Rear tyre wear on track

[AdamR]

Hello all,

Got some pretty high outside edge tyre wear going on at the rear on my 172 Cup when on track, after a bit of advice/feedback if poss please...

I have 1 deg camber shims both sides, which should put the camber around -2.5 (although realistically I think one is 2.5 and the other is about 2.2), but both outside edges are getting hammered. No play in the stub axles, rear bearings or beam. Front camber I have set to 2.8 and the tyres have worn pretty evenly across the tread.

Inside:



Outside:



Other setup info if relevant: RARB fitted and set up pretty stiff, running about 26-27psi hot, no rear seats etc so the back is pretty light, tyres are Federal RSR 595s, and I don't drive in a 'lift off oversteer' manner.

Do I just need more camber? I notice a lot of the touring cars have silly camber but didn't think I was getting anywhere near needing that much...

Cheers in advance for any input!
Adam

 

[ado]

Have you tried different pressure? What is the handling characeteristics of the car at the moment?

 

[AdamR]

I usually start the tyres around 25 at the rear, and they have been up as far as 29, but not for any length of time... I would have thought lower pressure would give more edge wear and higher pressure less grip?

The car is very balanced at the moment, grips well in the dry, slight understeer in the wet.

 

[Tony Hunter]

we only run 2.5deg on the rear on the race car,I wouldn't fancy anymore than that really.

 

[AdamR]

Cheers Tony, was hoping you would reply! Just put up with the rear tyres wearing funny then?

 

[Jay Payne]

rubbing on the arches?

i know what you mean about camber on touring cars but they're not all like it. depends on the suspension arrangement. as Tony said 2.5 is ideal from the tyre temperature testing we have done

 

[AdamR]

Hmmm, pretty sure its not the arches, the surface very much looks like wear from the track rather than scrubbing, its very even if you get me.

Ah I see, that makes sense. Had thought about trying to check temps but it seems you need a probe to get down into the tread, which is expensive and a bit OTT for just track days I reckon! Do you guys see wear like this or is it pretty even across the width of the tread? Thanks for your input!

 

[Jay Payne]

pretty even on the rears. yes u will need a probe to do it properly.

try less rear pressure. think we run closer to 24-25psi

 

[Dan519]

tyres too narrow for the wheels? it sounds like you have a very stiff setup, and the only movement anywhere is in the tyres. Certainly looks like the tyres are rolling over a lot

 

[AdamR]

Cheers Jay, will give a bit less pressure a go, although I have a feeling that might let the tyre deform more? Worth a shot though - cheers!

The tyres are 195s and the wheels are 6.5 or 7" (can't remember off top of head), they 'look' fine if that makes sense (can see a bit in the pics up top). I guess the setup is pretty stiff, yeah... So I'll just have to live with it?

 

[mikekean]

Sound like you need a bit more toe out on the rear, you will be running more toe in now from the camber shims so it will need correcting. Best thing to do is get the rear alignment measured then you know what shims you will need to but to correct it.

 

[AdamR]

Nice one dude, didn't think of that, makes sense though. I'll have a look over the weekend if I get chance. Amazing the difference half a degree here and a few minutes there can make eh...

 

[Toastfrenzy]

I have left the rear camber on mine alone, so 1.2 - 1.5 std on a cup (?) have quite a stiff set up and get even wear, 2.8 on front and on very slight outer edge wear (nothing to worry about atm). Though had to get the toe sorted once set up to 2.8.(run with 1 - 2 something's of tow out).
Would get it to a computer tracking garage, as presume the rear toe would also require adjusting if I'd altered the camber (only going from how the front looked when adding camber, toe was visibly out).

 

[AdamR]

The rear camber adjustment is literally just shims between the rear beam and stubs, so it doesn't change the toe anywhere near as much as when you adjust camber up front http://www.k-tecracing.com/show_product.asp?id=3630&appid=2

Yeah, 1.5 rear camber is standard according to the geo sheet I have.

 

[Tony Hunter]

Go for these,much better.

Plastic ones are rubbish,they squash and move.

 

[skydiver]

+100000000000000

 

[NorthloopCup]

The rear toe will need adjusting even if the car is lowered tbh. The rear beam is designed to work at the ride height specified by the Renault engineers so with lowering the car plus increasing the camber will increase the variation by a greater amount. I adjusted my rear tracking to get it back nearer to original when I cambered my beam.

Be careful when you adjust the rear toe though as to much toe out will make it want to swap ends, but the correct amount allows you to control the behaviour of the car on the throttle.

 

[Tony Hunter]

We went from 1deg toe out to .5deg toe out,made so much difference,great for track day's but in a race situation we needed more stability.

 

[AdamR]

Thanks for the input gents - much appreciated!

I can see how the plastic shims aren't up to track use, so first thing to do is get them changed I guess

Toe at the rear is current 10 mins in (standard seems to be ~0.5 deg toe in? http://www.cliosport.net/forum/attachment.php?attachmentid=11081&d=1155755988). So, it looks like a bit of toe out is the way to go, which will help the tyre wear too. I don't want to go too extreme, so if I shoot for 0.5 toe out and try and keep the camber similar at ~2.5 I reckon that will be an improvement?

 

[Tony Hunter]

Yes.

 

[AdamR]

Wicked, thanking you muchly!

 

[mikekean]

We went from 1deg toe out to .5deg toe out,made so much difference,great for track day's but in a race situation we needed more stability.

Is that 0.5 degree over all, or per side?

 

[Tony Hunter]

Per side