Talk:Understeer

From Wikipedia, the free encyclopedia

Contents 1 Table 2 More values 3 External Link 4 Diagram 5 Removing references 6 Tyre placement 7 Understeer values citation? 8 Dubious 9 Possible links?

[edit] Table

The section on actual understeering values says that "How much a car understeers can be measured in the number of degrees more the streering wheel have to be turned per G of force. Here are values for some cars.[1] The higher the number the more the car oversteers.". Howcome having to turn more rather than less means it oversteers? Shouldn't it read that "the higher the number the more the car understeers"? 62.169.74.64 03:45, 30 August 2006 (UTC)

Yes, you are right. I can't say I really like that list, there is no source given, and some of the number seem a little odd. I've measured a few of those cars, I'll check on Monday. Greglocock 06:17, 9 September 2006 (UTC)

Unless it has been removed there should be a source. The problem is that the web source don't give the full list. It's only available in the paper version. // Liftarn

how is this being measured. do all the cars have the same tyres or their standard tyres. because i don't believe, though could be wrong, that the Opel (vauxhall) Astra understeers less than a Impreza. if u want to compare the Astra VXR and the Impreza, which have similar power, im sure the astra understeers much, much more. let alone the torquesteer. Pratj 23:36, 9 September 2006 (UTC)

Usually you measure the linear range understeer by plotting the steering wheel angle (SWA) versus the lateral acceleration, whil driving around a constant radius, typically 30-61m. Usually you take the average gradient between 0.1 and 0.4 g, for a car. An alternative is to perform a swept steer, driving at constant speed and gradually increasing the SWA. These two methods give slightly different results. Many modern cars with good handling have a lot of understeer in order to improve their high speed performance, and yaw damping. These tests are done on the standard tires otherwise they are meaningless- changing tires can affect u/s gradient by 15 deg/g. Note that this a steady state linear range measurement, it does not addresss torque steer or limit handling. Greglocock 00:05, 10 September 2006 (UTC)

As it says on http://www.automobil.se/zino.aspx?articleID=10863 They drive the car around a curve of 50 m radius. First at 10 km/h, then increasing the speed. First they measure how direct the steering is (i.e. how much you have to turn the wheel at low speed). Then they plot a curve (see bottom of page) of steering angle (vertical) and side acceleration (horizontal). The slope of the curve shows how much the car understeers. Toward the limit of the car the curve turns abruptly showing at what speed the car terminally understeers (or sometimes terminally oversteers). // Liftarn

i understand. but would i be correct in saying that this by no means is a definite clue as to how a car would understeer under race track conditions? Pratj 14:43, 10 September 2006 (UTC)

Both yes and no. The car may oversteer if it looses grip on the rear wheels (for instance if applying too much gas in a curve). The values do show how much the car understeeers, but it's not entierly linear (even if most cars are very linear, the Morgan bean an exception) so depending on the side acceleration it may both oversteer and understeer on various conditions. // Liftarn

i think a mention of whether the car is rear wheel drive or front wheel drive should be made. as some of the rear wheel drive cars as u say will have a tendancy to power oversteer, wheras the front wheel drive cars will tend to understeer under most circumastances. Pratj 17:35, 10 September 2006 (UTC)

Hang on, these numbers mean very little in the context of a racetrack. They only apply over the linear range (where the tires are linear) - typically up to say 50% of the maximum capability of the car. The linear range understeer tells you NOTHING about limit handling. Greglocock 02:52, 11 September 2006 (UTC)

Shall we mention that this is by no means a measure of limit handling then. as i, and im sure many other ppl, would be slightly mislead by those results. Pratj 14:15, 11 September 2006 (UTC)

[edit] More values

these are for discussion only, as I can't give a source for them.

Car	My figure	Swedish mag
Nissan 350Z	35.0	19
Focus ST	34.8	33
Corvette	60.4	28
WRX	64.3	37

http://www.edccorp.com/pdfs/WP2004-3.pdf#search=%22%20%22understeer%20gradient%22%22

for some more examples

As you can see the Swedish measurements seem to be way off base. There are good reasons to believe that the 350Z could not be so low. I don't know how to resolve this.

