AI
I don't remember if I mentioned it or not, but for this last weekend I'd ordered up a new set or rear springs for the Pumpkin Racer. I'm not certain what the spring rates are that ship with the current kits. Mine's an early Spec. kit (#2911SP) but seems to be different from others in that respect.
When I first got the car I'd read the little aluminum tags on the springs to see what they were. I thought I remembered the fronts being 500 and the rears being 350s. Over the last season I have brought the car up to speed in various events at various tracks and was generally pleased with the handling in the larger, faster turns, but the the car had significant "push" in the slower corners.
Choices were to attack the slow corners more slowly or do something to lessen the push. I chose to increase rear spring rate. (Note: the Spec. Challenge cars don't have either front or rear anti-sway bars. You do it all with spring rates) I didn't want to sacrifice the fine high speed stability with the change, so decided to bump up the rear rate by 50# to 400 a side. This was enough below the fronts' rate to seem logical and still a significant enough increase to be meaningful for the car's feel.
Well, the 400s arrived from FFR quickly and it was a pleasure to find that a spring swap was such an easy job. Maybe 25 minutes a side including jacking the car and removing and replacing the wheels. That's the kind of project that I like!
Well, checking the bottoms of the old springs turned out to be an education in CRS disease. The rears were 300#, not the 350s that I had "remembered." Hmmmm, well, how's this more abrupt 100 pound rate change going to affect my handling when I expected to only massage it by 50#?
I'm delighted to say this is where I wanted it to be. If the old springs had been what I had thought, probably the 50# adjustment wouldn't have been enough. As it turns out, this is just what the PUSH Doctor needed to cure the patient. I've not sacrificed any of the higher speed stability in carossels and such but the car's turn-in and balance is far better in the tighter corners. The car responds much better to throttle input as well.
Here's what impressed me. It was easy to change the springs. I'd already done frame leveling, etc. before, so that wasn't hard to repeat with the new springs. The change was meaningful and "textbook" in response to what I wanted to change.
After the change and resetting ride height and leveling the car, I then took it to the county scales (+or- 20# accuracy!) and weighed front and rear axles, left and right sides and then each corner with me in the car. I found that there was about 60# or so difference in "Cross Weights" (or the diagonal sum weights). Back to the shop and a quick 1/2 turn of the left rear and right front spring perches to lessen the pressure these were exerting. Once more across the scales showed that I was now within 20# on the diagonal sum weights. Since the County doesn't need any more accuracy when weighing trucks filled with salt, that was as close as I could get.
After years of driving ancient English roadsters and newer "showroom stock" cars the ease of making all the adjustments that I've done to this car since I bought it 2003 has been a certain pleasure. It responds appropriately to input and is very "adjustable."
I think I'm content with the handling with the current 500F/400R combination. Many of the racers have gone to much heavier rates, closer to what an autocrosser might desire. I can't fault their logic as many of these same people are running at the front of their respective groups. My experience is with cars of "vintage" character, however, and now the FFR Cobra feels right to me. I do drive mine on the street, so these lighter spring rates are kinder to my old carcass, too.
Other info:
Driver weight = 200#
Car weight = 2540 w/driver & full 22gal. tank
Cross Weights - LF-RR = 1260#, RF-LR = 1280#
Tires (street) = 245-45/17 Hankook "Ventus"
Tires (vintage racing) = 225-60/15 Hoosier TD
Steering rack = standard location (no Ackerman mod)
The car tracks essentially equally in both left and right hand turns.
Best regards,
Tom
When I first got the car I'd read the little aluminum tags on the springs to see what they were. I thought I remembered the fronts being 500 and the rears being 350s. Over the last season I have brought the car up to speed in various events at various tracks and was generally pleased with the handling in the larger, faster turns, but the the car had significant "push" in the slower corners.
Choices were to attack the slow corners more slowly or do something to lessen the push. I chose to increase rear spring rate. (Note: the Spec. Challenge cars don't have either front or rear anti-sway bars. You do it all with spring rates) I didn't want to sacrifice the fine high speed stability with the change, so decided to bump up the rear rate by 50# to 400 a side. This was enough below the fronts' rate to seem logical and still a significant enough increase to be meaningful for the car's feel.
Well, the 400s arrived from FFR quickly and it was a pleasure to find that a spring swap was such an easy job. Maybe 25 minutes a side including jacking the car and removing and replacing the wheels. That's the kind of project that I like!
Well, checking the bottoms of the old springs turned out to be an education in CRS disease. The rears were 300#, not the 350s that I had "remembered." Hmmmm, well, how's this more abrupt 100 pound rate change going to affect my handling when I expected to only massage it by 50#?
I'm delighted to say this is where I wanted it to be. If the old springs had been what I had thought, probably the 50# adjustment wouldn't have been enough. As it turns out, this is just what the PUSH Doctor needed to cure the patient. I've not sacrificed any of the higher speed stability in carossels and such but the car's turn-in and balance is far better in the tighter corners. The car responds much better to throttle input as well.
Here's what impressed me. It was easy to change the springs. I'd already done frame leveling, etc. before, so that wasn't hard to repeat with the new springs. The change was meaningful and "textbook" in response to what I wanted to change.
After the change and resetting ride height and leveling the car, I then took it to the county scales (+or- 20# accuracy!) and weighed front and rear axles, left and right sides and then each corner with me in the car. I found that there was about 60# or so difference in "Cross Weights" (or the diagonal sum weights). Back to the shop and a quick 1/2 turn of the left rear and right front spring perches to lessen the pressure these were exerting. Once more across the scales showed that I was now within 20# on the diagonal sum weights. Since the County doesn't need any more accuracy when weighing trucks filled with salt, that was as close as I could get.
After years of driving ancient English roadsters and newer "showroom stock" cars the ease of making all the adjustments that I've done to this car since I bought it 2003 has been a certain pleasure. It responds appropriately to input and is very "adjustable."
I think I'm content with the handling with the current 500F/400R combination. Many of the racers have gone to much heavier rates, closer to what an autocrosser might desire. I can't fault their logic as many of these same people are running at the front of their respective groups. My experience is with cars of "vintage" character, however, and now the FFR Cobra feels right to me. I do drive mine on the street, so these lighter spring rates are kinder to my old carcass, too.
Other info:
Driver weight = 200#
Car weight = 2540 w/driver & full 22gal. tank
Cross Weights - LF-RR = 1260#, RF-LR = 1280#
Tires (street) = 245-45/17 Hankook "Ventus"
Tires (vintage racing) = 225-60/15 Hoosier TD
Steering rack = standard location (no Ackerman mod)
The car tracks essentially equally in both left and right hand turns.
Best regards,
Tom
Port Washington, WI 53074
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