compare them in theory. But what I was also wondering is what is more important, geometry or the suspension system?
I am interested in the commencal supreme dh because of the adjustable head angle. And as it theoretically seems the suspension system should be good.

The main reason that I want to buy something else is because even with custom dropouts the socom is still not a true DH bike geometry wise.

And I also found out that the leverage ratio curve goes from degressive to extremely progressive. So it kind of behaves like a dhx air but maybe even worse and that is something you really notice while riding. And maybe that is also the reason why the DHX sucked for me in the socom and why I needed loads of LSC.
and the axle path isnt exactly rearward but I never had problems with that I just think it could be better.

 

[Steve M]

Maybe if I also show what curve belongs to which frame it will be more interesting for some people.


By djamgils

As stated by DW and Socket the Session 88 has a similar curve as FSR.
You can also see the pro rise effect of a parallel floating brake (so parallel to the line trough the rear axle and the pivot point)
And you can also see that the vpp used on the socom is al over the place, like stated in the DW patent.

the reason why I am looking into this is because I am looking for a new frame. And I wanted to compare them in theory. But what I was also wondering is what is more important, geometry or the suspension system?
I am interested in the commencal supreme dh because of the adjustable head angle. And as it theoretically seems the suspension system should be good.

Geometry is ALWAYS more important than suspension... look at Oranges for a prime example, you can ride them as fast as anything even though the suspension is theoretically pretty terrible.

As for what is the optimum amount, you'd need to actually work out a dynamic wheel traction simulation to determine what was the most useful.

 

[djamgils]

Geometry is ALWAYS more important than suspension... look at Oranges for a prime example, you can ride them as fast as anything even though the suspension is theoretically pretty terrible.

As for what is the optimum amount, you'd need to actually work out a dynamic wheel traction simulation to determine what was the most useful.

yeah that is what I expected, regarding the geometry as well as regarding the simulation.

Do you know if that kind of simulation has ever been done by somebody? Or if it is usefull to do something like that?
I am thinking of possible subjects for my master graduation.

 

[Steve M]

yeah that is what I expected, regarding the geometry as well as regarding the simulation.

Do you know if that kind of simulation has ever been done by somebody? Or if it is usefull to do something like that?
I am thinking of possible subjects for my master graduation.

I've never seen anything like that in the MTB world, but I'd almost guarantee it's been done by motorsports teams. The problem is, when it comes to proper performance analysis (rather than just developing/proving methods of analysis), it's usually done by companies with a vested interest in improving their own performance, so the results aren't usually published. SAE technical papers have a lot of good stuff in them but by and large they're 10 years behind the actual automotive industry.

As for whether it's useful, definitely. Optimisation of a performance parameter by analytical techniques is always something that's considered useful.

 

[rbx]

You must first distinguish between rise caused by the weight shifting of the rider

and rise due to the linkage design..

IC behind the wheel will rise the rear end of the bike ADDING to the foward weight shift of the rider.

Perfectly parrallele linkage will be very neutral leaving only the weight of the rider to the rise the bike..this is the type i am priviling in my suspension design because i will shift my weight backwards and by having perfectly neutral suspension under braking, i know i am getting maximum traction...but thats the way I RIDE suspension design reflect the philosophy of the designer.

 

[djamgils]

You must first distinguish between rise caused by the weight shifting of the rider

and rise due to the linkage design..

IC behind the wheel will rise the rear end of the bike ADDING to the foward weight shift of the rider.

Perfectly parrallele linkage will be very neutral leaving only the weight of the rider to the rise the bike..this is the type i am priviling in my suspension design because i will shift my weight backwards and by having perfectly neutral suspension under braking, i know i am getting maximum traction...but thats the way I RIDE suspension design reflect the philosophy of the designer.

How do you define neutral, as 0% anti rise or 100% anti rise?
If you would have a parallel linkage the IC would be in infinity and the line from the tyre contact patch to the IC would be parallel to the linkage. When moving true travel you will change the angle of the linkage and thus drastically change the anti rise behaviour. when the linkage is horizontal without sag you would go from 0% anti-rise to pro rise when using travel.

And certainly you have forward pitch due to load transfer but the effect coming from the rear linkage can be influenced and thus reduce the total amount of pitch.

 

[Steve M]

What amount of anti rise would be the optimum? And are there more aspects when you consider braking performance?

With 100% anti rise you would have no attitude(is this the correct word for staying levelled) change while braking, this seems to be a very good thing but are there any negative effects to this?

As you said in the following post, if you had a constant rate of 100% anti-rise in the rear end, it would only hold the bike level if only the rear brake was applied. A bike with 100% anti-dive at the front and 100% anti-rise at the rear would still pitch forwards under braking, because application of the brake at one end of the bike would increase or reduce the normal tyre load at the other end of the bike.

There are dynamic negative effects to some methods of having 100% anti-rise in the rear of the bike, that are potentially positive effects if used for anti-dive in the front end of the bike. When the brake is first applied - or if braking force is suddenly increased by the wheel regaining contact with the ground after hopping - the rear suspension attempts to compress itself. When this happens, from simple conservation of momentum (movement of swingarm/wheel vs movement of bike/rider mass) and the limitations of gravitational acceleration (bike/rider mass can only fall so fast), the rear wheel is trying to decrease its traction, and this is often where harshness comes from - the suspension hits the face of a braking bump and tries to compress itself violently, then once it loses traction, the large spring force that has been built up from the excessive compression also extends it rapidly. I believe this is where the harshness of "brake jack" (excessive brake squat) actually comes from - not from any perceived "lockout" of the suspension, but from excessive out-of-phase motion of the suspension.

