Racing flats versus Regular training shoes

TheRoadRunner

Quick question that arose from a discussion on shoes in the training logs.

How much (if any) of an advantage do people feel they gain by racing in lightweight flats versus regular training shoes?

For me I think over 5k the difference could be 20 seconds although I have nothing to back this up.

The reason I ask relates to deciding on wearing a lightweight shoe or cushioned shoe for marathon running. If you scale my 20 seconds per 5km upwards this would be close to a 3 minute improvement over the marathon distance (again no evidence for this). However in my case I wouldn't get past 14 miles without cramping issues. I guess you need to train in racing flats to get use to them and build up certain neglected muscles/tendons.

Generally speaking, people seem to get so stressed about small differences in shoe weights (we're talking 50-60 grams) when they would be probably better off loosing a couple of lbs of excess body weight.

ecoli

TheRoadRunner wrote: »

Quick question that arose from a discussion on shoes in the training logs.

How much (if any) of an advantage do people feel they gain by racing in lightweight flats versus regular training shoes?

For me I think over 5k the difference could be 20 seconds although I have nothing to back this up.

The reason I ask relates to deciding on wearing a lightweight shoe or cushioned shoe for marathon running. If you scale my 20 seconds per 5km upwards this would be close to a 3 minute improvement over the marathon distance (again no evidence for this). However in my case I wouldn't get past 14 miles without cramping issues. I guess you need to train in racing flats to get use to them and build up certain neglected muscles/tendons.

Generally speaking, people seem to get so stressed about small differences in shoe weights (we're talking 50-60 grams) when they would be probably better off loosing a couple of lbs of excess body weight.

Never race out of flats so can't compare in terms of race performances however there have been times when I find that I am comparing times of sessions between flat's and normal trainers for my intervals. What I have found for these is that it is roughly a second per lap or so difference so you would be talking 4 sec/mile roughly. This seems to be a general consensus amongst many club runners I have run with as a rough guide however this is in relation to track surface as opposed to road so I would say your 20 sec on road for 5k would be bang on with my views.

You do need to get used to them though which is why my intervals and some of my shorter tempos are done in flats while the rest of training is done in normal trainers

I think the point you make at the end is the most important part. People spend alot of times being penny wise and pound foolish in terms of trying to save every gram on there feet while ignoring the elephant in the room of the extra lbs on the gut. Flats/ lightweight racers are great benefit but if the weight is up they are going to cause a whole load of injury problems in the long run

Seres

I have only one pair of racers that i got before june and have only ever wore them for races except for one or two trial runs at the start when i bought them .I've done 3 races since June and havent had any problems adjusting They are so light and fexible , do you really need to break them in or use them regularly ?

Gringo78

TheRoadRunner wrote: »

Generally speaking, people seem to get so stressed about small differences in shoe weights (we're talking 50-60 grams) when they would be probably better off loosing a couple of lbs of excess body weight.

Unneccessary weight on the body is usually carried around the gut, which in a good running style is generally only moving in a horizontal direction. The extra weight in the runner though moves from the ground up to say 80-90cm off the ground repeatedly 80-120 times per minute so 50-60grammes on the feet is as significant as say 1kg on the gut.

But agree, safer to get rid of the 1kg off the gut first before experimenting with flats as the risk of injury with flats is probably proportional to body weight anyway.

Murta

Seres wrote: »

I have only one pair of racers that i got before june and have only ever wore them for races except for one or two trial runs at the start when i bought them .I've done 3 races since June and havent had any problems adjusting They are so light and fexible , do you really need to break them in or use them regularly ?

Different for everybody. I for one, need to allow feet type to adjust to specific pair of shoes no matter how flexible. Then again, my foot biomechanics are pretty shoddy.

TheRoadRunner

Gringo78 wrote: »

Unneccessary weight on the body is usually carried around the gut, which in a good running style is generally only moving in a horizontal direction. The extra weight in the runner though moves from the ground up to say 80-90cm off the ground repeatedly 80-120 times per minute so 50-60grammes on the feet is as significant as say 1kg on the gut.

what about the extra energy required to carry the gut fat?

Gringo78

TheRoadRunner wrote: »

what about the extra energy required to carry the gut fat?

What I mean is 50g on a running show may seem an insignificant weight but its maybe the equivalent of 1kg on the gut. You have in a marathon a total upward vertical motion of your foot of 20km as well as the horizontal motion of 42km.

