STS2 MK1 suspension setup w/host XHead Part:2.0 - MR2 Owners Club Message Board
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post #1 of 389 (permalink) Old August 7th, 2008, 08:54 Thread Starter
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STS2 MK1 suspension setup w/host XHead Part:2.0

Continued from here:

https://www.mr2oc.com/showthread.php?t=298272

Lots of good info in the other thread. Read it and then ask questions please.
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post #2 of 389 (permalink) Old August 7th, 2008, 10:43
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So this would be the 'development' thread, right? Increasing/changing spring rates, tuning shocks (dampers), and what comes next, like altering balance for different surfaces, grip, conditions, etc etc?
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post #3 of 389 (permalink) Old August 7th, 2008, 11:54
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Originally Posted by mtbmr2
So this would be the 'development' thread, right? Increasing/changing spring rates, tuning shocks (dampers), and what comes next, like altering balance for different surfaces, grip, conditions, etc etc?
Actually, there are but two items left to work on. shocks and fine tuning (alignment and air pressure). I keep getting side tracked so I haven't yet done shocks.

As for altering balance for different surfaces, grip, conditions, etc... that is un-necessary. If properly setup, the balance shouldn't change much from surface to surface or in different conditions. In extreme ends of the spectrum, if the car was setup for good balance on a very slick surface, like HPT and you went to the ultimate grippy surface, like brushed concrete, the car may feel just a little tight. Maybe....

I seldom if ever change anything on my car for changing condition. When I ran the X1/9 I never did anything for rain other than put the rains on. That's it. The car was awsome. The Two is pretty much the same.

-Steve
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post #4 of 389 (permalink) Old August 10th, 2008, 08:27
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The only fine tuning I did so far to account for different course conditions were, tire pressures.
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post #5 of 389 (permalink) Old August 14th, 2008, 11:08
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Steve...were there any recommended changes to the CSP version of the setup other than stiffer spring rates to accommodate the grippier tires allowed in SP? (FWIW, if it affects your answer any, my car still has the stock open rear diff and will likely stay that way for quite a while.)

1989 Toyota MR2 (w/4AGZE swap) / 2006 Subaru WRX TR
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post #6 of 389 (permalink) Old August 14th, 2008, 12:00 Thread Starter
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Quote:
Originally Posted by Warp3
Steve...were there any recommended changes to the CSP version of the setup other than stiffer spring rates to accommodate the grippier tires allowed in SP? (FWIW, if it affects your answer any, my car still has the stock open rear diff and will likely stay that way for quite a while.)
From what i've seen with MK1's the open diff is actualy better then a LSD. I have theories but the butt dyno is always sometimes right.
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post #7 of 389 (permalink) Old August 14th, 2008, 12:45
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Quote:
Originally Posted by Warp3
Steve...were there any recommended changes to the CSP version of the setup other than stiffer spring rates to accommodate the grippier tires allowed in SP? (FWIW, if it affects your answer any, my car still has the stock open rear diff and will likely stay that way for quite a while.)
Not really. However, testing will tell. The only thing I would worry about is the open diff spinning the inside rear tire on corner exit. If this becomes an issue then you will need to tune that out.

A lower rear roll center, or higher front roll center is the best fix. If there isn't enough adjustment there to fix it then more front roll ratio bias is necessary.

I preferred the open diff in my DSP car and that is likely the preferred configuration in the STS2 car. But a CSP car will make more HP and torque so the available traction may be overcome.

My DP car has an LSD but the setup is tuned around it. The LSD does have a significant effect on the setup and must be accomodated. With that in mind, if you can get away without one in your CSP car, that is the way to go.

-Steve
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post #8 of 389 (permalink) Old August 14th, 2008, 17:37
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Quote:
Originally Posted by XHead
With that in mind, if you can get away without one in your CSP car, that is the way to go.
'splain the quoted sentence for me, if you would?
We (I) have almost exclusively been preached to about the advantages of a limited slip for limiting inside tire spin on corner exit.

