60 replies to this topic

[saiyuki]

Hopefully i will not get flamed as this question is not directed at F1 specifically, but it does seem to be the best place to ask
Which class (GT or NGT), has the greater Engine Braking?

Regards saiyuki

[cheapracer]

Moot point, engine braking is for 40 ton Interstate trucks that go over hilly mountains, not for car racing.

I get the feeling this is a carry over question looking for ammunition for another forum/thread's discussion?

Using the engine for braking other than those 'traffic moments' will only upset the car and damage the gearbox and/or engine or simply spin you. Grab any good driver incar video and watch that driver brake then downshift to a lower gear only well after the car speed has gone well into the required speed range for that gear. A big V8 video such as TransAm where things happen more slowly may help.

Of course this can happen very fast and you may think other wise and it appears they are "banging" down through the gears but they are not and the ones that are are at the rear of the field.

Mike Skeen's vids are pretty good, heres showing use of brakes not gears for slowing .... http://www.vido1.com...trans-am-at-roa
..... other wise type Mike Skeen Trans Am into Youtube.

[OfficeLinebacker]

Moot point, engine braking is for 40 ton Interstate trucks that go over hilly mountains, not for car racing.

JGR in NASCAR use some kind of weird engine braking thing, the cars belch black smoke in the turns.

[Spoofski]

JGR in NASCAR use some kind of weird engine braking thing, the cars belch black smoke in the turns.

Sounds like engine braking reduction/modulation. I wonder what the control strategy would be with a carb and throttle cable however.

[saiyuki]

Hmmm @cheapracer, i don't know why you get the feeling, but it's totally wrong. I haven't discussed or seen this question in any other forum i've visited, thats why i thought i would try here. It does seem though that perhaps i was wrong to ask in this forum.

[gruntguru]

Hmmm @cheapracer, i don't know why you get the feeling, but it's totally wrong. I haven't discussed or seen this question in any other forum i've visited, thats why i thought i would try here. It does seem though that perhaps i was wrong to ask in this forum.

On a scale of relevence to this forum your original question rates 8.6. The average rating for threads started on this forum is 6.3. The average relevence rating for all posts on this forum is 3.8. Your last post rates 2.4.

[J. Edlund]

As soon the driver releases the throttle and the engine is connected to the wheels there will be engine braking. On a racing car I can't think of a reason you would need a high engine braking performance though. The engine that require the most torque to turn over when driven by an outside source would however provide the highest engine braking performance.

[saiyuki]

@ J.Edlund Thanks for the info

[gruntguru]

As soon the driver releases the throttle and the engine is connected to the wheels there will be engine braking. On a racing car I can't think of a reason you would need a high engine braking performance though. The engine that require the most torque to turn over when driven by an outside source would however provide the highest engine braking performance.

Engine braking of course affects the brake balance by increasing the braking effort at the driven axle only. One good reason not to use it in racing - but perhaps a good reason to use it if a short term adjustment to brake balance was required (on dirt perhaps?)

[Ross Stonefeld]

Well it must be used for something, because everyone in racing is doing it. The guy in cheap's video looks like he's delaying it to minimise wear on the gearbox/engine more than anything.

[OfficeLinebacker]

Sounds like engine braking reduction/modulation. I wonder what the control strategy would be with a carb and throttle cable however.

Not sure, but we've talked about it a few times in the NASCAR threads, it's kind of a well-known thing for people who watch NASCAR closely, but it's not talked about in the press or anything because it's not interesting enough to the casual fan I guess.

[Tenmantaylor]

Engine braking is a useful thing to fall back on in a road car if your brakes fail and you have a manual car. My main understanding of engine braking in racing is 'engine braking reduction' (EBR) used in F1 sims like Rfactor and LFS. I believe it is used extensively in real F1 and before the standard ECU was introduced it was a much exploited area of electronic diff control under braking to stabilise the car.

