Anyone care to help with some setup problems?
Discussion
Hi folks
I hope all you racer-folks don’t mind this post in here, but as it’s Tuscan Challenge chassis specific I guess this is where the experts will be hanging out. I don’t race the car so any info shared isn’t going to be used against you in anger
, but it does do a real high number of track miles and my aim is just to pedal it as fast as I’m capable and do ‘personal bests’. Thanks in advance for your time on this post if it’s the sort of challenge you can assist with!
Here’s my problem – I’m no chassis/setup expert and while I’ve got the car set up fairly well (I think), there are two problems that I think are related – understeer and bad inside front tyre wear.
As background, the chassis and suspension are ‘standard’ (Penske shocks). At the front I have toe out of 1/8’, and 1/8’ toe in at the rear. Camber at the front is 4 degrees negative (way less than I’ve seen on the kosher racers), and negative 2 at the rear. The front ARB is in the middle position and there is no rear ARB (and no opportunity now to fit one since the tank’s there). It’s running the springs it raced with; don’t know the rating but obviously there’s more weight with the SBC as opposed to the AJP. Interestingly though the car does actually have its weight distributed 50:50 (it was weighed for the SVA).
I do run it on the road for fun on road tyres, but these queries regard slicks; I’m not really too bothered what it does on the road, it’s the track setup I need to work on.
Behind the wheel it feels like it handles really well; very controllable and ‘catchable’, even in the wet and I don’t want to upset that. The high speed handling seems spot-on in fact. But on slow to medium corners it understeers and that is the limiting factor on speed; put on more power and it just pushes wider scrubbing the front tyres, unless of course you provoke an oversteer.
Now here’s where I can’t work out what to do. As far as I understand it softening the front ARB should help the understeer. Likewise, putting on more negative camber at the front should help the turn-in. But I’m already getting hellish tyre wear on the inner edge of the inside tyre and these changes would (I’m speculating) make it even worse. I’m not aware that the other Tuscans rip their tyres up like mine does even with more camber.
The first pic is the aftermath of Oulton. I ran about 60 laps on the day starting out with a second-hand but evenly worn set of Dunlop (ex Challenge) slicks; 3mm depth across the tyre. The outside tyre has worn pretty evenly, but the inside tyre has had the ‘tread’ scrubbed off the edge and into a band round the tyre.
More importantly, it’s scrubbed through to the canvass in 60 laps! You can also see the angle of the wear. So on the face of it I’m thinking take some of the camber off, not put more on?
But now I’m looking at some photos (Knockhill, courtesy of John Stewart, Flat-Out photography) that has me thinking maybe the ARB is too soft…but stiffening it would make the understeer worse surely? This is McIntyres so 55mph at the point of the photo. Outside tyre is flat and given it’s distortion off the rim looks like it’s getting good grip. But the inside is scrubbing its edge.
More of the same.
And in this the inside tyre is actually off the deck, but there’s not much body roll…
More if it helps anyone diagnose what to adjust. This is braking for the hairpin – fair amount of nose dive but the springs don’t ‘feel’ too soft, and it doesn’t skip under braking.
Then the actual hairpin following, which is about 35mph. Again the inside tyre is scrubbing its edge.
Finally a slightly quicker corner – maybe 70mph or so. I guess running the kerb hasn’t helped but again the inside wheel is off the deck. But while on the previous slow corners the car does feel understeery, this is at the end of the straight into Duffus and behind the wheel this feels solid as a rock!
So, there we have it. What would you folks do to stop the slow speed understeer and inside tyre wear but not mess up the high-speed handling?
Many thanks.
I hope all you racer-folks don’t mind this post in here, but as it’s Tuscan Challenge chassis specific I guess this is where the experts will be hanging out. I don’t race the car so any info shared isn’t going to be used against you in anger
, but it does do a real high number of track miles and my aim is just to pedal it as fast as I’m capable and do ‘personal bests’. Thanks in advance for your time on this post if it’s the sort of challenge you can assist with!Here’s my problem – I’m no chassis/setup expert and while I’ve got the car set up fairly well (I think), there are two problems that I think are related – understeer and bad inside front tyre wear.
