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Discussion Starter #1
On a straight line, in order to reduce wheel spin, would it be a good idea to put 100-150 LBS into the trunk?

This is a 6 cylinder BMW turbo, with 800 whp. Car weighs 3100 LBS.

Tried several tires and played around suspension, still cannot solve wheel spin.
 

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You're gonna need to share way more info like, what tires? what kinda 60ft and ET? How are you recording wheel spin and how much are you getting?
 

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you mean your not going to follow the popular trend and over gear your car to provide traction? adding weight to slow the car down will work too...lol
this is a large reason why i left that innovative community(sarcasm); you have come to a better place.
my point is your solution and the other common one i mention is only a band-aid to the problem and still does not fix the fundamental issues; plus only hamper the performance of your car. the only saving grace from the mindless bmw community from over tiring their cars is that they are limited to about 26" max height.

tires can only provide so much traction. the weight necessary to provide maximum traction is proportional to the weight of the car; light car requires less weight to provide maximum acceleration when compared to heavier car. heavy cars will generally wear tires quickly and tend to be more finicky with traction; i.e. the propensity to unload is greater than compared to lighter cars. ill let you deduce what you want from this.

having shared that; what tires are you running? what psi are you running? what is your protocol in the water box? what spring rates? what struts? what body e30/e36/e46? being 3100lbs i assume minor weight removed from e36 or a heavy e30.

there are many variables that can hinder traction and one needs to be sure they are isolating as many as possible so that they can began looking in the correct place to fix the problem. making whimsical decisions can only get you so far and seeking help in this forum is a great start.
 

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Discussion Starter #5
you mean your not going to follow the popular trend and over gear your car to provide traction? adding weight to slow the car down will work too...lol
this is a large reason why i left that innovative community(sarcasm); you have come to a better place.
my point is your solution and the other common one i mention is only a band-aid to the problem and still does not fix the fundamental issues; plus only hamper the performance of your car. the only saving grace from the mindless bmw community from over tiring their cars is that they are limited to about 26" max height.

tires can only provide so much traction. the weight necessary to provide maximum traction is proportional to the weight of the car; light car requires less weight to provide maximum acceleration when compared to heavier car. heavy cars will generally wear tires quickly and tend to be more finicky with traction; i.e. the propensity to unload is greater than compared to lighter cars. ill let you deduce what you want from this.

having shared that; what tires are you running? what psi are you running? what is your protocol in the water box? what spring rates? what struts? what body e30/e36/e46? being 3100lbs i assume minor weight removed from e36 or a heavy e30.

there are many variables that can hinder traction and one needs to be sure they are isolating as many as possible so that they can began looking in the correct place to fix the problem. making whimsical decisions can only get you so far and seeking help in this forum is a great start.

Thank you. I feel you have experience with Bimmers.

Mine is a E36,turbo.

We dont drag race, we go to a F1 circuit and test from 60 to 130 mph. The F1 track is not prepared.

On a unprepared F1 track, when I go full throttle, wheel spin is a problem till 100 mph.

I ve tested the following tires:
Hoosier DOT Drag Radials 315-30-18
MT ET Street Radial 315-30-18

Both tires perform poor.

The manufacturers told me that these DOT drag radials wont work well on a "unprepared" surface.

Final drive was 3,23.

Tested 3,62 and got worse.

Tested 3,07. Did not improve traction.

tested 2,93 no good news.

tested 2,81 no good news, still wheel spin.

Thats why I ve asked whether 100-150 LBS of weight may or may not help traction.
 

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Discussion Starter #9
Did you try adjusting the rear shocks?

Double adjustables I hope?

