Recomended turning lock / turning ciircle

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Recomended turning lock / turning ciircle

Postby paulmason » Sat Aug 03, 2019 7:36 pm

Hi

Can anyone advise on the sort of minimum turning circle a typical 750formula can safely have.

After leaving my Firestorm build moribund for 4 years it's now built up to conform to Historic 750 formula regulations.

I am concerned that the front wheels have insufficient lock due to the short travel from the ex-single seater steering rack the car uses together with Triumph Spitfire front axle stubs. I believe I can overcome the problem by drilling the steering arms nearer to axle line.

Paul
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Re: Recomended turning lock / turning ciircle

Postby F1300Tony » Thu Aug 08, 2019 8:12 am

Sorry, I can't remember the figure, but you do not need as much lock as you might think. I feel I worked on the wheels turning 30 degrees and it was more than enough, but I might be miles out. What I am sure about is that what is a total pain shunting around the paddock is still OK to get around the Mallory hairpin. The right steering ratio is a balance between having the steering wheel too heavy for your strength and the speed needed to catch the car when the back end steps out. Other factors that add to the weight of the steering are the castor angle and scrub radius. The scrub radius is how far outside the centre of the wheel is to where the line of the king pin meets the ground. You need enough castor to make the car stable, particularly under braking, but not so much as to make the steering heavy. What is your current turning circle? The Herald/Spitfire was the tightest of all 4 wheelers at about 30 feet.
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Re: Recomended turning lock / turning ciircle

Postby Martin Kemp » Thu Aug 08, 2019 5:32 pm

On the Merlin I have a mini quick rack ( 2.2 turns) with a spitfire set up and I found that the steering was too low geared for driving in the wet so I shortened the steering arms to 2/3.
It is difficult to measure the Falcon at the moment because it doesn't have the correct number of front wheels, but it looks like 30 deg steering angle and it is just over 1 turn lock to lock. This is just about spot on for driving, but a little bit of a nuisance in the paddock.

I could easily increase the lock by shortening the rack stops which would leave the steering ratio the same, but I don't because if you hit something solid with the front wheels the steering wheel will spin onto full lock and the further it spins the more likely it is to break your thumbs.

Of course you are supposed to let go of the steering just before the accident but I have seen F1 drivers desperately trying to steer a car with no front wheels so I think I might also forget.

Martin
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Re: Recomended turning lock / turning ciircle

Postby paulmason » Thu Aug 08, 2019 9:11 pm

Thank you for your replies.

I have about 30 degrees on full lock so should be ok.

Steering wheel movement lock to lock is one and a quarter turns.

Paul
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Re: Recomended turning lock / turning ciircle

Postby Martin Kemp » Thu Aug 08, 2019 10:08 pm

Sounds good. You should have a better turning circle than the Falcon because your car has a shorter wheelbase

Martin
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Re: Recomended turning lock / turning ciircle

Postby GregSwan » Fri Aug 09, 2019 9:02 am

Martin, do you know (or can measure) the 2.2 Mini rack movement for one 360deg turn of the pinion (guessing somewhere between 1.8 and 2 inches)? Or if you’ve entered the Merlin for Donington perhaps I could measure. Thanks, Greg
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Re: Recomended turning lock / turning ciircle

Postby Martin Kemp » Fri Aug 09, 2019 5:50 pm

I was afraid you were going to ask that as the Merlin has gone to live down the road with some horses.
Still as I was passing I dropped in to see it and get an approximate measurement which is 2" per revolution of the steering wheel.
Actually on the Merlin the steering angle is only about 25 deg because I have fitted rack stops to stop the mudguards fouling the wishbones but it still has a reasonable turning circle.

Martin
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Re: Recomended turning lock / turning ciircle

Postby GregSwan » Sat Aug 10, 2019 2:56 pm

Thanks Martin... perfect.
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