As background, the chassis and suspension are ‘standard’ (Penske shocks). At the front I have toe out of 1/8’, and 1/8’ toe in at the rear. Camber at the front is 4 degrees negative (way less than I’ve seen on the kosher racers), and negative 2 at the rear. The front ARB is in the middle position and there is no rear ARB (and no opportunity now to fit one since the tank’s there). It’s running the springs it raced with; don’t know the rating but obviously there’s more weight with the SBC as opposed to the AJP. Interestingly though the car does actually have its weight distributed 50:50 (it was weighed for the SVA).
I do run it on the road for fun on road tyres, but these queries regard slicks; I’m not really too bothered what it does on the road, it’s the track setup I need to work on.
Behind the wheel it feels like it handles really well; very controllable and ‘catchable’, even in the wet and I don’t want to upset that. The high speed handling seems spot-on in fact. But on slow to medium corners it understeers and that is the limiting factor on speed; put on more power and it just pushes wider scrubbing the front tyres, unless of course you provoke an oversteer.
Now here’s where I can’t work out what to do. As far as I understand it softening the front ARB should help the understeer. Likewise, putting on more negative camber at the front should help the turn-in. But I’m already getting hellish tyre wear on the inner edge of the inside tyre and these changes would (I’m speculating) make it even worse. I’m not aware that the other Tuscans rip their tyres up like mine does even with more camber.
The first pic is the aftermath of Oulton. I ran about 60 laps on the day starting out with a second-hand but evenly worn set of Dunlop (ex Challenge) slicks; 3mm depth across the tyre. The outside tyre has worn pretty evenly, but the inside tyre has had the ‘tread’ scrubbed off the edge and into a band round the tyre.
More importantly, it’s scrubbed through to the canvass in 60 laps! You can also see the angle of the wear. So on the face of it I’m thinking take some of the camber off, not put more on?
But now I’m looking at some photos (Knockhill, courtesy of John Stewart, Flat-Out photography) that has me thinking maybe the ARB is too soft…but stiffening it would make the understeer worse surely? This is McIntyres so 55mph at the point of the photo. Outside tyre is flat and given it’s distortion off the rim looks like it’s getting good grip. But the inside is scrubbing its edge.
More of the same.
And in this the inside tyre is actually off the deck, but there’s not much body roll…
More if it helps anyone diagnose what to adjust. This is braking for the hairpin – fair amount of nose dive but the springs don’t ‘feel’ too soft, and it doesn’t skip under braking.
Then the actual hairpin following, which is about 35mph. Again the inside tyre is scrubbing its edge.
Finally a slightly quicker corner – maybe 70mph or so. I guess running the kerb hasn’t helped but again the inside wheel is off the deck. But while on the previous slow corners the car does feel understeery, this is at the end of the straight into Duffus and behind the wheel this feels solid as a rock!
So, there we have it. What would you folks do to stop the slow speed understeer and inside tyre wear but not mess up the high-speed handling?
Many thanks.
Guillotine said:
Tyre pressures?
and can we have the cambers in degrees please.
ta
27psi hotand can we have the cambers in degrees please.
ta
4 degrees front, 2 degrees rear
I think 4 degrees is way less than the cars race on, but looking at the pix I'm guessing more camber is going to make the problem worse, and at 4 degrees the outside wheel does seem to be flat on the tarmac on corners.
Guillotine said:
pressures ok
camber is a bit light. we run -6 (to -8 for twisty cicuit).;)
Wasn't sure of the figure, but knew it was more than me. But I'm guessing (only a guess mind) that putting on more camber is just going to put the inside tyre more on edge and make it worse?camber is a bit light. we run -6 (to -8 for twisty cicuit).;)
Guillotine said:
what is the tyre diameter compared to road tyre? slick = 640mm iirc.
