Steering, Suspension, & Brakes

tips, technology, tools and techniques related to non-driveline mechanical components

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MadMarx
Christian Marx
Germany
(54 posts)

Registered:
01/02/2014 11:54AM

Main British Car:
1977 Triumph IMSA TR8 Group 44 Canada Rover 4L

authors avatar
Rear spring rates - IMSA TR8
Posted by: MadMarx
Date: January 01, 2015 04:39PM

Hello to all and a happy new year.

I have bought the canadian Group 44 car last year and did some racing with it.

It becomes more and more evident that the car has trouble on the rear end.
On down shifts it likes to lock the wheels which makes it quite nerveous.
The engine brakes down the car a lot and with additionally aply of the brakes this locking comes in.

After careful measurement it seems that the rear springs are stiff with 310lb and second is, because of the stiff spring there is almost no rebound travelway, just an inch then the wheels are off the ground.

What do TR8 racers use on the rear coil over type as a spring?

Cheers
Chris





Edited 1 time(s). Last edit at 01/01/2015 04:39PM by MadMarx.


roverman
Art Gertz
Winchester, CA.
(3188 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Rear spring rates - IMSA TR8
Posted by: roverman
Date: January 08, 2015 04:44PM

So YOUR the proud owner ! Congratulations ! I have a Huffaker TR8 GT1, so rear rate should be similar. AIR, my rear is 250 lb/in ? I shall check. My car has a 3 bar set-up, with tunable IC., on single upper bar. I pulled the non-adjustable Carreras off, and went with double adjustable, QA1's. Good Luck. roverman.


tr8todd
Todd Kishbach

(390 posts)

Registered:
12/04/2009 07:42AM

Main British Car:
Re: Rear spring rates - IMSA TR8
Posted by: tr8todd
Date: January 11, 2015 07:40AM

My general rule of thumb was to go as low and soft as I could without letting the rear bottoming out.(175# to 300# on a 2600# TR8 with driver) Keeping the rear wheels on the ground on a bumpy track was always an issue. The softer I went in the rear, the stiffer the sway bar needed to be front and rear to keep the car from leaning.
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MadMarx
Christian Marx
Germany
(54 posts)

Registered:
01/02/2014 11:54AM

Main British Car:
1977 Triumph IMSA TR8 Group 44 Canada Rover 4L

authors avatar
Re: Rear spring rates - IMSA TR8
Posted by: MadMarx
Date: January 12, 2015 03:07PM

Yes, I'm the proud new owner. Was a really surprise when the car was offered to me.

The engine sounds so sweet.

I'm thinking about to go down from the 310 lb to a 220 lb rear spring.
And making the travelway a bit longer.
I did soften the car on the front also. Going down from 600 to 500 which cured the understeer.
The rear axle is located by a 4 rod system and a z-bar.
Seems to work pretty well.
Sway bars at front and rear. 28mm on front. The rear one I don't know....maybe 19mm.

I'm also not sorted out the tire question: Radial or bias ply.
Radials are hard to get in Europe and sold for gold.
Bias plys from USA are reasonable priced.
For the moment it seems the radials are faster but that is maybe a setup issue.
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MadMarx
Christian Marx
Germany
(54 posts)

Registered:
01/02/2014 11:54AM

Main British Car:
1977 Triumph IMSA TR8 Group 44 Canada Rover 4L

authors avatar
Re: Rear spring rates - IMSA TR8
Posted by: MadMarx
Date: January 12, 2015 03:08PM

BTW....a Huffaker is a great car to have. !!!


mgb260
Jim Nichols
Sequim,WA
(2463 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Rear spring rates - IMSA TR8
Posted by: mgb260
Date: January 12, 2015 03:51PM

Great car! I think your guess at 220 would be good. Most like 200-250 for rear coil overs. Look at Tire Rack for specs on American Track tires.


MadMarx
Christian Marx
Germany
(54 posts)

Registered:
01/02/2014 11:54AM

Main British Car:
1977 Triumph IMSA TR8 Group 44 Canada Rover 4L

authors avatar
Re: Rear spring rates - IMSA TR8
Posted by: MadMarx
Date: January 18, 2015 12:10PM

Very good I'm on the right trail with the 220 rate springs.
I think the car is too light to use heavier springs.

Cheers
Chris



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