How to get go cart handling (in theory at least)

[drees]

Boo asked in the BT Tech Front Tower Strut Brace thread:

Originally Posted by Boo

What's the difference between "reduced body roll" and "reduced turn-in lean"?

What's the minimum and least costly modifications one has to make to the standard/base edition Prius to get something resembling that "slot-car" handling I hear people talking about after putting Tom's braces on their Prius?

Well, a lot of people use "body roll" and "turn-in lean" the interchangably. At least, I think of them as the same thing or at least very similar, but if you really examine the two, you might interpret "turn-in lean" as the initial feeling of body roll at the beginning of a turn and body roll as more of a steady state issue. Personally, I would refer to the turn-in feel as just that, "improved turn-in".

As far as the minimum and least costly mods to make a standard Prius handle like one with the Tom's braces, the only alternative that I know of are the BT Tech stiffening plate ($145) and the to be released BT Tech front strut tower brace ($???), and you're still missing two other braces (not to mention the Sportivo suspension kit, which IMO should improve handling the most, see more later).

Tom's Racing make the following braces:

Tom's Racing Floor strengthening brace: $280
Tom's Front Suspension Member Strengthening Brace: $280
Tom's Front Upper Performance Rod: $250
Tom's Rear Suspension Member Strengthening Brace: $450
Tom's Sportivo Suspension Kit: $990

(Tom's prices pulled from Carson Toyota's website)

So while BT Tech has a replacement for the floor strengthening brace and soon will have one for the upper performance rod at and nearly half the cost, it's a no brainer to choose those over the Tom's pieces.

If you wanted to build the best handling Prius at the lowest price, I would suggest a set of upgraded swaybars, BUT NO ONE MAKES THEM (are you listening vendors?). These normally cost in the ballpark of $300-$500 for a front and rear bar and are typically regarded as the most cost effective bang-for-the-buck handling modification and has the added benefit of changing the ride quality of the car a negligible amount (for most reasonable sized bars). Stiffer swaybars would definitely reduce body roll and improve turn-in response much, much more than any suspension braces would.

I must insert the disclaimer before my next comment - I have not actually performed any modifications on my Prius yet, I am still in the research stages! But I have modified the suspension in my last three cars, a Subaru WRX (still own), Camry and Celica.

I have run strut-tower braces in both my WRX and Camry. I could not tell any difference before and after in body-roll or turn-in on either after installing the front strut-tower brace. I also added a rear strut-tower brace to the WRX (a wagon). All strut tower braces did make the car feel a bit more solid. I am of the opinion that strut-tower braces aren't generally worth the money unless you have already upgraded all other major components of your suspension (tires/wheels, springs, shocks/struts, swaybars).

Swaybars - Significant reduction in body roll on both cars. Best thing is that ride quality is unchanged under normal conditions.

Springs/shocks - Significant reduction in body roll, pitch, dive. Since they also lowered the car a bit, made the cars look better, too (IMO). Drawback is that ride quality suffers.

Other misc chassis braces - I haven't had the opportunity to try any other types of braces on my cars besides the before mentioned parts.

Frankly, I doubt some of the claims that others have made in ride differences with chassis braces. This would imply that the chassis in the Prius has a large amount of flex, but I simply don't feel it. I can tell there is a bit of flex in the hatch area because of the occasional creak back there when going over certain bumps, but that's not surprising given the lack of bracing back there. At best, all this bracing is going to stiffen the chassis up enough to make things feel a bit more solid, but the limits of the stock tires and suspension just aren't high enough to do much else.

When I am taking corners aggressively in the Prius, the main limitation I feel is the weak alignment (needs about 1-1.5* of negative camber in the front) and less than sticky tires. Swaybars would be my next choice of mods (rear first if only going with one to help combat the huge amount of push the car has) and then a mild upgrade in spring/shock rate.

[apriusfan]

Originally Posted by drees

..As far as the minimum and least costly mods to make a standard Prius handle like one with the Tom's braces, the only alternative that I know of are the BT Tech stiffening plate ($145) and the to be released BT Tech front strut tower brace ($???), and you're still missing two other braces (not to mention the Sportivo suspension kit, which IMO should improve handling the most, see more later).

