Hi,

I'm learning how to setup my DC2R and have done a great deal of research / schooling into the engineering/physics reasoning behind the practice. I now understand what is required to make my car handle well, however without benchmark data / testing I need some input from you guys...

I know on Mac Strut cars body roll has a greater effect on dynamic camber and lateral roll centre movement etc and thus the idea is to minimise body roll to around 1.5 degrees. Now, on a wishbone setup like in the DC2R I understand that the suspension movement is much more independant and has less of an impact on the dynamic camber / bump steer etc ... (Please correct or give input!)

Now -- SO final question is, what would the desired optimum total roll rate be for a DC2R? Is flatter always better or does minimal roll rate reduce mechanical grip?

Thanks!!!

 

0°

 

to tackle some different things....

is this a daily driver or track car??
if a track car is it on smooth surfaces? or rough like some autox venues?
if you are tracking then how do you like the car to handle??

what is you optimum ride height??

are you using aero devices??

i guess i could go on forever. i just believe that there are going to be various different optimums for different situations...maybe im thinking to openly...

 

come on. we are not discussing soap box derby cars.

back on topic..sorry.

 

The car is daily driven but I am prepared to have little compromise as the priority is for it to be 'quick' around a track. It is slowly being converted to a weekend only road registered track car.

I am currently running at max height on the street for clearance (Toda DA) however I am prepared to turn up to Sprint events 2 hours early to adjust everything to spec as required for track use. i.e. Once I know my optimum setting I can somewhat return to those specs when required.

I also understand that you need some roll so as to not overload the outside tyres on turn-in.. My question is what (From your experience) is ideal performance level on a DC2R.. ?

Aero -- I am currently working on a underbody kit (5 piece for ease of access to underbody parts) and eventually want to source a good aero front bar / splitter combo (P1 looks pretty good!)

I'm running 10kg/8kg springs which seem to be ok, although at this spring rate I want to increase the stock rear sway bar.. Again, I need to do the maths here but it all stems from the desired total roll rate..

Generally the tracks are fairly smooth, and roads are satisfactory (ie not too many potholes etc)..

With regards to ride height (for the track) again, I need to work out some angles etc but I understand the idea is to get the roll axis close to the CG?? Hmm .. So much to learn, but I am learning quickly!

 

ok. lets take a step backwards.

do you track the car or have you?? and no canyon/mountain/twisties doesnt count. lol.

 

Really it depends. And most of it depends on tires, and grip levels of the track.

(assuming this is a track car)


A good starting point would be 800lbs/in front springs with the OEM front sway bar 1000lbs/in rear springs with the 22mm rear bar (or 25 mugen if you can find one).

Again if this is a street car then completely disregard

 

so far this thread is moving down the right track. the tire you use, desired use and the really big one here: DRIVER PREFERENCE is huge. desired use is also a very broad term. the track or street you're on has a major impact on the ride height and rate you run. for example if you were going to time a 3 mile stretch of old country back road that had multiple waves, elevation changes and generally rough terrain you will be faster using something in the 350-500lb range than the 700-1000 rates you might use on a smooth race track with R compounds.

 

both of these guys kind of got to what i was waiting on your response to say depending on your response.

i know both of these guys did not give you a certain degree of roll you were looking for. but i dont know if a certain degree of roll is the correct answer at this point.(i am assuming from you content you have yet been on the track..but on the other hand it does seem you have done your homework.)

ok to some of what you discussed in your first post..lets just double your 1.5 for mccrapson and make the "correct roll rate" for double wishbone 3. also remember that your pivot points are determined from the factory unlike most "true" racecars where all geometry is made up from scratch. ok back on task but with that said the only arm lengths you can change with off the shelf product is adjustable camber arms. effectively you can make those arm shorter or longer to change the camber curve....ok this is off on a tangent a bit but just kind of digging in a bit for you to paint the full picture.

but slammed_hatch and drivesideways can attest. just because "3" is "correct" it might not be correct for you. if you have not tracked but plan to then wait and ride around with some buddies. or drive their cars and ask questions. go to track events and talk to drivers see what they say. i know you do your research so go ahead and keep digging. make your choices through that and get your setup started. once you hit the track you can start tuning your suspension from there.

ps. also to once you get your aero started. assuming it isnt being wind tunnel tested we will assume that it is efficient enough. but you will be able to take off some of the spring/roll rate because the downforce will help "neutralize" your roll.

hope this helps to shed some light. sorry for tangents and fragment sentences..i am kind of paying attention to other stuff at the moment. lol.

 

As an engineering major, I love theory but let's be realistic here. Regardless of the setting you are looking for, the real question is do you have a way to actually measure if you hit your target or not? Without some really fancy equipment, the answer is likely no.

There are so many freaking variables when you're on track it's not even funny so don't kid yourself that you'll ever find the right setup. Setup is all about compromises! Even on the same track on the same day you'll never have the optimal setting because the environment and your tires are constantly changing. Even F1 cars haven't figured out a way to do zero camber during braking and then add negative camber and toe out during turning (that would be bad *** though!).

If you're looking to get the most grip, get yourself a $100 tire pyrometer and a stop watch and start doing some testing. All the theory in the world will never be as fast as the real world and experience.

My $0.02.

 

Hi and thanks for the responses.

