Z4C // H&R rear anti-roll bar, Powerflex RTA bushes and fastest Cadwell lap yet

Added: 2026-05-23

[00:00:12]Hi folks, back in the Zed4 and we went to the racetrack. So last Wednesday went to Cadwell Park for an evening session and it was fantastic.

[00:00:22]um finally enjoying this car in exactly the way I really want to enjoy this car and exactly the the reason I bought it and what I envisioned when I bought it and what I hope to achieve in the project. So it it was one of those days where I'm like, "Yes, this is all coming together. I I really like the car already. I now love the car." Just quickly before I get on with the video, um, when I watch other people's videos, I go into the the description and I'm looking for the spec of the car because I want I see it on track and I want to see what the spec is and I obviously talk about the spec lots and all the modifications I do, but I don't have all the information there in the in one place. So, I I've started a an Instagram uh account for this car. So, it's uh CD um CDZ4, something like I'll put it on the screen so you can see what it is.

[00:01:13]Um, but if you want to know the spec of the car at any time, um, just give that a follow and go to the pinned post and it's a full current spec of the car and I'll continue to update that first pinned post so that if ever any anybody wants to know what the the full spec of the car is, it's right there.

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[00:02:10]Right. So, Cadwell last Wednesday and what do I enjoy so much? So, it was just an evening session. Um, I live about 20 25 minutes from Cadwell. Um, and for me, the way I want to enjoy my my car now.

[00:02:24]um is to do a day's work so I don't have to take a day off, use up my annual leave, finish a little early and drive to the track. Drive to the track in a in a whole car, you know, with the all the modcons and what have you. Um enjoy at the racetrack without the hu, you know, with the minor inconvenience of harnesses and stuff like that. Uh with the air conditioning on, God, I'm old, aren't I? But that's honestly the way I most enjoy driving a car now. thrash it around the track, have a car that feels like a like it belongs at the track and it's at home. Beat on some nicer cars, some Porsche cars, and then drive home in comfort. And that's exactly what I did on Wednesday. It was wonderful.

[00:03:04]Beautiful weather. It was sort of low low teens degrees, so it wasn't particularly warm, but it was lovely blue skies and that sort of evening sunshine. Just it was just perfection.

[00:03:14]And the car was f How about a corner this one?

[00:04:01]So, what's changed since the last time I drove it at the track? Um, the biggest change that we've made is we've added an H&R rear anti-roll bar.

[00:04:12]Um, in fact, it's pretty much the only one. I'll come on to one other minor change as well. So, we've added the H&R rear anti-roll bar. It's a 21 mm anti-roll bar, and I believe the standard one is an 18 mil anti-roll bar.

[00:04:26]This is a wait for this. This is a Z4 coupe 3 L SI.

[00:04:35]So, there is a 3 liter SI M Sport or Sport and an SE. And the M Sport or Sport or whatever it is um has a I think it's a 1 mm or.5 mm thicker rear anti-roll bar. Very posh. Um but this has got the basically the smallest rear anti-roll bar you can get on the coupe. Um so we've gone up from an 18 or whatever it is, I'll correct myself on the screen if it's wrong, to a 21. Um, and it's also uh got three mounting holes on the uh on the rear anti-roll bar on the ends. So, it can be adjusted many ways um to to dial it in. Um, of course, at the front I've got the Hodgekiss um 30 mm hollow anti-roll bar.

