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Correct size slicks

Started by _MAWLER_ , Feb 01 2006 04:45 PM

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29 replies to this topic

#1 _MAWLER_

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Posted 01 February 2006 - 04:45 PM

Hi everyone,

I'm getting ready to cut my diff and square up my wheel tubs and so have to pick the size rim I want to try and squeeze under there. From what I understand the width and wall of a drag slick is supposed to be matched to the rest of the car if you want to get the most out of it. Is this correct? If so, how do I go about choosing the right size slick, what are the deciding factors?

For my street rubber I was planning on using 15x8.5 rim with a 265 tyre. So I have to find out what size slick will this allow and whether that measures up with the optimum slick as chosen from above.

Totally out of my depth here so any help would be great.

Cheers,

Liam.

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#2 dattoman

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Posted 01 February 2006 - 09:16 PM

You need to factor the maximum RPM you want the engine to be running as you cross the line
The diff ratio you want to use
Then calculate back the tyre size you need to achieve this
Then see if that height tyre is available and what size rim it suits
Then buy some wheels and get your diff done

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#3 _LX406_

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Posted 03 February 2006 - 07:00 PM

You must consider the height of the tyre. I had 26x10" M/T slicks on my hatch, and I had to lengthen the wheel arches a bit to avoid scrubbing.

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#4 Struggler

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Posted 03 February 2006 - 07:14 PM

I personally like 28x9's but, as above, they require wheel arch trimming.

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#5 _MAWLER_

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Posted 04 February 2006 - 05:37 PM

O.k, thanks guys, thats the sort of thing I was after. It looks like I'm going to have get the car dynoed first to see where the max power is made etc. because I've never had a full tune on the new motor. Depending on that I may want to change the 4.11's to match in will a certain tyre size etc.

Taking the RPM and diff ratio what are the calculations that need to be done in order to come out with a tyre size?

Cheers,

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#6 _CHOPPER_

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Posted 04 February 2006 - 06:21 PM

If you can post your 1/4 mile terminal speed and the RPM where you make max. HP, I could do that in about a minute.

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#7 _MAWLER_

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Posted 06 February 2006 - 04:14 PM

Thats a very kind offer Chop and would be awesome but I can't really post info on either account because I havn't had this engine dynoed past 4000rpm (only had about 800 k's on the clock) and have never run it down the strip.

Does this mean I have to leave the purchase of rims and diff shortening till after I've done these two things?

Peace,

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#8 _QIKSLR_

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Posted 06 February 2006 - 05:37 PM

Aren't you seriously better off tweaking the diff gears rather than slick size?? On my torry I know for a fact the biggest I can fit in my flares is 26 diameter and 12"s wide. Thats actual measurements not "advertised sizes". So I figure jam the biggest slicks I can fit under it, get everything else going great, then tweak the diff gears to get the most out of it. You can buy a good quality brand of diff gears brand new for the price of a pair of slicks anyway. You can get practically any ratio between 3.0 and 4.5 without much trouble at all.

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#9 _CHOPPER_

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Posted 06 February 2006 - 06:09 PM

Thats a very kind offer Chop and would be awesome but I can't really post info on either account because I havn't had this engine dynoed past 4000rpm (only had about 800 k's on the clock) and have never run it down the strip.

Does this mean I have to leave the purchase of rims and diff shortening till after I've done these two things?

Peace,

I deally, put the thing together with parts you have and chuck it down the 1/4. Provided you don't run out of revs before the end of the 1/4, the MPH figure you get will suffice. Work out what size tyres you want to run. The bigger they get the less cheap they become. If you manage to find out the revs you make maximum power, I can then post a RECOMMENDATION. Yes, it would just be a guide, but it should be better than just guessing.

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#10 _jap-xu1_

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Posted 06 February 2006 - 07:24 PM

Aren't you seriously better off tweaking the diff gears rather than slick size??

a bigger diameter slick gives a smoother more controlled launh.
its best to go for the biggest diameter slick you can fit and then choose your diff ratio.

go here

http://www.speedworl...ex.com/calc.htm

and for metric imperial conversions go here

http://www.sciencema...onversions.html

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#11 _MAWLER_

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Posted 07 February 2006 - 04:46 PM

Those links were great thanks jap-xu1. If I was to look at it from the perspective of tyre first and diff ratio second it would add a lot more guesswork into making the most of the diff shortening. For example, I was originally planning to get the diff and tubs to match 265/60/15 rubber on 8 1/2" rims. This should be fairly easy and shouldn't involve moving suspension points I don't think. I then thought well what if that work is just to small to fit the perfect slick for my setup, shouldn't I make sure they will fit as well and make the most of the mods.

If I was to just choose a huge slick and rim then the relatively straight foward and cheap procedure might turn into major rear end work. Budget is tight at the moment and I can't afford to drop 3 g's instead of 1500 bucks.

What am I likely to be able to fit without moving suspension points or pumping the guards. I was already planning to make adjustments to the chassis rail at the rear of the tub.

What have ppl done, how much rubber are you running?

Cheers,

Ps. can someone explain the different measurements for drag slicks, I don't entirely understand what the figures are refering too.