Yes I have tracked the car, about 5 times now.. Unfortunately work commitments have prevented me from more track experience at this stage however I do race go karts.. I have spent considerable time developing the car in the last 12 months, getting it ready for a serious track session .. The car however will become a track only/rare weekend car within the next 12 months, so I am preparing it myself and keeping it road legal (only restriction in the event other than capacity).. I was hoping from experience there was a range of roll rate or conversely a range that doesn't work I'd be interested .. I have calculated the roll rate for my current setup (in a perfect world) and want to see, on paper, what I can do to improve the setup.

Oh, and I figure from stewing for a while, I may as well remove the front sway bar and increase the spring stiffness a little .. I guess the sway bar doesn't really seem to serve a purpose in a race car that can tolerate higher spring rates? And I would think that the indepence of suspension movement would assist with keeping tires in contact with the bitumen?

And yes I have a pyrometer which I will use when I get to the track, however I am looking to start with a good baseline to work from since I have limited opportunities to get to the track..

Hope that explains a bit -- thanks again for you help.

 

you are treading down a long painful but extremely satisfying road my friend!

You have obviously done a lot of research and learning, but in the world of vehicle dynamics there is no perfect and exact answer to anything. There is rules of thumbs, but nothing set in stone. that is what makes it so satisying when you find something that works for you.

I only have a few minutes, but I just want you to remember, absolutley everything is based off of the tires. Tires, tires, tires, tires, tires, you get the point lol.

So you need to ask yourself, are your tires going to be good quality street tires? something like the dunlop Z1 or the potenza re11's etc. or are you going with slicks?

Tires are the biggest part in your mechanical grip. So your whole suspension set up will be dicated on the type of tire you are using and how much lateral load they can handle. In reality everything should be based of off tire data, but good luck ever getting that (seriously, it is a tighter kept secret than some of the government secrets).

Anyways, in regard to roll rate and such. The best way to attack cornering and lateral load transfer and roll is to think about a desired roll gradient you want. This is where you pick from the rules of the thumbs. The higher the roll gradient the more "grip" (for a lack of a better word) you will have, the lower the number the more response you will have. The way to be fast around a race track you want as low of a number as your tires, and you as a driver, can handle. The roll gradient can range anywhere from .1 - 8+ deg/g to give you some perspective, around 7 is what your common stock grocery getter and family vans are at. 1 is what your full slicks, purpose built, leightweight race cars are. The full areo cars (think F1 and Prototype) is even lower, in the .125 range. 3 is about where your very high performance cars are at. So it is all to you to deside what you think is good for your ability and tires. If you are using quality street tires and you are somewhat new in the driving/racing scene I would shoot for around 3 deg/g to start.

Once you have your desired roll gradient you can work back and forth with roll rates, spring rates, and the such until you get close to your desire roll gradient.

Hope that helps you out man.

edit:

I forgot to add, even if this is going to be a weekend warrior car and still see city streets, you really dont want to be messing with raising and lowering the car a hole lot. What you need to do is get your desired ride height set, get the car corner balanced and aligned and dont touch it. You can play with alignment and the such, but you really dont want to deviate from the ride height as you will mess up the whole corner balance, and there goes everything you worked so hard towards. Just my $.02

 

Again the answer is "it depends"...

Some engineers/drivers love front sway bars, others hate them.

Both can be fast.

But to say what you said simply isn't true.


It seems to me that, in a long winded way agree with Tage, many "brain types" get wrapped up in theory and can never walk away from it. This just isn't the way things work. Mostly because we are driving tin can **** boxes that have a ton of flex, that would take some serious $$ to truly figure out, and because a HUMAN is behind the wheel. The human doesn't do everything perfect. So that is why, IMO, theory can only get you so far.

This blog isn't kept as up to date as Buddy intended but still offers a wealth of knowledge, http://buddyfey.blogspot.com/

Setup on race cars is what this guy does for a living, hes out at the track getting paid to setup some serious cars. He knows what he is talking about.

The roll question.. Typically you want around 1 to 2 degrees roll, again that is just a general guide line, it doesn't always hold true.

 

Thanks again guys.

Sorry assumed you would realise I am talking semi-slicks (A048R & R888) which I understand have a capability of approx. 1.1g ... Yep, understand its all around the tyres, but based off the tires I needed to work out a desired roll rate ..

The advice of between 1 - 3 degrees is useful thanks. I just want to work out in an ideal world without chassis flex etc what the current rate of roll is. I really had no idea what a normal vehicle was and what a race vehicle shoots for.. I understand also the the roll centre may need adjustment to reduce body roll at lower ride heights, but much confusion here, I need to do some more reading...

I guess my main purpose of this is to gain a solid understanding of why rather than adjust things blind like an idiot lol -- This exercise helps me learn I guess.

Thanks for the support -- Really appreciated. I'm just another bloke out there looking to learn and develop his knowledge for the passion And unlike other items, tuning the setup of the car is essentially free other than springs.. With so much time found/lost in vehicle setup, I'm focussing on the dynamics now.

 

p.s. Awesome link mate -- Thanks so much.

 

awesome. well like i think slammed_hatch said. more roll equals more grip and less roll angle equals stability(broadend terms with all things being equal. lol). but with that stated and like you said before...you are going to be running aero. so now you can take away some of that "static" or "supposed to" roll angle and let the aero piece help stabilize your car in a dynamic state.