[jackalope]

Just kinda mulling a few things over in my little pea brain, and was wondering about rear brake force as it relates to body position over the bike...The example that I thought of was someone riding down a 45 degree angle slope, with said riders' arse stuck way out behind the rear tyre...Does this actually increase the rear braking force (or more subjectively, "an increase in rear braking performance") as compared to someone riding over the saddle?? My first thought was that your bodyweight's force (i.e. gravity) would be applied through the pedals no matter how you configured yourself over the bike; so in essence it really doesn't matter...So your braking force wouldn't actually be increased...But for some reason, I also thought that distance was part of the force calculation and that perhaps by effectively lengthing your body, you could apply more force through the pedals...Or, does having you weight back just help the the rear end stay in contact with the ground and consequently help the rear brake work more 'effectively'? Now I really wished I hadn't slept through dynamics class 12 years ago

 

[Toshi]

if you rode without touching the handlebar you'd be right (in that all weight would just go down through the pedals) but you'd also be unable to position yourself anywhere but with your center of mass above the pedal spindle.

that you are able to position yourself elsewhere holds the key to this question: the force you apply on the handlebars, presumably much less in the downward direction when you scoot back over the rear tire, is the missing link you've been searching for.

 

[zedro]

weight distribution matters as far as traction; if you were riding a unicycle, 100% of your weight would be over the wheel no matter what. With 2 wheels, the distribution depens on your center of gravity (and acceleration/decelerations). So yeah, more rearward weight will equal better rear traction. But mostly people go rearward to not go over the bars, not to increase rear braking traction

 

[ChrisKring]

I really need to bust of a class in free body diagrams sometime when I have time to make a 3 hour post with diagrams. Anyone know of a site with instructions on a free body diagram / statics to just point these questions to?

We really need to write a FAQ to cover this stuff as well as other newbie type technical and general questions. I will volunteer to write some of it over next winter. Anyone else?

 

[dexterq20]

Just a funny thought: putting your weight way back will actually decrease the effectiveness of your front brake and make it easier to lock the wheel. The wheel with the most weight over it will have the best traction, and therefore the most braking power.

 

[Toshi]

Originally posted by dexterq20
Just a funny thought: putting your weight way back will actually decrease the effectiveness of your front brake and make it easier to lock the wheel. The wheel with the most weight over it will have the best traction, and therefore the most braking power.

er, this is true, but he was asking about the rear brake. (that the front brake is more powerful is a whole 'nother thread, and should be common sense.)

 

[zedro]

Originally posted by dexterq20
Just a funny thought: putting your weight way back will actually decrease the effectiveness of your front brake and make it easier to lock the wheel. The wheel with the most weight over it will have the best traction, and therefore the most braking power.

true, but seeing as we have proper control over both brakes separatly, it doesnt necessarily matter, we can still stop just as effectively assuming you adjust properly for it.

That becomes a problem in say cars/trucks where the front/rear brake distribution is set at the factory. If something affects the intended distribution, you can then get a premature locking situation and loose braking effectiveness. This is why race cars can adjust their brake power distributions; as the rear of the car gets lighter as fuel is spent, they continually reduce the rear brake distribution to avoid getting loose under braking.

 

[MMike]

from my favourite course ever...

 

[zedro]

Originally posted by MMike
from my favourite course ever...

yeah i loved vehicle dynamics too. The end of that article which basically says understeer conditions are prefered because people suck at driving caused a huge debate in class too...

 

[ChrisKring]

Originally posted by zedro
yeah i loved vehicle dynamics too. The end of that article which basically says understeer conditions are prefered because people suck at driving caused a huge debate in class too...

The idea here is that it is always better to go off the road straight (not sliding sideways) to prevent rollovers. Most drivers will panic in an emergency situation and lock the brakes up. With the car toe'd in, the car will understeer and go straight off the road. In almost all cases, the throttle will be the only way out of a bad situation.

I took the Skip Barber winter driving course. My college SAE funded the guys to come in and teach it. More than anything, it was really fun to put a car into a slide at 30+mph on a snowy/icy parking lot and not have to worry about getting arrested for reckless driving. Seriously, they should teach that stuff in driver's training.

Even more fun is drifting the FSAE car at close to 100mph in the uni parking lot.

 

[MMike]

Originally posted by ChrisKring


Even more fun is drifting the FSAE car at close to 100mph in the uni parking lot.

I guess you had the restricter plate removed?

 

[zedro]

Originally posted by ChrisKring
I took the Skip Barber winter driving course. My college SAE funded the guys to come in and teach it. More than anything, it was really fun to put a car into a slide at 30+mph on a snowy/icy parking lot and not have to worry about getting arrested for reckless driving. Seriously, they should teach that stuff in driver's training.

for my buddies cop training they used skid vehicles, but before that during the briefing they asked who in the class liked to practice fishtailing in the winter (a favorite canadian sport). Either the class was full of weiners or they were all afraid to admit to 'dangerous driving', but nobody in the class raised their hand except for my buddy. Basically their feeling was its a good thing to get to know the limitations of the car and how to maneuvre it during a loss of control.