I agree though, gut fat bad but 50g on a shoe hugely more significant than 50g on the gut.

By the way, Kayano's are one of the heaviest runners out there - they would feel like conrete blocks on me. In your case, being a fast, efficient and not overweight runner, I would guess your choice of racing flat may have been the issue. A Kayano weighs around 350g I think, the lightest racing flats are <200g but you get flats with varying degrees of cushioning. I use Asics DS Racers (all racing & training) which weigh 219g, but to pick them up and try them you would not think from the cushioning they are flats, cerainly looking at them you would not classify them as flats. I have a pair of Kilkenny XC4 flats (optional spikes) which weigh only 30g less than the DS racers but i would not do a 10 mile race in them.

So I think you could improve greatly on the Kayano's, something halfway between flats & Kayanos.

jeffontour

Seres wrote: »

They are so light and fexible , do you really need to break them in or use them regularly ?

I think if you're coming into a flatter style shoe from a large heel to toe differential standard trainer then you do need to take time to build up the miles. Not to break the shoe in but to ease your body into the change in style that flatter shoes tend to encourage.

This transition need not be as long of course if you're already a graceful fore/mid foot runner.

TheRoadRunner

Gringo78 wrote: »

So I think you could improve greatly on the Kayano's, something halfway between flats & Kayanos.

Yeah I tried the DS trainers myself earlier this year and still had issues with cramping. I suppose it's something to work on and get the legs use to less cushioning.

menoscemo

It comes down to your running style I guess.
I like to wear flat, neutral shoes for everyday running, and can get away with wearing flats in a marathon with no problem. If someone needs cushion and support in their trainers, wearing a racing flat in a marathon would be inadviseable.

Do they make me any faster? I don't know, but they certainly feel lighter and 'faster'. My only point of reference is running a mile race 15 seconds faster in flats than I did in Trainers a few weeks previous (I had turned up with spikes but they wouldn't let me use them on the track). I was a lot more tired for the first race though, so this is also a factor.

Krusty_Clown

Are we actually talking about racing flats though, or just lightweight training shoes?

DS Trainers/Mizuno Precisions/etc are not racing flats (in fact the Mizuno WaveRider is a similar weight to the DS Trainer). I have never worn racing flats, because I don't think I have the form, or would reap the benefit, but do all my races in Precisions, which are a very lightweight cushioned shoe (albeit less cushioned than the Wave rider).

Wave Musha, Wave Universe, Wave Revolver would be examples of Mizuno racing flats.

Seres

Gringo78 wrote: »

What I mean is 50g on a running show may seem an insignificant weight but its maybe the equivalent of 1kg on the gut. You have in a marathon a total upward vertical motion of your foot of 20km as well as the horizontal motion of 42km.

I agree though, gut fat bad but 50g on a shoe hugely more significant than 50g on the gut.

By the way, Kayano's are one of the heaviest runners out there - they would feel like conrete blocks on me. In your case, being a fast, efficient and not overweight runner, I would guess your choice of racing flat may have been the issue. A Kayano weighs around 350g I think, the lightest racing flats are <200g but you get flats with varying degrees of cushioning. I use Asics DS Racers (all racing & training) which weigh 219g, but to pick them up and try them you would not think from the cushioning they are flats, cerainly looking at them you would not classify them as flats. I have a pair of Kilkenny XC4 flats (optional spikes) which weigh only 30g less than the DS racers but i would not do a 10 mile race in them.

So I think you could improve greatly on the Kayano's, something halfway between flats & Kayanos.

thanks, where did you get this info ? I only got the racers recently because i wasnt too sure of the added benefit . I figured a decrease in weight of 40g from one shoe to the next was gonna have little or no impact on race times going by the improvements gained in time on 1kg body weight reduction ( think 1kg is bout 25sec over 10k , will prob be corrected on this )

christeb

Seres wrote: »

thanks, where did you get this info ? I only got the racers recently because i wasnt too sure of the added benefit . I figured a decrease in weight of 40g from one shoe to the next was gonna have little or no impact on race times going by the improvements gained in time on 1kg body weight reduction ( think 1kg is bout 25sec over 10k , will prob be corrected on this )

it's a similar concept to "rotational weight" in cycling. The weight in the running showe is far away from your centre of gravity, and moves a lot more in different directions, as gringo says. You are therefore 'pushing' this weight a lot more than the weight around your gut.

