Hello and welcome to Automotive Thinker!
I created this site so that I could share my thoughts with anyone who thinks like me; that is, thinks about cars and automotive technology all of the time. With this site, I hope to add upon and to expand my thinking in anything car related and I hope to do the same for you. I will mostly be writing about topics that concern high performance and racing, but not just limited to that. I will share my experiences, but am also very happy to scrutinize anything that’s suggested so don’t hesitate to contact me.
I hope that you will enjoy my site and we can learn from each other. Don’t be a stranger, and happy thinking!
About Me: John Milmont
Even though I hold a degree in business from Northern Illinois University, I have been passionate about cars and racing for longer than I can remember and have always tried to be as well read as I could on the subject. I have been club racing on and off for over 15 years with various clubs around the Chicago area; and like any grass roots racer, I have always done my own work and fabrication. I am educated and have experience on virtually every machine found in a typical machine shop. I have setup, trouble shot, and programmed CNC equipment, worked in fiber reinforced plastics, and can also lay down a good weld on anything that’s weldable. I have also had the honor of being on my university’s Formula SAE team when it ran its most successful year in 2007, finishing 19th out of 100+ schools worldwide.
These days, other than my day job, I find myself tinkering on a race car that my brother and I share. The car, now amazingly considered a classic, is a 1989 Pontiac Firebird Formula 350. The car is fully caged a set up for road course duty. The car always seems to be in a constant state of development and I struggle to think of anything on the car that’s from the factory other than the paint.
I’m somewhat hard to contact. I do not update my blog regularly as I fill a senior position in my day job that, sadly, occupies most of my time. I’m sure if you really have the will to contact me, you can figure out a way. The second best way to contact me is to send me a message on twitter.
15 Comments to "About"
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I assume your dad told you about my T-Top repairs on my 1970 Corvette. I think this could build into an interesting side business, but you need to be able to make the necessary internal parts.
Send my your email, and I’ll send you pics of what I’ve done. I’m sure you would be able to improve on my efforts.
Hi, I have a BMW 135i. I came across this website because of the 50/50 weight distribution article. I track my car frequently and have made a number of modifications, big front brakes, semi slicks, coil overs, front sway bar, some hp increase etc. I’m considering weight loss options where I can probably achieve 40 – 80kg additional weight loss at reasonable cost. The problem is the majority of this weight loss is from the rear. A 10kg weight bar BMW places in the rear bumper and a lightweight battery , rear seat removal. If you are faced with a.decision of less total weight and forward weight bias, or more equal weight bias and more total mass, would you always opt for less total mass and try and compensate the weight bias with tyre and suspension adjustment? Thanks.
I’m faced with the same issue with my car. My old trans-am, which is horribly unbalanced to begin with, has a glass hatch that weighs about the same of what your looking to remove. I think the best idea is to go ahead and remove the weight and tune it out with the suspension like you are saying. I have talked to some hard core racers that compete in some low level club type events, and really, those guys or more drivers than engineers – and I get the feeling that they are in over their heads with a question of this type – but they said they would rather have a car that’s lighter overall than well balanced.
I think there is eventually a point where if one end becomes so light, you wont be able to tune it out, but I think you are far away from that.
hi man i appreciate your article here about the carbon fiber repair can you email me for more detailed instruction i really need help please reply asap
Please ask questions on the article page. That way other people can see my response.
Hi John. I love the articles and I’m taking the rear bias weight distribution to heart (and somewhat to the extreme), and have a related question for you. I’m rebuilding a Volvo P1800 as an electric autocross car. Of necessity most of the batteries and therefore weight will be behind the driver. I am trying to keep it as low as possible, but I am running into a dilemma, some of the batteries (Tesla packs) will need to either be placed above the rear axle and higher than I would like, or behind the rear axle but low and even with the differential. So my weight question is this: What would give better handling characteristics, a cg that is higher but more centered or a cg that was lower but more rearward?
I would go with low and more rearward. The other killer of performance is a high CG. A good example of how important CG height is, is the Subaru WRX, even though those cars have a poor weight distribution, they have a lot of grip due to the low CG.
