Track car - coupe or roadster?

[Beesza]

Hi,
I’m toying with the idea of a 3.0si track day car (first foray into track driving.) Looking for guidance on coupe vs roadster. Not found much out there in regard to differences in performance and the track experience. Obviously aesthetics is a contentious topic which has been discussed in depth.

Is the coupe stiffer? Handle better?
I’ve read on other forums that there isn’t much in it weight wise, which surprises me. Is this true?
Does driving with the top down versus up have a noticeable effect on handling?

I like the idea of driving a track with the top down (clutches at dreams of F1). But the engineer in me says the coupe should perform better…

I intend the car to be for track use only so no winter points for the coupe

 

[TheDan]

Not that I am biased or anything....



But I would say roadster. With some suspension mods, brake upgrade and better tyres its a great track machine. I like having the option of roof open (dreaming of F1) or closed (more race car style). And yes, there is very little difference in weight between the two (the roof is remarkably light).

If you add a couple of strut braces you probably wont even notice the stiffness difference either.

 

[Mr Tidy]

Hi and welcome to the forum to begin with.

The 3.0Si is a great engine, really smooth and revs happily to the red line!

I've only had Coupes and never tracked one, but by all accounts the Coupe shell is much stiffer than the Roadster. But then the Roadster is said to have a stiffer shell than the revered E46 M3 Coupe, so it may not mattter which you choose.

According to the BMW brochure the Roadster weighs 1,385kg and the Coupe is 1,395kg so as you say very little in it. And they quote the same acceleration times for both.

There is a race series for the pre-facelift Roadsters with 2 classes, 2.2i and 3.0i, but someone on here has had some success racing a Coupe - here's a link to a long thread that you might find helpful! https://z4-forum.com/forum/viewtopic.php?f=2&t=112593&hilit=liam
although others have also had Coupes as track cars.

For a car dedicated to track days a Roadster would be a cheaper option, but I'm sure someone picked up a Coupe cheap as a Cat N or S for track use.

Anyway I hope you find what you want.

 

[brillomaster]

My e85 z4 track car was a roadster. Seemed to be cheaper than equivalent coupes ( i picked up a high miles 3.0i for £3000) and it is nice putting the roof down on a hot day.

Only mods i did were brake pads ( performance friction 08) and tyres (federal 595 RS-Rs) and it was very quick and very capable.

Only downside is i lost a potential trackday share option as she wouldnt drive a roadster on track, which was a shame.

 

[brillomaster]

Also, i think an e85 or e86 is a great choice for a track car. Sweet sounding, punchy straight six engines, good balance in the chassis. Lots of shared parts with an e46 3 series so easy to get spares. Only downside i can see is electric steering lacks feel, but really thats nitpicking, i loved my e85.

 

[Beesza]

Thanks for the replies. Z4’s seem like great balance of price vs performance. Can’t one to get one!

 

[patriot66]

Not sure if the E86 is any heavier than the E85 but it is MUCH stiffer and more aerodynamic.
"The Coupe's fixed roof increases torsional rigidity, resulting in a stiffness of 32,000 N⋅m (24,000 lb⋅ft) per degree of body twist on the coupe (compared to 14,500 N⋅m (10,700 lb⋅ft) per degree on the roadster), which improves turn-in and overall handling response"
So, purely as a track car the E86 would seem to be a better option

 

[ph001]

Unlike most convertibles, the Z4 was designed as a roadster first and the coupe came later (it’s usually the other way around). This means the rigidity was built in from the start so you should have no problems in that respect, both are capable track machines just with alignment, brakes and tyres.

 

[Ed Doe]

Honestly both the Roadie and coupe would be great on track.

The roadster does have a significantly less stiff chassis than the coupe as stated above but its worth remembering that the torsional rigidity value of the roaster is very similar to that the e46 m3 coupe, and that's raved about as a great track car.

End of the day you won't suffer scuttle shake or any other horrid traits associated with less sporty drop tops in either e85 or 86, so both will be perfectly entertaining, involving and fun for track.

I tracked my 3.0si coupe a fair few times, it was a hoot right out of the box, but I did end up with bigger from brakes, b12 suspension, a smattering of polybushes and a quaife lsd by the end. It was fantastic and I still miss it now. I'll whisper it for fear of offending the purists, but because the N52 engine in the 3.0si is significantly lighter than the S54, it actually felt to me like it had a keener front end than the M coupe I now have...!

Anyway digression aside, ultimately I'd go with your heart on this one - you can't go far wrong with either

 

[buzyg]

Don't get hung up on the torsional rigidity. The E85 chassis is plenty stiff enough. It's stiffer than a 360 spider, hardly a flippy floppy thing. The weight high up on the coupe is not exactly ideal, both are tiny fractions and we're hardy pro racers. So just go for the one that you fancy and can afford and enjoy it.

 

[Flyingfifer]

In terms of outright track performance the Coupe is simply superior due to the stiffer chassis however obviously you cant look at that in a vacuum and other considerations need to be factored in, the most obvious being cost, you could pick up 3 or 4 roadsters for the price of a coupe which when you're going to track it, that becomes very unpalatable. Added to that the fact that the E85 is reasonably close to the coupe in terms of its stiffness, the performance differences will only really be noticed on the absolute ragged edge where the coupe will handle better.

