Hey autocrossers: what are some significant mods?

[slugg]

I previously had it at 11.5" front ant back. Way too low. 12" in the front doesn't seem like much of a difference... I'll think about this some more.

Thanks, all, for the help with brainstorming

 

[exdeath]

I had to roll my front fenders a bit running 15x8 with the 225mm wide tires and remove the front fender liners.

Lol 15" rims, the tell tale sign of someone who is serious about racing. :awe:

 

[Howard]

Lol 15" rims, the tell tale sign of someone who is serious about autocross. :awe:

fixed

 

[thedarkwolf]

Lol 15" rims, the tell tale sign of someone who is serious about racing. :awe:

It is a miata. What size should I be running? I believe the "serious" autox guys run 13" but then I'd have to downgrade to the smaller 93 and older brakes. I guess all the spec miata guys aren't very serious either since they are sporting 15" rims.

 

[grjr]

It is a miata. What size should I be running? I believe the "serious" autox guys run 13" but then I'd have to downgrade to the smaller 93 and older brakes. I guess all the spec miata guys aren't very serious either since they are sporting 15" rims.

you need to put some 24's on that ride son :thumbsup:

 

[thedarkwolf]

Now I'm serious boy

 

[Imported]

I can't say with 100% certainty, but 15x9s should fit a stock NB.. They fit on the previous owners suspension (KYB AGX + I'm not sure what springs) and they fit with my coilovers right now as well. You may experience a little rubbing at full lock but should be fine otherwise.

Mine's adjusted to around 12" from center to fender if IIRC. Either 11.5" or 12". Currently on 949 Racing's Xida Club Sports 700F 400R. As harsh as they may seem, they're amazing just for daily driving if I were to do that. Beats out the PSS10s I had on my G35 in comfort handily.

 

[JCH13]

I can't say with 100% certainty, but 15x9s should fit a stock NB.. They fit on the previous owners suspension (KYB AGX + I'm not sure what springs) and they fit with my coilovers right now as well. You may experience a little rubbing at full lock but should be fine otherwise.

Mine's adjusted to around 12" from center to fender if IIRC. Either 11.5" or 12". Currently on 949 Racing's Xida Club Sports 700F 400R. As harsh as they may seem, they're amazing just for daily driving if I were to do that. Beats out the PSS10s I had on my G35 in comfort handily.

Amazing for San Francisco daily driving, last time I was in SF your roads were smooth as butter! /jelly

 

[homercles337]

My local autocross club allows minor mods in the stock category, but as soon as you alter the ride height in any way, you're thrown in with the fully modded cars, but not full out race cars.

This conversation is about a thousand pages long at the 'tex. There is a guy over there (TechEd) who is a race instructor and raced for many years in many different classes. He claims that "lowering" improperly does more harm than good. Specifically, we were talking about the Eurospec Golf R v the US spec Golf R. The Eurospec is a centimeter lower, so people just wanted to lower the thing. According to TechEd this can be disastrous. Having driven the stock car for a couple months now, i am not in agreement with Ed. This Golf R has a wicked bump steer that needs to be corrected. I worked through some of the math and lowering about a centimeter should do it. Of course, most AutoX courses are totally flat, so i suppose there would not be any bump steer problems.

 

[JCH13]

This conversation is about a thousand pages long at the 'tex. There is a guy over there (TechEd) who is a race instructor and raced for many years in many different classes. He claims that "lowering" improperly does more harm than good. Specifically, we were talking about the Eurospec Golf R v the US spec Golf R. The Eurospec is a centimeter lower, so people just wanted to lower the thing. According to TechEd this can be disastrous. Having driven the stock car for a couple months now, i am not in agreement with Ed. This Golf R has a wicked bump steer that needs to be corrected. I worked through some of the math and lowering about a centimeter should do it. Of course, most AutoX courses are totally flat, so i suppose there would not be any bump steer problems.

Bump steer will rear its head when you throw weight transfer into the mix, when you brake or hit the gas weight transfer will pitch the car and cause it to change steering angle.

FWIW the 'lowering with disastrous results' is probably from screwing up the roll centers without appropriate compensation in spring rates to maintain or increase the axle's roll stiffness.

 

[homercles337]

Bump steer will rear its head when you throw weight transfer into the mix, when you brake or hit the gas weight transfer will pitch the car and cause it to change steering angle.

FWIW the 'lowering with disastrous results' is probably from screwing up the roll centers without appropriate compensation in spring rates to maintain or increase the axle's roll stiffness.

Bump steer is a specific effect caused by suspension compression and changes to camber as a result. What youre thinking of is lift-off oversteer, or roll-steer. The car in question is a fairly well balanced AWD 4 cylinder turbo. I have never been able to induce lift-off oversteer, or roll steer. The bump steer is nothing short of vicious though.