Tom's Racing make the following braces:

Tom's Racing Floor strengthening brace: $280
Tom's Front Suspension Member Strengthening Brace: $280
Tom's Front Upper Performance Rod: $250
Tom's Rear Suspension Member Strengthening Brace: $450
Tom's Sportivo Suspension Kit: $990

(Tom's prices pulled from Carson Toyota's website)

So while BT Tech has a replacement for the floor strengthening brace and soon will have one for the upper performance rod at and nearly half the cost, it's a no brainer to choose those over the Tom's pieces.

One edit to your list above - the Sportivo suspension is not made by TOM'S. It is a TRD product that is available through the parts department at any Toyota dealership.

Your claim that a BT Stiffening Plate provides the same handling improvement as the TOM'S Rear Suspension Brace is a bit on the speculative side. Presto has had both the BT Stiffening Plate and the TOM'S Rear Suspension Braces, and states the TOM'S Rear Suspension Braces are like the BT plate on steroids. I have personal experience with the TOM'S Rear Suspension Brace and would concur about the handling improvement that results - much more neutral handling in turns.

Originally Posted by drees

If you wanted to build the best handling Prius at the lowest price, I would suggest a set of upgraded swaybars, BUT NO ONE MAKES THEM (are you listening vendors?). These normally cost in the ballpark of $300-$500 for a front and rear bar and are typically regarded as the most cost effective bang-for-the-buck handling modification and has the added benefit of changing the ride quality of the car a negligible amount (for most reasonable sized bars). Stiffer swaybars would definitely reduce body roll and improve turn-in response much, much more than any suspension braces would.

There is also the contribution of suspension mounts as well. But as you observe in your comment on swaybars, there are no aftermarket alternatives. The one thing that the TOM'S bits (in particular, the rear suspension brace parts - there are two components to the TOM'S brace) do provide is a measure of compensation for the slop in the rubber suspension mounts.

Originally Posted by drees

...I have run strut-tower braces in both my WRX and Camry. I could not tell any difference before and after in body-roll or turn-in on either after installing the front strut-tower brace. I also added a rear strut-tower brace to the WRX (a wagon). All strut tower braces did make the car feel a bit more solid. I am of the opinion that strut-tower braces aren't generally worth the money unless you have already upgraded all other major components of your suspension (tires/wheels, springs, shocks/struts, swaybars).

The strut tower braces are part of a complete package. Which is why you do in fact see them on cars that have suspension upgrades. One car that comes to mind is the BMW M3. In addition to all of the other bits (springs, shocks, wheels, negative camber, sway bars, multi-link suspension in the rear), BMW has fitted a strut tower brace as the final piece of the picture.

Originally Posted by drees

Swaybars - Significant reduction in body roll on both cars. Best thing is that ride quality is unchanged under normal conditions.

Adding a stiffer swaybar will improve handling up to a point. But after that point has been achieved, you have to look elsewhere for gains.

Originally Posted by drees

Springs/shocks - Significant reduction in body roll, pitch, dive. Since they also lowered the car a bit, made the cars look better, too (IMO). Drawback is that ride quality suffers.

Plus, if progressive springs are used (which the TRD Sportivo does in fact use), there is the risk of damage to some rather expensive drivetrain bits from road debris. It is all part of a complete package.

Originally Posted by drees

Other misc chassis braces - I haven't had the opportunity to try any other types of braces on my cars besides the before mentioned parts.

The TOM'S floor stiffening plate will provide some improvement at the margin (last 5-10%), but there is also an issue with clearance between the cat-back exhaust and the plate. Personally, I don't see the utility of the TOM'S floor stiffening plate. Presto has purchased the TOM'S floor stiffening plate and has been threatening to actually install it. To date, I don't believe he has made good on his threats.

Originally Posted by drees

Frankly, I doubt some of the claims that others have made in ride differences with chassis braces. This would imply that the chassis in the Prius has a large amount of flex, but I simply don't feel it. I can tell there is a bit of flex in the hatch area because of the occasional creak back there when going over certain bumps, but that's not surprising given the lack of bracing back there. At best, all this bracing is going to stiffen the chassis up enough to make things feel a bit more solid, but the limits of the stock tires and suspension just aren't high enough to do much else.