It's on ex-challenge slicks [the very last set in my hoard!] so 640mm. Given the next set is going to have to be new and cost me a packet I want to get to the bottom of the problem now. Everything was measured on the slicks not the road tyres (which are R888s btw). I'm trying to get it 100% on track; whatever that does to road manners/tyres doesn't really matter as it just goes for the occasional forray on the Queen's highway to blow away the cobwebs and scare the good people of Fife Guillotine said:
Also it looks like your tyre is worn through in one spot. is it flat spooted by braking?
There are other spots around the tyre in the same state, but no doubt braking contributed to it...but only on the inside edge.Guillotine said:
60 laps on worn rubber aint bad btw
Yes, but all the other 3 tyres always wear evenly across the whole width. The Oulton example/pix was just easy to measure since I started with 4 equally worn tyres (all 3mm on the 'dimples'). Both rears and outside front are worn, but evenly and still have life left in them. Inside front is demolished on the inside edge and still measures 3mm at the outside, so the outside of that tyre is really doing nothing.Maybe another theory? I've been thinking about this for ages, and if the tyre isn't scrubbing out but is just rolling I suppose even on it's edge is shouldn't wear too much. So the inside tyre has to be getting dragged sideways slightly to rip the 'tread' rubber back, so maybe the problem is the outside tyre, although flat on the tarmac, isn't giving enough grip? What I'm maybe misunderstanding is I'm assumed that both front tyres should be sharing the work on cornering amd I can't see how the inside tyre can run flat on the tarmac with the camber. Should I be thinking that all the cornering at the front should be on the outside tyre only and the inside is just a passenger? On that basis I'd want to get weight off the inside tyre and not on it.
Sounds counter intuitive to me but maybe softening the ARB and increading the camber would put more grip on the outer tyre, meaning the whole front-end didn't understeer so less sideways force on the inside tyre? You can see I still haven't quite sussed out the dynamics of all this yet and setting it up has been a bit of trial and error.
Interesting problem there!
So basically you're wearing the right front tyre on the inside edge as it's hardly ever on the ground in a right hand corner. Most of the wear is probably from the tyre slowing down in the air and then being sped back up as it touches the ground again.
From the pictures the car does look a bit soft. Have you tried running the front roll bar on a harder setting? I know that a harder roll bar should give less grip but I have found in cars of similar layout (ginetta g50 and g40) that stiffening the front roll bar gives much more grip mid turn. The car is a little more vague and has less feel on initial turn in but once through that the front has a lot more grip.
If this does work you may have an issue with no bar at the rear however. If the rear is too soft on the ginettas they overheat the rear tyres quite quickly.
Coud be worth a try. Other than that wind some camber off the right front.
So basically you're wearing the right front tyre on the inside edge as it's hardly ever on the ground in a right hand corner. Most of the wear is probably from the tyre slowing down in the air and then being sped back up as it touches the ground again.
From the pictures the car does look a bit soft. Have you tried running the front roll bar on a harder setting? I know that a harder roll bar should give less grip but I have found in cars of similar layout (ginetta g50 and g40) that stiffening the front roll bar gives much more grip mid turn. The car is a little more vague and has less feel on initial turn in but once through that the front has a lot more grip.
If this does work you may have an issue with no bar at the rear however. If the rear is too soft on the ginettas they overheat the rear tyres quite quickly.
Coud be worth a try. Other than that wind some camber off the right front.
OK, things have moved on slightly - maybe. The tyre wear remains an issue, but where I felt the car understeer on tight corners, I've been comparing data logs with some other [very rapid] cars - like time-attack winning - and I'm actually carrying more speed at these points! So while the car feels like it's speed-limited by understeer, that limit is maybe just a real limit?
But it is coming out of slower tight corners (hairpins or 90 degrees plus), so putting the power on at say 50mph or so the car wants to push wide and I can feel the front struggling for grip. But maybe there's just no more grip to be had and I should just ease off a bit.
Wear remains high though on the inside edge of the inside tyre, but I've bought an angle gauge and pyrometer so next session I'll start messing around with the settings a little. Car laid up right now while I helicoil the back of the diff. Original diff bracket got ripped apart so made a monster strong bracket. It's still there, but the diff pulled off it, and just after I put in a higher ratio one
But it is coming out of slower tight corners (hairpins or 90 degrees plus), so putting the power on at say 50mph or so the car wants to push wide and I can feel the front struggling for grip. But maybe there's just no more grip to be had and I should just ease off a bit.
