Locked or spool differentials

[autogyro]

Can someone describe how V8 supercars get away so well with a locked diff? Is it basically what Cold Fussion said about tuning suspension & chassis around it?

Simply because the regulations control the set up.
Very basic red neck racing technically.

[riff_raff]

Are you sure you mean they use a "locked diff"? Which is basically the same as a spool or no differential at all. The only types of racing I know of where the cars don't use a rear diff are oval track racing, sprint cars, and drag racing.

[autogyro]

Are you sure you mean they use a "locked diff"? Which is basically the same as a spool or no differential at all. The only types of racing I know of where the cars don't use a rear diff are oval track racing, sprint cars, and drag racing.

Engine and drivetrain

All cars must be front-engined and rear-wheel drive. All cars use a 5.0-litre, naturally aspirated V8-engine with electronic fuel injection, capable of producing between 460 and 485 kW (620–650 bhp).[8] Manufacturers are free to choose between using an engine based on one from their own line up or a generic engine provided by V8 Supercars.[63] Both Ford and Holden use US-based racing engines with pushrod actuated valves and two valves per cylinder. Mercedes, Nissan and Volvo use modified versions of their own engines, with hydraulic-lift valves and four valves per cylinder.[55][64] All engines are electronically limited to 7,500 rpm and have a compression ratio of 10:1.[65]

Power is transferred from the engine to the rear wheels through a six-speed sequential transaxle with an integrated spool differential.[8] The individual gear ratios and the final drive ratio are fixed with drop gears at the front of the transaxle allowing the teams to alter the overall transmission ratio for different circuits.[66] The cars use a triple plate clutch.[8] The cars run on E85 fuel with a fuel tank capacity of 112 litres.[8][67]

An electronic control unit (ECU), provided by MoTeC, is used to monitor and optimise various aspects of the engine's performance. Numerous sensors in the car collect information which is then transmitted to the team, allowing them to monitor things such as tyre wear and fuel consumption and find potential problems with the car. The ECU is also used by officials during the scrutineering process.

[riff_raff]

The definition of a "spool" in regards to an automotive final drive is not a form of differential. A spool is basically a fixed connection between the left and right rear axles. The term spool came from NASCAR where they used tire stagger instead of a rear differential on oval tracks. Since they were required to use rear ends that were designed for a spider gear differential, the easiest way to convert the rear end to a fixed axle was to use a "spool" that coupled the axles. The spool is basically a rigid axle coupling that has the same shape as an empty differential housing.

[gruntguru]

Technically correct, but then who hasn't used the term "locked diff"? A contradiction in terms sure but it nicely describes the device we are talking about.

[J.A.W.]

Indeed, & I have even heard the term 'diff'..
.. used to describe the crown-wheel & pinion final-drive used on shaft drive (single-track) motorcycles..

[autogyro]

In the early days of oval racing in the UK it was a normal practice to either fit a hard steel bolt across the planet wheels in the diff or to weld it locked.

[riff_raff]

So I checked the technical regs of the Aussie V8 supercar series and they actually did use a spool that rigidly couples the L/R rear axles, and there is no differential function provided by the final drive. Obviously, this makes things a bit difficult when racing on road courses, but they somehow seem to make it work.

[gruntguru]

Plenty of series where the cars corner pretty fast with no differential action - Karts for one.

Main problem presented is turn-in understeer especially on tight radius corners. Typical setup tricks to compensate (the goal is to lose grip on the inside rear tyre so it can slip while car is yawing) include:
- rearward damping bias (promotes transient oversteer)
- lots of caster and scrub radius (produces "jacking" to unload inside rear tyre)
- all the usual oversteer settings - increase roll axis rake, rearward roll-moment bias, rearward camber bias etc

[autogyro]

A driver who 'throws' the car sideways to break rear traction also helps gg.

[mrluke]

Why is it not mandated for all cars to have a Spool or Locked Differential?
I can only think of one down side, it does not reflect current road car technology but in my opinion the positives are in the show; The cars would drive sideways more often especially at the starts, it would require greater throttle control, the cars would be more difficult to drive, harder to turn in to the corner going a little to deep or getting on the power to early or to hard would have more consequences i.e. more passing, transition from brake to throttle would be more difficult demanding better throttle control
Other positives would be much lower cost, less hydraulics, cooler oil, more reliable
Why would the teams not want this

WBB

Why would the cars be sideways more often?
They would have better grip off the start not less, all drag cars use a locked diff
The downside is really in slow corners and increased tyre wear, thats about it. It wouldnt make the cars slide all over the road. My track car has a fixed diff.

[autogyro]

Why is it not mandated for all cars to have a Spool or Locked Differential?
I can only think of one down side, it does not reflect current road car technology but in my opinion the positives are in the show; The cars would drive sideways more often especially at the starts, it would require greater throttle control, the cars would be more difficult to drive, harder to turn in to the corner going a little to deep or getting on the power to early or to hard would have more consequences i.e. more passing, transition from brake to throttle would be more difficult demanding better throttle control
Other positives would be much lower cost, less hydraulics, cooler oil, more reliable
Why would the teams not want this

WBB

Why would the cars be sideways more often?
They would have better grip off the start not less, all drag cars use a locked diff
The downside is really in slow corners and increased tyre wear, thats about it. It wouldnt make the cars slide all over the road. My track car has a fixed diff.

Dragsters do indeed use spool diffs but this is to equalise torque delivery, not to balance tyre traction.
Spool diffs on circuit cars induce under steer which usually results in a set up compromise to reduce it that is not the fastest for corners.
In actual fact a torque transfer diff with computer control would be more efficient for drag racing as it is for circuits but regulations these days totally stagnate development.

[Cold Fussion]

Why is it not mandated for all cars to have a Spool or Locked Differential?
I can only think of one down side, it does not reflect current road car technology but in my opinion the positives are in the show; The cars would drive sideways more often especially at the starts, it would require greater throttle control, the cars would be more difficult to drive, harder to turn in to the corner going a little to deep or getting on the power to early or to hard would have more consequences i.e. more passing, transition from brake to throttle would be more difficult demanding better throttle control
Other positives would be much lower cost, less hydraulics, cooler oil, more reliable
Why would the teams not want this

WBB

Why would the cars be sideways more often?
They would have better grip off the start not less, all drag cars use a locked diff
The downside is really in slow corners and increased tyre wear, thats about it. It wouldnt make the cars slide all over the road. My track car has a fixed diff.

It's compromised every where and not just in the slow corners.

[gruntguru]

A spool equalises wheel speed but not torque delivery. It is possible (common even) for the L:R torque split to be 0:100

[autogyro]

A spool equalises wheel speed but not torque delivery. It is possible (common even) for the L:R torque split to be 0:100

Torque delivery to the diff output is equal with a spool diff.
Torque delivery to the wheels is variable from any form of diff or drive system.
This is why engine bhp and torque is the least important thing in power train design.

Torque split is an airy fairy definition.
It should be applied torque and utilised torque.