Is there an optimal ratio between track width and wheelbase for a good handling car? As you can see from my sig, I am building a rather wide and short car that I want to handle well. It will have the track of a ZR-1 Corvette with the wheelbase of an MGB (91"). The wheelbase of a C-4 Vette is 96". That is only 5" shorter than a stock Vette but with the reduced overhang in the front and rear it looks considerably wider. I have had people say that the greater the width relative to the wheelbase, the better it will handle. Then there are others that say it will be "squirrley" because the wheelbase is too short for the width of the car. I was just looking at an article in Road&Track about the 959 Porsche and it seems to do OK with an 89.5" wheelbase.

If anyone can shed some knowledgable light on the subject I would appreciate it very much.

 

"Short and thick does the trick" often applies in life.

The wider track reduces the weight transfer from inside to outside tires during cornering, which helps all four tires work better.

The shorter wheelbase makes the car respond quicker to steering inputs, so "squirrely" might apply. You can help this with alignment (tad more front toe-in), spring rates and shock damping.

The 5 inch shorter wheelbase is probably fine.

What powertrain are you using? If it's MGB, you are probably way underpowering the suspension/tires available for the C4 suspension. If it's a powerful V8 conversion (300+ hp), the suspension change makes sense, but the hp/short wheelbase will definitely take some finesse when driving hard.

Ops, just noticed your forum nameand siggy. (Duh!) Yeah, you'll need an educated right foot. The front end will also be heavy which will slow down the steering response some.

One last question? why? That's a pretty small engine compartment, and not the stiffest chassis/body I've ever seen. My best buddy has a stock B he cruises, and an old friend swapped a 215 inch Buick (now Rover) V8 into his A back about 1966. That was a pretty clean job even before the factory did it.

My $.02

 

This car has a colorful past. It has also had a Buick 215, Borg Warner 4 speed, Jag independent rear suspension. Later in life, I changed the engine to another 215 but an Olds Jetfire (the turbocharged version) with about 10 lbs boost. The car was great to drive but parts got difficult to find and I was tired of it.

This iteration will have a cam, heads, bolt-on Lt1 that should make about 350 RWHP as best I can figure from the guys who post here with a 3.73 C-4 rear and T-56 6 speed. The car should weigh less than 2300 lbs and have close to a 50/50 weight distribution. I have the engine mounted substantially aft of the stock location.

The cockpit grows considerably when you widen the body 11.5" as does the engine compartment. The only thing left of the original MGB is the body skin and the door supports, the rest is a tube frame with stressed sheetmetal welded in to stiffen the structure. It will look exactly like an MGB when completed with the exception of slight bulging of the fenders to cover the 11" rear wheels and 315-35-17 rubber (except for the width of course).

I need to learn how to do a website so I can post pictures of the progress.

 

A-hah! Cool!

It'll look like a MGB like a New Mini looks like the old; a 1.3 times size version.

What springs and shocks. What width and offset wheels/tires front and rear? How are you choosing spring rates and anti-roll bar rates? C-4 steering rack or ?. I'm intrigued by your project.

 

Using coil-overs front and rear. QA1 12 way adjustable with 500 lb springs in front and 450 in back. This will give a suspension frequency of 130 cpm in front and 119 cpm in back. I put together a neat Excel program to calculate coilover spring rates with a few known inputs. Most of the reading I have done says that the frequency for Caddy style ride is 80 - 90 cycles/min. Performance road cars are in the 120 cpm range and flat out race cars approach 150. I'm going to start with the softest stock Vette swaybars, 26 mm tubular in front and 19 mm solid in back, who knows where it will go from there. I don't have a good data based way to select the starting point for the sway bars.

The wheels are ZR1 Vette sawblades, 9.5" wide 7.75" backspace in front with 274-40-17 Kuhmo Victoracer tires. The rears are 11" wide 7.5" backspace with 315-35-17. The brakes are 13" x 1.1" rotor ZR1 in front with 12" in back. I am using a Wilwood balance bar pedal setup with no power booster. I also made a slick program to determine the master cylinder sizes to use to get the right pedal pressure.

The steering is a stock fast ratio Corvette rack (2 1/4 turns lock to lock) with power assist. I'm using a Fiero column and u-joint shaft to hook it up. It's a perfect fit. The front suspension uses '84-'87 upper A arms with '88 up lower arms and uprights. It's an old Corvette cheater's trick to get more camber change with suspension deflection so you don't have to run so much static negative camber. It also lets me bolt up the big brakes without adapters. All the stock Corvette suspension pickup points have been duplicated on the tube frame so the suspension should work fairly well right out of the box.

The car will sit almost 2" lower than a stock MGB measured at the pinch weld and will have 6" ground clearance everywhere. The engine will fit under a stock contour hood.

My goals for the car are to be able to run in the 11's over 120 MPH, generate 1.0 g's lateral acceleration, get 25 mpg on the highway and be able to top 200 mph. The car will have a better power to weight ratio than a Viper.

