relation between horsepower and sway bars

I was just reading Dal motorsports NSX notes page, and I quote "with a high HP NSX get your hands on the biggest front bar you can find, because it is not big enough". The thickest front bar I know of is the Dali 1.25" trophy bar, and DAL said that realtime racing told him that is not enough and they went with a 1.75"!!!

That is just a massive front bar, but this is the second time I have heard higher HP wants a larger front bar on a mid engine car. I don't quite understand the relationship.

Also, they ran NO rear bar... Dali sells rear bars as thick as the front ones. Anyone ever use these? Billy advised me to go to a 1" track and Zanardi rear, so that is what I ordered but I am still trying to understand these two things: the relationship of HP to sway bars, and the rationale behind such a massive front bar and no rear bar. Is this mainly for traction on corner exit?

Which one inch bar did u go with?? Dali? Or is there another manufacture?

I don't know the answer to your question, but the Realtime car did not use a rear sway bar.

Dave, I think you should invest in the Milliken Book: Race Car Vehicle Dynamics. Would be a good resource to have on your shelf and might be able to answer a lot of your questions. Most of the book might go over your head but after reading a section 4-5X, some concepts tend to sink in (atleast for me they do).

I am in the process building a bladed ARB for the frt & rear. you can check my website below, its not ready for prime time as its lacking price and pictures which will come in a few weeks but most of the info is there.

Dave's question is not a quick direct answer so either read the Milliken book(for engineers) or Carroll Smith's(for racers alike), the theory/physics are the same to better yourself. You will get it after reading it a few times like Billy said.

the common sway bar 1.0 on the market has been around for over 50yr but many top class race cars use bladed type ARB 2.0 to turn/trim the car. There must be good reasons.

It depends on your understanding of the chassis dynamics, how well you know the suspension system more than just dampers and springs of your car, your sensitivity, your driving style, track condition, etc. and this is one valuable turning tool to help you lower your lap time.

Dal's 1.75/2.0" frt bar require major surgery on the car so its not quite doable for most of us here. There are many variables to determine the size of the bar or not using a bar. I was told it cost Rob around $1300-1400 for one bar since its a one-off but mine will be much lower than that since I committed to make 25 to lower the cost. It takes a lot more effort to build these bars not just bend and drill like the v.1.0.

There are ARB 3.0 on the market but that is most on supercars like the MP4 with electronics and hydraulics set up.

BTW, Dali Racing is disappearing......slowly

Liftnot good to hear you are working on something. Billy I will look for the book.

Back a long time ago, I found a sheet that listed all the sway bar wall thicknesses and diameters. It was not what is in the wiki or what is on dalis site. It was more thorough with oem part numbers. Turned out, the 2004-2005 cars had a thicker rear bar... Equivalent to a Zanardi bar. In fact the part number may have been the same. I clearly remember reading this, although I am not 100% it was accurate. Can anyone verify this?

TURBO2GO said:

Liftnot good to hear you are working on something. Billy I will look for the book.

Back a long time ago, I found a sheet that listed all the sway bar wall thicknesses and diameters. It was not what is in the wiki or what is on dalis site. It was more thorough with oem part numbers. Turned out, the 2004-2005 cars had a thicker rear bar... Equivalent to a Zanardi bar. In fact the part number may have been the same. I clearly remember reading this, although I am not 100% it was accurate. Can anyone verify this?

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I don't know the thickness difference, but they have different part numbers.

Zanardi = 52300-SL0-J01
02-05 = 52300-SL0-611

Gundan thanks, do the 02-03 show a different part number than 04-05?

Don't go too big. You won't be able to do this

TURBO2GO said:

Gundan thanks, do the 02-03 show a different part number than 04-05?

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02, 03, 04, 05 are all = 52300-SL0-611

RYU said:

Don't go too big. You won't be able to do this

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True... True...

GUNDAN323 said:

02, 03, 04, 05 are all = 52300-SL0-611

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I See. OK thanks.

When Cody built the infamous 920whp LoveFab "shop" car, he went with a larger (sorry, don't know the size) RM Racing front bar, and no rear bar.

We're still running this setup in it's turned-down-to-600whp state, with no complaints.

Brian

I think having to rear bar increases rear traction in corners by keeping the wheels more independent and planted.

TURBO2GO said:

I think having to rear bar increases rear traction in corners by keeping the wheels more independent and planted.

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I don't think that's quite right, unless by "to" you meant really meant to put "no". I think of removing the rear bar as almost like having the softest possible sway bar setting.

A softer rear sway bar = less oversteer.

I meant NO. No rear bar. I'm guessing it helps plant the tire better on corner exit. It's weird... You get Dali that ran a huge rear bar and then Dal that ran no rear bar, and the springs seemed similar. I haven't got that book yet I'm sure there's some explanation in there. There is a small side benefit to no rear bar. Unsprung weight weight reduction. Dal's setup was so extreme front and rear. A 2" bar eventually up front. TWO!!! and still no rear bar sounds like a recipie for the biggest understeering NSX ever. But apparently it worked.

TURBO2GO said:

no rear bar sounds like a recipie for the biggest understeering NSX ever. But apparently it worked.

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Trust me, big power cures understeer ;-P

Brian

and this also depends on driver preference. turbo2go i think that sway bar size greatly depends on your diving style and skill level.

I would pay more attention to how PD set up his car Than dali......the candycane handled like crap:wink:

I always thought that the higher hp cars that ran w/o a rear sway wanted the rear as soft as possible. And then would manipulate the throttle to get the car to turn.

