Long vs short wheelbase.

[chernaudi]

Much has been made of the Audi R10's wheelbase. At an estimated 2980mm( almost 118 in), it's probably one of the longest since the earliest LM cars. Where as the R8 had a 2740mm(107.9 in) wheelbase. How does this effect handling, as it seems that both cars are among the best handling prototypes out there right now.

[jhansen]

Personally, I don't think you can say that either the R8 or R10 are the best handling. Audi always seem to have the best overall package (especially at LeMans). The Zytek would certainly be at or near the top of the list in terms of handling. Largely due to the fabulous aero package.

Wheelbase is a factor I'm sure. Long and short wheelbase each have their merritts. Each has a trade off I would imagine.

Edit: The R8 was known to suffer from understeer. I think they tried to correct this in the R10 with the wider front tires. But then, the longer wheelbase may counter that a bit. This is definitely a question for the techies.

[I love 04s]

Originally Posted by jhansen

Personally, I don't think you can say that either the R8 or R10 are the best handling. Audi always seem to have the best overall package (especially at LeMans). The Zytek would certainly be at or near the top of the list in terms of handling. Largely due to the fabulous aero package.

Wheelbase is a factor I'm sure. Long and short wheelbase each have their merritts. Each has a trade off I would imagine.

Edit: The R8 was known to suffer from understeer. I think they tried to correct this in the R10 with the wider front tires. But then, the longer wheelbase may counter that a bit. This is definitely a question for the techies.

Couldn't agree more. The R8 did indeed suffer a little from inherent understeer, not sure what the R10 is like. I think you'll find that the Zytek 04s/Creation 02s was probably the best handling LMP in recent years......every driver that has had the joy of driving it all say it is simply unbelievable - all due to the enormous amount of downforce that aero package produced. If my memory serves me right Nick Minass' said that taking the Porsche curves in that car is something he will never forget......

As for wheelbase - im sure there is a techie here who could answer that one........

[chewymonster]

In production cars a longer wheelbase is always a good thing as it gives more passanger space and shorter overhangs, in race cars I don't really know.

[Bob Riebe]

Originally Posted by chewymonster

In production cars a longer wheelbase is always a good thing as it gives more passanger space and shorter overhangs, in race cars I don't really know.

Over-hang is the result of body and bumper system design; wheelbase can be either short or long, with large or small over-hang.

A long wheelbase car would be more stable on high speed straights but would be less easily "flicked" through an esses type of situation.
Bob

[johnh875]

Altering the wheelbase can also be a tool used to adjust weight distribution, perhaps the TDi engine being heavier than the previous petrol engine has an influence?

[HORNDAWG]

Also I would imagine the gear box is quite a bit larger(over all drive package), which also would effect the wheel base.
L.P.

[chernaudi]

I always thought that the Audi's probably had the best mechanical grip of any prototype. As for the Zytec type cars, how much of their grip was mechanical, as opposed to aero grip(Audi's tended to handle well even with minor areo damage, ie dive plane or fender louver damage). I feel that it's better to have mechanical grip as opposed to aero grip, because you don't have to run as much downforce, so you'll have the best of both worlds( straightline and cornering performance).

Indeed, the R8 did have some oversteering issues, but this seemed to be on cold tires and a full fuel load( which may be why we've seen rear tire only changes on the R8 from time to time). But I think that the R10's long wheel base was mostly for weigh distribution(which also may've had a hand in the R8's inital understeering problems).

Obvioulsy, the frontend push problems didn't hurt the R8, and I've also heard that sometimes, drivers have used it to their advantage(like going over the bump in turn 17 at Sebring).

PS: I've based my assesment on the R8's handling on the fact that it seems so stable and in control, maybe that's because of the understeer. And besides, this isn't NASCAR! In road racing, it's the speed coming through/off the corner that's helpful-and that's probably where the R8/R10's handling excelled.

[jhansen]

Originally Posted by chernaudi

I always thought that the Audi's probably had the best mechanical grip of any prototype. As for the Zytec type cars, how much of their grip was mechanical, as opposed to aero grip(Audi's tended to handle well even with minor areo damage, ie dive plane or fender louver damage). I feel that it's better to have mechanical grip as opposed to aero grip, because you don't have to run as much downforce, so you'll have the best of both worlds( straightline and cornering performance).