If I was going to build it, i would try to keep the rear weight distribution somewhere between 50% and 60% rear.
Stumbled onto your site and voraciously read everything! Some of the best explanations of complex topics in simple language that I’ve seen anywhere! If I may be so bold as to ask for your thoughts on a couple of esoteric items regarding fwd. I race a 1996 Honda Prelude on an asphalt 3/8 th mile oval (mild banking) in a Mini Stock class. “Rotation, rotation, where art thou rotation?” Fighting terminal understeer and getting some oversteer is an interesting suspension tuning challenge. At the moment the car has an open differential. I have done all the usual tricks: increased spring rates, poly bushings, Koni shocks with race valving, larger ARB front and rear, higher roll stiffness in rear, preloaded front ARB, stickier tires in front and old hard tires in the rear (no stagger allowed), using a pyrometer to set tire pressure and camber adjustments, widened front track width via wheel offset, lowered the car and used roll center adjusters, corner weighting with reverse crossweight, relocated mass (battery, fuel cell) low and left, set rear toe for rear steer, caster split at the front, etc.
I almost find it more fun to play Crew Chief and test various changes more than the actual racing.
Having done the above I’m down to a few ideas which I cannot find answers for. The wider track has of course moved the scrub radius from OEM slightly negative to very positive. This has numerous evil consequences but the reduced load transfer durring cornering by far outweighs the negatives. While I cannot run tire diameter stagger I was wondering if in addition to caster split what would be the effect of having the front wheels with different offsets so that one front tire had more/less scrub radius than the other? I read that changing scrub radius changed toe upon acceleration but the article only addressed rwd and I didn’t know how applicable this would be to fwd; in that I am trying to reduce understeer upon corner exit and also attempt to apply power earlier while still turning. If such a “scrub split” as described would help in any way would the front left want more or less scrub radius than the front right? Would the reduction of front track width with one wheel having more offset outweigh any advantage to such a scrub split or is it better to just get as wide a track width as rules allow?
Would having a lot of Ackerman accomplish this also? I’ve read that “excessive” Ackerman slows the car down due to increased inside wheel slip angle but that was once again referencing rwd. In fwd I would think that I would prefer having the front left tire pull the car to the inside with more Ackerman than geometrically required (unless this would increase the slip angle so much that the tire lost traction and slid). Your thoughts?
Finally, I’ve read that having the left side of the car lowered more than the right would not be beneficial, however this seems counterintuative. Wouldn’t having the car “pre tilted” into the left turn help, as in load transfer body roll could bring the car to level instead of the body roll inducing camber gain on the outside wheels as the suspension went into compression . A softer spring (or less ARB) could then be used which would help tire compliance with the track.
Sorry for the long message. I just love this stuff but some things aren’t addressed by Smith, Puhn et all and Miliken is far beyond my ability to understand.
Thanks in advance for your consideration.
I would like to see the source on where you read that scrub radius changes toe or has any other effect other than changing the loads that go into the steering and self-centering forces. Scrub radius is usually described as the distance between the point of steering rotation to the actual center of the tire’s tread. If you increase the track and scrub radius, toe should not change since the the axle is still on the same plane.
If you were to have a different wheel offset on each front tire, you are going to feel it both under braking and gas. The steering wheel will be pulling to side with the large scrub radius under braking and away from it while on the gas. This is not going to help anything. I would just go as wide as you can without making it unequal.
Ackerman is a really hard to measure and design for. The purpose of ackerman at high speeds is to compensate for the pneumatic trail of the loaded tire. In other words, to compensate for deflection in the tires carcass (sidewalls) which makes the tread of the tire not point to where the wheel is pointing. This means that, at speed and at full cornering load, the your outside tire is not turning as sharply as the wheel its mounted on is. In turn, if you were going to optimize the ackerman so that both front tires are following the same turning circle at speed, you actually have to have negative ackerman, that is that the inside tire turns less than the outside one. But yes, excessive ackerman, positive or negative would slow a car down.
