0Randy@DRM

There has been a lot of talk about suspensions lately and I hope to make people understand what they are running without breaking the bank. I don't care if you are running coilovers, leaf springs, or ride height, and anyone of the number of shocks out there. There is something for everyone to learn here and understand why and what is really happening. How can you tell if your shock is working for you and not against you during your normal driving condition??? Easy test!!!

So, today's homework assignment is to learn about the shock and it's importance on a car. There is a old but still very true fact about traction, "never let a loaded tire become unloaded".
When the wheel goes up and down there is a rate in which this is happening. This rate can't be measured without a very good eye, laying on the track at the apex. Or using a fancy shock sensor and trick computer $$$$. We have done it both ways in the past and it works very well. I see a lot of times people including myself getting the cart in front of the horse and not checking the most basic thing out there.

We have all seen the slammed look of a corvette. Well it's not always done right and without any testing to make sure things are still working right. As the wheel moves up into the fender, it is called bump travel. So from ride height to full bump is what we will be your homework assignment. The reason for this homework is to see how much of the shock you are really using and how much of your "good handling" is really just a feeling in your gut. Once the shock get to the bump stop or bottoms out there is no where for the tire to go, but airborne. Never unload a loaded tire!!!

This is the assignment that I have been talking about. Take 2-4 zip-ties, brighter the color the better. Wrap them around your shock shaft. I use either a wire cutter, or a nail clipper to take off the extra end. Then pull the zip tie all the way to shock body. Then take the car out on your normal drive. DON"T run over 6X6s or anything stupid. Just drive down your twisty road, lap around the track, down the river road, or some other fun drive. Then jack the car back up and see where the zip tie ended up. Report back your findings.

Randy

RC45

Randy, I am doing a 7 hour "Test and Tune" on Friday.

I was hoping to gather a number of "tests" to perform to make the track time worth the effort and expense.

I have a helper to gather tire temps, oil and water temps etc - and I guess now we can gather bump travel data.

Any other things you suggest we gather/measure/view during the sessions?

ScaryFast

That's so obvious it's brilliant. I have some nice pink ones that I'll be using next weekend at the track...

So if you're only using 1/2 of your shock's total travel, is that an indication that you're too highly damped?

BrianCunningham

Thanks for the tip

mgarfias

No, suspension travel is a function of spring rate (in ride) or roll rate (in roll). The dampers control how fast the suspension moves, but not how far.

If you're only using 1/2 of your travel that means you're not hitting bumps, or you're not using the full travel the car is capable of. If you're not using the travel it could be for a number of reasons. Could be you're sprung too stiffly, or you're simply not driving hard enough. The travel info alone won't tell you that, you need the butt-o-meter hooked up to interpret what the travel is telling you.

TheNick

Better hope you don't see any bumps anywhere on the road you are driving. The second you do - your test is over. The point of measuring bump travel is to make sure you have enough travel while the shock is in its applicable range. This applicable range for racing purposes would <3in/sec piston velocity - any bumps are going to cause a piston speed that is much much higher than this.

A better homework assignment would be to fab up some damper pots out of cheaper off the shelf parts than what is readily available from the expensive instrument companies.

Bill Dearborn

Even hitting a bump the zip tie would still show max shock travel incurred while driving and whether or not the shock is bottoming out.

Bill

Everett Ogilvie

I also think the method has some merit. It might be hard to take zip tie info from a street ride and directly translate it to come up with track settings, but on a track test it might provide some insight for track settings. When Andy Pilgrim drove the Mosler on the track he suggested this very method to gain some insight into the front suspension action of the car. I think his advice might be some of the best that one could get!

Z06_BluByU

FWIW
people have used this method for years on teh full suspension mt. bikes.. (to check ait pressure settings in the shock - dampening rate). instead of a zip tie we use rubber o-rings... works nice to ensure you are getting maximum travel in that application (and dont have too high a dampening rate - i.e. too much air pressure in teh shock, thereby restricting travel).

gkmccready

I just slide the bump stops up and see where they end up.

Hitting the bump stops isn't unexpected and certainly isn't the end of the world... some cars, like Miatas, actually use the bump rubbers for tuning since there really isn't enough travel sometimes... I think if you check "Tune to Win" or "Engineer to Win" you'll find several paragraphs of information about using bump rubbers to tune...

