Agreed on all points, but again, I'm just talking theoretical.... so I probably wont calculate a change in grip :P
Agreed on all points, but again, I'm just talking theoretical.... so I probably wont calculate a change in grip :P
well, the thing is... this does become a trade-off game.
Stampie's stated that the minimum wheelbase is around 77"... although it's practically around 80", I'd guess... since the 77" is "from pulley to rear wheel hub center". The question is, will sticking to that minimum mean that the CG ends up higher, than if you stretched out to 90", and afforded the design more room to position the main mass components (engine/driver/diff/?) lower?
edit:
also, it hasn't been clear... when we're talking about "long arms", are we talking about a-arms (that are 'lateral') or 'trailing arms' (which would be 'longitudinal')? or both?
ProDarwin said:The turning radius of the back of the car is a function of the front wheels minus the wheelbase.
Not necessarily. Some of the fastest and most impressive autox'ers I've head the pleasure of watching appeared to be keeping the rear tires following almost exactly on the same line as the front tires...If you catch my drift.
Driven5 said:ProDarwin said:The turning radius of the back of the car is a function of the front wheels minus the wheelbase.
Not necessarily. Some of the fastest and most impressive autox'ers I've head the pleasure of watching appeared to be keeping the rear tires following almost exactly on the same line as the front tires...If you catch my drift.
That, as mentioned already, is a function of the tires' slip angle. Radials have a much sharper curve than bias plies which have fairly low and lazy curves, and the same ratio occurs with sidewall height - shorter sidewalls, peakier slip angle curve.
No car will corner like it is on rails, but something with bias ply slicks (do people even use these for autocross?) will corner with the rear wheels describing a larger radius than the fronts at max grip.
Knurled. said:Driven5 said:ProDarwin said:The turning radius of the back of the car is a function of the front wheels minus the wheelbase.
Not necessarily. Some of the fastest and most impressive autox'ers I've head the pleasure of watching appeared to be keeping the rear tires following almost exactly on the same line as the front tires...If you catch my drift.
That, as mentioned already, is a function of the tires' slip angle. Radials have a much sharper curve than bias plies which have fairly low and lazy curves, and the same ratio occurs with sidewall height - shorter sidewalls, peakier slip angle curve.
No car will corner like it is on rails, but something with bias ply slicks (do people even use these for autocross?) will corner with the rear wheels describing a larger radius than the fronts at max grip.
well, it certainly isn't unheard of at $Challenge... {cough} AMX {/cough}, the rules regime under which the discussion 'originated'. Although, clearly this discussion is broad enough to cover non-challenge autocross.
In reply to sleepyhead the buffalo :
Given that there is not a cost limit on tires, any slicks would be allowed for the Challenge. At least how I read it. For sure, the concept car I have in my brain would be tired with slicks, as it's a DM basis car. But I still don't see that happening any time soon.
Knurled. said:Driven5 said:ProDarwin said:The turning radius of the back of the car is a function of the front wheels minus the wheelbase.
Not necessarily. Some of the fastest and most impressive autox'ers I've head the pleasure of watching appeared to be keeping the rear tires following almost exactly on the same line as the front tires...If you catch my drift.
That, as mentioned already, is a function of the tires' slip angle. Radials have a much sharper curve than bias plies which have fairly low and lazy curves, and the same ratio occurs with sidewall height - shorter sidewalls, peakier slip angle curve.
No car will corner like it is on rails, but something with bias ply slicks (do people even use these for autocross?) will corner with the rear wheels describing a larger radius than the fronts at max grip.
The math theory still has value though, as IF the rears operate at a radius > front radius-WB, then that difference in radius is made up by slip. The longer the wheelbase, the large the difference, the more slip required.
Interesting thread.
Wheel base to track ratio was mentioned early in the discussion. In my research for the design part of my build I found that F1 cars usually have somewhere around a 1.7:1 ratio. My understanding is that the ratio seems to be in relation to quickness of response to steering input. The closer to square on wb to track, the quicker the response. case in point, a go cart with short wb to track vs a top fuel dragster with it's 300ish wb & very narrow track.
Caster angles also come in to play here as does polar moment of inertia & other factors.
Most slicks being used at events are bias ply; for my car/class Hoosier doesn't even make a radial slick in that size (10" diameter wheel).
Used bias ply slicks are very cheap and abundant....what's not to love. Although I confess that I buy brand new ones as for autocross they last me over a year.
ProDarwin said:Knurled. said:Driven5 said:ProDarwin said:The turning radius of the back of the car is a function of the front wheels minus the wheelbase.
Not necessarily. Some of the fastest and most impressive autox'ers I've head the pleasure of watching appeared to be keeping the rear tires following almost exactly on the same line as the front tires...If you catch my drift.
That, as mentioned already, is a function of the tires' slip angle. Radials have a much sharper curve than bias plies which have fairly low and lazy curves, and the same ratio occurs with sidewall height - shorter sidewalls, peakier slip angle curve.
No car will corner like it is on rails, but something with bias ply slicks (do people even use these for autocross?) will corner with the rear wheels describing a larger radius than the fronts at max grip.
The math theory still has value though, as IF the rears operate at a radius > front radius-WB, then that difference in radius is made up by slip. The longer the wheelbase, the large the difference, the more slip required.
Which is, very neatly, part of why short wheelbase cars feel more squirrely: the difference in vehicle attitude at a given slip angle in a given radius corner. Long wheelbase cars can be at a more significant slip angle while feeling to the driver like the back end is still behind the car, so to speak.
Knurled. said:ProDarwin said:Knurled. said:Driven5 said:ProDarwin said:The turning radius of the back of the car is a function of the front wheels minus the wheelbase.
Not necessarily. Some of the fastest and most impressive autox'ers I've head the pleasure of watching appeared to be keeping the rear tires following almost exactly on the same line as the front tires...If you catch my drift.
That, as mentioned already, is a function of the tires' slip angle. Radials have a much sharper curve than bias plies which have fairly low and lazy curves, and the same ratio occurs with sidewall height - shorter sidewalls, peakier slip angle curve.
No car will corner like it is on rails, but something with bias ply slicks (do people even use these for autocross?) will corner with the rear wheels describing a larger radius than the fronts at max grip.
The math theory still has value though, as IF the rears operate at a radius > front radius-WB, then that difference in radius is made up by slip. The longer the wheelbase, the large the difference, the more slip required.
Which is, very neatly, part of why short wheelbase cars feel more squirrely: the difference in vehicle attitude at a given slip angle in a given radius corner. Long wheelbase cars can be at a more significant slip angle while feeling to the driver like the back end is still behind the car, so to speak.
The analogy with planes is remarkably similar. Longer planes with wide wings feel stable and secure but are dead ducks in a dog fight. For the twisting and turning you want short wings and a short length, but yes the skill levels go up. Only the very the very best can really manage the demands and reaction times.
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