Wear remains high though on the inside edge of the inside tyre, but I've bought an angle gauge and pyrometer so next session I'll start messing around with the settings a little. Car laid up right now while I helicoil the back of the diff. Original diff bracket got ripped apart so made a monster strong bracket. It's still there, but the diff pulled off it, and just after I put in a higher ratio one
Hi again,
this is what a worn out Tuscan slick looks like...
http://www.tvrmonster.com/newscllbrands11.html
and a pic of mine exiting a slow hairpin (Melbourne - Donny) we're three wheeled at most slow corner exits. The flatspot on there is due (as ben said) to the free wheel picking up again on exits.
You can see, we run them much softer than yours.
The quicker they are, the faster the tyres go...yours is wearing further across as you are running less camber than normal.
Andy
this is what a worn out Tuscan slick looks like...
http://www.tvrmonster.com/newscllbrands11.html
and a pic of mine exiting a slow hairpin (Melbourne - Donny) we're three wheeled at most slow corner exits. The flatspot on there is due (as ben said) to the free wheel picking up again on exits.
You can see, we run them much softer than yours.
The quicker they are, the faster the tyres go...yours is wearing further across as you are running less camber than normal.
Andy
Edited by Guillotine on Tuesday 2nd August 18:29
Andy,
I'm just learning about this finer issue of car set up, at the moment as you know.
Am i right thinking that his understeer could be due to too many heat cycles through the tyre leaving it with less grip at the same tempreture as a fresher tyre,the Dunlop is quite a hard wearing tyre but to go to the canvass would indicate a well used tyre ? but then i'm confused as he isn,t getting understeer on entry.
I would tweek up the ride height at the rear, putting more weight over the front, not make the front harder as some are thinking of and soften the rear to maintain apex to exit weight.Why isn't he getting under steer on entry at the moment?Is it because he is set hard at rear or front or both ?
I'm just learning about this finer issue of car set up, at the moment as you know.
Am i right thinking that his understeer could be due to too many heat cycles through the tyre leaving it with less grip at the same tempreture as a fresher tyre,the Dunlop is quite a hard wearing tyre but to go to the canvass would indicate a well used tyre ? but then i'm confused as he isn,t getting understeer on entry.
I would tweek up the ride height at the rear, putting more weight over the front, not make the front harder as some are thinking of and soften the rear to maintain apex to exit weight.Why isn't he getting under steer on entry at the moment?Is it because he is set hard at rear or front or both ?
Edited by wadsapple on Tuesday 2nd August 21:48
wadsapple said:
Andy,
I'm just learning about this finer issue of car set up, at the moment as you know.
1 Am i right thinking that his understeer could be due to too many heat cycles through the tyre leaving it with less grip at the same tempreture as a fresher tyre,the Dunlop is quite a hard wearing tyre but to go to the canvass would indicate a well used tyre ? but then i'm confused as he isn,t getting understeer on entry.
2 I would tweek up the ride height at the rear, putting more weight over the front, not make the front harder as some are thinking of and soften the rear to maintain apex to exit weight.
3 Why isn't he getting under steer on entry at the moment?Is it because he is set hard at rear or front or both ?
Hi MateI'm just learning about this finer issue of car set up, at the moment as you know.
1 Am i right thinking that his understeer could be due to too many heat cycles through the tyre leaving it with less grip at the same tempreture as a fresher tyre,the Dunlop is quite a hard wearing tyre but to go to the canvass would indicate a well used tyre ? but then i'm confused as he isn,t getting understeer on entry.
2 I would tweek up the ride height at the rear, putting more weight over the front, not make the front harder as some are thinking of and soften the rear to maintain apex to exit weight.
3 Why isn't he getting under steer on entry at the moment?Is it because he is set hard at rear or front or both ?
1 Yes, but the whole car will go away as all the tyres degrade (generally) and alot of laps isn't the same as alot of heat cycles. I think 4 or 5 hrs is what the endurance boys do before changing.
