Help With Geometry Settings For Sprint Car

[allanallen 528 2 Cars]

AVO have confirmed that they are 250lb front springs.

 

From what I have found so far, getting new torsion bars and an ARB from anyone recomeneded is going to be £500+ which is beyond the current budget.

 

If the front to rear spring stiffness is the issue, how would getting softer springs for the front help, maybe in combination with just doing the bigger rear ARB?

Don't be put off by the cheaper bars, there's loads of people running them (myself included) with no probs whatsoever. Infact the likes of pug1off etc afaik are selling the cheap bars with a load of 'mark up'!!

A cheaper route though as you've suggested would be to drop the front spring rate and fit a bigger rear arb. I'd go with a hefty rear arb firstly and see what you think, then move onto the springs.

[fliprio 9]

The cheap ones I have seen are from here http://www.torsionperformance.com/ which are £220 for the bars and £110 for the ARB.

 

Maybe a 25mm rear ARB and sorting out the front geometry to see what it feels like and go from there

[allanallen 528 2 Cars]

Yep they're the ones, there's generally group buys going on quite often on various forums (306gti6, 106rallye etc) and I think the bars are around the £180 mark ????

[Batfink 201]

There's a company on eBay at that sell reasonably cheap arb's and torsion bars. Might be worth a look. It's probably the same place

Edited April 22, 2013 by Batfink

[camgti 56]

25mm, although not much bigger than 24 will probably be a little overkill for the road, especially in the wet.

 

As allan has suggested, get the rear ARB in there and see how that improves things. Its certainly going to help but I still feel the front spring rate is still a little high to match the rear. Its unbalanced due to the spring rates and how they affect weight transfer as far as i know.

 

Dropping the front spring rate will get the balance closer. Or up-rate the rear bars. Which will probably be the best step. 21mm bars will be a good compromise for the street and track.

 

Cam

[TT205 42]

I'd second being more cautious with ARB size - 25mm is very stiff - fine maybe if you are doing a really wide smooth track like say Donnington but if you are doing the 'Mickey Mouse' tracks for sprints and hill climbs (ie barely wider than the car, lots of very tight corners and often quite rough) then the driving style is far from smooth - more akin to lobbing it at the corners

 

Personally I would stick to something like 23mm - bear in mind this will make a huge difference to your current handling and if you then decide you want it even more oversteery sell it and buy a bigger one - £110 isn't a lot to gamble

[welshpug 1,626]

106's run 24 mm as std, i'd not worry about going 24 being too stiff!

[EdCherry 34 1 Cars]

You cant compare the two cars here mei, they have different leverage and bar lengths.

[fliprio 9]

someone has offered up a 24mm chopped and resplined 306 GTi-6 bar from my wanted add, so I will give this a go and see what its like

 

And yes TT205, some of the tracks are quite rough, the Dimarche sprint in Aldershot was my first sprint and the surface was far from smooth :-) Good fun though.

[allanallen 528 2 Cars]

With your current front springs I don't think a 24mm arb will be overkill at all. My road car runs a shortened 306 24mm arb, standard bars and eibach -30s and it hasn't ever tried to kill me ????

[fliprio 9]

good to know, I expect the eibach springs a bit softer than 250lb, but these are cheap and easy to change if I need to, I will just try one thing at a time and put the standard GTI bits I take off onto my 205 Rallye

[camgti 56]

Great news. I think you will really like it.

 

We are about to do the same to a mates car. A re cut 24mm items with standard bars. 30mm lower eibachs at the front ( or maybe standard re set front springs ) and yellow konis dampers. He will eventually go up to 21mm bars for the road/track.

 

Looking forward to your results and what you think of it.

 

Cam

[welshpug 1,626]

You cant compare the two cars here mei, they have different leverage and bar lengths.

 

 

They aren't that different.

 

Sandy's approximate @wheel figures for the 106/Saxo, the ARB is the same length, torsion bars a little shorter.

 

18mm 90lb/inch

19mm 110lb/inch

20mm 135lb/inch

21mm 165lb/inch

22mm 195lb/inch

23mm 235lb/inch

24mm 280lb/inch

25mm 330lb/inch

 

 

 

Right

so doing a few calc's and verifying things. Im not one to take someones

word as gospel so did some digging. This graph that everyone is using

for torsion bar rates is in my calculations for anti roll bar rates.

 

Here it is:

 

 

 

Edited April 26, 2013 by welshpug

[Batfink 201]

Eibachs will certainly not be anywhere near 250lb. More like 130lb. I don't think it's a progressive spring. Even if it was it would start at roughly 80lb and when fully compressed would be 220lb max. It's a road spring rather than a race modification

[Henry 1.9GTi 36]

When I had my car in bilstein yellows with -30mm springs (as said above probably around the 150lb mark) I had just a 25mm ARB at the rear everything else standard and the handling was lovely!

