3000m rear springs advice needed

[plasticpig72]

I've just bought a 3000M and it rides alot lower than my 3000S.
Looking at past bills of work that has been done it's noted "short springs rear" that were fitted at DG's. That is to Spax shocks that were already on the car thus reducing ride height.
I would like to put back to normal ride height.
I wondered what the logic was to fit short springs to standard shocks.
Surely they cannot operate correctly, short springs should have short shocks.
If short springs are fitted to standard length shocks they would bottom out and damage the shocks.
Alan

[racerbob]

I think that the bump stops would come into play before the shocks bottom out, don't understand why only the rear springs are altered though ? Probably stiffer at the rear to confer roll in corners, does it handle OK ? if so might be worth living with for a while before altering, I don' think the shocks are at risk.

Bob

[anonymous-user]

plasticpig72 said:

I've just bought a 3000M and it rides alot lower than my 3000S.
Looking at past bills of work that has been done it's noted "short springs rear" that were fitted at DG's. That is to Spax shocks that were already on the car thus reducing ride height.
I would like to put back to normal ride height.
I wondered what the logic was to fit short springs to standard shocks.
Surely they cannot operate correctly, short springs should have short shocks.
If short springs are fitted to standard length shocks they would bottom out and damage the shocks.
Alan

Alan,
It maybe that the previous owner wanted to lower the car, hence the Spax, presumably with adjustable platforms.

The car should be able to cope with some reduction in spring length - how much shorter are they than standard, and are they the same Spring rating (stiffer Spring = more effort to compress and again, a reason to be less concerned)?

Johm

[plasticpig72]

that is exactley my way of thinking. If you fit shorter springs they should be stiffer springs but also shorter shocks should be fitted. The working travel of the shocks must be the same as the springs.
The static height of the 3000M is 1.5" lower than the 3000S but that is the tyres.
WHY OWNERS FIT LOW PROFILE TYRES WITHOUT INCREASING THE WIDTH TO KEEP THE SAME ROLLING DIA IS BEYOND ME.
Alan

[racerbob]

How does increasing the width of the tyres help with maintaining the correct rolling diameter ?
If you want to check if the shocks will work properly you have to measure the existing static suspension height of the shocks,record the dimension, then take one off and measure how much more travel they will allow, but again usually the bump stops will make contact before shocks bottom out, your probably worrying unnecessarily, but worth checking to ease your mind. Did you not look at the car before you purchased it ?

[anonymous-user]

Maybe he meant low profile tyres with larger wheels?

[Dollyman1850]

plasticpig72 said:

that is exactley my way of thinking. If you fit shorter springs they should be stiffer springs but also shorter shocks should be fitted. The working travel of the shocks must be the same as the springs.
The static height of the 3000M is 1.5" lower than the 3000S but that is the tyres.
WHY OWNERS FIT LOW PROFILE TYRES WITHOUT INCREASING THE WIDTH TO KEEP THE SAME ROLLING DIA IS BEYOND ME.
Alan

Allan. Spring length and shock length are unrelated.
You choose springs and shocks to carry out 2 different purposes.
A spring can alter in free length and rate and be used on various open length shocks.

When choosing shocks you should first ensure that the fully open length or fully bottomed out length does not allow your drive shaft U/J's to bind..I have seen classic TVR's where this has happened.
You then choose springs to suit your proposed ride height allowing some degree of adjustability generally in conjunction with adjustable spring platforms on the shock bodies.

You can then start thinking about altering wishbone geometry to allow further tuning of ride height dependant upon what you want to achieve.
You can then start to experiment with longer shocks, twin spring set ups and droop limiting devices…

Belive me there are many ways to set up car suspension.

Finally with tyres.. you never just increase width when reducing aspect ratio since tyres have an optimum rim width for their diameter..The best rule of thumb is to actually slightly stretch the narrowest recommended width tyre on the maximum width wheel, again dependant upon what you want to achieve with the car..

I see many classic TVR owners with 205 tyres on rims where actually a 195 would work better and reduce tyre roll.

N.

[plasticpig72]

What i thought was if the original width of tyres is 185/80 then if you go to 70 aspec then you need to fit 205 width to maintain rolling dia and maintain ground clearance.
I think that i will fit 185/80 as original to have original ground clearance and original gearing. If you fit 185/70 you effectively lower the diff ratio and rip the exhaust off on the first speed hump(sleeping policeman)
Alan

[Dollyman1850]

plasticpig72 said:

What i thought was if the original width of tyres is 185/80 then if you go to 70 aspec then you need to fit 205 width to maintain rolling dia and maintain ground clearance.
I think that i will fit 185/80 as original to have original ground clearance and original gearing. If you fit 185/70 you effectively lower the diff ratio and rip the exhaust off on the first speed hump(sleeping policeman)
Alan

Original width on 15's was 165 I believe.

So comparing 165 / 80 / 15 with say 195 / 65 / 15 gives you the following info.:

Rolling Radius…202.63cm versus 199.33
Total diameter..64.50cm versus 63.45cm
Sidewall height 13.2cm versus 12.68cm

Speedo error 1.6% at an indicated 30mph actual speed will be 29.5mph!!

N.

I am no expert on early M's but I don't think the original Tuscan / vixen type alloy had 185 / 80's fitted as std.
It was certainly a 165/15 on a vixen
Back in the day on other cars with smaller wheel diameters the std common 165 width on a full profile tyre was always changed to a 185 / 70 profile and I suspect this would be the case for the Tuscan type alloy in the day.

Edited by Dollyman1850 on Monday 11th July 18:52

[plasticpig72]

On my 1976 3000M the very old spare tyre is 185 x 14".
On my 1978 3000S the tyres are 185 x 14".
In the "TVR Owners Handbook" "M" series page 4 tyres are quoted 185 HR 14" Radial Ply Tubless.
I think i will fit 185x14" on the original "T" slots and have max ride height.
Alan

[Dollyman1850]

plasticpig72 said:

On my 1976 3000M the very old spare tyre is 185 x 14".
On my 1978 3000S the tyres are 185 x 14".
In the "TVR Owners Handbook" "M" series page 4 tyres are quoted 185 HR 14" Radial Ply Tubless.
I think i will fit 185x14" on the original "T" slots and have max ride height.
Alan

Are you're talking about the newer cars with the tidgy diameter wheels..

T slots are a tad wider so I would compare the 185 / 80 with a 205 / 70 14 again the differences are very slight and the choice of tyres in a better performance rating probably greater
N.

Edited by Dollyman1850 on Monday 11th July 19:20

[bluezeeland]

plasticpig72 said:

On my 1976 3000M the very old spare tyre is 185 x 14".
On my 1978 3000S the tyres are 185 x 14".
In the "TVR Owners Handbook" "M" series page 4 tyres are quoted 185 HR 14" Radial Ply Tubless.
I think i will fit 185x14" on the original "T" slots and have max ride height.
Alan

Thats is correct, 185/80HR14 > Michelin' - very good/very expensive....Vredestein' not very good/not very expensive (but probably good enough for 'normal' use, as in 'not ditch-finders'....)
Regarding the shocks/springs, if they're past their best, call Venn and get a new set....

Edited by bluezeeland on Monday 11th July 19:51

[anonymous-user]

1972/3 3000m. I've gone standard Spring lengths, 10% +

Intend to run the car a little higher than a normal 3000m (V8 motor) got adjustable platforms so something to play with. 15 inch wheels min to clear big front brakes, will be trying to run standard (original profile tyres)