this is more or less a rhetorical question.... Where is the best placement for the weight in a car for it to handle the corners best? on my new roadster, i have the motor set WAY back compared to my other cars is there some mathmatical formula to figue the best engine placement or is it relying on too many other factors? an old friend was telling me its best (for track roadster racing) to try to keep the axle centerlines and crank centerline on somewhat the same plane....so i've been shooting for that... i have 110" wheelbase and the motor set back about 18" from the front axle centerline i was thinking that in this place with the driver...the weight balance will be just forward of the center of the car...I have a heavy banjo rear which creates alot of unsprung weight where the frontend is alot lighter...maybe the larger softer rear tires will help this?... the minimal movement of the suspension im guessing will factor out some of the unsprung weight into the soft tires and have it ride pretty well..... im not going to change things as this is where most parts work out....but it all just got me thinking a little farther then my seat of the pants decision to put it there thanks alot Zach
This question directly relates to my Mallock and my Jasag. The Mallock looks a lot closer to a Roadster, but the Jasag is very similar with more Aero... They both have about a 40:60 weight distribution Front to Rear, same as a Formula Ford, which used the same basic Engine. The Engine, Gearbox, and Diff are offset to the Left ( right Hand Drive, English Cars...) to compensate for the weight of the driver. I still have had passengers in my Mallock, but that threw the balance off ( more bias to the Rear, and to the left ) Still very driveble and fast, but less ideal as without a passenger. And it only weighs about 1000 Pounds, so the weight of a person has more effect... For the street Id probably go closer to 50:50 F:R
in general, most sports type street cars are within 10% of 50/50 distribution. one big thing to keep in mind along the lines of your crankshaft centerline is, the torque tube should be running uphill at least a little so the gear oil doesn't fill the tranny. crankshaft centerline inline with axle centerline makes a torque tube with 0 degrees of angle. none of this setup has much to do with a roadster though. with straight axles, drag link steering and transverse leaf springs these cars do not handle well. in general the roll centers on our cars are to low, the transverse leaf requires too much stiffness in vertical compression to control the weight transfer in roll. I'm sure ryan could give you a much better lesson on chassis dynamics than I could begin to give you.
thanks guys.... This is all just thinking about things....I'm more or less building the car just as a basic hot rod. but with my extra stiff tube frame and being so low to the ground...it got me thinking! metalshapes....i dont think i will get too close to that balance of your cars....I'm thinking hauling a passanger close to my weight will help with the balance though....problem is.....risking their life too!! RevKev I was thinking of running a baffle in the torque tube in order to contain oil in the rear...but thanks for pointing it out Zach
The closer to the center of the car you place the heavy components the better it might handle BUT THE LESS FEEDBACK TO THE DRIVER RESULTS! So when you see some munchkin F'1 Driver up front motor behind and the gears ahead of the diff....... you begin to understand In the case of Porsche the engine is set to the rear where it is protected by the driver when objects are struck head on...... And remember the crank never touches the bearings......well almost never
Is this a street car built in race car style or race only? Road race or turning left only? looks like a cool project.
The key to handling is balancing the weight. To do that you need chassis scales on all four wheels. The front to rear balance is inportant but can be adjusted with spring rates, shocks, and sway bars. The important issue is diagonal weight :left front - right rear to right front - left rear. This has to be as close to even as possible. I have four or five books that could help you if needed. I built, crewed , and drove road racing cars for nearly 30 years, chassis set up won more races than moter ever did. Jim H
thanks everyone i dont need to get too terribly involved with this specific car.... its basically a do-all street racer from 1949 dry lakes, dirt track, hill climb, road race, etc. im trying to make it fit all categories I'm guessing the farther front you put the motor the more "loose" the car will drive...so by me having it where it is...not centered, I'll be able to hang the back end out in the corners and power my way through the motor in this car is a flathead V8....im shooting for a smaller stroke and bore with a light balanced assembly for high quick revving i just want it to be alot of fun to drive.....im not actually going to race anyone ......ok well maybe!!
well yes and no. having too little weight on the front end won't allow the car to turn. but having too much weight on the front end won't allow the car to turn either. just like an airplane it has to be balanced right to handle. having all the weight up front will make the car want to stay going in the same direction. this is the reason you want as much weight as possible in the center of the car. it's called the center of mass of the car. take a yardstick and tape a weight to each end and hold it in the center and see how much force it takes to spin it back and forth. now move these weights toward the center and try again. now this time shift the weight so that their is more weight on the imaginary front of the yardstick and spin it. the back moves more, but the front doesn't want to move at all. this situation makes a car that will push very badly until you get back into the gas and try to power steer it at which point it will spin around on you like a top.
This is an interesting post to me because I am just starting to build couple cars bassed on 70s dirt mods but will be raced on dirt ovel, drag and road corse.I am really interested on what the road corse guys have to say about the straight axles
Zack, My '26 trpu was around 55% on the rear at about 3/4 build point. Need to borrow a set of digital scales again. I'm gonna guess i got closer to 50/50. I'll check around on a set of scales tomorrow. Charlie
Hey Zach, I have a book called 'Racing & Sports Car Chassis Design' I scanned a page that I thought may help http://img.photobucket.com/albums/v605/jimmyschev/Untitled-1.jpg I can scan the whole chapter if you want & anything else you may need.
