upright clearance

[the weldmeister]

how much clearance between the upright and the inner surface of the wheel would you say is safe enough?

we were thinking of having about 4mm.

[the weldmeister]

how much clearance between the upright and the inner surface of the wheel would you say is safe enough?

we were thinking of having about 4mm.

[Ben C-M]

If you've checked the wheel in all extremeties (full bump, droop, all camber/toe/steer settings) and you have 4 mm, then the only to worry about are your tolerances.

I think 4 mm is a bit too close. If your jig puts it a bit off, deflection of the wheel/tire/suspension components might put it close enough to touch. That being said, in 2005 our uprights were so close to the wheel we had to shave part of the head of the outboard tie rod/toe link bolts and round the corners of our uprights because they scraped the inside of the wheel.

It's all a matter of comfort- If you can jig it well enough and feel confident you've accounted for everything in your checks, you don't need to leave more then minimal clearance; just make sure you check it manually at all settings before you run it.

/Ben

[Dr Claw]

dont forget about bolt clearances too for UBJ's and LBJ's.

also, magic rocks exist. they are sprinkled all over your parking lot and your not even aware of it - sorta like lucky penny's at the mall.

maybe its not a big concern since they dont really cause immediate failure, but you'll see a wear band on the inside of a few of your wheels that you cant explain.

[Korey Morris]

We have a set of keizers with this wear mark on the inside. Our 2003 car had about 0.125" clearance between the brake caliper and wheel so we frequently catch these magic rocks. We had to grind down the heads of the bleed valves on that car.... Ah memories, that was my first job as a freshman on the team!

http://www.engr.uky.edu/~kamorr0/keizer.jpg

We don't use the shells anymore, but I don't really think that it is a problem.

[Biggy72]

I'm not sure why anyone hasn't said this before, but your wheels will flex. Some will flex more than others and the clearance needs to account for this. Our keizers last year flexed quite a bit and we ended up with some nice machining because of it. This should become especially apparent if you're running where your tires can get hot.

[the weldmeister]

ok.. so 3mm of clearance wasn't enough...
do you think 5mm should be enough, or should we play it safer? we've got keizer wheels too, and we're a first year team.

having scratches from magic rocks wont do any serious damage i guess, but its not something i'd want happening on my car. wheel flex shouldn't create a problem for more than 2-3mm clearance right?

being a first year team, we should probably play it a little safe. how much clearance would you suggest?

[fade]

whats the predicted camber and toe stiffness of your wheel+hub+bearing+upright assembly?

[the weldmeister]

thats' an interesting question, fade. i really don't know... we haven't yet finalised the designs yet, and i hadn't even thought about calculating camber and toe stiffnesses. can you please elaborate on this, how to calculate it, and what should be a good target?

thanks

[JHarshbarger]

This is said over and over again; if you're a first year team, design to finish endurance. If you design your car at the limit, it will often end in failure, even with experienced teams. And it's not the designs that are the problem (in most cases), it's the fabrication. Build a good solid that will get you through competition and get you experience. Make your uprights, a-arms, and joints solid and experience the whole competition. If you put your suspension together and your wheel doesn't fit over your upright, you've just lost a lot of time and possibly a chance to compete. I would just play it safe and give yourself plenty of space and expect some fabrication/design errors.

Good luck!

[the weldmeister]

thank you, Joel!!

hope some of my teammates are reading this!

[the weldmeister]

i'm waiting for a reply, fade!

[Superfast Matt McCoy]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by the weldmeister:
thats' an interesting question, fade. i really don't know... we haven't yet finalised the designs yet, and i hadn't even thought about calculating camber and toe stiffnesses. can you please elaborate on this, how to calculate it, and what should be a good target?

thanks </div></BLOCKQUOTE>

You could FEA the assembly, or you could use what you learned in Solids and calculate an estimate with the stiffness of the material and the shape of the parts. Or you could do a static test with a rope, one of those fish scales and a fat guy.

[NetKev92]

I'll suggest the controversial answer: undersize your brakes so you have huge clearance like 20mm. You may not brake as deep as the other cars there, but you won't have any of the mentioned problems and you have one less thing to worry about that might cripple or at least ding the car. Unless you have good track and autocross drivers, they won't feel comfortable using the full potential of the brakes anyway.

