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Problem 2 - Handling?


caterhamnut

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ok - next one. Car handling, which is always subjective - though as I spend all my life in our car, I think I can tell when something changes!

 

Please have a look at the picture linked below, with a description of the 'problem'. Its at the bottom of the page under 'set-up problems?'

 

here

 

What do you think? Tire wear on this car has always been very even under normal use. Steering definitely feels different.

 

Any ideas?

 

Could I have cracked anything in the chassis - reason I ask is thatthere can be a lot of creaking and groaning sometimes under our car, when entering a drive way for example, where the chassis is 'twisted' as you turn up a steep incline. Sounds like it comes from in front of us (as opposed to around the rear axle) Rivets stretching the ali bodywork? I just have visions of a cracked weld somewhere deep under cover! Does this happen? Could this be related to different steering feel?

 

Car felt great around Castle Combe at the recent action day (lapped the whole field hee hee!) but feels very 'darty' on the road.

Appreciate your time!

 

New site! mycaterham.com

here

50,000miles in 2 years

 

Edited by - angus&tessa on 11 Sep 2003 00:14:23

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I've had a look at this and the "symptoms" look to me to be the result of a track setup (toe-out and substantila neg camber) on the road. A lot of neg camber will wear the inside edges of the tyres excessively on the road, and in so doing will smooth them off, wheras the outside edges of the tyres will keep the "graining" effect from track use for longer. I've gradually increased the neg camber on my car to 2.25" with a dash of toe-out, and now the tyres wear fairly evenly on track but the car feels pretty unstable on the road at times, especially where cambers/poor surface come into play.

 

Personally I rotate my track tyres and run then on the road a bit between races/track days. I always run my fronts contrary to the direction arrows, and the rears with the direction arrows, for dry track use. I then often switch the fronts to the rear and therefore run all the tyres the opposite way to theor "usual" roation on road to flatten them off. This is particularly useful with tyres like CR500;s where the tread can really ruck up around the edges of the "V" shaped patterns. It seems to prolong tyre life... I also look carefully at what the tyre wear says about my driving style and the pressures/setup I'm running, for example for much of this year I was wearing out the outside front tyre more than any other, I softened the front ARB, and now I'm not slipping the front outside as much, and am going quicker...

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BTW - saw the results of NOT running enough neg camber on the road last week at Combe when someone in my session took all the tread off the outside couple of inches of a set of nearly new CR500's!

 

Personally I'm 99% likely to be running a blade, bird, ZX-12 or similar Caterham in the 750MC Road Going Bike-engined series next year, current planning is to use ACB10's. Now from looking back through the history on here these want very little neg camber, so I'm fairly confident that this setup, for road use with my road tyres (RE720's), will feel better than the current setup which is really not ideal for the road. Probably not of interest to you as you drive the thing to track by the look of it, but has anyone else found this?

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Thank you jwyatt - certainly sounds like the right symptoms for the result *confused* ! - but what could have caused the change in set up, bearing in mind I have adjusted nothing, and that this set of tires were wearing evenly.

Peter C has already given me a sensible list of things to check - just looking to see if anyone has had a similar tale.

 

New site! mycaterham.com

here

50,000miles in 2 years

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Assuming nothing has gone wrong with suspension etc, and that nothing obvious like rake, ride heights, or cornerweights have altered (they do need regular fiddling) then most likely it is the tyres - often a worn tyre will feel very different to a new one of the same type. Looks like you haven't run the 48's for long, or had a set on low tread before...
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Thanks Mick - I know for afact that our floor rivets need replacing (hence the crane!) and had wondered if this could be a cause of the noise - not least because they must provide a fair amount of rigidity to the car - better get them fixed and see if it makes a difference.

cheers *smile*

 

New site! mycaterham.com

here

50,000miles in 2 years

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I'm no expert on this, I'm just looking at it from a geometry point of view rather than based on knowledge of handling. So if this is bunk, would someone please say so !!

 

Angus, you mention that you have 195 rears and 185 fronts and it sounds like this is a recent change. If the rolling radius of the 195s is larger, could that extra bit of height at the rear tilt the car forward, and thus change the effective castor (not camber) angle? If so I think this might cause the handling symtoms you describe; castor is responsible for steering self-centering and "weight".

 

Secondly the raising of the rear could be shifting the center of mass of the car a fraction more towards the front wheels, making it ride a fraction lower at the front. This will put the front tyres slightly more on their inside edges to begin with....

 

 

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