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oldtuckunder

Rocking N Rolling, Slipping N Sliding But Not Quite Sideways

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Had some fun at Curborough on the Figure 8 circuit at the RSSOC sprint on Sunday, first twisty sprint I have done in the Vitesse, and as you can see from the pictures new thicker anti roll bar being prepared in the workshop right now! On most Hill Climbs its brake and corner, but at Curborough on the 8 it Squirt, brake, hard right, hard left, squirt and repeat... And it showed up some deficiencies in my current set up!  Running the high profile tyres didn't help (it only started raining as we left!) have a look at the rear tyre on a couple of the shots! I have other shots that show how right on the limit I was at times!

Alan

 

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Looks like fun  :)

 

You might not like the effect of the thicker anti-roll bar........ I tried one on my Herald - turned a nice, pointy little car into an understeering horror.

 

I have some dual rate (300/530) springs here that might help.  As previously mentioned they aren't quite right as they just reach the 530 rate (on my car at least) when at rest but they do have the effect or reducing roll.  Ride is fairly bone-shaking on the road though.

 

Are those 5.5" or 6" rims?  Sidewalls look bulgier than mine I think?

 

Nick

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Running 380 springs currently, and yes those rims are 5.5" which is the max I can use in that class, funny as they are TR7 rims and their specified tyre was a 185/70 

 

The other 13" rims I have with 60 profile 175's are only 5" but feel completely different and much more precise, but I think that may be a lot to do with having a very flat tread with almost square shoulders. 

 

I may stick with the 1/2" roll bar as the next three events are Hill Climbs and I always liked the quick turn in, but as its fairly easy to swap I thought I'd try the 7/8 for a few road tests.

 

Have adjustable platforms on the front dampers, so may just try winding the springs up a bit harder and see what that feels like.

 

Will probably have to swap back to the lower profile 13" tyres for the next events, which is a shame as the gearing with the 70 profiles has almost been perfect, just that extra second or two being able to hold a gear instead of changing up, quite often means a couple of gear changes saved!

 

Alan

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Consensus seems to be that the 7/8 roll bar is too strong. However I have it in my GT6 and  Im yery happy with it. 5,5 x 13 with 175 / 70 / 13. These are semisports thus veeery sticky.

 

Quite neutral in curves and it does not hmmm how to express    "lean on the nose" ?????

 

Martin

 

 

 

 

 

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As Nick implies, the right ARB thickness depends on the coil spring stiffness, and on the rear spring stiffness.

SofS has a 1" ARB, 600lb/in coils and a rear spring whose stiffness I don't know but is "very".

 

It's neutral into corners, maybe a understeering on the limit, but on public roads is like a tumbril, with steel wheels!

John

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I'm running a very stiff decambered rear spring, with an anti-camber kit as well, and up until Curborough I have always liked the cornering which I always described as neutral to oversteer. Although I am also battling playing with the different tyres (its starting to be a joke, Alan arrives with rain tyres on and it guarantees a dry day!)

 

So here's a question for you suspension Guru's Anti-Roll bar chassis mountings, should they grip the roll bar and try and prevent it turning, or should they let it rotate as easily as possible. Some comp prep notes say they are best made out of nylon or alloy and should be frequently lubricated i.e allowing easy rotation, whilst the standard ones using rubber or poly bushes almost seem to grip the bar as tight as possible whilst providing a bit of flex/rotation within the limits of the elasticity of the bush material. Thoughts? 

 

Alan

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Well got the 7/8 bar fitted, not quite 10 mins as I decided that as its unknown how it will affect the handling, that I wanted to be able switch them quickly at an event if I choose, now after a bit of work I have two anti roll bar kits and I think it is only a 10-15 job to switch. Joh Wolfe's drop links make it easier as I not fighting those horrible rubber things.

