620R vs. Atom 3.5R on track

[JohnCh]

I watched a rerun of Fifth Gear that pitted the Zenos, Radical, Atom, and 620R against each other in a series of knock out tests. The tests and order were chosen in such a way that the Atom and 620R would be pitted against each other in a short race at the end. Although it's not surprising that the mid engined Atom would have a lot more traction out of corners, I was a bit surprised how unstable the 620R looked. Croc, as I recall you've driven one on track. Does this mirror your experience?

 

Fast forward 52 seconds for the track action.

 

 

-John

[Croc]

A couple of things to keep in mind:

• The Atom 3.5R has 350hp versus the 620R at 309hp
  
• The Atom is about the same weight as the Caterham despite being larger tarmac footprint - the skeleton frame helps here
  
• The Atom has 60%+ over its rear wheels from its rear (not mid) engined layout so it will always give good traction relative to the Caterham
  
• The Atom is longer so that helps reduce twitchiness on limit
  
• The Atom is wider than the Caterham plus has roughly 1 inch extra width on each of its wheels that helps
  
• The Atom has an aero package with front and rear spoiler and its less of a brick than the Caterham - one with front end downforce and one with nothing
  
• The Atom has IRS as standard
  

 

The Caterham has size compromises built in by its heritage legacy. Its short wheel base makes the car quite quick to rotate when it snaps at the limit. It will understeer if you stick it into the corner without respect for weight transfer. So will the Atom. Both have light front ends I find but I drive around that by modifying my normal driving style to accentuate weight transfer to the front before turn in and also trail brake to control the rear end in the first third to half of a corner.

 

My first day with the 620R was at Estoril circuit. You can see 2/3rds of the way through the lap, the car snaps on me at a slow corner - its hindered by its tire footprint.

 

 

Give me some break re my relative driving prowess, I am not an ex-F1 driver, I am brand new to the 620R and Estoril track but the speed on the speedo shows how quickly it spools up.

 

The problem of the S3 Caterham is that it is too narrow. The SV being 4 inches wider helps that. There was an old test at Donington I participated in. A bunch of us drove three cars on track each - an S3, an SV and a CSR, each with the same Duratec engine with about 210hp. The fastest lap times were in order - the CSR, the SV and the S3 pretty much irrespective of who was driving. So that shows:

 

1) Width of chassis contributes meaningfully to the cornering ability

2) IRS is an advantage over a de dion semi live rear end

 

The CSR chassis with its SV proportions and IRS would be a better comparison than the 620R if the same drivetrain were installed.

 

The Atom does not have those constraints being a more modern chassis design unencumbered by tradition. Add the aero package and the downforce this brings plus the wider rubber, then it will always look more composed than the Caterham on the limit on the track. With its big hp advantage then it could blast past on the straight.

 

The good thing about that comparison is they used 2 very good drivers - Jason Plato and Karun Chandhok. I would have been interested in the cars being swapped between the drivers. Plato is a touring car chap and used to having less aero and more driving compromises than Chandhok who is more used to a high aero open wheeler style of car. It may be of marginal effect and it certainly would not have changed the end result but I suspect Plato would be happier at the limit with the Caterham.

 

The Atom's performance advantage comes at a cost. Using the US dealer website then the Atom 3.5R as shown in the video is around $95-100k. The 620R in that video probably is around $75k all in, may even be less with the pound where it is today.

 

Anyway, I like Caterhams (and sevens generally) because I prefer the look of them and appreciate their family tree.

Edited March 22, 2020 by Croc

[JohnCh]

Thanks Mike. My surprise wasn't that the Atom was faster -- honestly, I couldn't care less about that sort of thing, as it's the driving experience that matters most to me -- it was simply the apparent instability of the 620R in that video. I can't recall seeing any other S3 Caterhams behave that way on track and was curious if that was exacerbated for entertainment value or if at 310hp, the S3 has reached a stage where it's finally more engine than chassis.

 

Although I see where you had a moment, it certainly doesn't appear you were fighting the car like Chandhok. I suppose that could be down to show, track temp, or you were showing far more respect to the throttle.

 

Now since you responded nicely and scored extra points for posting a video, I'll leave it to Shane to comment on your driving ability :jester:

 

Thanks,

John

[Croc]

I suspect there was some acting in the video. Think back to Top Gear when they first tested the yellow R500. That was similarly wayward - rather spectacularly. The later 620R test was exciting but tidier. You and I both know (well at least I do) that smooth and tidy is usually the fastest way around a track.

 

I'll leave it to Shane to comment on your driving ability :jester:

 

Shane? Really?

 

[xcarguy]

I suspect there was some acting in the video. Think back to Top Gear when they first tested the yellow R500. That was similarly wayward - rather spectacularly. The later 620R test was exciting but tidier. You and I both know (well at least I do) that smooth and tidy is usually the fastest way around a track.

 

 

 

Shane? Really?

 

 

You guys are soooooo nice.....let’s have some remedial training.

 

.....for the unfamiliar, Croc can fill in the gaps.

 

 

 

Since this is remedial......I suppose we should also add this....skip to 5:00 on the vid for the good stuff.:jester:

 

Edited March 23, 2020 by xcarguy

[Vovchandr]

Personally I have a soft spot for the Atom.

 

It's the reason I have a 7!

 

Story is pretty straight forward.

 

See Atom on TG and fall in love with a "dream car"

Have a local get an Atom to further induce desire

Realize Atom is unreasonable to register and isn't really affordable ever so start a Locost

Look into a Locost long enough and you start to idolize a 7

Get a 7

 

However after owning a 7 and looking back on it all, you give me a choice between those two above and I'd pick the 620R. Change that I'd even pick a R500.

