The great weight debate

OK - so which is better? As heavy as possible or as light as possible? I reckon it's got to be lighter = faster. Lower weight means less tyre deformation, less load on the bearings and so less rolling friction.

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Submitted by scottishcarties on February 16, 2008 - 22:49.

Great Weight Debate.....

Trying to think back to Mechanics lectures! Guess it is down to Momentum vs. Intertia...and also the specific hill?

More weight takes more force and time to accelerate...but once moving will be less sensitive to isolated areas of resistance (poor road surface; slight uphill / flat area.....) but rolling resistance will always be more, tho' pretty much constant

I've seen luige guys add weight for courses with flat sections....and it seems to work.

Maybe academic.....if the pilot weighs 14 stone and the cartie half of that, cartie weight might matter less than the number of pies carried.......

jocklandluge | October 19, 2008 - 19:14

weight v. pragmatism

I'd always try to make the soapbox as light as possible, because you can always add ballast to make it heavier if you need to, whereas it is somewhat harder to do the opposite.

Anonymous | October 20, 2008 - 10:28

Hi all I'm from Tasmania

Hi all I'm from Tasmania Australia and I can answer that one. Theres a perfect weight for every cart / track. But carts that weigh 50 to 65 kg do well here. Heavy ones tend to be slow as off the line.........trikes

trikesrule | October 23, 2008 - 09:06

heavy vs light

Our old course at Belchford definitely gave an advandage to heavier carts because the last 100m were more or less level, therefore the heavier carts were able to make use of their extra momentum. A continuous downhill will give advantage to neither (Gallileo demonstrated this). Interestingly our new course with it's chicanes and no level parts seemed to advantage the lighter carts. As pointed out by the first comentator, added weight creates disadvantage due to added drag on bearings and tyres. The other disadvantage with higher weight is where there are chicanes or other changes of direction. The gravitational force acting on the cart is directly related to it's mass and as Newton worked out acceleration = force divided by mass. If you have a look at the excellent page http://www.motivate.maths.org/conferences/conf49/c49_gravity.shtml it explains how whilst the gravitational force acting on the cart increases with it's mass, the acceleration is inversely affected by the mass. The mass, therefore, cancels out. I think I understand it but will be pleased if someone can explain it better whether or not I am correct. I look forward to this developing. Thanks Stephen for this forum. Richard Black.

Anonymous | October 25, 2008 - 00:03

Heavy Vs Light

The Cairngorm Extreme course certainly seemed to favour the heavier carts if you go by the results although I have no detailed info on all the competitors cartie weights or gross weights. ( Good if Stephen could post these) If you watch the starts on youtube the heavier carts were not slow off the mark, in fact some took a good lead. I thought I was doing ok on the day going into the first hairpin but watching the vids on youtube convinced me I was being a 'woos' and breaking far too early. Testified to by Colin flying past on my outside yahooing happily only to be caught again after the second part of the hairpin. This suggests to me that in this case his superior speed was achieved by more bottle in tackling the corner and that my heavier cart and better line round the corner allowed me to overtake as his speed bled off at the start of the incline/flat. As pointed out earlier greater weight must be taken into account when changes of direction are made and side forces on wheels and linkages increase expotentially. I am not saying a light cart will corner quicker than a heavy one but the only way to find out how quick any cart will go round a particular corner is to push it to the limit which in the case of Cairngorm Extreme was the maximum speed the cart would achieve 'in free fall' going into the first corner. In the time trial my maximum noted speed was 64mph and I am doubtful if the wheels could have taken the side loading. - 'Woos' More important than weight vs light is what goes with the weight or light cartie, ie, the overall construction, aerodynamics and lack of noise. -

Loud Yahoos are always acceptable!

peasnbarley | August 27, 2009 - 20:04

heavy v. light v. pragmatism

I think I have all the data in the scrutineering records, although I've not looked at them since the event. I'll try and remember to dig them out and publish them as you're right - it would be interesting to see if there is a correlation.

