Handling and set up

Handling and set up

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Discussion

T0MMY

Original Poster:

1,558 posts

175 months

Monday 6th August 2018
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What set up changes could you make to reduce the propensity of a car to oversteer off the throttle, without making it more understeery when balanced or on the throttle (i.e. not just adding more rear grip)? I'm hesitant to make changes to the geo as the handling's pretty good in general but I was wondering if the fact the car has (what seems to me) quite a lot of positive rake might be the reason it's so twitchy off the throttle or on the brakes?

Car in question is front mid-engined and RWD by the way.

E-bmw

9,105 posts

151 months

Tuesday 7th August 2018
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I am struggling to think how a rwd car would oversteer "off the throttle" unless there is something major wrong with the suspension, has it been checked out & aligned correctly?

T0MMY

Original Poster:

1,558 posts

175 months

Tuesday 7th August 2018
quotequote all
I'd say most RWD cars that are reasonably sporty and "adjustable" are going to potentially oversteer when you're off the throttle, you want to be able to run the whole gamut from oversteer to neutral to understeer just by transferring the weight around.

The geo is set up as per the manufacturer's recommendations and as I say, it's far from terrible, just maybe a bit too pointy in slower corners.

Steve H

5,224 posts

194 months

Wednesday 8th August 2018
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It would depend on the model and what adjustments you have available, options might include -

lose a bit of rake (drop the rear/raise front)

reduce rear toe out (if it has much)

damper changes (soften rear/firmer front)


Any of the above could alter how it feels on quicker turns as well but you'd have to try it to know......



How about driver options? Reduce trail braking into slow corners? More progressive steering?


TBH if it's stable into quicker turns and a bit lively into slower ones I'd mostly think that's a fun thing to drive, pretty ideal for trackdays biggrin.


T0MMY

Original Poster:

1,558 posts

175 months

Wednesday 8th August 2018
quotequote all
Steve H said:
It would depend on the model and what adjustments you have available, options might include -

lose a bit of rake (drop the rear/raise front)

reduce rear toe out (if it has much)

damper changes (soften rear/firmer front)


Any of the above could alter how it feels on quicker turns as well but you'd have to try it to know......



How about driver options? Reduce trail braking into slow corners? More progressive steering?


TBH if it's stable into quicker turns and a bit lively into slower ones I'd mostly think that's a fun thing to drive, pretty ideal for trackdays biggrin.
I was playing with the damping at Rockingham on Sunday as I'd had the shocks rebuilt so they were quite a bit stiffer than they used to be. I have settled on a softer rear to dial out some oversteer in general but had got it about right for most situations so didn't want to go any further in that direction. I'll maybe try playing with the rear ride height at the next track day as like I said, it has quite a bit of rake.

In terms of driver options, I do already drive round it obviously but I feel it costs me time in some places. I was trying to find a good example in the videos from the day but it's quite subtle and hard to really see because obviously the car looks stable when you keep it stable! I noticed it most in the first left of Brooklands chicane where I can trail brake into the corner but then have to give the throttle the tiniest of tickles just to put some weight on the rear as otherwise it will slide at the back. Doing so then gives a smidge of understeer and I think I'd be quicker if I could come off the brakes and stay off the throttle before turning into the righthander. It's a very fine line between oversteer off the throttle and understeer on the throttle at those low speeds. If you've got sharp hearing you can just about hear the throttle blip at 4.49 in this video...

https://www.youtube.com/watch?v=FIZbEIWdpNo

It's also a bit of a handful to turn into Yentwood and Tarzan where again you need to trail brake in to be quick but have to be very careful once you've got quite a bit of steering lock on and pretty much have to be very slightly back on the throttle before the apex which again induces slight understeer. On the other hand the "adjustability" on the throttle is perfect in faster corners like Gracelands so the aim would be to maintain that whilst dialling it out in slower corners (which obviously may not be physically possible to do!).

E-bmw

9,105 posts

151 months

Wednesday 8th August 2018
quotequote all
T0MMY said:
I'd say most RWD cars that are reasonably sporty and "adjustable" are going to potentially oversteer when you're off the throttle, you want to be able to run the whole gamut from oversteer to neutral to understeer just by transferring the weight around.

The geo is set up as per the manufacturer's recommendations and as I say, it's far from terrible, just maybe a bit too pointy in slower corners.
OK, well we are going to have to disagree then as I have driven many "sporty" RWD cars & never experienced oversteer "off the throttle".

HustleRussell

24,602 posts

159 months

Wednesday 8th August 2018
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I'd say your car is handling well. As said, try less rake.