Something I was also wondering about, if you would have the same anti rise curve with a different mechanical layout would it then still react the same under braking?

Not necessarily - you have different components of anti-rise caused by the wheel couple moment, and the height of the pivot above the axle. For example, a singlepivot with the pivot at axle height, and a parallelogram floater, has 0% anti/pro-rise at that point in its travel. If you remove the parallelogram floater, you will have a couple moment from the wheel's rotation that tries to compress the swingarm by rotating it forwards, but have no vertical moment arm from the horizontal deceleration force that has been translated to the axle (tractive force at the tyre x radius of wheel = horizontal force + couple moment at axle). If you keep the parallelogram floater but move the pivot up much higher, you no longer have the wheel's couple moment effect trying to compress the swingarm, but instead you have a vertical moment arm between the axle and the pivot for the horizontal force to work with to create a compressive moment.

In static/kinematic analyses, these two effects are not considered separately because traditional analyses simply use the position of the instant centre to calculate pro/anti-rise under braking. However, if the rotating mass of the wheel is considered significant, then under varying traction/slip conditions (ie wheel hop over braking bumps leading to the wheel locking and unlocking repeatedly, or at least accelerating/decelerating faster than the mass of the bike/rider is), dynamic analysis would show that the mass of the wheel would act to provide sharp increases and decreases in compressive moments.

Basically, this means that you can have a high-anti-rise bike like a Lahar (high pivot with floater) that is less harsh than a bike with the equivalent level of theoretical anti-rise but with an IC that is lower and closer to the rear wheel. If you plot a locus of IC positions for equivalent anti-rise (will be a straight line going up at some angle from the rear tyre's contact patch) you will be able to directly compare two such setups.

And merry christmas!

 

[4speed]

I have ridden bikes with no floating system before and got really used to it,found the bike squatting under braking to be really normal,then tried a bike with floating system that had been custom made,even though it was stopping suspension lockout under braking,it jacked the rear of the bike under hard braking,put it down to the force of the floating system was fighting the spring pressure and forcing the rear to jack under braking,now riding my new lahar the bike so settled under braking it awesome,could be due to the sprung to unsprung weight ratio.

 

[dirtdigger]

I have ridden bikes with no floating system before and got really used to it,found the bike squatting under braking to be really normal,then tried a bike with floating system that had been custom made,even though it was stopping suspension lockout under braking,it jacked the rear of the bike under hard braking,put it down to the force of the floating system was fighting the spring pressure and forcing the rear to jack under braking,now riding my new lahar the bike so settled under braking it awesome,could be due to the sprung to unsprung weight ratio.

I've locked out the floater on my lahar so its not a floater anymore and it rides a lot better IMO

 

[fluider]

...
Basically, this means that you can have a high-anti-rise bike like a Lahar (high pivot with floater) that is less harsh than a bike with the equivalent level of theoretical anti-rise but with an IC that is lower and closer to the rear wheel. ...

Socket, why do you consider Lahar with floater to be a high-anti-rise design? I plotted its anti-rise according to Tony Foale's article and I'd say it has 60% anti-rise at maximum. I don't know if floater is exact parallelogram with swingarm, but it seems it isn't parallel.

1) If floater is parallel to the swingarm: cca 25% anti-rise (lower red)
2) If floater is almost parallel, convergent with swingarm: cca 30% anti-rise (upper red)
3) If we removed floater: cca 60% anti-rise (yellow line)
4) If we placed "reversed" HorstLink on the swingarm, leaving brake caliper on the flex stays, then IC would set cca 50% anti-rise (green line).

Tony Foale's article on Diving under deceleration ...

 

[djamgils]

I thought that the line from the tyre contact patch trough the IC that goes trough the CM is the 200% line. So all your anti rise values should be multiplied with 2.

 

[fluider]

Tony Foale's description of rear suspension anti-rise caused only by rear braking defines anti-rise percentage by intersection of CoM vertical line and line from rear-tyre-contact-patch to the IC.

Projecting CoM on the vertical line passing through the front axle (like in case of anti-squat of rear suspension) would describe front suspension anti-dive caused only by rear braking, IMO.

 

[Steve M]

You are correct Fluider, I was mistaken in calling it a high-anti-rise design. However, the point I was making about the separation of braking components remains

 

[xy9ine]

I've locked out the floater on my lahar so its not a floater anymore and it rides a lot better IMO

how'd you do this? aaron suggested just tossing the brake rod & bolting the caliper mount directly to the swingarm. like to give it a try, but a bit hesitant about drilling a hole through the swingarm. hmm...

 

[dante]

Tony Foale's description of rear suspension anti-rise caused only by rear braking defines anti-rise percentage by intersection of CoM vertical line and line from rear-tyre-contact-patch to the IC.

Projecting CoM on the vertical line passing through the front axle (like in case of anti-squat of rear suspension) would describe front suspension anti-dive caused only by rear braking, IMO.

those diagrams look remarkably similar to what dw was trying to explain to me over way too many mojitos one night in Vegas...