There must be some calculations on the web somewhere. Personally, I find a huge difference even in my training shoes. The Kinvaras I use require a lot less energy than the Lunar Trainers I alternate them with.

TheRoadRunner

Krusty_Clown wrote: »

Are we actually talking about racing flats though, or just lightweight training shoes?

Both really. Original post was more concerned with racing flats but light weight training shoes can be considered as well

Krusty_Clown

TheRoadRunner wrote: »

Both really. Original post was more concerned with racing flats but light weight training shoes can be considered as well

I picked up a few pairs (and put them straight back down again!) at the expo last week, and was amazed by the difference between the two. The racing flats were closer to a delicate slipper than a typical running shoe. Does anyone here actually wear proper racing flats?

TheRoadRunner

Krusty_Clown wrote: »

I picked up a few pairs (and put them straight back down again!) at the expo last week, and was amazed by the difference between the two. The racing flats were closer to a delicate slipper than a typical running shoe. Does anyone here actually wear proper racing flats?

Eh yeah me, I think. I wear asics DS racers up to and including 10 mile races.

menoscemo

Krusty_Clown wrote: »

Does anyone here actually wear proper racing flats?

RQ wears them for every single run.

I'd wear flats (I have Brooks green silence, Saucony Kinvaras, Mizuno Musha and Nike Lunar racers) for all speedier training runs and all races. I have even started to wear the Kinvaras for some LSR's and recovery runs.

I have Lunar glides for other 'standard' runs.

I used to wear Pegasus for all my runs and would get some ankle and Knee injuries from time to time, since i switched to more 'minimalist' shoes I haven't had any injuroes to speak off.

Flat shoes suit my gait and foot strike, (I'd be more likely to get injured in a bigger clunkier shoe with more cusioning/support) but I believe they are not suitable for everyone.

TheRoadRunner

menoscemo wrote: »

Flat shoes suit my gait and foot strike, (I'd be more likely to get injured in a bigger clunkier shoe with more cusioning/support) but I believe they are not suitable for everyone.

menoscemo, are you going to be barefoot soon. It seems you are on that path

BeepBeep67

Krusty_Clown wrote: »

Does anyone here actually wear proper racing flats?

Yes - but I wouldn't go more than 5k in them and they're fine for shorter track workouts.

BobMac104

I have a pair of Asics hyperspeed 4's and a shiny new pair of adidas adizero pro 4's. The adizeros had their first 8 miler this morning and really enjoyed them. very light, very firm forefoot and good grip + very bright orange!!. If I had a few more weeks i may have used them for DCM but i will use the Asics instead as i feel confident in them.
I would prefer if both had no heel toe diff at all but its not too bad. (4/5mm i think)
I do most miles in vibrams so the flats are like marshmallows to me for the first few minutes when i change over.

TFBubendorfer

Krusty_Clown wrote: »

Does anyone here actually wear proper racing flats?

My beloved Lunaracers only weigh 170g each.

menoscemo

TheRoadRunner wrote: »

menoscemo, are you going to be barefoot soon. It seems you are on that path

Nope I'm stopping here. I'm too afraid of stones and Glass.

dev123

What is the definition of a racing flat?

My understanding is that it is independent of weight. Racing flats are light weight due to the fact that they have little or none of the wave, air, gel technology lumped into the sole but are Kinvara's, Green Silence or DS Racers actually considered flats? Or are they more minimalist?

Does it not relate more to the heel-to-toe drop of the shoe rather than the weight?

A Kinvara may feel like a flat to somone who has just stepped out of Kayanos but I don't believe that makes them a racing flat.

Krusty_Clown

Well there you go.. I wouldn't have considered running in racing flats unless I was significantly faster, as I would've have thought than any weight advantage would be greatly off-set by the heightened risk of injury given my weight and running form. You live and learn..

menoscemo

dev123 wrote: »

What is the definition of a racing flat?

My understanding is that it is independent of weight. Racing flats are light weight due to the fact that they have little or none of the wave, air, gel technology lumped into the sole but are Kinvara's, Green Silence or DS Racers actually considered flats? Or are they more minimalist?

Does it not relate more to the heel-to-toe drop of the shoe rather than the weight?

A Kinvara may feel like a flat to somone who has just stepped out of Kayanos but I don't believe that makes them a racing flat.

Yes, they are flats. Kinvaras have a 4mm drop from heel to toe, which is almost nothing. Less than most 'Racers' (e.g Lunar racers have an 8mm drop).

