How many seconds a lap for suspension mods?

[dtfastbear]

I've got an '86 Carrera cab that I've been doing some track work with over the last year. The only suspension related mods I've got are Bilstein sport shocks, 15x7 & 8 Fuchs with Kumho Victoracers and reasonably aggressive negative camber, corner balance and lowering.

My question is, how much do you gain on the track by doing additional suspension mods? How much time will be gained by changing out the sway bars for larger and/or adjustables? How much of a difference will larger torsion bars make?

Since I've never been through the entire evolution with a car, I'm wondering if those who have done it one or two steps at a time can share their experience? For any given track, how many seconds did you pick up with each step along the way?

Thanks in advance for any experience you can share.

Dean

[Victor]

Hi Dean,

My buddy and I both have 3.2 Carrera's. My suspension is standard with Koni Adjustables. His has bilstein sports, is lowered, has stiffer bars and competition pads.

He will dispute this to his bitter end (April 13th Track Challenge) but we WHERE both in roughly the same time bracket. I have since added semi R rated rubber and this has made a MASSIVE difference to the handling. The car now sticks to the road like on rails, but I am yet to confirm how this transfers to lap times. The other thing I have learnt is that a faster car does not make a faster driver. For example, the new shockers did not make my lap times go down.

[dtfastbear]

Thanks for the input, Victor. I hear you about the R rubber. I totally understand that tires make a bigger difference than just about everything else. I've just made the move from Kumhos to Michelin Pilot Sport Cup tires, and while I know they are much better track tires than the Kumhos, I don't have enough time learning their handling characteristics to be much faster on them yet. I've only gone a fraction second faster than I was going previously (2:12.7 down from 2:13.5 CCW at Thunderhill - I know you're in australia, so this is probably meaningless ) I think I'll eventually get more out of the tires.

That's why I'm looking for someone who had some good baseline experience with laptimes, who then slowly made changes to their own car and saw quantifiable differences, positive or negative.

Comparing cars with different mods with different drivers is interesting, but I believe driver ability can out-weigh by a large margin most suspension modifications.

Thanks again for the input!

Dean

[makaio]

Hopelfully Mike McKee from Davis, CA will chime in. He runs a SC that has had the supsension mods done (bigger t-bars, shocks, etc...). I know he started with a pretty much stock car, and was pretty consistant, then upgraded the suspension.

I have only met him once, but I can say that he can drive, and smooth too.

[cstreit]

THis also depends on how you use it.

You might, for instance, upgrade to coil-overs, but if your curent torsion bars aren't really being overtaxed trhough movement, weight,e tc.. than they won't improve your times...

It also depends on the track, on a long high speed track suspension won't have as much of an impact as on a shorter tight one...

[gumba]

Hi Dean,
I would suggest the 22mm f&r adjustable sway bar, (23 mm Smart Racing if can can afford them) and having Smart Racing re-valve your shocks. We noticed about a 2 sec. improvement. I usually change my sway bar settings at every track and as the tires wear. The Michelins will probably be 1-2 sec. faster than the Kumhos. Not necessarily accumulative. Torsion bars 22 front and 28-30 mm rears is pretty common. I believe yours biggest improvements will come from lots of seat time.
'73 targa track/street 3.2
'73 S coupe street 2.4
'68 crewcab 2.4

[APKhaos]

I'm with Chris & Gumba.
How much longer is your average drive with your newest Callaway driver?
My car is still several seconds/lap faster than me, AND my darn golfclubs can still play 5 or 6 strokes better than I can.

Seat time, seat time, seat time. Making the driver better is more fun and cheaper.

[Jack Olsen]

If you want an instant kick in the pants, invest in wider wheels. 8's and 10's with 225's and 275's will make a huge difference.

Stiffer suspension pieces will help too, of course.

[dtfastbear]

Hey guys, thanks for all the tips. Just to clarify, I'm not thinking about doing any mods to my car to buy any time on the track... In fact, I'm not considering doing any mods at all! I'm happy with the car the way it is. All I'm focused on is improving my driving. I agree 100% with you guys! I bought the Michelins instead of the Kumhos because they'll last longer. My next set is going to be Toyos unless I really do get amazing wear from the Michelins.

I'm just curious how much the potential of the car is raised by these mods once one IS driving the car up to the potential of the stock suspension. I'm wondering how much I'm giving away to other cars in my class because all of these mods are allowed, but I haven't and won't be making them.

Thanks again for taking the time to respond!

Dean

[jluetjen]

Jack -- You let me down. I was going to point to your recent thread to support the conclusion that most bolt on mod's will have far less of an affect then what you "belt in".

