Tim Pruitt

Car: 88 924S
Car Weight with Driver: NASA - 2760#, PCA GT4S - 2600#
Tires: Hoosier R3S05, 225-50-16, Front and Rear
Brakes: Stock 924S Rotors with Hawk Blue Pads
Suspension, Front: Koni Sport Shocks, 350# Hypercoil Springs
Suspension, Rear: Koni Sports, 30mm Hollow Torsion Bars
Car Use: Race Only

Could I improve braking efficiency by raising spring rate in front and rear e..g. LEDA Coilover Shocks gas reservior double adjustables with 550#/500# Springs?

Could I further improve braking with Turbo Rotors and Calipers?

Could I further improve braking with fiberglass fenders and wider tires in front and rear (equal to 944 sizes)?

If you had a budget of $5000, where would you spend your money?

MarkM

Tim,

Invest your 5 grand in a paint booth. I didn't think you had to use your brakes anyway.

Looking forward to watching you next week!

JCP911S

Wider tires will give you more grip and improve stopping distance.

Firmer springs will reduce the time it takes weight to shift in transients. It will not improve braking per se, but will allow you to get on and off the brakes quicker so it will improve overall lap times.

If your brakes are not overheating and you can lock up the tires with your current set-up, changing brakes really won't make quantitiative improvement... tires are the limititng factor.

Money spent improving handling and reducing weight will give you the biggest bang for the buck.

38D

Yep

Tim Pruitt

Mark,

Ran my fastest lap ever at Road Atlanta this past weekend duirng 944Cup qualifying (1:45.475). Not bad for a 924S on the suspension noted above. BTW I spent enough $$$ on paint and bondo in 2005. Do not want to repeat that again. We will find out if I can beat that lap time when I get down to GT4S weight during PCA race in 2 weeks. CU there.

Matt Marks

Seems to me that decreasing front dive *should* allow for more rear braking force to be used provided that you can set enough rear brake bias and/or run aggressive enough pads to take advantage of this. I would also assume that you would have to be able to lock your rear brakes with your current setup to take get any increased braking performance from reduced dive.

Agree with all of the above on spending on the suspension - much more bang for your buck.

RedlineMan

Hey;

You will indeed get better braking with better suspension. Think of the springs pushing the tires into the pavement and you'll see why. The bigger springs will push harder. More front bite (to a point), less weight shift, dial in more rear brake. It's a winner all around if you don't go overboard on rates.

Double adjust is overkill (considering where you are now), but everything else looks right to me. Those rates are about what I recommend to my customers when they purchase Ledas. Save the money and go with oil only for now (they work just fine), but get the gas ports installed so you can update if you want. I almost demand my customers do that. You're silly not to.

If you can do what you are doing now with that "wimpy" suspension, your competition is in trouble, post purchase!

Tim Pruitt

John,

I know the gas reservoir double adjustable is probably overboard but, I do not want to redo anything. Without the reservoirs will I only have adjustment for rebound? Or are the oil shocks double adjustable too?

How hard is it to add the gas reservoirs later?

Thanks for your input,

Robert W. Bausum Jr.

Oh My God! a 1:45 at Road Atlanta in a 924s! It is just sick!

I have sat here for a half of an hour trying to think of something to say.

Arghhhhh.

I have followed Tims progress very closely. He is ready for the Double Adjustables. He can notice the smallest of changes in the car. I think he'll be able to take full advantage of the adjustments available.

Lemming

Agreed

Benton

Tim,
Congrats on the accomplishments. You should come hit the kart track with me sometime... I know you would love it! I'll give you a free ride in my kart.

ckuhtz

Especially since that's what you drive in a turbo. Congrats, Tim, very nice work indeed.

j/k Bob. Did you fix the list yet?

Tim, few years back I did a good bit of looking into suspension dynamics (I'm sure Bob remembers the antics ), and what I walked away with is that what substantially stiffening springs does seem to act as follows:

On smooth surface, it reduces impact weight transfer (weight transfer itself cannot be reduced without shedding weight itself, it's a function of acceleration, length of lever and mass at the end of the lever), suspension travel is reduced (presuming matched dampers), therefore geometry should settle more immediately from the driver's point of view. -> improved laptimes, if for no other reason than driver confidence as the car goes stable faster. On soft suspension, load transfer can be very unsettling. Depending on track, this can also work against you if the track is particularly rough (wavy surface for instance, where you want compliance), and in fact you want compliant suspension (which is more than just spring rate).

And then there's driver preference, as changing the compliance or non-compliance of the suspension will alter dynamics of over vs understeer based on driving style. Cause, people are quick with loading up spring rate all the way around, bias towards front, bias towards back.

After talking to a lot of people and doing a lot of theoretical looking around, that's what I walked away with: It's all about the nut behind the wheel, and whatever you can do to make her/him more comfortable behind said wheel is what will make the car fast.

Or those are my $.02. Let the bigotry begin ;-)..

(Wow. After all these years on rennlist, I'm just now finally actually posting on rennlist web forums. ;-)

RedlineMan

Tim;

Your mates here might be painting you as a very deliberate guy. Someone who likes to wrap his head around a scenario and understand it fully. That could be an impression anyway. Anyone who can take a meager setup like you have now and exploit it to the extent you have is either Savant, or the person I described above.

In your case, double adjust may not be overkill in terms of your ability to exploit it. Yet, it will throw significant curves into your M/O if you are indeed that measured methodical person I surmized you could be. D/A enters a lot more variables into your tuning. It is an exceptionally powerful tool, but only to one who can wrap his brain around the complexities it brings with it as well.

If you are the incremental type, go with my suggestion. You can very easily upgrade to remote reservoir and/or D/A at any time thereafter... IF you get the gas ports.

If you like a challenge, then go for it all!

Tim Pruitt

John,

I'm a Mechanical Engineer. Enough said .

Thanks everyone for the feedback to date.

JoeMag

Here's kind of an interesting analysis I came by in a book on chassis engineering. It was comparing weight reductions and end of back straight speed for a car the weighed 3000lbs with engine that has 300ft lbs of torque. ...obviously short back straight, and there's lots of assumptoins here, but is shows the much more significant effects of reducing rotating mass.

...the 15lb reduction for drivetrain was assumed to be 13" dia steel disk.