Indeed, the R8 did have some oversteering issues, but this seemed to be on cold tires and a full fuel load( which may be why we've seen rear tire only changes on the R8 from time to time). But I think that the R10's long wheel base was mostly for weigh distribution(which also may've had a hand in the R8's inital understeering problems).

Obvioulsy, the frontend push problems didn't hurt the R8, and I've also heard that sometimes, drivers have used it to their advantage(like going over the bump in turn 17 at Sebring).

PS: I've based my assesment on the R8's handling on the fact that it seems so stable and in control, maybe that's because of the understeer. And besides, this isn't NASCAR! In road racing, it's the speed coming through/off the corner that's helpful-and that's probably where the R8/R10's handling excelled.

Don't get me wrong, I marvel at the R8. It brought me back to sportscar racing. It is without a doubt an undisputed champion. I think what makes the R8 so amazing is that is at or near the top in many categories. Reliability is certainly its best strength. A good trait for an endurance racing car. The FSI motor was very managable with good power and good economy. The chassis was like a tank and stable. The build quality of the car is maybe second to none. The aero was solid, but maybe conservative (or more likely built for LeMans). Mechanical grip? I don't know. Never heard much said about it.

You asked about the best handling car. The R8 is certainly up there. But I think the Zytek takes it in that category. Its aero advantage allows for those extra tenths of a second. And no amount of mechanical grip will help you through the fast bits like good aero. It's only hiccup is that maybe it has too much downforce for a track like LeMans.

I also wonder about the Pescarolo. The aero package seems good. But again, probably more suited to faster circuits.

[Hammerdown]

From what I've picked up it sounds like the R10 does understeer, but also has power oversteer due to the colossal torque and the fact that the drivers can't hear the engine note change when the wheels spin. Although I've also heard it said that the R10 has traction control. Maybe it doesn't work very well! I would think that, generally speaking, longer w/b is more likely to understeer, and short oversteer due to weight transfer.

As for the Pesca, it certainly seems to have lemans optimised aero. On the short circuits, the Creation and Zytek can outpace it (on lap times anyway!), but they are nowhere near at LM.

[I love 04s]

I think Monza LMES Qualifying in 2005 showed the aero performance of the Zytek when they beat Pescarolo to pole on a track that really should have suited Pesca down to the ground.

On the Le Mans note, Brabhams 3.34.xx in the 04s in 04 would suggest that the Zytek is still very quick on a clear lap.....the trouble is that the car relied so much on momentum that as soon as traffic appeared the seconds just flew away.......this is where drivers such as Brabham and Shimoda really showed their worth - they both had the ability to scythe through traffic like it wasnt even there.

[JAG]

Slightly off topic.

If you cast your minds back to Group B rallying in the 80's Audi were being trounced by the new mid engined 205 T16.

To combat this Audi literally cut a chunk out of the middle of the car believing this would improve the handling.

In fact the car was almost undrivable with twitchy, unpredictable handling.

When Audi went back to the drawing board they discovered the 205's wheelbase was actually the same as the the origninal 'long wheelbase' Quattro.

The 205's advatages came from far better weight distribution, from the mid engined layout, and short overhangs, combined with the stable long wheelbase.

[Adam43]

Interestingly Porsche's prototypes seemed to get longer and longer, over time. Signer mentions this in 24:16 although hasn't really gone into details (upto the chapter I'm on).

Bob Riebe has the general philosophy behind it, but it is also another thing that may have to be compromised.

I would imagine that generally a car designed for Le Mans might be longer than one designed for sprints at twister tracks. I wonder how much hat bears out through history.

[Adam43]

While catching up on some reading over Christmas (the car is still in the garage ) I came across a letter to MotorSport from Peter Felder (p28 vol LXXXIII Jan 2007). It refers to the 1974 Interseries 917-20 (sic? 30?) and its adjustable wheelbase! How did this work?

http://www.racingsportscars.com

For more pictures see p203 in Porsche 917 The Heroes, the Victories, the Myth.* This book refers to the car having "served for wheelbase tests". It won four times that year.

*More reading to catch up on...

[chernaudi]

Wouldn't all LMP cars suffer from understeer to some degree, as I doubt that they have a 50/50 weight disribution, irregardless of wheelbase? The Panoz probably came closest, but it was a areodyamic as a brick due to it using a front mounted engine.

