ACB10 and Suspension Geometry

[MikeE]

OK - I bought my 1600 Superlight back in April and have experienced two very enjoyable trackdays (Goodwood and Folembray) running with the original spec R500 wheels and CR500 tyres.

 

 

I'm picking up a new set of KN Minators (13" * 6" all round) and ACB10s tomorrow for use on the Lydden trackday next Saturday.

 

So:

 

1. What do I need to do (get done) to the suspension to use (or get the most from) the ACB10s?

2. I keep hearing people talk about the front geometry needing tweeking, how do I do this and by how much?

3. I also understand you should change the dedion ears to adjust the camber?

4. What will be the effect of leaving the suspension as is for the Lydden trackday and getting the suspension tweeked in the future (reason I ask is I don't think I can get it done before Saturday)?

5. As the car was originally specced with CR500s does this mean it has the standard geometry or something closer to an ACB10 geometry?

 

 

And finally how should I go about scrubbing these new ACB10s in before the trackday?

 

thanks,

Mike.

 

[F355GTS]

Mike

 

ACB10's are crossplys so are designed to run without camber both front and rear. If you check your current ears you will find a number stamped on the top (normally) mine are 1.5. Recommendation is to change to .5 or .25. The front should also have camber reduced to a similar level. The effect of not doing it is excessive wear on the inside shoulders (like I wore a 1" band of the tread off in one trackday.

 

The setup on mine set by RH Motorsport for ACB10's/ Slicks is

 

Front .25 Camber, 1/4 degree toe out

Rear .25 Camber, Parallel toe.

 

Now I've no idea what it's like, I'm running at Donington on Wednesday and it is a track car only, the above settings may well be hopeless for the road.

 

One thing to watch for is that being crossplys you may well experience tramlining on the road

 

for scrubbing see below from Avon's site

 

Use of Racing Tyres

 

For most purposes, racing tyres will benefit from an appropriate 'Scrubbing in' procedure. This provides the best combination of performance and longevity under race conditions.

 

There are several difficulties that arise when using racing tyres if they are not scrubbed in prior to use. The most common is "Cold Graining", where the layer of the tread compound in contact with the track, fails in shear with the layer below. The result is a very visible low frequency, high amplitude rippling effect. This is more common with new tyres particularly when used in wet, damp or greasy conditions.

 

Cooper-Avon Racing Tyres recommend that a standard scrubbing in procedure be used whenever possible (conditions and regulations allowing). This consists of subjecting the tyres through one gentle heat cycle, gradually loading them up whilst avoiding drifting the car. This should take about three to four laps of a circuit where the lap time is in the region of 60 to 100 seconds. The last lap should only be about 80% race speed. If possible, scrub in at least one new set of tyres during free practice, and put these aside for the race. In this way you will know that they have been balanced correctly, and have no slow punctures etc. Getting this done early is important as the qualifying session may become wet or be red flagged, which could force the use of new tyres in a race.

 

When regulations or circumstances do not allow the above procedure to be carried out, then the following should be borne in mind: -

 

* Graining of the loaded front tyre can be avoided if it is ensured that they are fully up to temperature before pushing hard.

* It is relatively easy to generate temperature in the driving tyres as they are transmitting power most of the time. The front tyres, however, will need to be given more time and be loaded up progressively before they will be 'In' fully. It should be noted that it is the loading of tyres that introduces the significant heat, not sliding or wheelspinning.

* For qualifying, the best results have been shown to have been achieved when the front and rear tyre temperatures are the same when measured at the base of the tread. If pushed too early, the rear will come in before the front causing understeer, and taken to the extreme, cold graining as detailed above.

* It is quite possible to get the rear tyres to go off before the front tyres come in, which will lead to a car that is never balanced, making set-up and qualifying very difficult.

 

 

Thus to get the best from a set of scrubbed tyres, look after the rear tyres by not using full power out of corners, and instead work the front tyres progressively without inducing large amounts of understeer. When the fronts are fully up to temperature, go for a time (really hooked up lap). Push hard for 2 to 3 laps, and then back off the pace for a lap to allow the tyres to recover, and to get some clear track. Repeat this procedure for the best results.