So, Randy, once you know you can use the full travel, what's next?

mousecatcher

randy, what is the point of this exercise? if you are hitting the bump stops that doesn't indicate that you are unloading the tire. does it? i interpret "unloading the tire" as losing rebound control.

Slalom4me

From a handling prespective, my vote is that bottoming the chassis is
preferrable to bottoming the suspension.

Providing expendable 'skids' for this purpose is part of vehicle preparation
at some levels.

.

Bill Hetzel

Yep, we bottom the chassis a lot (different cars) but keep it just slightly bottoming by adjusting ride height. I use the chassis wear strips made of high abrasion resistance polymer rather than steel or alum.

I've used orings on shocks for a long time but just to see where the travel is and it varies track to track.

0Randy@DRM

I have both of those books. Carrol is a very smart person don't get me wrong at all. Lets say you spent a million dollars on a shock and spring package, would it be good idea to ride around on the bump stop??? Great books, but there is many ways of skinning a cat.

Randy

0Randy@DRM

Well guys and gals,
I have been emailed, pmed, called and even got a phone call on my cell. What is the point you are trying to make? I don't really have a good point besides it's good to know what you have and what you are working with. There is no right and wrong with learning, it just happens. The simple data that you can get from a simple test like this is 100 times more important then, "I think". Then what you do with the data is all up to you. If you think you have a problem with your setup, and don't feel like posting that is fine. There is a huge amount of smartness (is that a word) on this forum, and many things that can be learned. I would rather not put on my boots anymore this summer, it was a long winter, so no bashing or crap talking.

What made me think of doing this post? Well last weekend I moved into my new house, I got the truck and trailer unloaded, my wife's car, and a couple of my cars. Well the last thing was my old Audi (future iceracer). The car was packed down, with my little travel tool box, (75 pounds ) about 50 boxes of shotgun shells, garage tv, vcr, and a bunch of other crap. Well I was in the mood to have some fun after all the moving. I took off down a dirt road. If you average about 65-70 mph on the dirt road, you can beat the person doing 55 on the highway. So doing about 90 mph, I got into some wash boards in the middle of the turn. After I started hearing the rear shocks bottoming out. I knew it was going to get hairy. About 90 degrees to the road. Well thanks to my ninja like skills I made it out ok.

Then with the few phones calls in the past week about people swapping stock shocks that have been lowered. "The lower rear bolts have been bent" . I see your guy's great videos, but see snap over steer 9 times out of 10 it is caused by front shocks bottoming out. A couple weeks ago, I went up to BIR going into 4, there was at least 3 cars without enough shock travel in the front. And etc and etc and etc and etc.


This is for you guys, I'm not trying to sell, not trying to bash, not picking a fight, not telling you it's wrong.

Randy

mgarfias

Randy -

If I remember right, he didn't advocate running on the bump rubbers, but merely suggested it was sometimes used, and then explained out to tune the packers so they could be more graceful in their effect.

I'm pretty sure he said on a bumpy track to raise the car rather than going to stiffer springs to keep it off of the ground.

And yes, I agree there are many ways to skin a cat. When I raced r/c cars years ago, I used o-rings on the shock shafts and would go run a few laps without hitting the curbs to tell me how much travel I was using.

This is a good exercise, even if you don't end up with good data because you have to think about it, and just might learn something.

lbs90ZR

Sounds like a great thing to try and will be in a couple weeks, picking apart this idea would be like picking apart a free beer.

0Randy@DRM

Humm,
I think just maybe I raced against you back in the day with a R/C car. I went to the nationals down in Scottsdale, I can't think of the name of the event or the track. Good thing I got a trophy, I won the B main, which was pretty cool!!! I used the o-rings too

Randy

mgarfias

Probably not, I did all of my racing in california. And stopped as soon as I bought my Z06.

froggy47

Hi Randy,

Thanks for helping us guys out.

Not to make this more difficult, but a couple of questions before I get out the zip ties.

My shocks are inverted style (new Pfadt's). Do I still put the zip up to the shock body? I would think yes.

Should I adjust the shocks full soft? Full hard? Race setting?

Thanks.