-Zack
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post #9 of 389 (permalink) Old August 15th, 2008, 01:33
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I think what he is saying is that if you are NOT spinning the tires on corner exit, then you don't go through the added expense of installing one.
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post #10 of 389 (permalink) Old August 15th, 2008, 08:52
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I'm not sure it has to do with 'expense'.
Steve pretty much prepares his cars to the very limit of the ruleset so, there is a setup reason he didn't include one in his DSP X1/9.
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post #11 of 389 (permalink) Old August 15th, 2008, 10:21
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Quote:
Originally Posted by mtbmr2
'splain the quoted sentence for me, if you would?
We (I) have almost exclusively been preached to about the advantages of a limited slip for limiting inside tire spin on corner exit.
Well, like everything else, I counter conventional wisdom.

The LSD ties the two rear tires together under acceleration and that causes throttle understeer as the rear tires try to drive at the same rpm. We want the car to be able to turn under throttle so an open diff is preferred as it allows the rear tires to rotate at different rpm under acceleration.

The throttle understeer can transition to throttle oversteer as the power breaks the rear tires loose (assuming you have enough power) as it breaks BOTH rear tires loose thus reducing lateral grip.

So the LSD will make the car push in the center and loose on exit of most corners. In faster turns and transition, taken at full throttle, the car is likely to have a severe throttle push. This is due to all of the weight transfer to the rear tires under full throttle.

So the trick is to not unload the inside rear. Again, thinking of the car as an X more front roll stiffness reduces weight transfer across the rear axle and improves grip on the inside rear. So you get less inside wheelspin on corner exit. And a lower rear roll center reduces mechanical weight jacking across the axle.

Zach is right, cost and effort of installing an LSD in the DSP car was never an issue. I tested one and didn't like it. I would assume that an STS2 Mk1 is similar in power/weight ratio to my DSP car. But way less grip So the setup dynamics should be similar.

The DSP car had no budget. I spent whatever time and money was necessary to achieve the desired results. However, the DP car has more than enough power to demand an LSD. So the setup has been tuned around it. Roll center and roll ratios have been set to tune out most of the LSD induced faults. In fact, this has been the biggest issue I have had tuning this car. It has only been this season that I have the car driving the way I want it.

-Steve
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post #12 of 389 (permalink) Old August 15th, 2008, 14:19
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So me being in C-mod, with my 20v blacktop (the motor is stock)
I'd get far more out of stiffer spring rates, then trying for a LSD.

If/When I get a supercharger for it, and get bumped up to D-mod, that's the time to worry about the LSD.

This is definately some good information in these threads.
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post #13 of 389 (permalink) Old August 15th, 2008, 14:47
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Quote:
Originally Posted by Pyrgnome
So me being in C-mod, with my 20v blacktop (the motor is stock)
I'd get far more out of stiffer spring rates, then trying for a LSD.

If/When I get a supercharger for it, and get bumped up to D-mod, that's the time to worry about the LSD.

This is definately some good information in these threads.
I don't think you are reading the rules quite right or you don't have an MR2 chassis because C-mod class is for formula fords, sports 2000, etc. An MR2 doesn't fit into that. You are thinking of Street Modified 2 is my guess which if that is the case a supecharger is allowed in that class as well.
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post #14 of 389 (permalink) Old August 15th, 2008, 14:53
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Quote:
Originally Posted by MtyMseHarmer
I don't think you are reading the rules quite right or you don't have an MR2 chassis because C-mod class is for formula fords, sports 2000, etc. An MR2 doesn't fit into that. You are thinking of Street Modified 2 is my guess which if that is the case a supecharger is allowed in that class as well.
I was about the post the same thing (but suggesting he meant D-Mod to E-Mod), but then I realized he is in Canada, so I'm not sure what ruleset he is using.
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post #15 of 389 (permalink) Old August 15th, 2008, 16:25
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According to CASC-OR rules, changing the number of valves or camshafts is strictly prohibitted, and as such automatically knocks you into a mod class. C mod for me, because I'm under 2 liters of displacement (personally I think this is BS, but if I want to race at certain locations, I have to stick to their rules)

