Finally Mapped

[Robsbc 0 1 Cars]

Depends what manifold you're using, the Jenvey/Longmans manifold gives clearance issues, but ours don't.

 

Yep your right Sandy...Should have said with Jenvey manifold

[Rob Thomson 6]

Hmmm.... I'd forgotten I'd posted on this thread the other night. Probably something to do with an eleven hour drinking session beforehand. Sorry for being slightly more forthright than usual.

 

I'm currently having a new engine built for the Rallye, and it's being based on the 1360cc iron block rather than the alloy version for the reasons mentioned somewhere above by Dave Baker. I'm someone who cares much more about handling than straight-line performance, so I will confess to being a tiny bit apprehensive about the results. But only a tiny bit, because I'd really be amazed if I noticed the difference; I'm just not that good.

 

But if it does handle like a bag of s*ite, then there are ways to address that. Moving the battery to the boot would pretty swiftly address any weight distribution issues, and again - I just don't think I'm good enough to notice any effect that might have on the polar inertia of the car... The 106 still has a steel bonnet, glass windows, and loads of other things that can be changed/moved to help things if I need to.

 

I just think a lot of the issues mentioned above only really matter if you're called Michael Schumacher.

[GLPoomobile 958]

Hmmm.... I'd forgotten I'd posted on this thread the other night. Probably something to do with an eleven hour drinking session beforehand. Sorry for being slightly more forthright than usual.

 

I'm currently having a new engine built for the Rallye, and it's being based on the 1360cc iron block rather than the alloy version for the reasons mentioned somewhere above by Dave Baker. I'm someone who cares much more about handling than straight-line performance, so I will confess to being a tiny bit apprehensive about the results. But only a tiny bit, because I'd really be amazed if I noticed the difference; I'm just not that good.

 

But if it does handle like a bag of s*ite, then there are ways to address that. Moving the battery to the boot would pretty swiftly address any weight distribution issues, and again - I just don't think I'm good enough to notice any effect that might have on the polar inertia of the car... The 106 still has a steel bonnet, glass windows, and loads of other things that can be changed/moved to help things if I need to.

 

I just think a lot of the issues mentioned above only really matter if you're called Michael Schumacher.

 

Rob has just managed to sum up exactly what I have been thinking all along throughout the entire off topic section of this thread!!!

 

But I'm not a track boy so I didn;t bother to say anything as my opinion probably doesn't count for much

[rally ax 0]

Aye Rob,,for someone who's 7'11" or "freakishly tall" like yourself I wouldn't be too worried about polar inertia either !?

[Sandy 189]

Hi, i'm Michael Shumacher.

[Batfink 201]

i've driven many variants of 205 gti's and their engines and i've not been able to notice the effect of the engine type on the handling. What I am able to notice is the difference with different size brakes and wheel/tyre combinations.

[PumaRacing 1]

nothing to do with balance. in actual fact a FWD car is better with more weight at the front. in it's location at the front of the car it may not be ideal but at least it aids traction. putting it in the back moves it a long way from the CofG so you are not helping the handling.

 

Of course you're helping the handling because you're moving the CoG back. Trying to have all the weight AT the CoG is another issue - that of polar moment of inertia but that isn't the point here. Any fwd car has too much front weight bias and you reduce that by moving things as far back as possible.

 

 

Ideally you want it as low down and as close to the CofG position as possible. If we were talking RWD it makes sense to put it in the back. eg RWD car with 65% weight up front and 35% at the back will almost certainly be slower than a FWD car of the same split. Hence BMW's 50/50 weight distribution. on FWD 50/50 would make for a truly awful traction! Apologies as it's all off topic but the reality of the Iron block is in actual fact being in the front is not as bad as it seems - it's more the simple fact of adding weight. If you fitted the iron block and then lay it down (touring car style) and moved it back then the extra weight would be negated!

 

Traction is an issue but it obviously depends on the power of the vehicle and the available grip. On many cars it will only be an issue once, getting off the line. On more powerful cars then it might be an issue at higher speeds. What this says is everything is a compromise and the ideal solution to weight distribution on one vehicle might not be ideal on another.

 

There's a very simplistic notion that the ideal situation for cornering is when the weight distribution is 50/50. This is on the basis that all four tyres would then be under equal cornering loads. In fact the true measure of ideal weight distribution is when all four tyres are 'working as hard as each other'. This takes into account not just the loads imparted by the vehicle mass but also by steering inputs and traction.

 

F1 obviously has this down to a fine art, not just by testing but my computer simulation of vehicle performance. The cars run so much ballast they can achieve almost any weight distribution and you might think that the starting point for a rwd car would be 50/50. In fact this turns out to be far from ideal. The solution that uses all tyres to their fullest capability involves about 61% rear 39% front weight distribution. Of course this is a function of the power, tyre size and downforce and wouldn't necessarily be the correct solution on a lower powered rwd car with no downforce.

