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Front suspension Phase 2 (Triumph)
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calex_fr
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Joined: 18 Jul 2008
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Location: Champagne (France)

PostPosted: Sun Oct 12, 2008 4:11 pm    Post subject: Reply with quote

calex_fr wrote:
Ok I can mesure 1 and 2, but for the diameter of my anti-roll bar I must take off a wheel !

My anti-roll bar is very special fitted I find !


1 is 17cm

and here you can see the angle :



Not easy to mesure, but flat.
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Alexandre Contat

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Dave-M
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PostPosted: Sun Oct 12, 2008 8:23 pm    Post subject: Reply with quote

Thanks Alex, That is just what I needed to see
Regards
Dave
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Ph.2 Ford 1500 GT
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Dave-M
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PostPosted: Sun Oct 12, 2008 8:32 pm    Post subject: Reply with quote

Anyone got any thoughts as to why our cars are running a catsor angle of between 10 and 14 degrees.
The picture below shows a typical example (hope you don't mind Rod).

Regards
Dave


Last edited by Dave-M on Mon Oct 13, 2008 11:34 am; edited 1 time in total
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Paul Narramore
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Location: Aylesford, Kent.

PostPosted: Mon Oct 13, 2008 8:13 am    Post subject: Reply with quote

Sadly the car's designer Richard Parker is no longer with us and I doubt if the question was asked whilst he was alive. Why he deviated from the existing Herald/Spitfire castor angles, I don't know. Presumably is gives more self centring behaviour.

One Ph2 I drove had so much bump steer it felt positively dangerous, and that was whilst being driven on a local (bumpy) motorway. But that's another problem.
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calex_fr
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PostPosted: Mon Oct 13, 2008 8:49 am    Post subject: Reply with quote

I find that, perhaps can it help you :

http://auskellian.com/paul/links_files/spring%20free%20length%20calculator_v7.xls

Quote:
Achieve Better Suspension Geometry—Lower and Stiffen the Front

The purpose of good suspension geometry is to ensure proper positioning of the tires relative to the road for good grip, which results in safer and faster handling. Changing wheel alignment and lowering the Spitfire—particularly the front end—can do a lot for handling. Most Spitfires have their front ends too high for optimum suspension action. Lowering brings the c.g. is closer to the ground, which helps reduce roll in turns, which helps maintain proper suspension geometry during turns, which keeps the tires in proper contact with the road so they can grip, which enables faster speeds through turns. Dive during braking and squat during acceleration are also reduced, and bump steer will be changed yet limited. But it's not just a matter of lower is better, because too low is bad (not enough ground clearance for everyday use, and bad suspension geometry that makes handling worse). The right amount of lowering, especially the front, optimizes the geometry of the suspension links so that the car will roll less for a given c.g. location. Good front suspension geometry for an all-around Spitfire is when the lower A-arms are about parallel with the ground. This happens when the compressed length of each front coil spring is about 7 inches installed on a standard damper (shock absorber) with fixed lower spring perches and with the car at rest on level ground. Having the lower A-arms about parallel with the ground favorably locates the car's roll center while also lowering the c.g.


There are a three basic ways to lower the front: shorten the stock springs, replace them with shorter ones or install front dampers (shock absorbers) that have adjustable spring perches. Adjustable spring perch dampers allow fine adjustment of static ride height and provide the most flexibility, but they are expensive and you can avoid having to use them if you pick the correct stiffness and free length of coil springs. The least expensive way to lower the front is to simply cut one free coil off one end of each of the stock springs. This shortens and slightly stiffens the springs, and the pigtail left by this operation will compress and not be an issue once installed in the car. On the Spitfire 1500, this will result in the desired installed static coil length of about 7 inches. Alternatively, you can cut about half a free coil off one end of each spring and then heat and carefully reform and flatten the cut ends. However, this is not easy to do correctly. The application of too much heat can ruin the temper of the springs, and getting two springs to come out the same is difficult and not guaranteed. In either case, this shortening of the stock springs will stiffen them approximately 10 percent, and this additional stiffness is good because it will limit suspension travel and help offset the loss of suspension travel distance that comes with lowering. Another way to go with the Spitfire 1500 is to install springs from a mk3 or mkIV Spitfire. These springs are shorter yet softer than the stock 1500 ones, so the front end will come down. This works, resulting in an installed spring length of about 7¼ inches, but this approach has the disadvantage of softening while lowering, thus increasing the likelihood of bottoming-out the suspension. Running out of suspension travel and hitting the bump stops is harsh and potentially damaging to your car. A good way to go is to replace the stock springs with shorter and stiffer ones that have the right combination of stiffness and free length such that the target installed length of about 7 inches is achieved. Some Spitfire parts vendors sell such springs, or you can use my spring calculator to specify your own, which you can then buy from a multitude of vendors that sell 2½ inch inside diameter coil springs to racers and custom car builders. Be advised that going too stiff will limit body roll but may make for an unpleasant ride on the street, and not going stiff enough may allow too much body roll and will increase the chance that you will bottom-out your suspension on the bump stops. The front coil springs that I use on my 1978 Spitfire 1500 are 250 pound per inch stiffness and 10 inches free length. They have an installed length of 7 1/8 inches in my lightweighted car and they are neither too stiff nor too soft for my tastes, and the car handles very nicely. Here's how this setup turned out:
Something that you should do when lowering the front (even if you use stiffer springs, which will reduce the amount of travel for a given load) is to make sure you have adequate suspension travel before hitting the rubber or rubber-like bump stops contained in the front shocks. Trimming the front bump stops to be no less than 1/2 inch thick but no more than 3/4 inch thick should ensure adequate travel while also protecting the shocks against internal damage.