I guess a racing Flat is a light shoe with litlle drop from hell to toe (maybe less than 10mm?)

BobMac104

menoscemo wrote: »

Nope I'm stopping here. I'm too afraid of stones and Glass.

ever try it? Its actually grand. ive only ever done a couple of miles at the end of a run and on a lovely tarmac path that was used alot so it was clean enough. Its a cool feeling but you do get a few stares though. Ive tried it alot more on grass (around pitches etc) and its great fun. Not an every day practice for me but like i said its a bit of fun every now and again.

I can feel a few :rolleyes:'s coming along.....

TFBubendorfer

menoscemo wrote: »

Yes, they are flats. Kinvaras have a 4mm drop from heel to toe, which is almost nothing. Less than most 'Racers' (e.g Lunar racers have an 8mm drop).

I guess a racing Flat is a light shoe with litlle drop from hell to toe (maybe less than 10mm?)

I have a different interpretation. Just because the Kinvaras have little heel-to-toe drop does not make them a racing flat. As light as they are, I count them as lightweight trainers, and the Lunaracers are my preferred racing flats, and it has nothing to do with the amount of heel drop (which, to be perfectly honest, I do not even notice).

About 2 months ago I was wavering which shoe to wear for a race. The Kinvaras felt so good and light in training that I was about to pick them, but did one run in the Lunaracers just to be sure. The difference was amazing, and it was all down to the reduced weight. I wore the Lunaracers.

Seres

TFBubendorfer wrote: »

I have a different interpretation. .

you think its down to weight only then ?

menoscemo

TFBubendorfer wrote: »

I have a different interpretation. Just because the Kinvaras have little heel-to-toe drop does not make them a racing flat. As light as they are, I count them as lightweight trainers, and the Lunaracers are my preferred racing flats, and it has nothing to do with the amount of heel drop (which, to be perfectly honest, I do not even notice).

About 2 months ago I was wavering which shoe to wear for a race. The Kinvaras felt so good and light in training that I was about to pick them, but did one run in the Lunaracers just to be sure. The difference was amazing, and it was all down to the reduced weight. I wore the Lunaracers.

I would wear lunarracers for races up to HM and Kinvaras for marathons. Yeah I agree that the lunarracers are lighter (6.5 oz I think?) and a bit faster but the Kinvaras are only about 7.5oz themselves, so it's not like theres that much difference.

I'd consider them both to be racers

T runner

TFBubendorfer wrote: »

I have a different interpretation. Just because the Kinvaras have little heel-to-toe drop does not make them a racing flat. As light as they are, I count them as lightweight trainers, and the Lunaracers are my preferred racing flats, and it has nothing to do with the amount of heel drop (which, to be perfectly honest, I do not even notice).

About 2 months ago I was wavering which shoe to wear for a race. The Kinvaras felt so good and light in training that I was about to pick them, but did one run in the Lunaracers just to be sure. The difference was amazing, and it was all down to the reduced weight. I wore the Lunaracers.

The lunar-racers are almost perfect for the marathon. You do need cushioning for the marathon but it must be light weight to maintain cadence. Also the very flat shoes with no drop are only suitable for people running close to 5 minute miles in a marathon (at speeds where the calves and ankle have a big range of extension). Otherwise, cramps etc in the calves.
Lunar racer tick all the boxes IMO.

Is there good traction on the triangular lugs on the Kinvavra may i ask?

Gringo78

I do every single run in Asics DS Racers. Have Lunaracers also and as they are lighter again than the racers I wear them in shorter races (up to HM) but only in dry conditions....they're sh*te in the wet. I'm slightly faster in the lunaracers but prefer the DS racers

dev123

After a quick search on-line there seems to be agreement that racing flats could knock 3-5 minutes off your marathon time

http://www.marathonbible.com/marathon-racing-flats.html

http://www.the-fitness-motivator.com/racing-flats.html

Now if we can agree on what a racing flat actually is it would be pbs for everyone in the audience

Pronator

I wore the DS racers in the Rotterdam marathon this year. It was the first time I have put on a lighter shoe for a marathon. Apart from needed two hip and knee replacements afterwards :eek: they were fine.

If I was to wear a pair of asics 2160's and run a 5k I would not be much slower than wearing the DS racer. I think the benefit of wearing a lighter shoe (not necessarily a flat) would be more pronounced the greater the distance you cover.