 

On a fwd car the front tyres are handling most of the mass plus the steering inputs and the traction inputs. They are always going to be massively harder worked than the rears so anything you can do to help this will improve performance. Removing weight from the front of the car altogether is ideal but if the component has to be retained somewhere than the best place for it is at the back.

[smckeown 1]

oh boy, this is going to be interesting, PR advising outside engine the engine world.

 

Having had the benefit of tuition and spoke personally to old FWD mini racers (one still having a track record around combe) , they don't agree with you dave

 

There is a definite case for having significantly less than 50% weight distribution at the rear to actually make it more tail happy.

[Sandy 189]

This is a tricky subject in a way, because it only serves to explain in part why the 309GTi frankly IMO handles better than the 205GTi. Not faster necessarily, but better balanced certainly. That leads me on to the massively off topic point, that some of us describe "Handling" in terms of how the car feels to drive through corners and some of us describe handling in terms of how fast the car can corner. The latter is better described as grip and not handling.

Edited February 6, 2007 by sandy309

[Batfink 201]

but Sean thats not what Dave is saying. Dave is saying you can move weight back until you get to the optimum cornering loads for a fwd car and the 205 is not set up as optimum by a long way. One of the reasons why the 309 handles better - because its not as nose heavy. there will be generic optimum weight distribution for FWD cars. Anyone actually know what it is?? Dougs near standard 309 felt much better handling than kates 205 with coilovers and LSD due to a far better feel through the car. It wasent faster but surprised me a lot!

Edited February 6, 2007 by Batfink

[PumaRacing 1]

but Sean thats not what Dave is saying. Dave is saying you can move weight back until you get to the optimum cornering loads for a fwd car and the 205 is not set up as optimum by a long way. One of the reasons why the 309 handles better - because its not as nose heavy. there will be generic optimum weight distribution for FWD cars. Anyone actually know what it is?? Dougs near standard 309 felt much better handling than kates 205 with coilovers and LSD due to a far better feel through the car. It wasent faster but surprised me a lot!

 

There won't be a single optimum weight distribution for fwd because it'll depend on power to weight and therefore traction issues. However there's a general rule which is that the lower powered the car the more the ideal weight balance will move rearwards and for higher powered cars you just have to sacrifice balance to get grip for acceleration which means proportionately more weight at the front.

 

It would be interesting to build a car with a mid engine but fwd and ballast to change the position of the CoG while maintaining the same total weight and see if anything unusual came to light. It might even turn out that although traction would be awful the optiming cornering speed might need a 50/50 or even rearwards bias just like a rwd car. Pat Symonds the engineering director at Renault wrote an article on their computer simulation of weight distribution v lap time in F1 and his program could probably answer this question for a theoretical fwd car.

[Rob Thomson 6]

Having had the benefit of tuition and spoke personally to old FWD mini racers (one still having a track record around combe) , they don't agree with you dave

I've also 'had the benefit of tuition' but personally thought it was all a load of bollocks and the 'expert' really didn't have much of an idea what he was talking about. It was all driving-by-numbers than actually relying on talent. Anyway, I'm very cynical of such experts.

 

Having said that, I think you misunderstood Dave's point.

 

There is a definite case for having significantly less than 50% weight distribution at the rear to actually make it more tail happy.

Doesn't that contradict your other arguments; that you therefore want more front weight bias to loosen up the back end? And also, having watched most of your track videos, Sean, I don't think I've ever seen the tail move even slightly....?

 

Certainly the worst possible outcome of my new engine would be if it stopped the 106 oversteering, the little bugger slides like a good'un, steer it on the throttle all day long.

[Sandy 189]

It depends on a whole heap of things in addition to or complementing coner entry/stability/adjustability/exit, traction and braking, not least the constraints of the car's structure (no such thing as a "stiff" shell), the suspension layout (track/wheelbase relationships, roll axis, roll stiffness, roll axis migration, pitch resistance....), wether it can be altered or not within rules or physical constraints, tyre properties are an enormous factor (construction, sizes, compound, slip angle/yeild and the progression of those, wear), steering system and bump steer constraints even, I've surely left some things out, but above all, driving style.

[niklas 1]

Certainly the worst possible outcome of my new engine would be if it stopped the 106 oversteering, the little bugger slides like a good'un, steer it on the throttle all day long.

 

If a FWD track car doesn't oversteer on turn-in, it's really time to get worried!

 

 

It's interresting to hear about what balance a car should have and how important it all is. The next thing, obviously not mentioned on this forum, is in which end the car should have its driving wheels.

But the fact still remains, in sprint races there still aren't any 50/50 balanced RWD that "owns" the imperfect 30/70 FWD's over and over agian.

Where it really becomes an issue is in endurance races where the way too biased weight distribution to the front have its tribute on the tyre wear and the FWD's wears drive shaft joints more rapidly.

This is some quite interresting facts to keep in mind...

[veloce200 3]

Of course you're helping the handling because you're moving the CoG back. Trying to have all the weight AT the CoG is another issue - that of polar moment of inertia but that isn't the point here. Any fwd car has too much front weight bias and you reduce that by moving things as far back as possible.