 

Atom is a better track toy as Croc described in many detail. However a 7 is just a better car.

[Croc]

Atom is a better track toy as Croc described in many detail. However a 7 is just a better car.

 

I am not sure the Atom is always the better track toy - for me anyway. It depends on your preferences. Using the video Atom, I hate aero on track cars as I find it psychologically difficult to rely on something I cannot see at 130mph. I tried an F3 car when I was in my early 20s after being reasonably successful in Formula Ford and Formula Vee but I could not wrap my head around how much you can push an aero car - I could not judge it. Its not just me - a forum member with a Radical (lets call him Jeff for examples sake) had similar issues trying to get how much faster you can push with downforce and assessing when you are at the limit.

 

I prefer the Caterham on track as it is more tactile - I can feel the mechanical grip vary through my butt. I know exactly where I am in the middle of the cornering process and can compensate accordingly with throttle or wheel. If you have ever grabbed air then you know how it is not tactile.

[Croc]

You guys are soooooo nice.....let’s have some remedial training.

 

.....for the unfamiliar, Croc can fill in the gaps.

 

 

Was that the day I had your Dad in the passenger seat in my Caterham and I was waiting for you to catch up so we could play tag?

 

If it was, then the best bit was Larry shaking his head and saying to me "Thats my boy!" after watching you do your earth moving escapades in the passenger side rear view mirror.

 

:rofl:

[xcarguy]

Was that the day I had your Dad in the passenger seat in my Caterham and I was waiting for you to catch up so we could play tag?

 

If it was, then the best bit was Larry shaking his head and saying to me "Thats my boy!" after watching you do your earth moving escapades in the passenger side rear view mirror.

 

:rofl:

 

That, indeed, was the day.....but I don’t recall your waiting around for me to catch up.

[BruceBe]

I'll echo Croc's comments about S3 vs SV vs CSR. On the same day at the same race-track in competition, a CSR is far more composed than an R500 Duratec, at similar lap-times. I believe that the SV and CSR are "faster" than the S3 chassis due to this composure - it's just more difficult to click off consistent fast laps, in race traffic, when all that "milking the cow" is going on through the corners. The SV benefits from the slightly increased wheelbase and wider-track - once it hits the limit, the dynamics are similar to the S3 - the limit is just a bit higher. The CSR is a different beast - it feels like a more modern car. Once a CSR takes a "set" in the corner, it's easier to maintain composure, apply power, and keep mechanical grip.

 

Indeed - aero/download cars are a different beast. They are often over-sprung when not "in the air". As a result, they can get a bit twitchy and/or wash-out in slow-speed, tight corners. However, well-designed download cars are an experience from another world, once the aerodynamics are functional. It *is* a driver challenge to become confident, competent, and fast in a download car. Lovely stuff, if you can invest the time and get comfortable with the very dynamic handling characteristics.

 

-Bruce

[Croc]

...it's just more difficult to click off consistent fast laps, in race traffic, when all that "milking the cow" is going on through the corners.

 

Having observed quite a few people from this club forum on track, I can attest to that euphemism in their cornering styles.

However, the end results are more like 15 year old teenage boys! :rofl:

 

 

It *is* a driver challenge to become confident, competent, and fast in a download car. Lovely stuff, if you can invest the time and get comfortable with the very dynamic handling characteristics.

 

Yes, I failed!

 

The CSR is a different beast - it feels like a more modern car. Once a CSR takes a "set" in the corner, it's easier to maintain composure, apply power, and keep mechanical grip.

 

Thats very well said - exactly how it feels in my CSR.

[Kitcat]

I always have assumed that, with its 50-50 balance, a se7en would be more manageable on the track than the tail heavy Atom, esp in the hands of we amateur drivers. The Atom's 40-60 front/back distribution is similar to the 911's.

[Davemk1]

It seems to be fairly simple - the Caterham has more torque than the tires can put to the ground given it's weight and weight distribution. The Atom has wider tires and much more weight on the rears so it can put power to the floor and it doesn't battle power-on oversteer and wheel spin every time the driver gives it the boot.

 

I autocross against a well driven supercharged Atom at nearly every event I do (owned by a local friend of mine) and its ability to put power down far surpasses my Westfield S2000. It weighs just a bit more, makes much more power and can put it all down so the acceleration can't be challenged. Yet it's extremely rare for it to post a faster time and it comes down to two key things....first is that the Westie is narrower and in slaloms and sweepers that makes my course shorter and that adds up quickly. Secondly the Westie is much better in violent transitions with much less tendency for it to wag its tail or spin due to having a more even weight distribution and a much lower polar moment of inertia.

 

I'm sure that on an open track like the Atom and Caterham were on my friend's Atom would just walk away from my Westfield with ease.

 

dave

[BruceBe]

The weight distribution argument, with respect to putting power down is valid. One is a rear mid-engine car (Atom), and the other is a front mid-engine car.

 

I would guess that the Westie's lower tendency to over-steer has more to do with roll-couple distribution, and managing weight transfer due to driving style/skill. The biggest speed part in a car is behind the wheel.

 

Cheers,

-Bruce

[Croc]

In my track tag times with non-wing Atoms at NJMP, I have always observed them to have a nervous front end that washes out somewhat in corners. So the weight distribution argument works both ways in terms of advantages and disadvantages. It will depend on the track format. On an open track, 350hp vs 309hp in similar weight cars usually has a predictable outcome.

 

Still, I enjoyed watching the full Fifth Gear episode last night to see what happened to the Xenos and Radical. They should show that more on tv. There are only so many re-runs of Ancient Aliens I can take!