Ohlins Motorcycle Shocks

[BenB]

Has anybody ever looked at using Ohlins motorcycle dampers on a FSAE car? It looks like they have a pretty wide selection:
http://www.ppsracing.com/products.html

I was trying to find information on piston sizes strokes and lengths, but I can't find any anywhere. Ohlins doesn't even seem to have them on their website.

Does anybody know the characteristics of these kind of shocks? I imagine they are somewhere between a mountain bike shock and a regular car shock.

[BenB]

Has anybody ever looked at using Ohlins motorcycle dampers on a FSAE car? It looks like they have a pretty wide selection:
http://www.ppsracing.com/products.html

I was trying to find information on piston sizes strokes and lengths, but I can't find any anywhere. Ohlins doesn't even seem to have them on their website.

Does anybody know the characteristics of these kind of shocks? I imagine they are somewhere between a mountain bike shock and a regular car shock.

[Composites Guy]

I looked into it. I picked out a couple of models from their website that I thought looked good (small) and called them for dimensions and weight. It turned out they were ENORMOUS for a FSAE car, and not too cheap either. In case you are just starting out in FSAE make sure that you check out the following:

1. cane-creek double barrels ~$550
2. the new FSAE specific Ohlins double barrel ~$600
3. Penske quarter midgets (not on their website)~$180
4. Ohlins St44 ~$600
5. risse shocks
6. spax shocks
7. koni shocks

In my oppinion #1 or #2 is best for FSAE if you have the $$. #3 is best on a budget.

[HenningO]

From what I've heard from Malcom at Cane Creek, they won't be offering a FSAE deal for the "traditional" Cane Creeks. Instead you have to turn to Ohlins USA and MSI for the FSAE specific Ohlins-branded Double Barell

[MrSwa]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Composites Guy:
I looked into it. I picked out a couple of models from their website that I thought looked good (small) and called them for dimensions and weight. It turned out they were ENORMOUS for a FSAE car, and not too cheap either. In case you are just starting out in FSAE make sure that you check out the following:

1. cane-creek double barrels ~$550
2. the new FSAE specific Ohlins double barrel ~$600
3. Penske quarter midgets (not on their website)~$180
4. Ohlins St44 ~$600
5. risse shocks
6. spax shocks
7. koni shocks

In my oppinion #1 or #2 is best for FSAE if you have the $$. #3 is best on a budget. </div></BLOCKQUOTE>

6. spax shocks ~$400
7. koni shocks ~$600 (double adjustable w/ discount)

We use Spax last year and they seem to be good. They valve them to your specific coner weights. The fact that they come from the UK makes it difficult to get in a hurry, but they're good.

[BenB]

I'm waiting to hear back on piston sizes from Spax, but those look awesome. Very small, externally double adjustable, light, and cheap.

I hope their piston is bigger than the double barrel...I am not using very much travel at all so I need a bigger piston to move an acceptable amount of fluid. Other than the piston size the double barrel would be a perfect shock!

I am planning on using the St-44 on the rear where I have more room.

[flavorPacket]

what size is the piston in the DB?

[BenB]

I'm not sure on the DB off the top of my head, but I am fairly certain it uses the same size coil over spring as the Fox Vanilla RC.

The Fox had a 1" piston and since the DB is a twin tube shock it should be less than that. Its probably pretty close to 1" though.

Again I THINK the ST-44 has a 1.5" piston. That should move almost 2X as much fluid as a MB shock.

[Composites Guy]

I'm no shock expert, so I'm trying to find the logic in this. You use a piston with a large diameter so that you get a large dispaced volume of liquid. I'm guessing that this gets you a fluid flow that can be more consistently valved off? As a trade off (and because there is a lower bound on the damping that the large-shock manufacturer can provide) , since you are using such a large piston, you must use a rocker-arm motion ratio which causes the shock to travel much less than your wheel travels. However, your ball joints and bolted connections on either side of the shock have a certain amount of inherent slop in them. This slop (when felt at the wheel) is exaggerated by your motion ratio. For this reason I always stuck to motion ratios near 1. When you couple that with the extra weight of a large shock like the ST44 I don't understand why you wouldn't want a smaller shock like the double barrel.

The double barrel would provide you with damping close the that of what you need with a 1:1 motion ratio.

Interested to hear you thoughts.

[flavorPacket]

smaller piston/shaft ratios create higher internal hydraulic forces, which magnify any friction and compressibility effects. Plus, with less fluid, you have less heat dissipation and less room for adjustability.

In our dampers we have a 32mm piston and have no problem getting the curve we want with 1:1 motion ratios.

[BenB]

flavorpack beat me to it. What he saidhttp://fsae.com/groupee_common/emoticons/icon_smile.gif

edit: By they way in '05 I put our Vanilla RCs on the dyno and because smaller piston shocks operate at higher pressures there was an undesirable amount of friction from the seal. Its not noticeable most of the time, but if you are trying to damp out high frequency low amplitude vibrations (like from road noise) it is hard to get the characteristics you want because the friction of the seal is doing a lot of the damping as apposed to the valves.

You also get a lot more hysteresis when you have a lot of stiction involved.

[HenningO]

I would be weary to choose anything but the DB without know the adjustability range. The DBs have an outstanding adjustability. Valving for your specific corner weight sounds more like a sales argument then anything else. With the DBs you've got full control over both low and high speed damper coefficients and to some extent the location of the knee.