What tire pressure in the drag radials?
car has adjustable coil over kit.

rear springs soft, shocks at the softest, with this combination wheel spin.

rear springs soft, shocks at the stiffest. With this combination wheel spin continues.

tested different tire pressures, 15 psi, 17 psi, 19 psi, and no improvement:(
 

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yes weight distribution is very important, especially with heavier cars. as i mentioned earlier there needs to be xxxx lbs of force on the tires for them to provide maximum grip if this force is not there they will shake/lose traction if the power is. having said that, adding weight over the rear tires(preferable behind the axle to help ensure more weight over the tires) can help provide the forces the tires need to provide traction. just be very mindful adding that kind of weight without it being almost permanently part of the vehicle; if for some reason it become free during a crash the results can be catastrophic. if you want to experiment with adding weight for the time being(it is band-aid) i would try and integrate it into the bumper. weight between the axles has negligible effects on weight distribution but the farther that weight is behind an axle the greater the impact it will have; hence recommending in the bumper if you do decide.
if the car does not feel unstable at high speeds i would try to even lower the tire pressure more, i.e. 13lbs; provided you still have the tires.
those hoosier radials will be the better choice of the tires you listed. have you put any heat into them prior to the run? they will need some heat and i would try and take notes of what does not work. e.g. drop the hammer in 2nd gear and sit still for xx amount of seconds at xx mph and note the effects; generally want to see some smoke coming off the tires for a second or two....much more than that seems to be wasteful.
maybe others will suggest even less psi, provided the car is still stable.
if you already offloaded the tires and are searching for new ones look into 15's with much more sidewall, this will likley improve your situation also.
also about your shifting: do you flat shift between gears? or do you have a standalone to pull ignition to take the load off? one thing about radials is when they spin the often do not recover unless you pedal the car where as a slick can often garb sooner. having the ignition pulled during a wide open throttle shift may provide a softer shock to the tires and also help that zf tranny last a little longer.
i have things to do today but i will check back with some of the answers to the questions we have asked. because you were a good sport provided my rather caustic comments i thank you for being the bigger person.
 

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Discussion Starter #11
Thank you very much for the detailed answers.

My answers are after your questions:

just be very mindful adding that kind of weight without it being almost permanently part of the vehicle; if for some reason it become free during a crash the results can be catastrophic. if you want to experiment with adding weight for the time being(it is band-aid) i would try and integrate it into the bumper.

That has been a fear for me as I was not going to fix the added weight, and will fix the weight.


if the car does not feel unstable at high speeds i would try to even lower the tire pressure more, i.e. 13lbs; provided you still have the tires.

Car felt "ok" at 140 mph with 14 lbs of tire pressure. But as this is a circuit test, we do run for 1-1,5 hours and the sidewalls' color changed to cream white. There was a lot of stress on the side walls.
I suppose These dot drags were not designed for continuous use, I think for short bursts of time.

those hoosier radials will be the better choice of the tires you listed. have you put any heat into them prior to the run? they will need some heat and i would try and take notes of what does not work.

I ve heated the hoosiers up to 170 F. No good news. Have a pyro checked at inner contact patches as well as outer. But no good neews.


if you already offloaded the tires and are searching for new ones look into 15's with much more sidewall, this will likley improve your situation also.
When I go with 15s I need to remove rear brakes but will test this.
Do you still think that 15" tires will give better traction on an unprepared road course such as this F1 circuit?

also about your shifting: do you flat shift between gears? or do you have a standalone to pull ignition to take the load off? one thing about radials is when they spin the often do not recover unless you pedal the car where as a slick can often garb sooner. having the ignition pulled during a wide open throttle shift may provide a softer shock to the tires and also help that zf tranny last a little longer.

I will try this. Thank you very much.
 

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the answer we were trying to provide just became more difficult finding out this sounds like a dual purpose vehicle. the taller sidewalls will not be conducive to lateral loads so you will have to compromise with which venue you want the car to shine more.

i do not feel comfortable offering any advise on where the compromise should be made.

generally road course cars like as stiff a suspension as the course allows to keep the suspension geometry consistent and prefictable; often solid bushing are used as well for the same reason. just enough suspension travel to keep the tires in contact with the road.

i do not know enough about setting up drag racing irs suspension to describe how different they are from road course cars but it is safe to say it is different. i would image some sort of slow rebound would allow the weight that is transferred under hard accell to stay over the rear tires longer; lending itself to more potential traction? if i assume correctly, one would need a much softer spring rate than road course cars to allow significant weight transfer over the rear on a 60mph hit. this is only a guess and i ask for you to confirm or deny my suspicions before you think about integrating any of it.

im afraid there is no free lunch here.
 
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