Dinan Spring Rates FYI

[cobra]

Hey guys,
I've long wondered what my Dinan spring rates were, so I had them measured. There is a lot of speculation on various posts that they're "slightly stiffer", but I couldn't find any concrete data.

Front: 175lb/in (13% stiffer than stock)
Rear: 477lb/in (29% stiffer than stock)

For reference I also measured the stockers, and they align closely with the numbers on the fatcat website (155F, 380R).
Front: 155lb/in
Rear: 370lb/in

[Tbonem3]

Thanks, cool to know! Here's my intel. Source is Eibach iirc, there is Eibach's pro-kit specs in here:

U.S. M3 Coupe Spring Rates Spring Rate Front 25 N/mm (143 lbs/inch) Spring Rate Rear 60 - 120 N/mm (345 - 685 lbs/inch) Eibach Pro Kit Spring Rate Front 27 N/mm (155 lbs/inch) Spring Rate Rear 66 - 132 N/mm (375 - 750 lbs/inch)

Did the shop give you the higher end of the rears' progressive rate? 477# would be the initial.

Do you remember what section of fat car website mentioned stock rates?

Also, the rates changed from pre facelift to post I think, could explain difference between #s, not sure or maybe machine calibrations.

[cobra]

Thanks, cool to know! Here's my intel. Source is Eibach iirc, there is Eibach's pro-kit specs in here:

U.S. M3 Coupe Spring Rates Spring Rate Front 25 N/mm (143 lbs/inch) Spring Rate Rear 60 - 120 N/mm (345 - 685 lbs/inch) Eibach Pro Kit Spring Rate Front 27 N/mm (155 lbs/inch) Spring Rate Rear 66 - 132 N/mm (375 - 750 lbs/inch)

Did the shop give you the higher end of the rears' progressive rate? 477# would be the initial.

Do you remember what section of fat car website mentioned stock rates?

Also, the rates changed from pre facelift to post I think, could explain difference between #s, not sure or maybe machine calibrations.

1. I only tested the first 3 inches of spring travel, and the rate was very linear. I can test further displacements if it makes sense. Do we know how far the front and rear springs are compressed with the car sitting statically? I guess we know the weight is roughly 800lbs per corner so the fronts would be compressed about 5" and the rears would be compressed about 2.4". Someone correct me if I'm wrong.

2. The very first line on the Fat Cat page shows 155/380 spring rates for a stock E46 coupe.

My M3 is a 2005 6MT coupe with all the options, maybe they went up slightly after the facelift.

I did test one spring on two different machines and got the same value within 3lb/in so I am fairly confident in the calibration.

[FBloggs]

Thanks for taking the time and effort.

[Tbonem3]

1. I only tested the first 3 inches of spring travel, and the rate was very linear. I can test further displacements if it makes sense. Do we know how far the front and rear springs are compressed with the car sitting statically? I guess we know the weight is roughly 800lbs per corner so the fronts would be compressed about 5" and the rears would be compressed about 2.4". Someone correct me if I'm wrong.

2. The very first line on the Fat Cat page shows 155/380 spring rates for a stock E46 coupe.

My M3 is a 2005 6MT coupe with all the options, maybe they went up slightly after the facelift.

I did test one spring on two different machines and got the same value within 3lb/in so I am fairly confident in the calibration.

Ya, might need more than 3" of compression to reach higher rate, in the rear, but I would have expected different results, honestly. Front is linear afaik.

Also, I still couldn't find Fat Cat's mention of rates, do you mean home page when you say "first" page? on https://fatcatmotorsports.com/ ?

[r4dr]

Also, I still couldn't find Fat Cat's mention of rates, do you mean home page when you say "first" page? on https://fatcatmotorsports.com/ ?

It's on the spreadsheet, first table. Maybe a new sticky wouldn't be a bad idea, with spring rates listed for all common aftermarket options with sources.

https://www.fatcatmotorsports.com/FC..._M3_Online.htm

[usdmej]

Hey guys,


For reference I also measured the stockers, and they align closely with the numbers on the fatcat website (155F, 380R).
Front: 155lb/in
Rear: 370lb/in

spring rates for the Ohlins R/T coilover offering in comparison

Front: 400lb/in
Rear: 630lb/in

[cobra]

spring rates for the Ohlins R/T coilover offering in comparison

Front: 400lb/in
Rear: 630lb/in

Those are pretty stiff!

[usdmej]

yea, a little suprising to see how soft the stock spring rates are compared to aftermarket coilover options

a popular TCK coilover spring option is 400/500 front/rear although they offer anywhere from 300/400 to 650/700 options

[mrgizmo04]

Yeah, aftermarket options want to be the one stop shop for the only thing that you swap out on your car to get a "sporty" ride. Swap the coilovers with 10 knobs that you can adjust, which can control lateral body movement, without the need to do anything with swaybars (they use high front spring rates instead + knobs), and thus sacrifice the front to back comfort of the car settling (i.e. the flat ride concept).

Sent from my SM-G950U using Tapatalk

[cobra]

Ya, might need more than 3" of compression to reach higher rate, in the rear, but I would have expected different results, honestly. Front is linear afaik.

Also, I still couldn't find Fat Cat's mention of rates, do you mean home page when you say "first" page? on https://fatcatmotorsports.com/ ?

From 0 to 3 inches it's 370 and from 3 to 4 inches it's 540. That's as far as I could compress it. So it definitely does ramp up once you get further into the stroke.

[Tbonem3]

Makes sense, just like stock. Thanks for confirming.

[Drewrivera]

I have the dinan on a set of B4 and they look( visually) like the back is lower than the front. They feel fine from the street daily drive i do. But i don't know much about them numbers so i can't really say. What would be that perfect grey area where it's not too stiff or too soft. ?

[r4dr]

I have the dinan on a set of B4 and they look( visually) like the back is lower than the front. They feel fine from the street daily drive i do. But i don't know much about them numbers so i can't really say. What would be that perfect grey area where it's not too stiff or too soft. ?

How long have you had them on the B4s? I have an E91 on Eibach springs (so slightly lower than sport suspension) on B4s and the dampers are on their way out after 26k miles. Someone I know said B4s really don't like being lowered.

[Drewrivera]

How long have you had them on the B4s? I have an E91 on Eibach springs (so slightly lower than sport suspension) on B4s and the dampers are on their way out after 26k miles. Someone I know said B4s really don't like being lowered.

You know they are probably right as i was trying to stray away from that wheel gap with a small drop. But i guess that's where the pro kit , or something else comes in. I've had them on for about half a year and came from koni h&r set up. But the koni died out. I was thinking of going back to the h&r springs. I'm probably not giving the B4 enough travel to bounce with the dinan springs as i bottom out at times. Especially when people are in the car, i scrape.