I also notice all the most skilled drivers i know were also the most reckless ones in their youths. Not that kids should, err....nevermind.

 

[MMike]

Originally posted by zedro
for my buddies cop training they used skid vehicles, but before that during the briefing they asked who in the class liked to practice fishtailing in the winter (a favorite canadian sport). Either the class was full of weiners or they were all afraid to admit to 'dangerous driving', but nobody in the class raised their hand except for my buddy. Basically their feeling was its a good thing to get to know the limitations of the car and how to maneuvre it during a loss of control.

I also notice all the most skilled drivers i know were also the most reckless ones in their youths. Not that kids should, err....nevermind.

When I got my license, I took driver's ed at Young Drivers of Canada, (above Zellers on St. Jean and Hymus there...). I did it in the summer. But they told us that on the first snowy day, to go find an empty parking lot and spin the car around a few times to see what it's like.

 

[ChrisKring]

Originally posted by MMike
I guess you had the restricter plate removed?

Uhh, yeah. The 18mm (or whatever it was) max opening sucked. We had a huge plennum (sp?) and an extremely long tapered intake and it still sucked having to suck air through such a small hole.

But with the 600 CBR motor with the air opened up and our proto FI system on it, the car made crazy power. Most people couldn't drive it at all since they couldn't get it moving without spinning a donut. We had to gear it down so that it was drivable by some of the grad student shmucks that were the project leaders. Way too much politics involved. I helped out for only 2 years and got frustrated.

The best thing about FSAE was that it had a real motor. The baja car was lame with the tiny lawn mower engine on it.

 

[MMike]

Originally posted by ChrisKring

The best thing about FSAE was that it had a real motor. The baja car was lame with the tiny lawn mower engine on it.

It was a SNOWBLOWER engine thankyouverymuch...and if used correctly you could get it going pretty well!

Our FSAE team was useless... I will never forget their group meeting in "the cage" (our work area) . They were knee-deep in Ninja 600 engine parts and their meeting was to decide whether to paint the car like a Maclaren or a Williams

We rolled our eyes at them a lot.......

 

[zedro]

Originally posted by ChrisKring
The best thing about FSAE was that it had a real motor. The baja car was lame with the tiny lawn mower engine on it.

yeah the Baja projects i've seen in general are pretty lackluster. With such low power and speeds, no one bothers to tune good suspension systems because its not all that critical.

I'm guessing the internal problems associated with SAE teams is fairly widespread, i was always hearing about the BS comming out of that arena. Pretty much killed my motivation to join in, hence my bike project was born.

 

[MMike]

Originally posted by zedro
yeah the Baja projects i've seen in general are pretty lackluster. With such low power and speeds, no one bothers to tune good suspension systems because its not all that critical.

I'm guessing the internal problems associated with SAE teams is fairly widespread, i was always hearing about the BS comming out of that arena. Pretty much killed my motivation to join in, hence my bike project was born.

That is really too bad. It kinda sounds like we were the last of the Mohicans. During my tenure, there was always at least a core group of people who were really keen to keep things going. Obvioulsy with Dr. Krepec (RIP) knocking down roadblocks for us, that helped a lot.

Te groups may have been small, but it kept the politcs to a minimum. I'd talk to some of the US schools and they'd say they had like 40 people on the team. That just blew us away. We were always 4-6 people.

It was a total blast.

And even with the small engine, I got the car in the air and rolled it over a few times. And driving full speed into a lake is pretty fun too.......

 

[zedro]

Originally posted by MMike
That is really too bad. It kinda sounds like we were the last of the Mohicans. During my tenure, there was always at least a core group of people who were really keen to keep things going. Obvioulsy with Dr. Krepec (RIP) knocking down roadblocks for us, that helped a lot.

problem is, theres too many people that 'just want to drive the car'. Further complicating things is they transfered most of the SAE projects to Capstone, which pretty much sent me running. I just had too many bad experiences (read: all) with forced group projects where guys were freeloading, missing deadlines or simply not submitting any work that i couldnt bare to put the 'big' project into someone elses hands. If i'm gonna do all the work, i might as well get all the credit and make my own headaches.

I once had a guy invite himself into my project a month after it started and 2 weeks to deadline, do none of the work alotted to him, and then not even bother to study his part of the oral presentation; basically on his turn he just stared at the slide with his jaw wide open not having a clue at what he was looking at, and me having to jump in and do his whole segment of the presentation. That was the last straw for group work for me at Concordia.

In all fairness there were some keeners there, mainly the people responsible for the new Baja and FSAE chassis', but there were also alot more weak links and drama there.