Greglocock 02:52, 11 September 2006 (UTC)

[edit] External Link

I've added an external link to a graph on my website. If it is inappropriate delete it. It is sort of original research, but more accurately a demonstration of a well known equation. Greglocock 05:33, 25 September 2006 (UTC)

Hi Greg - not sure if anyone without some serious technical knowledge would understand this one, think this section needs to be simplified where possible Driver sam (talk) 15:46, 26 May 2008 (UTC)

Aye, mediocrity will always defeat excellence. Greg Locock (talk) 04:18, 27 May 2008 (UTC)

[edit] Diagram

i moved someones diagram request from the main page to the talk page,

if we make a diagram how do we use it on wiki? Pratj 12:27, 14 October 2006 (UTC)

i made this image. its a bit basic but it illustrates what understeer is (if u can spend more time and make a better 1 please do, i only had 5 mins). i just don't know how u edit the page to include the picture. so if someone would show me or do it themselves i would be grateful. Pratj 20:25, 14 October 2006 (UTC)

I don't know how to illustrate understeer, as opposed to oversteer. Your diagram is as good as any. The difference, in an accurate diagram, would be a tiny change in angles. Anyway, to add an image, look in toolbox on the left under the search box. Upload your file to the server. Then when you are editing hit the "editing help" link in the row of buttons beneath the edit box. This tells you the command to link to an image. Well this is baffling, you've done it? I'll move it. Change the words if you like. Greglocock 20:44, 14 October 2006 (UTC)

why has the diagram been deleted de to copyright? i made it so surely it belongs to me? Pratj 13:48, 24 October 2006 (UTC)

Perhaps you didn't state it as clearly as you should have. // Liftarn

Yeah, thanks for that (sarcasm). Pratj, can you load your picture file up using the media links, and remember to click on the button that says that it is your own original work etc. Then reload it into the page as before. Greglocock 19:45, 24 October 2006 (UTC)

I don't think I have gotten anything deleted, but I have had peaople asking for source when it clearly says "Taken by myself". Some people don't seem to check things first. // Liftarn

can't u just revert it. if not i will load it up again. Pratj 21:55, 24 October 2006 (UTC)

The important thing is that the image has a clear copyright/license tag, such as {{GFDL-self}} or similar - as mentioned on the upload page. The automatic scripts and editors who check these things will delete an image without a copyright/license tag. -- Solipsist 10:00, 25 October 2006 (UTC)

i did that last time, but i'll do it again sometime today Pratj 10:24, 25 October 2006 (UTC)

Can someone please include a diagram which illustrates the phenomena clearly? 143.53.7.186 02:54, 7 December 2006 (UTC)

[edit] Removing references

Go on, tell me why the reference to Carroll Smith was removed? Most articles I write get pinged for not including references Greglocock 21:46, 27 December 2006 (UTC)

[edit] Tyre placement

Not very happy with the "Common Practice" section. Fitting new tyres to the front doesn't increase understeer, it usually reduces it. The potential safety problem is that it can induce lift-off oversteer. -- Ian Dalziel 16:25, 1 January 2007 (UTC)

yeah, i agree. the problem is understeer normally results in increased front tire wear. so u have no choice. Pratj 18:33, 1 January 2007 (UTC)

Pratj- I'm glad you are sorting that horrible para out, the one that Liftarn hit with the BF cite G. As to Ian's point The correct thing to do is to move the least worn old tires to the front axle, and fit the newies on the back. There's optimism for you Greglocock 23:06, 31 January 2007 (UTC)

Indeed - but that isn't an answer to my point, it's agreeing with it! Fitting new tyres to the front does NOT increase understeer, so the item is completely wrong, reference or no reference. The reference doesn't mention understeer, by the way. -- Ian Dalziel 06:39, 1 February 2007 (UTC)

[edit] Understeer values citation?

There's a citation in "Understeer values" but it doesn't link to anything. Disappointing, as I've like to know where the numbers came from...

They came from the sports car magazine Automobil, but the link will do no good since the list is only published in the paper version. // Liftarn

[edit] Dubious

"However, in certain cars and under certain circumstances(e.g when there is a small amount of grip still available) the understeer can be reduced by applying full power to the wheels rather than braking"

This either needs to be amplified up into an explanation of when and how, or deleted, in my opinion. At the very least is the editor talking about linear range or terminal? front wheel drive or rear? It just looks like an anecdote to me. Actually the whole of that Design section needs a complete rewrite, and a better structure. I'd suggest separating FWD and RWD, linear and terminal, etc etc. Greg Locock (talk) 22:57, 22 January 2008 (UTC)

I m talking about a front wheel drive car. And I m talking about when there is some grip left available. It sounds really wierd but if you ve wathced for example MotoGP (not entirely irrelevant) you may have seen cases where the bike seems to be going off track, and the driver applies full power and keeps the bike on the track. The same thing happens with my car, and possible many others. It is a Nissan Almera and I can kill the understeer by accelerating. This DOES NOT apply when the car has reached its physical limits of grip. Unfortunately I don't know how I can explain it better or give a citation. 147.27.47.82 (talk) 10:16, 23 January 2008 (UTC)

I think MotoGP and FWD are, to say the least, a hard stretch to combine. Shall I go and ask a real live MotoGP tire engineer? Is an Almera FWD or RWD? What you are describing is throttle-on tuck-in - I see it all the time in a RWD on gravel, although not on the limit. Greg Locock (talk) 10:29, 23 January 2008 (UTC)

Take a look at this, maybe it will help http://www.iwsti.com/forums/driving-tips-techniques/22357-do-you-ever-accelerate-midst-turn.html The user WE_R_ND describes that when he accelarates in a corner his car doesnt push to the outside of a turn. It is about an awd car.

