hi guys, competing in Targa again this year and we discovered the rules of our class has changed and we're able to add a pan hard rod now. So here are a couple of photos of the mount on the axle. I'm still waiting for some laser cutting for the body mount and will add more photo's as more gets done. Aim to have it all done for Winton next month
Nice work as usual Colin.
Hi Colin, I'm fairly new to all this, can you please explain the benefits/purpose of a panhard rod.
Thanks
Nick
Thanks Scott
Hi Nick
The T-piece that provides the lateral location of the rear axle on 105 has a few drawbacks. One of them is the rear roll center is determined by the point at which the t-piece connects to the diff. As this is at the top of the diff 105's have a very high rear roll center, coupling this with the low front roll center (particularly if you lower the car) you end up with a very steep roll axes. This is one of the main reasons for the "twitchiness" of 105's and the need to run very stiff front springs and very soft rear ones, which can introduce problems of its own. So the main reason for the addition of the pan hard rod is to lower the rear roll center.
The second job performed by the t-piece is to act as a top trialing arm to limit the rocking forward and backwards of the axle under acceleration and braking. While it does a pretty good job of this because there is effectively only 1 arm there can still be some movement of the diff, particularly under heavy breaking. So I'll be adding 2 additional top trailing arms further outwards near the original lower trailing arms
Thanks Colin, well that makes perfect sense. As I have bought just about everything I can off Vin to improve the handling of mine; I look forward to seeing your future pics so I can at least plan to appease my unreasonable desire to spend more money on these cars that we love. ;D
Nick
Just out of interest, what's the functional difference between a panhard rod and watts linkage?
both are methods of laterally supporting an axle, the pan hard rod is more simply however it has the drawback of the pan hard rod moving in an arc which translates to the axle shifting side to side as it moves through its suspension movement. With a panhard rod the coll center is dermined by the height of the point on the pan hard rod that the center line of the car passes through, the roll center of a watts link is determined by the pivot point of the actual watts link. Watts links are better in nearly all aspects, unfortunately not allowed under the rules i have to comply to.
Following on from Colin - any tranaxle car has a watts link - many have converted the link to the back of the di dion to be adjustable ie so you can move the locating point up and down therefore allowing adjustment of the roll centre.
Quoteany tranaxle car has a watts link
Is this entirely true scott? as you can have IRS in a transaxle car so no need for a watts link
I meant all "transaxle" alfa's ran a watts link - ie alfetta, 75, 90, giulietta etc - not "any" transaxle cars.....
sorry, misunderstood :)
Quoteadjustable ie so you can move the locating point up and down therefore allowing adjustment of the roll centre.
absolutely that can be a very useful tuning aid indeed, similarly by moveing the pan hard mounts up and down the roll center can be modified, which is what all those holes in the mount are for (actually there a few more holes since that photo as I decided I needed to add some "lightness" ;D)
Finished the body mount this afternoon, the heat has slowed me down a bit, to hot to be welding!, just need to machine up a few spacers, make up the control arms and order some new rear springs should have it all done by Winton (I hope!)
some more
Well it's finally all finished. Haven't driven it yet, still got to put the gearbox back together and fit it in, next weekends job. Went together OK should be an interesting day at Winton as we've changed a lot of things at once- roll centers, spring rates, ARB settings and shock settings!
Excellent work Colin, as always.
For those that don't know Colin, he does all this with one hacksaw blade and the ruler on the back of his cigarette papers. Amazing.
and the hacksaw blade is missing some teeth.
Quick update
got the car back together today and took it for a quick blast around the block, must say all feels very promising. Feels like the gearbox is finally sorted to, looks like a bent selector shaft was to blame for the problems I've been having with it since i put the car together. Can't wait for Winton!!
Be interesting to know how you find it now you've designed-out the rear wheel steering on roll that was such a major accomplishment of the original designers. As far as I can see, this is what gives these cars their forgiving character, and though the 105 setup doesn't do it as well as the De Dion rear, it still works pretty well. Perhaps under the controlled conditions of racing it's less important, but don't give folk the idea that this is necessarily an improvement for the road.
That's the first time I've heard the term "rear wheel steer" in regards to a 105. Are you refereeing to the axles ability to follow the arc of the lower trailing arms due to only having effectively one top trailing arm in the centre of the diff? I'd never really considered this as design advantage. I'm guessing, due to the angle of the rear trailing arms, there would be a counter steer effect from the rear on cornering. From my experience and research designing a rear wheel steer system for a small Motorkhana type race car I found that at low speeds counter steer was defiantly an advantage as it added the vehicles ability to change direction but as the speed of the vehicle increased this could de-stabilise the vehicle significantly. I remember reading that most modern cars that boast four wheel steer are electronically controlled so that at low speed there is a counter steer while at high speed the rear will start to parrel steer. I guess the draw back to this, and the main reason I added 2 top trailing arms was to reduce compliance under heavy braking and acceleration.
And your correct about it not necessarily being a good idea for the road, anyone that knows my car knows it's not a "drive to work" machine, and hope I didn't give anyone the impression that this was the sort of thing you would want do to your classic 105!
Quote from: Colin Byrne on February 19, 2009, 01:33:51 PM
I remember reading that most modern cars that boast four wheel steer are electronically controlled so that at low speed there is a counter steer while at high speed the rear will start to parrel steer.
