Read end and Rear Suspension Options

[Fast&Loud]

I’m still a ways away from getting a kit, but I continue to read the forum. Some great stuff here. Additionally, I spent some time watching youtube and found a number of fails/wrecks of roadsters. As far as I can tell, the vast majority were due to lack of knowing the limitations of the car, and/or ego driving the gas peddle. Basically, too much power plus light weight plus short wheelbase equals car going sideways really quick. Some end badly, some not so much. But, my takeaways were 1) know the car limitations, and 2) don’t let ego make decisions.

That said, I’m left wondering how the type of rear suspension and rear end (e.g. limited slip?) might minimize these occurrences. Any recommendations for a build that can reduce spin-outs?

Thanks!

[edwardb]

IMO your conclusions are correct. Incidents are most typically related to not knowing the car and not knowing personal capabilities. Lots has been written about how these cars will bite you, and that's certainly the case. But in my experience, with a properly set up build and reasonable care when driving, they're neither hard or scary to drive. Quite the opposite in fact. But lapses in skill or judgement may not end well. Having said that, I don't think there's a huge difference in rear suspension setup as it relates to incidents with the possible exception of the donor based 4-link, which has some geometry issues. Any of them will bite if given the chance. Your choice should be between 3-link and IRS. The main difference between the two will be ride quality, with the IRS being superior in my experience. Almost without exception, limited slip is the norm for these builds.

[BradCraig]

I just made this decision and went with the IRS for ride quality and I wanted a modern drivetrain. Do the math as well, by the time you buy or rebuild a straight axle, add brakes, etc, you are darned near the cost of an IRS. My math was as follows: $2500 F5 option, $600 for full salvage IRS pallet including brakes. If you price out a solid axle and add brakes you are not saving much (if any) money. No brainer for me. As far as wrecking, most come from showing off. Play stupid games and get stupid prizes! Good luck!

[GoDadGo]

Pick your poison but please steer clear of the 4-Link if at all possible.

My friend Donnie has the IRS in his MK-4 and my pal Jerry the 3-Link in his Daytona.

Both Handle Fine, but Jerry's car plants the crap out of the tires at the expense of ride quality.

I went with the 3-Link because of the simplicity of that set up plus I like to go to drag strip from time to time.

Ride Quality Is Vastly Improved With The IRS and I think it really enhances the value of the car if you ever decide to sell it.

Also consider going with a Torsen or Truetrac (TSD) style differentials because they really smooth out the torque over clutch or ratcheting types.

Torsen:
https://youtu.be/JEiSTzK-A2A

Truetrac:
https://www.youtube.com/watch?v=lZmsY2YvVsc

Ratchet Type:
https://youtu.be/AuZqG7pTabw

More Info On Popular Differentials:
https://youtu.be/6QUP4Ag30yI

[CraigS]

Go IRS w/ the stock Ford clutch type lim slip. Increase front spring rate 100-200 pounds and/or add a front swaybar from Forte. Both will move handling balance a little toward understeer which provides a little more rear grip. Build your engine w/ a little more top end and a little less low end torque. And the MOST important suggestion; go run a couple of seasons of autocross. Besides learning the car, where else can you drive as fast as you want, but never be over 60 mph, and have virtually no chance of hitting anything. At some event you will perfectly nail a 2nd gear 35 mph corner and go to full throttle to 55-60 before slowing for the next corner. You will smile for an entire week after that.

[NAZ]

If you've never driven a high performance or high HP to weight car then you may want to consider taking a driving course and have a professional teach you so you can fully utilize your new car once it's complete. Yes, I know you can get some experienced amateur cone smasher to run around the cone zone with you and give you pointers in your own car. Some coaches can be excellent and some, not so much.

Or you could get professional training from a world-class school in a car that has more HP than your car and give you top notch training and confidence to hit the ground running. https://bondurant.com/high-performance-driving/

[ProJoe]

you may want to consider taking a driving course and have a professional teach you so you can fully utilize your new car once it's complete.

