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A bit of history.
In the 80s, my riding buddy and I were into vintage racing Aermacchis - otherwise known as Harley Sprints - which were known for precise handling. We rode them on the street too, but we both had GS400s for putting the miles on, and also GS750/850 rigs for long hauling or two upping. We both noticed that the 400 chassis was prone to 'nebulousness' - the steering just wasn't very precise, especially cornering on bumpy roads, and also was downright scary on gravel. The gravel road thing was attributable in part to the 18" front wheel which was bound to be less gravel friendly than a 19", but the spooky front end was a mystery.
I did the usual fork spring stiffening which made it worse if anything, and tapered roller head bearings, which were nice but no fix. Having so many other race wrecked parts to deal with, I just left it at that and lived with it. It wasn't going to spit you off, and we weren't racing them; well, not officially….
I recently had a '78 frame alongside an '82 in the shop and while trying to figure out if a '78 tank would fit an 82 frame I noticed a subtle but telling difference in how the top tube attaches.
Because I can only attach one pic per post - or so the 'mechanism' says - I'll have to post the shot of a later frame after.
The other GS frames all have the top tube having braces just behind the coils going to the top frame rails. This is not only much stronger structurally, but also stiffens the top tube laterally because it is three point mounted rather than just welded to one side of a tube. The later frame feels just like a smaller version of the four cylinder bikes, which is a good thing. And it's not wasting the inherent stiffness of the upper rails in a lame transfer to the head tube.
In theory, this mod would double the lateral stiffness of the top tube at a cost of zip. I consider the original frame design to be a failure in this area; no engineer would give that a pass. And Suzuki as much as admitted that when they updated the frame. The new one is almost overdone, but I think that two little gusset tubes welded in behind the coils would do jet as well and also take a lot of stress off the original attachment point. There isn't a lot of room to work in, but there looks like enough.
Anyone who does't think that stiffness in this area is critical should look at a GS500 frame. That fixed it.
I'm not presently about to do this mod as I'm still looking for a candidate for 'rustoration' , but felt obliged to pass the thought on. Comments?
In the 80s, my riding buddy and I were into vintage racing Aermacchis - otherwise known as Harley Sprints - which were known for precise handling. We rode them on the street too, but we both had GS400s for putting the miles on, and also GS750/850 rigs for long hauling or two upping. We both noticed that the 400 chassis was prone to 'nebulousness' - the steering just wasn't very precise, especially cornering on bumpy roads, and also was downright scary on gravel. The gravel road thing was attributable in part to the 18" front wheel which was bound to be less gravel friendly than a 19", but the spooky front end was a mystery.
I did the usual fork spring stiffening which made it worse if anything, and tapered roller head bearings, which were nice but no fix. Having so many other race wrecked parts to deal with, I just left it at that and lived with it. It wasn't going to spit you off, and we weren't racing them; well, not officially….
I recently had a '78 frame alongside an '82 in the shop and while trying to figure out if a '78 tank would fit an 82 frame I noticed a subtle but telling difference in how the top tube attaches.
Because I can only attach one pic per post - or so the 'mechanism' says - I'll have to post the shot of a later frame after.
The other GS frames all have the top tube having braces just behind the coils going to the top frame rails. This is not only much stronger structurally, but also stiffens the top tube laterally because it is three point mounted rather than just welded to one side of a tube. The later frame feels just like a smaller version of the four cylinder bikes, which is a good thing. And it's not wasting the inherent stiffness of the upper rails in a lame transfer to the head tube.
In theory, this mod would double the lateral stiffness of the top tube at a cost of zip. I consider the original frame design to be a failure in this area; no engineer would give that a pass. And Suzuki as much as admitted that when they updated the frame. The new one is almost overdone, but I think that two little gusset tubes welded in behind the coils would do jet as well and also take a lot of stress off the original attachment point. There isn't a lot of room to work in, but there looks like enough.
Anyone who does't think that stiffness in this area is critical should look at a GS500 frame. That fixed it.
I'm not presently about to do this mod as I'm still looking for a candidate for 'rustoration' , but felt obliged to pass the thought on. Comments?
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