Julian Thompson Posted June 18, 2003 Share Posted June 18, 2003 Having just shelled out £240 on a new sump pan due to the car bottoming out, I am keen to stop this happening again So. Why does my car bottom out. 1) I could raise the rideheight but this is a crap idea for handling. 2) I could fit stiffer springs but it understeers its cock off anyway, so this can't be a very good idea. OR 3) Could I fit bump stops to the dampers to stop this happening? OR 4) Could Len's pushrod suspension be the best idea 😬 because, I am led to believe it is "rising rate" - will this make the car much stiffer as the compression load increases 🤔 Link to comment Share on other sites More sharing options...
philwaters Posted June 19, 2003 Share Posted June 19, 2003 I thought it was the other way around - what you have is raising rate due to the angle change of the damper as it moves with the moving wishbone. As the angle of the damper changes relative to the top mount this changes the effective rate of the springs. i.e. the leverage the wishbone has changes. This is why a wide track car with, say, 250lb springs will feel sfter than a normal track car with the same springs. Whereas the pushrod set-up maintains the same ratio due to the damper being mounted separately. But, the good news for your justification, is that the normal set-up gets softer as it compresses - I think. So going to push-rod would increase the stiffness for a given spring rate, etc, once compressed. But - call Len, I'm sure he can put you straight... but that's how I understand it. Phil Waters You mean you can drive these? I thought it was just there to polish 😬 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 19, 2003 Share Posted June 19, 2003 Nah. Currently it is falling rate. FWIW when I changed to 250lb/in it improved the handling and kept the sump off the deck. Link to comment Share on other sites More sharing options...
Julian Thompson Posted June 19, 2003 Author Share Posted June 19, 2003 So presumably, anyone wanting to run 250lb springs would have to stiffen the rear up and/ or fit a thinner arb at the front to help with the understeer? Link to comment Share on other sites More sharing options...
philwaters Posted June 19, 2003 Share Posted June 19, 2003 Doh! I knew it wasn't constant (1:1)... although I'm right that it gets softer at it compresses arn't ? That's what I've always thought anyway. FWIW, I run 300lb fronts (on a LA) and it never gets close to the deck! Phil Waters You mean you can drive these? I thought it was just there to polish 😬 Link to comment Share on other sites More sharing options...
scooby dooby doo Posted June 19, 2003 Share Posted June 19, 2003 at the rear its all pretty much straight up and down so the rate is constant with linear springs. at the front the rate falls due to the geometry changes. you could fit progressive springs which get stiffer in a greater than linear fashion as they compress but they seem to be a matter of preference - I found I didn't like the ones Caterham offer. So I'd recommend you increase the ride height, stiffen the springs, or firm up the damping. The latter two will promote understeer (not sure about the ride height change ) so you may want to soften the fron ARB. If everything is adjustable (ie you make the change with dampers and ARB) then it can easily be reversed on the tracl) HOOPY R706KGU Hoopylight R Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 19, 2003 Share Posted June 19, 2003 Understeer is a lot more complex than just the matter of relative roll stiffness front and rear. The contact patches have to work together. The castor and static camber have to work with the steering angle to bring the tyres into stable contact with the ground. Consider this. If you trade roll stiffness from the rear of the car to the front of the car, but overall roll stiffness remains the same, the car will tend more to understeer. If you fit a stiffer front antiroll bar with no other change, you increase the roll stiffness of the entire car, so you might hold the front tyres more consistently flat to the ground (remember the rears are on a de Dion axle, so they have very consistent camber angles) giving more grip at the front than you lose through the increased weight transfer in roll. See. It isn't obvious. I did all the sprints last year with 250lb/in front springs and the 18mm front antiroll bar. I have driven many trackdays with this setup and understeer is not a problem... but other aspects of the car setup may be helping the spring setup to work effectively. My standard setup was on standard Bilsteins and standard progressive rear springs with the rear antiroll bar on second softest position. Link to comment Share on other sites More sharing options...
scooby dooby doo Posted June 19, 2003 Share Posted June 19, 2003 so adjustable everything will let you play around and see what works. but probably means you'll spend half your track time in the pits playing ❗ HOOPY R706KGU Hoopylight R Link to comment Share on other sites More sharing options...
Julian Thompson Posted June 19, 2003 Author Share Posted June 19, 2003 Arrrgh. Not so simple then. But it is a good excuse to buy the freestyle pushrod suspension, yes 😬 Link to comment Share on other sites More sharing options...
rjc Posted June 20, 2003 Share Posted June 20, 2003 As posted elsewhere I had a sorry tale with a smashed sump. My condolances I was absolutely gutted when it happened to me. Caution is needed here, particularly given the mention of understeer. Caterham recommend 70mm clearance between bottom of sump and flat level floor. If you drive on the road then resist the temptation to set much less than that. Then start investigating handling. Likewise I originally suffered from manic understeer. Having set the car low I had also inadvertently got the car running on the bumpstops at the front. So ! if you do set the ride height very low you can find that the front dampers are compressed so much you end up riding around on the bumpstops at the front. This can lead to manic understeer because the suspension travel is all used up and has no useful movement left for the corners. Sit in the car and get someone else to check if you still have about 10mm of free travel of the damper rod before starting to compress the rubber bumpstop. Also make sure that you are not getting coil bound at the front (the spring compressing and using up all the space between the coils). Caterham Vauxhall Race Spring sets are green springs with wide coil windings. They fit the standard Bilstiens with adjustable platforms and wide top seats. If you borrowed a set and made sure there was the bumpstop + 10mm free travel of the damper rod (Irrespective of ride height for the moment) at the front, and adjusted the back to suit you could carefully see what effect that had on the handling. Then you would have a place to start the long voyage of discovery regarding setting the suspension/ ride height/ wheel and tyre choice to give you the car handling of your dreams. Having raised the ride height and fitting a stiffer spring set than standard I found the handling of my car was very much improved indeed. Car set up is neither straightforward nor simple, expert help usually pays dividends. Buying a set of Freestyle pushrods won't automatically solve the problems, however Len is very knowledgable and a chat with him would not be a bad thing. Link to comment Share on other sites More sharing options...
Allan Haighton Posted June 20, 2003 Share Posted June 20, 2003 of course, you could gain a few mm of clearance by putting some shim washers between the engine mounts brackets and the mounting rubbers.... Link to comment Share on other sites More sharing options...
Julian Thompson Posted June 21, 2003 Author Share Posted June 21, 2003 Many thanks for your efforts. Link to comment Share on other sites More sharing options...
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