If dtfastbear is concerned about $/second, then the best value can be gained by seat time at the track and maybe a good drivers school. I maintain that changes to car are only meaningful if the driver is consistant enough (+/- .5 seconds a lap) to take advantage of them.

[dtfastbear]

I'm only concerned about how many $/sec I've SAVED by working on my driving, John, not how to spend to go faster

As I said, I'm not looking to buy any time by making mods, I'm just wondering how much the limits of the CAR are raised with these mods, not how much faster I would go...

Thanks,

Dean

[ChrisBennet]

I think a Cab is not as responsive to suspension improvements as a Coupe. At a certain point, a stiffer suspension will just cause the car to flex. I think the biggest improvement I ever made in my car was going to stiffer torsion bars (22f/29r). It just made the car more predictable and easier to drive.
-Chris

[jluetjen]

Dean;
'Sorry -- I didn't mean to sound condenscending. For some reason, I often find it interesting to view the world from a statistical viewpoint (Go figure! ). A couple of observations that may shed some light on your question...

* In the average SCCA Regional race with Spec cars (say SR) with a large field, the spread in lap-times may be 4-5 seconds a lap or more.

* The same scenario in the Run-offs will generally have a tighter distribution (let's say 3-4 seconds) and be centered somewhat higher. So the fastest guy in the regional may still be good enough to be in the top-5 at the Run-off's

* In general, an F1 field is within 2-3 seconds of the pole time. The same applies to CART on a road-course in what are semi-spec. cars.

Now the average mechanical change in suspension may net .5 seconds a lap above an optomised set-up.

Conclusion: The signal to noise ratio of the limits of the car versus the limits of the driver is VERY low. That's the fun of the sport -- some people may feel that changing the shocks is the best improvement, others the wheels. The problem is so complex that the only way to sort it out is to run the race!

[chrisp]

From my persepctive and watching locals at Lime Rock Park (a very handling oriented track);

A stock SC that can do 1:10 will do about a 1:01 or 1:02 with:

8x17, 9x17
Michelin/Hoosier DOT-R
Bilstein custom valved shocks (softer than sport)
23mm front, 31mm rear t-bars
Stiff aftermarket sway bars
All bushing upgrades.
Track alignment
Lowered to about 24"F/23.5"R
Car at class weight limit (2550 +/-)
Full roll cage (signif reduction in lap times)
Race seats/harnesses
Corner balanced
Motor within rules (stock but optimized)
SSI's and back dated exhaust

[ChrisBennet]

John,
I think comparing race cars prepared to the limits of the rules with a 911 street car is a bit of an orange and apples comparison. The street car is going to leave a lot of (handling) speed "on the table".
But I agree that the driver makes the most difference in either case.
-Chris

[dtfastbear]

No offense taken, John! I'm asking these questions because I'm curious, so all the responses have been informative.

A little background as to why I'm asking:

I have a special case in the events I run. I have a European car, and therefore a 0.8 point higher compression ratio than a US car. Given the rules in my local PCA region for autocross and time trial, this one "modification" puts me straight into a class where all sorts of suspension mods (swaybars, camber plates, torsion bars, coil-overs, open wheel sizes, fender flares, etc) and engine mods are legal. I've just got my almost stock car with 15 extra HP (over the US car), so I'm wondering how much time I'm giving away to the cars that've actually MADE these mods.

That's why I'm interested!

Thanks,

Dean

[gumba]

Hi Dean,
KM is a very open class. Aside from suspension mods & engine mods, you have to take into account car weight, trans gearing ect. At TH the KM timerange isabout 2:00 for the fastest and 2:20 + for the slower (less experienced drivers) The lightest cars in KM are around 2100 lbs +/- 50lb. If you figure 10 h.p. p/100 lbs that alone is about a 60 + h.p. over your car. A nicely set up street car w/the suspension changes I mentioned above would make the car 2-4 faster (at TH) over stock.

[tobluforu]

Were neighbors! Do you have a pic of your car? Wondering if I have seen it.

[dtfastbear]

It's an old picture, and the car rarely seems to have the street wheels on it any more (track fuchs instead!) but here it is:



Hey Gumba - I always forget about the weight factor... I know that makes a big difference! My car weighs in around 2950, maybe more with the rollbar in it.

I'm running 2:12's at TH now, and I'm certainly not ashamed of those times, but it sucks to be 10 seconds off the pace in my "class". I just compare my times to the LP guys, which is where the car should be in my opinion.

Thanks!

Dean

[tobluforu]

I've seen you a few times. I'm pretty sure one time you were a few cars back of me going up mt tam a while back. Nice car!