effect of lighweight wheels on straight line performance

[Steffen_Leitgeb-LSWGmbh]

That lightweight wheels have a big effect for the speed and safety of race cars is well known - that´s why in most racing there is a reglement which limits materials and forces a minimum weight.
It is not known to many that the reduction of rotational mass means basically more hp at the wheel if it comes to positive acceleration.
This is what I wanted to show here:

 

Acceleration test shootout today 🙂
Leitspeed LSL01 vs Lotus Original Forged of Lotus Evora S.
delta in kg: 9,6 in favour of the LSL01

Testing result averaged over 4 test runs each:
LSL01: 5,07 s
Lotus Original: 5,21 s
delta: 0,14 s 50 - 120 km/h 
same outside conditions

Procedure:
Lotus Evora S IPS, standard engine, Komo Tec headers, K&N filter
run start in 2nd gear @2.500 full throttle, 50-120 km/h (no aero involved, starting from very low rpm just like on the dyno, staying in one single gear)
4 testing samples each to minimise driver and measuring errors but there were none in the files.

See the screenshot of the data analysis graph.
Measuring tool Racelogic VBOX Sport 20 Hz GPS

The delta in acceleration performance will be there on every acceleration area (positive and negative) on track and road. So lightweight wheels do make a difference even on straight line performance.

[LoW8]

Thanks for sharing.

I'm sure lightweight wheels do make a positive difference, but if you had Pirelli's on the standard wheels and PS4S on the lightweight wheels (as pictured) I'd say the grip difference between these two tyres would make more of a difference than the wheel weight. 

Also, what was the weight difference between the tyres (tyres often vary by several kg between brands), and the date of manufacture of each tyre (age)?

 

[KAS-118]

I think the weight will make an appreciable difference.

Firstly, its unsprung weight - which can greatly improve the handling characteristics. Secondly, in respect of straight line performance this video shows the difference that a Titanium exhaust - which is 15kg lighter than the standard - and only produces 2.5 bhp more, can make.

https://www.youtube.com/watch?v=FC-WuvZvVrQ

This Article  https://suspensionspot.com/blogs/news/improve-your-track-car-reducing-unsprung-weight states that a 1lb reduction in unsprung weight is theoretically the equivalent of a 20lb weight reduction in sprung weight (although in real world scenario's it says its more like 6 to 10lbs) 

So Steffen's wheels are an approximate conservative equivalent of a 30kg reduction in sprung weight. Thats a hell of a lot. 

[LoW8]

Agreed.  BUT, moving from 5yo Pirellis to brand new Michelin PS4S makes a staggering difference to grip levels under hard accelleration.  Surely this needs to be taken into consideration.  For the test figures to be 100% accurate, you'd need the car to be on identical tyres (both brand and age).

I'm very familiar with the impact of unsprung weight, that's why I believe the tyre brand is of such importance (in addition to grip). I found with my Elise that one brand of tyres (in the tiny 17" size) actually weighed 3-4kg MORE than the previous. With the tyre weight being even further from the centre point than the wheel, this difference is notable, especially wiith large 275/20 tyre. The PS4S may actually weigh less, but provide more grip (obviously unknown), this is why both wheels need the same tyres fitted.  

Not having a go, but when we're talking about 0.14s difference in accelleration, all things need to be equal for the test to be 100% accurate.

 

Edited September 19, 2018 by DBG

[KAS-118]

Ideally you are of course right - but I think it should be pointed out that the acceleration was timed between 50-120 km/h rather than a standing start - so the difference in grip of the tyres would have a reduced affect 

Edited September 19, 2018 by KAS-118

[LoW8]

Understood, but a very minimal reduction in grip, could very much contribibute to the 0.14s difference, so thought it was worth noting.

[ramjet]

All looks good, but is this bordering on a case of diminishing return on investment?

[slewthy]

Interesting - I hadn't considered rotational mass having an effect but of course it does -  it makes total sense.

However, as outlined above such tests must be subject to massive additional influences when measuring such small differences. I would not be confident that the result was not just a product of something else or even chance. Do such tests also produce confidence limits? So what is the +/- in the result to produce a 95% outcome? Probably not without additional tests as said by DBG.

Plus, what is the outcome of 0.14s difference? Even if it is a real result, does it make a difference in the real world?

