I've been wondering lately about how practical/manageable a spool would be on a powerful MR car like the GT40. Now I know what a spool is and what a spool does. I know that it makes parking-speed maneuvers a pain, and that it acts as a yaw damper and induces corner-entry understeer, but I wanted to hear your first-hand experiences with a spool. It would also be interesting to discuss if and how one can tune out its undesirable handling effects, or if necessitates a different driving style. Finally would you say that really high power/weight ratios, on the order of 600bhp/ton, justify using a spool?
I used a locked (welded) diff one time as a budget racing solution and I had no problem under power but lifting off suddenly in turns (if you had to in an emergency) the stability became unpredictable at best and unsettled the chassis in a major way. That was my one experience of it and I never repeated it or wanted to either.....
A Detroit Locker gave a similar experience and took some getting used to!
Mini spools and spools have one problem in street cars as you turn corners one tire turns more that the other. This results in one tire slipping which causes excessive tire wear. In oval track racing cars this is over come by running stagged tire diameters (take a dixie cup and lay it on its side and roll it The cup will roll in a circle) I had a 1969 GTO I used to drive on the street and drag race the car felt very twitchy on decelleration kind of scary at 130mph. I have welded spider gears nothing worse than being on the pole and spinning out because they let go and 15 cars coming straight at you. That will make you pucker up the seat cover a bit.
__________________ Speed is never a question of how Fast you want to go, but how much you want to spend to go Fast.
With the rear weight bias of the 40 its going to push/undesteer like a pig on slow corners, and take a brave/stupid driver to get the best out of it in faster stuff. Aussie V8s & NZ V8's use spools, but that is from a control/rules point of view to try and keep cars similar in performance. They make the car a pain to move in the W/shop, wheel dollies & flat floor are a must.
My preference is Tru-Trac/Quaife/DPI screw gear types- simple-consistent-tough.
I think if you alter your driving technique to suit it would generally be OK. although I feel there is a risk of getting caught out in tight corners if for some unexpected reason you can't get weight transfer forward on turn in. Theres a lot of discussion on this thread Spools or welded diffs on track cars
Cheers,
__________________ Russ
° Scratchbuild. Spaceframe Mk1 wide body. Dry sumped, forged, 351W. LSD930. 10's & 14's.
Most parts now sourced. Body 80% done. Chassis, rollcage 95% finished. Suspension 70% built. Engine starting to build, and trans in a million pieces.
I had to resort to using a locked differential for one race in my SCCA American Sedan Camaro when I did not have time to rebuild a third member (9" Ford). All I'll tell you is that any driver who isn't religeous at the start of a race on a high speed track like Brainerd International or Road America / Atlanta - WILL have a lot of religeon by the close of the race...
I think I had to replace not only my nomex but the steering wheel as well!
I have video of the white line on the bottom of Turn-1 at BIR as I entered the corner at 160MPH. That while line was snaking around like a ribbon tied to a fan..
I vowed right then and there that I would *never* drive a locked diff car again and that if given the choice I would chose an open diff over locked..
That was 10 years ago and I still fel the same way....
__________________ Regards - Randy
GT40 Replica G50-331-Weber IDAs
My build site: http://www.GT-Forty.com
Effect of a spool/locked-diff on handling? 
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