understeer explanation for the s2
Discussion
concerning this discussion on the understeer of the s2 and the changing of the tyre sizes, i read with interest the report that i've copied below, i just have some problems with the explanation, if i'm labouring under a false impression please let me know, i'm not anti s2, i'm not anti what they've done with it, i'm just anti explanations that don't make sense, if it was doen for safety, i have no problem with it, just say so, anyway...
For anyone interested, Nick Adams of Lotus gave an explanation on the OLC BBS some time ago for the change in tyres sizes on the S2. The main points were as follows:
- The original Elise used an off the shelf tyre set and as a result did not have the ideal handling balance Lotus wished for. Essentially, the car had a bit too much front grip in the dry (making it more prone to lift off oversteer) and a bit too little front grip in the wet. The latter was essentially due to the front tyres being a bit too wide for the low front axle weight of the car (less than 1/3 of that of a typical FWD hatch for which the tyre was designed) resulting in the water getting under the tyre.
- The narrow front tyre on the S2 (and VX220) was chosen not to promote understeer as everyone seems to think, but to provide better front end grip in the wet. The narrower tyre increases the front contact patch pressure, thus cutting through the water better.
- All things being equal, the above would reduce dry weather grip too much so the compound of the tyre was softened to compensate for this. Lotus claim that this works and that ultimately in the dry a standard S2 will stay neutral longer than a standard S1.
- There is however a slight problem with the above approach, which explains why some S2 drivers experience excessive understeer. Softening the tyre to compensate for reduced width only works fully when the car has settled into a corner and achieved maximum weight transfer to the outside wheel. In practical terms this means the S2 requires a gentler approach to turning in so that the outside tyre can load in phase with the build up of lateral g. Drivers, on the other hand, who turn in abruptly will be more likely to get unwanted understeer as the lateral force will build up quicker than the car can roll and load up the outside tyre. Once the understeer has started its too late regardless of the tyre eventually getting the benefit of the weight transfer (as dynamic friction is less than static friction).
- So in a nutshell the S2 needs to be driven with smooth inputs to the helm to get the best out of it. If driven so, a standard S2 will stay neutral at marginally higher speeds than a standard S1 in the dry and at considerably higher speeds in the wet.
Hopefully my memory is good and that is an accurate summary of the official line from the Chief Engineer on the S2 project. As an automotive design/development engineer myself it all seems perfectly sound, although I will admit that ride and handling is not my particular field of expertise.
So next time that someone says that the S2 has skinny tyres to cater for hairdressers or some other section of society deemed to be unskilled drivers you will know that they are talking out of their ill-informed arses. In fact it seems that the exact opposite is true; the car requires a degree of finesse to perform to it's best as fully demonstrated by the time achieved (in the wet) by the Stig on Top Gear last Sunday.
ok so here goes
1)The original Elise used an off the shelf tyre set and as a result did not have the ideal handling balance Lotus wished for.
this could well be true, we know that the elise was built on a shoe string budget and on a tight timetable, that and the relative comercial failure of the elan would make it hartd to persuade any tyre producer to make a tyre for a car that may be sold in small numbers and may fall apart where it was glued together, that and there wasn't as far as i'm aware, such a light, mid engined car that already existed in nay form for them to use the tyres for.
2)Essentially, the car had a bit too much front grip in the dry (making it more prone to lift off oversteer) and a bit too little front grip in the wet. The latter was essentially due to the front tyres being a bit too wide for the low front axle weight of the car (less than 1/3 of that of a typical FWD hatch for which the tyre was designed) resulting in the water getting under the tyre.
i'm not going to get into the argument of the grip balance ( personally i'll risk the lift off oversteer to reduce the understeer, although what would the effect of using the same front and wider rear tyres be on the lift off oversteer?) and yes the front of the car is very light, but would a better tread pattern taking into account the lightness of the car not help here, and is he suggesting that pirelli p zeros were designed for a fwd hatch? has anyone ever come across a fwd hatch that had these as the standard fitted tyre or recommended upgrade?