(Sent from my phone whilst sitting in a traffic jam)

 

[Steffen_Leitgeb-LSWGmbh]

Thanks for the concerns:

tires:
Michelin PS4s on the Leitspeeds (2017)
Pirelli Corsas Lotus Original (2015)
So basically the Pirelli as a Semislick should have more grip … in theory. Was stored well, never overheated on track, road use only.

tire grip:
tire grip was taken out of the calculation by the driving profile chosen - accel. from 2.500 rpm IPS car in 2nd gear. Because it was not needed to show impressive values, it was necessary to drive like a dyno run. 
This produced only low acceleration and repeatable g figures, I posted them as average in the graph.
Max 0.44 g longtitudinal peak accel. is really very low today and every tire can cope with that to my experience in vehicle testing business
The biggest G increase was when applying full throttle at 2.500 rpm where the rate of change was 0,29 g / 0,5s - which is low too.
Can´t be seen in the graph, sorry.
Please check the g-long graph and you can see a very linear power supply which is typical for a supercharged engine and perfect for tires.  
(I supply Racelogic VBOX Motorsports products to German industry, racing and automotive media, so I have some insight in these testing procedures).

road grip:
At the same place where I am measuring regularly private cars I can reach a negative g-force of -1.1 g with the Evora and then ABS kicks in.
Road was clean as I had checked before.

warming and rear tire pressures according to the Lotus manual:
Pirelli: 2.6 bars rear
Michelin: 2.2 bars rear

I drove the car before measuring both times approx. 7 km country road to warm engine, gearbox and tires evenly.

Testruns:
each wheel set was driven 4 times, incl. changing direction 2 times to even out track influences or wind influences, track is 100% flat
the runs were averaged and the delta of 0.14 is the also averaged delta

Later this day I will give you the total weight of Lotus Forged Original with Pirellis and the Leitspeeds with the Michelin PS4s.

Is such a small difference really important?:
On a winding road or track day or even on an Autobahn competition with a Porsche or Audi RS this small advantage adds up massively.
So it no longer stays a single 0.1 s. 

Lightweight wheels make you quicker everywhere (except Vmax) without big technical changes or a change of drivestyle and you save tires, shocks and bushings too. 
The Evora gets simply more alive. Makes much more fun to drive.
Looks are a different point of view. Not the topic here.


 

 

[Steffen_Leitgeb-LSWGmbh]

Total rear wheel weight comparison:

Leitspeed LSL01, Michelin PS4S: 21,32 kg = 9,5 rim, 11,82 tire
Lotus Original forged, Pirelli Corsa: 23,72 kg = 12,1 rim, 11,62 tire

I´d say the comparison in the accel. testing above is usable and credible.
It can help to "quantify" the effect of more lightweight wheels in further discussions on a valid basis.
 

Edited September 20, 2018 by Steffen_Leitgeb-LSWGmbh
Additional info

[KAS-118]

@Steffen_Leitgeb-LSWGmbh so the original calculation was that a set of your wheels were 9.6kg lighter; the above shows 2.4kg per rear tyre + wheel so x 4 would actually be 9.6kg (I acknowledge the fact that the front wheels are lighter than the rear) which is the same as the direct wheel to wheel comparison.

So yes, give you were timing accelerating from about 30 to 70mph - I think you have demonstrated that there is an advantage.

I guess what would be a really good comparison is your wheels and tyres v's standard wheels (but the same tyres) around a timed lap - as the continued befits from a lower unsprung weight would be more accumulative. However, I assume this would be very expensive to set up and do ☹️

Unfortunately, 0.14 secs in cold reading just doesn't sound much - but its a 3% improvement which is certainly worth while. If you had a lap time of 1m 20 secs and reduced that by 3% you'd be knocking 2.4 secs of the time - which might sound a much more worth while benefit. 👍

[Steffen_Leitgeb-LSWGmbh]

Thank you for your comments @KAS-118.
You are right. I think when there is enaugh time I can repeat that on a race track with a professional driver and two identical tire sets.

The 3% improvement is a good value to explain a) the overall performance increase and b) compare the cost efficiency to other lightweight tuning products too.

What does the 0,14 s really say?
A performance gain of 0,14 s on a accel.-distance of just 125 m is not small. It is really big!  
I thought this is clear.
You are carrying this advantage all around a race circuit as you have explained very well and it may end up in an advantage in seconds over several laps.
And all without taking the car apart or changing many parts … simply change the wheels.

 

 

-> I did that special straight line testing as I was asked frequently by potential customers "how big" is an improvement in straight line acceleration.
And I thought such a testing is the most easy demonstration which can be the first basis for further judgements.

 

 

[Champale]

Nice job doing this test, Steffen!  There have been a number of articles/tests over the years in car and motorcycle magazines about the improvement in performance that lighter wheels can make and even though the original equipment Lotus 'forged' wheels on a 400 are relatively light for their sizes (by my measurements about 21lbs front, 27lbs rear), they can be improved upon.

Here is an article by Car and Driver magazine about the difference that the factory fitted carbon fiber wheels make on the amazing GT350R:

https://www.caranddriver.com/news/tested-quantifying-the-performance-benefits-of-the-shelby-gt350rs-carbon-fiber-wheels

[Steffen_Leitgeb-LSWGmbh]

Yep. Carbon is a difficult material but it can be made most lightweight. I expect some progress there in future but the costs for aftermarket carbon wheels stays big.

Evora 400: Our basic LSL01 wheel beats the Evora 400 standard wheels by 5,5 kg the set and d the super light Evora 410 Sport wheels still by 4,1 kg the set.

[Champale]

That is fantastic.  