 

Had a short 15 min test drive before it got dark, and the conclusion is uncertain!  if anything the turn in felt even quicker and couldn't detect any increasing understeer, didn't dislike the experience or wanted to rush back and swap it back. Maybe the stiffer bar is a better match to the stiffer front and rear springs and dampers, time will tell!

 

Did mean to ask what dia anti roll you had fitted Nick?

 

Alan

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Standard skinny one.  Also standard and somewhat-saggy-from-age rear spring with telescopic dampers (elderly but good Armstrongs on chassis extension brackets, so the effective rate is a little increased due to the more vertical angle).

 

At the front I have 350 lb springs (10.5" free length) on Koni adjustables set near fully soft.  As a road car it's fine (for a small chassis Triumph anyway).  Bit soft and roly-poly for track work, but that's not what it's mostly for.

 

I guess if you already have a stiffened rear end you can get away with increasing the roll stiffness at the front without undue oversteer...... whatever works! 

 

The other thing to remember is that even a solid Vitesse convertible has all the torsional stiffness of a wet fag packet so make things too stiff and you just get (more) flex elsewhere.

 

Nick

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Some further road testing indicates that the Vitesse seems to like the new thicker anti roll bar, so I'm going to run it at Gurston next weekend. That will be the real test as pushing it at 10/10ths is likely to reveal things that one just can't replicate on the road unless its a brown trouser moment!

 

Alan

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Your ARB should rotate freely in its chassis brackets.   The idea is to transmit suspension movement from one side to the other.  Gripping it at the chassis would just add to that corner's springing.

But like suspension links, the less flexible the medium that holds the bar, the better will it be located, and the more efficiently it will work.     As there is no angular movement of the central part of an ARB, roller bearings are ideal, while spherical joints are best for the drop links to the suspension.

I have the latter, but nylon bushes for the chassis bearings.

John

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Thanks John that's how I have set it up so that it rotates, but only in Red Poly's at the moment, may have a look at something smoother and firmer over the winter, also have JW's spherical drop links.

 

One of the reasons I asked was that the couple of Spitfire's I have dismantled recently both had the anti roll bars just about frozen in the pivots, combination of hard distorted rubber, rust, mud and with the U bolts up about as tight as they would go. Had no idea what they were supposed to feel like, especially as my original was in Poly's and rotated fairly easily.

 

Alan

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Isn't the choice of the front ARB a function of the rear spring type?

I thought the thicker ARB would only be used to compensate the roll-softness of the swing spring?

 

I bought a  GT6 swingspring  and a thicker ARB one year ago for my 13/60.

But I don't know if I should fit them, as I like actually the car's original handling, with 155 Dunlop tyres on 4,5" Vitesse rims (1,9 /2,0 bar though ). The car seems nicely balanced with slight positive camber at front.

Never experienced jacking & tuck under, when chasing modern cars on A roads... :ermm:

 

Patrick

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Hi Patrick

 

Your right conventional wisdom is that don't use the Swing Spring ARB unless using a Swing Spring, as I believe if used in the wrong combination it promotes understeer.

 

However in my set up I suspect all conventional approaches are a bit redundant, having had major mods to front & rear spring rates and heights, damper settings, and adjustable camber etc front and rear, and rear anti-camber kit. So to some extent I just have to play to get the nicest set up. Prior to Curborough (and possibly the skinny sticky tyres) I had no real complaints about the handling, but I think I found the current limit so am playing to improve. 

 

Given how stiff and low the current set up is, it may well be that the thicker ARB is a good match, a couple of Hill Climbs this weekend may change my mind though!

 

Alan (will it rain this weekend?)

 

Oh PS. The jacking and tuck under are normally provoked by poor driving or rather "don't change your mind mid corner" don't lift or brake in a corner, doesn't solve all the problems but usually keeps you out of trouble.

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Hi Alan,

 

I've been looking at the pictures again.

What tire pressures have you been using? It seems that your rear 185/70 could do with some more. I would try to add another 0,3bar.

