Hassman
Senior Member
- Joined
- Jan 17, 2011
- Bikes
- Suzuki DRZ 400SM Matchless G3WO -41
As we all know the most up to date and cutting edge in motorbike suspension is the upside down front forks and a central rear shock connected to the swing arm.
What many people may not know (or for that matter really care to know) is how the motorbike industry arrived at today’s solutions, so here I will enlighten you all and give you something to start to talk about with strangers in the awkward silences such as when stepping into a crowded lift or on a bus.
Once upon a time motorbikes were bicycles with a strap on (strap on engine that is, don’t get any ideas), bicycles were not sprung but with the added weight of engines and added speed now seemed to be a good time to do something about it.
Here we see an early motorbike still with pedals and no attempts at suspension other than springs in the seat.
This was the standard for many years to come on most bikes, front suspensions were in the pipe though and various marvelous ideas took form and were tested.
Here an early HD solution with some type of springer fork with a spring in a cartridge, this is probably from the 20’s.
The workings of a springer front end:
Husqvarnas rubber band suspension from 1951 –note the complete lack of any form of damping.
Here a 1931 bike with a girder front end, the girder did not really have damping per se but one could tighten up the bolts in the linkage and thereby increasing the friction and hence get a crude form of damping.
The telescopic front fork as we are used to see today was launched in 1934 by Nimbus and the year after by BMW who also put hydraulic damping on them and since they have pretty much stayed the same –and for those of you who think that upside down forks are a new thing, think so no more… it was very common for the un dampened forks to be built “upside down” for the same reason that we have them upside down today –rigidity.
Telescopic front forks are not without troubles and with materials and technology back then it was not possible to get them stiff enough for “hard work”, so in addition to the girder front ends surviving for many years to come, other solutions were also on the table.
An Earles leading link front fork very common on bikes fitted with sidecars.
A Greeves trials bike with an interesting front end.
And here a Sachs with a similar design.
As stated the telescopic forks had drawbacks that were hard to overcome with the technology available back then –mainly problems with rigidity and the fact that there were two springs/shocks that had to be precisely made and set up to do the same thing at the same time as the one on the other side of the wheel, this meant that the girder front end was still to be used well into the 60’s.
Here a 1969 Douglas TT bike, note that the bike has no rear suspension, a girder front and the most hideous seat in the history of mankind, the rider must have been brave indeed to ever get himself in a situation where people may take a photo of him on that bike with that seat, a bit as when we see pictures of our parents in the 70’s and they are wearing bell bottom trousers, embarrassing!
In today’s motorbike world all manufacturers apart from Bimota and BMW are sticking religiously to their upside down telescopic front ends.
BMW Telelever
BMW Duolever
Bimota Tesi has a hub center steering system –basically a forward facing swinging arm, they were not first with that though as British James had this in 1910.
The problems with standard front end suspensions that it took the industry so long to remedy are:
Stiction –the fact that the seals when not in motion tends to stick slightly to the fork tube and this increases the initial force needed to move the fork tube.
Wheel base –as the suspension works up and down, due to the front fork angle not being 90 degrees to the chassis the wheel base also changes, this can make the bike unstable when braking hard or when going over bumps.
Dual springs/dampers –as opposite to a modern rear end the front has two springs and dampers that needs to be set up exactly to match each other, if one is hard/softer/more or less damped than the other the wheel will actually flex somewhat sideways rather than just up/down.
Stresses on the head stock –with the front wheel being so far away from the head stock the front fork acts as a massive lever so the forces on the head stock when braking and steering are immense.
As you can understand not all of these issues are totally sorted out yet, there is still stiction but by using different coatings to a lot less degree than before.
Wheel base still changes as the suspension works and this leads to front wheel chatter -the front wheel is more or less constantly accelerating or decelerating in comparison tot he rear wheel, the industry solution to this has been to allow for this when manufacturing the tyre.
With today's very powerful and heavy bikes and larger front tyres the forces on the head stocks are getting larger and larger.
BMW’s and Bimota’s solutions deal with all of the above issues, so did John Brittens design which was (unless I am misinformed) a girder mated to a telelever “swing arm”.