As for small piston sizes, when I ran the DBs in a dyno last year, the guys that owned the race shop where amazed how little hysteresis there were in the shocks.

OK, I admit I am biased towards the DBs... http://fsae.com/groupee_common/emoticons/icon_wink.gif

[flavorPacket]

HenningO, I don't think you don't need much (if any) external adjustability in a FSAE damper. Once you find your curve, you keep it!

And if the DBs have little hysteresis, so what. You can design around it as long as it's quantified. Ok, that's easier said than done, but it's not impossible.

And as long as the shock is built well, which the DB is, there shouldn't be much hysteresis.

[BenB]

I should mention that I am FSAE alum, and not in FSAE anymore. I really liked FSAE so now I am designing a F1000 car which is pretty simular to an FSAE car (in that it is a small formula car with a sportsbike engine).

The guy I'm working with on shocks (who happens to be a FSAE judge) is advising me not to use mountain bike dampers on a bigger car because he doesn't think they would be competitive. His reason is the piston is too small. This in theory should increase the hysteresis and the gas spring rate which are both undesirable.

I know F1 shocks are very small (somtimes mountain bike size). They might be using a really bitch'n seal system in the DB like an F1 damper that would take care of the hysteresis problem.

I'm anti-DB at all, I'm just going to use a small piston damper as a last resort just because the idea makes me nervous. haha

[flavorPacket]

the only reason to use a small damper is because you don't have room or can't have the weight of a big one. That's why F1 dampers are so small. Well, that's unless they're doing something crazy inside like playing with seal friction and hysteresis on purpose...

[Peter7307]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
That's why F1 dampers are so small. </div></BLOCKQUOTE>

F1 teams also have a budget which allows them to be replaced after every two hours or so on the race track if needed.

Pete.

[HenningO]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
HenningO, I don't think you don't need much (if any) external adjustability in a FSAE damper. Once you find your curve, you keep it! </div></BLOCKQUOTE>

Sure, once you've found an "optimum" curve you'll stick with it. But finding that curve is far quiet complex for an experienced race engineer and thus very complex for a student. So, you need the adjustability.

You could build simulations models, and try to find the "optimum" curve in the simulations. But I think for FSAE it's not worth the effort, finding the right curve on track, takes a couple of hours. So, you need the adjustability.

Plus, being able to soften up the dampers when running in wet can translate to seconds on the lap time. So, you need the adjustability.

All people at Ohlins I've been talking with says that the DB is a racecar shockabsorber on mountainbikes and not the other way around...

[flavorPacket]

HenningO, you say finding a good curve takes a professional a long time. Then you say you can do it in one day of testing. Which is it?

[HenningO]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by flavorPacket:
Which is it? </div></BLOCKQUOTE>

My bad, what I tried to say, is that with some basic calculations you can in the ballpark of how much damping you need. With a day of testing you'll get even closer. So you'll need all the adjustability you can get.

[BenB]

If anybody was wondering. SPAX got back to me about their shock. It is also a 25mm(1") piston. They do advertise it as a race car damper.

So 2 shock manufacturers have a 25mm piston for a damper advertised for a race car. I think thats enough to convince me.

[welder]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Again I THINK the ST-44 has a 1.5" piston. That should move almost 2X as much fluid as a MB shock </div></BLOCKQUOTE>

Expect they'd likely both be the same, a TT44 - a 3 or more way ohlins - has a 44mm piston in the car range, and 46mm in the motorcycle (or off road range at least).

[Fyhr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BenB:
If anybody was wondering. SPAX got back to me about their shock. It is also a 25mm(1") piston. They do advertise it as a race car damper.

So 2 shock manufacturers have a 25mm piston for a damper advertised for a race car. I think thats enough to convince me. </div></BLOCKQUOTE>

According to this pdf, http://www.silverstonetuning.com/pdf/Trakspax.pdf the double adjustable spax shocks cost 352 GBP incl VAT, which equals 715 USD, and without VAT 607 USD. Do you get some FSAE discount on them or did you mix up currencies?

[Drewbe]

Recently checking up on the forum I realized I have information pertinent to this discussion. I followed up on Malcolm to find information on the new [Cane Creek - Ohlins] FSAE damper package and I was directed to a new contact:

Kevin Miller
MSI / Ohlins
101 N. Gasoline Alley
Indianapolis,In. 46222
317-241-7500
kmiller@motorsportsspares.com
"We will be carrying the FSAE dampers from our company,we should be recieving them just after thanksgiving. They will come 200mm free length,57mm stroke,8mm ID bearings and a 36mm 250lb spring,the cost will be $595.00 each."

Basically every team that intends to purchase a variant of the Cane Creek damper package now has a standardized product that is sold from MotorsportsSpares. Email Kevin and I'm sure he will reiterate all of this as well as attach technical info and test data.

Good Luck,
Drew

[95M3Racer]

Kevin at MSI is awesome! Service is second to none, and their knowledge about Ohlins probably exceeds that of Ohlins USA.

They just built me a custom set of Ohlins for my BMW E46 racecar, and they did an outstanding job. I've worked with Ohlins USA while at another company, and I know how tough it is to deal with them sometimes, and I just wanted to say that you all will enjoy working with Kevin@MSI.

Goodluck and enjoy a fantastic damper!