One thing that lowering the front will also do that is favorable is to push the camber of the front wheels toward the negative. An otherwise stock 1500 will end up at around 0.5 to 1 degrees of negative camber just by lowering described above such that the lower A-arms are parallel to the ground. Some negative camber at the front is desirable in that it aids entry into turns, and a little bit such as 0.5 to 1 degree negative will not cause uneven tire wear. Front camber is adjustable using shims between the lower A-arms and the frame. Another thing that lowering the front end will do is change the at-rest toe setting, so be sure to realign the front wheels. 1/16 inch toe-in as prescribed in the repair manuals is a good setting for all-around street use. I've developed a simple, quick and inexpensive way to make your own front toe adjustments. Bump steer, which is the change in toe and steering behavior due to motion of the suspension, is a feature of the Spitfire, and lowering the front suspension exacerbates it by increasing the angle of the steering tie rods. While bump steer is still acceptable with the aformentioned changes, shimming the steering rack to raise it to make the steering tie rods more horizontal at rest can help compensate.

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Alexandre Contat

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Dave-M
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PostPosted: Mon Oct 13, 2008 9:01 am    Post subject: Reply with quote

Yes Alex, That's the sort of thing that I have and it will be intersting to compare results.
Regards
Dave
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zefarelly
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PostPosted: Mon Oct 13, 2008 9:39 am    Post subject: Reply with quote

look at my top wishbone arms . . . . they're shortened . . .

http://www.throbnozzle-racing.co.uk/gallery/ROchdale/rochdale.htm
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calex_fr
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PostPosted: Mon Oct 13, 2008 9:53 am    Post subject: Reply with quote



I don't know, perhaps engine/gear mounts ?
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Alexandre Contat

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Paul Narramore
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PostPosted: Mon Oct 13, 2008 5:56 pm    Post subject: Reply with quote

Joe
What's a Rochadale? Very Happy
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zefarelly
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PostPosted: Tue Oct 14, 2008 12:43 pm    Post subject: Reply with quote

Eets a Rochdale with an Italian tweeest Rolling Eyes
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calex_fr
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PostPosted: Wed Oct 15, 2008 9:25 am    Post subject: Reply with quote

Perhaps that can help you :


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Alexandre Contat

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Dave-M
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PostPosted: Wed Oct 15, 2008 10:02 am    Post subject: Reply with quote

Good find Alex, I have printed it and will compare to our Rochdales dimensions.
Regards
Dave
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calex_fr
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PostPosted: Wed Oct 15, 2008 11:09 am    Post subject: Reply with quote

Yes it will be interesting to see that :


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Alexandre Contat

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zefarelly
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PostPosted: Thu Oct 16, 2008 7:54 am    Post subject: Reply with quote

Turners handle well and are competitive so it might prove wise to copy that! and scrap the Rochdale subframe!

I also have one in the workshop so I can check it for reference
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calex_fr
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PostPosted: Thu Oct 16, 2008 8:02 am    Post subject: Reply with quote

zefarelly wrote:
Turners handle well and are competitive so it might prove wise to copy that! and scrap the Rochdale subframe!


yes, and Triumph front shape has good reputation, it does work well on our Rochdale !
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