simon's learning what to do with the polo thread

[sambb]

ha ha yep mine was a dog like that too. Yep that's why getting the f:r roll distribution so that the inside rear feels like it skims the deck is the way to go. The rear toe will get that rotation thing happening. As a bodge you can pump up the rears so they are running on their centre lines more and then they will start to slide more. In comparison to what I have now, a stiffer front bar will get you out of trouble but the car will still pitch forward in the same circumstances. It'll roll less but the nose will still be driven downward and you still get that feeling that you are just eating through all your (limited) front camber and once its gone you are pig understeering again so you have to be really careful not to go in too hot. The stiffer spring rates really do change things as the car doesn't pitch and heave and stays sled flat - but by then you have no comfort!

[Sydneykid]

You guys have been busy while I was away in Alaska some short comments follow;
I wouldn't use a circlip style (height adjusting) sleeve on a strut, they are OK for double wishbone, where there is no side loading on the shock (strut) body. We use weld on sleeves, which means removing the damper from the strut body as they don't like welding temperatures. Bonus is that strengthens up the strut body so it doesn't bend as easily (retains camber).

There is a direct correlation between the spring rates and the amount of camber required. It's all about maintaining the tyre contact patch as the chassis rolls ie; softer springs need more neg. Keeping in mind that if the lower control arms are level (parallel to the ground) or point upwards towards the wheel then it will lose camber as the spring compresses, AKA a regressive camber curve. What is desirable is progressive camber curve, adds negative camber as the spring compresses to retain the tyre contact patch as the chassis rolls.

The theory of increasing the rear roll stiffness only helps understeer until the diagonal weight transfer gets excessive (insufficient negative camber) ignores the turn in advantage that increased rear roll stiffness provides. ie, we don't need to turn the steering wheel for as long and/or as much.

Run out of time, sorry, I'll get back to it when i can.

Cheers
Gary

[Sydneykid]

Each tyre has a preferred spring rate, that's effective rate, what the tyre feels. For us A050's work best around 300 to 350 lbs/inch as an example. So with, say, 0.9 leverage and movements ratios (MacStrut) that means a spring rate around 370 to 430 lbs/inch (6.5 to 8.0 kg's/mm). That's quite a bit of spring for a road car (think handling not comfort) but we can run a fair bit less than that if we have enough bump damping coupled with enough anti roll. For a FWD car we need to be cognisant of not having too much anti roll on the front as it limits inside wheel traction. Which is not a problem on the rear of course.

Generally speaking most FWD "sporty" models have a reasonable amount of front anti roll standard, so I tend to limit them to small swaybar upgrades on the front, if at all. Again not the case with the rear of course, where I haven't found the limit on many cars.

With a combo road and track car what I have found is a compromise on spring rates can be compensated for with lots of caster which has no handling downsides compared to lots of neg camber (wears out tyres real fast, increases braking distances, reduces acceleration traction etc). I have had road cars with 9 degrees of caster and only 1 degree of neg camber that handled pretty well on the track and had pretty good ride comfort at the same time. So my suggestion would always be to crank on as much caster as physically possible and then add camber as required. My rule of thumb is 10 degrees total, say 9 caster plus 1 camber, 6.5 caster and 3.5 camber etc. That's where I start on sedan based race cars.


As we increase the front traction (via tyre contact patch) we find that less steering lock is required for a shorter amount of time. We can straighten up the steering wheel earlier for a better corner exit, get on the throttle earlier and harder, which as a bonus makes the straights longer. Rear toe out is anther big help for the same reasons.

With 10 degrees total it shouldn't be necessary on road tyres to have an effective front spring rate more than 150 and 200 lbs/inch (depending on the tyre). Provided there's enough rear anti roll and toe out. A small increase in the front anti roll won't hurt.

In summary, we can get away with softer than ideal spring rates, but we need to compensate with geometry. Plus institute a driving technique that gets the turning over early in the corner entry so we aren't hanging onto to steering lock deep into the mid corner and we are all straight by the corner exit. Late apexes don't hurt either.


Cheers
Gary

[Sydneykid]

A bit of shock theory.

Simplistically shock absorbers are "timing controllers", they increase the amount of time taken for suspension compression (bump) or extension (rebound), than springs with no dampers. We can use that as a spring rate substitute, but we also have to be aware that it's time limited. Even with drastically increased bump damping a car will eventually lean in long corner. If we "shorten" the corner (refer previous post) then the damper has a shorter time in which it has to limit the lean.

Cars with a "lot" of bump damping ride slightly better than cars with an equivalent "lot" of spring rate. Of course there is limit, where the bump damping still gets uncomfortable.

A good compromise road and track car is not easy to achieve and takes a full suite of "tuning techniques" to achieve. There is no silver bullet in that, doing 1 or 2 things isn't going to work magic, we need to use the full magazine.


Cheers
Gary

[sambb]

Hmm nice rule of thumb. I like rules of thumb. I can tell you on mine that the inside 1/1/2 in of my road Toyo R1R's are completely bald with 2.75 degrees of neg camber so more than the 6 degrees pos caster I have would be nice. Seems I'm a bit short of the magic 10 degree total
Gary does what you said about being able to soften the car off when the geometry is good hold true for the rear. Eg I'm about to properly space the stub axe out and re shim it in the process. If I go up from 1.6 degrees neg camber/ 2mm total to out, to 2 degrees neg/4mm toe, is it likely then that I could come back on the bar or springs a bit?

