Roll centres + Rubbish saloons

[Al Weyman]

Dennis there is one thing that you may or may not have considered when you amalagmate with you know what, there is a minimum weight limit and you may well be able to get your car on the limit with fibreglass and plastic, the Pug can only go down to that limit or its illegal. You had a facility to add punitive weight in ModProds why did the organisers never see fit to implement this rule?

PS I think I may well be out with you guys next season and may well have to put my car on a diet as well (and me)!

[greenamex2]

Originally Posted by Al Weyman

Dennis there is one thing that you may or may not have considered when you amalagmate with you know what, there is a minimum weight limit and you may well be able to get your car on the limit with fibreglass and plastic, the Pug can only go down to that limit or its illegal. You had a facility to add punitive weight in ModProds why did the organisers never see fit to implement this rule?

PS I think I may well be out with you guys next season and may well have to put my car on a diet as well (and me)!

Minimum weight for 1600 = 640Kg, my car = 840Kg

Minimum weight for 2000 - 704Kg, Mod prod Pug 205 = 740Kg

It will help but I don't quite think I am going to find another 200Kg on a car that is already 120Kg lighter than standard! I figure I can get 50-60Kg out with the new regs.

Whilst, like everyone else, I can play with pressures, dampers, springs rates, angle grinder etc I still need that extra 'edge' from somewhere.

As nobody ever really dominated a particular class in Mod Prods at all circuits then the weight penalty was never implemented.

[dtype38]

Originally Posted by Denis Bassom

It will help but I don't quite think I am going to find another 200Kg on a car that is already 120Kg lighter than standard! I figure I can get 50-60Kg out with the new regs.

Needs some imaginative interpretation of the rules. Take our Jaguar XJS championship:- standard road car is around 1800kg and most people thought that getting 300kg off that was impressive until someone came along with one that needed ballasting up to the minimum weight limit of 1350kg!! And that's with some strict rules about no carbon fibre, no major structural modifications etc. etc. Just goes to show what's possible if you try (although a scratch build helps).

[greenamex2]

I'm impressed, although the Corolla didn't exactly come 'fully loaded' compared to a XJS.

Probably explains why some XJS can perform wonders around a track despite having just about everything going against them. Definitely development over design.

Anyway, I'll probably keep with a rear panhard rod for the moment but level it up (Goran's geometry thing, an ever present problem on a car lowered about 4 inches and still higher off the ground than a pug).

Do I RAISE the roll centre or LOWER it?

Keep in mind I am only talking an inch or so.

[Al Weyman]

Fibre glass bonnet, doors, bootlid, perspex alround, I bet there must be what 100kgs or so there Dennis, get it down to that then the rwd format over the Pugs Fwd may start to play a role. At least the Pug will not be able to go much lighter with or without perspex and fibreglass components so worst way the gap will definitely close.

[greenamex2]

Originally Posted by Al Weyman

Fibre glass bonnet, doors, bootlid, perspex alround, I bet there must be what 100kgs or so there Dennis, get it down to that then the rwd format over the Pugs Fwd may start to play a role. At least the Pug will not be able to go much lighter with or without perspex and fibreglass components so worst way the gap will definitely close.

'Unfortunately' all the panels that will be replaced have already been extensively lightened. It's going to be interesting to see the weight loss any way.

As you implied, at least there IS a weight limit to help level things up a bit.

[Notso Swift]

Not allowed to change the block, well then you are in a bit of trouble. Can’t believe they have 1.6’s with 2.1’s in the same class, but sometimes that is the way these things fall. Realistically there are not any other small light RWD sedan’s available, the old ‘rolla and the Escort sort of cover everything. BMW’s are getting too heavy, and everything else too old.

With 220 hp you are on the money for a 4A-GE, Even the Formula Atlantic only get about 240 bhp and they are using the best of everything, mega revs and have regular rebuilds - measured in hours not seasons. Forced induction is the only way you will get significantly more power (and torque), and I bet that either changes your class or is not allowed.
I think you can bore and offset stroke and you will get it to 1720?? This will help at least your torque, if not power.
With the weight, the rear hatch will save the most weight, I remember helping a friend fit one and it almost broke my back! (Actually you could be 2 door not 3 door, both were available)
Don’t be concerned if the car is a little higher than what “looks” right I would be more concerned with how it gets around the circuit - often with strut fronts and a beam rear this means lowering the back more than the front, my old Suzuki looked like it had a pile of bricks in the boot .

The other thing you can do to save (at least) 50+ kg is go AE82… if you can’t beat the FWD brigade then join them!

[coln72]

Ever thought of using a 7a crank etc to push it out to 1.8l or to convert to a watts link with a adjustable pivot point to change the rear roll centre?

[Al Weyman]

As you implied, at least there IS a weight limit to help level things up a bit.