As you mention in your disclaimer, you haven't installed any of the braces, so you are at a bit of a disadvantage in making your assessment. Experience gained modifying the suspension of other cars does not necessarily transfer to the Prius. Further, your comment about flex in the hatch area is indicative of flex in the body structure. Remove flex in the body structure, and the suspension can do a better job of what is was designed to do.

Originally Posted by drees

When I am taking corners aggressively in the Prius, the main limitation I feel is the weak alignment (needs about 1-1.5* of negative camber in the front) and less than sticky tires. Swaybars would be my next choice of mods (rear first if only going with one to help combat the huge amount of push the car has) and then a mild upgrade in spring/shock rate.

Negative camber can certainly improve things, but it can also mask other things that if improved along with negative camber would result in a truly stunning ride. Given that the camber is not adjustable in a cost-effective context, you need to look elsewhere for improvement.

My recommendations based on my experience with the Touring edition that I own is that a package of things can be done to improve the handling of the car. How far you proceed down the suspension modding path is a personal decision.

The first change would be the BT stiffening plate (lowest cost modification). If you want more improvement, then things start to get costly.

The next set of mods could be either wider tires (205mm) or springs and shocks. If your tires are wearing out, then 205mm tires would seem to be a reasonable decision (since the tires are going to need to be replaced anyhow). An intermediate step could be to go with 195mm tires if 205mm tires are too much of a challenge to the budget. If you have upgraded the tires and installed the BT plate, and want more, then you are looking at suspension braces and springs and shocks.

An intermediate step on the springs and shocks front would be the Touring edition springs and shocks. If a Touring edition owner has upgraded to TRD Sportivo, there will be a set of Touring edition springs and shock available for a quite reasonable price. The benefit of the Touring edition springs is that they are not progressive and so, will not lower the car's ride height. If after having done the springs and shocks thing, you still want more, then the TOM'S bits are in your future.

My personal journey has been to fit 205mm tires (Michelin Pilot Exalto A/S) on lighter and wider wheels (Motegi Traklite in 15x6.5) to avoid any adverse impact on mpgs while getting the benefit of the wider rubber. I have the Touring edition springs and shocks, so no changes there. The last mod was to fit the TOM'S front (upper and lower) suspension brace along with the TOM'S rear suspension brace. Combining the 205mm Michelin tires with ceramic compound brake pads in front has got the stopping distance down to 110 - 115 feet for 60-0 stops. I have to be careful hitting the brakes, because cars in back of me have almost rear-ended me (I have heard the tires lock up and in other instances, the car in back swerved onto the median strip to avoid hitting me) on a few occasions.

[Boo]

Thanks drees. Thanks apriusfan.

I think your thoughtful posts make for one of the most informative and useful pages on this forum, and certainly the best page for the subject matter. Reminds me a lot of nyprius' initial post and thread "Tire Upgrade ... Lessons Learned".

Very much appreciated.

[apriusfan]

Tom,

Thank you for your kind words. Where I can contribute what I have learned, I do it in a spirit of sharing. As I travel the road of life, I learn from people who have walked the path ahead of me. I am presently learning about the Prius' transaxle oil and the break-in process from bwilson4web.

Good luck on your quest.

[V8Cobrakid]

i have the bt stiffening brace. it helps, but i'm still looking to change to the trd suspension.

i recently changed my tires to 215/45/17 tires. they weigh in at a lot and my mpg hit is kinda big.. but handling seems maxed out. unfortunetly the tires are heavy so the steering isn't as quick and nible as it could be.

after i get the suspension i'll probably purchase light weight rims and tires. I'll most likely keep my tire size the same and purchase a tower brace.

.... it's fun when vsc turns on before trac turns on..

[drees]

Originally Posted by apriusfan

One edit to your list above - the Sportivo suspension is not made by TOM'S. It is a TRD product that is available through the parts department at any Toyota dealership.

Thank you for the clarification.

Originally Posted by apriusfan

Your claim that a BT Stiffening Plate provides the same handling improvement as the TOM'S Rear Suspension Brace is a bit on the speculative side.