I absolutely cannot agree with this any more.

look for local organizations that offer High Performance Driver Education (HPDE) courses. https://www.nasaproracing.com/ has regions all over the country.

for your first day they will put you in a classroom and give you an instructor in the passenger seat to teach you the basics of driving fast and safely on a road course near you. you will be on track with other first time drivers and there are very strict rules about passing and etiquette. The cost-per-minute of HPDE versus autocross doesn't even compare if you consider how much seat time you get in a single weekend on track.

we used to require all our drifters go through HPDE1 before joining our sessions. it is an invaluable experience and tool.

[Fast&Loud]

I absolutely cannot agree with this any more.

look for local organizations that offer High Performance Driver Education (HPDE) courses. https://www.nasaproracing.com/ has regions all over the country.

for your first day they will put you in a classroom and give you an instructor in the passenger seat to teach you the basics of driving fast and safely on a road course near you. you will be on track with other first time drivers and there are very strict rules about passing and etiquette. The cost-per-minute of HPDE versus autocross doesn't even compare if you consider how much seat time you get in a single weekend on track.

we used to require all our drifters go through HPDE1 before joining our sessions. it is an invaluable experience and tool.

Thanks NAZ and ProJoe, excellent advice! I have a friend that races professionally and he's already given me some suggestions on which companies provide quality instruction. I look forward to these.

F&L

[Fast&Loud]

Go IRS w/ the stock Ford clutch type lim slip. Increase front spring rate 100-200 pounds and/or add a front swaybar from Forte. Both will move handling balance a little toward understeer which provides a little more rear grip. Build your engine w/ a little more top end and a little less low end torque. And the MOST important suggestion; go run a couple of seasons of autocross. Besides learning the car, where else can you drive as fast as you want, but never be over 60 mph, and have virtually no chance of hitting anything. At some event you will perfectly nail a 2nd gear 35 mph corner and go to full throttle to 55-60 before slowing for the next corner. You will smile for an entire week after that.

Thanks CraigS! Autocross sounds like fun, I'll look into that.

I'm a bit of a newb when it comes to suspensions so I have a few questions re: your suggestions, I'm trying to better understand how the springs affect the overall balance and traction. From what I can conceptualize, heavier (increased) front spring rate when decelerating will reduce the forward lean of the vehicle, putting less weight on the front wheels, and retaining more weight on the rear. Thus, less tendency for the rear end to drift laterally (especially in turns). But, during hard acceleration, that mean less weight transferred rearward, and thus, less traction on the rear wheels and raising the chances of the rear end getting squirrely. Do I understand these correctly? It seems that there's a balance to strike if you are looking for a car that can do both reasonably well. Again, I might have missed something and I welcome any feedback.

Re: building the engine with a little more top end and a little less low end torque, what are your thoughts on using taller rear end gears to achieve this? I'm guessing these are not an apples-to-apples ways of retaining traction on the rear, but wanted to ask.

Thanks!

F&L

[Fast&Loud]

Pick your poison but please steer clear of the 4-Link if at all possible.
My friend Donnie has the IRS in his MK-4 and my pal Jerry the 3-Link in his Daytona.
Both Handle Fine, but Jerry's car plants the crap out of the tires at the expense of ride quality.
I went with the 3-Link because of the simplicity of that set up plus I like to go to drag strip from time to time.
Ride Quality Is Vastly Improved With The IRS and I think it really enhances the value of the car if you ever decide to sell it.
Also consider going with a Torsen or Truetrac (TSD) style differentials because they really smooth out the torque over clutch or ratcheting types.
Torsen:
https://youtu.be/JEiSTzK-A2A
Truetrac:
https://www.youtube.com/watch?v=lZmsY2YvVsc
Ratchet Type:
https://youtu.be/AuZqG7pTabw

More Info On Popular Differentials:
https://youtu.be/6QUP4Ag30yI

GDG, thanks for the info and especially those videos! Lots of details in there.