When I get the time and opportunity I shall bore you to death with rear end suspension developments…
Hassman
What many people may not know (or for that matter really care to know) is how the motorbike industry arrived at today’s solutions, so here I will enlighten you all and give you something to start to talk about with strangers in the awkward silences such as when stepping into a crowded lift or on a bus.
Once upon a time motorbikes were bicycles with a strap on (strap on engine that is, don’t get any ideas), bicycles were not sprung but with the added weight of engines and added speed now seemed to be a good time to do something about it.
Here we see an early motorbike still with pedals and no attempts at suspension other than springs in the seat.
This was the standard for many years to come on most bikes, front suspensions were in the pipe though and various marvelous ideas took form and were tested.
Here an early HD solution with some type of springer fork with a spring in a cartridge, this is probably from the 20’s.
The workings of a springer front end:
Husqvarnas rubber band suspension from 1951 –note the complete lack of any form of damping.
Here a 1931 bike with a girder front end, the girder did not really have damping per se but one could tighten up the bolts in the linkage and thereby increasing the friction and hence get a crude form of damping.
The telescopic front fork as we are used to see today was launched in 1934 by Nimbus and the year after by BMW who also put hydraulic damping on them and since they have pretty much stayed the same –and for those of you who think that upside down forks are a new thing, think so no more… it was very common for the un dampened forks to be built “upside down” for the same reason that we have them upside down today –rigidity.
Telescopic front forks are not without troubles and with materials and technology back then it was not possible to get them stiff enough for “hard work”, so in addition to the girder front ends surviving for many years to come, other solutions were also on the table.
An Earles leading link front fork very common on bikes fitted with sidecars.
A Greeves trials bike with an interesting front end.
And here a Sachs with a similar design.
As stated the telescopic forks had drawbacks that were hard to overcome with the technology available back then –mainly problems with rigidity and the fact that there were two springs/shocks that had to be precisely made and set up to do the same thing at the same time as the one on the other side of the wheel, this meant that the girder front end was still to be used well into the 60’s.
Here a 1969 Douglas TT bike, note that the bike has no rear suspension, a girder front and the most hideous seat in the history of mankind, the rider must have been brave indeed to ever get himself in a situation where people may take a photo of him on that bike with that seat, a bit as when we see pictures of our parents in the 70’s and they are wearing bell bottom trousers, embarrassing!
In today’s motorbike world all manufacturers apart from Bimota and BMW are sticking religiously to their upside down telescopic front ends.
BMW Telelever
BMW Duolever
Bimota Tesi has a hub center steering system –basically a forward facing swinging arm, they were not first with that though as British James had this in 1910.
The problems with standard front end suspensions that it took the industry so long to remedy are:
Stiction –the fact that the seals when not in motion tends to stick slightly to the fork tube and this increases the initial force needed to move the fork tube.
Wheel base –as the suspension works up and down, due to the front fork angle not being 90 degrees to the chassis the wheel base also changes, this can make the bike unstable when braking hard or when going over bumps.
Dual springs/dampers –as opposite to a modern rear end the front has two springs and dampers that needs to be set up exactly to match each other, if one is hard/softer/more or less damped than the other the wheel will actually flex somewhat sideways rather than just up/down.
Stresses on the head stock –with the front wheel being so far away from the head stock the front fork acts as a massive lever so the forces on the head stock when braking and steering are immense.
As you can understand not all of these issues are totally sorted out yet, there is still stiction but by using different coatings to a lot less degree than before.
Wheel base still changes as the suspension works and this leads to front wheel chatter -the front wheel is more or less constantly accelerating or decelerating in comparison tot he rear wheel, the industry solution to this has been to allow for this when manufacturing the tyre.
With today's very powerful and heavy bikes and larger front tyres the forces on the head stocks are getting larger and larger.
BMW’s and Bimota’s solutions deal with all of the above issues, so did John Brittens design which was (unless I am misinformed) a girder mated to a telelever “swing arm”.
When I get the time and opportunity I shall bore you to death with rear end suspension developments…
Hassman
