Friday, January 13, 2006 - 04:46 pm, by: Adam Brown(82ajb)
This is more of a drag racing question, but this is the most appropriate section i thought. Went to Willowbank on wednesday night for the first time since replacing the factory clutch and adding front mount intercooler. I was running 16" rims with 225/55 tyres at 24psi. I was having a bad night for a few other reasons (My shifter came loose and couldn't select a gear! Quite embarrassing having to push a soarer off the drag strip. Easy fix fortunately...), but i couldn't seem to get it to hook up well. From the launch all through first gear i just got violent axle tramp (hence the 2.8 60ft times off a .6 reaction!). Is this a suspension, tyre, technique issue? How do i solve it. I could only manage a 14.08, but i know mid 13's are possible.
Unfortunately its a "feature" of the Soarer suspension setup. Stiffening the swaybar doesn't solve it & solid diff mounts doesn't solve it. There are some really weird bushes that can be replaced which help, but I'm not sure if any of us manual owners has it sorted out with a 100% fix. Perhaps Manny can shed some more light on the situation, as I still experience axle tramp on take off also.
Peter , just a suggestion , could we have a fast way to access the ALSC archive search(direct link). A lot of people wouldn't know where to start looking for it as i didn't. So they miss the volumes of good information, resulting in questions like, whats the red button for?
Saturday, January 21, 2006 - 06:09 pm, by: Damian Ware(Frozenpod)
Adam I know it is the tyre pressure but that is dangerously low.
Even for the drag strip where you are trying to get maximum grip just on take off I cant see how going that low will achieve this. Given that the tyres are the point of contact with the road they are the most crucial suspension component without good tyres and the correct pressure the best suspension in the world is useless.
At 24psi the tyres could become that spongy that they are also adding to the problem.
Even 32psi is low even though it is the recommended on most cars it can cause damage to tyres.
I am currently running my tyres at 41psi front and 39psi rear. In the winter I drop them back a few to get a bit more grip while braking.
If I am incorrect about the tyre pressure for the drag strip please correct me.
Its common for drag racers to have less than 20 psi in their tyres. They use slicks that have a soft compound and high walls. The tyre twists up under launch and unfurls as it gathers speed. I have heard of pressures as low as 16psi. Its debateable how much difference it makes with street tyres.
As Andrew rightly mentions, low pressures are used in true drag circumstances. A set of tyres I'll be purchasing shortly come with an instruction manual which states that for the width and profile of this particular tyre and the weight of the Soarer, I should run 16psi. It all depends on what you're running and the proper settings/specs for the situation.
I've just fixed my axle tramp problem. I did it in stages and here are my results:
sub frame support bushes: not a big difference in tramp.
Replace HSDs with bilsteins- no difference
I got jack of tramp so I bought the diff pinion support bush set (superpro), new donut(thanks Omar) and a tube of sikaflex 227
I installed the bushes and used the sika to fill all the voids in the subframe, diff (ears) and donut. Also installed a new bolt in the diff rear, one had shaken loose (!!) then did a fastener check all round. Also re installed the HSDs
After 3 days (sika cure time) I took it for a spin. it still tramped! then remembered the damping adjustment on the HSDs was not set. Turned them up to 6 clicks (clockwise) and another road test revealed tramp was gone!
time for a motorkhana
Additional info: I run 275 rear tyres (Falken FK452s) which, as I understand- wider tyres promote tramp. Rear ride height is 350mm cwg, I would prefer higher clearance.
The voids in the rear diff support bushes, diff ear bushes and tailshaft donut allow movement. I used Sikaflex 227 to fill the voids (after a thorough cleaning)
The Sika 227 has a similar flexibility to the stick rubber, and sticks very well. It is often used to repair bushes and engine mounts- the web has loads of examples of it.
There's a few tricks to doing it though. Because 227 is a humidity cure polyurethane sealant (unlike standard silicone)it sets faster in wet/ humid weather. The thickness of applied filler really affects cure time. I did the job in halves- filled one side of the rear diff mounts one day, waited 2 days, then did the other side.
It takes a while to do properly (cure times and removing the diff) but is well worth it. No more tramp for me