I've looked at the figures for Catterline and there seems to be and inverse relationship between weight and time (i.e. lighter == faster). In fact there almost seems to be a "sweet spot" at between 40 and 45 Kg, with carties lighter than that losing the benefit somehow. However, it's not a conclusive result as it's not comparing like with like. It may be that the lighter carts are also better constructed. A better test would be to use a three or four carties and do several runs with different amounts of ballast so that the only thing that changes is the weight.

I think trikes is right in that there is an ideal weight for each course. Certainly the heavier carties seemed to hold their speed better through the flat land section at Cairngorm, as this video clearly shows (watch how the cart takes Alford Bowling Club on the exit of the hairpin, only to be re-taken about 100 yards further down the track).

That then implies that you need to be able to adjust the weight for different courses, and that brings me back to my original, pragmatic, assertion, which is that it a lot easier to make a light cartie heavier than it is to make a heavy cartie lighter. i.e. make your cartie as light as possible and then add weights as appropriate.

scottishcarties | August 28, 2009 - 09:09

Heavy Vs Light - pragmatism

Certainly building light allows alteration for various courses and it would be true to say that the Alford Bowling cartie (Runfree) was purpose built with the Cairngorm Extreme course in mind. It was also built taking into account that we had no idea what to expect as far as loading forces, handling characteristics and material failure points. As I was the driver and builder I built strong for survivability in a crash and that equals weight unless you go for special and expensive materials. 'Runfree' was beaten in two races at Cairngorm; first as shown in the video above by Cairngorm and then again in the final, again by Cairngorm and of course Night Train. I have to say Cairngorm caught me off guard and up to then I was confident in the belief that I could do as before and catch any of the carts going up the straight after the hairpin, or at the top of the incline/flat. However the differences in speed/weight were too close to allow any real lead to develop between the carts and it came down to first round the hairpin without breaking would win. The final was somewhat different in that Night Train cleared the hairpin with Cairngorm nearly running out of road on the inside of the hairpin and me breaking hard not to run into the back of him. After that I could pace Cairngorm but had lost too much momentum to overtake on the outside. Time trials come up with the fastest cart on any particular day but head to head racing brings to the fore a lot of variables that are difficult to quantify and plan for. If I build a MK2 cartie it would again be purpose built but this time designed to achieve a maximum recorded speed of 75 - 80 mph down the cairngorm course as well as being able to take part at venues like Catterline. Again to attempt these sort of speeds it would need to be strong, have a roll cage (OK so some say that sucks!) and designed to handle like a car.

That seems to take me back to something like Runfree with an arodynamic body shell rather that the half a roll of duck tape we used to stop the wind blowing up my trouser leg! The trouble is I think we are too close to the weight limit to allow this without some major cutting out work, but then this is where half the fun is.

Edit Job after going over notes I made at construction stage :-

http:/hypertextbook.com/physics/mechanics/acceleration

http:/en.wikipedia.org/wiki/Normal force

In our real world cartie racing is conserned with forces described as 'Normal Forces'.

peasnbarley | August 29, 2009 - 16:24

racing tactics

Very interesting, and especially the observations about the way racing against other people changes things. I've heard the same sort of things from other people recently, and it seems that being forced to brake more than you wanted to is a common problem. Perhaps, if you think you're going to corner faster or brake less than the cartie in front, it's worthwhile braking a little earlier to open up the distance between you so they can grab a big handful of brakes and you can then aim to catch and pass them on the way out of the corner rather than on the way in?

scottishcarties | August 31, 2009 - 12:36

Racing Tactics

Being a 'novice' I can only comment about Cairngorm and it has to be said that Cairngorm Extreme was/is something special. Thanks to Stephen for setting it all up for us! I don't think the Cairngorm intended to brake because if you watch vids of him taking the hairpin he seems to be on the limit his wheels will take. In the final I think he just tried to take the corner very tight and nearly ran out of road. Certainly his line was different than in the videos. I think there will be a lot of re-designing of carties this winter.

