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

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.

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.

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.

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.

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.

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.

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.

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.

 

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.

 

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.

 

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..

 

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.

 

sway bars would be cool....


previous celica alltrac (gt4) owner baby~~

 

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.

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).

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.

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.

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.

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.

Hawk.

 

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.)

 

Really to me the cheapest and most effective and certainly the easiest install is the BT stiffening plate. I only point that out for the OP and those others of you who have done no mods on your Prius yet but are considering them, and which ones to do first. The plate has probably the longest thread ever posted here on PC, well over 1000 posts, and takes about 30 minutes to install (if you're not mechanically inclined). Bottom line, its an easy install, and an effective addition.

I point this out because its on sale here now for much less than I paid for one, so its basically a no brainer. Good luck!!!!

 

If you are referring to the comparison picture where the stock spring is placed next to the Modellista spring, the picture is missing a ruler next to the individual coils. You can plainly see the difference in coil distance on the Modellista springs. This little debate is getting into the weeds, however. You contend the stock springs are progressive, I do not.

How long since you left? In the past 5+ years the roads have significantly deteriorated (there was even a ballot initiative that passed to fund infrastructure (things like roads and bridges) repairs). I could post pictures of examples of buckled roadways in the area, but that is beyond the scope of this thread. If a reader of this thread has bad road conditions where they live, then they should think twice before going with a lowered suspension.

As shipped from the factory, the camber is fixed (per the shop foreman at the dealer that sold me my Prius). You have indicated the availability of aftermarket products that can make the camber adjustable. One consideration regarding adjustable bolts as opposed to strut tower plates with fixed adjustment points is that with bad roads, camber can be shifted from the 'adjusted' setting by simply driving through a pothole or over a moderate bump (like at a railroad crossing). Just a FYI; again, it is up to the owner to decide how they want to proceed.

 

i've noticed.

as apriusfan as posted.. i've searched for tires the same size that are as light and a few that are lighter than the stock pruis tires. hard to find and really expensive. my goodyear quietcomforts blew out so i needed a replacement on a limited budget. 350 for all 4.

in the end, i'll get the trd suspension (sportivo.. whatever it's refered to) a few braces, and lighter wheels.

 

Yes, in terms of less costly handling modifications, I'm thinking that one should start with some or all of the following:

1. BT Tech Rear Stiffening Plate ($145 on sale).

2. BT Tech Front Tower Brace (when it comes out, and assuming it's priced around $150 or less).

3. Inflate Tires to around 42 psi front/40 psi rear ($0).

4. Wider and/or Better Gripping Tires ($400 - $500). This is expensive and non-permanent, but in my opinion, necessary for both sportier and safer handling.

I have 3 of these 4 (waiting for BT Tech Front Tower Brace to come out), and can report that the car's overall handling feels vastly improved over stock, but there's still too much body roll or lean for my tastes. I'm hoping that with the addition of the BT Tech Front Tower Brace, the car's handling will finally feel at least a little like a slot car (Slot Car Light, if you will).

 

I cannot seem to find a tire that would work well with my 17x5" Centerlines so for now they will remain in the shed because the milage hit with the Kumho tires was just too big. I am waiting for Michelin to come out with their next line of LRR tires. I'm banking on them making a 205 or 215 in the 17" size. A lightweight LRR 205/215 would be perfect for me. I loved the handling but hated the milage.

 

Thanks drees.

Yes, you mentioned it already with your description of the difference between turn-in and body roll. I'm going to give the BT Tech front tower brace a go anyway if it's $150 or less. At least I should get that improved turn-in feel out of it.

You also mentioned that stiffer swaybars were not available, so I can't go that route.

But I hope another set of used Touring Edition shocks and springs becomes available for cheap. My biggest regret was not test driving the standard Prius before I bought it. Even a 5 minute test drive around the block would have made me realize that I wanted the better handling promised by the Touring Edition. Curious, why didn't you get the Touring Edition?

 

Yeah at that price differential it's not worth it. In 07 the pricing structure was different. At the package 2 level, the difference was around $1000, which I think would have been worth it for the Touring Edition's shocks, springs, wheels, HIDs and foglights (the bigger spoiler means nothing to me too; and the tires, though wider/bigger, are reported to be like the Integrities).