6 replies to this topic

[Andy69]

So I had planned to bump up the spring rates on my autocross CRX over the offseason.  I currently have 24mm front torsion bars and 350# rear springs.  I'd planned to go to 29mm in the front.  What would be the proper rear rate for that front torsion bar?  450#?

 

I talk about that in the past tense because it appears to be a bit more complicated than just upping the spring rates, so I need to do a bit more research.

 

I currently have Tokico Illuminas on the car.  I was reading that other thread about them and it was mentioned that 450# springs are close to the limitations of the shocks.  I would assume that means the spring is more powerful than the damping force of the shock.  I would hate to break a shock, especially one that is hard to find. 

 

Soooo, some other options are necessary if I want to up that spring rate.  And I probably need to if I'm going to run national events with SCCA and be competitive.  I had some thoughts regarding what I read in the Autocross to Win series.  While adjustable shocks are nice, I really never change them much for autocross - 2 in front and 5 in the rear - so it seems to me I could use shocks that are not adjustable but valved in such a way that they would be optimal for my setup.  Anyone done that?

 

I plan to model my suspension over the offseason, which I think will help considerably in designing a competitive setup.  Probably would not be a bad idea to put my Illuminas on a shock dyno, either. Thoughts?

Edited by Andy69, 20 November 2014 - 10:07 AM.

[rallyxcrx]

Best to keep the suspension as tunable as possible. I see cars on the autocross course all the time, bounce, bounce, bounce, this is because they are running too much spring, and not enough shock. The shock controls the spring, keeping it from bouncing multiple times over one bump. The teins are the best choice at this point, adjustable, and you can lower the car down to where the roll centers will be happy, Dave

[squareback]

I'm glad to see that you are looking to up your spring rates. Beyond tires, appropriately stiffer suspension will give you the most performance gain. With 29mm bars, 450# springs are probably at the low end for autocross. When I went to 29mm bars on my GP Civic (which is much lighter than your CRX), I started with 500# springs, and it wasn't enough. It depends on your sway bar setup and how loose you prefer the car, but I'd plan on experimenting with different rates.

Regarding your shocks, the Illuminas are great for the street and mild upgrades, but they will have trouble keeping up with spring rates like you're talking about. The only shocks available new that can handle it are the Teins, and I have no experience with them to be able to tell you how well they work. Others have used them and like them, so they may be fine. Personally, I would find a set of used set of Konis for the car. Have them shortened and revalved (if they haven't been already), and you won't have to wonder if they are capable. Incidentally, there is a set for sale in the classifieds right now. Konis are somewhat expensive, but you'll be money ahead by getting them.

On your comments about using a non-adjustable shock-- yes, you could definitely do that if you can get shocks that are properly valved for your spring rates. I don't know of a non-adjustable shock available for our cars that is able to be revalved.

I don't remember everything about your car's setup, but I do recall that you have a roll cage from its previous life as a road race car. I would get rid of it first, as it's not necessary for autocross and just adds weight.

This is a good topic, so please add to it with any more thoughts or information.

[Omega Mugen]

Don't forget a rear sway bar.  It makes a huge difference on these cars.

[CSPCRX]

Squareback is spot on. 29mm bars will require higher springs than 500lb. I run 27mm with 500lb rears and i have an adjustable rear bar. My tokicos are maxed on these springs, bounce, bounce lol! I am going to switch to koni ITR race shocks in the rear as they can handle springs up to 1k.

[anjin]

I run 31mm torsion bars with 650 lb rear springs.  Tiens.  I removed the rear internal anti roll bar and found a 14mm integra bar worked really well on that set-up on the stock arm length. Wagon front anti roll bar.   I can dial oversteer in or out, both with the spring/anti roll bar combination, or through the tien adjustments.

 

I have tried running 350 lb rear springs with a significantly stiffer custom, adjustable anti roll bar. Probably equivalent to 21mm anti roll bar.  It worked, but I had mounting problems with the anti roll bar so I went back to the simpler set-up.  You could certainly try that before springing for better dampers.

[Andy69]

Thanks for the info.  Regarding dampers to match the springs, the Tokicos are right out.  I've been in contact with someone who has a pair of revalved yellows for sale, and while expensive, I think if they are right for my application I'd be money ahead.  They are shortened 1.5" revalved for a 2000 lb car with 27.5mm torsion bars and unknown rear spring rate and used on a road course.  This is not as stiff as I want to go so my concern is that the revalving won't quite fit with what my plans are.   How much of a "range" does a revalve like this cover, meaning if a damper is set up for, say, 500lb springs, how much can you push that?  600?  700?  If they are revalved with 27.5mm bars in mind and I go 29, is it going to be too much for them?  I don't know.

Edited by Andy69, 21 November 2014 - 09:08 AM.