If the event goes ahead again next year it would be great to have a timed section on the fastest part of the course where speed records could be set and broken with feedback to the spectators? Hearing the views of other competitors would be very interesting and I am surprised there are not more posts.

peasnbarley | September 2, 2009 - 21:54

Speed trap

"How fast were they going" is by far the most common question. Maybe we should invest in one of these - I'm sure other events would get some use from it too.

The pictures of Cairngorm's cartie were quite alarming, but on closer inspection I don't think it's the wheels themselves that are the problem. If you look at the wishbones you'll see that there is quite a lot of roll in the corner, with the outside suspension much more heavily compressed than the inside. I think that is what give the wheels the alarming camber, and if it had stiffer springs or an anti-roll bar it would corner a lot better.

scottishcarties | September 3, 2009 - 10:05

Speed trap gun

I think the radar gun would add a lot to the event, for both competitors and spectators.

peasnbarley | September 4, 2009 - 21:19

I heard Border Bogie have

I heard Border Bogie have police coming with one of theses

Anonymous | February 28, 2010 - 23:21

Speed gun for Border Bogies

There will definately be at least one speed gun there, as Scottish Carties will be bringing theirs along. It will be present for all the races in the SCA Championship.

scottishcarties | March 1, 2010 - 13:04

Hi,just to add my thoughts.

Hi,

just to add my thoughts. From Team Rookets perspective we had two drivers and we both had one practice and one qualifying run and all runs were captured on the video. The times for each driver were more or less the same for both runs, but Iain's times were slower than mine. From the videos there is not a significant deviation from the lines taken and if anything Iain is the more experienced driver and neither of us used the brakes until we got to the finish line (honest). The only difference between us is weight, I am a good bit heavier than Iain - conservatively more than a stone.

To add to the mechanics of the weight, we were not the lightest especially with me on board, and proved the old momentum and inertia laws, we were slow to get going, but once on the move our speed picked up quickly. The best way to show this is by watching our on board video of the crash, where we were last away, but by the time we were getting to the hairpin we had started to accellerate. Probably the worst place for the speed to come on. Unfortunately, it meant either A, taking the high line to overtake the cart in front or B, braking and slowing down again. To our demise I chose option A and got onto the loose stuff : speed, gravel, wet, nutter in gravity racer too proud to hit the brakes : with the end result being stuffed into the hay bales.

http://www.youtube.com/watch?v=Wz1PQGy2Y38&feature=PlayList&p=943DF85D7932CC32&index=2

http://www.youtube.com/watch?v=wJ72EaZUD-Q&feature=PlayList&p=943DF85D7932CC32&index=8

azuma | September 8, 2009 - 20:37

On Azuma's thoughts

Great to hear some other views and to find out why the skid happened! A well built cartie and a fairly spectacular crash and the bold boy walks away unscathed. (Very good news )

I don't suppose hitting the brakes would have helped much in the circumstances and probably would have made things worse. Sound that you got her going again so quickly. If anything like that had happened to me I would have been well stuffed because all my team support had been pinched to help out on the course. I had enough problems getting a coffee and the manditory pee.

peasnbarley | September 8, 2009 - 23:49

Interesting stuff

Interesting stuff tere Azuma. Did you have your onboard camera running for the practice and qualifying runs? If so, it might be interesting to work out the split times and see where you lost and gained time. I suspect the big difference is on the flat section, where the heavier carts seemed to hold their speed much better.

scottishcarties | September 10, 2009 - 08:08

Yep the camera was running

Yep the camera was running for all the runs and can be found on you tube

practice 1

http://www.youtube.com/user/hunroo4#play/uploads/4/pBmAQEkaiZo

practice 2

http://www.youtube.com/user/hunroo4#play/uploads/2/9t9AxQ2pj1g

qualifying 1

http://www.youtube.com/user/hunroo4#play/uploads/1/8QSIUVyiuIs

qualifying 2

http://www.youtube.com/user/hunroo4#play/uploads/0/iIa4Y9zmNAc

azuma | September 10, 2009 - 21:40

All those pies paid off!