 

I would hazard a guess that for sprints / hilclimbs you might want to look around the 200lb front region with no arb at all for traction out the tight 2nd / 1st gear stuff and then see how it feels with your 24mm rear bar. IMO you will need more beef than this at the rear.

 

I currently run 25mm torsion bars and 25mm arb. 350lb front and 21mm front arb. Handling is absolutely ace now. But it could still do with a little less body roll and very high load stuff

 

edit: oh and I wanted to say with standard torsion bars and the uprated 25mm rear bar I snapped 2 and one started slipping in the splines. 1 snapped with solid one snapped was welded and snapped at the weld. spline slipping bar was solid. would also recommend 309PUG very good quality stuff. worth thinking about if you ever run into trouble. I check my rear arb is still in one piece every time I bolt check now

Edited May 3, 2013 by Henry 1.9GTi

[fliprio 9]

The 24mm GTI-6 bar is now in, turn in seems to be much improved, it seems to have much more desire to turn in nicly, mid corner and exit still needs some work.

 

Mid corner it seems that I can wined on a fair amount of steering lock without much change in direction, it almost feels like it snaps in your hand a bit but no tyre squeel. - this is all on small roundabouts to try and simulate small sprint like corners.

 

As many have said above, the exit problem is wheel spin needs a proper diff

 

Maybe some 200lb springs and a proper geometry set-up is next on the list.

[Henry 1.9GTi 36]

before I had a diff I found a huge difference in getting the power down when fitting the 25mm rear arb, and as said was on alot softer front springs than you. Maybe disconnect one front ARB drop link and see how you find it getting the power down.

 

glad the 24mm made it better though they really do feel nice with good turn in.

[kyepan 291]

do you have a front strut brace? a decent quality one. as we found even with a diff, that it made a noticeable difference out of corners and mid cirber

[fliprio 9]

do you have a front strut brace? a decent quality one. as we found even with a diff, that it made a noticeable difference out of corners and mid cirber

 

Its an upper OMP brace, not sure if that means its a quality one or not :-)

 

[Batfink 201]

The OMP one does work. Kyepan and I did back to back testing to check :-) I'd bet you can go stiffer with a custom one

[Rich_p 23]

£110 for the arb? Is that through one of the pre mentioned group buys?

I emailed for a quote this morning on a 28mm 309 length arb and they want £130 plus £20 for delivery.

[Anthony 1,000]

Increased material costs for bars over 25mm will be the reason for the disparity I suspect

[fliprio 9]

£110 for the arb? Is that through one of the pre mentioned group buys?

 

 

I emailed for a quote this morning on a 28mm 309 length arb and they want £130 plus £20 for delivery.

 

 

 

Torsion Performance quoted £110 for the 25mm 205 length ARB, that was just from emailing them, no group buy or anything.

 

I got my 24mm GTI-6 ARB that had been cut off and re-splined both ends for £100 delivered, which worked out well.

[fliprio 9]

Don't be put off by the cheaper bars, there's loads of people running them (myself included) with no probs whatsoever. Infact the likes of pug1off etc afaik are selling the cheap bars with a load of 'mark up'!!

A cheaper route though as you've suggested would be to drop the front spring rate and fit a bigger rear arb. I'd go with a hefty rear arb firstly and see what you think, then move onto the springs.

 

Time to try some softer front springs me thinks

 

They are currently 250lb, my choice is either 200 or 180lb - so im going to try the softest at 180lb and see how it goes.

 

They are currently 8" long springs, as im going softer will I need 9" springs to keep the same ride height as the initial preload will cause more compression of the spring and I don't want it any lower than it is - and before someone points out the obvious the adjustable sprint platforms on the coil over body are stuck solid as the shock body has rusted.

[camgti 56]

I believe that due to not having a good diff ( tran x/ Kazz etc ), your missing out on that final piece of the puzzle. Which would be the extra grip and exit speed your missing. With the setup you have now. Having the plate diff will pull the car tight mid/exit of a corner and transfer more weight to the rear, where the roll stiffness ( not sure of correct term here. Cameron or someone please confirm this as dont want to lead anyone stray here, with miss information ) of the car is. Then its a matter of learning how to add the power at the correct times etc ( not assuming your already doing this ) to 'balance' the car.

 

This was from experience in my car. At the time was running a Quaife diff, 21.3mm rear torsion bars, 24mm arb in a 309 beam, Koni Yellows with eibach springs. Once i changed to the Plate ( Tran x ) diff it was a world of difference. Your able to get on the power earlier, brake later and exit like a slingshot.

 

Cam