Also if I compare your car with Martin's GT6, it seems the Vitesse is a bit higher on the rear. On the second picture the car appears to be almost free of lateral forces, so no reason to induce "transfer leaning" from rear to front.

But pictures may also be misleading, as it could be a hill down...or you might have tipped the brakes before the next bend

 

Patrick

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Hi Patrick

 

All good thoughts! At Loton I tried using Nicks pressures of 28 front 26 rear, and had lots of squirmy experiences (although achieving a PB there) so at Curborough where the shots are from I thought I'd up the pressures as I wondered if it might help and went up to 33 front and 30 rear to see if it would dial out some of the squirm, which it did a bit, but as you can see from the pictures on 5.5 rims there is a lot of sidewall defelection. Not sure if I want to go any higher as it will reduce tread contact even more as the SN832's have very round shoulders. One of the problems with the SN832's is that they are actually very soft and grippy in the dry so you can see in the pictures that they sort of hold on until it all gets too much, then I think they squirm and slip. I actually got them for wet days but the rain fails to materialise when I put them on! and I have to drive to and from event on same tyres if I stick to roadgoing class so can't change wheels at event. I normally run on lower profiles with a very square shoulder which tend to just have a progressive slide, so none of the wind up squirm I'm getting with the SN832's.

 

The Vitesse is higher at the rear than the GT6, and the body line does sweep up towards the rear, in the first shot definitely braking hard so down a bit at nose, I have a feeling that the zoom and perspective of the shots makes things appear worse, On the fourth shot that is just a lot of G force roll weight transference to the front right, the 6 pot is a heavy lump and right at the front in the Vitesse.

 

Whilst I'm running a heavy decambered rear spring, the front is a fair bit lower than standard (trolley jack won't go underneath with 60 profile 13") So the stance is a bit nose down anyway, normally works well in sharp hill climb corners for turn in, but may not be helping with rear roll on faster sprint corners.

 

Lots to experiment with!

 

Alan

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I've been errr, "experimenting" with the SN832s in actual Alpine conditions.  They certainly are grippy and I was having more trouble than usual getting the tail around in tight hairpins.  Also really quite hard to get them to actually squeal though they start making odd slipping noises well before that.  I was gifted with an uninterrupted run up the lower part of the old San Bernardino pass, in dry sunny conditions  :yes:  :devil: .  Definitely needs more throttle area - runs out of puff in second gear too.

 

Nick

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Given how stiff and low the current set up is, it may well be that the thicker ARB is a good match, a couple of Hill Climbs this weekend may change my mind though!

 

Alan (will it rain this weekend?)

 

 

Oh boy did it rain at Wiscombe, and then some at Gurston

 

I love these SN832's  :yes:  :yes:  :yes:  :yes: and I think the new arb works well!

 

More anon (have to rip out and start fitting new kitchen sink unit today as penance for having so much time away playing!) but at least one outright first in class, and maybe more when results are calculated. Watch this space!

 

Alan

 

PS. Nick glad you had fun!

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Ah yes the trees! 

 

For those not familiar with Wiscombe found a couple of Videos worth a few mins watching, although not in the Wet!

 

 

 

Slightly worse that the trees is the F'ing big gate post on right at 0.42 in the second video (neatly disguised as a small straw bail!) and the tyres and shrubs on the right (which are disguising a big stone wall).

 

First time at Wiscombe, so got there early enough to walk the hill before practice started. Hill was damp from overnight rain and sky was grey with clouds scudding overhead threatening rain which was promised by early after noon.

 

Paddock at Wiscombe is a sloping field, which was already cut up from an event the previous weekend, so they impose a rule that you must follow a hard track to the top of the paddock and then turn down the grassy slope to your allotted space (if you brake and slide past tough you have to go around and try again!)  Driving or trying to drive up the slope risked exclusion) so yes a lot of mud around and it got worse during the day.  The Mud adds an interesting dynamic at Wiscombe as all the cars arriving at the start line have mud on/in their tyres, which gets neatly deposited from the start line down to the sharp first left hander so can get a bit interesting at that bend.