It's a really useful setting for adjusting the 'coast' (off throttle) characteristics of car behaviour or adding braking stability in certain braking zones by optimising the setting to match the requirements. The setting on F1 cars is to offset the naturally occuring engine braking by keeping a small amount of throttle applied when the driver lifts from insanely high revs. The EBR setting is how much throttle remains applied automatically by the ECU until the revs have dropped suffiently to not cause a problematic amount of drag to the wheels. If this setting wasn't there the friction of the engine at 19000rpm (especially at lower speeds where less DF is being generated) would lock the driven wheels very easily and cause a lockup or spin.

In FSR the place I found playing with this setting helped most was in the Maggots/Becketts comlex and Club corner at Silverstone which are very high entry speed corners but require hardly any or no braking. Using a very low ERB setting (read: high amount of engine braking) here meant the car could be driven with only the throttle; a large lift bled off enough speed and brought the back end around enough and pulled the nose in to the apex as the rear rear wheels are effectively braking in isolation. Controlling the yaw of an F1 car at 180mph with just the throttle and nailing an apex is pretty cool.

[cheapracer]

Well it must be used for something, because everyone in racing is doing it. The guy in cheap's video looks like he's delaying it to minimise wear on the gearbox/engine more than anything.

Everyone? I posted evidence to the contrary (that you're making an excuse for) now post yours thanks.

Winners by the way.

Edited by cheapracer, 16 August 2010 - 16:53.

[cheapracer]

Hmmm @cheapracer, i don't know why you get the feeling, but it's totally wrong. I haven't discussed or seen this question in any other forum i've visited, thats why i thought i would try here. It does seem though that perhaps i was wrong to ask in this forum.

I did put a question mark at the end of the err, question.

No this is a good forum for an answer to that but I am unaware of the classes and the engine regs that would identify engine braking such as engine size, car weight, standard or non standard flywheels and compression ratios etc.

[Ross Stonefeld]

Everyone? I posted evidence to the contrary (that you're making an excuse for) now post yours thanks.

Winners by the way.

You posted a youtube link to a club racer.

[cheapracer]

You posted a youtube link to a club racer.

Slipstreaming and passing the Corvette at near 200 MPH didn't indicate he is something above a club racer?

http://mikeskeen.com/resume.html

Theres a number of recent record setting Nurburgring incar runs on this page all with professional drivers in factory road cars obviously wanting to use every fast technique they can but not one slams down through the gears ....
http://www.streetfir...x?t=nurburgring

[SteveCanyon]

Well it must be used for something, because everyone in racing is doing it. The guy in cheap's video looks like he's delaying it to minimise wear on the gearbox/engine more than anything.

I'm a racer and never ever do it.
I'll go straight from top (5th) gear on my car into 2nd as I finish the braking into a corner if that's what's needed. As mentioned above, relying on engine braking & going down through the gears is generally a bad idea.
The middle pedal stops the car.

[Ross Stonefeld]

So why is it top drivers in top cars in top racing series are going down the gears as soon as they can? Theres an F1 race next weekend if anyone isn't sure of what I'm talking about.


cheap, all you've done is post the CV of a guy driving production raced cars in regional/amateur series. I'm not saying the guy is crap, just that he's not the gold standard of how race cars operate or are driven.

[SteveCanyon]

So why is it top drivers in top cars in top racing series are going down the gears as soon as they can? Theres an F1 race next weekend if anyone isn't sure of what I'm talking about.

Hate the break the news to you, but you have no choice with a sequential-shift gearbox.

[Ross Stonefeld]

Sure, you can't skip gears, but neither are they waiting until the last minute to go down the gears. Maybe when we talk about engine braking we're talking about definitions, but any high end race car is downshifting very soon after the application of brakes. They aren't chirping down at the last minute, there's some definite rev-up when they downchange.

[Greg Locock]

Incidentally the actual amount of engine braking is fairly small compared with the proper brakes and aero drag. Isn't it just the fmep?

