Am I a moron?

[Rontele]

Spats,

The last person who challenged pechelman's engineering was turned into a rubix cube.

[pechelman]

I'm pretty sure you're way off base here and this is the first I've heard of anything like that), it doesn't decrease as much as the weight increases.

Firstly, no, I am not way off base here and Im actually correct.
The numbers above each curve, ie 1.4, are the tires friction coefficient.


When increasing the normal load on a tire the less the friction coefficient.
It has to do with the different mechanisms by which tire rubber produces friction, and in this case, predominantly the hysteresis frictional mode.
For more information on this subject, I recommend THE RACING & HIGH-PERFORMANCE TIRE by Paul Haney.

As far as the rate of decrease with the rate increase, i cant really comment because these curves differ drastically with construction, rubber, pressure, surface, and all sorts of wonderful things that make a tire engineer's life "interesting"

For a bike though, I dont think this is really a big issue. The rear tire load difference from a 16.75 and a 17" CS isnt that significant, and really goes to how one weights their bike as that is much more significant as you can move your CG by not just inches but FEET.

Also, with regard to putting more weight on the tire you dont want to slide, I think you're mistaken. Ever drive a gocart? People lean inwards to weight the inside tires to more evenly load all 4 tires. The more evenly loaded they are the better they preform and more total grip you have available.
Its most definitely not the inside tires theyre concerned with about sliding as its the outside ones which will peak earlier and break free.

In one sentence, weight transfer, lateral or longitudinal, is generally a bad thing with regard to maximum grip and friction. (things change a bit on a bike on dirt though)

Try it yourself. Lean all the way back, take a hard turn, and tell me what happens. Besides being difficult to steer, if you go fast enough, your front tire pushes and you go down.

Im not sure I was ever arguing that if you get your weight all the way back into a turn that you wouldnt push, cause you will. What I was saying, is that with a shorter rear and TT, this allows me to get your weight whereI want easier. On my last bike I always had trouble getting back behind my saddle and I never had trouble getting forward. To me this says I need a slightly shorter rear and a shorter TT.

Think about it: if it really made much of a difference, tandems (with five-foot chainstays!) couldn't turn at all.

I think the difference here is in the turn radius, like with skis and sidecut.
Or just turning radius on cars. Obviously the wheelbase also effects this, but the CS is part of the WB. And again, my primary goal here with the short CS is to be able to get back and have a shorter bike on top.

If you want a really long front end, you'll either have to seriously hunker down and forward in turns and while climbing, or you'll have to increase chainstay length. This may be worth it for easy manualability, but based on my experience, I think people obsess way too much about short chainstays and then wonder why climbing sucks so much.

Im really not concerned that much with climbing to be honest.
Ive got a fork that locks me way down and changes the geo significantly.
Plus I generally dont go on rides with super techy climbs very often and that is a compromise im willing to take.

Since when is 16.75" a really short chainstay though?
Im coming from a bike that I think has a 17 to 17.2" CS (I forget) and I always felt that if it was just a tad shorter, in addition to the TT, things would be much better in steeper\techy descents.

Basically, I didnt just pull these numbers out my ass.
I rode my last bike for 2 seasons in just about every type of trail we have here, found what I like, and found out what I didnt like. Lets just say I was "fit" by "trial&error".

[flowtron]

predominantly the hysteresis frictional mode.

It is now my goal to use this phrase when selling tires. Sick.

[pechelman]

good luck with that. hehe

yea, im a dork.
what can I say?

Sphericity?

[brettf]

My head exploded.

[kidwoo]

This thread got funny.

[Spats]

(Warning: nerd talk ahead.)

The rubber coefficient of friction graph is interesting. Thanks! However, I'm pretty sure it has no relevance to mountain bike tires:

That graph is measured from racing cars with race tires, which have slick tread and wide, flat cross sections, on dry pavement, which can generate lateral forces far in excess of any round-tired two-wheeled vehicle. Also cars create meaningful downforce. Note you have to get to 1.4G-2G before the graph stops monotonically increasing.

Expensive street-legal sports cars are doing very well to pull 1G on flat, dry pavement, and street-legal motorcycles get even less. A bicycle on dirt with narrow, knobby tires seems unlikely to match their grip.

Forces under 1G are still well within the monotonically increasing and nearly linear part of the graph you posted, which appears to mean that for bicycles, additional weight on a wheel will always result in more grip, all the way up to the limits of adhesion of the dirt.

This agrees with good motorcycle and bicycle riding technique and with all my riding experience. For instance, when climbing steep hills, we get much better traction when sitting than when standing, because standing moves our weight forward, off the driving wheel, and the best traction is gained when 100% of our weight is on the rear wheel, just before we loop out.

