Sir 51D3WAYS

You want something soft for a bump stop actually, not hard. Having some hard ass washers will simply limit up travel, yes, but they will cause the spring rate to suddenly go to infinite and you will slide off into oblivion. (well not really "spring rate" seeing that the spring isn't working anymore, but you get the idea.) Full size cars use an actual lump of rubber stuck on the chassis where the arm/hub contacts. Personally, I would use some shock o/x-rings, but high durometer (hard) ones. Normal shock o/x-rings are fine as well, but avoid the super soft ones as they collapse too easily. The o-ring acts as a sort of snubber and allows a somewhat more progressive increase in "spring rate".


Tamiya black o rings are good. As are their red o rings, and their blue x rings 50 durometer.
Hardest to softest.

Johnny Wishbone

iTrader: (6)

Full size race cars use bump stops on the shock shafts, material and configurations of many different variables Anything from teflon to soft plastic in normal shapes to xmas trees.

LzREngineering

So we reckon bumpstops/stronger damping may be the way to go?

DesertRat

iTrader: (2)

Maybe harder swaybars.

Nerobro

iTrader: (2)

Offhand, this is the option I like. But that then starts to mess with individual corner damping, and you end up having a stronger compromise between chassis and wheel control.

... Elastomer swaybars?

LzREngineering

what about those bodyshell standoffs that mount to the c-hubs? (commonly used on awesomatix but available for other cars - can't remember who makes them)
that would put some of the weight transfer directly onto the wheels, reducing the chassis roll and also eliminate the shell catching on the top of the tyre.

Sir 51D3WAYS

That's the posh option.

(I remember older (passenger) cars had chassis mounted bump stops and Koni sold shocks with a rubber/foam bump stop on the shaft, which were considered an exotic upgrade. This was ever such a long time ago.)

0010

iTrader: (4)

Does anyone know where to get those standoffs?

30Tooth

iTrader: (1)

Next time you're at the track test an oring on the shock shaft, I use them on my tc6. While it doesn't avoid bottoming out it makes it less violent.

​​​​​

LzREngineering

Ok, so, Friday night racing on the gray rug @ Worcester. Grip is always a bit low to begin with here, as the carpet gets rolled up between meetings and it takes a while for the line to clear. Due to timing computer problems there were only 2 qualifiers and a final tonight.

Changes I've made prior to this meeting: up to a 2.7 spring on front. 1x o-ring on shock shaft (front only).

Car was very stable in 1st round. No bouncing. Got a solid time in.

By the second round a small bump had appeared in the gaffa tape between the carpet on the entry to a slow speed chicane in the middle of the track. No-one else seemed to have a problem with this bump but my car was reacting horribly and bouncing off line. I had to take a very wide line around it and didn't improve my time despite the grip being up and having turned up the motor. The car still felt great on the remainder of the track.

For the finals, I raised the front ride height by about 0.5mm. More tape was laid over the bump but my car was still not happy with it. It wasn't the worst it's ever been but still would skip across the track as it crossed the bump. I'm pretty sure nothing was catching on the track; the body shell I was running has been trimmed very high.

I saw other cars in the mod final running very low shells and noticeably catching on the bump but it didn't knock them off line at all.

So pretty sure this is a bump related issue but especially bumps in loaded corners.

Does this help give some idea as to what's happening/what may be causing it?

Sir 51D3WAYS

Pretty sure it's now suspension related. Need to mess with the spring/shock/ARB package. Probably shock.(assuming that you aren't running some ridiculously hard spring)


Have you ruled out UJ wear/binding and ride height? (something ridiculously high not 0.5mm higher)

robk

iTrader: (22)

Why don't you put orings on all 4 shock shafts, and push them up to the shock bodies before a test run. Once you finish , look at how far they were pushed down on the shafts. If they were run down to the perches, you know you bottomed the shocks. At least it would give you an idea if you're even bottoming. You might also want to put light colored masking tape on the chassis bottom to see where the chassis is contacting or dragging.

Maybe these are dumb ideas, but I'm not sure how else you can get actual feedback on what the car is doing.

LzREngineering

Not dumb ideas at all! But in practice I don't think the o-ring method will work very well on short travel shocks (maybe on a buggy). The tape method would also produce inconclusive results but could work well in certain situations. I really need to get hold of a high FPS action cam and film either the problem corner or from inside the car.

LzREngineering

Probably shock related as you say. There is a small amount of wear on the spool outdrives but nothing causing binding. I swap the outdrives side to side occasionally to minimise wear but there's always a fair bit of play due to them being steel-on-steel. I could try alu outdrives with blades for a lot less play but I've got a feeling that would make things worse if anything.

Ride height is a factor but I was running about 5.5mm-5.7mm by the end of the night and others were on 5.0mm-5.2mm with no problems.

30Tooth

iTrader: (1)

Please post head on and rear end diff level so I can look at the suspension geometry and shock angle.