My first ever track event is over. The good news - the car didn't break and the engine didn't blow.

This is going to sound like I had a lot of issues (and actually, I did), but I think in general the day was a success. All you have to do is place this event in the perspective that it's my first attempt at car building, I tried new things and am learning a lot in the process.

Since I am so inexperienced with driving I felt that an experience person would be the correct choice for the first seat. I enlisted the help of a local driver named Glen, known to many at the tracks as a guy that can drive anything. Good choice.

Glen started out by noting the horrendous brake effort, pedal travel is good but the brakes just don't work. Press as hard as you want and the car keeps going. I am going to swap out the pads first to some EBC greenstuffs and if that doesn't fix it I don't know what it could be. I would expect the brakes to at least lock up....

Next he noted a slight miss in the engine while accelerating out of corners and this may be a fuel pickup issue. I'll have to maybe add a swirlpot to solve this or a different tank. As the day wore on, the miss got worse. According to the megasquirt forums it's possible that the ecu is resetting itself and I have to look into this.

Biggest issue IMHO The car oversteers. And it does so quickly without warning. Lowering tire pressures relieved some of this, but I think that the issue is related to the springs and dampers. I need to drop the spring rate significantly and add an ARB. Also the dampers should be dyno'd and the valving set for the car.

Also, the steering effort is too light and doesn't inspire confidence. This may be partially caused by the 60-40 weight bias, but my feeling is that since I changed the wheel/tire size I think the scrub radius location is now outboard of the centerline of the wheel . To fix this I intend to reduce the KPI from 16 to 12 degrees. Easily done with the upper balljoint I am using.

The steering itself lacks any self-centering. This should be fixed by adding more caster. I have around 4 degrees caster right now and will go to 6 degrees. Another simple change.

Basically I am not even in the ballpark yet. However, my test driver noted that with these fixes we may be getting a lot closer into the ballpark, and the car has a lot of potential. So you can see, I learned a lot about the car and what needs to be done before the next round of track driving.

BTW - I had a blast! Lots of people came by to see the car and everyone was very interested in it.




that's me in the grey shirt and floppy hat.

congrats steve, car is looking good even if it does need a few tweeks under that gorgeous body

rock on steve, its all part of the fun! Nothing too horendous there, just a bit of tweaking!

Glad to hear that basically all went well. NO major problems, you still have an engine, didn't crash so overall a good day. Every car requires a few tweeks to set up right and most have a manufacturer to ask. Only problem being you're that person this time round. General opinion for 7's seems to say that 7º or so of castor is about right, and spring settings take some sorting out.

do you have wider tyres at the back ?

whats the toe in set at ?

can you swap springs back to front ?

generally need more castor for feel the lighter a car is .

Considering the amount of money/resouces/people that the manufacturers throw at their cars and the amount of breakdowns they have I'd say thats a great success.

Give yourself credit where it's due, you continue to do a superhuman/professional job on this project and I'm sure I'm not the only one who is amazed you haven't been snapped up by a major manufacturer

best of luck with the modifications!

Hey, thanks for the encouragement guys.

The rears are 235/45-17 and the fronts are 215/45-16.

Toe is 1/16"

Springs are same front and rear - I know... problem - this will be solved before next go-round.

More interesting news: SURPRISE! The car weighs more on the precision scales at the track than on my analogue ones at the shop. Total weight is 1,580Lbs with a full tank of gas (as seen in the photos above). Where did it all come from?! Bodywork, hinges, brackets, turbo, piping, rollbar, windshield, they all add up ... 1,000lbs across the rear wheels for the 60-40 split. Dyno run confirms 145Hp and 111lb/ft torque on 5psi boost.

Sounds quite a sucesss to me!.

On the self Centering issue, was it causing a problem or was it just because you were looking for it?.
Our MkIndy didn't self centre at all the first few times we took it out and we never even noticed!

We only set our car to self centre for the SVA and then retuned it to a neutral position because the tyres were on the verge of scrubbing to get it to self centre.

I can't say it was a problem, but my personal preference is that it have some tendency to return to straight line running. Why does SVA require it?