2 The fronts are already working quite hard but balance seems good. Adjusting ride height will effect balance badly (he seems quite happy with overal performance)
3 rare to get turn in problems on a big car with big rubber. If you have it its usually excessive rebound or front spring rates too high.
BTW, I'm only a punter on here mate, Ben's WAY more qualified in car set up/training etc etc.
Highly recommended.
Andy
Incidentaly TVRolet...what are your spring rates and on what dampers?
Guillotine said:
wadsapple said:
Am i right thinking that his understeer could be due to too many heat cycles through the tyre leaving it with less grip at the same tempreture as a fresher tyre...
Incidentaly TVRolet...what are your spring rates and on what dampers?But I had started to question the tyres myself as the culprits. I bought a few sets of second hand slicks that had been used in the Challenge series, so I'm guessing they could be 8 years old or more! I've been working through them over the years and they're all I've ever ran on the car on track so nothing to compare against. I'd always just assumed that the old tyres would just offer less grip but otherwise the wear pattern would be the same as new tyres. My current thinking is that maybe the tyres are just giving all they can and looking at the photos of the car all the tyres seem to be flat on the road except the inside front which is on edge or lifting. If the car is actually drifting and scrubbing rubber then the tyres flat on the road would wear evenly, but the inside front would tear its edge. I'm just wondering now if the car is actually set as best I can (or near enough) and with grippier tyres it maybe wouldn't be scrubbing so much and so would save the inside front?
The car still has the Pi data logger (and spends most of its time at Knockhill) and where I feel it's oversteering at McIntyres (and the hairpin) it's pulling 1.15g which is maybe all the outside front can handle on old tyres?
Still plan to do some experimentation with settings though - even bought a 'how to make your car handle' books
Good morning,
I,m sure some one will be along to advise on the tyre issue you might have with 8 year old rubber,I'd use them to lean my boat up against the harbour wall
If you take a spring off the damper you will find the weight number stamped on the top of the flat part of the coil where it sits on the shoulder of the ring usually.Is the chevy lump Iron block ?
I,m sure some one will be along to advise on the tyre issue you might have with 8 year old rubber,I'd use them to lean my boat up against the harbour wall
If you take a spring off the damper you will find the weight number stamped on the top of the flat part of the coil where it sits on the shoulder of the ring usually.Is the chevy lump Iron block ?You can't be doing too badly if you are pulling 1+g, to start with.
It's been a few years since i had anything to do with TVR Challenge cars, but looking at the pics and the description a few things come to mind.
Lifting the inside front tyre on power on out of corners is obviously going to give you understeer, because you have transferred all the weight of that corner to the other side and some to the rear. Tyres increase grip with vertical load, but not linearly, so your efficiency (efficincy = lateral g) will reduce massively.
As the cars in the pics look to be squatting a lot on power on, and you have understeer i'd suggest stiffening the rear springs. This will help stop the front inside lifting and negate some understeer. You can easily test this theory to a limited degree by increasing the damping on the rear significantly. If it feels less likely to understeer after doing that test then for the next time out put some stiffer rear springs on.
I'd suggest the Chevy lump might be heavier if this is a problem the race cars don't have, but, i'm pretty sure the above will help solve the problem.
It's been a few years since i had anything to do with TVR Challenge cars, but looking at the pics and the description a few things come to mind.
Lifting the inside front tyre on power on out of corners is obviously going to give you understeer, because you have transferred all the weight of that corner to the other side and some to the rear. Tyres increase grip with vertical load, but not linearly, so your efficiency (efficincy = lateral g) will reduce massively.
As the cars in the pics look to be squatting a lot on power on, and you have understeer i'd suggest stiffening the rear springs. This will help stop the front inside lifting and negate some understeer. You can easily test this theory to a limited degree by increasing the damping on the rear significantly. If it feels less likely to understeer after doing that test then for the next time out put some stiffer rear springs on.
I'd suggest the Chevy lump might be heavier if this is a problem the race cars don't have, but, i'm pretty sure the above will help solve the problem.
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