As far as pre-tilting your car, yes i dont see why this wouldn’t help. Production cars have a limited camber curve and adjustments. If tilting your car gives more camber in the proper direction, then yes, it would help. But what it does not do is change load transfer. Load transfer is hard to describe when cornering. Believe it or not, soft or stiff springs do not change the total amount of load transfer. What springs do is change what end of the car gets the load first and also the amount of body roll. They also have an effect on responsiveness. When cars roll, the outside tires tend to lose camber, and really, that’s the primary reason why you want stiff springs – is to prevent the car from rolling so you maintain a good contact patch. If you pre-tilt the car, yes, you might be able to run softer springs because the car will be more level when cornering.
As far as combating understeer at corner entry, one thing to take into account is the roll center height. On my car, the front roll center lowers a lot quicker than the rear. Low roll centers have the effect of making the suspension softer when cornering. So, naturally, my car tends to suffer from oversteer if its just lowered without any consideration to this. I don’t know how your car behaves when its lowered, maybe its opposite. You said you have roll center adjusters, i would like to see how you have those installed. I have seen these on a Porsche race car, but its not something i thought i would see on a production car.
If you can, lower the front roll center, and raise the rear. This will have a similar effect as putting in a smaller front bar and stiff rear one. You also said that you installed a aftermarket front sway bar? I would take it that one is much stiffer than the factory one, i would put a softer one in or the factory one.
It sounds like you understand the general concept – stiffer rear tends to make oversteer. But on my car, there is one thing that no one takes into consideration, and that is the bump stops. I dont know if you car does this but i found that the bump stops are an integral part of the springs. The car rides on them all the time in its factory form and they add a very large and progressive amount of rate. I have been meaning to actually put my bump stops on a spring dyno, but from my estimations, its adding somewhere like 500lbs/in. Just massive. So check to see if you car does this, this would effect oversteer/understeer and make the suspension not very responsive to metallic springs/ARB changes.
Furthermore, i know many FWD guys run big rear ASB’s and actually get the car to lift the inside rear tire off the ground. I read that this was ok to do in FWD cars, and i don’t see why it wouldn’t be since that tire pretty much does nothing.
Lastly shocks have a huge and little understood effect. On my RWD car, cranking up the front rebound stiffness has a huge impact on how much power i can put down. With very stiff front rebound, my car cannot lift the front and transfer that weight to the rear. As you would expect, the same is true when i increase the rear bump stiffness. But no one ever thinks about the front effecting how much power i can put down in a RWD car. In a FWD car, i dont know how this would effect you. I would think you would actually want stiff rebound in front and stiff bump in the back.
Dont be afraid to make radical changes to test something. When i told people i was running a 2300lbs spring on the front of my car they thought i was crazy since they were running 800lbs spring. They failed to understand the leverages and bump stops on the car. Even after i did the math on the car, i still couldn’t believe that 2300lbs springs were right until i just did it and it worked.
Best of luck,
John, I am building a off road vehicle that could be used for daily driving all from scratch. I am having second thoughts about my brake system using solid rotors and wanted to ask your opinion on it.
John, I have a 1969 Volvo P1800. It has coil springs all around. Rear wheel drive. This car needs noticeably less steering input to keep it in a straight line when it has a full tank of gas in it, about 70lbs. I think the front end geometry is changing slightly, perhaps toe in or camber with the full tank. What front end settings would change the most with the added weight of a full tank of gas? Rich B.
I dont know your car but this sounds really strange. I can feel the difference in my race car as the fuel gets lower on the track, but not on the street. It sounds like your car has some sort of bump steer problem. The general rule is that you shouldn’t have the alignment go from toe-in to toe-out when the suspension moves. This means, if your car gets toe in under compression (like my car), you should not have the suspension aligned with a little toe out when its at rest, so when the suspension is compressed, it crosses into toe-in (or vice versa). This change in toe from out-to-in can be unsettling to the driver. So in my example, its best to have the static toe set with a little toe in so it only gets more under compression.
I don’t know what you are experiencing, but its probably something with the toe.
