Heaviest Front Spring Rates For a Road Going V6 75

[Duk]

What sort of torsion bar sizes are people using for their road going V6 75's?
Please, no mention of standard TB + Koni Yellow's as being good enough, 'cause they aint.

Currently I have standard TBs and 105lb/in coil springs over Koni Yellow's, but I want more spring rate without turning the car into a brick (sorry MD  ).
Standard TB are 22.8mm and give a wheel rate of 93lb/in.
A spring over the shock absorber gives about 62% at the wheel, so my combined TB/spring gives a 158lb/in wheel rate.

A 25.4mm TB has a WR of 143lb/in.
A 27.3mm TB has a WR of 191lb/in.
A 28.7mm TB has a WR of 233lb/in.
* A 30mm TB has a WR of 279lb/in.
* A 32mm TB has a WR of 360lb/in.

Minimum WR would be similar to 27.3mm TB, that would require a 160lb/in coil spring.
A 175lb/in spring and TB would give a 201.5lb/in WR. The extra spring rate would help control the mass better, but would it still be streetable?

I think the Koni's run to much bump valving to try and hide the lack of spring rate (which doesn't work), so revalving would be a great idea if/when I start using higher rate front springs. I emailed Toperformance (Aussie Koni distributor) about revalving (mainly bump valving) for higher spring rates, but got SFA of a reply. Does anybody know of anybody else who can revalve Koni's?

[Sheldon McIntosh]

I'm running 32mm TBs on the track car, combined with yellow Konis (which haven't been revalved to suit yet), which I thought would be hellishly stiff on the road.  It's actually bloody fantastic on the road, and I will be doing it to all future V6s I own.  Cuts down any hint of wallow on freeways, and over expansion joints and such the car is just so flat and composed.  It's definitely not too harsh over bumps (except for very, very sharp ones), and overall I would say the ride is more pleasant than with standard TBs. 

My girlfriend even managed to fall asleep on the last EMR I did in the car, so the ride can't be too bad.  Although as I'm doing my engine swap at the moment I did discover a couple of cracks in the headers.....Carbon Monoxide doesn't make you sleepy does it?

Are you in Melbourne Duk?  If so, you're welcome to have a drive of the car when I finally get it back on the road.

[Sheldon McIntosh]

Forgot to say.....

Vin will have an idea where to get the Konis revalved, he also has the specs to give them for certain TB sizes.

Should also add, concerning the ride etc, I'm definitely not one of these guys that think "the harsher the ride, the better the handling must be".  Far from it, as far as I'm concerned a track car is for the track, a road car is for the road, and rarely if ever will the twain meet.  I was just so surprised at how the 90 felt on the road with the big TBs, and my girlfriend, who is not interested in driving or cars at all, thought the ride was just fine as well.  She hates that the footwell gets so hot these days, and that it's a bit noisy.  But the ride is acceptable.

[Duk]

Wow, 32mm on the street being great  . I think I'm seriously underestimating what I need here.
I calculate a wheel rate of 360lb/in for 32mm TB, quite massive! What size rims and tyres are you using?

Cheers for the offer to drive your car, but I'm in little ol' rural South Oz, would be great to have the experience tho.



*Carbon Monoxide does make you sleepy (and dead eventually  )

[Duk]

Should also add, concerning the ride etc, I'm definitely not one of these guys that think "the harsher the ride, the better the handling must be".  Far from it, as far as I'm concerned a track car is for the track, a road car is for the road, and rarely if ever will the twain meet. 

I hear you  .
This is a road car 1st, 2nd and 3rd and my favorite piece road is fiendishly bumpy, so control is where it's at rather than a jack hammer hard, chassis smashing ride.
Cheers for your input and info 

[Sheldon McIntosh]

What size rims and tyres are you using?

Standard 15x6 wheels with 205/50 Yokohama Advan A048 (that's a 'race' tyre with a reasonably stiff sidewall for those playing at home who don't know the tyre).

Wow, 32mm on the street being great  . I think I'm seriously underestimating what I need here.

I was surprised as well.  And having said that, 28mm or similar might be just as good, if not better on the road.  All I've tried are the various standard set-ups, and my current one.

Cheers for the offer to drive your car, but I'm in little ol' rural South Oz, would be great to have the experience tho.

Oh well, if you're ever over this way, or if there is someone in the club here whose opinion you trust and whose driving I trust we could work something out.  How are you working out the wheel rate?  (My google is broken)

[Sheldon McIntosh]

so control is where it's at rather than a jack hammer hard, chassis smashing ride.