Straight Axles havent been fasionable ( or flavor of the month..) since before Mid Engines became the accepted way of doing things. But I think Straight Axles and Front Engines ( with a healthy setback ) have a worse rep than they deserve. They built Cars for Brittish Clubmans Racing ( thats what my Jasag is, the red car I posted earlyer ) till about the mid 90's And these cars were always really close in laptimes to Formula 3 Single Seaters ( And they used the same tire sizes ) Also, at some point a Lister Jag ( maybe it had a SBC..) was converted from IFS to Straight Front Axle by using Kurtis parts. And after that it was much faster than the other Listers... Somebody told Arthur Mallock once that the only advantage a straight axle has over a Independent Suspension setup is that the wheels are straight on the Road ( in other words, no lean ) He told him " no, the advantage is that they are straight at all times..." Although he was talking about the Rear suspension, his cars did have IFS.
When I built my Roadster, I was carefull about Weight distribution, Centre of Gravity, Suspension Setup, Shocks, Etc. I think it Handles really nice...
The first Lotus 7 (actually a 6, I think) had a I beam, but Mr. Chapman soon saw the light. Around 1960 Rodger Ward kicked butt at Lime Rock with a straight axle midget against some heavy weight foreign competition, but his advantage was a superior power to weight ratio. And on any given weekend shifter karts are taking FTD at the local autocrosses, and they don't even have conventional suspension much less a axle, but their advantage is power to weight to tire. However, apple to apple, a straight axle will never be superior (or even equal) to a ifs in a lefty-righty scenario. If they were, you can bet Rodger Penske would have them on all his cars
Apple to apple is hard to do.... Most if not all the racecars being built right now with straight axles are that way because the rules say they have to be that way. The only ones I can think of are the Clubmans ( again ), where Cars with IRS, De Dions and Live Axles all competed on the same track with the same tires and engines. The Live Axle cars were in the winners circle as much as the other ones... Edit. I bet you could build a Roadster out of a Brookville Body, Repro Rails, SBC, Aftermarket Ibeam and a 9" that would turn really respectable laptimes. I guess the names "Bug" and "Parasite" are taken, so how about " Moth"...?? Imagine about 20 or 30 of those on the Track, fighting for position...
I'm refering to IFS, IRS is another matter. Example: 2 Lotus 7s (again) built identically with same engine, weight, tire size, compound etc. But one with a straight front axle and the other with ifs. Put them on a road/autocross course and the ifs will always outhandle the straight axle. As far as rules requiring staight axles, that isn't exactly true, the World of Outlaws couldn't care less what front suspension is on the cars. In fact Sammy Swindell built a ifs Woo sprinter back in the 80s-90s but soon ditched it as it gave him no advantage. The northeast supermodifieds can (and some do) use ifs but the vast majority use a straight axle, again, no real advantage. Both cases are not apple to apple, they are specific cars built for a specific purpose.
You could be right about that.. But I'm pretty sure lotus already had a IFS ( swingarm ) with the MK2 ( 1949 ) And Yeah, I was talking about IRS VS Ind. But I wouldn't hesitate to put a car with front & rear beams on the Track. BTW... Im pretty sure Colin Chapman experimented with a F2 or F3 wedge car ( that makes it 60's/70's ) that had a Dedion and some sort of Non Ind Front Susp. Not as succesfull as he had hoped, or he would have built more. And Ferrari was experimentimng with a De Dion Formula 1 car sometime in the 80's... So even guys at that level were willing to spend time and money to find out if it would give them an edge or not...
Always wondered why the De Dion rear never gained more popularity, seems like a rear suspension with the advantages of both a irs and a beam all in one. BTW, I've always been enamored with the Mallock/Clubman type racers, they kind of remind me of slingshot dragsters with bodywork racing on the road course. You probably already know of this website, but if not, he's got a lot of quality pics of Clubmans, and others, in the U.K. http://www.gear-tooth.com/
The cars I am building will be ran with some vintage dirt track groups. That is why I have to use a straight axle and try to make it work road racing as well
No, I didn't... Thanks for the link. I wonder what the Indy Racers would look like now if the organisers would have banned the Rear Engine Cars after Jack Brabham brought his Cooper there... And if it would be more fun to watch... Maybe they'd look like a larger version of this.
I read a magazine article, back in the 80s, of a interview with one of Penskes designers. At the time all the indy cars were all tunneled and such, and he said that with all the aerodynamics they could put the engine anywhere they wanted and it wouldn't have made a bit of difference. They might have looked something like this:
thanks everyone for all the great info jimmyB I'd love to read the rest of that if you have time...no rush this is all giving me alot to think about for my next project (27T race car) I'll have an update on the current model-A early next week i hope. You all can then see what you think of how it will handle thanks alot! Zach
A low-slung, lightweight, high-powered 27 with decent weight distribution, good brakes, and good tires will be a killer on an autocross course, even with straight axles. The downside will be when the pavement starts to wobble and the suspension begins to lag. That's when IFS and IRS start to look better. Take a serious look at old front-engine Indy and Champ cars that were built with tube axles. Great handlers that did well on ovals and road courses, dirt and asphalt. They eventually got overwhelmed by lighter and more aerodynamic mid-engine designs (damn that technology), but were not really bad sports cars. Also take a look in particular at the Kurtis 500S for inspiration...
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