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Discussion Starter · #1 ·
I have 2 Evo 4 GSR's sitting on my path.....One belongs to a friend and the other is mine.

My car has a Blitz DSBC, 5Zigen Exhaust with CAT still in place and an APEX induction KIT.
The other E4 is totally standard.

The standard model is actually quicker off the mark than mine! Even if I turn up the boost !!!.
Not by much but I can feel a difference...... I am rather dissappointed.

I have the Compomotive wheels with 215/45/17's fitted. The standard E4 has OZ wheels with 205/50/16 tyres.
The diameter of the wheel|PLS|tyre is about an inch smaller and I have come to the conclusion that this must be the reason.

My friend thinks that the car is not a good motorway car and beg to differ as mine seems fine.

At 80mph my engine speed is about 3900rpm. I will test my friends to see what the difference is

Can anyone let me know if the gearbox ratios are different on a E5 and E6 ? I think that they may be as the E5 has 17inch wheels and the E6 has 18's !

I may try 215/40/17 next time.....Anyone care to comment ?

jonathan
 
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Discussion Starter · #2 ·
Well I have now found out that my rolling radius is too big by 7mm which explains the difference in size.

Better fuel economy maybe ?......Yeah right !

Jonathan
 
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Discussion Starter · #3 ·
be interested to hear whether fitting the slightly lower profile tyres makes a difference for you.
I also am using 215/45/17's so could be suffering similarly.

I would have thought the larger total diameter would have increased the acceleration not decreased it, but then again I only got a grade C at physics 'o' level many years ago http://www.ltregister.f9.co.uk/graphics/Wilk.gif border|EQU| 0 align|EQU| middle >

Mind you, my fuel economy is already shocking - somewhere around 17-18MPG around town!! Don't know if I could handle anything lower
 
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Discussion Starter · #4 ·
Also bear in mind that larger diameter wheels means more weight (more metaland less rubber), so it is normal that the acceleration of the car is not better (even worse) than the standard car. But roadolding should be better.

Good luck

Tarik
 
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Discussion Starter · #5 ·
When you check your friends car for speedo vs tacho, you should see the same as your own car as the speedo is gearbox driven. The difference will be that your speedo will be showing a lower speed than when you had the original wheels on (indicated speed vs actual speed).

Ref the car having better road holding, you now have more unsprung weight which isn't really what you want http://www.ltregister.f9.co.uk/graphics/sad1.gif border|EQU| 0 align|EQU| absmiddle >. This is why a lot of high performance motorcycles went to upside down forks.
You may have more rubber on the road, but the dampers now have more work to do.
 
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Discussion Starter · #6 ·
I think if you check, you will see that the E5 and E6 both run on 17s, the new E7 however is running on slightly wider tyres 235s compared to 225s on the E5/E6. My friend has just fitted the 235s to his E5 so I will let you know how he gets on.
 
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Discussion Starter · #7 ·
I have 17x7 alloys on my car.....7inches wide.
i understand that the E5 has 7.5 wide rims and 215 tyres.

Can i fit 215/45/17 to my wheels ? I worked out that the rolling radius is the same as the 205/50/16 fitted to an E4.

Will the 215's sit OK on the rim ?

I suspect that they won't really ........

Jonathan
 
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Discussion Starter · #8 ·
Tarik

the roadholding on a car with heavier wheels is less good than on a car with lighter wheels!
 
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Discussion Starter · #10 ·
Jonathan,

In response to your question to Claudius, see my response earlier in the thread about unsprung weight. It is desirable for the full weight of the car to be carried by the suspension. Wheels, brakes, tyres and to a certain extent suspension arms etc are not carried by the suspension and need to be kept as light as possible. The heavier the unsprung weight, the harder your suspension has to work and hence worse road holding
 
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Discussion Starter · #11 ·
It is also the reason the 6 evolved from the 5 with forged aluminium suspension components, reduces the unsprung weight.
 
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Discussion Starter · #12 ·
Thank you for your assistance RS Pilot.

Tarik: Unsprung weight is weight of parts of the car that is not contained by the suspensions, ie. weight that no matter how good your suspensions are will not be affected by them.
The lighter the car, the better, everybody knows that. What lots of people who fit 18 or even 19 inch aftermarket wheels to their cars dont realise is that the bigger wheel wheighs more than the smaller one. For roadhoilding improvement, do the following:
- get good suspensions (single tube gas shock absorbers with the right springs)
- keep the weight of your car low
- keep the weight of the unprung masses as low as possible, lower it for improvement. As I said before, you can change the bump and the rebound of your dampers, but if your wheels are too heavy, that won't change anything.

Unsprung masses are calculated this way: count half the wheight of the damper itself and the suspension arms, add the weight of the brakes (this is also why ceramic brakes are so much better, because they're lighter) add the weight of the wheels and tires, screws, valve caps.

A good suggestion when changing wheels would be to buy magnesium wheels. They're lighter, more resistant and more expensive. I was quoted £435 by Graham Goode for the SPEEDLINE 20/21 HTC magnesium 11 spoke wheel. They're £400 here in France.
 
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Discussion Starter · #14 ·
Yeah Heave Ho, that's a good example of a car with a shitty engine that's fast (relatively): no wheight and low unsprung masses. A Go- Kart!
 