 

Our Triumph Class had running orders in the high 90's so it was probably around 10 ish before we got our first practice run, there had been a light shower but on the whole the first half of the course across open ground was drying the top half up through the trees wasn't really expected to dry. There had been a few stoppages when people forgot that "Practice is Practice" and had minor off's but not too bad. Everyone took it easy, especially as most of us in the Triumph class hadn't been to Wiscombe before, and yes coming out of the bends and applying power even lightly induced some wheel spinning twitching.  Just for fun on the return run down the hill I thought I'd test how slippy it was and performed some really hard braking at all the points that it had felt slippy going up, darn me the SN832's just gripped try as I might I couldn't provoke a lock up or a slide. Hmm maybe the track isn't as slippy as it felt, maybe harder braking might not be a problem.

 

By the end of the first practice run and the forecast for the afternoon looking worse, the organisers decided that second practice would be cancelled and that the next run would be an event run. Remarkable despite leaden skies the rain held off as the running order progressed, again the odd off but no major hold ups, just getting to our class and the skies darken again, first few in my class set off in the dry, just as I get to the line drops of rain appear on the windscreen "bugg.r" but thought hang on the braking felt good, half the track is nearly dry, this could be the only good run of the day go for it!  I did! it was a bit hairy coming out of the bends, but the SN832's really allowed me to keep the braking late, and it felt good and I reached the finish paddock with one of those "OH yes give me another run right now feelings".

 

Turns out that run was 3 secs quicker than anyone else in the class, and yes whilst it stayed dry for lunch break, then the drizzle started, then the rain, then a Mini dumped a sump of oil in the Esses, they tried their best, but as the rain got heavier they had to give up trying to clean the track so event was cancelled. Some classes had managed two timed runs, some later in the running order like us only one, and to be honest whilst we had been queuing for about an hour for our second run even if they had cleaned the track the conditions had deteriorated to the point that nobody unless an idiot would have bettered their morning run.

 

So by chance my decision to go for it second run in the morning paid off! First time I have ever had best outright time in class, and with the handicaps another first for the Vitesse!

 

Happier with the SN832's (ran 28 front 30 rear) and the thicker ARB felt good also. Bourne out by Sundays runs at Gurston, but that's a story for another day!

 

Alan

 

PS.Nicks Joke about the Vitesse convertible being as stiff as a wet fag packet and stiffening things up somewhere might induce flex elsewhere, I had doors popping open several times over the weekend, need to have a play with some catch realignment before Shelsley next weekend. 

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Fine effort - 3 seconds is a lot there!

 

My comments about the torsional stiffness of Vitesse convertibles are not jokes - but, unfortunately, the literal truth!  After MANY hairpins last week all my body mount bolts need tightening up again........

 

I don't have problems with doors self-opening.  More a case of doors not opening.

 

Nick

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Bolts! Bolts! its attached by Bolts!  H'm will have to take a look  :yes:

 

Yes my doors seem to have gone into bugger to open when I want to, but self opening on hard corners, mode.

 

Alan

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PS.Nicks Joke about the Vitesse convertible being as stiff as a wet fag packet and stiffening things up somewhere might induce flex elsewhere, I had doors popping open several times over the weekend, need to have a play with some catch realignment before Shelsley next weekend. 

 

OTU,

You really should get a front roll hoop, braced to the back.    Even when it's bolted to the floor boards, ir makes the whole car much, much stiffer!

 

John

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Might make Wiscombe a bit less Scarry too!

 

I have had it in mind, but the frequent engine rebuilds in previous years have eaten most of my budget, hopefully now resolved, only a few more events this season!

 

Will have to do some research and find out how much a custom front cage might cost.

 

Alan

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