Mechanical Grip

[Lurker27]

Bigger tires are always faster. A lot of the theory about contact patch and tire pressure and weight and such never really applies - Bigger tires WILL generate more grip, always.

I'd recommend getting a cheap infrared thermometer/pyrometer and recording tire temps inside/outside/center on each wheel after every run.

Read the entire site "Autocross to win" by Far North Racing. It's easily the best AutoX resource on the internet.

[nrubenstein]

Bigger tires are always faster. A lot of the theory about contact patch and tire pressure and weight and such never really applies - Bigger tires WILL generate more grip, always.

I'd recommend getting a cheap infrared thermometer/pyrometer and recording tire temps inside/outside/center on each wheel after every run.

Read the entire site "Autocross to win" by Far North Racing. It's easily the best AutoX resource on the internet.

It's definitely a good rule for autox. There does actually come a point on track where more tire costs you more time in the straights than it gains you in the corners. (But that isn't really relevant in street cars.)

[Jean]

Bigger tires are always faster. A lot of the theory about contact patch and tire pressure and weight and such never really applies - Bigger tires WILL generate more grip, always.

I'd recommend getting a cheap infrared thermometer/pyrometer and recording tire temps inside/outside/center on each wheel after every run.

Read the entire site "Autocross to win" by Far North Racing. It's easily the best AutoX resource on the internet.

We were both faster today than yesterday, same course but reverse grid. 55.1 for the co-driver and 55.3 for myself, both times beat the last years' SM champion in his e36 m3 on 275s....

I put new rear pads today, and we went down a few psi to about 26/27psi. We did use an infrared temp gauge and camber is good, even temp.

The main issue we both agreed on is the rear diff, it must be worn out, very easy to spot when it unloads and when it hooks up with were spinning a 225/50 v710 like no tomorrow.

So, for now next mod is going to be a better rear diff (Suggestions please?) with more lock-up, ratio is working out just about perfect.

And once these tires are done, will have to step it up to 275s, maybe on something like 15x9-9.5 .

We'll also try stiffer rear springs, car is for the most part neutral, only as the tires got hot did we start noticing a little bit of understeer (we had like 4 re-runs due to down cones or other cars dnf's) so we'll up the rear rears from 675 to maybe 750 and see how things change.

[Jean]

When you say heat cycled I assume you meant by the tirerack prior to use?.One thing with r-comps is they are a little harder to tell whats going on,no noise feedback so they can lock quite easily.Part of it is the added - camber reducing front contact patch,especially the inside front while trail braking.I've always been a little too aggressive with the trail braking,slowly learning to brake very hard slightly earlier(and mostly going straight) and then less trail brake pressure as you bend the car in.
What kind of diff are you currently using?

Correct, ordered these from tire rack with the heat-cycle option. Not our first time on r-tires, just really can't put the power down coming out slow corners. Diff is a 3.64, no idea on mileage but it deff is an area where improvement is to be had.

[nrubenstein]

Also, I don't know what rear suspension you are running, but you may want to try a bit less rebound damping in the back. Rebound, after all, will prevent the shock from extending quickly to keep the inside tire on the ground.

...obviously this can be a tradeoff in other areas.

[Jean]

Shocks aren't adjustable, they are just bilstein sports that I had re-valved for my car (rates/height/weight) :(

[L8 apexr]

Bigger tires are always faster. A lot of the theory about contact patch and tire pressure and weight and such never really applies - Bigger tires WILL generate more grip, always.

I'd recommend getting a cheap infrared thermometer/pyrometer and recording tire temps inside/outside/center on each wheel after every run.

Read the entire site "Autocross to win" by Far North Racing. It's easily the best AutoX resource on the internet.

Thats not an accurate statement at all,for sure wider is better sometimes but if you can't get heat in a wide tire the narrow tire will be faster.

I suggest keeping the infared in the toobox for checking things like brake rotors,header pipes and coolant hoses but not for checking tires.You need to use a probe pyrometer for tires,the surface temps cool too fast exposed to air and give hugely inaccurate information.
I'm new to bmw's,is the diff a plate or vlsd?.The part most people don't think about(me included,learned the hard way 10 years ago)is that once the suspension is sorted and running on r-comps the diff becomes FAR more important.The extra cornering force means the outside rear gets nearly all the weight so there's very little grip for the inside wheel to help drive the car.If the diff is weak it'll show up then,on streets or stockish suspension the diff likely shows little signs of age.
From what I've read the os gikken is the diff to use if you can swing the cost and they make one to fit.I'm hoping to have one down the road,I don't think the stock vlsd in my a-mod car will like the slicks-I have huge areo this year which may help but not sure yet.

[Pinepig]

You diff might be slipping a bit and not even the 25% lockup it came with from the factory. Take a look at this,

http://forums.bimmerforums.com/forum/showthread.php?t=1115194

This is absolutely something that you could do, you can even add extra disks to give more lockup.

Take a peek at this too, he can get 40% disks too.

http://cgi.ebay.co.uk/BMW-LSD-CLUTCH-DISC-SERVICE-KIT-188MM-LSD-25-/150581041823

[Jean]

Yeah that is not something I think I should nor can do! lol.

There is gotta be someone local who can bmw diffs w/o spending an arm and a leg. Maybe I'll just start calling places in yellow pages or something. But really I would rather go to someone who is recommended.... and knows what they are doing.

[nrubenstein]

Thats not an accurate statement at all,for sure wider is better sometimes but if you can't get heat in a wide tire the narrow tire will be faster.

I suggest keeping the infared in the toobox for checking things like brake rotors,header pipes and coolant hoses but not for checking tires.You need to use a probe pyrometer for tires,the surface temps cool too fast exposed to air and give hugely inaccurate information.
I'm new to bmw's,is the diff a plate or vlsd?.The part most people don't think about(me included,learned the hard way 10 years ago)is that once the suspension is sorted and running on r-comps the diff becomes FAR more important.The extra cornering force means the outside rear gets nearly all the weight so there's very little grip for the inside wheel to help drive the car.If the diff is weak it'll show up then,on streets or stockish suspension the diff likely shows little signs of age.
From what I've read the os gikken is the diff to use if you can swing the cost and they make one to fit.I'm hoping to have one down the road,I don't think the stock vlsd in my a-mod car will like the slicks-I have huge areo this year which may help but not sure yet.

I've never seen a BMW that couldn't use more tire in the context of conepacking. Unless it's wet out, getting heat in isn't an issue. Even full tilt DSP E30s run 275s or 285s.

[Lurker27]

The Z3 3.15 is torsen, maybe try that?

[Jean]

Ratio is not ideal, 3.25 was not right either. I want to keep the same ratio I have as it's working out even on the bigger lots.

[craz azn]

Shocks aren't adjustable, they are just bilstein sports that I had re-valved for my car (rates/height/weight) :(

Do you know offhand what the redone valving was?

[L8 apexr]

I've never seen a BMW that couldn't use more tire in the context of conepacking. Unless it's wet out, getting heat in isn't an issue. Even full tilt DSP E30s run 275s or 285s.

Depends on the tire and your location.:D

Up here in the north and nothing but asphalt lots getting heat in the tires is a major problem regardless of what your driving.

[Jean]

Ok question.

this is a "SET" so two clutches, so I would just need two of these yes?

http://cgi.ebay.co.uk/BMW-LSD-CLUTCH-DISC-SERVICE-KIT-188MM-LSD-25-/150590537395?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item230fe53eb3