3)- The narrow front tyre on the S2 (and VX220) was chosen not to promote understeer as everyone seems to think, but to provide better front end grip in the wet. The narrower tyre increases the front contact patch pressure, thus cutting through the water better.
ok yes i can see thinner front tyres would cut through stading water better, but i also seem to remember that people talk about the front contact area being the same due to the greater pressure on the thinner tyre producing a bigger foot print, no assuming the both front axles are the same, and if the foot prints are the same, then surely the pressure is the same, and since it is this pressure which helps with driving on we roads ( as opposed to driving through standing water) then surely there is no advantage most the time, and lets face it, any car driving through stading water is at risk of aqua planing, surely it's a tread problem
4)- All things being equal, the above would reduce dry weather grip too much so the compound of the tyre was softened to compensate for this. Lotus claim that this works and that ultimately in the dry a standard S2 will stay neutral longer than a standard S1.
as far as i can see, softer compound=less life
as i understand as well, the softer the compound, the more temprature dependent it is, which means that on a track once it's warm, yes i'm sure that's true, but in the uk where it's cold for 6 months of the year, then i suspect the tyres often don't get anywhere near the temprature they need to generate the same grip, yes i know thinner tyres will generate more heat, but once in contact with a cold road that's gone, surely this is worst in the wet? the very reason that the thinner tyres were put on.
The other point is that although on a smooth track the contact area may be the same, what about on our rough public roads, does a narrower tyre suffer more or less from pot holes, white lines, variations in tarmac where they've dug up the road, both in grip and in suspension?
5)the difference in the way you have to drive, is it me or are they saying, if you think it's understeering, it's not our fault, it's yours for being a bad driver, which is kind of the excuse they used for the lift off oversteer, i think they used the expression " novice driver"
let me know wat you guys think, i'm not complaining abouyt the s2 or saying the s1 is better than the s2 or visa versa i just think lotus owe it to be honest, and stop blaming things on the drivers, see lotus, no drivers=no lotus
For anyone interested, Nick Adams of Lotus gave an explanation on the OLC BBS some time ago for the change in tyres sizes on the S2. The main points were as follows:
- The original Elise used an off the shelf tyre set and as a result did not have the ideal handling balance Lotus wished for. Essentially, the car had a bit too much front grip in the dry (making it more prone to lift off oversteer) and a bit too little front grip in the wet. The latter was essentially due to the front tyres being a bit too wide for the low front axle weight of the car (less than 1/3 of that of a typical FWD hatch for which the tyre was designed) resulting in the water getting under the tyre.
- The narrow front tyre on the S2 (and VX220) was chosen not to promote understeer as everyone seems to think, but to provide better front end grip in the wet. The narrower tyre increases the front contact patch pressure, thus cutting through the water better.
- All things being equal, the above would reduce dry weather grip too much so the compound of the tyre was softened to compensate for this. Lotus claim that this works and that ultimately in the dry a standard S2 will stay neutral longer than a standard S1.
- There is however a slight problem with the above approach, which explains why some S2 drivers experience excessive understeer. Softening the tyre to compensate for reduced width only works fully when the car has settled into a corner and achieved maximum weight transfer to the outside wheel. In practical terms this means the S2 requires a gentler approach to turning in so that the outside tyre can load in phase with the build up of lateral g. Drivers, on the other hand, who turn in abruptly will be more likely to get unwanted understeer as the lateral force will build up quicker than the car can roll and load up the outside tyre. Once the understeer has started its too late regardless of the tyre eventually getting the benefit of the weight transfer (as dynamic friction is less than static friction).
- So in a nutshell the S2 needs to be driven with smooth inputs to the helm to get the best out of it. If driven so, a standard S2 will stay neutral at marginally higher speeds than a standard S1 in the dry and at considerably higher speeds in the wet.
Hopefully my memory is good and that is an accurate summary of the official line from the Chief Engineer on the S2 project. As an automotive design/development engineer myself it all seems perfectly sound, although I will admit that ride and handling is not my particular field of expertise.
So next time that someone says that the S2 has skinny tyres to cater for hairdressers or some other section of society deemed to be unskilled drivers you will know that they are talking out of their ill-informed arses. In fact it seems that the exact opposite is true; the car requires a degree of finesse to perform to it's best as fully demonstrated by the time achieved (in the wet) by the Stig on Top Gear last Sunday.
ok so here goes
1)The original Elise used an off the shelf tyre set and as a result did not have the ideal handling balance Lotus wished for.
this could well be true, we know that the elise was built on a shoe string budget and on a tight timetable, that and the relative comercial failure of the elan would make it hartd to persuade any tyre producer to make a tyre for a car that may be sold in small numbers and may fall apart where it was glued together, that and there wasn't as far as i'm aware, such a light, mid engined car that already existed in nay form for them to use the tyres for.