Perhaps I am confusing the parts or you misread my post? I definitely did not mean to compare the BT plate and the Toms' rear suspension brace. I meant to compare the BT plate to the Tom's floor brace, aren't those two braces replacements for the stock floor brace? Let me know if I need to clarify my original post.

Originally Posted by apriusfan

The one thing that the TOM'S bits (in particular, the rear suspension brace parts - there are two components to the TOM'S brace) do provide is a measure of compensation for the slop in the rubber suspension mounts.

But the Tom's rear suspension braces don't actually replace any rubber suspension mounts/bushings, do they?

Originally Posted by apriusfan

The strut tower braces are part of a complete package. Which is why you do in fact see them on cars that have suspension upgrades. One car that comes to mind is the BMW M3. In addition to all of the other bits (springs, shocks, wheels, negative camber, sway bars, multi-link suspension in the rear), BMW has fitted a strut tower brace as the final piece of the picture.

Modern cars are so much stiffer than cars made even 10 years ago. But even on my 96 Camry with stiffer springs/shocks bigger wheels and sticky tires, I couldn't not quantify any handling difference with a front strut tower bar. Subjectively the car felt better, but I could not take corners any measurably amount faster like I could after adding stiff springs/shocks/swaybar/tires.

Originally Posted by apriusfan

Adding a stiffer swaybar will improve handling up to a point. But after that point has been achieved, you have to look elsewhere for gains.

Definitely.

Originally Posted by apriusfan

Plus, if progressive springs are used (which the TRD Sportivo does in fact use), there is the risk of damage to some rather expensive drivetrain bits from road debris. It is all part of a complete package.

How so? Even the stock springs are progressive. If you mean that because the TRD springs lower the car slightly (appx 1" from what I understand) then yes, you do slightly increase the risk of scraping on things, but I haven't found ground clearance lacking on the Prius myself.

Originally Posted by apriusfan

As you mention in your disclaimer, you haven't installed any of the braces, so you are at a bit of a disadvantage in making your assessment. Experience gained modifying the suspension of other cars does not necessarily transfer to the Prius.

Most definitely. If someone wants to send over some pretty Tom's bits, I'd be more than happy to subject them to some objective testing.

Originally Posted by apriusfan

Further, your comment about flex in the hatch area is indicative of flex in the body structure. Remove flex in the body structure, and the suspension can do a better job of what is was designed to do.

No argument here. The lack of a rear firewall contributes to some additional flex in the rear of the car. That's why I commented that I found a rear strut-tower brace (it's a cross brace that fits horizontally right behind the rear seats) useful in my WRX wagon, but there is no such brace for the Prius. There's another company that makes a product for the WRX called the X-Brace. That measurably stiffens up the chassis of the WRX sedan, through the use of well engineered triangulation.

Originally Posted by apriusfan

Negative camber can certainly improve things, but it can also mask other things that if improved along with negative camber would result in a truly stunning ride. Given that the camber is not adjustable in a cost-effective context, you need to look elsewhere for improvement.

Camber is not adjustable in the front of the Prius? I haven't actually looked at the struts, but typically on strut suspensions one of the bolt holes is elongated with an oblong bolt which provides +- 1-2* of adjustment.

I'd have to disagree about alignment masking other things - A performance oriented alignment is typically one of the first things suggested to do - especially since the alignment from the factory is often not that accurate.

Your suggested order of suspension mods looks pretty good.

What brake pads specifically did you get?

[hyo silver]

Originally Posted by V8Cobrakid

...i recently changed my tires to 215/45/17 tires. they weigh in at a lot and my mpg hit is kinda big.. but handling seems maxed out. unfortunetly the tires are heavy so the steering isn't as quick and nible as it could be...

Granted, the stock 185s are too small, but at some point larger tires will only make things worse instead of better. It sounds like you may have found that point with the 215s. The Prius just doesn't have the muscle to move such big feet.

