This is not strictly polo related but just general car prep.

The first on the discussion is chassis rigidity, not this has a big deal to what the car will be used for if strictly track then fully stripped with weld in cage and stitched chassis seems to be the main deal. But what I want to know is what would people do for street use I personally don't wanna a cage many different reasons one being I want to build it to be as much of a street sleeper as I can but be fast as it can be on the track so to get the rigidity that a cage gives I will be getting a chasiss brace that is a big square cross brace that bolts up under the car to tie the front and the rear of the car together which is also lighter than a cage some ground clearance is lost but the car won't be low enough to cause a problem.

That deals with the centre of the car now it down to front and rear strut towers are strut braces enough to deal with the added stresses of harder suspension or would stich welding them be needed aswell. I've been looking into it and some say it's worth it some don't. The rear strut brace would be weld in and the front bolt in to make engine remove easier.

Also I've seen many other braces out there such as ones that tie the front wich bone bolt to the rear I personally don't see this much use as I can't see the subframe flexing obviously I can look into stich welding the subframe seams as the car will be in pieces over winter so that would be doable. Same with wish bones if seen poeple do them on here just wandering why this is? Do the pressed steel items tend to split or is it again to stop them flexing?

I would like to hear people's opinions on here. There seems to be less and less car discussions on here now it more just can I do this how do I do that can some spoon feed me and all that crap.

I look forward to hearing poeples opinions.

Harris is quite a specialist in the chassis department from what I've heard, so if he chimes in that would be a good read..

I'm not but I am a big believer in good handling in a car, and the uphill struggle of balancing a FWD.

The most important thing for me is balance, the car can be as stiff as you like, but if its not balanced you'll get handling characteristics that while predictable can be quite undesirable.

I know the litlle 106 GTi's suffer from lift off oversteer quite badly, the rear is that stiff in contrast to the front, hence why you see them cocking a wheel on corners some times.

I've never really come across even coming close to that in my polo, it just tends to understeer because of the flexibility at the back, maybe I'm not pushing hard enough, but I'm not about to go find out on a road.

I would like to say the Polo has the better ability to be finely tuned to your liking, as its not even close to stiff from the factory (although I do believe the valvers have ARB on the front?)

Anyway I'm going off on a tangeant here, A fast road car needs to be able to cope with the lumps and bumps of normal roads, I would suggest the two strut braces, a good set of springs and dampers and some polybushes, maybe a thicker ARB if you have one fitted, of the fitting of one if you don't, welds might crack over time with the bumps etc. and I dont think they would add all that much performance wise, for the work involved and the scenario they are in.

Braces might be a good idea, and if they are bolt on, run them individually, paired up, full set and see which configuration feels best for you, being able to drive confidently is better than worrying about might happen if your a little too aggressive.

The theres alignment of the suspension and what tyres you want to run too, but you might want to save that for another day?

Don't want me warbling on haha

Some good points there. The car in my question is a mk2 jetta so a bit longer wheel base than a polo. It has a front a rear arbs with the rear being a lot thick to try and stiffen it up. Agreed the car will need to deal with use on the road although I only use it 4 times a month 5 at the max then I plan a track day each month when the weathers good so will be good grounds to test each month and see what works and what doesn't.

As for welds cracking the idea of stich welding the seam instead of one long weld means the panels with still have flex so won't be complitley solid. I'm focusing one the handling as the car will be stripped down and re build over the winter months meaning any major work can be under taken then.

I'm hoping the under floor centre brace will help stop a lot of the chassis flex as the rear becomes light under extreme cornering 70mph plus round oval roundabouts, (I was not letting the audi tt get away from me) as I pitched in perhaps to fast the front stayed solid but the rear became light granted I was still on the brakes slightly which didn't help but it's a characteristic I would like to dail out.

I'm still yet to test spring weights which woudk probaly help a lot but I would rather try to stiffen it up other ways first than trying stiffer springs and making it horrible on the road.

As for alignment mines been set up on 4 wheel alignment so is pretty spot will be done at the start of the year after a major rebuild along with the corner weights checked and adjusted to get the axles load side to side the same.