 

you've already mentioned polar moment on many occasions so you know yourself why sticking the battery in the boot is not right on a FWD car. I've not looked at them but I doubt any of the touring cars with FWD have the battery in the boot. For example if you were racing clockwise oval in RHD FWD car you'd have it behind your seat to help grip on the inside front - in this example if it was stuck out on LHR it's not going to help. There are of course instances where it may work - eg your cornerweights are out and sticking the battery in another place just happens to sort the handling out. However I imagine you are trying to explore the optimum set up here.

 

In fact the true measure of ideal weight distribution is when all four tyres are 'working as hard as each other'. This takes into account not just the loads imparted by the vehicle mass but also by steering inputs and traction.

 

absolutely.

 

F1 obviously has this down to a fine art, not just by testing but my computer simulation of vehicle performance. The cars run so much ballast they can achieve almost any weight distribution and you might think that the starting point for a rwd car would be 50/50. In fact this turns out to be far from ideal. The solution that uses all tyres to their fullest capability involves about 61% rear 39% front weight distribution. Of course this is a function of the power, tyre size and downforce and wouldn't necessarily be the correct solution on a lower powered rwd car with no downforce.

 

the 50/50 discussion was centred around tintop F-RWD not M-RWD. I agree that 50/50 on RWD is widely regarded by many as "optimum" but often F-RWD and M-RWD as you say will favour more rear weight distribution. It's damn hard to get 50/50 with F-RWD in a production car so BMW have led us to believe it is "optimum". Your point about more rear weight bias is a wise one and it explains why despite all logical thinking R-RWD (911) does actually work!

 

On a fwd car the front tyres are handling most of the mass plus the steering inputs and the traction inputs. They are always going to be massively harder worked than the rears so anything you can do to help this will improve performance. Removing weight from the front of the car altogether is ideal but if the component has to be retained somewhere than the best place for it is at the back.

 

agree, but the best place for the weight is not the back it is low down towards the c of g to minimise changes to polar moment.

 

I don't think this thread should descend into a suspension set up thread I take much of the blame for steering it off course in the first place!

[veloce200 3]

This is a tricky subject in a way, because it only serves to explain in part why the 309GTi frankly IMO handles better than the 205GTi. Not faster necessarily, but better balanced certainly. That leads me on to the massively off topic point, that some of us describe "Handling" in terms of how the car feels to drive through corners and some of us describe handling in terms of how fast the car can corner. The latter is better described as grip and not handling.

 

309 handles better as it has a better relationship between track, cg height and wheelbase.

[Sandy 189]

Those aren't the only differences! The most crucial one to my mind is the weight distribution, which is why my Trio with 309 GTi bars handled even better than the 309 GTi, less weight out front.

[maxi 36 1 Cars]

You lot and your f***ing track cars........ While you are all arguing over whos going to be Senna, Schumacher and Nigel Mansell, people like Mark and Myself will be off having fun in our motors day to day.

 

Maxi

[Ahl 4]

You lot and your f***ing track cars........ While you are all arguing over whos going to be Senna, Schumacher and Nigel Mansell, people like Mark and Myself will be off having fun in our motors day to day.

 

Maxi

lol! Exactly!

[niklas 1]

You two don't know what you're missing

[smckeown 1]

And also, having watched most of your track videos, Sean, I don't think I've ever seen the tail move even slightly....?

 

1 - I have a 205 with very high levels of grip at the rear, more than most cars on the forum

2 - Even though i posted vastly improved times at anglesey last year (circa 8 secs quicker), i'm still relatively slow and have low levels of skill

[smckeown 1]

You lot and your f***ing track cars........ While you are all arguing over whos going to be Senna, Schumacher and Nigel Mansell, people like Mark and Myself will be off having fun in our motors day to day.

 

Maxi

 

 

lol! Exactly!

 

Some of us like to take advantage of the 205s legendary motorsport heritage and ability. We all love pugs, just in different ways

[veloce200 3]

You lot and your f***ing track cars........ While you are all arguing over whos going to be Senna, Schumacher and Nigel Mansell, people like Mark and Myself will be off having fun in our motors day to day.

 

Maxi

 

mine's my daily driver as well . got a bad back to prove it to!

[taylorspug 7]

I've not looked at them but I doubt any of the touring cars with FWD have the battery in the boot.

 

The only one ive seen was Dynamics Integra from a couple of years back (never took a look at last years). However i figure they must have had a serious forward bias of weight and were struggling a little, as the power steering reservoir etc was also in the boot with the battery.

Edited February 7, 2007 by taylorspug

[eeyore 0]

Graph is on thsi forum...

 

Both Dave W & Karl said that engine peaked @ 7800rpm when I last asked them. Even the article talks about 7800rpm

i can confirm that sandy is right and it peaked@ 7000rpm! as i was sat on the wing at the time! ive also got the dyno plot read out somewhere.