Ross Nicol
GT40s Supporter
I'm trying to retain my 18° of steering angle for the reasons you describe Kalun.
Ross
Ross
What causes heavy steering at racing speeds
- Thread starter Russ Noble
- Start date
Chris Duncan
Supporter
Increased outer offset could be more room for bigger calipers/brakes, suspension points further outboard for increased footbox room and scrub...
Pete McCluskey.
Lifetime Supporter
Ross "Bloody Hell" what tyre pressures do you run in the dry?
Jim,
°j°u°s°t°°f°o°r°°u°°p°e°t°e°
How nice thank you.
Jim,
°j°u°s°t°°f°o°r°°u°°p°e°t°e°
How nice thank you.
Ross Nicol
GT40s Supporter
Pete - 23 lb cold pressure in the slicks all round.
Russ - I know I seem to have hijacked your thread but we are still on topic. The reading I have done today on 'scrub radius' seems to confirm that too much can lead to heavy steering and too little or zero can leave you with no feel in the steering as well as heavy steering while parking.
Ross
Russ - I know I seem to have hijacked your thread but we are still on topic. The reading I have done today on 'scrub radius' seems to confirm that too much can lead to heavy steering and too little or zero can leave you with no feel in the steering as well as heavy steering while parking.
Ross
Ross Nicol
GT40s Supporter
Some pics - Cortina upright, Original Rotor/hub, Slick tyres after PI race meeting.
Ross
Ross
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Ross, why such high tyre pressures ? Have you checked cross tyre temps after a race ?
Pete McCluskey.
Lifetime Supporter
Just beat me to it Frank, Ross grab a temp gauge if you don't already have one and measure the temps across the tire, after a couple of hot laps. Ideally no greater variation than 10 degree's F. from inside, middle, outside is aimed for.
Russ N,
My comment was not necessarily directed to Iains setup, it was a general comment as to what can be achieved by mounting shocks/spring on a "linkage' system rather than direct to wishbone.
I am not in agreement with zero scrub radius, perhaps Kalun Likes finger tip steering, it is but one of the many things that go to steering load.
There is no "rule Book" that states X amount of scrub radius is excessive, it all depends on the package and what the designer wants to achieve.
Looking at a front suspension in isolation does not give you the total picture.
Ackerman
here is a series of plots
Vehicle configuration
Wheelbase 2159 Track 1346 KPI Static 9.5º castor 4º Toe in 1mm Max shock travel in bump 50mm in droop 30mm. Steering rack ahead of the front axle
The only change in the plots is the location of the tie rod at the steering arm
First plot #94
The ackerman is behind the rear axle by 70% of the wheel base
second plot #85 the tie rod location has moved outboard 9mm
The ackerman is behind the rear axle by 23.5% of the wheelbase.
Third plot # 80 the tie rod location has moved outboard a further 5mm
The ackerman 1.97% behind the rear axle Basically 100% ackerman.
Fourth plot #70 the tie rod location had moved outboard a further 10mm
The ackerman is 13.23% ahead of the rear axle approx 86% ackerman.
The tie rod location has moved a total of 24mm. Toe change ( out) on bump steer has increased dramatically (% wise) whilst the toe out in turn has gone from 0.58º to 3.10º @ 30º turn.
The golden rule " you should only change one thing at a time,but you cant"
Who would have thought that moving the tie rod location to change the ackerman characteristics would also have changed the bump steer. The changes to bump steer in the plots may well change a car from good to bad handling.
My comment was not necessarily directed to Iains setup, it was a general comment as to what can be achieved by mounting shocks/spring on a "linkage' system rather than direct to wishbone.
I am not in agreement with zero scrub radius, perhaps Kalun Likes finger tip steering, it is but one of the many things that go to steering load.
There is no "rule Book" that states X amount of scrub radius is excessive, it all depends on the package and what the designer wants to achieve.
Looking at a front suspension in isolation does not give you the total picture.
Ackerman
here is a series of plots
Vehicle configuration
Wheelbase 2159 Track 1346 KPI Static 9.5º castor 4º Toe in 1mm Max shock travel in bump 50mm in droop 30mm. Steering rack ahead of the front axle
The only change in the plots is the location of the tie rod at the steering arm
First plot #94
The ackerman is behind the rear axle by 70% of the wheel base
second plot #85 the tie rod location has moved outboard 9mm
The ackerman is behind the rear axle by 23.5% of the wheelbase.
Third plot # 80 the tie rod location has moved outboard a further 5mm
The ackerman 1.97% behind the rear axle Basically 100% ackerman.
Fourth plot #70 the tie rod location had moved outboard a further 10mm
The ackerman is 13.23% ahead of the rear axle approx 86% ackerman.
The tie rod location has moved a total of 24mm. Toe change ( out) on bump steer has increased dramatically (% wise) whilst the toe out in turn has gone from 0.58º to 3.10º @ 30º turn.
The golden rule " you should only change one thing at a time,but you cant"
Who would have thought that moving the tie rod location to change the ackerman characteristics would also have changed the bump steer. The changes to bump steer in the plots may well change a car from good to bad handling.
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Ross N,
Have you got your tyre rotation correct ??
This clearer set of pictures than previously posted, me thinks outside of tyre working very hard. That crap on the tyre looks more like your own rubber than pickup after the event. Have a chat to your tyre supplier
Have you got your tyre rotation correct ??
This clearer set of pictures than previously posted, me thinks outside of tyre working very hard. That crap on the tyre looks more like your own rubber than pickup after the event. Have a chat to your tyre supplier
Trevor
So the swing radius of the control arms and tie rod (all travelling in the same radius or as close as possible) is obviously more important than the Ackerman if you had to choose.