I am hoping nick does come along and give some tips. I currently run a forward rake to dial out a lot of the under steer problems I had when I first built it this could probably being adjusted slightly as was done before the thicker arbs when on,

As for suspension bushes again this is a tricky one as to go for poly bushed or not. I have a set for the wish bones and rear beams both front and rear arbs are polybushed already. Will fit the the rest and then test to see if there's an improvent I suppose the most will be in the rear beam only time will tell on that one.

We will come on to tyres brakes and all the other stuff once we have a few more poeple views on the chassis first. Think of it as we are build a car in our heads from the ground up.

If it's worth anything I don't think the lightness of the rear is inherent to the stiffness of the vehicle, I would say thats more related to the transfer of weight and a frontwards rake, if I read it properley, you'd probably find that planting the right foot would sit the rear back down, and dependant on speed and grip either cause understeer or pull you round, but you probably know that anyway.

My car is very rear biased, I can chuck it in as fast as I dare knowing that the fronts will let go before the backs, I've only ever had the backs hop a little, never lose traction. This is mostly due to the fact that I like to corner using the balance of throttle and steering angle, I dont want a car that might snap into oversteer on the road because I don't like the thought of hitting road furniture when I get a tank slapper on because the car doesnt have the power to pull it out of a slide.

Anyywaaaayy If I'm wrong and you meant it gets light midcorner then that could definately be due a number of things around the rear, and if its effectively carrying nothing back there then bear in mind that the dampers have a stiffer effect, because they have less weight to deal with.

its hard talking about vehicle stiffness without talking about suspension because its that that introduces the load to the main chassis. Is it stiff across the axle, and soft dampers/springs are unloading the inside wheel and transferring all the load to one tyre? or is it soft across the axle and stiff springs/dampers are fighting against each other through the chassis, is it too stiff all round with no leniancy and its simply too much speed? is it too soft all round and its just flex across the springs/dampers and chassis?

I'm not qualified to say, its intriguing though

I would say theres a lot to find with alignment, a bit of camber (ON THE FRONT WHEELS SCENE KIDS) will help midcorner grip for sure, Toe is personal preference, what can you live with? twitchiness and fast response, or stability and slower response?

I think you should definately polybush as much as you can, remove all the unwanted play with OEM bushes, they are made for comfort and longetivity on normal road condtions.

Yeah are correct in the wieght tramsfer to the point where I let of the brack I must say it was poor driving on my part going way to fast then realising I was to late on the brakes so had to stay one em which unsettled the rear naturally it will always do that as the front is nose down with all the weight being at the front anyway. Planting the right foot would of made things a whole lot worse causing understeer and most likely 4 wheel drifting. The car has never let go to point it's controllable it's a seriously planted car slower corners are no problem it's was this one time that I went for a fast corner I blame the tt for making me race .

The front is no concern that has been set up and is spot on only understeers when I want it to and grips well at any speeds can chuck it at almost any speeds and it will grip. Just the rear will probaly drift out to much to handle. I would prefer over steer but not huge oversteer I suppose it's just diffence in driving styles my car will gradually lose the grip the harder I push it as the front will stick the rear can't keep up and starts to slide will never snap out well hasn't so far. I predict it's loading one side and the inner wheel going light.

If the chassis was slightly stiffer in the middle it would help to reduce some of the laterally loading a on the tyres meaning that the suspension can do what's it's designed for where as the body doing what it wants and the suspension following it.

Does camber in the rear wheels help in grip obviously if it is loading one wheel that wheel would have full contact at the full corner speed but the inner wheel would have even less so kind off a catch 22.

I'm also not qualified to say my main specialty is engines and brakes. So I can make em fast and stop but can't obtain max corner speeds becuase of the tiny adjustments that I need to make to get it working well.

The suspension on it is sowm mid range coilovers nothing fancy but stiffer then the factory stuff that's all that kinda mattered when I started building I never thought I would be going this fair but I built an engine for some fun and now I'm here. Tyre wise is 205/50/15 toyo proxies I opted for that tyre size for many reasons one being the varity of road conditions the car will deal with. It allows so side wall flex so can handle uneven roads as well as smooth tracks.

We have also gone way off topic. So back to it would be advise to stitch weld the seams on the strut towers or are strut braces enough to strengthen it back up. We will out the light rear end to rest with me saying it was down to drivers error coming onto the brakes to late then have to trail them on the first part of turn in.

Edited 12 September, 201412 yr by mattieboi6n