I have heard some mumblings about minimum weights being to low in the smaller classes so maybe it would be worth asking for a revison on those to coincide with the merger, if it is about levelling things up I am sure they may be receptive to fresh ideas and now is the ideal oppertunity.

Incidently does anyone know how to bend a large sheet of polycarbonate, I cut a sheet to shape to replace my glass hatch which believe me is seriously heavy (100 kgs plus) as it is made out of 8mm glass but I could not bend the thing to shape.

Terry (?) who unfortuntaly died in a freak accident used to race one of those Dennis and he was a front runner. I recollect the car was definitely not in the weeds and more or less ran on the stock size wheels and tyres but it was very very fast.

[dtype38]

Polycarb can be permanently reshaped at highish temperatures. I make new headlight shells for mine in the oven. I find it starts to go "plastic" at around 120-140deg C and goes quite floppy once its up to 160-180deg. It's important not to keep it hot for long though as it'll start to bubble and go opaque after a couple of minutes. For a screen though, it's just gonna be getting there that's gonna be the problem. Perhaps a large propane garage heater?

[Highside]

Back to the over stearing thing - what is the weight distribution of your AE86 Denis?

I think a previous reply said that changing to a plastic rear hatch would save a lot of weight, but is it in a place where you can aford to lose it?

Is there anything you can shift back in the car to get more weight over the axle?

Must say - I know your wagon can be a handful at times, but following your car at Pembrey was mighty impressive, and it does make some ace noises .

Still - if you think your car is over weight - try mine. With the new rules I am looking at being 320kg overweight at the moment, even before you add the 95kg nut that holds the wheel!

[Highside]

Originally Posted by Highside

Still - if you think your car is over weight - try mine. With the new rules I am looking at being 320kg overweight at the moment, even before you add the 95kg nut that holds the wheel!

Sorry - just re-read the rules, and my car is actualy 418kg overweight...



...I give up.

[Al Weyman]

Originally Posted by Highside

Sorry - just re-read the rules, and my car is actualy 418kg overweight...



...I give up.

Bloody Hell Highside what are you racing a 7 series BMW! My 87 IROC Camaro (5.8 V8) all glass and steel (except bonnet) 'only' weighs in at 1325kgs and I thought that was overweight, then there is me of course and I am seriously overweight!

[Highside]

[quote=Al Weyman]Bloody Hell Highside what are you racing a 7 series BMW![quote]

...Ha! No but it feels like it.

It's an E30 M3 Evo II (all original so body is a bit heavy).

Currently the car weighs 1160kg (with very little fuel and without me in it) according to the scrutineers scales at Pembrey. My target weight for Classic Thunder type rules is a stunningly light 742kg.

Anyway - I'm in danger of Hijacking Denis' thread here so I might start a new one on where on earth I am going to lose all that weight from - there must be some lighter M3's about....

[Al Weyman]

As I said some of the minimum weights are not quite right IMHO (and others).

[greenamex2]

Hijack away Highside, everybody seems to have lost interest in my roll centres anyway!

[phoenix]

I haven't!

But I think your handling problem lies elsewhere, as I mentioned earlier.

The back end isn't working as it should. For one reason or another it is too stiff (which could be down to something broken or 'tight') or it could be the diff - if it has a slipper.

[greenamex2]

Originally Posted by phoenix

I haven't!

But I think your handling problem lies elsewhere, as I mentioned earlier.

The back end isn't working as it should. For one reason or another it is too stiff (which could be down to something broken or 'tight') or it could be the diff - if it has a slipper.

It's just stiff enough to stop the dampers bottoming out.

OK, thats not strictly true. A couple of races ago the car was 'slow' so I set about checking eveything, and I mean EVERYTHING. Turns out the that it was 'slow' because I replaced the datalogger and entered the wrong tyre diameter!!!!

However, in my investigation I found that the rear springs (not coil over) were being bent significantly 'sideways' as well as being compressed. This is effectively increasing the compression rate.

So, to fix this I went to coil over (allegedly, I hope nobody in my class is reading this, Mr Stubbs) and the rear travel increased 30% immediately on the same effective spring rate.

I am now increasing the ride height and bump to stop the bottoming out. I don't believe it is bottoming out on all corners but it is oversteering on all corners.

In my investigation I double checked that no other binding was occurring and nothing else was broken, it wasn't.

As the oversteer can be invoked on corner entry, mid corner on a neutral throttle and corner exit I discounted the LSD being a problem. I also have two LSD's and they both exhibit the same behaviour.

So, assuming when the rear is stiff enough to stop bottoming the oversteer still happens what is left.

Geometry, I will be able to further fix this next year but am stuck at the moment.
Tyre pressures/temperatures, they are fine according to the probe.
Spring rates, I can't soften them are the damper will bottom out again.
Damper setting, ditto on bump, rebound is to be played with at the final few meeting.
Rear anti roll bar, I don't have one. Past experience has shown it just causes oversteer.
ROLL CENTRES, hence the thread.