I'm guessing, based on what you said, that in had the first practice and qualifying runs. Some rough timings from the vids show you both got to the hairpin in about the same time, but from the hairpin to the sugarbowl Ian was about 8 seconds slower. He last another ~15 seconds from the sugarbowl to the finish.

My guess is that is down to you not slowing down as much after the hairpin and on the last few hundred yards of the course, where the speed drops off slightly.

So - at Cairngorm at least - it seems that weight is an advantage.

scottishcarties | September 11, 2009 - 17:38

TV coverage

Has any of the footage of the cairngorn event been shown on telly yet?

azuma | September 10, 2009 - 21:55

TV coverage

It's not been shown yet. I've seen a pre-production copy of the programme and it looks really good, although the only bit I understood was my interview (it's in gaelic). Apparently it'll have subtitles when it is broadcast. I have their footage of Roy's crash too, and I'll put it on youtube after the programme has been broadcast.

I don't know when it'll be braodcast yet, except that it'll be in the first half of November. It's a programme called "Air an Rathad" (On the Road) on BBC ALBA.

scottishcarties | September 11, 2009 - 09:16

How is Roy doing? can you

How is Roy doing? can you divulge what happened to cause the accident or is it not possible to pinpoint the exact cause?

Any information to stop another accident is always helpful.

azuma | September 15, 2009 - 22:44

Enthusiasm not curbed

Roy is recovering and is his usual self, although somewhat less mobile for the time being. He keeps talking about "next year", so clearly it's not dampenend his enthusiasm. He's been using his enforced time off to draft some new safety rules. We'll probably be heading down to Cadwell together in November.

I'll put the video of it on youtube after the Air an Rathad piece has been broadcast, so you'll see for yourself what happened.

[Edit]

He's out of the wheel chair and now scooting around on crutches. He's got an automatic car too, so he's back on the road again.

scottishcarties | September 16, 2009 - 09:05

see you at Cadwell. Mind you

see you at Cadwell. Mind you got to get moving and get it all rebuilt.

azuma | September 17, 2009 - 22:01

Weight v. Speed - heavier is faster!

We did some testing yesterday to see what effect weight has, and came up with some fairly clear results.

Basically what we did was several runs down a dead straight hill, increasing the ballast throughout the experiment. There were pegs every 15m, and we used a video camera pointed out the side of the cartie to record each run so we could get the times between each peg by analysing the resulting video. We did three runs with no ballast, three runs with 10Kg and two runs with 25Kg. Taking the average from all the runs at each weight, the results showed a clear increase in speed as the ballast was increased. Not only was the top speed higher with more ballast, but the acceleration from a dead start was higher too.

I'll write it up properly and publish the results soon.

scottishcarties | September 21, 2009 - 10:24

Weight v. Speed

Hopefully I will get chance to do some testing of my own before cadwell. I currently have no ballast but I could add upto 75kg of it for cadwell. Not sure what to use for ballast yet, fixed ballast such as lead, steel or bricks or removable water ballast, I will most likley go for steel though as it is 8 times denser than water. I don't physically have space inside the car for 75 litres of water. While I have a pile of bricks and bits of concorete I think fixing them securly to the cart would be too difficult.

Anonymous | September 21, 2009 - 19:11

I wouldn't use water as a

I wouldn't use water as a ballast, even though some of the rule sets actually mention it. Unless the container is completely full, it will totally screw up the handling by shifting the CoG to the outside when you go around corners.

scottishcarties | September 21, 2009 - 21:32

Ballast

Can let you have six cast ballast plates that came off a grass spiker unit at the bowling. They are bored ready to fit with two bolts. Measure about 9" x 2" but will check if you want them as to exact measurements and weight.

Anonymous | September 22, 2009 - 10:36

Weight vs Light - heavier is faster!