I came across your site because of a link a friend sent me to do with progressive rate springs. He has a BMW M2 and the stock suspension was rather good – but now with KW progressive rate springs and stock shocks, it rides horribly and easily hits the bump stops! He’s going to go back to stock…
I also read with interest your article on 50/50 weight distribution because I too thought that having a perfect 50/50 was the best for handling and lap times. I’m glad that it isn’t, because both of my cars don’t have anywhere near this, but I am interested in improving both of them for fast twisty road driving, and possibly the occasional track use.
The two cars I have are a 2018 Audi RS3 sedan which is totally stock (for now!) and a 2009 Audi S5 V8 coupe in manual that has been supercharged with an APR Stage 3 kit. It also has some supporting mods such as Milltek downpipes and catback, clutch, etc.
The main problem I seem to be having with both cars is excessive, uneven tyre wear when I push them too hard. The second problem is more with the RS3 – it just feels like it wants to push wide, whereas the S5, seemingly less so – so the RS3 feels less enjoyable to drive than the S5 does. So I have a series of questions for you – it would be awesome if you could provide some answers if you can!
Firstly, the RS3 – as it comes with an inbuilt G-force meter, I have tried to identify how many G’s I can do before excessive tyre wear (on both inside and out, but more on the outer edge) starts. It seems to be about 0.7 to 0.8 G and I cannot get it to do anymore than 1.0 G before it starts understeering, which is on the stock Pirellia P Zero tyres. I have a friend with a 718 GTS who has done 1.63G on street tyres! The outer edge of my tyres (mostly the fronts) can be chewed up quite badly after just a few minutes of driving at 0.7 G and above which I think is quite unacceptable. The inside edges also wear quite badly but not as bad as the outer edges. It almost looks like the tread has melted together and just worn away!
The car also runs a tyre pressure monitor and I believe the recommended pressure is about 38 psi. I run usually about 35 psi in the winter so that when I am having a fang, tyre pressures increase to about 38 psi – if I am pushing very hard, perhaps 39-40 psi.
The car also has adjustable suspension but this tyre wear problem seems to occur no matter which setting I use!
Interestingly, it runs 255/30R19 tyres front and 235/35R19 rear (with 9.0″ and 8.5″ width wheels respectively) – Audi’s reason for this was to try and reduce understeer (normally it runs 235’s all round but the front 255’s are part of a Performance Package).
1. How do I get it to stop chewing out tyres, especially the fronts? (Other than driving slower of course!)
2. How can I get it to handle neutrally, perhaps with a little oversteer?
3. What are your tyre recommendations? As in, widths and sizes? I have access to a set of TTRS 19 x 9.0J wheels which I am planning on running all-round with 255 tyres all-round. Due to the finicky Haldex AWD system, it will complain when a non-square setup (other than the custom OEM tyres) is used because of the slightly different rolling diameter (the OEM tyres have identical rolling diameters). I don’t really like the P Zeros and the only other way I can see to avoid the Haldex complaining is to go with a 255 square setup – my favourite tyres right now are Michelin PS4S. Also, a square setup will allow me to rotate my tyres!
Now for the S5: as previously mentioned, this feels fairly light to drive, and has less understeer than the RS3. I can trail brake fairly heavily into a corner and it doesn’t understeer much at all. About the only time it really understeers is under heavy acceleration exiting a sharp corner. It has a lot of mechanical grip and I am running 275/30R20 all round with Michelin PS4S. When I do this, it chews out the outer 2″ of both front and rear tyres – they go a bit “furry” (whereas in the RS3 they just look like they’ve melted!) – and the inside edge seems to be OK. I am unsure if my car has the optional Audi Sports Diff (a rear LSD) – it probably is running the stock open rear diff – but cannot feel any tyres scrabbling for traction, even with WOT out of a hairpin in 2nd gear!
As far as I know, it is running the stock suspension all round (I bought the car 2nd hand) and am quite happy with the ride. The handling is quite nice too, so my question for this car is more around the excessive outer edge tyre wear. The suspension seems fairly well controlled – and it never bottoms out, so I think if I could keep the stock shocks and springs and make adjustments elsewhere, this would be preferred. However, I can definitely be persuaded otherwise if you can provide reasons why I should upgrade it!
