Smaller Rims

[Rev]

Well thanks to TGTT advice on earlier posts my Sera has finally ditched the 17's
That is 17x7x40 offset Rims 9.98kg 205/17/40 tyres ( 580 Dia ) now 15x7x38 offset Rims 5.85kg 195/15/50 Tyres. Total old 18.14kg vs new 13.63kg Weight saving 4.51kg ( 9.94lb )/ wheel

This gives improved comfort, braking and acceleration but a few other things also happened -

Acceleration
- Car moves off the mark easier I dont have to wait for the wheels to rotate before I can accelerate hard.
- Acceleration is more responsive but still need to change back from overdrive to accelerate quickly but overdrive is generally more useful.
- Boost feels different the torque increase makes the car feel like it is boosting sooner but it is just accelerating more at the same boost.

Noise
- I can still feel every bump but the bumps are dampened like punching a timber floor through carpet rather a concrete one.
- Road Rumble is significantly quieter a better driving experience.. I'm told noise will increase as the tyre wears, unless I buy softer tyres.

Handling
- Handling on curves over ruts is more sure footed the car does not slip side ways as before.
- Turning is worse for quick pointing. It seems I have to turn the wheel further before the car responds from straight line driving.
- Turning tight corners at speed the car can feels a little floaty compared to before.
- Lighter steering turning from stationary and Sharp turning from stationary at 90 degs is better the car does not want to go sidways.
- Suspension is quicker so I can now go faster over speed humps with less jumping of the back of the car.

Gears
- Auto gear changes appear more frequent as load difference is sensed by the auto box and convertor lock up point may have changed.
- One negative is the box now wants to change to OD while I am accelerating hard. This results in a huge loss of power as there is a mismatch with the gear box that stalls the engine. It feels like fuel cut and can be dangerous if overtaking or going hard up a hill.

Throttle
- Throttle control is much more tiring on the driver as gears are changing more and you need to be properly match throttle to speed.With the heavier wheels it was more point , shoot and brake style driving.

Brakes
- Braking is much improved. I don't have to dwell on the brakes as much and hold the brake pedal contantly down hills.
- Can now use the throttle to slow the car when cruising. I can stop the car on the spongy part of the pedal travel before refusal.


Further testing in the wet TBA

- Under steer or over steer
- Turning at speed down wrong cambered hill
- Round-about skidding

Fuel consumption difference TBA.

 

[Jay]

Yip. One of the biggest mistakes to make is massive rims on a little Starletto..

 

[Rev]

Too right Jay
I didn't realise how subtle the changes can be. I think the ecu is now using different fueling. My guess is the long term fuel trim has changed due to less load. I am getting more knock on idle and some smoother idle at times also. I used to get big power increase with the A/C on as it adds timing and I had plenty of extra fuel to burn but so far I don't notice the same kick.

 

[Paul_JJ]

Good too hear from you Rev. I suggested smaller rims years ago -) Finally you've fitted them! I would reset the ECU just in case, it wouldn't do any harm surely. I don't see how knock on idle would be related to bigger wheels, but everything is possible -)))) Big Rims has only one benefit - better MPG at constant high speed, but they're disaster in city! What is the Sera weight by the way?

 

[dark_knight]

bigger rims versus stock brakes.. hmmm.. i think i'll keep my donk rims.. lol

 

[dac69er]

Too right Jay
I didn't realise how subtle the changes can be. I think the ecu is now using different fueling. My guess is the long term fuel trim has changed due to less load. I am getting more knock on idle and some smoother idle at times also. I used to get big power increase with the A/C on as it adds timing and I had plenty of extra fuel to burn but so far I don't notice the same kick.

come off it, you only changed your wheels!!!!!!

 

[Rev]

Fair enough Dac point taken , could be a coincidence but the car was behaving like it does when leaned out slightly with the safc. Usually if leaned and revs drop with inj DC too low for my large injectors engine is too rough so idle knock reading goes up but knock was also up further up the rev range. Normally I go to zero knock above 1100 rpm it was not going to zero and needed slightly higher than 1100rpm so i wondered if some different fuel trim was happening..

@paul thanks for your assistance especially boost level testing made me realise I had to do something. The Sera is a little heavier than the Glanza Stock auto is 970kg kerb wt and stock manual 930kg kerb wt , I would say I am currently around 960 kg.

@knight Stock Sera front brakes are already larger than the Starlet. Contact patch 2046.8sqmm vs 1669.1sqmm or 51.05dia piston vs 46dia piston. I would like your stopping power but for now I can say lighter wheels ( with smaller centre of mass dia. ) and stock brakes make this car a lot safer.

 

[dark_knight]

stance and whatever else comes along with it..

i agree that most lads here build their cars for more paaaaaaaaaaaaaaaaaaawaaaahhh!! but i took a slightly different approach and i'm building for stance. whatever power/handling/efficacy i get along the way, i can live with.. but i do concur. smaller rims do make the car handle a tad better all round.. while not looking half bad either..