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Tr4A and anti roll bars


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Folks, I was reading the thread “Tr4 tyre choice and neg camber advice”, and have a question regarding anti-roll bars and the Tr4a.

After visiting part supplier sites from the US and the UK, it appears that Tr4a front anti-roll bars are listed either as “Tr6 type” or there isn’t a listing at all. Yet apparently a front anti-roll bar was a Tr4 factory option. Why were anti-roll bars not offered for the Tr4a, yet reintroduced for the Tr6?

What about rear anti-roll bars on IRS vs a live axle Tr4a?

On a technical note, should anti-roll bars always be fitted as a pair (front and rear), or is front only sufficient?

thanks

Jim

Edited by Tr4aJim
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Hi Jim

as i understand it a front anti roll bar on the irs cars promotes understeer, and the rear anti roll bar promotes oversteer

so fitting a front in isolation is ‘safe’ but not a rear in isolation.

my 6 has a pair, fitted i believe  by Racetorations in the 1990s along with their telescopic rear shocks and a full polybush set and a lsd.

the car handles really well, significantly less roll than standard and much more traction especially in damp conditions.

so, IF you’re happy with a firmer ride then front and rear arbs might be a good idea?

suggest you find someone local with a car to try?

steve

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Last point first - yes.

fitting only a front bar will change the handling by stiffening up the front increasing  across car weight transfer reducing roll. That deforms the tyre “ footprint” which reduces the grip which means the turned tyre understeers ( the car runs wide on the corner) . The rear of the car will have more grip and pushes straight on.

Having a rear anti roll bar as well mimics the same effect there, reducing roll, increasing across car weight transfer deforming the tyre footprint which reduces the rear grip and bringing the rear of the car around. The idea is to balance the grip at either end to give the overall handling effect you want.

As regards anti roll bar TR4 optional fitting that was amongst various items, and offered on the basis of you knowing what you wanted... big mistake. 
ALL manufacturers offer understeer as standard handling characteristic... because it’s safe. Go into a corner too fast, turn the steering wheel... and the car goes straight on, wait patiently car scrubs off enough speed and although running wide then adopts the steering wheel input and trundles around the corner. 
Whereas what the general public wants a” demon handling  tweek”  because race cars have anti roll bars - right. 
The front anti roll bar fitted in isolation will increase the standard understeer by maybe double but reduce the car rolling. The correct cure is to fit both front and rear and balance the handling . 
Increasing the tyre pressures at either end will improve the handling by reducing tyre deformation ( stiffer tyres deform less) and so less understeer or oversteer depending upon which end is increased.

Mick Richards

 

Edited by Motorsport Mickey
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Thanks guys!

Mick, if I may pick your brain a bit more; I have seen many “sport” cars come from the factory with pipe size front bars, and pencil size bars in the rear. Why the large size difference?  Also, as my TR4a has a live rear axle, would fitting a rear bar designed for a Tr6 (IRS) be a mistake? Were rear bars offered for the Tr4 from the factory?

BTW - one of my winter projects is to follow your instructions for setting bump steer.

Jim

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12 hours ago, Tr4aJim said:

Thanks guys!

Mick, if I may pick your brain a bit more; I have seen many “sport” cars come from the factory with pipe size front bars, and pencil size bars in the rear. Why the large size difference?  Also, as my TR4a has a live rear axle, would fitting a rear bar designed for a Tr6 (IRS) be a mistake? Were rear bars offered for the Tr4 from the factory?

BTW - one of my winter projects is to follow your instructions for setting bump steer.

Jim

Pick away Jim,

As regards...

" I have seen many “sport” cars come from the factory with pipe size front bars, and pencil size bars in the rear, why the large size difference " refer to my earlier posting where I said  "ALL manufacturers offer understeer as standard handling characteristic... because it’s safe ".

The overriding handling characteristic from manufactures is set at understeer (made to understeer more by "pipe sized front bars" with a very stiff profile) and then mitigated against by fitting a rear anti roll bar of much smaller dia (pencil size even) calculated to erode enough of the understeer characteristic to attempt to balance the handling at just the understeer side of neutral. No matter how good the average driver (and TR drivers are obviously driving gods so it shouldn't apply to them) if a manufacturer turns out 20,000 sports cars in one year that oversteer as standard, within 2 years you'll only have 15,000 of them still left on the roads but on the other hand the manufacturer knows he'll be fighting 5,000 law suits from grieving relatives all accusing them of making an unsafe car after the drivers have spun off over cliffs or into oncoming traffic. This characteristic can be recognised as being very similar to fitting new tyres onto the front instead of correctly at the back as recently discussed on the forum. Losing grip at the rear on public roads is deadly, always try and ensure the characteristic is understeer...it's safer, and then mollify it with other methods.