[Sydneykid]

Hmm nice rule of thumb. I like rules of thumb. I can tell you on mine that the inside 1/1/2 in of my road Toyo R1R's are completely bald with 2.75 degrees of neg camber so more than the 6 degrees pos caster I have would be nice. Seems I'm a bit short of the magic 10 degree total
Gary does what you said about being able to soften the car off when the geometry is good hold true for the rear. Eg I'm about to properly space the stub axe out and re shim it in the process. If I go up from 1.6 degrees neg camber/ 2mm total to out, to 2 degrees neg/4mm toe, is it likely then that I could come back on the bar or springs a bit?

Hopefully not, the extra camber and toe "should" result in faster times/higher speeds carrying more lateral G, hence more roll.

Yep, 2.75 is extreme for road car, can you use, say, 1 on the road and then flick it to 2.75 for the track?


Cheers
Gary

[sambb]

Yeah I can change camber easily with the MCA adjustable tops. I'll still be going through rears with 2 degree neg on the back though. I'm due for street tyres so I'll buy non directional so that I can move them around to eek a bit more time out of them.

[simon k]

I missed you Gary!! hope you had a great trip - Alaska is on the bucket list... the lady who usually signs my invoices at work is over there at the moment

I'm waiting for some photos to be posted from the event on the weekend, there should be some pictures of my tricycle...

Guesstimating some rear bar measurements, the 2" OD, 1.85" ID rear bar on my car is 10x stiffer than the 20mm solid bar sold by whiteline etc. - somewhere in the region of 2800lb/in against 253lb/in. My rear springs should be somewhere around 180lb/in effective rate against ~90lb/in for standard springs

That leaves the front springs and bar stock. Sam's opinion is that the rear bar and stiffer springs at the back are overpowering the front, so until I do something with the front, I should either keep the rear bar and try the softer (H&R) springs or remove the rear bar.

We use weld on sleeves, which means removing the damper from the strut body as they don't like welding temperatures. Bonus is that strengthens up the strut body so it doesn't bend as easily (retains camber).

Cost is a factor so initially I assume it'd be cheaper to find a spring that goes in place of the existing front spring, rather than buying the sleeves and springs... except the coilover springs may be cheaper on their own?

Converting the B8s to coilover means buying the sleeves and then suitable springs. Where you say "removing the damper from the strut body" it looks like that's just taking the nut off the bottom and unscrewing the insert (I found a video) - I don't need to let the oil out - which is good. Weld the sleeve top and bottom, repaint, assemble, install...

No doubt there are good sleeve kits and bad sleeve kits - do you have a recommendation? I'm not clear on what happens with the strut top/bearing too, is the standard bearing retained or do we need something different up there? Some sleeve kits come with a conical spring retainer, should that work with the standard strut top with the bearing removed?

I have more thoughts and questions but I've gotta run too - I started typing this at 10am, it's 5:30 now

[simon k]

oh, have you seen this?


vsusp.com with guessed dimensions

[Sydneykid]

I missed you Gary!! hope you had a great trip - Alaska is on the bucket list... the lady who usually signs my invoices at work is over there at the moment

I'm waiting for some photos to be posted from the event on the weekend, there should be some pictures of my tricycle...

Guesstimating some rear bar measurements, the 2" OD, 1.85" ID rear bar on my car is 10x stiffer than the 20mm solid bar sold by whiteline etc. - somewhere in the region of 2800lb/in against 253lb/in. My rear springs should be somewhere around 180lb/in effective rate against ~90lb/in for standard springs

That leaves the front springs and bar stock. Sam's opinion is that the rear bar and stiffer springs at the back are overpowering the front, so until I do something with the front, I should either keep the rear bar and try the softer (H&R) springs or remove the rear bar.



Cost is a factor so initially I assume it'd be cheaper to find a spring that goes in place of the existing front spring, rather than buying the sleeves and springs... except the coilover springs may be cheaper on their own?

Converting the B8s to coilover means buying the sleeves and then suitable springs. Where you say "removing the damper from the strut body" it looks like that's just taking the nut off the bottom and unscrewing the insert (I found a video) - I don't need to let the oil out - which is good. Weld the sleeve top and bottom, repaint, assemble, install...

No doubt there are good sleeve kits and bad sleeve kits - do you have a recommendation? I'm not clear on what happens with the strut top/bearing too, is the standard bearing retained or do we need something different up there? Some sleeve kits come with a conical spring retainer, should that work with the standard strut top with the bearing removed?

I have more thoughts and questions but I've gotta run too - I started typing this at 10am, it's 5:30 now

With an inverted shock just unbolt the shaft from the bottom and slide out gently, rattle gun is best. Then weld the sleeves (bottom only) on in the appropriate place, which means knowing what free height spring you are going to use first. I have a stock of sleeves and spring seats (top & bottom) plus lock rings. I just need to know the strut leg OD, and the spring ID, most likely 62 mm (2.5"). I have some new Eibach and H&R springs in stock of the right rate that might suite I just need to know the free height. With the dimensions I can let you know the cost. I may also have some used springs, when you send me the dimensions I'll check.

The top spring seat needs a spacer between it and the strut top so that the spherical bearing can articulate. I have plenty of different sizes, just need the dimensions.

Once you have a strut that can support race style parallel springs then there's an unlimited choice of spring rates. There's a cost at first, but it pays off over time.

I can't say as I have ever had a rear spring/bar combo that "overpowered" the front. You can get too much spring and then it gets nervous at the rear, especially under brakes. But that's about it. As a result I wouldn't waste time on "softening" the rear, spend the valuable time the front.

With a 180 lbs/inch rear spring (effective) rate something around 250 lbs (effective 200 lbs) would work OK on the front.


Trip was great, all the wildlife, whales, sea lions, bears, mountain goats, etc. Plus we dropped in at the Boeing factory in Seattle on the way home, bonus.


Cheers
Gary