Mk3 motion ratios.

[Dimman]

I'm thinking about getting back into Supras, have been doing some suspension research and would like to know if anyone knows the front and rear motion ratios on these cars. I currently have no car to measure off of.

Search brought me this:

http://www.supramania.com/forums/sh...-shocks-drop&p=1843582&viewfull=1#post1843582

Which has the Mk4 ratios, but while the front design may be close I would prefer an accurate figure and disagree that the rear would be similar because the spring/shock locations are quite different between them.

Thanks in advance,
D

 

[supraguru05]

Since the shock on the rear is attached to the hub it is 1:1 the front shock is 9 inches in and the arm length is 14 so the ratio is (9/14)^2

 

[Dimman]

Since the shock on the rear is attached to the hub it is 1:1 the front shock is 9 inches in and the arm length is 14 so the ratio is (9/14)^2

Awesome! Thanks!

I'll be picking up a new for me Mk 3 in a week or two, so nothing to measure yet.

For the rear, it doesn't matter that it doesn't share the same pivots as the lower links? So the only thing to pay attention to is the change in angle of the spring/shock as it travels?

 

[supraguru05]

The angle matters but I prefer to just simplify it since the main reason for the motion ratios is to determine the installed rate of the springs. I measured it just to confirm and over 3 inches of travel it was pratically 1:1 and withen my measurement accuracy.

 

[Dimman]

I'll be do some frequency calculations/estimates with the stock rates and some of the available combinations once I dig up some reasonable unsprung weights (wheels and tires are the easy part). Then maybe some weight transfer stuff (without bars for now...).


This will be for a fair-weather weekend street car that I will be starting with autocross next year (for learning the car rather than competition, as I'm not concerned about classing or mod limits) and then a few trackdays per summer in the PACNW region. Tires will probably be 255/35R18 front and rear with tires along the lines of Dunlop Star Specs or Hankook RS3’s.

I would appreciate any comments or corrections.

Thanks again,
D

 

[LordDigital]

Why bother doing this ,when spring rates from the factory racing program to the top aftermarket suspension manufacturers are all well known?

Here are the facts

- Group A Factory Racing Program (TRD/TTT) spring rates are known
- John Smith's (AUS Group A Program) Spring Rates are known
- SpecFab Group A racing Program (All Private EU cars) spring rates are known (used for sure on MIL cars and believed to be on RAS and Benami)
- Almost all of the high end JDM coilOvers used the same well known spring rates

 

[Dimman]

Why bother doing this ,when spring rates from the factory racing program to the top aftermarket suspension manufacturers are all well known?

Here are the facts

- Group A Factory Racing Program (TRD/TTT) spring rates are known
- John Smith's (AUS Group A Program) Spring Rates are known
- SpecFab Group A racing Program (All Private EU cars) spring rates are known (used for sure on MIL cars and believed to be on RAS and Benami)
- Almost all of the high end JDM coilOvers used the same well known spring rates

For me a lot of it has to do with understanding the 'why', not just copying the 'what'.

A spring (coil) rate tells you basically nothing without knowing a lot more information. You want properly matched shocks, and just give your coil rate to a shock valver/builder guy nothing productive will happen. Wheel rate is much more useful, and for that you need coil rate, mounting angle and leverage/motion ratio. Beyond that there is frequency, so you also need to know the unsprung and sprung weights on the corner. Frequency also is a better comparing method for 'hardness' of a suspension (with same shocks).

The other issues are intended use isn't as extreme as a Group A car (see above) and preference. How much the springs control vs the bars. That's what my plans for auto-x and track days will be for. I want to be able to make good decisions, or at least ask good questions, when it comes to making changes.

 

[supraguru05]

I already have a weight transfer calculator for our car. I will upload it when I get home today. It has accurate unsprung weights in the sheet, but has assumed roll centers since I havent mapped those as a function of travel yet. This type of analysis is usefull for determining how much of a weight transfer change a bar or coil change creates. This is usefull in dialing the car in for different corners in different tracks. For instance at mid ohio you set the car up for the keyhole and then try to make it through 1 and the one prior to the carosel with that setup.

Also if you provide me the rates you mention above I will add them into the spring stickies.