Yes, I should have mentioned control.  The body control with the big TBs is just so much better.  I don't have to wait for the body to stop moving before I can do the next thing anymore.  

I remember years ago when playing GranTurismo2 on the Playstation, I'd always tune my cars with very stiff springs and relatively soft damping - just cos they always seemed to be easier to control and faster that way.  That's what the car feels like now with the stiff TBs.  It's also got 200lb rear springs, Vin suggested them as the perfect match for the 32mm TBs.

[Duk]

How are you working out the wheel rate?  (My google is broken)

The TB to wheel rates listed in my 1st post were posted on the Alfa BB (except I calculated the 28.7mm bars).

The method I use starts from the known standard rate and TB diameter, and goes:

93/(22.8^4) or 93/22.8/22.8/22.8/22.8 = 0.000344146

New WR: 0.000344146 x New TB Diameter^4

32mm TB: 0.000344146 x 32^4 or 0.000344146 x 32 x 32 x 32 x 32 = 360lb/in.

[MD]

Carbon Monoxide doesn't make you sleepy does it?

Some trivia..

Carbon Monoxide has eight times the affinity to haemoglobin than oxygen which means that these cells will carry carbon monoxide around the body instead of oxygen in the presence of such atmospheres and the consequence of that is your old fella drops off..... hahaaa. ( I know you know the real consequence!)

[Typhoon90]

If Konis are too had in bump, you could safely get away with a slightly thinner oil in them to adjust your bump valving. If they are adjustable, then you'll have all the adjustment in the world, even with much lower viscosity oil. Of course, this will soften rebound damping, but that's generally a good thing on a road car.
I know my Volvo's Konis are bone jarringly hard when only wound about 1/3 the way in.

Regards, Andrew.

[Duk]

Koni Yellow's are only adjustable for rebound. Cool idea about using a thinner oil tho 

[Sheldon McIntosh]

I remember when I was racing motorbikes, a thinner oil, or a lighter fluid, in your forks could help adjust damping.  And there was always the cautionary tale of the guy who had been advised to put a lighter fluid in his shocks, then wondered why his forks didn't work after he'd filled them with "lighter fluid".

Probably an urban myth, but they are out there, as we have learnt from other threads on this forum.....

[Duk]

Hey Sheldon, do you use any other suspension upgrades on the 90?

At the front I have Vin's long shank top ball joints, polyurethane top control arm and caster mount bushes and overhauled lower control arms. Seam welded the top shock mount/top control arm mount box section. Triangulated brace inside the front guards. Also planned is a K shaped top brace that will join the major engine bay box section (I have no concerns with running a coil over helper spring  ) and possibly a brace that links the lower chassis rails and steering rack cross member, but it's gunna be a tight fit with an engine and 2 exhaust pipes down there.

The arse end has polyurethane Watt's linkage bushes and I made and installed, but have yet to try, a spherical bearing for the main Dedion pivot point. Stupid low, unknown rate King springs.

Other planned mods are bump steer correction, higher rate adjustable height rear springs to match the (as yet undecided) front springs. Fit polyurethane bushes to the anti roll bar chassis mounts and spherical rod end links (at the front). Also, modified top control arms that will let me run more caster angle and let me ditch the lower shock mount that I made (return to standard design).

[Sheldon McIntosh]

Hey Sheldon, do you use any other suspension upgrades on the 90?

Not yet, haven't even uprated swaybars, but most of what you list there is on the to-do list.  I kinda like the idea of doing one thing at a time and seeing what difference it makes on the track.  Unfortunately it means that progress is slow since we don't have that many track days per year.  I definitely need to do all my bushes pretty soon though. 

I would love to see and read more about what you have done there, it sounds like a very well sorted car. 

[Duk]

I've decided to err on the slightly softer side of things.  

I ordered some 225lb/in, 1 7/8" diameter springs for the front. Combined with the standard TB, that will give me the same wheel rate as a set of 28mm TB (233lb/in).
For the rear, I ordered 175lb/in springs and adjustable height spring seats.

After today's little drive (in my S13 Silvia) through my favorite little spot, it re-emphasized that overly stiff suspension is not a good idea. My basically standard suspension (standard springs but with PU bushes, gas shocks and 'bars) MR2 is much more composed and sure footed than the Silvia, and that's an AW11 MR2 with their reputation for twitchyness (which it is)