 

It should be noted that there is always going to be a slight performance peak from new tyres, but it will only be possible to take advantage of this if the car is balanced on its tyres. A correctly scrubbed in set of tyres will always give more consistent performance over its lifetime than a set that has been used hard from new, even if it hasn't grained.

 

 

Mark

[Peter Carmichael]

The amount of static front camber is related to the amount the car rolls in corners. Although the front geometry incorporates camber compensation, it reduces rather than eliminates camber change.

 

If the car is stiff in roll, then the static camber should be small.

 

If the car is soft in roll, then the static camber should be a bit larger.

 

For ACB10s, use approx half the camber you would for a radial. The de dion setup obviously doesn't suffer from any camber change, so 0.25 degree gets both inside and outside tyres pretty flat to the ground. Some of the racers run at zero degrees.

[MikeE]

So my next question is..........who can adjust the front suspension for me - I'm in Fleet Hampshire (Micheldever Tyres maybe?). Does it entail popping the upper wishbone ball joint?

 

How much are the 0.5 dedion ears and what chance of sourcing them and fitting before Saturday (how hard are they to fit yourself?)

 

Thanks,

Mike.

[F355GTS]

Mike

 

call Caterham for the Ears, as far as fititng them it should be quite easy but you need to remove the rear brake disc so large socket required (41mm I think???). The front requires the upper wishbone to be 'popped' and then adjusted as required.

 

If you want somebody else to do it/ check it you could try Roger at RH Motorsport in Abingdon (he did mine!) 07768515326, he can also check ride height and flat floor it

 

Mark

[Julian Thompson]

Sorry to be a thread terrorist , but what are Yoko 032R's like in comparison to the ACB10's and do they need the suspension altering?

[Peter Carmichael]

A032s are radials and therefore need more camber than ACB10s to work optimally.

 

Worth noting that for road use you shouldn't run that much camber because you never lean on the car that hard in the corners. For track use you run more camber as defined by tyre temperature readings.

 

Allegedly.

 

I tend to run one setup all the time and ACB10s all the time according to the principle of keeping things simple.

[felix.klauser]

> call Caterham for the Ears, as far as fititng them it should be quite easy but you need

> to remove the rear brake disc so large socket required (41mm I think???).

 

You can remove the entire rear hub/disk/driveshaft assembly on each side in one piece, saving you the need to undo the driveshaft nut. Remove and secure the brake caliper and then undo the 6 bolts that hold the hub to the aluminium ear and the aluminium ear to the end plate of the DeDion tube. You can then carefully withdraw the driveshaft from the diff and take the ears off.

 

Edited by - felix.klauser on 24 Sep 2002 16:50:43

[AndrewD]

Mike

 

You beat me to it for the wheels but they are getting me another set to try out at Anglesey. Ooerr, 6 x 13s all round instead of my nice steamroller 7's at the front and 8's at the back.

 

Andrew

Yellow SLR T777XXX

[F355GTS]

Julian

 

IMHO 32R's are a nicer tyre in terms of feel/ handling on track, particularly on rough/ uneven surfaces and grip is similar to ACB10's. The downside is they're v. v. heavy compared to ACB10's, but then again they are half the price

 

Mark

[MikeE]

So being realistic it doesn't look like I'm going to get the geometry sorted by Saturday (in time for Lydden) - it'll have to become a winter project

 

I've got a brand new set of ACB10s to play with, am i likely to cause excessive wear to the inner edge of the tyre on just one trackday (BTW I'm in the novice (green?) group)? i.e am I going to knacker £400 worth of tyres in one trackday

 

Mike.

[F355GTS]

Mike well I did, but I wasn't hanging around, try not to induce excessive amounts of oversteer

 

Mark

[Fast Westie]

Mike

You could wind out the top ball joints by 2-3 turns and reset you tracking. This will reduce the camber.

 

The car in front is a Westfie1d