This also means that (assuming the wheel is not being driven) the greatest traction in a turn occurs when weight is distributed evenly between the two wheels, because putting more weight on one wheel takes it off of the other. Given that neutral riding position on most mountain bikes is more like 40/60 for race hardtails and up to 30/70 for freeride bikes, and that losing the front is much worse than losing the rear, the problem is generally how to get more weight on the front tire.

This is why dirtbike riders put their inside leg forward in corners: they are trying to keep as much weight on the front wheel as possible to keep from pushing and going down. (Watch a motocross video: they're already jammed forward on the gas tank, up near the handlebars.)

As long as the slope of the curve is positive, greater weight = greater traction, and my point stands. The only place the curve trends downward is under lateral forces far greater than any bicycle tire can possibly see.

For a bike though, I dont think this is really a big issue. The rear tire load difference from a 16.75 and a 17" CS isnt that significant, and really goes to how one weights their bike as that is much more significant as you can move your CG by not just inches but FEET.

Yes, you can move your CG around, but when you are standing on the pedals, you also want to keep your arms/upper body loose so your bike can absorb bumps and not throw you around. There's only so far you can move either way without bracing yourself against the handlebars, which you really want to avoid.

Also, when climbing steep hills, the balance is actually very delicate: you're trying to maintain as much weight as possible on the rear without going over. Too short a chainstay makes climbing a giant PITA (doubled over to avoid looping out) instead of just a grind.

If you're mainly doing steep downhills, this biases your weight forward and obviously a long front end/short back end makes more sense. Also if you're doing a lot of jumps, long chainstays tend to get kicked up by the lip and make you endo, so I can see why kidwoo rides what he does.

Also, with regard to putting more weight on the tire you dont want to slide, I think you're mistaken. Ever drive a gocart?

Yes. I've also taken an intensive two-day class learning to dirt-track motorcycles, which is a lot more applicable to mountain biking, not to mention riding motorcycles for many years before I ever touched a mountain bike, so I'm not completely talking out my ass here.

The reasons you lean inward on a go cart are so the inside tires don't lift off the ground, and because it's hard to stay steady with the forces of the turn pulling at right angles to your body.

In one sentence, weight transfer, lateral or longitudinal, is generally a bad thing with regard to maximum grip and friction. (things change a bit on a bike on dirt though)

Of course...we're talking about the static case. The dynamic case involves real math, not just handwaving.

Im not sure I was ever arguing that if you get your weight all the way back into a turn that you wouldnt push, cause you will. What I was saying, is that with a shorter rear and TT, this allows me to get your weight whereI want easier. On my last bike I always had trouble getting back behind my saddle and I never had trouble getting forward. To me this says I need a slightly shorter rear and a shorter TT.

I agree on the shorter TT. I'm just not sure the shorter rear will do what you think it will. How tall are you, if you don't mind me asking?

Since when is 16.75" a really short chainstay though?
Im coming from a bike that I think has a 17 to 17.2" CS (I forget) and I always felt that if it was just a tad shorter, in addition to the TT, things would be much better in steeper\techy descents.

Are you sure that's from the CS or from not being able to get behind the saddle? As you said, .5" of CS shouldn't matter much compared to the massive change in body position that is possible if you can really get behind the seat...

Basically, I didnt just pull these numbers out my ass.
I rode my last bike for 2 seasons in just about every type of trail we have here, found what I like, and found out what I didnt like. Lets just say I was "fit" by "trial&error".

Of course not...I actually agree with the short TT/slack HA theory, and it's how I'm designing my frame. I'm just not sure the combination of kicked-out front wheel and really short CS will have exactly the effect you think it will.

[pechelman]

forgive me for not breaking out my reply too much but im tired from travel and a long drive

i mentioned the whole rubber thing somewhat anxiously as i thought it might insight this kinda response. I was just mentioning it as a little tidbit of info, and even mentioned in my post above that it didnt really make a big deal. I was also referring to just the rubber itself and not the tire as a whole.

At what point do you consider a chainstay to be "too short".
16.75 really doesnt seem that short to me when a lot of bikes are in that range.
The reason for me going short again, is to have a shorter wheelbase and a shorter top tube with a slacker HA, allowing me to more easily get behind the saddle, also being able to get forward, and not feeling locked into turns.

Also, it sounds like we might have different preferred trails and riding styles and bike setups. Again, Im planning on running a fork i can lock down significantly, thus shifting my weight way forward on steep techy climbs. This is a compromise *I* am willing to make and while I can accept you may not be willing to do so, this doesnt affect my decision, cause ive made up my mind.

