Widetrack - Effective Spring Rates

[Tazio]

The angle of the spring and shock absorbers as fitted to a widetrack car reduce the actual spring rates but by how much?, If I have 250lb springs, what is their actual effective spring rate?, Anyone know?

[Richard Price]

Tazio,

''think you're referring to effective wheel rate.

I did some geometry in a spreadsheet a few years ago. I'll if I can dig it out tomorrow.

[Jonathan Kay]

The theory:

(The links are a link... )

...

Previous discussions in the archives suggest there are several variants.

Jonathan

[Richard Price]

Tazio,

you should now have a couple of messages from me

[Simon.Rogers]

Jonathan 

I used to use that diagram and theory but I found it more accurate to actually measure the wheel motion ratio.  It gives more accurate results across a range of cars.

[Jonathan Kay]

I was hoping you'd spot this... do you measure every time or are there known values for Caterham configurations?

Thanks

Jonathan

 

[Simon.Rogers]

I have my own figures for the various models.  There is clearly a small change between the models but I feel it is the engine weight combination that makes more of a difference.

 

[Jonathan Kay]

Thanks

Jonathan

[Speedtrip]

Sorry to high jack the thread....

When I test drove a seven prior to buying It was in a 310S S3 and the car felt really quite comfortable and seemed to handle well when pushed. I ended up buying a slightly heavier 360R S3 with the wide track suspension and have found it less compliant, harsher and it probably doesn't handle as well, certainly on bumpy corners. Only used on the road.

If there's not much difference in spring rates why is one different to the other or is the function of the dampers?

Cheers,

Andy

[Paul Deslandes]

If it doesn't handle bumpy corners you might want to check bump steer.  As a first step check the height of the steering rack above the chassis cross member plate that it sits on.  More info in the article here.  There are a couple of appendices to the original article at the end of the on-line version so be sure to scroll right to the end.

Correcting it if it's wrong can be a huge improvement in general, on-the-road handling.  In all cases that have been reported back to me, the addition of 9 or 10mm spacers under each rack clamp does the trick on either standard or narrow track and both the earlier common top fixing and the later separate top wishbone/shock absorber mounting.

Paul

[Speedtrip]

Thanks Paul.

An excellent article and definitely worth considering!

[mikecocker]

I could be wrong here, but I thought the bump steer problems of the past had been sorted with the introduction of the offset rack mounting bracket. This has been standard since before the introduction of the 270,360,420 range.

Maybe the differences Andy felt were more to do with differing specs between the 2 models , ie wheels/tyres, road/sport suspension, anti roll bars etc., and also the set up of the car.

I know my own car which is R spec can be uncomfortable on some minor roads with lots of camber and dodgy margins, but track days and sprinting it feels great.

Maybe a case of horses for course.