Handling problem - Avon ZV1 problem?

[slngsht]

Originally posted by Jim F

 

Hello, All;

I'd like some input

from those of you who have experience with the Avon ZV1 185/60R14 tires that came standard on my car. I haven't seen any comments on this tire since joining 10/07. The car is an '03 wide-track DeDion Roadsport w/LSD & was Caterham dealer built. From day one it hasn't wanted to track straight on the freeway at speed or on "spirited" county road drives. Before I start investigating the "squirreliness" for a solution, I thought you experienced driver/owners would have some informative comments/suggestions/observations. Tire pressures are set at 20 psi all around, and the car seems to have a bit of oversteer on both right and left hand tight corners. My previous two Sevens ('61 109E Lotus & '79 BDA Caterham) were very neutral handling, but then not as technologically engineered and sophisticated as my current Caterham. Could it also be that I haven't really "scrubbed" the tires in yet and the tread is taking more bite or grip? Thanks in advance for your comments!!!!!!!!!!

[athens7]

Jim-

If you haven't checked the alignment lately, it's a good place to start. My car (2005 SV Roadsport with Avon ZZ3 205/45ZR16 street tires) was set up by the dealer with a little toe out and no camber, good for autocross turn in, but bad for straight line road driving. Now I'm set up with a little more than 1 degree of negative front camber and zero toe, the rear ARB on the 2nd softest position, 18 psi front and 19 psi rear. The car is much more stable in a straight line, and still turns in well. Also, rake (the difference between front and rear ride height) can have an impact on oversteer/understeer. Caterham recommends 15mm rake (higher in back). My car came set up very low in front, with 30mm rake. I adjusted it to 20mm by raising the front end, which seems to keep the car neutral to slightly oversteering. The Avon ZZ3s break away fairly easily, so the car always feels a little loose, but they are easy to recover. I believe the ZZ3 is the successor to the ZV1.

[Boxologist]

the allignment on a caterham is usually pretty static. hoepfully nothing is drastically off. the ZV is an absolute disaster of a tyre. rock hard. poor dry grip, poor wet grip. first set of tyres that were on my 7 and was very thankful for the second set of wheels and wearing teh tres out on 7-7-07.

 

Azenis are available in 14" and would be an IMMENSE step up.

[Davemk1]

In my mind there are a number of things that could give you the effect you are seeing. I think it would be time well spent to go down the list and verify that everything is as it should be. This way you'll at least know all is well before changing tires and adding another variable.

 

I seriously doubt your issue has anything to do with your current tires not be scrubbed in well enough. Unless they are still new and still have mold release on them you should be good to go.

 

 

Toe

Camber

Ride height

Rake

Rear thrust angle

Rear Toe

Tire pressure

Sidewall stiffness

 

dave

 

 

[Kitcat]

Add caster to the equation too-the more positive caster you have, the more the wheels will want to point straight (tho it will increase steering effort too). That and adding some toe-in should solve the problem.

 

Positive caster is illustrated by the front wheels of a shopping cart, which due to that "alignment", point straight naturally as you push.

 

I should add that I was unable to fix my handling woes with alignment tweaks: it was all the tires' fault and when I upgraded to Toyo RA1's, all was better.

[gjslutz]

On my Birkin if I run any toe out, it is all over on straight road 100+ speeds. It is much better with 1' toe in and still will turn in ok. I also run -3' camber for my R888 Toyo tires. With that set-up it tracks well at speed also. The R888 heat up quite fast, so are great for track & autoX. Wet they are ok, just avoid ANY, ANY standing water. The oversteer could be from the shocks setting being too stiff, and the compound is too hard for the power.

 

Many more here have more insite to this than me.

[WestTexasS2K]

Caster should be half of the kingpin angle. So for most cars that is 5 or 6 degrees of caster. The more caster the better the car tracks. Should be able to drive with no hands. If the car is low on caster it will be very darty and difficult to hold on a straight line. The turn in will be very light and extremely responsive.

 

For a car that sees street duty I prefer a tad bit of tow in 1/8" a lot of people say tow out for better steering turn in. Is that ever a problem for a 7? A 3000 lb car ok, not on a seven in my opion.

 

Check bump steer. A general rule of thumb is the steering rack and tie rods should be level with the ground if it run up or down hill you will have bump steer issues with the slightest wheel movement. Lower control arm should be parallel to the ground and the upper control arm should be higher at the wheel than on the chassis. Most of that should be done from caterham but just double check. I have seen the tie rod end mounted to the wrong side of the spindle which will cause the tie rod to run up hill.

 

I would also try lowering pressures to 17 or so.