[00:05:20]Uh that's also got three settings per side, so lots of adjustment there as well. Um, when installed the rear anti-roll bar from H&R, uh, I've installed it on the firmst setting, so the, uh, the hole that's closest to the bar. Um, and the fronts are currently on the softest setting. So, I've got sort of my raciest uh, most rotaty over steery setup currently. Um, the front bar is roughly equivalent to about 10% stiffer than an E46 M3 27 mil bar. So, it's just a little bit stiffer than that, but fairly comparable to a 27 mil M3 bar. I can obviously ramp that up much further by using the other the other holes at the front. Um, and before I tell you how it felt, uh, the other change, so I was using for dry setup a 225 square, uh, part worn Dunlop dures, um, I bought two more 225 part one derzes um because a couple of them were knackered from blight and it's particularly hard on the um, the front tires actually um, but particularly hard on the the front outside corner. at Blightton. Um, so I bought another pair so I could sort of maximize my usage of this set of wheels, uh, set of tires rather. Um, unfortunately when I went to collect them, they were in fact 215. Um, but they were so cheap that I couldn't say no to them. So um, we've actually got 215 part one donut dresses at the front and two um, part ones on the rear. Um, I say part one cuz they've been raced on and so they have been heat cycled out a little bit. So they're not they're not quite as nice as a nice black set of fresh rubber. Um, but yeah, 215 225.

[00:07:11]We've introduced a bit of a stagger, so that will of course affect the balance a little bit. And they are I'm fully mindful. Look, I'm I'm using those tires cuz they were cheap. Um, I'm mindful they're basically too small for the car.

[00:07:23]So they're a compromise. But hey, they're cheap and they, you know, cheap doesn't preclude fun in this instance.

[00:08:11]So, we know the car was a little bit limited by the tires that are fitted.

[00:08:15]You know, they are track tires. They're good track tires done dures. They're a little bit heat cycled and 215 front, 225 rear. You know, they're too too small for the car. And and on the track that that that showed because they didn't have the heat capacity that a a better size tire would have. Um and so they they sort of they very quickly lost a bit of grip through heat. Um but the car was was fairly quick. It was it it really impressed me both in the the way that the car felt, the enjoyment that I got, and also the the lap times. So, um I'm sure there were quicker things out there on track, but I didn't come across them. Um you know, I was comfortably driving past anything I came across. Um and my best lap of the day was a 142.4, um which I think is pretty good.

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[00:11:14]Um, I didn't string together for a perfect lap. I really didn't. You know, traffic and um tires been in their right operating window. F1. Um they just they just didn't come together. So, I didn't put together a perfect lap. When I did get a free track, I tried to sort of put together a bit of a banker lap as a bit of a baseline for the lap time. So, I wasn't trying to, you know, push the fastest I possibly could. But 142.4, I think, is pretty respectable for what's a, you know, a proper car. Um, pretty modestly sized tires, all bit they're nice track tires. Um, and fairly modest power at what what do we think we're at now? 265 something like that. So, I was really pleased with that. The optimal in fact was 141.7.

[00:11:58]So, something to aim for next time. And of course, 142 141. I think we really need to try and go sub 140, don't we?

[00:12:07]That would be a real achievement in this car without ruining the car. Don't go stripping it out. Don't go doing anything too Larry, but it would be I it would feel like a real accomplishment if I could get this car down to something that I could drive to the track and home in comfort and do a sub 140. Um, now I could fit 245 AO 52s and I'm pretty sure I could do that next time out, but I'm not going to do that cuz I'm not made of money and I've not got, you know, 12,3400 quid to spend on nice fresh fast tires.

[00:12:41]So, yeah, we won't be doing that. I'll try and find a cost-effective way of of doing it like I do with with everything in this car. Um, I do splurge on on some things. Some things I I really want, like the the seats, I think, were an example where I splurged. The rear diff from Quaith was obviously something that I thought the car really had to have.

[00:12:58]Um, but apart from that, I try to be really thoughtful about the way I spend money on this car, so it doesn't run away with itself as being an expensive project.

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[00:14:05]So, the car felt fantastic. We've basically only made that that change of the H&R bar. Um, and the balance is easily the best it's been. Finally, the car rotates. Um, and that's something I've really struggled with this car. It, you know, it doesn't want to turn. When I first took it to the track, um, it did rotate on C on on braking. It did rotate, but it was sort of a weird passive tow out at the rear that was causing it to rotate. So, it was quite a quite a disconcerting feeling. Um, felt very vague, somewhat unpredictable, and it wasn't that I was You could learn to drive it. you could you got two sessions in and you could drive it using that rotation. Um but it was it didn't feel natural. It didn't feel precise. Um and wasn't a nice way to drive the car. So we've sorted that and I'll come I'll come back to that shortly. Um but this is now the first time the balance of the car feels better. Um I think for Cadwell the balance is nice.

