NB- GPvR NCT test

[optical illusion]

Only heard about this today and never realised. People who have a GPvR should insist that their car is driven and not put on the rollers under any circumstances. With LSD this could be an absolute disaster...

There is someone it happened to recently currently trying to claim from the test centre, as they blew his engine. Not worth the risk.

[Myfeckin FTO]

Presume you are talking about the brake test with an LSD equipped car. I've had to ask the NCT centre not to put the Zed on the rollers previously for this reason - in most cases they just don't know if your car is LSD equiped.

[optical illusion]

Indeed I am. Sometimes they insist even if you tell them, so I would be walking away...

[gfalls]

Pardon my ignorance, but what difference does LSD make to the rollers? Does the same count for a rolling road then?

[Dilogoat86]

It shouldn't be an issue on a rolling road because both wheels are on the roller, or both hubs are bolted to the dyno. The NCT centre test each wheel individually for a seperate brake test.

[gfalls]

That explains it then...

[Myfeckin FTO]

It shouldn't be an issue on a rolling road because both wheels are on the roller, or both hubs are bolted to the dyno. The NCT centre test each wheel individually for a seperate brake test.

The NCT won't brake test a 4WD car or LSD equipped car on the rollers as there may well be a difference on the torque transfer across the wheels. In additon the torque of their own rolling road could also cause issues with diffs and drivetrain. I'm not saying that there def would be damage - but they won't take the risk if advised. AFAIK the brake test on the NCT/MOT is calculated on each individual wheel so if you brake an LSD equipped car then there will be torque transfer across the axel which will lead to at the very best an inaccurate brake test reading and at worst a slipped timing belt etc.
The NCT would just do a road brake test to ensure brakes are working ok - not very scientific but they don't have the neccessary equipment (decelerometer) at the moment.

Gfalls - A rolling road testing power will allow both wheels to move independently and at different speeds - no issues with LSD's there.

[mcgon1979]

Im a bit ignorant myself on this stuff. I did my GPvR NCT test in October. No problems. brake test scored fine, and as far as I am aware no damage to my car? ooops

[mcgon1979]

Im a bit ignorant myself on this stuff. I did my GPvR NCT test in October. No problems. brake test scored fine, and as far as I am aware no damage to my car? ooops

great. you'd think they could put it on the website or ask the driver if the car has an LSD. planks. I resisted going for the test for so long. years. then was forced to when the penalty points thing came in... won't be going back as long as I own the car. It's good till Oct 2011 though.

from the offical manual

8. The use of a roller brake tester is not appropriate on hybrid vehicles or on vehicles with a permanently
engaged four wheel drive, limited slip differential or belt driven transmission.

http://www.ncts.ie/pdf/nctmanual.pdf

[optical illusion]

Im a bit ignorant myself on this stuff. I did my GPvR NCT test in October. No problems. brake test scored fine, and as far as I am aware no damage to my car? ooops

Understandable, but I'd prefer not to take that chance.

[mcgon1979]

Im a bit ignorant myself on this stuff. I did my GPvR NCT test in October. No problems. brake test scored fine, and as far as I am aware no damage to my car? ooops

Understandable, but I'd prefer not to take that chance.

for sure. If I was going back tomorrow with this information I would not be putting it on the rollers.

[mcgon1979]

just to clear up any misunderstanding about this. The type of LSD in an FTO cannot be damaged by going on the rollers at an NCT. Here is why:

Geared LSDs wear the gears and their supports rather than the clutches of the clutch type and the cones of the cone type, but both output shafts have to be loaded to keep the proper torque distribution characteristics. Once an output shaft becomes free (e.g., one driven wheel lifts off the ground; or a summer tire comes over ice while another is on dry tarmac when the car goes uphill), no torque is transmitted to the second shaft and the torque-sensitive differential behaves like an open differential.

Most FWD LSDs are geared diffs and behave this way. FWD and RWD often use the clutch type LSD and this could indeed blow an engine or do serious damage. As it happens the FTO uses the latter type. So no worries.
Still... If I was going back I'd say its an LSD just to avoid them being able to fail me for brake imbalance etc

[Myfeckin FTO]

...........Geared LSDs wear the gears and their supports rather than the clutches of the clutch type and the cones of the cone type, but both output shafts have to be loaded to keep the proper torque distribution characteristics. Once an output shaft becomes free (e.g., one driven wheel lifts off the ground; or a summer tire comes over ice while another is on dry tarmac when the car goes uphill), no torque is transmitted to the second shaft and the torque-sensitive differential behaves like an open differential........

Every days a school day! However this now begs the question as to the effectiveness of the FTO's LSD if when one wheel losses traction on a slippy surface or raises in the air (quite common on a track) that the LSD just spins away the power on the unloaded wheel. Kinda the point of actually having a diff I would have thought?