Wrong?

to a degree having a thick front and no rear bar is a setup for understeer...so yes driving style has to be adjusted ,but you can feel more confident in the rear of the car at the apex with that setup.Now most of PD's races were short sprint type formats and his nsx good old #42 was very competitive against some big names and budgets.

Is there anyone that DOES run a big bar out back like a Dali 1"? It sounds like almost everyone here runs a small or no rear bar.

Yeah, I don't think anyone that has tried a large bar like that in the rear on an NSX kept it on very long - I'm sure the book Mr. Johnson recommends will mention something about the fact that sway bars - the bigger you go, are DECREASING traction AT THE TIRE from turn-in to exit...that is why so many guys run the large front bar and OEM rear as they don't like the NSX's inherent tendency to rotate sharply on turn-in - they get near the limit on entry speed in a fast corner and as they turn in they're met with a low polar moment of inertia specific to mid engine cars (40/60 weight distribution) and the "ass end hangs out" before they even get back on to the throttle. The other common scenario for the perceived need for a bigger front bar is past turn-in, adding throttle, and your met with wheelspin - power on oversteer in this case. If you make the rear end as compliant as possible, theoretically you will have the most traction at the rear tire and less at the front. I think driving style is a major influence on your choice of sway bar - as in what are you comfortable with, what is just barely manageable, and what is actually faster on the lap timer?

So you can see why theoretically you wouldn't want a larger rear bar? It would take grip away from the rear tires from turn-in to exit which this car does not need. When I bought my car it had Dali streets front and rear (7/8") and I simply did not like the way the car "felt" regardless of hole positions. When I installed a set of 91 OEM bars before my track day last weekend, I noticed on the sway bar bushings it read 18.5mm front and 17.5mm rear, so there is a slight front bias in stiffness right from the factory, mated to an original spring rate bias of about 50lb.s stiffer n the rear on a 91 (I have KW V3's at 347/347lb. currently). My opinion is its a balance issue, fine tuning of the balance, and its going to change maybe a little or a lot depending on different track layouts, tire sizes and compounds, power adders, and constantly adapting to the car as mentioned above. I think its regarded as a "safe" setup for an NSX to have the 1" bar up front and something soft out back as its going to PROMOTE understeer from the moment you turn the steering wheel in.

I'm really comfortable at the moment with the OEM bars and do not plan on switching them. I'm in the process of getting stiffer springs for the KW's and I'm thinking of emulating the 91 spring rate bias of a 50lb stiffer spring in the rear. Springs don't physically take traction away at the tire like a sway bar (maybe if you go to 1000lb.s or something?) they simply change the body roll characteristics which is a product of the weight distribution of the car - where is most of the weight and what effect will that have under braking, turning, and accelerating? There again I have found alot of guys running the harder front spring with the harder front bar - under braking the nose will dive less and under acceleration the tail will squat more theoretically aiding in more compliance from the rear of the car, but go too far and your just going to have wholesale understeer everywhere which is not what these cars should handle like IMHO.

SlipAngle79 said:

I'm really comfortable at the moment with the OEM bars and do not plan on switching them. I'm in the process of getting stiffer springs for the KW's and I'm thinking of emulating the 91 spring rate bias of a 50lb stiffer spring in the rear. Springs don't physically take traction away at the tire like a sway bar (maybe if you go to 1000lb.s or something?) they simply change the body roll characteristics which is a product of the weight distribution of the car - where is most of the weight and what effect will that have under braking, turning, and accelerating? There again I have found alot of guys running the harder front spring with the harder front bar - under braking the nose will dive less and under acceleration the tail will squat more theoretically aiding in more compliance from the rear of the car, but go too far and your just going to have wholesale understeer everywhere which is not what these cars should handle like IMHO.

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Swaybars are far more effective at reducing body roll than springs alone. Also heavier rear springs reduces how much the rear travels/squats under acceleration and can reduce forward traction. It's all a very involved and complex system. The whole goal is to get your F-R roll distribution correct for balance, and control the tire's movement under pitch, heave, and roll.

stuntman said:

Swaybars are far more effective at reducing body roll than springs alone. Also heavier rear springs reduces how much the rear travels/squats under acceleration and can reduce forward traction. It's all a very involved and complex system. The whole goal is to get your F-R roll distribution correct for balance, and control the tire's movement under pitch, heave, and roll.

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Thank you Billy. So a harder front spring OR a harder front bar if you had to choose? I know, each car is modified and driven differently. I'm anticipating understeer from 80mph up with JUST the rear wing. I figure slightly more rear spring will neutralize this but I could be wrong, and I also could add a front splitter but that will certainly take me out of TTB class for time trials because of points...kind of lame anyway as I think I will just move up a class and build the car the way I want for fun. I have to say my car feels good right now but the balance is oversteer at the limit. If I left it how it is now, OEM sways and 347/347 then add the wing, I wonder if it won't be just right?

Not that I am a pro but IMO your springs are on the soft side. Springs do so much more than control lean... Dive and squat are under spring control only.

I will also say this although Billy may have more to add. When talking about suspension setup and improvements everyone always talks about sway bars and spring rates, and no one ever addresses the dampers. We act as if $2K is the limit of what you'd want to spend and that anything higher is sort of a waste or beyond what the average person would want. But I do have some experience in this area with both $10,000 KW's and $9000 JRZ's. Top quality dampers allow higher spring rates at the same comfort levels. I am at Midnight Raven's house once a week, I am getting a ride in his car or driving it on KW V3's with 347's once a week. My car is a targa and not as stiff, on 800/550.. more than double the rates up front and I can tell you: My car rides better. Nevermind the handling. You can feel it. The car is a bit more tight and buttoned down. It isn't in the sway bar nor in the springs, it is in the dampers.