[00:15:11]Uh I think at blighting it would be nice. Perhaps if I was trying to set a fastest lap time, I would like to just perhaps slightly soften the rear. So, it's three-way adjustable each side. So, if I just put one of the rear sides down to two, so it's sort of like five out of six, uh, hard still, um, and left the front bar where it is, um, that might be where I'd go just to give myself just a little more rear end confidence that it wasn't going to wasn't going to snap on me. Um, perhaps I could soften it off a little bit. And for the Nurburg Ring, I will soften it off a little bit on the rear um, just to give me more um, more security. You know, I' when I'm at the ring, I don't know the track. Uh I know CAD well very well. Um I would rather have the security of a little bit of under steer at the Nurburg Ring, especially high-speed places, um than I would, you know, a of over steer um when I don't expect it. Um but yes, the balance was really nice. Finally, it feels reactive. It feels like it turns when you want it to. It rotates. It's adjustable. Finally, it's it's driving like a car that's at home on the track.

[00:16:25]Um, and so I am so thrilled with it.

[00:16:28]It's It's been a battle to make this chassis drive well at the track, and we've we've finally achieved it. It's by no means dialed in, so I'm sure there's improvement to be made. I I set the cold pressures and then went out on track and did basically three sessions with with a small break. I didn't even bother checking the hot pressures, so tire pressures were probably all over the place, but I was enjoying it. That's the main thing, isn't it? Most notably, I would say Mansfield and Barn are two corners that are unpleasant if your car wants to push on. Uh, and on both of those corner, it was it was substantially easier to rotate the car in and then not wash out on the corner exit or or in the middle of the corner to corner exit. So, you know, you could finally get on the power a little bit earlier. Um, and that no doubt obviously helps, you know, carry a lot more speed onto the following straights. So, drastically improved and I'm really starting to feel like I'm getting somewhere with this car.

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[00:18:59]Now what I said I come back to with regards to that passive toe uh passive toe out at the rear that we'd we'd felt before. Um that was really unnerving at Cadwell and what I did to change that. I was previously on um Mer HD rear trailing arm bushes uh with some polyurethane limiters as well. That was they were actually fitted by a previous owner to try and um eliminate some behavior that they didn't like. Perhaps it was the same thing that they were trying to eliminate or an even worse version of that. Um, however, I've gone for the Power Flex uh Power Flex Black series um sort of track biased uh rear trailing arm bushes. So, they're a a fairly stiff polyurethane bush. Uh don't need the limiters as well. And it is completely cured that completely. So, I'd reserve judgment previously cuz I haven't actually driven this car on the semislicks in full dry since they were installed. Um, but yeah, cured it completely. So, I think that's a really really good modification. not terribly expensive, but that um that um unwanted movement in the rear trailing arm bush and that uh rear toe that or toe out that it can create um or perhaps that movement through from toe in that the car is set at across neutral to toe out really creates some sort of uncomfortable and unwanted behaviors at the track. especially when you're somewhere like Cadwell where it's, you know, it's a really technical track and there's lots of bumps and undulations.

[00:20:34]There was lots going on previously. Now it feels pretty stable. Um I've still got plenty of rear tow in. I might um reduce that a little bit about 2.5 mil each side is what I've got at the minute. Um so I'll probably reduce that a little bit. Maybe try 1.5 mil per side. Now I'm comfortable. I've got that sort of uh passive tow out solved with the uh with the Power Flex rear trailing arm bushes. Um I don't think you need to worry too much about um NVH with them.

