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I agree Donnie. I don't think there's much that can be done with the current shocks. I'm looking at alternatives. I made changes for the Danville event and the car was really bad.

The set up that was on the car when I got it from you had 800 lb/in springs on the front and 300 lb/in on the rear. The motion ratio in the front is .5/1 (or 1/2) and the rear is .75/1 (or 3/4). There was no droop in the front (and hardly no bump either!). There was next to no droop in the rear (with driver in the car). I think I figured out some of the rational for this setup. The LSD was worn out (brass friction rings were worn out), so it acted like an open diff. Any time the rear wheels lifted, you could put power down on the pavement. So, since the car doesn't use swaybars, I believe, the stiff springs in the front (800 lb/in) were put in place to limit roll and help keep the rear wheels on the ground (and it definately did help with that). But with very little droop in the rear, the rear tires where still coming off the ground. I couldn't feel it because I had put an 80% LSD kit on the car, but thanks to Spratte's awesome photography work, I could see the inside rear tire was slightly off the pavement as I was going through the slalom.

So, I dropped the front spring rate to 300 lb/in and increased the rear to 350 lb/in (primarily because that was the only matching pairs of springs that I had access to). When I corner balance the car (inc driver weight) the front tires have 170 lbs each and the rear have 210 lbs each (total of 760 lbs). But the car handled horribly at Danville. The suspension was binding on rebound (e.g., push down on the suspension and it would only partially rebound and wouldn't rebound to the same point when repeated). I also had alignment problems that I was able to correct in between morning and afternoon runs. But the car had way to much oversteer and was too soft.

One other design issue with the car is that they offset the engine so that the chain drive would be centered on the chassis (thus they didn't have to deal with using different lenght drive axles). This puts more weight on right rear (~ 50-70 lbs). So, when I set the ride height where I want it, the corner weight is out of whack. When I balance the corner weights, the chassis is tilted to one side (@#$%&).

So before I head to a TnT. my goal is to resolve the following issues:
1 - work on spring/shock setup
2 - look into possible sway bar setup
3 - resolve the shifting issues
4 - fix that damn warped rotor!!!

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Rob Harvey
919-697-5485
1997 BMW M3
1992 Acura Integra (Simon)

we actually used really high end mountain bike shocks on our FSAE car (FOX shocks I think) and they worked fairly well, and there was a good variety of spring rates available. However, our car was considerably lighter than yours (485 lbs total when dry), at least its another place you can look for parts. If I recall though, they weren't cheap

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2012 MX-5 Sport SUV

Brice, the car has mountain bike shocks on it now. While they are probably fine for FSAE competition, I don't believe they are a good long term solution for a race car application. They simply aren't valved for the very high speed stuff you're going to see, and in fact I believe that can wear the valves out internally. I believe that may be what happened to those shocks and may be why they just kept lowering it until it ran on the rubber bump stops (believe it or not, a decent piece of rubber can be as good as a crappy shock sometimes).

I'm sure they work pretty well for a little while, but a long term solution they are not. Rear shocks for a motorcycle aren't much bigger but also have a wealth of spring options, are made for the more rigorous environment, and can often be found in adjustable form for not a lot of money. You can also usually get rebuildable and revalvable ones.

Rob, short of building a new car, I'm not sure you can resolve that centered-diff issue. But then again I think you knew that. I think you can reasonable retro better shocks into a better place. I don't recall enough of the rear layout, but I'm betting a rear swaybar is possible. I'm certain a front one is. Look at Speedway Engineering:

http://www.1speedway.com/Swaybars.htm

While I doubt they have a bar short enough for you, I'm pretty sure they'll make whatever you want. What's nice is they make three piece bars, so you can guess at what rate you need and have them make a bar that matches that. Then you get a set of their generic arms for it and have those machined to what you need. Fab some mounts and slap it on. If you need a different rate, you order a different center bar with the same splines and length and just drop it in. You should be able to make your arms adjustable, too, pretty easily to help avoid having to get multiple bars.

This is the same system Eric used on the CS Spyder way back when and at one point I think he owned seven different bars. I don't think you'll need more than two, if that many, but it's nice to know you can get radical if need be.

Within the next couple months I may be able to help with fabrication on the arms for that project as I may be buying a CNC waterjet machine. The arms they sell can be worked with, but they're *really* large for your application so you'd want to remove a LOT of metal for weight savings. I think we could pretty easily cut new ones easier than you could do all that work to those. Or they may be better swaybar options out there you've already looked into. I just like their work and three piece bars in general.


--Donnie

You obviously know more about this specific car than I, but we ran mountain bike shocks for the 4 years while I was @ Duke FSAE with no problem on "Agnes", our test car. These shocks are a lot more than 4 years old though, not to mention the weight difference. We also spent almost $2k though on our shocks :O, probably a bit more than Rob wants to spend on shocks, especially with the durability concerns you mention.

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2012 MX-5 Sport SUV

found this

All,

Do to the amount of interest we (Ohlins) have gotten lately about Dampers for the FSAE we have decided to put together some packages for university purchase. Please note that while our prices may be higher then what many teams are used to there is a good reason that we have more championships than any other damper manufacture. Also as an alum of FSAE I understand that in the past few years the cars have progressed to a point that quality dampers are a huge asset to most teams. On to the shocks.