Last edited by Pyrgnome; August 15th, 2008 at 16:28.
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post #16 of 389 (permalink) Old August 15th, 2008, 22:39
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Quote:
Originally Posted by Pyrgnome
So me being in C-mod, with my 20v blacktop (the motor is stock)
I'd get far more out of stiffer spring rates, then trying for a LSD.
Well, that depends on the motor's output, the car's gearing and wheel/tire package. I would assume the Blacktop to have a little less HP/torque than my 16 valve DP motor. And I would assume it to be heavier. DOT tires or slicks? 13s or 15s? Is the car spinning the inside rear now?

You should always set the car up first and then determine if you need the LSD.

-Steve
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post #17 of 389 (permalink) Old August 16th, 2008, 13:31
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Quote:
Originally Posted by XHead
Well, that depends on the motor's output, the car's gearing and wheel/tire package. I would assume the Blacktop to have a little less HP/torque than my 16 valve DP motor. And I would assume it to be heavier. DOT tires or slicks? 13s or 15s? Is the car spinning the inside rear now?

You should always set the car up first and then determine if you need the LSD.

-Steve
Right now I'm running on Avontech RA's.
They take too long to heat up to be effective for autocross, but they are a tire that I can abuse, and not worry about. (they are great for track days though) I'll likely be upgrading to 710s next year, depending on how things go with my wedding in the spring.

Currently, I'm not having any issues with the car spinning the back wheels.
(that I can tell) the exhaust is loud enough, that normally I can't hear a whole lot from the tires, but it doesn't feel like it is, and I'm not seeing abnormal tire wear. Also, I have a couple of people that will normally spot for me for weird things happeneing on track, and they haven't said anything yet.

I've been playing with my alignment recently, and it has greatly improved things. I'm on heavy stock 14" rims still, and am only putting 122HP to the wheels. Torque peaks around 4500 RPM if I remember correctly (dyno plot is at work).

Currently I'm doing things on a bang per dollar basis on this car.
seeing as I already have coilovers, and Koni's, spring rates seem like a reasonably afordable upgrade, untill I can get a set of lighter wheels.
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post #18 of 389 (permalink) Old August 18th, 2008, 09:17 Thread Starter
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After getting the tire pressures the car performed very well. Neutral with very slight tendency for understeer....did not touch any of my other settings.

Very happy now although it was confirmed when throwing some of our cars on the scales that I have a 400lb dissadvantage over the CRX's in the field Diet coming this winter
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post #19 of 389 (permalink) Old August 18th, 2008, 12:30
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OK, a slight tendancy for understeer is right where we want to be. It much easier to now dial out the understeer than dial out oversteer. Remember that the car's natural tendancy is to oversteer due to the rear weight bias.

The understeer can likely be dialed out with air pressure. Lower front and higher rear and toe settings.

As for the car's weight, I expeced that problem. I know exactly the weight of Mike King's STS2 CRX as I have seen it on the scales myself. Yes, you need to get the car's weight down but you won't get near the CRX. I wouldn't worry about it. Remember, my DSP X1/9 weighed 1940 lbs while there were Rabbits and Sciroccos that were in the low 1700s to high 1600s. I was 350 lbs heavier than my closest competitors when that car won its Championships.

-Steve
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post #20 of 389 (permalink) Old August 18th, 2008, 13:24 Thread Starter
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Yeah there are a few things I can do legaly in STS2 that will loose some weight. I think 2250 is attainable.

Biggest thing I need to work on though....the nut behind the wheel, I swear I have been focused on the car for so long now I forgot how to drive
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