Rear coil springs for a stock Lotus Seven

[jbcollier]

What is commonly available today is 1.9" ID, 14" long, with a 100 lb rating.  These are harsh for road use.  Better would be the same with an 80 lb rating.  Does anyone know of a source for them?  Redline sells 100 lb springs.

 

Otherwise I'm looking at either getting them custom made ($1K a pair) or stacking two 7" - 160 lb springs (may be travel limited).

[Anthem]

Afco

 

https://www.afcoracing.com/store.aspx?itemid=3432&prodid=19272&pagetitle=14"-Chrome-Coil-Over

[jbcollier]

Thanks but those 2 5/8" ID

[jbcollier]

Found some old stock at David Bean, 1.9" ID 16" 75 lb springs.  Pretty much stock S2/3 springs.  That was their last pair though and probably no plans to reorder.

[EdWills]

Hi John.

Glad to hear that Dave Bean came through for you.  If anyone else needs springs or dampers for a Seven, you can check at: https://www.anglocanadianlotus7.ca  and click on "Lotus Seven Series 2 and 3 Dampers (Shocks) and Springs".  There is a spring manufacturer mentioned who produces springs for Avo shocks.  I haven't checked to see if the supplier is still in business, but an email may confirm if springs are still available.  

Lotus (Colin Chapman) deliberately kept poundages low for the Lotus Seven. The original Redline company advised that for track work, the spring rates could be drastically increased at the front, but with the state of some of our Alberta roads and highways, the ride - with heavy poundages - would probably shake out any of the fillings in your teeth.  75 or 80 lbs. rears seems to be a good option...  W.  

Edited Thursday at 09:51 PM by EdWills
correction

[jbcollier]

I can get the springs made up, no problem.  For a reasonable price I need to order 50.  For a single pair I’m looking at $1200 to $1800.  I think that’s why they’re no longer available.  Not enough demand to justify making 50.

[7Westfield]

Another source might be "Damperman" on the WSCC forum

he works at Spax, and supplies a lot of the Westy folks

[11Budlite]

Just for reference, I checked my old Birkin springs and they were 1.9" ID, 14" length, 150 lb.

[jbcollier]

I think we might be comparing apples and oranges.  Was your Birkin a live-axle?  Were you running narrow tires (165/80R13)?  I also assume your Birkin had a proper space frame not a Chapman-ordered, willowy one that the S2/3 Lotuses came with.  Yes, the TC engined frames were better braced but mine is a lowly crossflow with a pavement toasting 84 hp.

[IamScotticus]

3 hours ago, jbcollier said:

 pavement toasting 84 hp.

You probably got more chick's with that bonnet scoop!

Edited Wednesday at 03:05 AM by IamScotticus

[11Budlite]

Yes, my Birkin was a 2001 live axle. It was just for a reference point, I realize you probably wouldn't want that rate spring on a original S2/S3. The Birkin was introduced in 1983 and was supposed to be a pretty accurate reproduction of an S3. Maybe they used a lower rate spring on the early cars?

[11Budlite]

On 2/24/2025 at 2:44 PM, jbcollier said:

 or stacking two 7" - 160 lb springs (may be travel limited).

 

Wouldn't you have to stack two 7" - 80 lb springs to get the result you wanted?

[11Budlite]

Another just for reference. Don't know if you've seen this website: https://www.anglocanadianlotus7.ca/lotus-seven-series-2-and-3-dampers-shocks-and-springs/

 

Maybe check with Tony Ingram to see what he has: https://lotus7.com/LOTUS_7_parts.html

Edited Wednesday at 12:27 AM by 11Budlite

[jbcollier]

Don't ask me to explain why, but stacking two springs gives you a reduced rating.  With two having the same rating it gives you a working rating half that.

 

Stacking Spring Equation:

(Top Spring Rate x Bottom Spring Rate) / (Top Spring Rate + Bottom Spring Rate) = Rate

Example:

200 x 200 = 40,000 (Top Spring Rate X Bottom Spring Rate)

200 + 200 = 400 (Top Spring Rate + Bottom Spring Rate)

40,000 ÷ 400 = 100 Rate

 

Curtesy of Landrum Spring

 

It is more commonly used to make a dual rate spring with springs of different rates.  You can also add stops that cut out one spring at a set point in the travel.  All glorious fun for the hardcore, high-speed, off-roader.

[MV8]

An easier way to think of the spring stacking is that it is the same as adding them side-by-side where the load is split, like a balance bar dual brake master system. The pedal load is less than either circuit until one side runs out of travel. You can see it in the video in the recent topic about restoring the Professors car. Also like 20% percent of the workers carry 80% of the load for the shop/office because 80% run out of bandwidth/travel early.

I doubt you have more than 6 inches of total damper travel by design. I suggest using a single, 80# 1-7/8 x 10". Subtract 10 from the fully extended seat-to-seat length (not spring free length), then machine UHMW rod for an upper seat spacer (2.25 x 1.875 x 0.50" seat washer optional). The spacer ID is the shaft OD. The spacer OD is 2.25". The step is 1.875 ID x 0.325". Machine the upper id to clear any protrusions from the standard upper seat if any so the spacer sits flat. I have cad again now if you'd like me to draw it for you in dxf for a machinist but you need to provide the missing info.

The installed upper spacer will be difficult to see. The spacer can be made thinner if you give up some or all the lower seat adjustment range. UHMW is similar to delrin but not as slippery or as expensive. A machinist should charge much less for cutting plastic instead of metal and you can have the washer laser cut through the mail but there is usually a minimum order.

You could make an upper seat or adapter out of aluminum instead of an add-on plastic spacer but it would be heavier.

Edited Wednesday at 09:38 AM by MV8

[jbcollier]

Faulkner's got back to me and they are a much more reasonable £125 per spring for a total of $320 not including shipping. Indeed a much more digestible sum.

[IamScotticus]

Are springs marked with the rating?

Edited Thursday at 02:32 AM by IamScotticus

[jbcollier]

Supplied by Redline.  Look to be from Faulkner.  I was told they were 100 lb springs and they look to be.

[EdWills]

If you can find a set, DSK manufactured a very good quality set of springs for autocross use with 125 pound fronts, and 90 pound rears.  This would not be too extreme for road use on a Seven.  W

[pethier]

Years ago I bought an Eibach gift certificate from a guy who had got it as a prize at an autocross.  It was good for a package OR for any four springs from stock.

 

I had a Lotus Europa.  Eibach had an extensive catalog of springs for sprint cars.  I was able to get springs that would give me the ride-heights and rates I wanted for autocross.  I didn't have to get dampers with adjustable perches.

 

The certificate was not good for custom springs, but these sprint-car springs were not custom, but catalog items.