The main thing with both cars is that both are road cars. The S5 is the weekender while the RS3 is the daily. While I may take either to the track, this is probably unlikely, but I do take them out of long drives with various car groups in twisty backroads so they must ride well and have plenty of clearance too. The S5 probably sits at a “good looking” height (maybe a 10mm drop would be ideal) whereas the RS3 looks like it could do with a 10-20mm drop.
Any help and guidance, or pointers to good references, would be much appreciated! If you have any specific products or kits you know of that are suitable for either of my cars, please let me know. I am totally new to the aftermarket suspension area so am unsure what to look for in kits, or whether to go for a semi-custom setup, or what sorts of testing to do, etc!
Audi has had a long reputation for making cars tuned with a lot of push in them. It seems like you are confirming this.
Anyhow, there are a number of small things you can do to try to balance out the handling like installing stiffer bushings, increasing front camber and playing with tire pressure. But really, these are very unlikely to have much of an effect. If you want to make a real difference, you are going to have to change the spring rates. This can be done three ways. Through the swaybars, springs, or to a lesser extent, through the shocks. You will want to focus on the rear suspension and on increasing the rate.
The easiest place to start is with a adjustable aftermarket rear swaybar. My 350z also had a lot of push from the factory similar to what you are describing. I got the biggest swaybar I could find which also happened to have 3 adjustment settings. On the softest setting, it brought the car really close to balanced. My car came from the factory with a staggered tire setup with narrow tires on the front, when I switches to a square setup, combined with the swaybar, it made the car perfectly balanced. I have never needed to use any other setting on the bar. You should know that adding a bar like this is going to introduce more harshness into the ride, not only from the stiffness of the bar but because of the hard urethane bushings they use.
Your Audi’s add an extra layer of complication due to the 4wd system. It could be that the system is tuned to prevent oversteer. I have a feeling that when the car starts to get sideways, the haldex is going to send the power to the front wheels. But, being 4wd also allows you to run stiffer rear springs without hurting acceleration like it does to my rwd cars.
Changing out the rear springs would be the next step, but this is much harder to do than just changing the swaybar. There is nothing special or magic about the springs on the car, but changing out the springs for something else without the ability to adjust the ride height is going to cause the car to be at the wrong height. So its best to have a coil-over system or some sort of adjustable spring perch. Coilovers are nice since they use standard spring sizes and you can get those springs in any rate you wish. If you are going to do this, its going to take some experimentation and you will have to buy a number of springs. I have quite a few laying around… It would be easiest to get a known good coilover kit that is designed for your car.
As far as your cars wearing out the outside edge of the font tires, its bound to happen, but there are some things you can do to reduce this. Those little things I first spoke about? The bushings and camber? Those are a good place to look. Bushings do add a lot of harshness, and camber can be hard to change since many cars are not adjustable. You may need aftermarket control arms or adjusters to get any real camber into the suspension. You will have to see what others have done and whats out there. Also, when you are going through a corner and the car is pushing, don’t give it any more steering angle than what it needs. Turning the wheel more than what the car can physically take just wears out the tires faster.
As far as tires, I’m shocked that your car came with wider tires in the front. Really, on a car that has a front weight bias and that has power going to the front wheels, this makes perfect sense. This is indeed a way to try to reduce understeer. I’m surprised they did this because of the looks standpoint. There is this idea that cars just look better with fat rear tires, even if it makes no sense dynamically. My recommendation is to follow what the factory did and also to use tire widths that are recommended for your wheel width. All tires have a recommend wheel width, use those for optimal handling.
I can go on and on, but I’m limited on time right now. Let me know if you want me to go into any more detail into anything or into something that I didn’t cover. Ill try to answer later.
Hi again John,
I just wrote to you about my RS3 and S5.
I put the incorrect wheel specs for the stock RS3 wheels and the TTRS wheels I am planning to use.
The correct wheel specs for the stock RS3 wheels are:
Front: 19 x 8.5J ET46
Rear: 19 x 8.0J ET42
The TTRS wheels are 19 x 8.5J ET43 all round.