 

[MMike]

Originally posted by zedro
problem is, theres too many people that 'just want to drive the car'. Further complicating things is they transfered most of the SAE projects to Capstone, which pretty much sent me running. I just had too many bad experiences (read: all) with forced group projects where guys were freeloading, missing deadlines or simply not submitting any work that i couldnt bare to put the 'big' project into someone elses hands. If i'm gonna do all the work, i might as well get all the credit and make my own headaches.

I once had a guy invite himself into my project a month after it started and 2 weeks to deadline, do none of the work alotted to him, and then not even bother to study his part of the oral presentation; basically on his turn he just stared at the slide with his jaw wide open not having a clue at what he was looking at, and me having to jump in and do his whole segment of the presentation. That was the last straw for group work for me at Concordia.

In all fairness there were some keeners there, mainly the people responsible for the new Baja and FSAE chassis', but there were also alot more weak links and drama there.

Oh there were "just want to drive" guys too. But as the group leaders we made it clear to them that in order to drive you had to earn in. And those guys never hung around long enough to see the thing on all 4 wheels anyway. I guess that's why we kept the groups so small. We were complete assholes to the people we didn't like (because they wouldn't pull their weight). So we chased them away...... I drove the car a lot....

 

[RaID]

Originally posted by ChrisKring

Even more fun is drifting the FSAE car at close to 100mph in the uni parking lot.

im glad our car isnt the only that is so oversteer friendly

Originally posted by MMike
Oh there were "just want to drive" guys too. But as the group leaders we made it clear to them that in order to drive you had to earn in. And those guys never hung around long enough to see the thing on all 4 wheels anyway. I guess that's why we kept the groups so small. We were complete assholes to the people we didn't like (because they wouldn't pull their weight). So we chased them away...... I drove the car a lot....

weve got our driver selection atm and it becoming a bit of ahssle with everyone wanting "ideal conditions" for their drive
but at least our group of core ppl doing work is a lot bigger then what yours sounds like
plus it actually counts towards our degree as its our final year project, so if you dont pull your wait you dont pass

 

[jackalope]

Total thread hijack...
But interesting nevertheless...The ME crowd always have the best college stories; as compared to the mundane CE senior design / club tales...We were putting dye in streams to calculate Q and watching ball bearings sink in columns of oil...Building concrete canoes, etc...ZZZZZZ

Meanwhile, the SAE crew was out driving homemade CART racers like Stevo McQueen wheeling his Bullet 'Stang around Frisco's side streets...

 

[RaID]

Originally posted by jackalope
Total thread hijack...
But interesting nevertheless...The ME crowd always have the best college stories; as compared to the mundane CE senior design / club tales...We were putting dye in streams to calculate Q and watching ball bearing sink in columns of oil...Building concrete canoes, etc...ZZZZZZ

couldnt agree more, the one concrete related subject we had to do (still cant understand why, i think the reasoning is that we'd know what a CE is on about when we talk to them)
was pretty much the most boring thing ive done at uni,

the only concrete im worried about is the one underneath my wheels

 

[zedro]

Originally posted by RaID
plus it actually counts towards our degree as its our final year project, so if you dont pull your wait you dont pass

that doesnt stop the slackers. On the Supermileage team, in the 4 man drivetrain group 2 guys had done exactly nothing all year. In the final crunch time the team leader had a mild heart attack so he was forced to take a weeks stay at the hospital. Do you think that motivated them to at least handle the things he couldnt? nope, no change, nothing done. And despite being wastes of skin and the faculty being aware of the situation, they still get a chunk of the group mark with a passing C+ (the project was an A-). Honestly going to Uni in engineering is too much of a fad at our school...

i do regret not getting involved in SAE though, would love to have done some chassis developpment for the Baja.

 

[MMike]

Originally posted by zedro
that doesnt stop the slackers. On the Supermileage team, in the 4 man drivetrain group 2 guys had done exactly nothing all year. In the final crunch time the team leader had a mild heart attack so he was forced to take a weeks stay at the hospital. Do you think that motivated them to at least handle the things he couldnt? nope, no change, nothing done. And despite being wastes of skin and the faculty being aware of the situation, they still get a chunk of the group mark with a passing C+ (the project was an A-). Honestly going to Uni in engineering is too much of a fad at our school...

i do regret not getting involved in SAE though, would love to have done some chassis developpment for the Baja.

That's so weird to hear this. With the exception of the slackers we chased away, on all of the projects, people worked night and day (literally) to get the cars built.....well with the exception with Formula. They worked hard, but could never really get their sh|t together.

But never was a project completely abandoned. And we never got course credit for any of it. We just did it because we REALLY wanted to do it.

Hell.... a bunch of us got dragged back the year after we graduated to work on the HEV Intrepid! We built it exclusively on Saturdays! (Damn you George!)