Im 5'10 with around a 30-32" inseam depending on whose jeans i buy.

Im not really sure why youre focusing in so much on the chainstay here.
Its the whole package im looking at with balancing wheelbase, toptube, headangle, and chainstay. In one way or another everything effects everything and its about finding the right compromise for me. If I went to a 17.5" CS with all the other numbers Id want, there'd be almost no physical way to make that bike just because of physical constraints. Ie, make the CS too long, and you have to shorten the TT a lot to make WB, etc etc etc.

also, ive mentioned in my above posts before this tire stuff, that i was fully willing to make compromises on my numbers, since no bike out there is really perfect. A longer chainstay is the first thing Im willing to compromise on so long as the TT, WB, BB,and HA are what I want. (ie custom el ciclon with a 67* HA)

and technically, the reason you lean inwards on a cart is to evenly load the tires.
with no suspension other than the tire pressure and the only means of weight transfer being geometric, moving your CG is a very important part about maximizing grip.

Not flipping over is just a side effect.

Sorta chicken and the egg i know.

Talk to me about pressure driving velocity, as opposed to the other way around, and we'll get into a big argument

[Arty50]

My bike is shiny and blue. Mom says that makes it go faster. I can ride gud.

[frorider]

this engr geek is with spats on this one.

at any rate, no need for me to mention the preston since that was already covered.

a friend of mine rides damn fast on his blur 4X. i'm not a big SC fan but damn he was tearing things up last october on some moderately techy but steep DH's.

[pechelman]

here just to post that the corsair marque is pretty hawt looking

as are the

soul cycles matador
morewood ndizia st
corsair konig

browsing mtbr is dangerous when you have nothing to do all afternoon

[scrublover]

How about this?

http://swdracing.com/6gun.html

I just put down a deposit on a custom 6 Gun frame. 66deg HA built around my 66ATA, so it'll go between 66-68. And still have and acceptable level of slackness if I want to run a 160mm fork rather than the 180mm. 16.5" stays. 15" seattube, with a reinforced insert so I can use my 27.2mm Gravity Dropper post without a shim. 22.5" toptube, dropped low for lotsa' clearance. Regular 10mm QR drops (using a Hadley rear hub with it's bolt on 10mm axle, not a real thu-axle, but way stiffer than regular QR) Take the same i2i and stroke as a few shocks I have laying about, plus tweakable a bit with different sizes. (7.5" x 2")
Zip tie cable guides where I want them. All the hardware and bearings are standard available metric stuff, and the bearings are Enduro Max stuff. Steve thinks it'll come in weight wise about even with my Preston. The custom stuff will address the few things I'm just not digging with it. I want the bike to feel like my hardtail, just...squishier. I want to be riding "in" the bike, not on it.

With it being beefy steel, it ought to be plenty stiff for my skinny ass, and no issues for me with the single pivot at all. Best part? Quoted price: $900 without a shock, for a CUSTOM frame, in steel, which I like.

Or buy my medium 07 Transition Preston frame that'll be up for grabs once this frame is on the way here...

[Spats]

pechelman: I don't know why I didn't think of this before (busy arguing with you ) but your bike is a Bionicon Golden Willow. Travel, BB height, chainstay, wheelbase, and head angle are right in your desired range, and if you're willing to deal with a fork lockdown, the adjustable geometry is totally intuitive and works about 5 times better than any I've used.

You could probably even get away with the Edison (6") because the adjustable geometry works so well for climbing and it's still only about 32#. Plus the new Edison frame is sexy.

I rode the Edison for a weekend at Downieville and their system is absolutely the nuts. If they built a 29er I would have bought it on the spot. Paul (the US rep) is a great guy and offers excellent customer support.

Here's the geometry chart:
http://www.bionicon.com/standard.xml...00001c1cf4a497

[pechelman]

yea ive been intruiged by bionicons golden willow

just not keen on that much proprietary stuff

im really stoked about the possibility of the corsair marque or konig.
and if not that
then a custom Walt Works with a Ventanna rear or a Curtlo with a Ventanna rear would do the trick.

As well as the dreaded SC Blur 4X.

sounds like there are more options out there now that ive scoured MTBR a bit.

[Spats]

yea ive been intruiged by bionicons golden willow

just not keen on that much proprietary stuff

The fork and shock are actually built by X-Fusion, who are easy to get hold of. Plus Paul @ Bionicon is awesome, and I bet you will get better CS out of him than Fox, Manitou, Rock Shox, etc.

I was kind of worried about proprietary stuff too, but when I rode the Edison I realized it worked so well I wouldn't care about ever swapping it out. It really feels like it was designed as a complete bike by actual engineers (which it was), instead of just being a set of frame geometry that has whatever parts were cheapest that year hung off it.