2)Essentially, the car had a bit too much front grip in the dry (making it more prone to lift off oversteer) and a bit too little front grip in the wet. The latter was essentially due to the front tyres being a bit too wide for the low front axle weight of the car (less than 1/3 of that of a typical FWD hatch for which the tyre was designed) resulting in the water getting under the tyre.
i'm not going to get into the argument of the grip balance ( personally i'll risk the lift off oversteer to reduce the understeer, although what would the effect of using the same front and wider rear tyres be on the lift off oversteer?) and yes the front of the car is very light, but would a better tread pattern taking into account the lightness of the car not help here, and is he suggesting that pirelli p zeros were designed for a fwd hatch? has anyone ever come across a fwd hatch that had these as the standard fitted tyre or recommended upgrade?
3)- The narrow front tyre on the S2 (and VX220) was chosen not to promote understeer as everyone seems to think, but to provide better front end grip in the wet. The narrower tyre increases the front contact patch pressure, thus cutting through the water better.
ok yes i can see thinner front tyres would cut through stading water better, but i also seem to remember that people talk about the front contact area being the same due to the greater pressure on the thinner tyre producing a bigger foot print, no assuming the both front axles are the same, and if the foot prints are the same, then surely the pressure is the same, and since it is this pressure which helps with driving on we roads ( as opposed to driving through standing water) then surely there is no advantage most the time, and lets face it, any car driving through stading water is at risk of aqua planing, surely it's a tread problem
4)- All things being equal, the above would reduce dry weather grip too much so the compound of the tyre was softened to compensate for this. Lotus claim that this works and that ultimately in the dry a standard S2 will stay neutral longer than a standard S1.
as far as i can see, softer compound=less life
as i understand as well, the softer the compound, the more temprature dependent it is, which means that on a track once it's warm, yes i'm sure that's true, but in the uk where it's cold for 6 months of the year, then i suspect the tyres often don't get anywhere near the temprature they need to generate the same grip, yes i know thinner tyres will generate more heat, but once in contact with a cold road that's gone, surely this is worst in the wet? the very reason that the thinner tyres were put on.
The other point is that although on a smooth track the contact area may be the same, what about on our rough public roads, does a narrower tyre suffer more or less from pot holes, white lines, variations in tarmac where they've dug up the road, both in grip and in suspension?
5)the difference in the way you have to drive, is it me or are they saying, if you think it's understeering, it's not our fault, it's yours for being a bad driver, which is kind of the excuse they used for the lift off oversteer, i think they used the expression " novice driver"
let me know wat you guys think, i'm not complaining abouyt the s2 or saying the s1 is better than the s2 or visa versa i just think lotus owe it to be honest, and stop blaming things on the drivers, see lotus, no drivers=no lotus
Very interesting post Piquet. I have to say I agree with some of the points you have raised. I think the thin tyre argument for the road in the wet is a little weak. Certainly thin tyres will be better all things being equal but in my experience tread pattern is far more important. For example my mini has far narrower tyres than the cars I've had before but I have found that the mini is far far better in the dry than in the wet. My thoughts is that the standard tyres are not good at getting rid of water. I certainly will be changing the tyres for a wider but better pattern effect when these have run out.
Pzeros are fitted to Porsche (IIRC) and they are RWD. The comment I got from a tyre specilist was that the pzeros are a high performance tyre and were designed for a heavier car (eg BMW M3, Porsches etc.). I've just looked on the pirelli database and the smallest size Pzero is 185x55x15 all the rest have a wider width and/or fit wheels with a of 15" or greater, Certainly NOT FWD hatchback size.
As you say I think its Lotus trying to put the blame back on the driver.
>> Edited by smeagol on Monday 23 December 16:13
Pzeros are fitted to Porsche (IIRC) and they are RWD. The comment I got from a tyre specilist was that the pzeros are a high performance tyre and were designed for a heavier car (eg BMW M3, Porsches etc.). I've just looked on the pirelli database and the smallest size Pzero is 185x55x15 all the rest have a wider width and/or fit wheels with a of 15" or greater, Certainly NOT FWD hatchback size.
As you say I think its Lotus trying to put the blame back on the driver.
>> Edited by smeagol on Monday 23 December 16:13
Lotus also claim that under identical circumstances the S2 is a marginally faster car round their test track than the S1, and the S1 is measurably lighter . . . whether this is PR or BS I cannot say, the people I know who drive S2's and who have owned S1's rate the S2 as an easier car to drive at the limit and rate the S2 as equivalent or better car than the S1 in terms of lap times on known tracks in comparable conditions . . .
None of them mention understeer.
Make of that what you will
Fd
None of them mention understeer.
Make of that what you will
Fd
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