Questions For Bob

I’m looking to get just a couple of questions answered by someone who knows, and by everything I have been enjoyably reading, I believe that Mr. Bob Bolles is the person for me to get my answers from. I know you must get hundreds of emails and requests every month for “just a quick question” to be answered. Well, regrettably, I believe this may fall under that same category. I’m part of a team that races an IMCA-style asphalt modified in Virginia. Our driver has been racing for more than 30 years now, and he has an incredible way of explaining things for me to understand. I joined the team at its inception, and have been bitten by the circle track racing bug. I had always been into drag racing and, well, this is much more than I had ever imagined it would be.

My mind is very detail and engineering oriented. I want to know the “why” all of the time, and due to this need to know why, I was able to help our team work out quite a few bugs with the brand-new chassis that we had built for this year. We got the front moment center to a place that is tremendously better and more responsive from what it came to us from the chassis builder. This has gotten me into the subject of creating a “balanced” car geometrically. My questions are these:

1. How do I find out the “roll angles” of the front and rear suspensions?

2. How do I figure out the angle/plane/path in which the car feels the turns via centrifugal force? (We race at Langley Speedway, a 3/8-mile, 4-degree banked oval, with very little straightaways)

3. Is there a print publication similar to C. Smith’s Racecar Engineering that I can purchase that is written by Mr. Bolles?

4. Is there a way I can send direct emails in the future to get a personal response from hopefully the same person, so I always get the same person’s advice? I try to keep my sources minimal, so I’m not confusing theories or concepts.

Thank you for your time and consideration. Cheers.

—Darren Mix

Darren,

You sound like you’re in a place where I was back when I first started. This is the most fun you’ll have racing at this stage of your “career.” You’ve already seen the positive results of a more beneficial location for the moment center and now need to move on to the balance stage of setup development.

What I’m going to provide next might, to some, sound like an advertisement, but it is what it is. You asked, and I’m providing the information.

1. There is only one source for finding the roll angles and that’s a software program that uses patented and proprietary codes for calculating those roll angles and it’s distributed by Chassis R&D. With current published information, it would be nearly impossible for you to do that yourself. Search online for this software. You can also use trial and error and the methodology is provided in articles written in CT regarding tire temperatures.

2. Again, see answer number one. The direction of forces verses track banking angle is outlined in several articles we have presented in CT over the years. It’s a fairly complicated process to evaluate those forces and convert them to a roll angle.

3. I have a new book that is a refinement of Stock Car Setup Secrets (now out of print) and it’s titled Advanced Race Car Chassis Technology by HP Books publisher.

4. I have a CT email address. See the end of the commentary part of this QA.

Sway Bars and Spring Rates Relationships

I’m from Colorado and run an Asphalt Late Model. I have a technical question concerning splined sway bars and front coilover spring rates. Are the spring rates additive?

Let’s say I gain 200 pounds more in a larger bar, but want to keep my total spring rate the same from the old existing setup. Would I drop my coilover springs 200 pounds between them? Is there a direct correlation between them?

We are trying larger bars for a somewhat flat track at Colorado Speedway. Is it trial and error method to find that correct spring rate or can we use a total between bar/springs to get close? Thanks.

—Douglas Cox

Douglas,

There is no direct correlation between sway bar rate and spring rate as to the effect on the setup. The rates of both will influence roll angle and stiffening the sway bar rate will offset softening of the front springs.

Most asphalt teams are now—not at my urging, by any means—running softer front springs and larger sway bars in order to reduce the height of the front of the car in the turns and reduce the roll angle to keep the left front down.

In doing this, we need to keep in mind that you can go too far, meaning run too much sway bar and too soft a front spring rate. What most teams have settled on is a medium rate 3/8-inch bar and around 175- to 200-pound front springs in a coilover Late Model car such as yours.

In order to help reduce the rear roll to equal the reduced front roll for a balanced setup, you need to increase the right rear spring rate, but not too much. If you’re used to running a 200- or 225-lb/in RR spring, you might need to run a 300- to 350-lb/in spring to balance the roll tendencies.

Some teams force this issue of holding down the LF and go to much higher RR spring rates of upwards of 600- to 800-lb/in rates and this only reverses the imbalance and puts too much loading on the LF tire. These setups will fade in a few laps whereas a balanced setup will keep going to the end of the race.

There will be a roll angle of around 1.5 degrees with this balanced BBSS setup, but that’s not at all bad. Rather, you get the benefits of reduced roll, a lower front end, along with a balanced setup that won’t fade. You will get a slightly higher LF valance than a level car, but that’s OK.

Motor Mounting vs. Weight Distibution

I have an idea that I have been wanting to try and I’m shopping around for input. It really is something I’m sure few have tried but I think it just may make a difference, and amazingly still be legal.

I race a second-gen. Camaro in UMP Street Stocks. The motor can be set back no farther than one plug, even with an upper ball joint. I want to leave the motor in that location but not mount it to the crossmember at the side motor mounts. I want to still utilize side motor mounts but fabricate that mount to be tied into the chassis behind the mid plate.

I even want to mount the mid plate so that it’s tied in farther back. Basically, all the weight of the motor would be mounted around the firewall. I originally thought it would take some weight off the front end; but thinking about it more, I don’t believe it will. It should be no different than mounting weight over the rearend or by the bumper.

Front weight in static form shouldn’t change, but it should in dynamic. I know I will have to add weight in front with all the bars necessary to make this strong enough to work, but I think it just may be worth it. What are your thoughts on this? I’m getting mixed reviews.

I haven’t really asked too many except for those close around me. If it works, then not everyone needs to know. I think it should transfer more weight to the rear. Not sure if the chassis will know if the motor is actually mounted farther ahead. I believe it should think the motor is mounted back. Scratch your head a little bit and let me know what you think. Thanks.

—Jim

Well Jim,

This will teach you to write to CT, now everyone will know. You’re correct in the fact that the car will feel the weight of the motor in relation to where it’s mounted, regardless of the mounting method.

I can save you a lot of trouble by telling you, and others, that this method is not going to produce the effect you think it will. Weight and placement are what counts. The weight and placement are unchanged with the new motor mounting system, in static or dynamic situations.

What you’ll end up with is a very dangerous mount where several hundreds of pounds of engine will be cantilevered some distance from the firewall and be prone to breaking off and flying out of the car at some point in time.

The structural integrity needed to prevent this occurrence would be way too heavy to be of much use, and as I stated above, to no real advantage. Once it’s solidly mounted to the chassis, the car knows only that X amount of weight is located in Y location. The dynamics are unchanged from the standard engine mount method.