It's usefulness/danger lies in that it changes the front/rear proportion.

[saiyuki]

@ cheapracer, sorry i jumped on you. I missed the question mark you referred to, and would like to apoligise

Onwards...........

[shaun979]

IMO, only reason to downshift early is to keep some time in reserve (before turn in) in case there is human/mechanical/electronic error and a shift is not executed properly, and to keep driver composed for turn in.

Downshifting really late is easier on the engine, gearbox, fuel consumption (though minute) but more difficult to judge since you lose "throttle-blip resolution" even with electronic blips, much less a human doing it. The reduced amount of engine braking also allows better control of true brake bias, though some might say they want to use it to influence bias at will, to a degree.

[gruntguru]

Sure, you can't skip gears, but neither are they waiting until the last minute to go down the gears. Maybe when we talk about engine braking we're talking about definitions, but any high end race car is downshifting very soon after the application of brakes. They aren't chirping down at the last minute, there's some definite rev-up when they downchange.

I think the downshifting functions best when the road-speed/engine-speed/gear-ratio are matched even if the clutch doesn't get engaged.

[Spoofski]

I think the downshifting functions best when the road-speed/engine-speed/gear-ratio are matched even if the clutch doesn't get engaged.

The short braking times (~2s) of an F1 car mean there is little time to pick and choose when to downshift: it needs to be done as soon as coming off the throttle as possible. An additional benefit of early d/s is that the car's pitch settles sooner. As a consequence there is a lot of focus on reducing torque transients at the rear. Bikes do the same for broadly similar reasons: although the braking times are longer so is the settling time. This is one reason for using a slipper-clutch although these days the clutch tends to be used in conjunction with throttle/rear torque modulation strategies.

[Tony Matthews]

The middle pedal stops the car.

I know we are talking racing procedures, but on the road it helps to remember that the brake pedal is there for a purpose. Many years ago in my home town a local business man - also an engineer - had a Lotus Elite. For some reason his driving style entailed using the brakes as little as possible, relying on engine braking whenever possible. One day he met a situation which necesitated an emergency stop, but the pads were so glazed with lack of use that an accident ensued.

[desmo]

"Glazed with lack of use"? Really?

[Tony Matthews]

"Glazed with lack of use"? Really?

That was the term used at the time - as the pads make slight contact I imagine thousands of miles without hard use may have polished the pads. I may well have been misinformed in detail, but that was the considered reason for the accident!

[Lee Nicolle]

To me engine braking is part of the braking and the car should be set up to use it. Any half decent piston engined car usually has high compression and light flywheel clutch etc. Meaning you have a lot of natural engine braking. Very usefull for balancing a car on high speed corners. Obviously the driver has to match revs with road speed for slower corners but if you are not using it you are stupid. And going 5 to 2 is dumb, how the hell do you get the gear to go in without wrecking the gearbox?And locking up the rear of the car?
And I have done a lot of motorsport in 40 years! Using the engine braking is part of the braking!
On road cars using engine braking is a very good idea, and when towing or driving commercial vehicles imperative. Manual or auto. On long inclines clicking back 1 gear generally saves you frying the brakes, and often keeps you under the speed limit too. I so often see dumbasses fly by me on hills and you pull up alonside them at the bottom and you can see the brakes smoking, brake dust everywhere. meanwhile I have arrived at the same time with minimal brake use. And that includes government buses with 70 people on board!!

[SteveCanyon]

And going 5 to 2 is dumb, how the hell do you get the gear to go in without wrecking the gearbox?And locking up the rear of the car?
And I have done a lot of motorsport in 40 years! Using the engine braking is part of the braking!

I do it perfectly every time, thanks for asking.
I don't have any of me in the racer doing it but here a lap in the Corolla I ran in the five Malaysian 12 Hour races I did. At the end of the long straights you can see me go from 5th to 3rd each time.