Don't know really, just does over here.

Maybe incase you take your hands off the wheel, collapse slip, or helps in case of a blow out are the kind of things I can think of.


Or to scrub and wear your tyres out quickly lol, because thats all ours was doing!

Steve, I had EXACTLY the same problem with my brakes - two feet on the pedal and still not enough braking

All solved with a change of master cylinder bore size. I went down to 0.65" front and 0.7" rear and now it does what its supposed to. I was sent a little spreadsheet that works out the right sizes for everything and it really worked for me.

Good to hear that you are getting to grips with it now

[Edited on 7-2-07 by RazMan]

quote:

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Originally posted by RazMan
Steve, I had EXACTLY the same problem with my brakes - two feet on the pedal and still not enough braking

All solved with a change of master cylinder bore size. I went down to 0.65" front and 0.7" rear and now it does what its supposed to. I was sent a little spreadsheet that works out the right sizes for everything and it really worked for me.

Good to hear that you are getting to grips with it now

[Edited on 7-2-07 by RazMan]

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quote:

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Originally posted by RazMan
Steve, I had EXACTLY the same problem with my brakes - two feet on the pedal and still not enough braking

All solved with a change of master cylinder bore size. I went down to 0.65" front and 0.7" rear and now it does what its supposed to. I was sent a little spreadsheet that works out the right sizes for everything and it really worked for me.

Good to hear that you are getting to grips with it now

[Edited on 7-2-07 by RazMan]

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Unless you have extremely hard racing pads that haven't had a chance to heat up I doubt if a pad change would make much difference. I would tend to look at the hydraulics i.e. is the pressure getting to the calipers - are the brakes properly bled and, are the flexible hoses not bulging, are there no blockages and is your brake balance right. I ask this because it sounds strange that you are getting the pedal travel but not the clamping force.

Congrats on the project - I think its an impressive looking car that puts many of the commercial kit car designs to shame.

First of all HUGE respect for getting to this stage.

The difference between EBC Greens pads and regular pads is noticeable but definitely not going to cure the described problem.

Looking at your gallery it looks like you're using slidey pin calipers, to me the order to search in would be (Not wishing to sound remedial):

1. Is it bled properly
2. Is the system developing sufficient pressure?
3. Are the calipers working right? i.e.
i Could the pads jam?
ii Are the pistons free?
iii Are the slidey pins free?
4. Did your driver have chicken legs?

Having said all that I doubt all 4 calipers a not right so at least one wheel should have locked assuming thats there's not air in both the front and rear systems so my votes on the wrong size MC's

Here's a fugly test: swap the MC's front to rear to see if you can improve the rear with the smaller diam front unit (i assume) if that works the the MC's are the wrong size.

The other way to reduce the oversteer is stick wider wheels on the back.
Flares and 315's would upset the lines of the body a bit though.
Or narrower ones on the front could you do that with the rims available?

My other recommendation is do one thing at a time and make big adjustments so you know definately what the effect of the change was.
For example if its over-steering now then try and do enough that it'll under-steer then at least you'll have book-ended the problem and know the range of settings you need to work in.

[Edited on 7/2/07 by Doug68]

Looking awesome Steve, congrats on getting some laps on the car.

You are showing admirable self restraint, letting someone else do the pedalling.

Have sent you the brake spread sheet Raz revers to, as well as one I put together on suspension travel and rate calculation, as per Staniforths books.

Cheers

Fred W B


[Edited on 7/2/07 by Fred W B]

quote:

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Originally posted by sgraber
So any other thoughts? Don't the pads sound suspect?

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oh, and EBC pads suck!

I heard of rear midengined cars running 165 wide (narrow) tires at the front to overcome the oversteer!

Would a rear spoiler get rid of some of the oversteer?

Well done, btw. Reading about your project is really inspiring me to get a move on with mine. I'm hoping to start building this year.

[Edited on 7/2/07 by Dantheman]

quote:

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Originally posted by Dantheman
Would a rear spoiler get rid of some of the oversteer?

