Wheel rates and 1/4 midget shocks

[Nihal]

I was wondering how all the teams that ran 1/4 midget Tanners or Penskes achieved the wheel rates they designed for. The springs on the Tanner website only come in a range from 85# to 155#/in.
I'm guessing to get a Wheel rate of around 2 times your corner weight(Assuming the corner weight is an even 125 all around + 180lb driver) you would use something like a 130# spring (to allow rate adjustment in either direction) with a motion ratio of around 1.6:1.
Would you run into issues with bottoming out the 1/4 midget shock using such a high MR? How much travel is available in these 1/4 midget shocks? Anyone have any general dimensions?
Thanks for any input

[Nihal]

I was wondering how all the teams that ran 1/4 midget Tanners or Penskes achieved the wheel rates they designed for. The springs on the Tanner website only come in a range from 85# to 155#/in.
I'm guessing to get a Wheel rate of around 2 times your corner weight(Assuming the corner weight is an even 125 all around + 180lb driver) you would use something like a 130# spring (to allow rate adjustment in either direction) with a motion ratio of around 1.6:1.
Would you run into issues with bottoming out the 1/4 midget shock using such a high MR? How much travel is available in these 1/4 midget shocks? Anyone have any general dimensions?
Thanks for any input

[Denny Trimble]

The Tanners come in 2" and 3" strokes last I checked a couple years ago. The penskes are 2.7" stroke. We run the penskes with 1:1 installation ratios, linear, and springs within the range you listed.

[SnailRacer]

We used the penskes and had custom springs made by Cannon Racecraft. They were surprizingly cost-effective, and seemed to be good quality though we never got to measure the actual spring rate to check for accuracy.

[Matt Gignac]

We're looking at the 1/4 midget Penskes, and are wondering about the serviceability. How easy are they to re-valve? Off the shelf, do they give close to acceptable damping curves? Ideally we'd like something with external compression and rebound adjustment, but given the cost of these and what we've heard from some other teams, we think we could make due without these adjusters if they're easy to service.

Maybe I haven't been looking hard enough, but haven't found any good documentation on these shocks (only a bunch of vendor sites). Could any of you lead me to some good information, maybe a service manual or something?

Thanks

Matt Gignac
McGill Racing Team

[Nihal]

Hmm so I'm guessing that my inital estimate for wheel rate is a little high. Custom wound springs are another option if I wanted to keep my higher wheel rate, but I'm a little wary of the price and accuracy. I have to do more research in that dept. What kind of suspension frequencies do you guys run?

[Derek Carboni]

I did the 2004 Cornell suspension and I used the 2 inch stroke Tanners (I think they were 2 inch, it's been a while) with custom valving. We used a motion ratio slightly less than 1, about 0.9 and the max spring rate available from Tanner. We tested the springs and they were pretty well spec'd.

So you can see our wheel rates are a lot softer than you were expecting and we design around atleast 2.25 inches of wheel travel to make sure we have the specified minimum of 2 inches of wheel movement. The soft wheel rates helped on the bumpy course in 2004.

[SnailRacer]

We ran a bit softer than you were planning (~115 lbs/in wheel rate... i think that worked out to around 2.5 hz), which does come in handy on an old rickity parking lot.

[jack]

derek, the tanners we use have a stroke that is a little over 2" (i think 2.5"), so we can use a motion ratio of 1:1. if i remeber correctly the guy that spec'ed the dampers for our car said that our stroke was the shortest available that tanner made. i wonder if they stoped making 2" stroke dampers, or teh guy on our team was wrong...

we run the tanner g2's and have similar numbers that everyone else has mentioned. i guess nobody blew it too bad...

[jack]

i just checked, it looks like our tanners have a 3.1" stroke. man, i swear that guy said that was the shortest stroke available..oh well..

[Nihal]

Hmm thanks. What are the Tanner internal like? How is their perofrmance on the Dyno. I have heard that their valving is very simplistic and such. Have they changed their design recently? Do you get much bottoming out and what not at low ride heights with such low wheel rates?

[Nihal]

Also what kind of roll angles did you guys achieve with those wheel rates? How much sway bar did you end up running to control the roll? I should also ask what kind of RC hieght to CG height moment arm did you use to control the roll? Man it would be nice to have an ADAMS simulation of the car and track and such.

[Denny Trimble]

You can do it all in excel with simple equations, almost every vehicle dynamics book will spell them out for you.

You will see FSAE cars with roll gradients from 0.5 to 1.5 degrees per lateral G, typically.

[Nihal]

I have been using a spread sheet and inputing CG height, MR, Springs etc. So far with a 1:1 ratio I have about a 1deg roll angle, but I have to double check my numbers as I did it pretty quickly.

[Kirk Feldkamp]

Geez Nihal. Are you going to drive that car one of these days or just keep talking?! Shut yo jibba jabba and get back in the car!

-Kirk

[Derek Carboni]

Yeah, I faintly remember now that the Tanner's have well over 2" of travel, but I could probably sit down and write down every dimension for every part that make up the damper. The internals are very basic, it has a floatiing piston that can be tricky when trying to bleed it. It doesn't have the greatest seals or bushings around the shaft...but it works, we only had a few blow up. They are cheap, easy to rebuild and a good platform for experimenting with piston and valve design, if you have a dyno.

We are fortunate enough to have had an alum from '01 really push for a dyno, so we have a shock dyno running on simple software on an old windows 3.1 or 95 machine (no joke, it's so old).

The pistons that come with the Tanner (we always used their original design, I never used the new design, I think because it was slightly longer, or had much longer stroke and I already had pistons for the old design) are just plastic with two holes, one for flow each way. You can get a valving kit which has "carbon fiber" shims with a centered hole and one offset hole so that it limits flow through only one of the holes each way. This allows you to have separate compression and rebound damping. But you can only get progressive curves this way. I made custom pistons out of aluminum and bought steel shims to play around with damping curves.

Good luck, they are cheap and tunable but it would be difficult for anyone without a dyno or some other way to get quantifiable measurements, you'd be flying blind.

Denny's right on about roll gradients, ours is in that range. We ran low, above ground roll center heights. And about bottoming out, we never really had any problem with it.

[Matthew Robinson]

After all the hype on the "New Style" Tanners their new seals and piston design werent anything that worked well for FSAE stuff. Also the stroke did increase. The previous generation that was really made by Tanner and not their new parent company was better suited for our purposes

[McFly]

The Penske shocks are pretty easy to revalve, probably takes about 15 min to change them and get them back on the dyno. Like Derek said, it will be hard for anybody to get acceptable damping without a shock dyno. Coming right out of the box I do not believe that any shock will give you the curve that best suits your car. Also they should be different for front and rear. The penskes do have a travel of 2.7".

Has anybody ever been able to find a company that makes helper springs for these 1/4 midget shocks? I talked with probably about 10 companies last week and nobody makes the helper springs.

[kwancho]

Which Penske model exactly are we talking about?

[Penske06fan]

We have Penske 7600 1/4 midget shocks and are having hard time finding springs. Could anyone tell me what there car weighs and what amount of spring rate you are running?

New Formula team looking to compete in 2007.

[kwancho]

Wow, the 7600's have a stroke of like 6". Is that right? Are you using the whole stroke?

[Storbeck]

Hey, where are people getting these penske quarter midget shocks from?

[magicweed]

I was also looking for a link to a retail site, or will I actually have to use the phone to find these things?

[Penske06fan]

Where we got ours from was Indy Motorsports. They are in Gasoline Alley just south of the Indy Motor Speedway. The contact person was Anita Milikan.