OT but while we're on the subject of diffs - I've just today finally upgraded the Zeds rear diff from a viscous unit to a proper clutch unit - a Kaaz 2 way that I had converted to a 1.5 way for road use. The viscous unit was terrible at distributing power (as could be seen at the last couple of 1/4 miles). Haven't driven it yet (as theres a pile of other things being addressed) but it'll be interesting to see the difference.

[mcgon1979]

However this now begs the question as to the effectiveness of the FTO's LSD if when one wheel losses traction on a slippy surface or raises in the air (quite common on a track) that the LSD just spins away the power on the unloaded wheel. Kinda the point of actually having a diff I would have thought?

Its better than an open diff for accelerating where both wheels have some contact with the road. i.e. straight line acceleration where both drive wheels have at least some contact with the road will be handled more effectively as the torque is matched to each wheel in an effort to eliminate 'torque steer'. In a sharp turn while accelerating the torque will also be different on both drive wheels and the diff will help keep the torque to each wheel closely matched. but if there is a total loss of contact, i.e. on ice, or in the air, yep, they act like an open diff.

from wiki "Geared LSDs are dependent on the torque and not on the speed difference between the output shafts. Such differentials may not be adequate on extremely slippery surfaces such as ice (or thin air, when a drive wheel loses ground contact altogether) Geared LSDs may be used: to reduce torque steer in front-wheel drive vehicles;"

[gfalls]

So... What's "Traction Control" all about then? Is it like LSD?

[Dilogoat86]

Traction control physically retards the engine when it senses a traction drop. The idea is to allow the car more time to find traction before it loses it completely. A prevention rather than a cure. The idea of an LSD is to make cornering better. You can accelerate around a corner without understeering by the outside wheel getting more power than the inside wheel. The outside wheel has to travel a further distance around a corner and thus should travel faster than the inside wheel. LSDs make this process a lot easier and safer.

[EDIT] That's not why LSDs were actually invented though. There's a lot of info about them on wiki and the web.

[Muad_dib77]

However this now begs the question as to the effectiveness of the FTO's LSD if when one wheel losses traction on a slippy surface or raises in the air (quite common on a track) that the LSD just spins away the power on the unloaded wheel. Kinda the point of actually having a diff I would have thought?

Its better than an open diff for accelerating where both wheels have some contact with the road. i.e. straight line acceleration where both drive wheels have at least some contact with the road will be handled more effectively as the torque is matched to each wheel in an effort to eliminate 'torque steer'. In a sharp turn while accelerating the torque will also be different on both drive wheels and the diff will help keep the torque to each wheel closely matched. but if there is a total loss of contact, i.e. on ice, or in the air, yep, they act like an open diff.

from wiki "Geared LSDs are dependent on the torque and not on the speed difference between the output shafts. Such differentials may not be adequate on extremely slippery surfaces such as ice (or thin air, when a drive wheel loses ground contact altogether) Geared LSDs may be used: to reduce torque steer in front-wheel drive vehicles;"

OK let me see if I understand this right..

The FTO LSD is good as long as you have grip on both wheels..but if you go cracked and loose traction altogether on one wheel it will still spin and leave the other wheel sitting..like a non limited diff..


Odd..

[mcgon1979]

yep. you have it right. It's main benefit is to counteract the effects to Torque steer (when both wheels on the ground). If you have one wheel completely free, on ice or in the air, it will spin yes.
I suppose the best way to think of it is: If you floor a car without LSD on gravel or slightly wet road one wheel will probably end up spinning and taking 100% of the torque. That won't happen in the FTO once both wheels are on the ground and have at least SOME grip.

[gfalls]

After a bit of research. LSD is mechanical, and traction control is electronic. Both doing roughly the same job..?? I think that's right.. Open to contradiction though.

[Myfeckin FTO]

After a bit of research. LSD is mechanical, and traction control is electronic. Both doing roughly the same job..?? I think that's right.. Open to contradiction though.

Nah - you can combine an LSD with traction control/stabilty control (like I have in my Zed) but they are very different. Traction/stability control systems vary widely but most modern cars traction control systems involves braking or cutting power to the relevant wheels individually to ensure car stays stable. Thats fine for most family cars but slowing a car to make it more stable isn't much fun (or fast) in a sports or racing car - an LSD is a must have. For instance in the Zed when I really want to push on (1/4 mile/track day) then I'd turn off the nannying traction control system and let the LSD provide reliable distribution of max power to each of the rear wheels without having the loss of power or speed that would occur with the TC/VDC on.

[Dragonheart]

Can I go into the NCT so and tell them I have an LSD, (though its GPX not GPvR), and request that the brake test isnt done via the rollors? Though I'm confident itll pass anyway but if I wasnt confident and wanted an easy way out could I do it?

[Myfeckin FTO]

Can I go into the NCT so and tell them I have an LSD, (though its GPX not GPvR), and request that the brake test isnt done via the rollors? Though I'm confident itll pass anyway but if I wasnt confident and wanted an easy way out could I do it?

I guess it depends on the monkey in the NCT centre but an easy way for them to see if your car has an LSD is that when you turn one driven wheel the opposite wheel should spin in the other direction.