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Could there be a little roll steer? You could, as a last resort, change the position of the steering rack to have it counter steer a little. The book "competition car suspension" from Allan Staniforth could be a great help in understanding and wisely changing the set up of your car. It's a highly recommended read!

congratulations on your first proper run! you ve got this far so im sure youll sort it. good luck!

It sounds like the pads and brake disks haven't be properly bedded in. Have they?

About the oversteer, it sounds like rear toe-out in bump (bumpsteer). Check using a string and floor jack. While you're at it, check the front too.

Is the wheel rate roughly 1/2 the sprung weight at each corner of the car? Not spring rate, wheel rate? Very stiff rear springs could cause the oversteer, and an ARB will only make it worse, if installed at the rear.


[Edited on 2/7/07 by kb58]

Wow, thanks for the responses gentlemen. The brake system has been gone over several times to make certain there are no issues. BUT - I'll do it again. Maybe I need someone ELSE to do it.... 2 pair of eyes and all that.

Fred, I got your spreadsheets and am going to use them today! I am very excited to get those, so thank you!!!!

I'll keep you updated with my findings.

quote:

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Originally posted by kb58
It sounds like the pads and brake disks haven't be properly bedded in. Were they?

About the oversteer, it sounds like rear toe-out in bump (bumpsteer). Check using a string and floor jack. While you're at it, check to front too.

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Forgot it was de dion. Depending where the trailing links attach, it is still possible to have toe-out for a one-wheel bump... Check with a string.

Is wheel rate approximately 1/2 the sprung weight at all four corners?

[Edited on 2/7/07 by kb58]

An obvious question is whether the trailing arms at the back are parellel with the road at normal ride height - if not they will cause rear over or under steering on roll depending on which way they are pointing.

Another quick and ugly check of the brakes is to check the disc temperature (carefully if you are using a wet finger and not a thermometer) after braking hard a few times to see if they are equally hot.

Congrats Steve - I know how much of an effort it is to get to that stage AND how much effort is still required to get half-decent performance!

Stick at it though, as you cannot beat the feeling of achievement when you start to get the results you want!

sgraber, whilst searching posts I came across the fact you bought a copy of susprog3d but were yet to use it?
If thats still the case this might be a good time to break it out to find out what your suspension is doing.
The spring rate calcs if nothing would make it worthwhile.

U2U me if you need any help getting the thing going.

Gratuitous screen grab attached:
Rescued attachment Susprog3D.jpg

Hi there.

First of all, congratulations on what you have achieved so far! An amazing job - don't be too downbeat!
As far as I remember, when Sylva first launched the Mojo, it had a De Dion rear end and suffered from excessive understeer caused by rear end roll. At first they tried stiffer springs but ended up back on the soft springs but with an anti-roll bar at the back. This I believe worked, although developement was halted when race-series rules allowed them to use wishbones (I think). I realise that this is probably like comparing apples and bananas but hope it gives encouragement! (I expect reciprocation in several years when my project finally gets on the road!!!!!!)

JC

Seems like a lot of those gone before me have been in the same place. That's nice to know. I agree that at least I have someplace to start from because I have actually built something and started testing it. Sometimes it's better to just get something built to have a place to start the inevitable changes from. Plus, as was said, if I can get some positive changes made, it will feel like I've done something right!

Doug, you have u2u.

Hi Steve. Congrats. Are you sure you really do have an oversteer problem? A taught midi is likely to feel that way to a driver who has just stepped out of a regular car. Did it actually spin on corners when pushed? Maybe it doesn't need much changed at all. Just needs a bit of getting used to. Did it feel stable at speed in a straight line? Can you turn in under hard braking without it spinning? These are the real tests. The fun is just begining.

i agree with you there steve, i think its the only way really. i already want to change my rear setup and havent even finished the body work yet. can you still pick up the front end by the way? i can still get the front wheels an inch off the floor and im not exactly worlds strongest man!

Steve:
Let me start off by saying congratulations on such an important milestone! It's great to see just how far you've come!