F&L

[Jeff Kleiner]

F&L,
There is much more to it than spring rates. The combination of the cars being rear heavy (did you realize that?) with a low center of gravity and front suspension with designed in anti dive geometry results an very little “forward lean” as you call it. Conversely both the IRS and 3 link incorporate geometry to promote “squat” under hard acceleration (the 3 link features optional forward mounting points for the upper link so that it can be varied to achieve a balance between forward and cornering traction). Spring rates are a major player in handling; the factory springs promote understeer. Increasing the front rate without a corresponding change to the rear will make this push even worse while increasing only the rear will bring it more to neutral or cross over to oversteer. Yes, juggling gear ratios (both in the transmission and final drive) can change how engine torque is delivered but no matter how you get there a given tire can only hold traction for X amount of torque. In the end the best way to regulate how much power/torque gets to the ground is through a well trained right foot!

Jeff

[toadster]

I'd also think that if you can build in traction control and ABS that helps MANY get out of unwanted situations, but that adds $$$ and complexity on top of the build...
there are plenty who have done this relatively inexpensively with Mustang Cobra components, others have gone with custom ECUs, etc...

I ordered the IRS (well, it came with the 25th anniversary setup) but that's what I wanted like many have stated - ride quality is improved, and resale value - EVERYONE will ask if it's an IRS setup...

less than a month till my car gets here :)

This forum is a treasure trove, read read read! and read some more! ask questions - most are more than willing to help, and MANY have answered the same questions a few dozen times :)

[mike223]

Additionally, I spent some time watching youtube and found a number of fails/wrecks of roadsters. As far as I can tell, the vast majority were due to lack of knowing the limitations of the car, and/or ego driving the gas peddle. Basically, too much power plus light weight plus short wheelbase equals car going sideways really quick.

Any recommendations for a build that can reduce spin-outs?



The vast majority of "lost control" wrecks in these sorts of (high powered, short wheelbase) vehicles are caused by getting the rear loose and then stepping off the throttle pedal (often accompanied by stepping on the brake pedal).

You can't do it.

Engine (or other) braking transfers the weight off the rear and quickly makes a bad situation (that the driver chickened out of) completely uncontrollable.


You have to practice and master the skill of straightening the steering wheel and dropping back to neutral or slightly leading throttle in that situation - reflex quick.

Either that or don't ever chance it (it can bite you quick).


Autocross is the perfect format to work on that skill - you don't really want to be learning that skill at track day speeds (IMHO)...



This bears repeating:





In the end the best way to regulate how much power/torque gets to the ground is through a well trained right foot!

[NAZ]

F&L,
There is much more to it than spring rates. The combination of the cars being rear heavy (did you realize that?) with a low center of gravity and front suspension with designed in anti dive geometry results an very little “forward lean” as you call it. Conversely both the IRS and 3 link incorporate geometry to promote “squat” under hard acceleration (the 3 link features optional forward mounting points for the upper link so that it can be varied to achieve a balance between forward and cornering traction). Spring rates are a major player in handling; the factory springs promote understeer. Increasing the front rate without a corresponding change to the rear will make this push even worse while increasing only the rear will bring it more to neutral or cross over to oversteer. Yes, juggling gear ratios (both in the transmission and final drive) can change how engine torque is delivered but no matter how you get there a given tire can only hold traction for X amount of torque. In the end the best way to regulate how much power/torque gets to the ground is through a well trained right foot!

Jeff


Well said.

[GoDadGo]

Any recommendations for a build that can reduce spin-outs?

Thanks!

Knowing the handling and power is everything, especially being Super Savvy with that Go-Go-Go-Dad Right Pedal.

As for me I installed an MSD Adjustable Circle Track Rev Limiter and I keep bumping it up 100 RPM at a time as I learn.
Operation range for my 383 is 2,200-6,200 RPM with the Redline of 6,500 so I still have a ways to go.
Currently I have it set at 4,300 RPM which settles the tires as I shift though the gears.

Tire spin still occurs pretty quickly even with this super low current rev-limiter setting.