[Lee Nicolle]

I do it perfectly every time, thanks for asking.
I don't have any of me in the racer doing it but here a lap in the Corolla I ran in the five Malaysian 12 Hour races I did. At the end of the long straights you can see me go from 5th to 3rd each time.

5/3 depending on gearbox ratios maybe though not good practice but 5/2 is dumb and slow and so easy to unsettle [or lock up] the rear of the car. And tear the gearbox to bits.

[shaun979]

if speed is low enough before the accurately matched blip, the rear won't lock and the gearbox won't blow up... what are you talking about? There's no reason you can't do 5-2

[SteveCanyon]

if speed is low enough before the accurately matched blip, the rear won't lock and the gearbox won't blow up... what are you talking about? There's no reason you can't do 5-2

Quite correct. There's nothing wrong at all with going 5th direct to 2nd gear if you do it properly and I do. If the car had a 6th gear and we used it I'd still do the same.
In the racer the braking distance/time is short enough there isn't really enough time to go down through the gears anyway so why be dancing on the brake pedal if it's certainly not needed and is more likely to upset the car.

5/3 depending on gearbox ratios maybe though not good practice but 5/2 is dumb and slow and so easy to unsettle [or lock up] the rear of the car. And tear the gearbox to bits.

Ah-hem, that car in the video is a FWD not a RWD, and it survived quite well for the entire 12 hours. The same gearbox in a different Corolla does the job in 24 hour races as well.

Edited by SteveCanyon, 20 August 2010 - 09:13.

[Ninja2b]

Engine braking is a very useful tool in motorsports. So long as you can control it effectively, it's an additional way to slow the car down. No point throwing away free braking...

[cheapracer]

Engine braking is a very useful tool in motorsports. So long as you can control it effectively, it's an additional way to slow the car down. No point throwing away free braking...

Really?

Please explain because I totally disagree....

[Spoofski]

So long as you can control it effectively,

@CR
This bit is quite important.

[cheapracer]

@CR
This bit is quite important.

Explain away, I'm all ears ............

[mariner]

I love the US "jake brake" which uses valve control on a high compression diesel to modulate engine braking on long down grades. It makes a wonderful but very noisy popping sound i.e


The best bit is that local town councils put up signs " no jake brake" to stop the noise so as the truck comes off the hill into town with faded friction brakes they switch off the jake brake and th truck careers through town brakeless !! ( just kidding)

Of course the Europeans being so much more environmental than Americans use electric Telma retarders which are silent.

[Spoofski]

Explain away, I'm all ears ............

Well, me dinner's ready so I'll save the long answer 'till next time. In the meantime: why do you suppose things like the Weismann quick-shifter (free-running on overrun) are not used in F1, and Sprag clutches are not used in MotoGP? Wouldn't everyone just dump the clutch as soon as they hit the brakes if braking torque is such a problem?

[Spoofski]

I'm all ears ............

You must be a very handsome lad.

[Spoofski]

OK,

1 It's physically impossible to lock the brakes of a high downforce car from high speed (without power assistance) meaning that the car is underperforming under braking. As stated above, EB is free braking, why waste it especially when it is adding genuine performance under braking?
2 When permitted by the regs, software can control the braking phase in a manner similar to inverse traction-control. In its basic form this gives a kind of ABS.
3 Following on from this it is possible to have a dynamic brake-balance control system which can vary corner-to-corner and which can mitigate the shifting balance during braking with open- and closed-loop components. In both of these cases the braking torque is needed to give enough control authority.
4 Even with no electronics a decent driver will use the under-rotation of the rear wheels to control the yaw on turn-in. As I mentioned above this is difficult in F1 because of the short braking distances hence the reason electronics came to play such a major part in it all.
5 There're probably more but it's been a while since I dicked with this stuff.

I haven't encountered the quick-shifter brake-bias controllers which I believe are now in common use, but my (hazy) understanding of them is that they are a mechanical/manual method of partially emulating point 3 above.