The TR4 doesn't have an anti roll bar as standard and when racing Kas Kastner only fitted rear bars on his TR4s (his were TR4as from memory) to modify the understeer inherent (by increasing the footprint "squirm" at the rear reducing grip there ) and leaving the front as supplied from the factory. Cars only drive around corners without having measureable "slip" (not skid, that's a loss of traction) on their tyres if the side ways forces are of the level generated by a very nervous nun on her first journey after passing her test...ohh and she's wearing slippers !  Any forces generated onto the tyres sidewalls (more on this in a second) called slip, causes the tyre footprint to be reduced which alters it's grip coefficient. Even without trying we all account for this "slippage" and vary the input of throttle (which increases the rear tyre slip ) which helps overcome the natural understeering tendency built into them and  allows the car to describe an arc around the corner more or less as we require. 

Presumably the live axle TR4a will handle very similar to a TR4 with live axle and I had a Triumph Dolomite anti roll bar on my race TR4, so I'd be surprised if the forces applied at the rear will be much different and a TR6 anti roll bar will be somewhere in the park. Again refer to my earlier comment on a posting that "If a car goes around a corner like it's on rails...you're not driving it fast enough" the necessary overcoming of grip at one end or the other alters the car as it is driven through the corner.

Mick Richards    

Edited by Motorsport Mickey
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Thanks Mick! That’s a class on suspensions right there!

Marco, no I wouldn’t say it “rolls”. Here’s the thing. Last year I did a complete rebuild of the front suspension; springs, bushings (poly), shocks, the works, plus a new alignment. Afterwards, the car felt much more responsive to steering inputs, tracked straight as an arrow, and was more controlled when hitting bumps, etc. However it did feel like it was now oversteering when cornering. I found myself correcting to center more while negotiating a corner at speed. Nothing severe mind you, but noticeable. That made me wonder if the front wheels were behaving more independently in turns with the new hardware, and if a front bar would make them work more in unison.

Or, I was just use to the handling with the tired old components, and it’s behaving now as it should!

Jim

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In Kas Kastner's TR4 Competition Preparation Manual a front anti-sway bar, Triumph Part No. 510584, is recommended for both track and street use. Kas states that when using an 11/16" diameter bar " cornering power is greatly increased". It will keep the rear tires in better contact and increases understeer, as Mick describes above. Kastner recommended using a limited slip differential and changes to the steering geometry for negative camber. He also recommended the installation of torque rods on the rear live axle springs to minimize windup.  Regarding the TR4A IRS he says that a rear sway bar was still in development. This version of the Preparation Manual is dated from 1965. Some of the same information was also described in a 1962 article from Car and Driver that is reprinted in the TR4 Brooklands book.

The attachment was downloaded from Paul Anderson's excellent website: http://tr4a.weebly.com/

 

TR4 Competition Manual-1.pdf

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2 hours ago, Andy303 said:

Here is an interesting tutorial on handling corrections from the Mid Ohio region of the Porsche Club of America (MORPA). Fairly generic and should  apply to TRs as well as 911s, I think.

  http://www.morpca.org/drivers-education-guide/understeer-oversteer/

 

 

I think you'll find that will muddy the water Andy, on the front page it correctly describes what understeer and oversteer are and their "cures" yet in the last closing paragraph it says "Stiffer front sway bars will in many cases will decrease understeer because of decreased body roll and better camber control ." Whilst earlier in the corrections for understeer it describes as "softening the front anti roll bar (decreasing thickness) as a cure for understeer. These two quotes directly contradict and that's because the Porsche is very stiff and heavy at the back and handles differently.

I can guarantee that ANY fitment of a front anti roll bar on a TR will cause the built in initial understeer to increase to UNDERSTEER much greater than the original. Of course if you drive it sedately you'll never find that out because the stiffness causing weight transfer and understeer will never be applied.

Mick Richards 

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2 hours ago, Andy303 said:

In Kas Kastner's TR4 Competition Preparation Manual a front anti-sway bar, Triumph Part No. 510584, is recommended for both track and street use. Kas states that when using an 11/16" diameter bar " cornering power is greatly increased". It will keep the rear tires in better contact and increases understeer, as Mick describes above. Kastner recommended using a limited slip differential and changes to the steering geometry for negative camber. He also recommended the installation of torque rods on the rear live axle springs to minimize windup.  Regarding the TR4A IRS he says that a rear sway bar was still in development. This version of the Preparation Manual is dated from 1965. Some of the same information was also described in a 1962 article from Car and Driver that is reprinted in the TR4 Brooklands book.

The attachment was downloaded from Paul Anderson's excellent website: http://tr4a.weebly.com/

 

TR4 Competition Manual-1.pdf 3.56 MB · 4 downloads

You'll find that Kas moved on with his handling and in this download from Car and Driver magazine 1966 he describes as how the TR4a does not have a front antiroll bar but does have a rear 9/16 th inch rear anti roll bar fitted to make the handling more balanced and neutral.

feb66 Kastner anti roll-highlight.pdf

 

I agree with him, I just came at it from a different method and ended up developing a racing suspension for my TR7 V8 that didn't have anti roll bars...front or rear.

