View Full Version : Selection Of tyres
manifold
10-05-2011, 02:46 PM
Going by the logic that there is more weight distribution on the rear (probably more that 60:40 in formula cars. Why we use same size tyres in front than the rear?
Since load is more at the rear the rear will reach a higher slip angle at a given speed than the front which means that there will be over steer.
y not use a fatter tyre at the rear to get more grip and compensate the front geometry to under steer. Ultimately gaining more speed via the corner.
In fsae cars same tyres running on front and rear, I was wondering why?
manifold
10-05-2011, 02:46 PM
Going by the logic that there is more weight distribution on the rear (probably more that 60:40 in formula cars. Why we use same size tyres in front than the rear?
Since load is more at the rear the rear will reach a higher slip angle at a given speed than the front which means that there will be over steer.
y not use a fatter tyre at the rear to get more grip and compensate the front geometry to under steer. Ultimately gaining more speed via the corner.
In fsae cars same tyres running on front and rear, I was wondering why?
Joe17
10-05-2011, 02:47 PM
Because Racecar.
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by manifold:
Going by the logic that there is more weight distribution on the rear (probably more that 60:40 in formula cars. Why we use same size tyres in front than the rear?
Since load is more at the rear the rear will reach a higher slip angle at a given speed than the front which means that there will be over steer.
y not use a fatter tyre at the rear to get more grip and compensate the front geometry to under steer. Ultimately gaining more speed via the corner.
In fsae cars same tyres running on front and rear, I was wondering why? </div></BLOCKQUOTE>
If this is joke, then maybe i the burnt of it
But anyways,
Can you change front/rear weight transfer dist. without changing tires? yes
Weight dist. is not usually past 60:40, unless you are Maryland. Most cars with small engines are around 55:45 I reckon. To be fair, Maryland is far past 60:40 and they do run a "fat" tire in the rear. Mmmmmm fat tire...
"Oversteer" is hard to pinpoint, esp since the dynamics of the car can change a great deal at different speeds. There are contributions to steering stability/instability other than lateral force at the cp. FSAE cars are typically subjected to very tight corners and high steering angles. Oversteer is not a constant and is not determined solely by weight dist and tires.
Will you get more "grip" with an "overweight" tire (calling it fat may hurt its feelings). Different tires' temperature changes differently over time. What if your terminal understeer/oversteer characteristics not only changed with vehicle speed but were heavily influenced by time as well?
Some oversteer, or over-yaw-acceleration might be beneficial on some parts of the race track, especially an FSAE racetrack.
Mike Cook
10-05-2011, 05:09 PM
mmmmmm fat tire.
https://lh5.googleusercontent.com/-w0gbpTOTk3I/Tm7K5QaNXQI/AAAAAAACln0/4dOiIzm1zfA/DSC04847.JPG
RANeff
10-05-2011, 05:36 PM
Mmmm not as fat, fat tire
http://www.gotcone.com/pgallery/images/2011_scca_tirerack_solo_nationals/fsae/img_5087.jpg
In all honestly, there are a few teams who do run wider rear tires. Mainly german
exFSAE
10-05-2011, 05:49 PM
Left Hand > New Belgium
RANeff
10-06-2011, 12:32 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by exFSAE:
Left Hand > New Belgium </div></BLOCKQUOTE>
Odells, Rouge, Stone, Southern Tier, New Glarus, etc. > New Belgium
manifold
10-06-2011, 07:51 AM
cheers
manifold
10-06-2011, 08:01 AM
@ raneff you wasted too much of your time writing these things ,if you could have written something that could have been helpfull
exFSAE
10-06-2011, 08:31 AM
Fine. How about this.
1. Just because you have reward weight bias doesn't mean your car is going to oversteer.
2. This is FSAE. Not exactly high level racing. Tire options are limited. Sometimes (often even) better to just use 4 of the same tire than wildly different fronts and rears.
Get back to fundamentals, man.
Adambomb
10-06-2011, 11:28 AM
We've been running big'n'littles since 2009...
http://www.sae.stuorg.iastate.edu/zenphoto/cache/formula/chassis/the-car-2009/IMG_1878.JPG_595.jpg
RANeff
10-06-2011, 11:13 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by manifold:
@ raneff you wasted too much of your time writing these things ,if you could have written something that could have been helpfull </div></BLOCKQUOTE>
You could have run a Pacejka model by now instead of relying on this forum to do your work for you!
manifold
10-07-2011, 05:26 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RANeff
You could have run a Pacejka model by now instead of relying on this forum to do your work for you! </div></BLOCKQUOTE>
i am not relying on forum for the answers ,i have decided the setup,was just expecting a healthy conversation
exFSAE
10-07-2011, 08:45 AM
Well the fact of the matter still is, just because you have rear weight bias doesn't mean your car is going to oversteer.
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by manifold:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RANeff
You could have run a Pacejka model by now instead of relying on this forum to do your work for you! </div></BLOCKQUOTE>
i am not relying on forum for the answers ,i have decided the setup,was just expecting a healthy conversation </div></BLOCKQUOTE>
I don't recall reading a "PLZ give me the anzers ASAP iz critical"
In short, some teams have larger tires, some don't. As long as you can justify with math or simulations that your choice is a good one, you'll be fine.
buggaero
10-07-2011, 09:51 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by manifold:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RANeff
You could have run a Pacejka model by now instead of relying on this forum to do your work for you! </div></BLOCKQUOTE>
i am not relying on forum for the answers ,i have decided the setup,was just expecting a healthy conversation </div></BLOCKQUOTE>
Saw a lot of cars over steering during the autocross in Italy this season.A lot of them. Had a close look at most of them beforehand. And i can tell you they were within that 55:45 range.
manifold
10-09-2011, 12:00 PM
yes rear weight biasing is not the only reason the car is going to oversteer,but ya it is probably the important reason why a car will.
lets take some factors into account just for the sake of discussion.
static factors-
weight distribution(front or rear bias)
suspension ,chassis tune up
tyre preassure,wear,type
dynamic factors-
cornering speed
throttle
braking
steering
weight transfer
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