Your lines are very symmetrical i.e. your entries are wide and swooping. It makes me wonder whether your front spring rates are too low.

ETA: Likewise, front roll stiffness

but try rake first, it's free.

Steve H

5,224 posts

194 months

Wednesday 8th August 2018
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I'd agree with Russel about the entries, they do look pretty early although I'd expect going later and sharper to make turn-in-oversteer worse than the lines you were using there.

Just flicking through that video though I'm not seeing many issues on entry to the slower corners and more oversteer than understeer on the exits.


dunc_sx

1,607 posts

196 months

Wednesday 8th August 2018
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E-bmw said:
OK, well we are going to have to disagree then as I have driven many "sporty" RWD cars & never experienced oversteer "off the throttle".
I'm afraid I agree with Tommy in that rwd cars get lift off over steer when provoked. Anything that upsets the speed the driven wheels want to turn at will potentially lose traction on them.

A few questions/points for consideration from me are

1. How tight is the diff?

2. How evenly matched are the revs on your down shift? You could try revving higher during down shifts to see if that helps

3. Can you adjust the rear anti roll bar stiffness? Try softer?

Dunc.

HustleRussell

24,602 posts

159 months

Wednesday 8th August 2018
quotequote all
dunc_sx said:
2. How evenly matched are the revs on your down shift? You could try revving higher during down shifts to see if that helps
Having watched the video. Wouldn’t recommend that to the OP!

Kawasicki

13,041 posts

234 months

Wednesday 8th August 2018
quotequote all
Try some extra rear camber and both a little less and (obviously at another time!) a little more rear tyre pressure. What does your suspension look like? How far away are your spring aids at the rear?..if you have any! Are there any photos of your car from outside mid corner? Your car looks a bit too oversteery to be fast, so I think you could improve it a bit...i.e. you are not being daft!

T0MMY

Original Poster:

1,558 posts

175 months

Wednesday 8th August 2018
quotequote all
HustleRussell said:
I'd say your car is handling well. As said, try less rake.

Your lines are very symmetrical i.e. your entries are wide and swooping. It makes me wonder whether your front spring rates are too low.

ETA: Likewise, front roll stiffness

but try rake first, it's free.
Steve H said:
I'd agree with Russel about the entries, they do look pretty early although I'd expect going later and sharper to make turn-in-oversteer worse than the lines you were using there.

Just flicking through that video though I'm not seeing many issues on entry to the slower corners and more oversteer than understeer on the exits.
Thanks chaps, that's a good point about my lines, especially noticeable at Yentwood where I'm turning in well before the cone on the outside. Sounds odd to say but I genuinely can't quite decide if that was a deliberate (albeit unconscious) thing due to the way the car behaves on turn in or just due to poor technique/inexperience. I'll have to try to make a real conscious effort to turn in later on my next trackday and see how I get on. I'll also try dropping the rear progressively and see what effect it has.

E-bmw said:
OK, well we are going to have to disagree then as I have driven many "sporty" RWD cars & never experienced oversteer "off the throttle".
I don't think I'd want a trackcar that wouldn't oversteer when you lifted off the throttle, FWD or RWD, as that would suggest to me the balance was so far towards understeer that you don't have full control over how the car behaves in a corner. I haven't driven a huge array of cars but Elises, Caterhams and even MX5s will do this. The BMWs I've had (E30 and E36) were much more "stable" and would generally only oversteer under power or quite violent weight transfers so maybe that's what you're thinking of (just going by your name!)?

T0MMY

Original Poster:

1,558 posts

175 months

Wednesday 8th August 2018
quotequote all
dunc_sx said:
A few questions/points for consideration from me are

1. How tight is the diff?

2. How evenly matched are the revs on your down shift? You could try revving higher during down shifts to see if that helps

3. Can you adjust the rear anti roll bar stiffness? Try softer?

Dunc.
1. Not sure what you mean by the tightness of the diff really...it's an LSD off a Sierra in not great condition.
2. it's a bike engined car so you can kind of take the piss with mid corner gear shifts as they're so smooth it doesn't really upset the car that much. I find it much harder to heel and toe smoothly than in my MX5 so don't generally do it on track any more as I found it was upsetting my braking more than it was benefitting my downshifts if you see what I mean. In my MX5, not doing so would massively affect corner entry but in this it doesn't seem to (watching the RGB series these cars race in it doesn't look like they rev match either for the most part).
3. I'd have to add a rear anti roll bar first!! No anti roll bars front or rear.