Mick Richards

 

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6 hours ago, Tr4aJim said:

Thanks Mick! That’s a class on suspensions right there!

Marco, no I wouldn’t say it “rolls”. Here’s the thing. Last year I did a complete rebuild of the front suspension; springs, bushings (poly), shocks, the works, plus a new alignment. Afterwards, the car felt much more responsive to steering inputs, tracked straight as an arrow, and was more controlled when hitting bumps, etc. However it did feel like it was now oversteering when cornering. I found myself correcting to center more while negotiating a corner at speed. Nothing severe mind you, but noticeable. That made me wonder if the front wheels were behaving more independently in turns with the new hardware, and if a front bar would make them work more in unison.

Or, I was just use to the handling with the tired old components, and it’s behaving now as it should!

Jim

"However it did feel like it was now oversteering when cornering."

Roll oversteer. Increase the rear tyre pressures by 2 lbs and try again.

Mick Richards 

Edited by Motorsport Mickey
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I love this:

- does it roll (what is the reason for your quedtion)?

- no, it oversteers (and I want to do something against it)

- drive with 2 psi more on the rear (this could work)

Very excited for the answer, Marco

 

Edited by Z320
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50 minutes ago, Z320 said:

I love this:

- does it roll (what is the reason for your quedtion)?

- no, it oversteers (and I want to do something against it)

- drive with 2 psi more on the rear (this could work)

Very excited for the answer, Marco

 

Every days a school day (for everybody)

Mick Richards

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Regarding a Live axle 4a which I have as well, I dont have roll bars either but I do have original (British Leyland issue) not repro rubber lower inner wishbone bushes on the front with hard polys on the top and Spax shocks set fairly hard plus on the rear original (BL again) front end of the spring eye bushes and blue poly bushes on the rear shackles plus 25% uprated lever arms (There is no tube conversion available for these cars) and in addition two spring clamps on each spring strategically placed to stiffen the rear springs. This gives very neutral handling with minimal body roll so you can take corners flat and then use the power to "drive" through the bends. It works for me at any rate.

Stuart.

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Thanks Stuart! What led you to mix rubber and poly bushes? I’ve only seen mention of either all rubber or all poly. What rear spring clamps did you use?

Also you bring up a good point. As I said, I rebuilt the front suspension with all poly bushes, but I still have rubber ones in the rear (the PO must have replaced those at some point as they looked in good condition). Could that difference in stiffness contribute to the mild oversteer I described?


Jim

Edited by Tr4aJim
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When I rebuilt the car it was done originally with all rubber, the lower inners and the rear spring eye ones being original real rubber are still as good now as when it was built but the top inners didnt last that long same with the shackle rubbers on the rear as they do a lot more of the work so they were replaced about ten years ago with the poly. The rear spring clamps were ones I inherited from a local club member since deceased who used them on his racing TR2 and told me the best places to fit on the springs. Picture taken before fitting the Alfins I have on there now.

Stuart.

 

Rear axle 006.jpg

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Jim: Don't overlook the importance of the rear shocks. I think the TR4A SRA is particularly sensitive to the quality of the lever shocks due to the "unique" mounting geometry that was inherited from the IRS design. I plan on installing up-rated ones in the spring. On my car I found that with the right side one was nearly devoid of oil and the car squirmed to the right on acceleration and then back to the left when I lift off . Topping up the shock improved things but it still has a tendency to yaw a bit. The spring shackle bushings may be suspect as well. This yawing may have been exacerbated by the presence a front anti-roll bar. I have only had this car since last April and while it looks great it sat unused for many years and I am still sorting out a lot of abuse and neglect from the previous ownership on the mechanical side.

Stuart: Thanks for relaying your experience. I see the spring clamp on the rear, is there one to the front in a similar location, i.e. past the end of the lowest leaf?

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On 12/30/2019 at 2:45 PM, Andy303 said:

Jim: Don't overlook the importance of the rear shocks. I think the TR4A SRA is particularly sensitive to the quality of the lever shocks due to the "unique" mounting geometry that was inherited from the IRS design. I plan on installing up-rated ones in the spring. On my car I found that with the right side one was nearly devoid of oil and the car squirmed to the right on acceleration and then back to the left when I lift off . Topping up the shock improved things but it still has a tendency to yaw a bit. The spring shackle bushings may be suspect as well. This yawing may have been exacerbated by the presence a front anti-roll bar. I have only had this car since last April and while it looks great it sat unused for many years and I am still sorting out a lot of abuse and neglect from the previous ownership on the mechanical side.

Stuart: Thanks for relaying your experience. I see the spring clamp on the rear, is there one to the front in a similar location, i.e. past the end of the lowest leaf?

Yes there is, you can just see its location at the bottom of this picture. Its located between the two original clamps on the leaves. I did originally try four clamps but it was too much.

Stuart.

Rear axle 004.jpg

Edited by stuart
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