First we have our budget offering of our 36mono damper that can be built with an eye-to-eye of 10” and a 3” stroke or spaced all the way down to 8.5” with a 1.5” stroke. These dampers can take either a, 1.875 or 2” spring. The FSAE price is $290 and the damper is not externally adjustable, though it is user re-valvable.

Next, would be our ST44 damper. This is a 2-way externally adjustable shock with a piggyback reservoir, though we could also do a remote hose reservoir. The eye-to-eye is 10.85” with a 2.76” stroke and it can also be spaced to 9.67” with a 1.57” stroke. It can take either a 2” or a 2.25” spring. Pricing will be $490. This is a true racecar damper and is very easy to revalve.

Third, we have a short version of the standard ST44 with all of the same feature as above with a 9.58” eye-to-eye and a 1.70” stroke. Prices for FSAE teams will be $570.

Finally for teams that hold up 7-11’s we can put you on the same equipment that we use in CART and the IRL, maybe even the Audi R8’s if it’s a big 7-11.

Please contact me directly for more information.

Scott R Besst
Ohlins dept at MSI
317-241-7500
317-241-0823 fax
shocks@motorsportsspares.com
www.motorsportsspares.com

p.s. Motorsports Spares is the Ohlins technical center for CART, The IRL, Grand-Am, ALMS, and all other forms of road racing. Sorry for how long this got.

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Silver Honda
Green Ford
Blue/White Suzuki
Red Triumph
Grey BMW

"Never let life be shaped by fear of its end"

No, you're a towel!

Man, if Rob could get them to sell him those ST44's at that price, that's a hell of a deal. Rob, I might can hook you up with shock dyno time if you want to learn to play with valving on a shock like that. Ohlins parts ship out of Hendersonville, IIRC, so UPS ground on that stuff is one day. The shims and stuff you need to play with valving are dirt cheap compared to the shocks, so you may even get away with trying the non-adjustable ones. I'll have the gear you need to pressurize them, too (you can use a mountain bike pump if you want to, but we'll have the stuff to do it with straight nitrogen, too). I have a shock dyno but am still learning to rebuild them.

It'll be harder to engineer them onto the car than to learn to revalve them, and I don't think getting them on the car will be that hard. I think you'll reclaim the weight gain of these shocks over the mountain bike ones by losing those actuator rods and linkage, too.

Man, I love armchair engineering someone else's car.


--Donnie

I found that on the fsae.com forum. It is from an old post so the prices are probably higher and I think they are for each shock. From what I have read a lot of the teams have tried ohlins and like them.

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Silver Honda
Green Ford
Blue/White Suzuki
Red Triumph
Grey BMW

"Never let life be shaped by fear of its end"

No, you're a towel!

Yeah, I noticed they were per shock, but that's still a great deal. Ohlins dampers are wonderful pieces of machinery. I can't say that about Koni...


--Donnie

Split.

I still think that some motorcycle racing shocks and springs seem to make the most sense for the FSAE car. Mountain bike shocks? I don't think those guys live and breathe the same kinds of wheel movements that we work with. For an FSAE rallycross car, maybe. Hey, that would be cool!

Then again, what do I know?

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Mike Whitney
whit32@gmail.com, 919-454-5445
V10, V8, V8t, I6, I6, V6, F4t, I4, I4, I4, I4, I2, 1, 1

Good motorcycle racing shocks cost almost $500 per corner anyway and are usually only single adjustable, IIRC.

From what I remember, the predecessor to the FSAE program as we know it was an off road buggy program. I think they found it easier to find places to "race" and "test" the road race car than they did the off road stuff, though, and people thought the on road stuff was more interesting anyway. Or at least "cooler."

Edit: Thanks for the split, BTW. I was thinking we should do that.

--Donnie

well, SAE sponsors two seperate competitions. The one you are thinking about is baja SAE. That program is significantly different than Formula SAE, the engines are specced (a 10 hp Briggs and Stratton), and the focus is on suspension design more than anything else, where as for FSAE, the engine must fit a set of requirements (displacement, restrictions, etc.) but engine choice is still up to the team.

http://students.sae.org/competitions/bajasae/

http://en.wikipedia.org/wiki/Baja_SAE

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2012 MX-5 Sport SUV

Rob - have you considered calling Koni NA and asking them for recommendations? I bet Lee Grimes would be entertained by a question like that...

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Mike Whitney
whit32@gmail.com, 919-454-5445
V10, V8, V8t, I6, I6, V6, F4t, I4, I4, I4, I4, I2, 1, 1

Don't make me slap you with a trout.

Seriously. For people who have dual purpose cars (autocross and street) that have Koni singles available, that's a *great* choice. For ANYTHING else I'd avoid Koni like the plague. You have been warned. Proceed at your own risk.


--Donnie

I'm not telling him to buy Konis, just ask for some free advice from a guy who has worked in the shock business for decades and has been very helpful to me. I have no idea what Koni sells for motorcycle applications. But anything has to be better than a 5 year old mountain bike shock...

You might be interested to know I just ordered shocks for my M3, and they aren't Konis

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Mike Whitney
whit32@gmail.com, 919-454-5445
V10, V8, V8t, I6, I6, V6, F4t, I4, I4, I4, I4, I2, 1, 1

IIRC you was looking into learning how to rebuild your own shocks at one point and you must have done a lot of shock research. So... what is the short version of why to avoid Koni for other the the basic SA shock.

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.