[rbx]

do you guys think that all the bearing failures were due to the close proximity of the pivots to each other which induced huge amount of forces in them or is it a false calculation of tolerances which resulted in to much play?

 

[ohio]

Originally posted by rbx
do you guys think that all the bearing failures were due to the close proximity of the pivots to each other which induced huge amount of forces in them or is it a false calculation of tolerances which resulted in to much play?

I know folks believe it was the placement of the dogbone so close to the BB pivot, which results in some pretty high forces through those bearings. My problem with that theory is that there are even greater forces from suspension compression through the dog-bone than the BB bearings (think hydraulic car jack handle to visulaize what I mean), and to my knowledge the last iteration of the design didn't have problems at the dogbone.

I haven't actually taken one apart, so I don't know the system too well, but it certainly COULD be made to work. It is not that different from numerous out suspension layouts in MTBing and MX. My guess is better choices in bearings... they probably used bearings with too small of an OD. Not enough surface area for 6061 to handle the forces involved (especially lateral forces).

 

[rbx]

Originally posted by ohio
I know folks believe it was the placement of the dogbone so close to the BB pivot, which results in some pretty high forces through those bearings. My problem with that theory is that there are even greater forces from suspension compression through the dog-bone than the BB bearings (think hydraulic car jack handle to visulaize what I mean), and to my knowledge the last iteration of the design didn't have problems at the dogbone.

I haven't actually taken one apart, so I don't know the system too well, but it certainly COULD be made to work. It is not that different from numerous out suspension layouts in MTBing and MX. My guess is better choices in bearings... they probably used bearings with too small of an OD. Not enough surface area for 6061 to handle the forces involved (especially lateral forces).

yes youre right ohio come to think of it the 'moto link' used in mx bikes actually have pretty close bearing spacing...but do you think that(if they could be fit)that cylindrical roller type bearings could handle this type of load?(needle are cool but they need tight tolerances and good sealing system)

 

[ohio]

Originally posted by rbx
yes youre right ohio come to think of it the 'moto link' used in mx bikes actually have pretty close bearing spacing...but do you think that(if they could be fit)that cylindrical roller type bearings could handle this type of load?(needle are cool but they need tight tolerances and good sealing system)

I don't really know the setup well enough to comment, but I would guess that would solve some of the problem. You'd still need an angular contact bearing of somekind to handle the thrust load (a dedicated thrust bearing would be a waste though) on the axle. I'd bet the problem was with the aluminum the bearings were pressed into, more than the bearings themselves.

 

[Thylacine]

From a guy I know who has worked on a few, he said that they were cheap and nasty bikes, with bad tollerance issues in terms or bearing preload/press fit and just generally bad fit issues. That white tape stuff that plumbers use and Coke cans were mentioned a few times as a remedy to eek another week out of an already crap bike

Also, low pivot swingarm bikes dont have the correct rear wheel trajectory IMHO when we're talking 6+" of rear wheel travel. The wheelbase starts to shrink and you know that cant be a good thing.

Anyway, good riddance...time for sometime new I guess.

Ooop...look at that.....6pm Friday, time for beer

 

[FRzealot]

As a (former) owner of 2 of these, the problem is really simple- can't get too into the actual physics of it, but the linkages are not thick enough.

The 2002 models upgraded to a thicker dogbone and rocker, which helped to reduce breakage, but when something twists the wheel (acting like a 13" lever arm) the linkage just isn't sturdy enough...

I loved the bikes, tho. A little flexy, a little expensive, but they took everything I gave them. Also very reliable in my cases.

 

[rbx]

i did a quick calculations on a rear suspension system thats very similar in design to rm7...as constant factor i assumed that the rider is 250lbs and the 'security factor is 5' well ended up with some huge forces going throu the main pivot and the dogbones pivots!!!

main pivot=8642lbs(each)
dogbone pivots=3830lbs(each)
seatstay/rocker pivot=5195lbs(each)

1)i must have miscalculated because but if im right then the rm7 was WAY underbuild.

2)maybe the security factor is to high!!

 

[FRzealot]

It seems that everything would be stouter if the bearings were larger all-around... any thoughts?