Jim
°n°o°°p°r°b°l°e°m°°p°e°t°e
So the swing radius of the control arms and tie rod (all travelling in the same radius or as close as possible) is obviously more important than the Ackerman if you had to choose.
Jim
°n°o°°p°r°b°l°e°m°°p°e°t°e
Ross Nicol
GT40s Supporter
Frank and Pete - Tyre temps have been taken post the major camber adjustments and have confirmed tyre pressures pretty right and camber under control. In other words the temp at tyre centre matches the inner and outer and all 3 are within a good band. Not to mention the car feels really hooked up.
Ross
Ross
Ross Nicol
GT40s Supporter
Trevor - Yes the outsides do appear to be working hard and I think the inner edge appear like they could do with more camber. Over all though they look a lot better than they used to.
Ross
Ross
JimC,
Thats my philosophy, varying rack up down back forward plus raise and lower the tie rod at the steering arm to give the desired toe in toe out in turns and or bump steer. FWIW I find ackerman in excess of 100% easier to work with as I am not stuck with the values given by 100% or less ackerman and I dont push cars around the pits.
Thats my philosophy, varying rack up down back forward plus raise and lower the tie rod at the steering arm to give the desired toe in toe out in turns and or bump steer. FWIW I find ackerman in excess of 100% easier to work with as I am not stuck with the values given by 100% or less ackerman and I dont push cars around the pits.
Ross ,
With what did you measure your tyre temp, if you used one of those heat seeking non contact devices they will not give you a true picture. The tyre appearance belies the even temp situation
With what did you measure your tyre temp, if you used one of those heat seeking non contact devices they will not give you a true picture. The tyre appearance belies the even temp situation
Ross Nicol
GT40s Supporter
Ah yes I have been using the heat seeking missile infra red type Trevor. I will lash out before Sandown race meeting and buy the proper temp probe type. I'll rotate the tyres prior as well. Everything I'm reading seems to confirm steering will be heavy with a large gap between steering pivot and tyre centre (scrub radius by name I believe).
Ross
Ross
Check with the avon yoko guy at the track, he had a very small unit that was reasonably priced.
Swap left front for right front dont have to change on the rim, check also the back ones
Scrub does contribute but it is not the be all and end all of handling
Swap left front for right front dont have to change on the rim, check also the back ones
Scrub does contribute but it is not the be all and end all of handling
Ross, please forgive me if you've already given the data that covers this, but how much further outboard is your tyre centreline from the hub face compared with the original torana? I'm asking because a large change in wheel offset over the original spec will wear the bearings prematurely.
The Federal Office of Road Safety sets the maximum permissable change in offset as 25mm per side, but this is of course going to be conservative on a road car. With slicks even this much may be a bit of a worry if you're using standard bearings.
Sorry if this thread is turning into "suggestions that will cost Ross a lot of money", but I support Jac Mac's suggestion of reducing the wheel offset and lengthening your wishbones to keep the track the same (ensuring all the bolt on bits will still fit) particularly if the current load is going to hurt the bearings. The resultant lighter steering would be a bonus.
The Federal Office of Road Safety sets the maximum permissable change in offset as 25mm per side, but this is of course going to be conservative on a road car. With slicks even this much may be a bit of a worry if you're using standard bearings.
Sorry if this thread is turning into "suggestions that will cost Ross a lot of money", but I support Jac Mac's suggestion of reducing the wheel offset and lengthening your wishbones to keep the track the same (ensuring all the bolt on bits will still fit) particularly if the current load is going to hurt the bearings. The resultant lighter steering would be a bonus.
Ross Nicol
GT40s Supporter
Richard offset is 1/8" inboard of the wheel centre.Not sure why you mentioned Torana.Bearings haven't been a problem in 4 years of racing. This discussion has been great for me, I've learnt a hell of a lot and yes you hit the nail on the head.I won't be rushing in to major changes unless I'm absolutely sure of the benefits.Money is definitely an issue. I'll only have time to correct the uneven caster before Sandown race meeting and hopefully have new 2nd gear synchro in the ZF. This year seems to have flown by.
Ross
Ross
My initial reaction was more camber required, not just from the pick up but the graining looks less worked on the inside edge. On my Prosport slicks which are 9 inch wide at the front and 12 at the rear on 17 inch rims, cold tyre pressures are 15 and 17 psi. However my car is 825 kg less driver. Your pressures are my wet tyre pressures.
Or just go through the corners a little quicker to lean the car more and work the whole contact patch. But then that might make the steering heavier!!!!
Paul Thompson 'Hooligan'
Admin
Hi Ross -
I've used 21.5 front and 23 rear (psi) on Avon Slicks - and when it hooks well you really feel the difference.
Be careful about fitment and swapping side to side, as I was informed by Avon Tech, that they should be fitted according to lap of rubber, (denoted by 'xx's on Avons) and it's different for front/rear, so a side to side swap should really require a remove and refit on the rims too, as you'll be reversing the direction of rotation when swapping side to side... It is apparently unusual, but delamination can occur at the 'join' if direction of use is reversed mid-term...
I've used 21.5 front and 23 rear (psi) on Avon Slicks - and when it hooks well you really feel the difference.
Be careful about fitment and swapping side to side, as I was informed by Avon Tech, that they should be fitted according to lap of rubber, (denoted by 'xx's on Avons) and it's different for front/rear, so a side to side swap should really require a remove and refit on the rims too, as you'll be reversing the direction of rotation when swapping side to side... It is apparently unusual, but delamination can occur at the 'join' if direction of use is reversed mid-term...
