Jump to content

TR4a Rear Springs


Recommended Posts

Hi All

I was speaking to someone from the TR Shop yesterday and discussed rear IRS springs for the 4a. Some time back I know owners were fitting these only to find the ride height was too high. Sounded like either too long or rate too high. I'm guessing they must have a rate in the region of 100 to 115 pounds as standard?

But he says this has now been overcome and the rear ride height is now 'correct' when new springs are fitted. Has anyone fitted a set of these of late from the TR Shop and what's the verdict?

Regards

Kevin

 

Edited by boxofbits
Link to post
Share on other sites

Not for a while but the last pair I had for a 6 were fine and ride height was good, they were slightly uprated ones and red painted.

Stuart.

Link to post
Share on other sites

Many thanks Stuart that’s encouraging especially as they are slightly uprated, as the original car always feels a bit soft at the rear - as long as new springs don’t make it understeer.. my car sits a bit low on the nsr corner and has destroyed the damper rebound rubber over time , so I’m assuming the spring has gone soft as I can’t see the osf getting longer! 

Thanks again

Kevin

Edited by boxofbits
Link to post
Share on other sites

As I recall the original TR4A rear springs were around 280lb/in and were way too soft. As they sagged, they caused a lot of bottoming. 5s and 6s had heavier springs. There are several threads on this site.

I have 390lb/in on the front and Goodparts 470lb/in on the back. I have Koni telescopics all round set on the softest setting. The ride is very good even on our poor roads. We have done some high mileage trips with a lot of luggage with no problems with wheel travel. Whilst the spring rates seem high, both the front and rear springs are located at about 2/3 of the length of the suspension arm, so the effective wheel rate is lower due to the lever effect. The car sits level but I did have to put a spacer under one rear spring to get it level. 

If you do go for higher rate springs at the back, you should replace the front ones as well to keep the handling balanced.

Rockie

Link to post
Share on other sites
4 minutes ago, Rockie51 said:

As I recall the original TR4A rear springs were around 280lb/in and were way too soft. As they sagged, they caused a lot of bottoming. 5s and 6s had heavier springs. There are several threads on this site.

I have 390lb/in on the front and Goodparts 470lb/in on the back. I have Koni telescopics all round set on the softest setting. The ride is very good even on our poor roads. We have done some high mileage trips with a lot of luggage with no problems with wheel travel. Whilst the spring rates seem high, both the front and rear springs are located at about 2/3 of the length of the suspension arm, so the effective wheel rate is lower due to the lever effect. The car sits level but I did have to put a spacer under one rear spring to get it level. 

If you do go for higher rate springs at the back, you should replace the front ones as well to keep the handling balanced.

Rockie

Thanks Rockie

Interesting info. They do feel soft at the back. With harder springs all round do you get any loss of grip at all? That’s an unusual set up being harder at the back , so do you not get understeer ? I wonder if they softened it at the factory because of scuttle shake? The chassis flex is considerable as when you jack it up it twists all over the place so stiffer springs might well be a good option. It’s on my project list!

Kevin

Link to post
Share on other sites
10 hours ago, boxofbits said:

The chassis flex is considerable as when you jack it up it twists all over the place

Kevin

Errr it shouldnt Im afraid, I would be having a very good look at it to see why.

Stuart.

Link to post
Share on other sites
10 hours ago, stuart said:

Errr it shouldnt Im afraid, I would be having a very good look at it to see why.

Stuart.

Bit of over exhuberance on my part  Stuart! It’s not that bad but does flex when jacked up in places , but probably depends where also, but you’re right it’s not that bad!

Kevin

Link to post
Share on other sites

I don't get understeer Kevin. I did my first track day in the TR last year (just after my 72nd birthday :ph34r:) and my only problem was a spin caused by snap oversteer. I put that down to running slight positive camber at the rear as well as having 195/65 tyres. I believe that the wider tyre causes jacking with the camber change of the rear suspension, meaning very little rubber on the road which in turn causes sudden loss of traction and mildly terrified driver. I have a set of Richard Good's adjustable trailing arm brackets but I have not had time to fit them. 

We are about to go to the Triumph Nationals which is a 4000 km round trip. I may go back to the 185/80x15 tyres that I ran previously as they raise the gearing by 7%, give a better ride and the higher more rounded profile gives better handling at the limit. We keep trying to second guess the original designers of our cars but they knew a thing or two.

All of the standard and aftermarket spring sets for road use have higher spring rates at the back than at the front. You are right about the flexible chassis. Whenever I put the car on jack stands, the doors are harder to close....  Most cars with seperate chassis use the flex as part of the suspension, except for old Land Rovers which have no suspension at all.

Rockie

Link to post
Share on other sites
8 hours ago, Rockie51 said:

I don't get understeer Kevin. I did my first track day in the TR last year (just after my 72nd birthday :ph34r:) and my only problem was a spin caused by snap oversteer. I put that down to running slight positive camber at the rear as well as having 195/65 tyres. I believe that the wider tyre causes jacking with the camber change of the rear suspension, meaning very little rubber on the road which in turn causes sudden loss of traction and mildly terrified driver. I have a set of Richard Good's adjustable trailing arm brackets but I have not had time to fit them. 

We are about to go to the Triumph Nationals which is a 4000 km round trip. I may go back to the 185/80x15 tyres that I ran previously as they raise the gearing by 7%, give a better ride and the higher more rounded profile gives better handling at the limit. We keep trying to second guess the original designers of our cars but they knew a thing or two.

All of the standard and aftermarket spring sets for road use have higher spring rates at the back than at the front. You are right about the flexible chassis. Whenever I put the car on jack stands, the doors are harder to close....  Most cars with seperate chassis use the flex as part of the suspension, except for old Land Rovers which have no suspension at all.

Rockie

The snap oversteer would have been spline lock not the width of your tyres.

Stuart.

Link to post
Share on other sites

I have TR Nord CV driveshafts Stuart so it wasn't spline lock. I think that I need to set the rear suspension with a small amount of negative camber when the car is unladen. It is slightly positive at present but goes to negative with 2 people and luggage so no problems on the road. On the track with one person and no luggage it was probably still positive especially on the LHS which was the side that let go. 

Rockie

Link to post
Share on other sites

Hi Rockie

what was the track surface like? Is it bumpy or uneven? The other thing is are you on the brakes going into a corner when it goes round as it could be too much rear brake especially when unladen and unloaded? Those springs seem mighty stiff at the back but I don’t have a clue what the actual wheel rate works out to be,  but there’s not a lot of weight over the back so you could go slightly softer and try it though you say all the spring sets are higher front than back. The wider tyre might also give too much flex and roll under ? Might be none of these but worth a thought!

Kevin

Link to post
Share on other sites

It was a smooth track Kevin. I vaguely remember lifting off slightly for another car. Unfortunately, I had several sessions that day and that was the only one where I did not have the dash cam running. So no evidence as to whether it was car setup or incompetent driver that was at fault. I strongly suspect the latter. 

As I have mentioned earlier, the location of the springs part way along the wishbone or trailing arm on the IRS TRs means that the nominal rate of the spring is not the rate at the wheel. So while it appears that running higher rate springs at the back would lead to greater roll stiffness and thus more oversteer, it needs someone much smarter and more experienced than me to explain what the real rate at the wheel is, and thus the front to rear roll stiffness ratio.

I still believe that my problem relates to the rear camber settings. Kas Kastner recommends 1/2 to 3/4 degree of negative camber at the rear. If I was to do another track day, I think that I would  adjust my car to that first. Don't hold your breath!

Rockie

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.