[LotusLeftLotusRight]

3 hours ago, KAS-118 said:

Unfortunately, 0.14 secs in cold reading just doesn't sound much - but its a 3% improvement which is certainly worth while. If you had a lap time of 1m 20 secs and reduced that by 3% you'd be knocking 2.4 secs of the time - which might sound a much more worth while benefit. 👍

Surely that calculation is only valid if you are accelerating all the time. A circuit contains a mixture of acceleration and braking and probably also zones of constant speed, where wheel weight will have no impact. I still think you're right though and that a proper back-to-back track test with a professional racing driver would prove the real benefit of lightweight wheels.

[KAS-118]

1 hour ago, LotusLeftLotusRight said:

Surely that calculation is only valid if you are accelerating all the time. A circuit contains a mixture of acceleration and braking and probably also zones of constant speed, where wheel weight will have no impact. I still think you're right though and that a proper back-to-back track test with a professional racing driver would prove the real benefit of lightweight wheels.

To be honest I'm expecting that there will be a greater benefit then 3%.

The test that has been carried out merely shows a benefit of the direct weight reduction of 9.6kg. However, in handling terns the benefit of unsprung weight to sprung seems to be a ratio oh 1:6 to 1:10.

The lighter weight will also benefit braking.

I'm not too sure on a track when a car isn't either accelerating, braking or being subject to some king of dynamic behaviour from cornering or turning - so I think that 'constant speed' will be a very rare event.

However, as Steffen' said he'll get them tested around a track when he gets the time we'll all have something to look forwards too 🙂

 

[TheKevlarKid]

Imo on a car that weighs as much as the Evora does the only 'real world' noticeable difference a 10kg lighter set of wheels is going to make is when you have to take them off the car and are physically having to handle them...

They look nice though! I'd be buying them on style not on the basis I'm getting 0.14s of better acceleration in the mid range, my arse could never measure that difference, my eyes would see it though...

 

 

[Steffen_Leitgeb-LSWGmbh]

On ‎21‎/‎09‎/‎2018 at 09:23, TheKevlarKid said:

Imo on a car that weighs as much as the Evora does the only 'real world' noticeable difference a 10kg lighter set of wheels is going to make is when you have to take them off the car and are physically having to handle them...

They look nice though! I'd be buying them on style not on the basis I'm getting 0.14s of better acceleration in the mid range, my arse could never measure that difference, my eyes would see it though...

 

 

Haha. Absolutely right. If you handle Lotus wheels regularly and constantly struggle to put in the bolts and make the wheel fit to the hub well you will realize how perfect the Leitspeeds mount instead - with a lot of caring for details in design the mounting is much better than any Lotus original wheel … and also you do not have any problems with your spine or back after putting them on your car because of the weight advantage 🙂 

[TheKevlarKid]

@Steffen_Leitgeb-LSWGmbh ask a question...

Can you manufacture the rears with different off-sets? I have a GTE Evora which the fronts are all but the same as the regular Evora, the rears however have a offset of 13.5ET.

[Steffen_Leitgeb-LSWGmbh]

2 minutes ago, TheKevlarKid said:

@Steffen_Leitgeb-LSWGmbh ask a question...

Can you manufacture the rears with different off-sets? I have a GTE Evora which the fronts are all but the same as the regular Evora, the rears however have a offset of 13.5ET.

@TheKevlarKid, sorry no, that big change (+55,5 mm) is not possible without a full redesign (new CAD, including a full production testing (bend fatigue, rolling, impacts)) of the rear wheel.
It was very difficult to make a functional superior wheel design to fit the standard Evoras (NA/S, 400/410) so I do not want to make a new wheel for the GTE which is even a more small production car.
Basically I did the job just because of the love for car and brand.

Maybe we could do the GTE via racing production but with a different basic design - Minimum qty is then 20 front and 20 rear, but we can not do 19/20, in racing we can do 18/19 only.

 

[TheKevlarKid]

Thanks for the response. I think we'd struggle to get 10 owners onboard...

[Bruss]

On ‎26‎/‎09‎/‎2018 at 11:20, TheKevlarKid said:

@Steffen_Leitgeb-LSWGmbh ask a question...

Can you manufacture the rears with different off-sets? I have a GTE Evora which the fronts are all but the same as the regular Evora, the rears however have a offset of 13.5ET.

Projex can.

 

 

[JayEmm]

FWIW, I have managed to get a few miles under my belt with Steffen's wheels (video coming soon) - although I can not discern any performance difference, I am reasonably confident the steering wheel is transmitting just a little more information than before, giving the car even more of that Lotus feeling we all love.

Plus, they do look absolutely amazing.

[LotusLeftLotusRight]

On 26/09/2018 at 10:20, TheKevlarKid said:

@Steffen_Leitgeb-LSWGmbh ask a question...

Can you manufacture the rears with different off-sets? I have a GTE Evora which the fronts are all but the same as the regular Evora, the rears however have a offset of 13.5ET.

Rimstock are exhibiting at Lotus70 on Saturday. Is it worth badgering them regarding the originals, or has that avenue been exhausted?