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Discussion Starter #1
i can get lighter wheels and tires if
i use 14's, but what is the difference
you think? the wheels look like 2 lbs
each, of crucial unsprung weight!

my ? is, what is the weight difference in
the tires?

thanks for your knowlege.
 

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Well, rally tires are heavy as crap already. The difference in 14" and 15" is not too big of a percentage, I would think. More of a ground-clearance issue, to me anyway.

If you decide on 14's, let me know. I have a buttload of 14x6 BMW Bottlecap style wheels (1984-1991 325i) to sell. The ones which are not perfect I sell for racing @ $150/set of 4. As a BMW racer, If you are willing to fly the Fastech Tuning logo and promote us, I could hook you up for a good bit less. Email me off-forum for specifics.

Lemme know if I can help out!

Brian Flanagan
Fastech Tuning
G2 BMW 323is #842
[email protected]:7
 

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Hey kid, the supply of 14 rally tirs is kinda sparse currently, so that's one consideration.
The advantage of the 15" is two-fold:
A)If you do stick in a good fast motor, and you combine it with the right rear diff ratio then you'll have one quick car which means you'll want big discs which you'll need 15" wheels for disc clearance
B) if you use the 15s, you can use the popular 14/62 size which has a 62cm diameter, and a nice low profile, snappy steering response combined with decent clearance

If you use 14s you limit disc size and ground clearance.

Now it's a wash with either size what you going to have to do in the rear end, both will be LIKELy hard to find and expensive, but you gotta do something or the next guy with just shorter gearing will massakrate you to death.

Hey Bimmerman how's the supply of 4.88:1 or even 5.15 ring and pinions for whatever size is the next size up from the teeeeeenie little '02 diff? You know the, the.... some silly numbers 325 or something. Anyway the size that uses the nice big ZF LSD from the 006 ZF series?

Combine the 5.1 and a standard box, skip 1st altogether, use the top 4 gears, almost like a poor mans close ratio.

PS: 15s have a bigger hole in the center and that hole does'nt weigh anything, in fact since the hole is 15 a full inch bigger it weighs less than the 14" whole, it's more nothing.













John Vanlandingham
 

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I was surprised when I weighed my 14 inch rim and tire. It came to 17kg (38lbs).

I saved over 2kg(4.4lbs) per corner by switching to 13 inch.

I know you are going from 14 inch to 15 inch , but I was quite surprised about the results.

I switched to 13 for 3 reasons.
-lowers the diff ratio (better torque)
-narrower tire (better for the soft dirt kind of roads and more grip)
-lower price per tire ( I bought a truckload for $12 each new)
-less weight means better acceleration

Disadvantages are.
-had to modify calipers
-have to search 100`s of rims looking for the right backspacing and right thickness of the rim)


Robert VanLane
 

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Discussion Starter #6
my 13'' steel wheels w/coopers weight
33lbs.
my bottlecaps bmw 14'' wheels w/streets weight
31lbs.
bottle caps weight 15 lbs. after looking around
at some other wheels they go down to 11 lbs for
15''.

thanks for the ideas.
 

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One advantage the "Bottlecaps" have is that they are very strong, which is very important in Rally. Another is that they are hubcentric, so the hub will carry the load. Many aftermarket wheels will be lugcentric, causing difficulty in balancing and forcing the lug bolts or studs (I HIGHLY recommend converting to studs, as the lug bolts are a huge PITA, especially during frantic trailside tire changes!) to carry the load.

Brian Flanagan
 

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Discussion Starter #8
my 13's steel wheels that i have coopers
on are 62cm/24.5 diem. they are 90's way tall.
RVL's coment on a smaller tire changing
my ratio is good. i have the ground clearence.
i have a 4.11 diff. you can go to around a 5
i think, but at how much $$$$, yeh like 800.

here is a good diam. reference.
http://www.tirerack.com/tires/kumho/ku_r700_spec.jsp

i'm liking the michy m. 23.5 diam. if i can find them?

thanks for the help.
 

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>
>i have a 4.11 diff. you can go to around a 5
>i think, but at how much $$$$, yeh like 800.
>
It is the single biggest performance upgrade you can do.
Instantly you have multiplied your engine torque by 20% plus more than it would otherwise be. it's a pretty cheap upgrade for the money, what would it cost for that M3 motor you are salivating over?

My 2000lb car has 5.45:1 w .92 4th for overall ratio of like 5.01, with the 62cm tires I go 105mph before I weeenie out. but I get there pretty damn quick.
















John Vanlandingham
 

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On a 2000 lb car (which I assume is G2 or P and thus needs to be good handling to make up for low HP), I would go with the 14" rims and save the weight. We had the choice on the '79 Arrow, and I went with the 15" rims to get more tire variety and ground clearance. The clearance paid off in the deep sand at Sandhills, but the extra weight is really showing up in excess wheel hop. I'm having to look into a whole different shock setup, and the larger weight in the 15" wheels & tires is part of that whole situation.

Mark Bowers
 

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Discussion Starter #12
yeh, i tnink you are right.
i need to keep it as light
and strong as possible.
your rwd right? do you run
a wider tire in the back?
keep the front narrower anf lighter.

i am used to counting grams in the
mtb bike stuff i do, now it is lbs's!:p

thanks alex
 

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Yep, RWD. But the problem on the Arrow is the rear (live axle plus heavy wheels/tires plus bad original shock design = wheel hop and bad shock travel situation). We run a narrower front tire on the Starion (RWD also), but that's to help front bite and turn more than anything.

Mark
 
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