4,300 RPM...Trans Ratio.......2.68.......1.80.......1.29......1.00.. .....0.75.......0.50
3.73 Rear.....MPH P/Gear....33.27......49.54.....69.12....89.17....118 .89...178.34

Limiter Set @ 4,000 RPM In This Video:

https://youtu.be/wOID7yvBRPU

[Gordon Levy]

There is a huge difference in a weekend occasional track car and a competitive road race car. Much depends on what drive train you plan on using as to what the best set if. My 5 link is the strongest suspension available with a high degree of adjust-ability. It is also the best ride quality of the live axle set ups.
You can make a car do 1 thing really well, everything else is a compromise. That being said, good adjustable shocks, good springs and proper adjustable sways bars help the tune ability.
Another mistake many make is rear gear. High torque engine packages like my stage 5 408/427 Windsors makes 550+lbft of torque is just about useless with a 3:73 gear. You just end up blowing the tires off it. Being that the car is so light it will do much better with a 3:27 or 3:55 and you will find yourself shifting far less. High rev engine such as the coyote like more gear as the power band is relatively narrow and the 3:73 will work better.
Once you have finished your car and want to learn it's limits you can contact NASA, ( national auto sport asso.), in your local region and sign up for their HPDE programs with NASA certified instructors to help get acclimated to driving on the track and the dynamics of driving your car and having fun with it. I am a national instructor and driver coach with NASA. Please feel free to ask questions.

[CraigS]

I like to think about spring rates, shock rates and bar rates like this. Starting w/ a given 'in the ball park' setup, stiffer reduces traction while softer increases it. Those three items are different in the way they affect the car, and when they have the most effect but, overall, the what is as my first sentence. Jeff is absolutely correct that going stiffer in the front will promote understeer. But you would only find that out at the limit of traction. For 99% of the time (when you aren't at that limit) you will have increased rear traction.

[rezell3d]

Gordon, what rear end housing is that 5-link system designed for?

[Gordon Levy]

8.8

[Fast&Loud]

There is much more to it than spring rates. The combination of the cars being rear heavy (did you realize that?)

Ha, I did not! That surprises me a bit, but I'm still learning about this car.



In the end the best way to regulate how much power/torque gets to the ground is through a well trained right foot!

I have never owned a Cobra, but I have learned this much in nearly every kind of vehicle. I just strikes me that the higher the power to weight ratio, the easier it is to get into trouble. Every driver, regardless of the platform, must remember this.

Thanks!

F&L

[Fast&Loud]

Knowing the handling and power is everything, especially being Super Savvy with that Go-Go-Go-Dad Right Pedal.

As for me I installed an MSD Adjustable Circle Track Rev Limiter and I keep bumping it up 100 RPM at a time as I learn.
Operation range for my 383 is 2,200-6,200 RPM with the Redline of 6,500 so I still have a ways to go.
Currently I have it set at 4,300 RPM which settles the tires as I shift though the gears.

Tire spin still occurs pretty quickly even with this super low current rev-limiter setting.

4,300 RPM...Trans Ratio.......2.68.......1.80.......1.29......1.00.. .....0.75.......0.50
3.73 Rear.....MPH P/Gear....33.27......49.54.....69.12....89.17....118 .89...178.34

Limiter Set @ 4,000 RPM In This Video:

https://youtu.be/wOID7yvBRPU

This strikes me as a brilliant idea. I've had it in my mind to find a large, open parking lot, and then experiment to see how the car handles in various states of throttle, braking, turns, etc. My father did this with me one night in an empty school parking lot while it was snowing to teach me how to handle road conditions. It's easy to learn when there's less to risk. But, the Rev Limiter is really a neat idea. Gonna have to look into this. Thanks!

F&L

[BradCraig]

This strikes me as a brilliant idea. I've had it in my mind to find a large, open parking lot, and then experiment to see how the car handles in various states of throttle, braking, turns, etc. My father did this with me one night in an empty school parking lot while it was snowing to teach me how to handle road conditions. It's easy to learn when there's less to risk. But, the Rev Limiter is really a neat idea. Gonna have to look into this. Thanks!

F&L

Agree, best thing my dad ever did was take me to a parking lot in the snow. Invaluable lessons! And it was in a 67 Camaro.

[GoDadGo]

Agree, best thing my dad ever did was take me to a parking lot in the snow. Invaluable lessons! And it was in a 67 Camaro.

You Don't Need Snow Or Even Wet Roads; Just Some Space To Play!

https://youtu.be/PCngiKoopkA