Good way of doing a test and the results may come as quite a surprise to some. I always felt in Cairngorm terms heavy was the best option because of the incline and flat land. However I can't work out why heavier type carts were so quick off the mark at the start. Not being an academic the only thing I can come up with is the difference between gravity and what is termed 'normal force' which as mentioned earlier is the force we are concerned with in cartie racing? Basically weight scales measure 'Normal Force' which varies as a cart accelerates, not gravitational force which does not change. Normal Force (FN) FN = 40kg \times 9.81m/s2 \times cos(40° = 300.6 newtons. http://en.wikipedia.org/wiki/Normal_force I presume but do not know if the weight FN is reduced to say 20kg on a 40 degree slope then the force vector = 150.3 newtons ? I would love to know if someone can come up with a definitive answer. Peasnbarley

Anonymous | September 21, 2009 - 20:15

Time v. Distance graph

It certainly surprised me. I want to repeat it with a bigger range of weights, to see if the speed increases continue or if there is a point where the returns diminish or even reverse.

Anyway - here's the graph (click on it for a bigger version);

scottishcarties | September 21, 2009 - 21:48

At last there is a sport for

At last there is a sport for fat pie boys YIPEE

azuma | September 21, 2009 - 20:07

SCA develops new training aid...

A Pie

Mmmmm pies

scottishcarties | September 21, 2009 - 21:28

SCA training Aid

I presume Mmmmmm infers that the aid should be eaten and as it certainly constitutes ballast where do you propose to fit the bolt to hold it in place?

Anonymous | September 21, 2009 - 22:12

Pie mounting bracket

Good point. Clearly the Personal Impetus Enhancer (PIE) is designed for adding mass to the driver as a dietary measure, although this would not address the situation where a driver becomes peckish during a run. Clearly we need to work on some form of onboard PIE dispenser.

scottishcarties | September 22, 2009 - 09:02

Back to the weight debate

I checked our carties weight today having borrowed two identical scales and came up with a weight of 61.50kg which came as a surprise because we had gone to Cairngorm ready to hack bits off the cart if need be, as our available scales were suspect. I don't know what Roy weighed us in at but when Stephen gets time it would be very interesting to see if the time trials & race results tie in with the graph results. Anyway good to know that we can now fit a (PIE) without breaking the weight rule! Peasnbarley

Anonymous | September 23, 2009 - 20:21

Cairngorm Weights

Here's all the data I have from scrutineering at Cairngorm. I think Roy has the few missing ones.

Cartie	Weight (Kg)
Crockle	94
Run Free (Alford Bowling Club)	60
Ticketyboo	55
Jim Ewen	45
Once a Fortnight	43
Team Rooket	52
Bandit	72
Cairngorm Stag	74
The Outsiders	97
Night Train	84
Slammer Mk III	36
Lotus Eater	60
Haldir's Arrow	96

scottishcarties | September 24, 2009 - 18:57

Weight

Our cartie name was changed from Terminated Velocity after our failure to make Catterline, to Runfree but the scribes on the day obviously missed that one! Anyway we thought we were one of the heaviest carties at Cairngorm and we were not so why was our cartie quicker than the rest? Our aerodynamics were poor, weight was middle of the road but our axles, bearings and wheels were good. These assets were enhanced by effective wishbones, suspension and accurate set up of the stearing geometry. In other words simply loading a cartie with extra ballast will not make a slowish cartie into a fast cart unless the reason for it being slow is rectified first. Simply my suggestion on some I noticed Night Train(Quiet) @ 84kg good wheels and bearings 1st Cairngorm (Quietish)@ 74kg reasonable bearings 2nd Runfree (Quiet) @ 60kg Good wheels and bearings 3rd Jim Ewan (Quiet) @ 45kg Good wheels and bearings 4th Crockle (Quiet) @ 94kg Fast but unstable in side wind. Team Rooket(Noise) @ 52kg Good cart bad bearings ? 11th Peasnbarley

Anonymous | September 24, 2009 - 22:24

Added weight may not be a panacea

I suspect you're right tht simply piling on the ballast is not necessarily going to be the best way to find extra speed. I'm not sure that comparing different carties gives anything more than a general indication, as there are too many other variables involved (e.g. streamlining, tyres, bearings, driving skill). Also - the dry weights of the cartie don't necessarily correspond to the overall weight when the pilot is on board.