Are there any modern cars that have it still? Thought that was a fad that died out. Low speed counter steer was intended for manuevres like parking, high speed parallel steering for things like quick lane changes. Don't think it drastically improved handling though. Porsche 928 had 'passive rear steer' in that under certain loads the outside wheel would toe in slightly. I believe RX7 (the second shape, the one that looked like a Porsche 944) had a similar set-up.
That said, four wheel steer works fantistacly well on front-end-loaders.
Quote from: Sheldon Mcintosh on February 19, 2009, 05:52:55 PM
Porsche 928 had 'passive rear steer' in that under certain loads the outside wheel would toe in slightly. I believe RX7 (the second shape, the one that looked like a Porsche 944) had a similar set-up.
That said, four wheel steer works fantistacally well on front-end-loaders.
Yep series 4 and 5 RX7 had the passive rear wheel steer and the Peugoet 306 had it as well
Nice work Colin by the way
QuoteThat's the first time I've heard the term "rear wheel steer" in regards to a 105. Are you referring to the axles ability to follow the arc of the lower trailing arms...
Yes. I saw the steering angle plotted as a function of body roll somewhere, along with those of the DeDion - sorry I can't recall where. But it was clear that the effect is that when you're reaching a degree of roll that's likely to equate to losing grip, you get a small degree of steering in the direction that follows the turn. I believe this gives the car a more "chuckable" feel. The DeDion does the same thing, but much better, as the steering stays almost dead straight until you hit about six degrees of roll, then the rear steering starts to come in quickly. It's affected by all the dimensions of the Watts linkage, including the centre piece, which isn't obvious until you think about what happens near the roll limits.
Of course, all these effects also depend on spring and rollbar rates too - go heavy and you get less roll - and independent of speed, unlike the mechanical RWS systems.
Quoteyou get a small degree of steering in the direction that follows the turn
if by following the turn means that the rear toes out, as I previously said, then by definition then the rear axle slip angle is reduced, following this then the lateral force generated by the rear tire must be reduced. At low speeds this is an advantage as it creates a reduction in the vehicles turning radius and a quicker change in direction but at limit handling this reduction in rear grip in comparisons to the front wheel grip will promote significant over steer. Coupling this with the instantaneous geometric weight transfer induced by having such a high rear roll center at the rear goes somewhere to explaining why when a 105 gets to the point of steeping out on the limit and is very hard to catch. It was this snap over steer at high speeds that drew us to adding the pan hard rod in addition to trying to match the front and rear spring frequency's .
QuoteOf course, all these effects also depend on spring and rollbar rates too - go heavy and you get less roll - and independent of speed, unlike the mechanical RWS systems.
I would imagine also that ride height would have a significant impact on roll vs toe angle,
Thanks for brining this up Cjheath , this has made me think very hard about why these cars feel so fantastic on the road but when driven on the limit are very nervous, As I've said I've always considered the single top trailing arm as a design flaw rather than an advantage!
So Colin, after Winton, whats the verdict??
For what its worth Colin had a big smile on his face after his first couple of track outings at Winton so I guess that what he did leading up to the weekend really worked.
Barry
Thanks for the brief chat while my car was being scruitineered on Saturday Colin. I had to get out of Benalla early Sunday, but dropped by Winton briefly, only to see flailing pairs of legs under your car- didn't want to interrupt! Probably a good thing though, looking over your car instantly creates the "I'll just increase the credit limit" justification that I can fall for rather too easily when it comes to 105's!
Best of luck at Targa
Yea had a fantastic weekend up at Winton. The car went really well and all the Mods did their thing. The handling changes where fairly dramatic, finally the car had some serious rear end grip and was very predictable passing over the grip limit, I could even start trailing braking into corners, definitely not a 105 anymore (it was understeering with the original front ARB!). We had a small problem with one of the axles pulling out of the axle tube, the brake calliper stopped it coming out all the way but did a fair bit of damage to the calliper and the disc. On inspection of the axle the press ring that holds the bearing into place had sliped down the shaft I think due to a combination of the tyre slightly rubbing on the inside of the guard and the extra rear end grip helped to pull it out. We bashed it back into place and was able to complete the day.
It's hard to say how much faster the car was going as I've never done the short track in that car before, but it felt great. We made a few spring and shock changes during the day to balance the car out a bit and were very happy about where it was by the end of the day. A few things to tidy up but can't wait for Targa now!!
Quote from: Colin Byrne on March 03, 2009, 08:29:45 AM
It's hard to say how much faster the car was going as I've never done the short track in that car before, but it felt great.
The confidence you have in the car and it's handling is probably far more important at an event like Targa. If you are tentitive about what it is going to do coming into or going out of a corner then it stands to reason YOU will choose to make the car slower through the corner. If however you can predict the cars handling much better than before, you will be able to get through the corner much faster.
Probably not entirley true at a circuit, but somewhere like Targa where the fences/trees/dropoffs/bus shelters etc are a lot closer than at a closed circuit.
Hey Colin, awesome work here!! - tell me, how has this modification worked out now two years on ? Still happy with it or did you move onto another design?
Hey Pancho
yea still happy with the mod. We had some trouble with the original design of the mount when we got to Tassie where the bumpy road caused some cracking isssues. Those problems have all been fixed now and I've had no other issues with it since then. I'm currently preparing for a Targa High Country and Next years Tas Targa and the only change being made to the Pan Hard Rod is the replacement of the rod ends with some softer nolathane bushes to help reduce some of the shock loads. The mod defiantly allowed us to take the cars handling to the next level