Like I said, if they made a 29er I'd already own one, and if the 29er market doesn't get a decent 6" fork and frame soon I may have to get one anyway.

[kellen]

I've decided too many people on the internet spend too much time on the computer and not enough time riding. Seriously, if some of you walked into a real bike shop and started talking about some of the things you write on here, most shop employees would help you out, but be laughing at you behind your back.

Bikes are 50% analytical and 50% subjective. Especially with FS mountain bikes, the number for subjective moves closer to 65 or 70%. Numbers are certainly a factor, but FFS, just because a bike measures a certain number from some point to another DOES NOT INDICATE HOW IT WILL RIDE!

Bikes are like clothes, you have to try them before you buy them. Buying a pair of pants just because they have what you think are the right measurements for you is the worst buying process ever concocted. I literally want to fall over laughing at how retarded some people who come into our shop are, because they look at certain bikes on our floor and write them off because the headtube angle is 1 degree off of what their ego-fueled all-knowing brain thinks is the perfect bike for them.

I could recommend 4 or 5 bikes that would probably be good for what you are riding (key concept here), but they probably don't fall into your "perfect dimensions" requirement or whatever you want to call it.

Moral of the story: Decide on a bike based on HOW IT RIDES, not how it measures.

Note: I'm venting because this is a chronic problem on almost all bike boards and is something that, well we'll just say "irks" me. Sorry if I ruffled feathers, it's the internet, you'll still wake up tomorrow morning.

[pechelman]

hence the reason im trying to ride as many of these as I can
unfortunately, this isnt always possible

and youve obviously read this thread
a lot of what im looking for has to do with fit and a low cg
seems to me those two things have a lot to do with fit and how the bike handles

and pray tell, what 4 or 5 bikes would you reccomend?

edit
and if looking at numbers is such a bad idea, then why did the first bike I rode with the numbers I wanted ride and fit and handle pretty much exactly how i wanted? I was ready to buy that last month, but its out of stock, So thats why im looking for something else.

[marshalolson]

I've decided too many people on the internet spend too much time on the computer and not enough time riding. Seriously, if some of you walked into a real bike shop and started talking about some of the things you write on here, most shop employees would help you out, but be laughing at you behind your back.

you're shop doesn't sell to triathaletes huh?

[kidwoo]

I've decided too many people on the internet spend too much time on the computer and not enough time riding. Seriously, if some of you walked into a real bike shop and started talking about some of the things you write on here, most shop employees would help you out, but be laughing at you behind your back.

Bikes are 50% analytical and 50% subjective. Especially with FS mountain bikes, the number for subjective moves closer to 65 or 70%. Numbers are certainly a factor, but FFS, just because a bike measures a certain number from some point to another DOES NOT INDICATE HOW IT WILL RIDE!

Bikes are like clothes, you have to try them before you buy them. Buying a pair of pants just because they have what you think are the right measurements for you is the worst buying process ever concocted. I literally want to fall over laughing at how retarded some people who come into our shop are, because they look at certain bikes on our floor and write them off because the headtube angle is 1 degree off of what their ego-fueled all-knowing brain thinks is the perfect bike for them.

I could recommend 4 or 5 bikes that would probably be good for what you are riding (key concept here), but they probably don't fall into your "perfect dimensions" requirement or whatever you want to call it.

Moral of the story: Decide on a bike based on HOW IT RIDES, not how it measures.

Note: I'm venting because this is a chronic problem on almost all bike boards and is something that, well we'll just say "irks" me. Sorry if I ruffled feathers, it's the internet, you'll still wake up tomorrow morning.

It's not everyone else's fault that you're stupid

[Particle]

My bike came with stickers. Most people think it's ugly. But it's awsum. And rilly rill fast.

[pechelman]

so im rilly rilly picky

its my damn right to be that way

[skimasterflex]

so im rilly rilly picky

its my damn right to be that way

Especially considering the coin we drop on these kind of toys

[pechelman]

ill delete mine if you delete yours

[t.odd]

ill delete mine if you delete yours

it's a deal!

[pechelman]

trigger being pulled on a shiny polished speshial version of a spesh enduro sl

HA: 66.5-67 with a 540mm A-C
BB: 13.7 unsagged with poofy 2.3" tires
BB: 11.9" sagged about 30-35%
TT: 23.25
CS: ~16.7
WB: 45" (a bit longer than I wanted, but whatever)

im a little stoked

edit for a pic
im just getting the frame tho


and for those wondering
yes i have ridden this bike before, like the way it rides, pedals, takes hits, climbs, and fits (especially the fit)