[00:21:06]Um again, I've gone with the the harder black series. Um and I don't think it's I don't think it's something that would ruin your car. Yeah, I think that's really good one for those that are on the track. Not terribly expensive. The power flex rear trailing arm bush. I think it's a good upgrade as well. So, I say I've mentioned the car felt really good. Um, and quite often when I've been in this car at the track, I've sort of looked longingly at sort of M2s or, you know, nicer cars. However, this time I didn't want to be driving anything else.

[00:21:37]And and that for me is, you know, quite an achievement. It means that the way I've progressed this car and the way I've built this as a project is finally coming good. It felt the right size for the circuit. It felt like it reacted like a car that was happy at the track.

[00:21:52]It felt like it had enough power at the track. You know, it's not a power monster, but Cadwell doesn't really need that. You can, you know, you you're relying more on the chassis and perhaps your track knowledge at Cadwell than you are an absolute power. Um M4 Touring, of course, was just pulling away on the straights, as were, you know, some other faster cars, but reeling them in through the corners is what it's all about for me. Um, and also if you've got a fast car, nobody's ever impressed when you're fast, are they? Nobody comes up to you if you've got an M4 or a 911 GT3 and goes, "Can't believe how fast you were."

[00:22:29]Um, unfortunately, we still had fairly major pad knockback at at the track. Um at Blighton I haven't experienced it but the past two times I've been to Cadwell I've had really quite bad pad knockback which you know I do know Cadwell well but it's such a technical circuit and you you're managing the weight and the weight transfer of the car so much that you really need to be able to rely on your brake pedal and of course some of the braking zones you've got very little runoff so I was having to settle the the pads before the corners with attack with the left foot. You know, in some places that's fine. In others, it's it's quite tricky to do and you really don't want to upset the balance. For example, on the rightander on the entry to the gooseeneck, um you've got quite little time between Chris curve and that. So to to make sure I wasn't upsettling the car up settling unsettling the car through Chris curve giving it a tap and getting that pad sat nice ready ready for the application down into Mansfield uh or even on the way into the gooseseneck I gave it a second tap on the way into Mansfield but that was just with the right foot just prior to the breaking zone. Um but yeah I'm I'm just trying to get across that Cadwell is not a place that you want pad knockback. Um I think it's the curbs. I'm very greedy with the curbs at Cadwell. Um I think you kind of have to be to be fairly quick there. So yeah, I've got to sort it. I really have to sort it before the Nurburg Ring. So I'm going to try a different pad. I'm on stock calipers front and rear still. Um I'm on EBC RPX at the front and they are quite a loose pad so they do rattle a fair bit on the road. Um so I'm going to go for something else. I don't know what yet. Um, but I really want to solve the problem. Uh, the rear I'm on pad RS RSL 29s and I I don't think they're the source of the problem. Um, I think it's the front brakes. So, um, watch this space. Um, need to fix that. I think longterm a brake upgrade, but just before the Nurburg ring off, I definitely want a brake pedal I can rely on. So, in summary, absolute enjoyment.

[00:24:42]Thoroughly enjoyed using the car at the track. Cannot wait to go back at the end of May. I've got another evening booked.

[00:24:48]I really look forward to that. Uh the car, the chassis, it all just feels so much better suited now and I haven't ruined it for the road. So, it's going in exactly the right direction. Um I felt a lot of reward and satisfaction from this. Um it it's what I envisioned the car being when when I bought it. And when I first drove it on track, I was quite disappointed. My expectations weren't high, but I thought this is really quite bad and needs a lot of work to get it where it needs to go. So, I'm I'm really proud of what I've achieved with the car. Um, it's it's now really nice to drive and is doing exactly what I hoped it would. Next video, I'm not sure what it'll be. I've got another track day at the end of May that I've mentioned. Um, I do hope to get some little modifications made before then perhaps or maybe just before the ring trip. Don't know what it's gonna Don't know what we're doing just yet. So, um um stay tuned and I'm sure there'll be some more videos. But I've got lots of lovely Cadwell footage now, haven't I? And I will have some more at the end of the month. So, I hope you've enjoyed the video and we'll catch you on the next one.