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#12 _jap-xu1_

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Posted 07 February 2006 - 04:56 PM

im not sure what you will fit in stock guards

28(tall)x10.5(wide)x15(rim size)

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#13 _pro386_

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Posted 07 February 2006 - 07:32 PM

28 x 9s will fit with just square shoulding the wheel tubs and play round with the wheel arces. 26 x 11.50 MT ET streets look good with a mini tub

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#14 _355lxss_

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Posted 08 February 2006 - 10:30 AM

im in the process of getting the diff and tubs done on my hatch. Im running a 15x8.5 rim with a 255/60/15, which is 26inches in diameter. Ive pulled the original diff out and trial fitted the rims and tyers which just fit under the stock gaurds with virtually no room for play. Im basicaly just getting the lower inner wheel tubs cut back to the chassis rails and moving the shocker mounts to the inside which will allow me to run the L60 (275/60/15) american racer tires.

I have a photo somewhere that i took of under the car when i stuffed the tires under the gaurds. I see if i can find it.

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#15 _jap-xu1_

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Posted 08 February 2006 - 10:51 AM

275/60/15 is the same as a 28/10.5/15 slick.
you can also get a bf goodrich and a yokohama tyre in that size which are made from much more street friendly compound that other brands

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#16 _MAWLER_

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Posted 08 February 2006 - 03:16 PM

A pic would be awesome 355lxss, let me see how close it comes etc. I was planning on a 8.5" rim as well, do you happen to know what offset your rims are?

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#17 _355lxss_

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Posted 08 February 2006 - 04:18 PM

The rims i have are an 8.5in deep dish with 3 3/8 back spacing. Ill try to dig up some pics tonight. You can see the rim/tire combo im using pictured in the aviator pic.

Edited by 355lxss, 08 February 2006 - 04:20 PM.

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#18 _355lxss_

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Posted 09 February 2006 - 06:17 PM

here are the pics as promised.

Posted Image

You can see in the pic above the extra inch i'll gain from recessing the wheel well flush with the chassis.
Also measured up the tire from wall to wall which was 11in wide.

Edited by 355lxss, 09 February 2006 - 06:22 PM.

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#19 _MAWLER_

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Posted 10 February 2006 - 10:47 PM

Thanks for the pics 355lxss. I was planning on trimming back to or even slightly moving the chassis rail at the rear of the tub as you have shown in the 2nd pic. I hadn't considered the inner wheel well at the front being an issue tho, I'm going to have to look at that as well and do some trimming to give the extra clearance to take out to the 275 region. How close is the tyre/rim to the shock, can you remember if we'll get away with it? I was hoping I wouldn't have to move the shock mounting points or trim the shock casing at all. Where you planning on having your diff shortened as well?

Cheers,

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#20 _QIKSLR_

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Posted 11 February 2006 - 10:47 AM

Thanks for the pics 355lxss. I was planning on trimming back to or even slightly moving the chassis rail at the rear of the tub as you have shown in the 2nd pic. I hadn't considered the inner wheel well at the front being an issue tho, I'm going to have to look at that as well and do some trimming to give the extra clearance to take out to the 275 region. How close is the tyre/rim to the shock, can you remember if we'll get away with it? I was hoping I wouldn't have to move the shock mounting points or trim the shock casing at all. Where you planning on having your diff shortened as well?

Cheers,

I've got the same problem. I don't think the front end of the tub is an issue on sedans. My tyre is about 10mm from the shock.
Posted Image

Heres some pics I took of a tubed non flared sedan. May be of use
Posted Image

Edited by QIKSLR, 11 February 2006 - 10:50 AM.

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#21 _355lxss_

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Posted 12 February 2006 - 10:50 AM

How close is the tyre/rim to the shock, can you remember if we'll get away with it? I was hoping I wouldn't have to move the shock mounting points or trim the shock casing at all. Where you planning on having your diff shortened as well?

from memory the upper shocker mounting point isnt an issue but the bottom needs to be relocated on the inside of the original mounting position. Im getting the diff housing shortened around 4 1/2 inches in total.

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#22 _MAWLER_

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Posted 12 February 2006 - 12:23 PM

Gee, 4 1/2 was a bit more than what I was expecting to be necessary, are you talking about 4 1/2 each side or 2 1/4 each side?

The only thing those pics do for me QIKSLR is to make me jealous!! Mini tubs, coilovers and panhard bar, or is it watts linkage, I can never remember which one is which :huh:

So looks like not going to be able to get away with it without moving the shock mount point, at least on the diff, moving the chassis rail in towards the centre at the rear of the tub, possibly rimming the tub at the front and who knows about height clearance.

CHOPPER, what is the best diameter rim to fit a 275/60 tyre on?

Cheers,

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#23 _CHOPPER_

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Posted 12 February 2006 - 01:17 PM

CHOPPER, what is the best diameter rim to fit a 275/60 tyre on?

I personally would put a 15" tyre on a 15" rim. For straight line action, probably 8.5-9.0" wide and try 20-25 PSI. A tyre pyrometer would be the best way to determine optimum pressure. Ideally take 3 readings, centre, inner and outer of the tyre. When the temps are equal after a run, leave the pressure there. If you make suspension alterations, the pressure may need to be altered. If somebody has an alternate method, feel free to tell us.