Well ironically everyone (including me) involved in the D-sports racer project had motorcycle backgrounds. My fabricator redesigned the entire suspension from narrow to wide track and stiffened the chassis. Other than the aforementioned wide track & long suspension links he also fabricated rising rate/progressive suspension linkages like the kind found on motorcycles. Much like motorcycles this made for the first bit of travel being ultra plush without it being so soft that the car bottomed out everywhere.
An additional benefit the first 1" of travel being soft was the braking; the nose had a small hard rubber lip on it, there was just enough dive that the lip dragged the ground and totally sealed of the underside of the car and the net effect was the car pulled 3Gs under braking. As for the negative effects of the dive, because I raced 2 stroke GP bikes first, I still have the habit of pre-loading the throttle on the brakes to get the rear end to squat.
My Datsun is set up on the soft side 225lb springs front and 150lb rear. Of all the things on this discussion of modern vs old I still gravitate towards the narrow track being the vast majority of the difference. After widening the cars track (via longer lower control arms and wider rear axle) rapid left to right transitions were much more stable. Prior to this the felt like a bike doing a near high side.
Knurled. said:
alfadriver said:
In reply to Knurled. :
IMHO, you are saying the same thing. It’s about geometry and how it interacts with the car and the tire surface. Having bad roll center control is bad just as is a camber curve that does not keep the tire on the surface.
"Camber curve" simplifies it too much, I think. For example, twin I-beam Ford trucks had one hell of a camber curve.
Roll center height/stability is more important, IMO. In fact I can't think of a suspension that gains camber as fast as the chassis rolls that wouldn't have all sorts of worse habits.
Simplifying makes it easier to understand. I see the same common thought wrt engine design and emissions. Even it results in a lot of “common sense” that is wrong
In the end, it’s still complicated 3D geometry relating the car to the tires. Which is far from easy to fully define to make work.
In reply to alfadriver :
Yup.
I do find it interesting that passenger cars have all but standardized on an A arm with two lateral links in the rear. (Kind of like the EG civics but simpler)
Knurled. said:
In reply to alfadriver :
Yup.
I do find it interesting that passenger cars have all but standardized on an A arm with two lateral links in the rear. (Kind of like the EG civics but simpler)
Which cars? I think they'll all be beam axles soon enough.
Driven5
UltraDork
6/29/19 2:40 a.m.
Knurled. said:
Tom_Spangler said:
I'm by no means an expert, but AFAIK, it's geometry, specifically relating to controlling the contact patch throughout suspension travel. Especially camber.
Camber is overrated as a geometry problem.
The real issue is proper control of what is known as roll center (but kind of isn't), anti-squat and anti-dive, and bumpsteer.
This is the suspension equivalent of saying:
"Horsepower is overrated as an acceleration problem..
The real issue is proper production of what is known as torque, gear ratios and tire diameter, and rpm"
And I fail to see where "camber curve" oversimplifies any more than "roll center" does.
Returning to the original comparison - could part of the lap time difference come down to the difference between a vintage race car and a modern race car's allowances for modifications? I posit that the difference between a tub 1200 prepared to current GTL rules and a spec piñata might be quite different.
In reply to Driven5 :
Don't leave out the antis. Those are super important as well.
I was horrified the first time I saw an Audi 5000 (200) front suspension up close. They have prodive geometry. As if having a wheelbase half the length of the car wasn't bad enough.
@Rons; Troy Ermish is the current GTL National Champ and he also happens to run vintage as well. There is a video online of his vintage 510 on the dyno and its putting out 178hp at the wheels. I don't know the weight of the car with driver but I think it's around 2100lbs. On Buttonwillows CW13 layout I believe he's turning 1:59 lap times possible 1:58s. Contrast that against against a Super Miata with around 145whp and they're turning 1:55s. I'd venture to guess his suspension is as trick as it can be and obviously his driving is top notch.
My car's suspension is prepped identical to 1973 C-Sedan championship winning 1200 with the exception of being 3" wider. My car also has slightly better brakes.