 

Some thoughts:

1) I think you might find the spring rates and suspension frequency to be high. Off hand I don't know the motion ratios for C4 suspensions, but my first guess is that it will be too stiff and with the low unit loading of the large tires on a 2500# vehicle, you'll bounce over every irregularity. The good thing about c/o's is that you can change springs easily and relatively cheaply.

2) My philosophy is to use as soft springs as will keep the car from bottoming (not original). I previously used suspension frequency calculations, but softer springs (and lower freq) worked better. If practice works better than theory, screw the calcs and rethink your theory.

3) Anti-roll bars. I'd maybe start with none, especially if you use the 500/450 springs. You'll already have tons of roll stiffness, so you might just use the front bar for final tuning. You might find you can just use the springs.

4) As far as body roll (camber change), your CG height should be around 20 inches. I would guess front roll center a few inches above ground, and rear maybe 10 inches or so. That gives reasonably low roll moment, so you might not get much wheel travel. You'll want to keep the tires from cambering too much because they are so lightly loaded.

5) 1.0 lateral g should be no sweat. How about 1.10-1.15 if you get the balance right and the tires stay upright.

6) As far as 200 mph: there probably isn't enough power (weight isn't really important for top speed) given the Cd is probably well over .40. That's good, because the car wil probably have lots of lift if you don't work on the aero a LOT. 150 should be VERY exciting, IMO. You think it's squirrely with all the weight on the tires, try removing about 25% off the rear!

If you don't mind, I'll look at a few more things you've mentioned.

Good luck!

[Edited mostly for grammar/spelling]

 

I was rather surprised to find .54 front motion ratio and .48 rear but those are the square of the actual measured shock travel divided by the actual wheel travel. Just looking at the attachment points it looks to be more direct. If you were targeting a frequency front and rear, what would they be? Frequency is the only thing I can calculate to come up with a spring rate. There is a site that follows the build of a independent suspension Cobra kit car and they went through the same sort of process when selecting springs. The factory recommended springs were way too soft and they ended up with 800 lb springs in front. I'll see if I can find the site and post a link so you cn read about it.

The mounts for the bars are there if I need to use them. Its a lot easier to build them into the car than trying to add them after the fact.

The lateral G expectations are pretty exciting! Not too many streeters will manage that.

The top speed may be a little optimistic but the car has a perfectly flat bottom almost like a belly pan and the windshield is removable. There will be a pretty effective air dam on the front and I will have a metal tonneau to cover all the cockpit except where I protrude (just for the speed run). When the car had the turbo Olds I pulled just over 6,000 RPM in 4th gear which penciled out to right at 150 MPH. That is with completely open cockpit and windshield in place. The car felt very stable. What kind of things can you do to kill the lift without resorting to wings and decklid spoilers?

What is your background and what part of the country do you live in?

 

Old SStroker

Take a look here http://eaglewoman.simracing.dk/cobra/ and look in the suspension project results section.

 

Upstate NY. GM trained Automotive Engineer, terminal gearhead. Like suspensions more than engines, but love engines.

Drive '96 Impala SS, '97 C5, son's 00 Carmaro SS, wife's Audi TT.
Love 'em all...for different reasons. Favorite car was my '64 GTO in '64 when I was 21, and a Pontiac Engineering "intern".

BTW, guy that put the 215 Buford and Muncie in the MGA was fellow Pontiac engineer. We were about 22 then.

"If some is good, more is better, and too much is just enough."
(loosely) from Stroker McGurk. Your 'B seems to fit this.

 

I'm X-Navy carrier pilot (Vietnam era) so I'm a natural born acceleration junkie. Can't stand cars that don't handle though. I love roadsters and this car won't even have provisions for a top and the side windows were gone 30 years ago. Roadsters with doors make it difficult to get chassis stiffness but I have done some raising of the door sills to help this out. There is nothing like having the wind in your hair while you are sucking your eyeballs back in their sockets.

I am just finishing an English wheel to make the new bulgey body panels with so I would really like to make a car from scratch for my next project. I'm thinking about a mid engined slalom car powered by a turbocharged Ford Duratec V6. 1400 lbs and 300 HP with a swoopy aluminum body (roadster of course). Someday before I die I want a '34 fenderless roadster with an enormous GMC blown big block. Enough fantasy.

I live in San Diego and would like to show you the car if you ever get out this way. Send me your e-mail address and I'll send you some pictures of what it looks like so far.

 

I knew we had something in common. I drove SLUFs (USAF A-7D) and Huns (F-100) in the same era. Got me addicted to g's also.
My runways were stationary, however.

Best buddy had an exchange tour with the Navy in SLUFs. He says lots of good things about Navy/Marine airplane drivers.

Eyeballs-in beats eyeballs-out any day.

Check six. You have a PM.

 

Longer also. I flew A-6's. Nothing like 0 to 150 kts in 220 feet or 130 kts to 0 in half that disatance.