Mantis
Mantis
7/7/20 7:29 p.m.

Hello there, I'm new here.

I recently bought a Honda Today JA4, which is a very light (1450lb / 650kg) Japanese Kei car. Dynamically it's pretty similar to an original mini, having similar horsepower, size, weight, and weight distribution. The suspension is strut in the front, and a weird form of Panhard solid axle in the rear.

The former owner has done a lot of upgrading, so it has adjustable suspension, a sway bar, bigger wheels, bigger brakes, chassis stiffening, stripped interior, a racing seat and a 4 point harness. 

It's the best handling car I've ever driven, running rings around my NA Miata. I'd like to continue modifying it for handling and so I'd like some advice.

Currently the weight distribution is extremely front biased, about 70:30. The famously handling mini has a similar weight distribution so I'm wondering if that's actually bad. If so, I'd like to move some things to the back of the car, particularly the battery.

I'd also like to install a roll cage with side impact protection so I can replace the doors with fiberglass skins safely. How strong of tubing do I need for a car this light? Top speed is probably 100mph on a good day.

​​​​​Any other advice?

MrChaos
MrChaos SuperDork
7/7/20 7:32 p.m.

how strong do you want the cage when sharing the road with 4k lb suv's?

Mantis
Mantis New Reader
7/7/20 7:46 p.m.

In reply to MrChaos :

I live in Japan so that's not a problem, most cars are only about 50% larger than me smiley

I want to do track days, autoX, and lonely mountain roads at midnight, not too interested in actual racing and with 48 horsepower I doubt I'm competitive in any class I qualify for anyway. I just want to be able to slide or tumble into the tire wall at 50mph safely.

MrChaos
MrChaos SuperDork
7/7/20 7:47 p.m.

look at the main rules body for what you will do and use what they say.  Most allow bolt in cages

 

z31maniac
z31maniac MegaDork
7/7/20 7:48 p.m.

In reply to Mantis :

A full-cage in a street car is typically a bad idea.

alfadriver (Forum Supporter)
alfadriver (Forum Supporter) MegaDork
7/7/20 7:51 p.m.

Seems to me that moving weight back just 1) puts some grip in the rear- which may not let the car rotate as easily, and 2) once it does, the moment of inertia means it will be tougher to stop rotating.

 

ojannen
ojannen Reader
7/7/20 7:53 p.m.

In reply to z31maniac :

On a car like a kei car or classic mini that is pretty much a rolling coffin, how much cage is a good idea?  Is there a middle ground between single skin doors withc ata lap belt and a fullifull cage that is safer for street driving?

CyberEric
CyberEric Dork
7/7/20 7:57 p.m.

Ahem, pics please, or we can’t continue. devil

Patientzero
Patientzero HalfDork
7/7/20 8:05 p.m.

Are you in Okinawa?

Mantis
Mantis New Reader
7/7/20 8:09 p.m.

In reply to CyberEric :

LopRacer
LopRacer Dork
7/7/20 8:14 p.m.

Like others have said full roll cages are not a great idea on the street where you are sans helmet, what about a 4 point with door bars? Would/could that tick the boxes for some side impact protection without putting metal tubing inches from your unprotected head?

 

Edited for "cool looking car, I like it"

 

Mantis
Mantis New Reader
7/7/20 8:14 p.m.

I'm north of Tokyo, near Tsukuba circuit actually. 

Alfadriver, that's a good point. I like mid and rear engined cars so it's hard to get over the unbalanced=bad mentality.

z31maniac, are cages still bad if they are too far away for me to hit my head on? There's quite a lot of head room since the driver's seat is on the floor and I'm short.

 

Mantis
Mantis New Reader
7/7/20 8:20 p.m.

In reply to LopRacer :

Fourpoint = rollbar? I'd actually honestly prefer that for visibility reasons too. My only concern is the canopy collapsing on my face, but I don't know how likely that is.

 

edit: ah, thank you smiley. Yeah, these things are really neat. The older generation is even cooler, looks like a scaled down CRX.

accordionfolder
accordionfolder Dork
7/7/20 8:28 p.m.