 

[exdeath]

Bump steer is a specific effect caused by suspension compression and changes to camber as a result. What youre thinking of is lift-off oversteer, or roll-steer. The car in question is a fairly well balanced AWD 4 cylinder turbo. I have never been able to induce lift-off oversteer, or roll steer. The bump steer is nothing short of vicious though.

Bump steer is caused by changes in toe as the wheel goes up and down. Its a function of the tie rod / toe link bar height and angle vs the control arm and not swinging in concentric arcs with the control arm. If those arcs cross, you'll get toe out one one side of the intersection and toe in on the other side, causing the car to push or pull and steer itself as the suspension loads and unloads.

Production cars with IRS are setup with bump steer on purpose for safety. Toe in on compression, toe out on rebound. When the car is leaning to the outside of a turn, the toe links keep the rear wheels of the car steering into the inside of the turn to help control over steer by pulling on the rear to the center.

 

[JCH13]

Bump steer is a specific effect caused by suspension compression and changes to camber as a result. What youre thinking of is lift-off oversteer, or roll-steer. The car in question is a fairly well balanced AWD 4 cylinder turbo. I have never been able to induce lift-off oversteer, or roll steer. The bump steer is nothing short of vicious though.

Bump steer is caused by changes in toe as the wheel goes up and down. Its a function of the tie rod / toe link bar height and angle vs the control arm and not swinging in concentric arcs with the control arm. If those arcs cross, you'll get toe out one one side of the intersection and toe in on the other side, causing the car to push or pull and steer itself as the suspension loads and unloads.

Production cars with IRS are setup with bump steer on purpose for safety. Toe in on compression, toe out on rebound. When the car is leaning to the outside of a turn, the toe links keep the rear wheels of the car steering into the inside of the turn to help control over steer by pulling on the rear to the center.

Exdeath beat me to it.

homercles337, you're new to ATG it seems, so I'll give you a primer: there are some users in here who know cars backwards and forwards, and some who have designed and built them from scratch. It will pay big dividends to listen carefully when good information is provided.

 

[homercles337]

Exdeath beat me to it.

homercles337, you're new to ATG it seems, so I'll give you a primer: there are some users in here who know cars backwards and forwards, and some who have designed and built them from scratch. It will pay big dividends to listen carefully when good information is provided.

Here is a suggestion for you, go to the VWVortex, then come here. I have been around a hell of a lot longer than you and am frankly insulted by your speculation. I dont need your "primers" or whatever you want to call them. I did not say anything different than exdeath, if i did the impetus is on you to clarify and not make baseless attacks.

EDIT: If you disagree with me, you also disagree with all of the Tex and Wikipedia.

 

[jlee]

Here is a suggestion for you, go to the VWVortex, then come here. I have been around a hell of a lot longer than you and am frankly insulted by your speculation. I dont need your "primers" or whatever you want to call them. I did not say anything different than exdeath, if i did the impetus is on you to clarify and not make baseless attacks.

EDIT: If you disagree with me, you also disagree with all of the Tex and Wikipedia.

I beg to differ.

Bump steer is caused by changes in toe as the wheel goes up and down.

Bump steer is a specific effect caused by suspension compression and changes to camber as a result.

 

[JCH13]

Bump steer is a specific effect caused by suspension compression and changes to camber as a result.

Bump steer changes toe, not camber. Camber change in compression, i.e. camber gain or loss, does not steer the car.

What youre thinking of is lift-off oversteer, or roll-steer.

I am not referring to lift-off oversteer, the result of traction loss of the rear wheels when the weight transfer of acceleration is removed. Roll steer, i.e. bump steer-like effects when one wheel goes up and the other wheel goes down, is not what I am talking about either. Oversteer and roll steer are two completely different behaviors.

The car in question is a fairly well balanced AWD 4 cylinder turbo. I have never been able to induce lift-off oversteer, or roll steer.

Unless this car's suspension has perfect toe and steering link geometry, i.e. 0 toe change during suspension travel, (nearly impossible) you have roll steered, regardless if you realized it or not.

The bump steer is nothing short of vicious though.

Possible, it might cause the car to pull in weird directions during acceleration or braking. Though I've never heard of anyone really upset about bump steer, even race drivers.

 

[homercles337]

I beg to differ.

What? Are you suggesting that camber does not affect bump steer? Seriously? Wow.

 

[JCH13]

What? Are you suggesting that camber does not affect bump steer? Seriously? Wow.

Seeing as you refer to wiki:

Wiki's Bump Steer article has no mention of the word "camber".

Wiki's Camber Angle article has no mention of the word "bump".

How to Make Your Car Handle does not mention "bumpsteer" in the camber section, nor does it mention "camber" in the bumpsteer section. Link.

Changing ride height can change camber and toe at the same time in some cars, like a mac-strut VW Golf, because it clearly does not have a perfect (zero change) bump-steer setup nor zero-camber-change setup.

Adjusting camber independently from all else does not necessarily change toe or bump-steer curves, though in some cars it might change due to specific cars' suspension hardware.