Personally with the above in mind, I would opt for the E85, its significantly cheaper, more readily available and close enough in terms of outright performance just makes the E86 a difficult to justify purchase for a track slag. That being said, if you can get one mega cheap.... the E86 is the best option.

 

[Argyll Andy]

In terms of outright track performance the Coupe is simply superior due to the stiffer chassis however obviously you cant look at that in a vacuum and other considerations need to be factored in, the most obvious being cost, you could pick up 3 or 4 roadsters for the price of a coupe which when you're going to track it, that becomes very unpalatable. Added to that the fact that the E85 is reasonably close to the coupe in terms of its stiffness, the performance differences will only really be noticed on the absolute ragged edge where the coupe will handle better.

Personally with the above in mind, I would opt for the E85, its significantly cheaper, more readily available and close enough in terms of outright performance just makes the E86 a difficult to justify purchase for a track slag. That being said, if you can get one mega cheap.... the E86 is the best option.

[ref]Beesza[/ref], don’t know if this would fit the bill, seems cheap enough https://www.ebay.co.uk/itm/124798324649?hash=item1d0e8f4fa9:g:i-MAAOSwSspgiqoF

 

[brillomaster]

that is cheap, and looks pretty decent to be fair. plus swap out the winter tyres and thats a set of track tyres paid for.

 

[Flyingfifer]

[ref]Beesza[/ref], don’t know if this would fit the bill, seems cheap enough https://www.ebay.co.uk/itm/124798324649?hash=item1d0e8f4fa9:g:i-MAAOSwSspgiqoF

Thats a brilliant find, the spec low as well which means less excess stuff to remove for the track

 

[Beesza]

In terms of outright track performance the Coupe is simply superior due to the stiffer chassis however obviously you cant look at that in a vacuum and other considerations need to be factored in, the most obvious being cost, you could pick up 3 or 4 roadsters for the price of a coupe which when you're going to track it, that becomes very unpalatable. Added to that the fact that the E85 is reasonably close to the coupe in terms of its stiffness, the performance differences will only really be noticed on the absolute ragged edge where the coupe will handle better.

Personally with the above in mind, I would opt for the E85, its significantly cheaper, more readily available and close enough in terms of outright performance just makes the E86 a difficult to justify purchase for a track slag. That being said, if you can get one mega cheap.... the E86 is the best option.

You’re dead right. If a good Roadster comes along, I’ll take it. Personally, I prefer the look of the Coupe and there must be a slight performance improvement (doubt I would ever notice, but still). From my search so far, roadsters and coupe appear to be similarly priced.

 

[brillomaster]

https://www.ebay.co.uk/itm/174802412466?hash=item28b30923b2:g:sikAAOSw7nlg31DX

this one leaves plenty of room in the budget for upgrades....

 

[Argyll Andy]

[ref]Beesza[/ref], don’t know if this would fit the bill, seems cheap enough https://www.ebay.co.uk/itm/124798324649?hash=item1d0e8f4fa9:g:i-MAAOSwSspgiqoF

Thats a brilliant find, the spec low as well which means less excess stuff to remove for the track

Yip, no point in paying extra for stuff you’re just going to take out. Seems to mainly be small bodywork issues and exhaust/emissions sensor noted and they’ll not matter on track, that’s what advertising stickers are for :wink: win, win IMO

 

[Beesza]

[ref]Beesza[/ref], don’t know if this would fit the bill, seems cheap enough https://www.ebay.co.uk/itm/124798324649?hash=item1d0e8f4fa9:g:i-MAAOSwSspgiqoF

Yep, that ticks the boxes. Should I be concerned about the 143k mileage? Obviously will need a test drive

 

[brillomaster]

nothing really to worry about with high miles - check for mayo in the oil, any fluid leaks and smoke from the exhaust, same as usual really. I'd say other things failing like water pumps, alternators and expansion tanks are all related to age, not mileage. check gearbox and clutch, and power steering are all ok.

but its a track car right? no point paying extra for a low miles car when you might bin it into a barrier, that money is better spent on track tyres and brake pads. you'd likely want to give any car a full service before taking it on a trackday anyways.

 

[Argyll Andy]

[ref]Beesza[/ref], don’t know if this would fit the bill, seems cheap enough https://www.ebay.co.uk/itm/124798324649?hash=item1d0e8f4fa9:g:i-MAAOSwSspgiqoF

Yep, that ticks the boxes. Should I be concerned about the 143k mileage and the lambda sensor issue which the seller flags?

The mileage shouldn’t be worrying if it’s been maintained properly. I know it’s not due a service for 10k, I’d be more interested in what’s happened before that.

With a car of this age, particularly when tracking it, you’d likely be doing preventative maintenance and refreshes anyway like water pump etc so that would also alleviate some of the mileage related concerns.

The lambada sensor is a common one when exhausts are upgraded but I’m sure someone more knowledgeable will be along shortly with a better answer