I figured there were three things, or a combination thereoff, that I could do with roll centres -

Raise them and then be able to run a softer rear spring due to the reduced roll couple.
Lower them which is supposed improve 'feel'.
Fix them so they don't wander up and down a couple of inches.

Any thoughts?


Of course, next year it's all change with track day tyres and weight loss so who knows what is going to happen!

[Highside]

Originally Posted by Denis Bassom

...So, to fix this I went to coil over (allegedly, I hope nobody in my class is reading this, Mr Stubbs) and the rear travel increased 30% immediately on the same effective spring rate....

I won't tell if you don't

Of course, next year it's all change with track day tyres and weight loss so who knows what is going to happen!

To be honest, I have been watching you race for nigh' on six years, and as far as I can remember that car has always been sideways - I'm not sure if it has gotten worse or not recently though has it?

With the change to 888's next year, trying to fix the handling when you are on T1-R's may prove a bit of a blind ally.

As you have already sewn up the class D championship, you don't need to get any more points, so why don't you put the car on 888's for the last few rounds, and then play around with the settings.

You may find you need stiffer springs etc to make the most of the extra grip anyway, and you will have the drop on the 205's regarding the new tyres.

You may find you have a whole new set of problems too, but at least you will have found them before the start of next season.

Cunning plan?

[greenamex2]

Originally Posted by Highside

I won't tell if you don't



To be honest, I have been watching you race for nigh' on six years, and as far as i can remember that car has always been sideways - I'm not sure if it has gotten worse or not recently though has it?

With the change to 888's next year, trying to fix the handling when you are on T1-R's may prove a bit of a blind ally.

As you have already sewn up the class D championship, you don't need to get any more points, so why don't you put the car on 888's for the last few rounds, and then play around with the settings.

You may find you need stiffer springs etc to make the most of the extra grip anyway, and you will have the drop on the 205's regarding the new tyres.

You may find you have a whole new set of problems too, but at least you will have found them before the start of next season.

Cunning plan?

I am slipping in a few mods to test before the end of the season. Can't afford/justify new tyres just yet though.

Funnily enough we have only just got enough front grip to get it to oversteer properly (rather than just through being an answer). The improvement in front grip came after a long thread regarding caster last winter, and fixing some of the rear suspension alignment problems that came from lowering the car 4-5 inches.

[COLIN STUBBS]

who do i see about a protest denis???????? as if i wasnt reading this!!! your threads are always good night time reading!was hoping to see you at mallory but the cars not quite ready after the aerobatic display at rockingham. really do need to wear these toyos out though so might still make it if its not oversubscribed.......

[Notso Swift]

Originally Posted by Denis Bassom

Hijack away Highside, everybody seems to have lost interest in my roll centres anyway!

Stand by what I said before:
Convert to a Watts link in the back and raise/lower the front to suit

[phoenix]

If the rear is not too hard or binding (which you are sure it is not) then the problem probably arises from lowering the car. Let me explain.

With a solid rear axle, lowering the car does not change the roll centre, so your rear roll centre is where it was before you lowered the car. Indeed, as you have now fitted coilovers the roll centre at the rear could even be higher, depending on where the lower end of the coilovers are mounted. As you have lowered the c of g too (by lowering the car) this gives an overal INCREASE in rear roll stiffness.

At the front the complete opposite is true. The front roll centre will now be lower as a result of lowering the car, because the lower arms will no longer be pointing upwards at the inner end, or if they are, probably very little. I suspect that since lowering the car they are either horizontal or even pointing downwards.

Whatever their actual position, the front roll centre will now be lower than it was, and ther rear roll centre is as standard. Lowering the roll centre increases the roll moment and therefore decreases roll resistance. You have therefore effectively reduced the front roll resistance and probably quite significantly.

The best fix would be to get the roll centre back where it was, either by modifying the inner mounting point, or the mounting to the strut - the kit from the USA mentioned earlier looks like an excellent solution.

Alternatively you could fit stiffer front springs to increase roll resistance, however IMHO (and many others) if you want to increase roll resistance to compensate for the lower roll centre it would better to use a stiffer front anti roll bar - which I believe was a suggestion made earlier in this thread.

If you do decide to increase the rear spring rate for the reasons you mentioned, then the front spring rate should be incerased to balance the car again, but the correction to the current problem would best be achieved with a stiffer anti roll bar.

[greenamex2]

I understand the front bit which is part of the reason why I already have 'super roll centre adjusters fitted' (the generally available stuff wasn't big enough).

As for the rear, I thought the roll centre was dictated by the point that the panhard rod crossed the centre of the diff housing and hence also reduced when the car was lowered?

Are we really say I probably need to knwo WHERE my roll centres are to then make a decision?

[phoenix]

Originally Posted by Denis Bassom

Are we really say I probably need to knwo WHERE my roll centres are to then make a decision?

One of the first things I said in this thread!