I want to do further testing on the effect of ballast on speed, but this time over a greater range to see if there is a point where the improvement stops. I suspect there is an optimum weight for a given cartie on a given course.

scottishcarties | September 25, 2009 - 08:15

You said :- "I'm not sure

You said :- "I'm not sure that comparing different carties gives anything more than a general indication," I think that is quite correct and sorry if my posting gave that impression. What I was trying to show was that noise equates to friction and a possible loss of speed. I add 'possible' because it depends where the friction is taking place as to how much effect it has. Excessive friction denoted by regular grinding and squeeks from wheel bearings will be bleeding energy and speed to a major extent. However friction anywhere on the cartie will detract from the 'energy store' and it is surely sense to minimise lose where this can be achieved. Tyre profile, wheel size, axles, bearing, body skin type, body weight and shape. Adding weight with ballast I would consider as fine tuning.

Anonymous | September 25, 2009 - 11:42

I think everyone noticed the

I think everyone noticed the noise from our cart (Team Rooket). We thought that by using smaller 16" wheels steel rather than alloy rims, that they would handle the side loadings better than larger diameter wheels. This is probably true, but most 16" wheels are from kids bikes and the bearings are deff not designed for high speed. Also, the wheels came with caged bearings, not ideal for reduced friction and reduced rolling resistance. New wheels, axles, brakes etc for Cadwell. Our cart has always been noisy due to the thin aluminium used for the bodywork. At least you know when we are on the course

Also noticed a whisper from the Cheats cart and can only put this down to the hydraulic brakes not fully releasing. This is a problem some downhill mountain bikers have experienced.

I was surprised at the range of weights. We thought we were pushing our luck around the 50Kg mark and any heavier would be a disadavntage, especially with me on board.

azuma | September 25, 2009 - 20:38

Whispering and other noises

Our cable disc brakes needed adjustment virtually after each run to ensure there was no binding. I felt the tow back to the top of the hill was the cause because the brakes were on/off quite a lot during the tow. I know our offside brake was shushing going up the incline during the final and I cursed myself for missing out on the brake check.

Some of the whispering noise comes from air friction on the spokes and wheels.

A vibrating whispering, is the sort of noise that comes from air molicules attaching and detaching from bodywork.

Azuma's comment on aluminium is spot on and we regret sheeting the floor and seat with aluminium without first sticking on some cushion tape before riviting the sheet in place. However learning from our mistakes, or making improvements as funds permit is all part of the fun of running a cartie. If Graham still has places at Cadwell Park our bodywork will probably still be half a roll of Denso tape which although it does'nt sqeek it does stick like hell to you trouser legs and makes getting in and out somewhat problamatic.

peasnbarley | September 25, 2009 - 21:31

There were some strange

There were some strange noises coming from Colin's cartie too, although I think they were coming from the pilot rather than the vehicle.

scottishcarties | September 26, 2009 - 12:15

Strange noises

Without a doubt that particular cartie and pilot should have won a special award for providing so much entertainment on the day. Colin gave it his best shot and his antics going down the course make great viewing on Youtube. Can't say I enjoyed his first squirt going into the hairpin with my eye full of water but then I should have had my visor right down. Having watched a few Youtubes I will need to fit a pigeon on the back of my cart & carry a copy of my birth certificate!

I have just noticed in a previous post that as well as having some strange noises and sqeeks this author has a strange spelling of squeak!

peasnbarley | September 26, 2009 - 15:27

Soapbox racer - heavier is better?