I plan on wearing the DS racer in DCM, I'll be crippled for days after but I think if you look at the many thousands of times you lift your feet over the course of 26.2 miles, 20-30g less for each lift has to make a difference:rolleyes:

Incidently, I bought a pair of DS sky speed, these are a neutral light weight runner and not a flat. As I pronate I would not wear these for longer runs.......you would need shades for these bad boys:D

dna_leri

Krusty_Clown wrote: »

Well there you go.. I wouldn't have considered running in racing flats unless I was significantly faster, as I would've have thought than any weight advantage would be greatly off-set by the heightened risk of injury given my weight and running form. You live and learn..

Krusty - I would recommend you try them for shorter racers. I got a pair of Brooks T5s earlier this year and have worn them for up to 10K. You really can feel the difference, though I used strides to get used to them first.

Even better I only paid 25 quid for my end of line 6oz rzcers.

RacoonQueen

T runner wrote: »

Is there good traction on the triangular lugs on the Kinvavra may i ask?

Not sure if it's comparable to the sort of runs you'd be doing in the mountains but I've worn them on the hills in the phoenix park(the grassy ones) in all sorts of weather and the grip is very good. No problems and no slipping.

As meno said, I wear racing flats and 'minimalist' shoes for more or less every run. The most cushioned shoe I wear is the saucony fastwitch 4;



Tonight I ran 11 miles in hattoris;



I plan on bringing up the distance in the hattori but have done 20 miles in lunaracers and will wear them if I do DCM.

I think it's more about training yourself to be able to run in them than anything else. There are some people with mad gait patterns who I wouldn't recommend them too but I've seen a few people who've posted in this thread run (trust me, I'm obsessed I actually watch how yee run) and I don't see why they couldn't run longer distances in racing flats.

Edit: I agree there's a difference between racing flats and 'minimalist' shoes hattoris, road-x and minimus are definitely minimalist compared to your traditional racing flat. Lunaracers are definitely a racing flat. I think I'd consider the kinvara's as more of a lightweight trainer to be honest. I won't be wearing them as racers any more, though I used to.

Edit 2: On the weight thing, I'll also point out that I'm probably around half a stone heavier than whats recommended for racing flats and have no injury problems. The last time I was out with a running related injury was May/June 2009 when I missed about 6 weeks from wearing mizuno wave creation.

TFBubendorfer

Seres wrote: »

you think its down to weight only then ?

Pretty much, yes. That's just my personal opinion, of course.

TFBubendorfer

T runner wrote: »

Is there good traction on the triangular lugs on the Kinvavra may i ask?

I never encountered any problems whatsoever. From dirt roads to wet asphalt, traction was never an issue.

They are not hill-running shoes, though. The lugs are not comparable to anything you'd have on Inov-8s or similar.

RacoonQueen

TFBubendorfer wrote: »

Pretty much, yes. That's just my personal opinion, of course.

You should get a pair of hattori or road-x 155. If you can do 50 miles in lunaracers you'll be able to do distance running in those shoes no bother.

Womens hattori are 3.8 oz compared to 4.5oz for the lunars - haven't had a chance to weigh the road-x yet.

pconn062

I get a bit confused by all this racing flat stuff. Could anyone recommend a good pair of racing flats that could cover all distances, maybe apart from marathon. Is there a flat that would work from 3-5k up to half marathon or would you have to have a few pairs? I feel my pegasus would do me for the marathon cause at the moment I am not chasing super fast marathon times so the extras support I feel would be better.

bart simpson

i have a pair of asics hyperspeed 4.....i only use them for races, i feel they knock about 5 sec a mile
i have done the dublin half in them, but i wouldnt do a full marathon in them, they are a bit harder on the feet alright but a full minute over a half or 10 miler makes them worth it and i feel the effects of waring them get less the more i use them

Hard Worker

Racing shoes are not just determined by weight. Primarily, it is down to the type of last the shoe is built on and the amount of flexibility in the shoe. Training shoes are designed with cushioning and support and can have all sorts of gadgets to stop foot roll etc.
It should be remembered that if you wear a training shoe ( support / cushioning ) in a race, you actually use more energy trying to get on your toes and race because you are working against the cushioning and gadgets. The more flexible the shoe, the less energy you will use. Basically, if you were to go out and run a 5 minute mile one day in trainers and the next day in racers, you would find the 5 minute mile in racers was so much easier.
This doesn't mean that you can change over immediately. You do need to adjust and build up your tolerance.
I'm surprised that RoadRunner and Krusty don't ( or feel they can't ) wear racers. Build up your 20 x 400 or 8 x 800 in them and wear them in 10K's and you will soon get used to them and find great benefit in them.

