TR6 TR4a IRS vs TR6 handling

OK guys - riddle me this. I completely rebuilt my TR/ suspension with poly, lower and stiffer springs from Goodparts, new shocks all the way around and adjustable TA brackets. Love the way it handles, neutral, eager to turn in and completely predictable.

If I do the same to my 4A, which I have except for the ride height being stock, she should handle equivalently, no? Maybe even a bit better due to less weight up front, right?

What do you think?

(4A needs her hood installed yada yada hence no direct comparison at this point)

I love TR6s but I seem to remember my 4A driving and handling better.

Never driven a TR6 to compare but it's the same design and pretty much the same parts so I would think they would handle the same. Not sure what the weight difference is between a TR4A engine and a TR6 engine.

Scott

Hi guys - quick search lists TR4a 2240 and TR6 as 2491, I'd imagine a good bit of that was the engine.

Is the 4A bit less understeer oriented?

The 2491 is late TR6 weight with additional crash protection and emissions equipment I believe. More apples to apples is TR4A 2240, TR5/250 2268 lbs, from the Triumph TRs by Graham Robson.

If the Robson book figures are correct (I didn't see a source, presume they were from the factory) the six must weigh about the same as the four, as the rest of the car is VERY similar other than an engine.

Huh, I would of thought the extra two cylinders would how added a hundrer pounds or more right there.

Not necessarily true, if you look at the blocks the six is of course much longer, but the four is wider, a guess here, but because the liners are separate in the 4, I would bet the castings have to be thicker to keep it rigid. I don't have the motor weights (I am sure you can get them somewhere) but I have had a 4A and a 250. about the only thing that would make a significant difference weightwise is the motor, most everything else is the same or similar, so if the above weights are correct the motors must be real close. When I was sniffing around on the web I didn't find motor weights, but did find a statement that the "six could be added with no weight penalty over the four"

Good point, wasn't thinking about that.

A lot of difference in the flywheels too.

Where the weight is located makes a difference too. Seems like the 4 engine sits farther back in the chassis. That engine weight list that has made the rounds for years lists the Triumph 2000 L6 at 403 lbs but no listing for a non-TR7 inline 4 (FWIW, the TR7 engine is listed at 290)

Stock wheels and tires? Remember the TR6 has wider wheels and tires, so that will make a big difference. I put the same size wheels and tires a TR6 uses stock on my TR4A and it made a big difference.

Dan B

Does the TR4 have sway bars? If not that makes a difference. I installed a rear sway bar and a thicker front sway bar on my TR6. It made a big difference. I also installed poly graphite bushings in the front and rear suspension.

Roger Williams book on improving the TR250 and TR6 said the fenders on the TR250 will not accomodate as wide a tire as the TR6. Food for thought?

BOBH

I've got 205/70-15's on the TR250 and had them on the TR6 as well. I can't recall what size tires I had on it but the 4a had TR6 rims too. Don't believe they've ever rubbed on the 250 or 4a but they rubbed backing up in the 6 at full lock. Lots of variables there but I don't think tire size is an issue.

bobh said:

Does the TR4 have sway bars? If not that makes a difference. I installed a rear sway bar and a thicker front sway bar on my TR6. It made a big difference. I also installed poly graphite bushings in the front and rear suspension.

Click to expand...

The TR4A does not have a sway bar by default however the standard TR6 one will bolt up assuming you install a TR6 radiator shield as well. Definitely one of things that I did on my car when I restored it.

Good point!

Scott

Front sway bar, as notes, is easy and I'd consider it manditory. Yes, I have a spare one. Ha.

The tire thing brings up an interesting point of dicsussion - stickier tires doesn't necessariy equal better handling. One of the worst things I did was put sticky tires on the Bugeye to replace the hard, narrow, slippery ones it had. Much less fun afterwards.

But I digress...

Hi All, I autocrossed both cars over the years and have set up both to the extreme. The TR6 could lift the inside front tire off the ground in hard turns, but not much fun to drive to the place of business. The 4A was a little faster on some courses but had a tendency to swap ends without any warning. The brakes were better on the 6. I could go into all that was done, but not enough time. One hint is rear shocks for autocross only, put in w50 oil and box in the rear frame work.

Wayne

Wayne - any ideas on why the 4A IRS wanted to swap ends more than the 6?

Skip, Best I could figure out, the 4A had wires that must have been worn and stretched in a turn without giving input to the driver, I had a good friend give it a run and it did the same thing in the same place. I hate to admit it but he was much better than I was. Still had lots of fun and won a few. They never have much shade at these things and my wife being English thinks the big yellow thing is evil and it turns out my skin was having a bit of trouble. Go figure.

Wayne

Wires not being as stiff makes sense - thanks Wayne.

So netting this all out they will handle differently.

I have owned a TR6 as well as my current TR4a with IRS, so will offer an opinion.

Comparing stock to stock the 4a is more fun to drive and has noticeably less understeer, but leans a bit more- both effects due to not having a front sway bar IMO.
The TR6 engine is probably no heavier or only marginally so, there are differences in the seats, carpeted trunk and other areas which add to the car weight, but it does extend further forward because it is longer.

For some reason the "hip wiggle" you feel from rear suspension geometry changes exiting some corners in a TR6 is much less noticeable in the 4a.

I have used a TR6 front sway bar on 4a for track use, but took it off for road driving to reduce the understeer.

I now have Triumphtune springs with Spax gas shocks front and back, I feel you need better shocks to control the stiffer springs. I also use wider wire wheels with 72 spokes for strength, and 195/60 tires, no clearance problems.When I did Solo1 events I used R compound tires of 205/50 which gave a lot of grip when hot, and the car was competitive on tighter tracks.
I felt the sudden breakaway exiting corners was due to the modern tires not suiting the relatively flexible chassis, I would definitely triangulate and gusset the chassis if building a race car. Spinning at 80mph at Mosport's Turn 2 with full Nascar smoke effects was very exciting!

Edited to add: I boxed in the diff mounts on both cars, and used poly bushings on the TR4a. Also had 2.5 degrees negative camber on front suspension and very little toe in.