Low Speed Bump experience

[260DET]

In my ignorance I had always thought that low speed bump (LSB) was more of a feel thing and did not have a lot to do with actual grip. Wrong! Having left the damper settings as recommended by the maker for a while, I thought it was time to play with some of the three way adjustments, thought a bit of LSB would sharpen up the feel a bit. Adjusted the front up a bit, it got a bit skittish there so screw up the back a bit to counteract that.

 

Goes out to my 'safe' circuit for some laps, after a lap and a half tyres should be warmed up, turn into a slow 90 degree corner. Whoa, back starts to come round, countersteer, back the other way, tank slapper in progress, hit a tyre bundle marker. A slight dent and some marks but otherwise OK. Hit the left front wheel so alignment may be out although toe looks OK.

 

Go back out, taking it easy, come into a similar corner, same thing wants to happen but I catch it this time. Not sure about the alignment so park it for the day. Video of second incident here

 

A few days later I get to talk to the bloke who made the dampers and recommended the original settings. He says LSB is the most important adjustment, for best grip run it as soft as possible while still able to get the suspension to set in a corner and for the car not to feel it wants 'fall over'in a corner. With some variation to account for driver preference. Once that is satisfactory then do a final tune using rebound.

 

Comment or whatever, please don't laugh at the video

[silverarrow27]

Hilarious, thanks for the lesson. At least it was at a track and you're okay!

[hoov100]

do you have a video of your car with the LSB at factory settings? You're car just looks flat and motionless, like the tires are doing the work, instead of the suspension.

Edited April 14, 2010 by hoov100

[260DET]

Looking at that video again it hardly looks like the back has stepped out, it happens so quick, caught the sneaky ***** that time though

 

There are a few of my vids on YouTube Hoov, the second last one is when the front had been adjusted but not the back. You are right, problem is that as explained to me when when turning the weight transfer is so quick the suspension does not get a chance to set. The procedure I'm now following will soften it up, give the suspension a chance to work.

[johnc]

Your shock guy is correct. For best grip you generally run as low a compression damping as possible while keeping the car from falling over on that corner. Compression damping controls sprung weight of the car while allowing the un-sprung weight to work over bumps Suspension compliance is important for grip.

 

Too much compression damping makes the car feel skatey (skittish) and tends to break loose suddenly. The car doesn't lean over on the tires and bite.

[gvincent]

Your shock guy is correct. For best grip you generally run as low a compression damping as possible while keeping the car from falling over on that corner. Compression damping controls sprung weight of the car while allowing the un-sprung weight to work over bumps Suspension compliance is important for grip.

 

Too much compression damping makes the car feel skatey (skittish) and tends to break loose suddenly. The car doesn't lean over on the tires and bite.

 

So John If I may ask a stupid question with 5 way adjustable Illuminas I should start at the lowest setting of 1 and then progressively work my way up or start at 5 and work my way back down?

 

 

Running Motorsport Blue lowering springs, 1" strut spacer in front LT1V8/T56 and 88 300ZX CLSD 1-7/8" Suspension Technics front sway. Lowered rear sway bar mounts 1" to clear drive shaft

All Poly bushings everywhere except for tension rods which are the aluminum cup and Nylon type.

 

Thanks,

Greg

[johnc]

So John If I may ask a stupid question with 5 way adjustable Illuminas I should start at the lowest setting of 1 and then progressively work my way up or start at 5 and work my way back down?

 

Thanks,

Greg

 

Well... that brings up a related issue with "street performance" shocks. Tokico Illuminas are designed for a street car that runs stock or slightly stiffer (50 to 100%) springs. The Illumina is designed to increase compression and rebound damping in a linear rate as you move up from 1 to 5 on the adjusters. The increase in rebound damping is nice. The increase in compression damping is there to compensate for soft springs. Unfortunately, you also get the drawback from higher compression damping (skatey handling) as you get into the 4 and 5 adjustment range. Its a tradeoff and IMHO the drawbacks outweigh the benefits when you get into the upper range of adjustment on the Illuminas.

 

Ideally compression and rebound damping are complete separate adjustments (Koni 8611). The next best is adjustable rebound only (Koni 8610) and the third best is a combined adjuster where the rebound rate goes up as an exponent of the compression rate as the shock is adjusted (Tokico HTS).

 

To answer your question, start at 1 and don't go beyond 3 for the MSA springs.

[gvincent]

Well... that brings up a related issue with "street performance" shocks. Tokico Illuminas are designed for a street car that runs stock or slightly stiffer (50 to 100%) springs. The Illumina is designed to increase compression and rebound damping in a linear rate as you move up from 1 to 5 on the adjusters. The increase in rebound damping is nice. The increase in compression damping is there to compensate for soft springs. Unfortunately, you also get the drawback from higher compression damping (skatey handling) as you get into the 4 and 5 adjustment range. Its a tradeoff and IMHO the drawbacks outweigh the benefits when you get into the upper range of adjustment on the Illuminas.

 

Ideally compression and rebound damping are complete separate adjustments (Koni 8611). The next best is adjustable rebound only (Koni 8610) and the third best is a combined adjuster where the rebound rate goes up as an exponent of the compression rate as the shock is adjusted (Tokico HTS).

 

To answer your question, start at 1 and don't go beyond 3 for the MSA springs.

 

Thanks John, I now understand, why I am bouncing all over the road on Infamous uneven New England patched pot hole roads, I definately need to back them down as well as get a new front wheel alignment, My 78 with stock springs and KYB shocks is much better behaved but doesn't take Smooth pavement corners as quickly.