Kawasicki said:
Try some extra rear camber and both a little less and (obviously at another time!) a little more rear tyre pressure. What does your suspension look like? How far away are your spring aids at the rear?..if you have any! Are there any photos of your car from outside mid corner? Your car looks a bit too oversteery to be fast, so I think you could improve it a bit...i.e. you are not being daft!
I'd like to explore a bit more camber front and rear really but not sure much more is possible. This car is £4000 worth of very agricultural kitcar with sierra uprights etc., no rose joints in sight! I'll have a play with tyre pressures though. Suspension looks like 4 rather old and rusty Protech shocks and unknown springs (no aids), but the shocks were just rebuilt so have some damping these dayssmile There are some photos of the car from my last day at Rockingham here, although this was before the shocks were rebuilt:

http://www.motorsportinfocus.co.uk/2018-event-gall...


Edited by T0MMY on Wednesday 8th August 19:55

Steve H

5,224 posts

194 months

Wednesday 8th August 2018
quotequote all
Anything is possible but I can't see more rear camber reducing oversteer on turn-in when the car hasn't really had chance to lean over and benefit from some neg yet.

Might tame some of the exit oversteer I saw on the video.....

T0MMY

Original Poster:

1,558 posts

175 months

Wednesday 8th August 2018
quotequote all
Steve H said:
Anything is possible but I can't see more rear camber reducing oversteer on turn-in when the car hasn't really had chance to lean over and benefit from some neg yet.

Might tame some of the exit oversteer I saw on the video.....
Not sure about the balance front and rear but looking around the paddock at other Caterhams and clones, I seem to have less camber than most at both ends. As I say though, I'll have to have a look and see how much more is possible.

Steve H

5,224 posts

194 months

Wednesday 8th August 2018
quotequote all
Every se7en is different in the ways you get to the sweet spot but on turn-in I'm not sure you're using all the camber anyway.

But again, the oversteer I saw was mostly at the exit.

T0MMY

Original Poster:

1,558 posts

175 months

Wednesday 8th August 2018
quotequote all
Steve H said:
But again, the oversteer I saw was mostly at the exit.
Yeah, I've got to say, what you and others have said after seeing the video has got me thinking that as much as I enjoy the way the car handles, maybe it would be a quicker car if I dialled out some of the oversteer altogether so could get more power down. The other video I have on YT from that day was following an Elise Trophy car (an Exige S2) and what really struck me was how much better he was able to exit the corners, especially the hairpin. No way could I have got as much power down as he was able to and I don't think they use especially grippier tyres in that series than I use (595RSRs). Better lines/more skill too of course, and more weight over the rear wheels, but still.

Been a really useful discussion for me, so thanks for all the repliesbeer

EDIT: Actually, I'm going to upload the video of the first session of that day just to clarify what I mean about the turn in oversteer as the video you've seen is much later on when I was managing it and it does indeed look like the problem is all on exit.

Edited by T0MMY on Wednesday 8th August 21:34

T0MMY

Original Poster:

1,558 posts

175 months

Wednesday 8th August 2018
quotequote all
Jesus, trying to cut and splice video on YT is a nightmare so I gave up and just pulled out 3 clips. These are all from the first 3 laps of the day when I was getting used to the car again, and the stiffer suspension. Even so, I wasn't taking the piss with the trail braking, just not managing the turn in quite as well as I was later in the day:

Yentwood:
https://www.youtube.com/watch?v=FEKZK8umoQo

Tarzan...you can just hear that although I feather the throttle to try to get some weight to the back of the car, it's not the throttle application that unsettles the rear:
https://www.youtube.com/watch?v=9LlLTfgv3kg

Brook chicane (to be fair, looks like I locked up the front left briefly so turned in a bit fast and a bit late):
https://www.youtube.com/watch?v=nRlx4axwIBU

As you can see, it isn't just an exit issue!

Steve H

5,224 posts

194 months

Thursday 9th August 2018
quotequote all
Yea the one at Brook you added a bit of lock as you approached the apex but that didn't happen on the other two.

On the other hand, I was picturing the oversteer at the entry point rather than towards the apex, I would have thought a bit of rake change would sort that out and it wouldn't need much to get a really nice balance.

BertBert

18,953 posts

210 months

Thursday 9th August 2018
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E-bmw said:
OK, well we are going to have to disagree then as I have driven many "sporty" RWD cars & never experienced oversteer "off the throttle".
Are you sure? If your corner entry speed is too high when you turn in, your wheels will slip. Depending on setup you will feel it as understeer or oversteer. No throttle required!
Bert