More about that cascade effect, and do I miss the bike stories?

I got a PM from another web site asking me about the bike stories I used to cover, and do I miss them? Well, yes, kinda. I miss being helpful and telling people how they could avoid the same fate if it could be avoided, I miss vicariously yelling at people about crappy infrastructure, but I don’t miss the death and destruction involved. Having been through one myself I know how painful it can be to survive a major wreck, ditto not surviving it. Not surviving is painfully boring but aside from that not bad. I’m the kind of guy that has to be doing something or at least planning with the possibility of doing something, and where I was didn’t have any fab shops or building supplies. And TBH that was my biggest problem covering bike wrecks, there wasn’t a damned thing I could do to prevent another except make note of what infrastructure would have possibly prevented the wreck.

Moving on to the cascade effect on the TGS2 moving the driver’s seat, I marked the body with where the roll hoop behind the driver would be with my feet all the way against the front axle.That black line is where the rear roll hoop goes.

You can see that the rear roll hoop is right in the middle of the bucket. That is not the ideal location for the front center bulkhead if maximum torsional rigidity is high on your list of priorities. Now if the rear hoop is used to triangulate the center bay and driver entry is from the front instead of the top I might could make it work.

Or I could make the TGS2 a two-bay design using the rear hoop as a tower in a bridge structure. This is a design that I’m not familiar with, at least not as familiar as a multi-bay construction. Basically in this construction all the loads are passed through a central structure and everything is triangulated around that. The important thing in this type of design is to keep all the load paths balanced with structure to connect everything directly because there is no secondary structure to carry the load around design gaps. If I don’t provide a triangulated path to carry the load that load will cause the frame to flex. This style of construction is considerably lighter for the amount of rigidity it delivers than the multi-bay construction I had used on the first iteration of the design, but it makes hanging the engine and rear suspension more difficult. And as I’m trying to visualize the structure I notice there is no way to put the bucket on the frame without making a jigsaw puzzle out of the body, so that’s out.

So back to integrating the rear hoop in the center of the wheelbase, again. Or not, I mean it’s not like I don’t have a design already, it’s just not optimum. All this hair-pulling is just trying to find a better solution with better balance. Well guess what, as long as I have 620 pounds of engine and transmission sitting just 10″ forward of the rear axle in a 1600 pound car the car is not going to be balanced. I’m going to have to give up front grip to keep the back end following the front, or install ridiculous rear tires which is basically the same thing.

This combination has a long history in T-Buckets because the construction techniques raised the rear roll center several inches above the axle, which caused jacking, or lifting the inside rear wheel as cornering load increased. This combined with high power caused severe oversteer which got patched by stupid wide rear tires. If you watch videos of Goodguys autocrosses you can see this effect when someone tries to run a T-bucket. Any power applied before the car is pointed straight results in the back end trying to pass the front. This was also the problem with the pre-1965 Corvair, the swing axle rear suspension had a very high roll center combined with rear weight bias caused by hanging the engine behind the rear axle and 4 equal-sized tires and you have the perfect recipe for leaving the road back end first. This car was designed during a period before computers were used to test designs and also during a period when GM banned participation in motorsports so designs were not examined with that potential in mind, which would have caught this blunder before it entered production.

And after that historical note I think it is about time to take my walk.


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