 

[LordDigital]

For me a lot of it has to do with understanding the 'why', not just copying the 'what'.

A spring (coil) rate tells you basically nothing without knowing a lot more information. You want properly matched shocks, and just give your coil rate to a shock valver/builder guy nothing productive will happen. Wheel rate is much more useful, and for that you need coil rate, mounting angle and leverage/motion ratio. Beyond that there is frequency, so you also need to know the unsprung and sprung weights on the corner. Frequency also is a better comparing method for 'hardness' of a suspension (with same shocks).

The other issues are intended use isn't as extreme as a Group A car (see above) and preference. How much the springs control vs the bars. That's what my plans for auto-x and track days will be for. I want to be able to make good decisions, or at least ask good questions, when it comes to making changes.

I understand your point ,I have engineering degree and appreciate the theory behind the numbers HOWEVER there are a lot more variables in the "right spring rate" equation than what we know. That is why with MA70 I follow the Kent Rafferty (who is Natinal SCCA Autocross champion with Supra) rule of thumb - stiffer is better. I can't agree more with you on the fact that for the proper valving you have to know the suspension parameters. I personally had Tein RAs with 10% over spring (20KG springs) and found these to be a little too stiff for the kind of tracks I'm running on and my weight (3040) ,thus I settled with Buddy Club racing Spec Dampers and 18KG springs.



Here is the info that I have on the "big dogs" spring choices for MA70:

John Smith AUS Group A program (Source) - Front = 28.5KG , Rear = 17.85KG

TRD/TTT Group A 1989 Setup (Source) - Front = 70KG

TTE/MIL (Used on MIL cars ,and possibly on Bemani and RAS) - (Source) - Front 21KG ,Rear 14KG

Interesting fact is that there are only 3 Supras in the world , actively participating in serous historic races and they all have 26 to 28 Springs in front ,that is Alexander Strik from Holland and David Scriven from UK. Keep in mind that all these cars ,including John Smith's supra ,are HEAVILY penalized with weight ,due to FIA regulations...

Top of the line Aftermarket Dampers such as Tein RA ,Cusco Zero 1&2 ,Buddy Club racing spec ,etc ALL USE the same exact springs 18kg front 10kg ,end of story

 

[te72]

TRD/TTT Group A 1989 Setup (Source) - Front = 70KG

Err... 70kg springs? That isn't a typo? I mean, I'm not the biggest fan of body roll, but that seems like a spring rate you might find on a medium duty truck...

 

[LordDigital]

Err... 70kg springs? That isn't a typo? I mean, I'm not the biggest fan of body roll, but that seems like a spring rate you might find on a medium duty truck...

It may look like a typo ,but FIA Group A was at the top of the Motorsport world back in the days and Toyota went a little crazy when trying to do the impossible (where impossible is defined wining with 7m-gte powered MA70). When 70kg springs were probably useless on most world tracks - they apparently worked for some tracks in japan. Also it is all about the scaling ,look at Dodge Viper for example which is another double wish car ,from memory street car spring rates were <400lb/in ,amateur racing rates IIRC ~1000lb/in ,Cup Series 2500 lb/in ,FIA GT professorial racing setups 50KG/mm or more!

 

[Dimman]

How much downforce did that Supra have, since that's the usual explanation of crazy rates in racing.

Looking at the frequency conversions (with some guesswork on things like unsprung weight and mounting angles) makes the Supra's rates look much more reasonable. Ranging from ~1.25Hz f/r stock, to around 2.0/2.4 Hz f/r for the MIL/Middleton race setup.

Car I'm buying has Tein SS on it and I calculated 1.7/1.9Hz f/r.

Edit: MIL setup would be closer to 2.1/2.6 Hz at 1500 kg.

 

[LordDigital]

How much downforce did that Supra have, since that's the usual explanation of crazy rates in racing.

Looking at the frequency conversions (with some guesswork on things like unsprung weight and mounting angles) makes the Supra's rates look much more reasonable. Ranging from ~1.25Hz f/r stock, to around 2.0/2.4 Hz f/r for the MIL/Middleton race setup.

Car I'm buying has Tein SS on it and I calculated 1.7/1.9Hz f/r.