I recently had an encounter with oversteer. I drive a Toyota MR2 Spyder (which has roughly the same weight distribution as La Bala). It was raining and I was accelerating in a turn and the back end lost control until the speed dropped. Apparently staggering the tires by 20mm isn't enough to keep oversteer in check. I was in an empty parking lot, so luckily nothing happened. I've since upgraded to a 3-setting adjustable solid 1" ARB up front and kept the stock rear ARB (3/4" me thinks). It now corners flatter and has understeer without power, and slight oversteer with power (140HP engine). I have never experienced oversteer in dry conditions. Overall I'd say it handles much better/safer. Also I read somewhere than a toe-in condition at the rear will tend to understeer/stabilize the car. I imagine you could adjust the toe on a de dion susp with application of generous amounts of heat!

Advice from people more knowledgeable than I say it may take you several tries to get the spring/shock settings right. Of course you can try the progressive spring avenue but I'm sure that can have a snag too, as you still have to get the rates right.

As far as the scrub radius goes, as long as you keep the same offset and outside tire diameter, it doesn't matter what the width of the tire/wheel is. The scrub radius will not change. However if the offset is different you will have to change the KPI to reach the desired scrub radius. If the tire radius is different, so will be your scrub radius. Here are some helpful links:

http://www.miata.net/garage/tirecalc.html
http://marksink.com/tire_wheel_offset/tires.html
http://www.1010tires.com/WheelOffsetCalculator.asp

All of this IMHO, of course.

Fred W B:
Where can I get a copy of those spreadsheets? Can you send them to me?

Re: Bump steer
Hi Steve, looking at your rear end setup, with the long trailing arms you have, there shouldn't be too much change in toe with the dedion. Did it feel like the outside front corner was dropping before it swung, or did it feel like the inside rear lifted for the swing? Usually you can dial it out with softer springs on the rear, or stiffer springs on the front but choice between the two will depend on what it 'feels' like. Good luck!! It looks great.

Do you have a tyre pyrometer? Measuring the temps across the tyres should give an indication whether the rears are being worked evenly - could indicate an unexpected camber change or some such.

Check out Keith Tanner's site www.cheapsportscar.com - he's documented all the things he did sorting the handling and brakes on his Miata-based 7.

Do you have access to a brake dyno? Our vehicle testing stations have drive on brake dynos that measure the actual brake performance - that could give you an indication whether the problem is at all 4 wheels, or just the front or rear.

Are MCs bottoming at full pedal travel - I had the clevis pin fall out of a Mini brake pedal and it wouldn't quick push the rod all the way into the MC. Gave about 75% braking - very sweaty palms! And I had a professional brake shop connect a dual-circuit MC back to front, so all the effort went on the rears - every brake application led to a 270* spin

Mightily impressed by what you've achieved - very inspirational.

Based on all the comments received here and by local sources, here is my list of fixes before the next track event.

Steering:
-Reduce KPI from 16d to 12d by moving the upper bj mount outward. re-adjust length of upper a-arm to achieve 2 or 3d camber.
-Install lock stops on steering rack to prevent overtravel condition.
-Increase caster to 7d.

Braking:
Step 1 - line sand pad faces to eliminate glazing as a possible cause.
Step 2 - increase rotor size
Step 3 - replace caliper with larger unit from Supra

Oversteer:
-Replace undersized brass bushings in rockers with sealed bearing units to eliminate binding.
-Change to softer springs.
-Adjust damping/rebound settings on shock dyno to better match car.
-Corner weight the car correctly with driver weight included.

Anything I am missing?

That should do it. You don't want to do too much at once in case you mess something else up. If possible, it's best to change only a few/couple of things at a time, to see what actually fixes the problem/was causing it in the first place. A lot of it may be suck it and see with a new car like yours, so you don't want to fix one thing, just to go cause another.

For at least the braking and oversteer categories I am going to do one change at a time. For the steering category I am certain that I need a decrease in KPI and an increase in Caster, and the rack is taking the steering arms over center so I have to limit it.

Fair enough then! If changing one things alters an other, then it is best to try and out it back where it was to start with.