Just found a really interesting thread on Physics Forums that gives all the maths behind the weight v. speed debate. Have a look at Soapbox racer - heavier is better?

Post #3 just about nails it, I reckon.

scottishcarties | October 1, 2009 - 10:54

Lightweight cart came joint first at belchford round 5

Something worth looking at is the results from round 5 of belchford. This was the round with no chicanes and thus was basically a straight course with no need to brake. Two carts got the same fastest times which were Crockle and LG, the LG cart only weighed 31kg empty making it one of the lightest there. The speed of a cartie is a function of a whole load of variables however the main ones I see, in order of importance are: Air drag (CdA)-- At higher speeds this is the main force acting to slow you down, reducing the CdA of your cart is IMHO the best thing you can go to gain speed. Air drag increases with the cube of velocity thus the faster you go the more important it is to reduce your CdA. For more info see http://en.wikipedia.org/wiki/Drag_coefficient Tyre drag (Crr)-- Tyre drag depends on the construction of your tyres, the size of your wheels, the pressure in the tyres and your wheel alignment/tracking. A better quality slick racing tyre will generally have less rolling drag than a cheap knobbly off a kids bike. A good quality tyre will also hold a pressure of around 100Psi or more. Wheel alignment is very important, if your wheels are not parrellel when running stright then your wheelss will scrub leading to extra tyre drag and rapid tyre wear. Also when the wheels are turned they should have accermann compensation (inner wheel turns more than the outer) to prevent scrubbing in turns) Weight -- The more weight you have the more there is for gravity to act upon. More weight will give you more inertia which is important if there are flat or uphill sections. Bearing friction -- This is IHMO insignificant compared to the CDA, regular catridge bearings are fine.

Anonymous | October 1, 2009 - 20:41

Aerodynamic drag is

I think you made a slight typo' there. Aerodynamic drag is proportional to the velocity squared, not cubed.

Appart from that, of course, you're right about the effect of aerodynamic drag. Above ~15mph it is likely to be the most significant cause of friction.

Considering the Belchford results, you could also have said that "heavyweight cart came joint first". Crockle runs pretty close to the maximum allowed, and I'd guess the pilot is a little heavier too...

All the results show is that a well made cartie will go faster than a less well made one, regardless of the weight. But that doesn't mean that the weight of a given cartie is not significant to that carties speed.

scottishcarties | October 2, 2009 - 08:59

Is low CdA always a good thing?

Aerodynamics are important and have a bigger effect as speed increases, but is it always a good idea to be as streamlined as possible? What if there is a tail wind? All other things being equal, won't the less streamlined carties get more of a boost off the line?

scottishcarties | October 5, 2009 - 14:07

On the saturday at Cairngorm

On the saturday at Cairngorm Extreme, if a cart had been fitted with a double aeroplane type tail that opened at right angles to the body, the cart would have taken off like s**t off a shovel. However if we are to believe everything we read as in the case of the Richard's Castle posting, the last thing I would want would be an aerodynamic shape!

I would certainly be flapping hard and shouting Nae Jessies here then!

Quote :- "The course is 550m in length, with a vertical drop of 50m and gives a speed of up to 45mph." I think you would probably hit more than 70mph with the brakes hard on!

peasnbarley | October 5, 2009 - 17:34

The map of the Richards

The map of the Richards Castle Soap Box course confirms the measurements.

scottishcarties | October 5, 2009 - 19:09

We are in a serious mood

We are in a serious mood today. Yes a 50metres vertical drop spread over a 550 metre course described as a gently sloping metalled private road.

And yes you posed a sensible question on aerodynamics and got a daft answer - sorry.

peasnbarley | October 5, 2009 - 20:10

Heavier = faster, but streamlined = even faster....

There's an explanation of why more weight = more speed on the Soapbox Racer Physics page. There is also some number crunching that explains why weight isn't everything and why a lightweight cartie will often outperform one that is significantly heavier.

scottishcarties | January 21, 2013 - 15:24

The great weight debate

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