Edit: MIL setup would be closer to 2.1/2.6 Hz at 1500 kg.

Down-force was regulated based on a simple rule - no additional aero was allowed other than the street cars. Since the evolution model Turbo A had the same ,not very useful 3 peace wing as the original JDM street turbo cars from 87 the down-force was probably about the same as what I get on my car today BTW all Group A Supras N/A cars were required to run with no wing , because this was the way Toyota submitted the paperwork in 86 ,regardless of that the N/A Supras were faster than the turbocharged because they were allowed to be 1030KG...

On the weight all turbo cars minimum weights were calculated based on the FIA rule of 1.7 multiplier of post 88 regulations ,thus MIL ,RAS ,TRD and TTE turbo Supras were all the same weight = 2954.2 x 1.7 = 5022.14 cc or 1400KG. IMO the reason for the 70KG springs had more to do with another FIA regulation - rim width ,which was limited to IIRC 9J with no limits on the wheel diameter - my guess is that as a result of the FIA regulations ,TRD Supras might've been setup to race with tires that had some gigantic diameter ,and the only way to avoid rubing was to run them like like a "go kart" with no suspension travel ,big caster ,etc...

 

[te72]

LD, 1030kg? How do you even GET a Mk3 to drop that much weight? I mean, I'm all for efficiency and replacing parts with lighter, more compact parts, weight redistribution, etc, but still... I have a hard time seeing there being over 500kg to pull out of a car. Blowing my mind here man!

 

[Dimman]

^ There was likely some gap between 'allowed' and 'possible'.

 

[LordDigital]

LD, 1030kg? How do you even GET a Mk3 to drop that much weight? I mean, I'm all for efficiency and replacing parts with lighter, more compact parts, weight redistribution, etc, but still... I have a hard time seeing there being over 500kg to pull out of a car. Blowing my mind here man!

i've asked myself the same question when I saw one of their cars for sale with weigh advertised as 1050KG(~2300lb). I did check multiple sources and it is confirmed that Bemani were able to take their weight down from 1100KG in 1987 to 1050KG in 1990. Keep in mind that they ran a very expensive and rather successful racing program ,with 3 race MA70 Supras and a budget in millions of dollars in todays money. Weight reduction included:

Use of magnesium for gearbox ,wheels ,engine parts ,etc
Use of aluminum for [25KG 2CuMg1 Cage] ,Doors ,hood ,hatch
Use of kevlar for intake! ,single seat ,driveshaft ,etc

 

[te72]

Use of magnesium for gearbox ,wheels ,engine parts ,etc
Use of aluminum for [25KG 2CuMg1 Cage] ,Doors ,hood ,hatch
Use of kevlar for intake! ,single seat ,driveshaft ,etc

I can see that. Stupid money and my lack of it sometimes.

Would LOVE a set of magnesium wheels that would be wide enough for the widebody...

 

[LordDigital]

I can see that. Stupid money and my lack of it sometimes.

Would LOVE a set of magnesium wheels that would be wide enough for the widebody...

I guess that you need some crazy offset wheels with the widebody and true Magnesium wheels are hard to find to begin with ,main reason is the fact that these were banned from most Motorsports events ~20years ago for a reason...

 

[te72]

I guess that you need some crazy offset wheels with the widebody and true Magnesium wheels are hard to find to begin with ,main reason is the fact that these were banned from most Motorsports events ~20years ago for a reason...

You know, the trouble really is finding a combination of size, offset, and style. Very rarely do I come across a set of used wheels that fit all three requirements. If I could find a *decent* set of magnesium wheels that could even be made to work (I would be a lot more flexible on offsets and sizes for this), in a style that wasn't absolutely ugly, and they were within a reasonable price? I would probably take a serious consideration of them.

Flash point be damned, I can't think of a better performance upgrade than losing 50% of your unsprung weight.

 

[Dimman]

^ I don't think it had anything to do with fire. I think they have difficult to detect corrosion and can spontaneously fracture. (Of course if you then have a high speed magnesium hub spinning and grinding on the road, maybe the fire hazard becomes an issue too? Shudder...).

There was a magnesium model of the TRD Sports T3 (maybe different model number, but similar style) like what Duane (upgraded supra) had before he went CCWs.