As another comparison point, the miata has plenty of stock brake capacity until you go to the track. You can fit 13" Keizers over Miata brakes. For cars a quarter the weight and autocross speeds, if you need to push the limits on clearances, you may not be realistic about your needs. Some of the autocross guys advocate the smaller earlier brakes on the miata. They have less rotating mass so acceleration is better and they don't need the excess stopping capacity.

[Steve Yao]

To say that your are sacrificing braking power by having a smaller rotor is a bit mis-leading when you have control over every element of your braking system. If you are working with a stock system such as a Miata, then changing to a smaller rotor will require more driver input to achieve the same braking potential. But that is not the case with FSAE. There are enough variables in a braking system that having a rotor much smaller than your available rim clearance is perfectly feasible for whatever driver input force you specify for a certain braking potential. The only real limit is your rotor material strength at temperature.

As far as upright clearance, 1-2cm seems adequate assuming a decent amount of system camber stiffness. Have you done any calculations to say what you give up by using only say half of your available rim clearance? Obviously forces increase, deflections might increase, might save some weight. You should ask yourself, Do you really need to use your max rim clearance or is there a better balance weight and performance with a smaller upright?

[satbat7]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by NetKev92:
I'll suggest the controversial answer: undersize your brakes so you have huge clearance like 20mm. You may not brake as deep as the other cars there, but you won't have any of the mentioned problems and you have one less thing to worry about that might cripple or at least ding the car. Unless you have good track and autocross drivers, they won't feel comfortable using the full potential of the brakes anyway.

As another comparison point, the miata has plenty of stock brake capacity until you go to the track. You can fit 13" Keizers over Miata brakes. For cars a quarter the weight and autocross speeds, if you need to push the limits on clearances, you may not be realistic about your needs. Some of the autocross guys advocate the smaller earlier brakes on the miata. They have less rotating mass so acceleration is better and they don't need the excess stopping capacity. </div></BLOCKQUOTE>

What is the dia of the miata rotor? and what is the clearence you get with the caliper on in 13" keizer?

[NetKev92]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by sat7:
What is the dia of the miata rotor? and what is the clearence you get with the caliper on in 13" keizer? </div></BLOCKQUOTE>

The early cars had 9.3" fronts and 9.1" rears. I made the swap up to '99 model rotors for 10.0" front and 9.9" rear. I've watched guys with early model cars run the 13" Keizers but I don't know their clearances. On my car, the front rotor calipers come out to a maximum radius of 5.875 inch. By math, the early cars' calipers should come out to a maximum radius of 5.525 inch.

As pointed out, FSAE cars can control a lot of parameters because you start from scratch. In generality though, your rotor's radius and the dimensions of your caliper around the rotor edge will set the wheel internal radius that you need to clear. My point is that even the early Miata has plenty of braking power for autocross, so it ought to be possible to get adequate brake power for a car 1/3 the weight in the same envelope.

[satbat7]

got ur point! thanks

[Bandit_06]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by fade:
whats the predicted camber and toe stiffness of your wheel+hub+bearing+upright assembly? </div></BLOCKQUOTE>

Correct me if I am wrong, but this is an extremely COMPLEX question to answer isn't it? If camber and toe stiffness were to be calculated (even approximately) one would have to account not only for the stiffness of each component in series, as well as the compliance due to the fit between mating components?

Would probably be a better idea to test it empirically on an assembly, if you actually wanted to know. I could see calculating the relative stiffness during the design stage to evaluate different design configurations...

[Mechanicaldan]

There are the correct answers that you give the judges, and then there are the rule of thumbs answers that you use as a starting point for your first car. http://fsae.com/groupee_common/emoticons/icon_wink.gif

In this case, if you have someone that has a thin thumb, that's probably enough clearance between the upright and the rim. It would be a good idea to learn the correct answer by the time you go through Design Judging at competition. Sorry I can't answer the "whats the predicted camber and toe stiffness of your wheel+hub+bearing+upright assembly?" question. I was an engine guy.

[Teemu Ristelä]

Here is a picture of our 2006 upright+hub+brakes assembly. The clearance between the rim and the caliper is about 1mm. Actually the only part that occasionally contacted the rim was the safety lock wire for the caliper attachment bolts, giving a nice finish touch for the rim http://fsae.com/groupee_common/emoticons/icon_wink.gif
It seems that the 10" Keizer wheel shells are stiffer compared to the 13".
http://www2.stadia.fi/~0303344/P1010068.JPG