Notwithstanding the above, EB is a feature of all engines: eliminating it requires either mechanical systems to freewheel on overrun, or an idle-throttle strategy to control torque to zero. In both cases you are wasting fuel and throwing away an exploitable resource.

[Tony Matthews]

From page 148 of Autosports very nice 60th Anniversary Edition - David Brabham on the Lotus 79 - "I arrived there pretty quickly, got on the anchors, used the gears to help slow the car."

[gruntguru]

1 It's physically impossible to lock the brakes of a high downforce car from high speed (without power assistance) meaning that the car is underperforming under braking.

But not technically impossible. Strange that competitors in the premier motorsport class would choose to leave a critical piece of performance on the table?

[Ross Stonefeld]

It's not impossible, but it's beyond the realms of what is achievable by the driver.

[gruntguru]

It's not impossible, but it's beyond the realms of what is achievable by the driver.

But not technically impossible to bring it within the realms of what is achievable by the driver.

Edited by gruntguru, 29 August 2010 - 10:58.

[Ross Stonefeld]

Well I suppose with the right rulebook an F1 car could accomplish most things.

[gruntguru]

Well I suppose with the right rulebook an F1 car could accomplish most things.

I'm talking about the current rulebook. Are you saying that the engineers can't design a non-assisted braking system that will lock the wheels at max DF or is the system deliberately limited to work within the shear capacity of the tread?

[Ross Stonefeld]

If it's non assisted, where is the force going to come from other than the driver's leg?

[cheapracer]

OK,

1 It's physically impossible to lock the brakes of a high downforce car from high speed (without power assistance) meaning that the car is underperforming under braking. As stated above, EB is free braking, why waste it especially when it is adding genuine performance under braking?
2 When permitted by the regs, software can control the braking phase in a manner similar to inverse traction-control. In its basic form this gives a kind of ABS.
3 Following on from this it is possible to have a dynamic brake-balance control system which can vary corner-to-corner and which can mitigate the shifting balance during braking with open- and closed-loop components. In both of these cases the braking torque is needed to give enough control authority.
4 Even with no electronics a decent driver will use the under-rotation of the rear wheels to control the yaw on turn-in. As I mentioned above this is difficult in F1 because of the short braking distances hence the reason electronics came to play such a major part in it all.
5 There're probably more but it's been a while since I dicked with this stuff.

I haven't encountered the quick-shifter brake-bias controllers which I believe are now in common use, but my (hazy) understanding of them is that they are a mechanical/manual method of partially emulating point 3 above.

Notwithstanding the above, EB is a feature of all engines: eliminating it requires either mechanical systems to freewheel on overrun, or an idle-throttle strategy to control torque to zero. In both cases you are wasting fuel and throwing away an exploitable resource.

1/ Besides being bullshit whats that got to do with the subject unless you actually think race drivers want the rear wheels to lock?

2/ So what, they are using engine overrun for another reason ....

3/ Again so what, what has this got to do with drivers using engine BRAKING?

4/ If you had left your argument that the throttle control and the use of engine torue either way can supplement driver control during the cornering phase after actual 'get rid of the speed' braking I would certainly agree with you, but your trying to throw off car balance control as engine braking.

5/ Oh you certainly dicked with it.

All you have indentified here is anti engine braking to stop causing **** control, not pro braking.

Edited by cheapracer, 30 August 2010 - 11:58.

[cheapracer]

From page 148 of Autosports very nice 60th Anniversary Edition - David Brabham on the Lotus 79 - "I arrived there pretty quickly, got on the anchors, used the gears to help slow the car."

? and ..... Wheres the context?

David was 14 years old in 1979 so we are talking about a retro drive and what condition was the car in - wooden pads etc?

Nice way to treat an old classic that I'm sure wasn't his besides by his own admission he obviously stuffed the corner up.