[omgitsroy326]

sway bars would be cool....


previous celica alltrac (gt4) owner baby~~

[apriusfan]

Originally Posted by drees

Perhaps I am confusing the parts or you misread my post? I definitely did not mean to compare the BT plate and the Toms' rear suspension brace. I meant to compare the BT plate to the Tom's floor brace, aren't those two braces replacements for the stock floor brace? Let me know if I need to clarify my original post.

The BT plate replaces the OEM chassis bar with a more robust implementation. However, the TOM'S Rear Suspension Brace consists of 2 pieces - an a-frame shaped bracket and another c-shaped bracket. The TOM'S a-frame shaped bracket competes with the BT stiffening plate for mounting points on the inside chassis rails (mounting points on the top of the a-frame). Additionally, the TOM'S a-frame shaped bracket has two further mounting points (at the base of the a-frame) that attach to the outside mounting points where the rear suspension member attaches to the car's chassis. The TOM'S c-shaped bracket attaches to the inside mounting points of the rear suspension member. The combined effect is to create a triangle approach to chassis stiffening, which also offsets slop of the rubber suspension mounts.

Originally Posted by drees

But the Tom's rear suspension braces don't actually replace any rubber suspension mounts/bushings, do they?

No replacement, but there is a stiffening effect when the rubber mount is sandwiched between two metal plates (which is what happens with the TOM'S rear suspension brace parts).

Originally Posted by drees

Modern cars are so much stiffer than cars made even 10 years ago. But even on my 96 Camry with stiffer springs/shocks bigger wheels and sticky tires, I couldn't not quantify any handling difference with a front strut tower bar. Subjectively the car felt better, but I could not take corners any measurably amount faster like I could after adding stiff springs/shocks/swaybar/tires.

That is a bit speculative. There was a whole back-and-forth in the 1100+ post BT Stiffening Plate thread about whether the BT stiffening plate actually stiffened the Prius' chassis. I don't propose to revisit the debate. I believe that by sandwiching the rear suspension member's rubber mounts along with the triangle effect of the a-frame chassis stiffener, TOM'S has been able to achieve a significant improvement in handling of the rear suspension on the Prius.

Originally Posted by drees

...How so? Even the stock springs are progressive. If you mean that because the TRD springs lower the car slightly (appx 1" from what I understand) then yes, you do slightly increase the risk of scraping on things, but I haven't found ground clearance lacking on the Prius myself.

The stock springs are not progressive. They (including the Touring edition's springs) are linear. Progressive springs cost more to manufacture than linear rate springs (due to the increasing spring rate as the spring is compressed (hence the term progressive)), which is why they are part of the TRD Sportivo package. If you want to see some nice road hazards to the undercarriage of the Prius, come up to the S.F. Bay Area. I am not saying you will suffer damage from road debris, just that the risk is greater with a lowered car.

Originally Posted by drees

Camber is not adjustable in the front of the Prius? I haven't actually looked at the struts, but typically on strut suspensions one of the bolt holes is elongated with an oblong bolt which provides +- 1-2* of adjustment.

Check the struts. Toe can be set; but not camber (or caster). I will check with the dealer's service dept. tomorrow, but my understanding is that the camber is fixed.

Originally Posted by drees

I'd have to disagree about alignment masking other things - A performance oriented alignment is typically one of the first things suggested to do - especially since the alignment from the factory is often not that accurate.

Absent damage to suspension components (such as can happen during transporting the car to the dealer), the factory alignment is actually quite accurate. My Touring edition suspension's alignment was right at specification. Road quality can certainly change alignment; it really depends on the road environment where the car is operated.

Originally Posted by drees

What brake pads specifically did you get?

Hawk.

[apriusfan]

Originally Posted by hyo silver

Granted, the stock 185s are too small, but at some point larger tires will only make things worse instead of better. It sounds like you may have found that point with the 215s. The Prius just doesn't have the muscle to move such big feet.

It really comes down to rotational mass. If you could get a tire & wheel combination in 215mm that weighed the same or less than the stock wheels & tires, you would not experience the mileage hit (or the steering problems). I spent the better part of an afternoon and evening on Tirerack.com to find the combination that I finally went with. (In addition to the weight issue, I wanted a wheel & tire combination that was also on spec for diameter and revs/mile, so there would be no issues with speedometer or odometer accuracy.)