And how much of the Zytec's handling can be atributed to it being(until this year) an LMP 675 car? And I can understand it's problems in traffic(having so much downforce, it seemed to be very areo sensitive) as well as it's engine having so little torque.

[jhansen]

The Zytek certainly does suffer from some momentum troubles in 925KG form. That little V8 must have to work extra hard. But again, in terms of handling, the car is just a gem. Just look at the driver comments. Stefan Johansson (who has driven an R8) raved about it at Laguna.

Stefan Johansson on the Zytek: “one of the best cars I’ve driven, hands down.”

http://www.sportscarpros.com/across-...ng/default.htm

[FIRE]

Originally Posted by AdamAshmore

While catching up on some reading over Christmas (the car is still in the garage ) I came across a letter to MotorSport from Peter Felder (p28 vol LXXXIII Jan 2007). It refers to the 1974 Interseries 917-20 (sic? 30?) and its adjustable wheelbase! How did this work?

In F1 they put a carbon plate were the engine/gearbox is mounted to the front of the car.

[Adam43]

Yes that has become the norm, especially now they have the shorter V8s. It is more than just that as he body work and ancilleries need to be modified to acheive this. How easy a job was it in that Martini 917-30?

In addition you would think that Audi could have had something similar with their removable back-end. Well not quite as it would be best in front of the engine (it saves lengthening propshafts!). Anyway, I am surprised that it isn't more common a change between different circuits, or are the gains relatively small for a practical change? It is a little cloud cookoo here.

[HORNDAWG]

Originally Posted by AdamAshmore

Yes that has become the norm, especially now they have the shorter V8s. It is more than just that as he body work and ancilleries need to be modified to acheive this. How easy a job was it in that Martini 917-30?

In addition you would think that Audi could have had something similar with their removable back-end. Well not quite as it would be best in front of the engine (it saves lengthening propshafts!). Anyway, I am surprised that it isn't more common a change between different circuits, or are the gains relatively small for a practical change? It is a little cloud cookoo here.

I do not believe the ACO allows it.
http://www.lemans.org/sport/sport/re..._ACO_fr_gb.pdf

3.1 and 3.1.1 a/ specifically.

L.P.

[MulsanneMike]

Originally Posted by AdamAshmore

Yes that has become the norm, especially now they have the shorter V8s. It is more than just that as he body work and ancilleries need to be modified to acheive this. How easy a job was it in that Martini 917-30?

In addition you would think that Audi could have had something similar with their removable back-end. Well not quite as it would be best in front of the engine (it saves lengthening propshafts!). Anyway, I am surprised that it isn't more common a change between different circuits, or are the gains relatively small for a practical change? It is a little cloud cookoo here.

I think the biggest issue would be from a homologation stand point as you homologate the car's dimensions and have only something like a +/-10mm
deviation allowed.

[Adam43]

Ah! Can't you homolgate two cars, two wheelbases? Clearly not worth it.

[FIRE]

Originally Posted by AdamAshmore

Yes that has become the norm, especially now they have the shorter V8s. It is more than just that as he body work and ancilleries need to be modified to acheive this. How easy a job was it in that Martini 917-30?

The "F1 solution" is a bit difficult with a tubeframe car...

[Adam43]

True, although I have an extendable shower rail.

[Randy]

I imagine Audi made the R10 long wheelbase because the torque of the engine was always going to make the car tricky to drive. Long wheelbase = stability.

[Mike_Wooshy]

Originally Posted by JAG

Slightly off topic.

If you cast your minds back to Group B rallying in the 80's Audi were being trounced by the new mid engined 205 T16.

To combat this Audi literally cut a chunk out of the middle of the car believing this would improve the handling.

In fact the car was almost undrivable with twitchy, unpredictable handling.

When Audi went back to the drawing board they discovered the 205's wheelbase was actually the same as the the origninal 'long wheelbase' Quattro.

The 205's advatages came from far better weight distribution, from the mid engined layout, and short overhangs, combined with the stable long wheelbase.

Very intresting I have an interview somewhere about Jean todt Insisting doing similar to what renault did with the R5 Turbo, But insisted on making the wheel base aslong as possible to counteract the twitchy unpredicatble handling of Shortwheel base cars ......
Back on topic ! I believe this was the reason for the R10's long wheel base to counteract the twitchy handling, while also helping with package to help fit everything in between the wheels