POLL: Front and Rear Spring Rate Ratio

chmodlf · Jun 2, 2006, 07:01 PM

OK Guys what do you prefer for your spring rate ratios front to back for Autox?

A. Lighter in front

B. Same front and back

C. Stiffer in front

Vishnu/Chronohunter likes softer in front by about 100lbs.

Most damper companies use higher in front.

Give your reasons to support your choice!

DuncanG · Jun 4, 2006, 04:35 PM

What are the motion ratios front and rear?

chmodlf · Jun 5, 2006, 06:32 AM

Quote:

Originally Posted by DuncanG

What are the motion ratios front and rear?

Please give us your insight...

DuncanG · Jun 5, 2006, 05:07 PM

Its pointless discussing spring rates until you know the motion ratio. I don't hence the question, but I'd expect the rear multilink has a much lower MR than the front struts.

jid2 · Jun 5, 2006, 10:10 PM

Define Motion Ratio for us. What does it descibe exactly? Displacement at the contact patch vs. shock stroke?

Killboy · Jun 6, 2006, 02:16 AM

Quote:

Originally Posted by jid2

Define Motion Ratio for us. What does it descibe exactly? Displacement at the contact patch vs. shock stroke?

Quote:

The motion ratio is the leverage factor of the suspension arm that the spring is pushing against.

Further explanation and formula are in the third section here called:

Finding Wheel Rates

chmodlf · Jun 6, 2006, 07:07 AM

The conversation about wheel rate is all well and good BUT to my knowledge none of the manufacturers provide this data. The purpose of this poll was to establish the general philosophy of the spring rate ratio front to back.

Not that we cannot go into wheel rate but let us not get distracted from the intent of the original question--i.e. in your opinion does the car handle better with higher rates in the front, same or higher rates in the rear.

Besides if the suspension arms used to calculate the motion ratio are the same (factory suspension) the are a constant and can be temporarily ignored so that we can find out a trend for front to back spring rate preferances.

If you want to do something usefull someone should measure the suspension arms so we can take the spring rates and do the calculation.

redvolution · Jun 6, 2006, 02:45 PM

Quote:

Originally Posted by chmodlf

Besides if the suspension arms used to calculate the motion ratio are the same (factory suspension) the are a constant and can be temporarily ignored so that we can find out a trend for front to back spring rate preferances.

Good point - although a car with greater track in front will have different rates than a standard car with the same track f/r.

That being said I tried a ratio of 1.25 f/r and found that it understeered a bit too much - especially through T6 at Sears Pt and T2 at Laguna. I upped the rear and ended up with 1.142 f/r and found that slightly better. 3mm spacers in front also helped. Now I've decided to drop the front down so I'll end up with 504/500 f/r. I debated for weeks whether to go with bigger spacers in the front but decided I wanted a slightly softer ride for the street, hence my decision to drop the front.

Very important to give the rears at least 1.5 laps of warmup with this setup.

chmodlf · Jun 13, 2006, 09:21 AM

bump

Noob4life · Jun 16, 2006, 03:41 PM

Since our cars are mac struts up front, the motion ratio is more or less 1:1.
We measured the rears back when we first designed our Evo coilovers, but I haven't got the data in front of me atm.
Currently a rear-biased spring rate setup is working well for us, but the actual rates of the springs is just as important as the ratio.

chmodlf · Jun 16, 2006, 04:05 PM

Quote:

Originally Posted by Noob4life

Since our cars are mac struts up front, the motion ratio is more or less 1:1.
We measured the rears back when we first designed our Evo coilovers, but I haven't got the data in front of me atm.
Currently a rear-biased spring rate setup is working well for us, but the actual rates of the springs is just as important as the ratio.

If you can please post your rates.

Noob4life · Jun 16, 2006, 04:21 PM

The setup in particular I'm talking about uses 10kg/mm springs up front, and 14kg/mm in the rear, which we dubbed the Select R2's.

chrisw · Jun 16, 2006, 05:39 PM

Quote:

Originally Posted by chmodlf

OK Guys what do you prefer for your spring rate ratios front to back for Autox?

A. Lighter in front

B. Same front and back

C. Stiffer in front

Vishnu/Chronohunter likes softer in front by about 100lbs.

Most damper companies use higher in front.

Give your reasons to support your choice!

I just upgraded my Ohlins to use the latest vishnu spec valving.

FWIW, the vishnu spec valving and spring rates maintain a similar spring rate ratio that the EVO has from the factory.

quoting off the top of my head, the front spring rates are about 7/10th of the rear spring rate.

I have experimented with different ratios, but keeping close to the stock ratio has always offered the best results.

The more important question is motion ratios, and the proper ride height to keep the roll center where its supposed to be. That has a greater impact on the rider performance than how stiff your springs are.

redvolution · Jun 19, 2006, 10:37 AM

Quote:

Originally Posted by redvolution

Now I've decided to drop the front down so I'll end up with 504/500 f/r.

It turned out to be 500/500 and so far I'm much happier with the ride on the street. A couple of mildly fast corners on the road suggest better balance but I won't know for sure until July 6th (next track day).

chmodlf · Jun 19, 2006, 03:07 PM

Quote:

Originally Posted by redvolution

It turned out to be 500/500 and so far I'm much happier with the ride on the street. A couple of mildly fast corners on the road suggest better balance but I won't know for sure until July 6th (next track day).

So are you saying that you get better rotation/understeer with equal rates vs. higher in the front?