TFBubendorfer

RacoonQueen wrote: »

You should get a pair of hattori or road-x 155. If you can do 50 miles in lunaracers you'll be able to do distance running in those shoes no bother.

Womens hattori are 3.8 oz compared to 4.5oz for the lunars - haven't had a chance to weigh the road-x yet.

Maybe, maybe not. But since I just had to chuck out the Kinvaras after only 525 miles on them because they hurt my shin (at least the pain stopped once I stopped using them), I'm a bit weary to try something even more minimalistic (not that the Kinvaras are minimalist shoes).

But yes, I did indeed wear the lunaracers in a 50 mile race and would (will ) do so again.

TheRoadRunner

Hard Worker wrote: »

I'm surprised that RoadRunner and Krusty don't ( or feel they can't ) wear racers. Build up your 20 x 400 or 8 x 800 in them and wear them in 10K's and you will soon get used to them and find great benefit in them.

You hit the nail on the head regards building up to wearing them by using them in training. I do use them for races shorter than 10 miles although I am usually sore for a few days. It's something I'll try and incorporate into my training over the next few months.

Krusty_Clown

Hard Worker wrote: »

I'm surprised that RoadRunner and Krusty don't ( or feel they can't ) wear racers. Build up your 20 x 400 or 8 x 800 in them and wear them in 10K's and you will soon get used to them and find great benefit in them.

Sounds advice. I'll pick up a pair and try them for the first time in Dublin marathon.

Gringo78

Krusty_Clown wrote: »

Sounds advice. I'll pick up a pair and try them for the first time in Dublin marathon.

All joking aside - if you are trying out racing flats (based on recent painful experience) do it at a track or loop circuit where you can change out of them conveniently. I tried to break in a new pair of Saucony Kilkenny XC4's and so put them on for a short 4-5 mile easy run - 2 miles from home I realised they were cutting the back of my ankles of me, the 2 miles back home was not pleasant at all and I thought about even running barefoot - 2 of the biggest blisters I've ever got for my troubles.

menoscemo

Krusty_Clown wrote: »

Sounds advice. I'll pick up a pair and try them for the first time in Dublin marathon.

Your used to Mizunos right? The wave musha should suit you, I picked up a pair in base 2 race a few weeks ago for €45. At 8oz they are not overly light and should be a good 'transition' shoe.

T runner

RacoonQueen wrote: »

Not sure if it's comparable to the sort of runs you'd be doing in the mountains but I've worn them on the hills in the phoenix park(the grassy ones) in all sorts of weather and the grip is very good. No problems and no slipping.

Excellent. I do a road/off road race in Sligo every year: need some grip for a grassy descent..that sounds perfect!!!!

As meno said, I wear racing flats and 'minimalist' shoes for more or less every run. The most cushioned shoe I wear is the saucony fastwitch 4;

I do likewise. Have all kinds of racers. Wave musha, brooks T6, DS racers, luna racers etc. Havent tried the Hattoris or minimalist stuff yet though.

Got there by buying each consecutive pair of trainers with slighly less cushioning and support. I have DS trainers too but dont wear them so much.

TheRoadRunner

The main thing I've learned from this thread. There are some serious shoe collectors on this message board. Imelda Marcos would be impressed

RayCun

as would Slogger jogger

pre

Pronator wrote: »

I wore the DS racers in the Rotterdam marathon this year. It was the first time I have put on a lighter shoe for a marathon. Apart from needed two hip and knee replacements afterwards :eek: they were fine.

If I was to wear a pair of asics 2160's and run a 5k I would not be much slower than wearing the DS racer. I think the benefit of wearing a lighter shoe (not necessarily a flat) would be more pronounced the greater the distance you cover.

I plan on wearing the DS racer in DCM, I'll be crippled for days after but I think if you look at the many thousands of times you lift your feet over the course of 26.2 miles, 20-30g less for each lift has to make a difference:rolleyes:
Incidently, I bought a pair of DS sky speed, these are a neutral light weight runner and not a flat. As I pronate I would not wear these for longer runs.......you would need shades for these bad boys:D

I bought creps for DCM

anymore

I started off running marathons in the lightweight Nike Lunar and really loved them but now have to use the heavier Nike structure for more support. Wish I could use the Lunars again though.