Ok maybe I havent understand well what the term understeer includes. (I'm definetely not talking about terminal understeer). Maybe the best thing to do is delete it...147.27.47.82 (talk) 10:48, 23 January 2008 (UTC)

Well, BBs are a lousy reference. What they talk about is real, but way beyond the scope of this article. that's a transient event. Greg Locock (talk) 11:02, 23 January 2008 (UTC)

wow, been a year since i left this article, i thought it was in good shape then. anyhow:

yes, the statement that actually applying full power can actually decrease understeer better than braking seems odd to me... braking can actually cause snap oversteer as the shift in weight to the front wheel provides better traction to the front wheels (and makes the back end light) causing a spin. i have actually heard of very few cases, particularly since the emergence of good ABS on modern cars, of braking actually increasing understeer but i do accept there is a limited possibility. however, applying FULL throttle is never going to reduce understeer. lets say i have 100 "grips" (G) from my front tires. with no throttle 100G are going towards turning the car, with some throttle 20G to transfering torque to the ground and 80 G for turning. accelerating hard around a corner it may be 50G torque, 50G turn... but as u see, from this basic formula i just invented that u only have a limited amount of grip, and the more grip going towards "moving" the car the less there is for turning resulting in understeer.

however, all of this is based on a front wheel drive car. it is possible to reduce understeer by deliberately spinning the rear wheels on a RWD car. therefore all you are doing is disguising understeer with power oversteer.

I think we should remove the statement, or make it a lot clearer unless some form of evidence can be found for it. Pratj (talk) 19:16, 28 January 2008 (UTC)

It's not just a FWD/RWD issue, but also the engine orientation that affects behavior in the corner. If you're driving a mid-engine car, then letting up on the gas or braking during a hard turn can result in snap-oversteer as mentioned in the previous sentence. In this type of vehicle, understeer may be what tempts you to slow down. The risk of snap-oversteer is the reason not to. 24.19.238.74 (talk) 09:07, 9 April 2008 (UTC)

[edit] Possible links?

Hi - I was reading this article and it seems to have quite an engineering focussed style of definition. I've done a but of research and found a few external references which may be useful for the reader with less of a physics / maths based background. There doesn't seem to be much out there but:

http://news.bbc.co.uk/sport1/hi/motorsport/formula_one/car_behaviour/default.stm - a BBC explanation of understeer and oversteer

http://www.drivingfast.net/car_control/understeer.htm - a dedicated article on understeer

Driver sam (talk) 11:57, 26 May 2008 (UTC)

Well I guess it depends on whether you want a schoolkid's encyclopaedia or a more generally useful one. The first article is too simplistic by far, the second one is confusing and unhelpful (it could be summarised as find what you are doing that causes the underster and then stop doing it). But it does at least suggest that things are not straightforward. Greg Locock (talk) 04:15, 27 May 2008 (UTC)

Many people use wikipedia as a first port of call when looking up automotive terms such as understeer and oversteer (probably including schoolkids!). Such terms, although commonly used in engineering are also useful for driving enthusiasts and anyone interested in motorsport. I'm sure you have an engineering background, but launching straight into relatively complex terminology doesn't help most people unless they have a residual knowledge on these topics. I'd welcome your suggestions on an external link which might help provide a more basic explanation, or I think it would be beneficial to have a 'dummies guide' to understeer at the start, same for the oversteer section. I'm not suggesting rewriting the article, but simply adding some more beginner friendly info. What did you find confusing in the second link, do you think there anything which could be re-written for this section? Would be interested to see what others think, or am I way off the mark here? Driver sam (talk) 16:17, 27 May 2008 (UTC)

I'm going to add the latter of the two articles primarily due to the decent illustrations. But as Greglocock has suggested, I do think there may be better links around so please feel free to suggest some. May do the same for oversteer, but would be great if someone could come up with a decent image for wikipedia on these topics. Driver sam (talk) 16:01, 10 June 2008 (UTC)