In reply to Mantis :

Even with 5/6 point harness in a crash you'll still most likely strike a tube that's "so far away from your head." There's a reason you have to have sfi padding AND a helmet in race series. The belts are meant to stretch. 

Cages in street cars is a never ending debate, but is generally a bad idea. 

Appleseed
Appleseed MegaDork
7/7/20 8:42 p.m.

You could try seam welding the chassis to stiffen it up. 

I always wondered the old saying that cages on the street are bad. If the cage is tucked really tight, would you still bonk your head? If so, would you probably have bonked your head on the car even without the cage? 

I'd say cage it, and then you have an excuse to wear a helmet all the time. If someone says that will get annoying, reply motorcyclists do it all the time. laugh

LopRacer
LopRacer Dork
7/7/20 8:43 p.m.

Yes by 4 point I am referring to a roll bar consisting of main hoop (point 1 and 2) and two down bars going back to rear shock towers, but now  I see I should call it a 6 point where two diagonal bars are added going forward off the main hoop towards the front foot well, this adds some side protection without adding a whole front cage.  This seems popular with drag racers here in the US.

Vigo (Forum Supporter)
Vigo (Forum Supporter) MegaDork
7/8/20 9:03 p.m.

Is it even feasible to lose all the weight from the rollbar/cage just by gutting the doors or replacing them with fiberglass skins? I doubt it. If you are gutting the interior but don't want a cage that adds safety issues on the street and dont have to follow any class rules  I would probably do a  roll bar a little further back than usual, a lateral brace between the a-pillars (through the dash area) and door bars inside the existing doors/hardware. I am not a cage builder, just a pragmatist with some grasp of physics. Cool car btw!

Vracer111
Vracer111 HalfDork
7/8/20 10:46 p.m.

You want the weight forward on FF... don't really want to shift it rearward/add weight to the rear. When I modded an Integra RS i shifted the weight more forwards by striping out interior and moving a lighter weight PC680 battery as far forward as reasonable and down as far as possible, resting right on the bottom front crossmember just behind the radiator...  it really liked to rotate more compared to stock. I ended up eating cones my first autocross event after modding it because it was turning in too much... had to readjust on how to drive it.

Weight low and forward in front of the wheels... acts as counterbalance in front of the wheels to help rotate the rear of the car. Shifting mass rearward would slow down the rotation. 65% to 70% front weight bias is definitely what I'd shoot for in an FF. 

Mantis
Mantis New Reader
7/12/20 6:56 p.m.

In reply to Vracer111 :

Turn in is the most important part of handling for me, so that's good to hear. The weight distribution is already at your recommended 70:30, would it be a bad idea to continue to shift it forward? Among other things the battery position can absolutely be improved.

Lopracer and Vigo, I like both of these ideas. I spoke with my cage expert friend, and he leans towards Vigo's idea. Apparently Japan's racing rules are far laxer than America's, and such a design would be completely acceptable.

Additionally, I looked more closely at the car and drew a tangent between the hood and the top of the proposed roll bar. Even if the roof fully collapses between these two points I'll still be clear of it. It would take a pretty specific sort of impact for a full cage to be necessary.

Mantis
Mantis New Reader
7/13/20 9:24 p.m.

I actually have two Todays so I took a picture of them together. The older one is bone stock, bought from a little old lady with only 30,000km on the clock. It's an automatic and has the lowest tier carbourated engine. 38hp. Still a really cool car and I'm looking forward to registering and refurbishing it to better than new.

boxedfox (Forum Supporter)
boxedfox (Forum Supporter) Reader
7/13/20 11:34 p.m.

In reply to Mantis :

So the Today of yesterday will be newer than the Today you have today tomorrow?

Mantis
Mantis New Reader
7/14/20 1:09 a.m.

In reply to boxedfox (Forum Supporter) :

I think a more important question is, will Will Smith smith? cheeky

 

Good one btw, this car's name is a goldmine.

buzzboy
buzzboy Dork
7/14/20 5:37 a.m.
Mantis said:

 will Will Smith smith? cheeky

Will Smith will smith.

 

CyberEric
CyberEric Dork
7/14/20 12:14 p.m.

Nice cars! Is the Today today’s City? Which was the Today of yesterday?

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