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Discussion Starter · #15 ·
lotus has good points one of them is the weight of the car evo 7 is heavier than the 6 what will the evo 8 weigh 1500 kg

a wrc car is 1230 kg so mitsubishi lets not go higher then
 
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Discussion Starter · #16 ·
As I see a few comments about karts I'll talk about a curiosity (I'll write about more seerious staff in the second part of my story):

One day I was lapping at a kart track outside Madrid with a friend's 100cc and shifter 125cc karts, when the owner of the place asked me to make a show with my red Evo VI TME. As you can imagine, a grippy and tight kart track is not the ideal place for my car, as it was almost impossible to fight understeering in those slow corners, but it was a great fun! Despite being such a tight track, I managed to quite a decent top speed in the straight, that ended in a difficult corner (downshifts all the way from 6th to 1st with the shifter kart!).

By the way, the Evo was no challenge for the karts: 4 seconds a lap slower in a 35 seconds lap.


Now, let's write about something more serious and related to the original topic:

A few months ago a U.S. magazine called Sport Compact Car, which is specialized in Japanese imports, tested how a couple of variables would affect the handling of cars. These variables were weight and wheel diameter.

One of the test cars was a race-spec Evo VI RS, and the driver was one of the top U.S. rally drivers.

I guess it's easy to undertsand the negative effect of weight. But, can we quantify how negative?

These were the lap time by weight results:

Lap times Top Speed
No ballast 1:03.7 96.1 mph
100-lbs ballast 1:04.0 95.8 mph
150-lbs ballast 1:04.7 94.2 mph


What about wheel size?

Lap Times Top Speed
16-inch 1:03.7 96.1 mph
17-inch 1:03.2 95.5 mph
18-inch 1:03.9 95.0 mph

The wheels used were Enkei NT03 (for 17 and 18 inches) and Enkei RF1 for the 16 inches, all of them relatively light. All tires fitted were BFGoodrich's Comp T/A ZR, as it was available in the 3 sizes (225/50-16, 225/45-17 and 225/40-18), which, by the way, have very similar rolling diameters.

Tarik, you may bee interested in the first conclusion: the result of putting an 18-inch wheel/tire combo is lighter than the 17-inch one. How come? The wheel is obviously heavier but the tire is lighter due to the thinner walls. Surprised to reduce unsprung weight with a bigger wheel? I remember mentioning in a previous post that when talking about engineering we should not take obvious conclusions for granted, as we may face many surprises. Anyway, keep reading as you may be partially right.

Anybody surprised about lap times and top speed? The car was clearly faster with the 17-inch combo, as the high walls of the 16-inch tire penalise the handling, while the 18-inch suffered from a worse acceleration.

But...didn't I just say the 18-inch combo was lighter than the 17-inch? How come that the acceleration is worse although they have a similar rolling diameter? The explanation is that rotational inertia is a significant factor in acceleration. As weight is moved outward, rotational inertia increases with the square of the distance from the center of the wheel. Not only was the wheel rim a half-inch further from the center (which alone would account for a 12% increase in rotational inertia), but the 18-inch was 8-inches wide while the others were 7, making the rim a larger percentage of the wheel's weight.

All the tests were blind, as the driver did not know the ballast or wheel/tire combo when he jumped in the car.

And finally, a less mathematical approach (another personal story to end this long thread). When I was beginning my rally career (which ended up being quite short, by the way) I remember asking one of the 'top' guys about the influence in weight. The answer was quite simplistic: 'In a stage, every 10 Kg you save in the car equals a gain of 1HP in the engine' (At the time I was rallying with a Gr.N Peugeot 205 Rally).

I guess it's enough. Thanks if you read the whole thing, bearing with my stories and my English.

Regards,
Rallyman
 
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Discussion Starter · #18 ·
Sorry, been away for a while

Claudius,
even though larger wheels weigh more, roadholding is better, because you (usually) reduce the height of the tyre walls, so there are less movements of the tyre under stress (when you turn), so shrper responses.

As for the unsprung weight, you must have had a wrong definition, because it is simply everything that is after the suspension. Unsprung weight affects a lot the suspension, because the reactionof it is slower if the unsprung part is heavier (example, the reactions of the wheel on a bumpy road).
Everybody tries to contain that weight so the car can have quicker reactions, and the suspensions can work properly. As a matter of fact, you can generalize that by saying that the closer you keep the weight from the center of the car the better (that's why F1s are mid engined...)

Cheers
 
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Discussion Starter · #19 ·
Tarik, I think you are wrong assuming a larger diameter wheel/tire combo is always heavier than a smaller one. Read my previous post.

Regarding the question about rallying in the U.S., I have only lived here for a few months, and there is a growing interest in the sport, but I don't think it will be perceived as a 'politically correct' sport in this society. I personally would not want to be involved in organizing events given the huge potential liability issues you may encounter.

Anyway, the manufacturers, traditionally Subaru but I guess Ford now too, are very interested in having a WRC event here, given the size of the U.S. market. There are plans to have a leg of the Asia Pacific Championship here very soon, and that's a first step to have a WRC event.

Subaru is making a big effort to identify their product with the sport. A good example is www.imprezawrx.com and there seems to be a great expectation on their new WRX finally making it over the Pacific, although in a 230HP version (still better than the European one). According to their website we'll only have to wait 31 days, and price has been announced at $23,995 (GBP 16,000).

I'm going to be away for a few days.

Regards,
Rallyman
 
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Discussion Starter · #20 ·
Jonathan.

I have today fitted 225/45/16 to my 16 rims all four corners.
Will do some speed test ,my E4 runs 82 mph at 4000 rpm ,speedo reading.
I will check to see if any difference.
I went for a little more tyre on the ground only 6mm or so but using the 45 reduced side wall a little.
Spoke to Yokohama tyres about what sizes I could and could not fit,This was about the widest for my rim width.
Went for SO 2s x4 225/45/16 ,as all tyre suppliers still live and breath the bridgestones.
cost £ 457.76 inc vat fitting balance and valves
tyres only £ 108 each inc vat.

cheers

Paul s
 
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